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2011

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Letters from Optical Engineering

Select this Article OPEN ACCESS		10-Gbps electroabsorptive modulated laser bidirectional optical subassembly using novel two-window flat package for passive optical network Jong Jin Lee, Kwon-Seob Lim, Jongdeog Kim, Seihyoung Lee, and Hyun Seo Kang Opt. Eng. 50, 120501 (29 November 2011); http://dx.doi.org/10.1117/1.3662417 Online Publication Date: Nov 29, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A novel 10-Gbps bidirectional optical subassembly (BOSA) comprised of a 1577 nm electroabsorptive modulated laser (EML) transmitter optical subassembly (TOSA) and 1270 nm avalanche photodiode (APD) receiver optical subassembly (ROSA) was developed. Here, a 10-Gbps microdevice compatible two-window flat package was proposed to simplify the EML BOSA structure, considering both the mechanical reliability and cooling performance. As a result, an optical output power of 8 dBm was obtained due to a high optical coupling efficiency of 60%, an extinction ratio of 7 dB, and a dispersion penalty at 20 km transmission of less than 1.5 dB for the EML TOSA. The APD ROSA sensitivity was –21.5 dBm at a bit error rate (BER) of 10⁻¹² and –27 dBm at a BER of 10⁻³ without forward error correction. In addition, the sensitivity penalty of the APD ROSA due to signal crosstalk was less than 1.2 dB.

Select this Article OPEN ACCESS		View synthesis distortion model optimization for bit allocation in three-dimensional video coding Feng Shao, Gang-Yi Jiang, Mei Yu, and Fu-Cui Li Opt. Eng. 50, 120502 (8 December 2011); http://dx.doi.org/10.1117/1.3665436 Online Publication Date: Dec 08, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In this letter, a novel optimized view synthesis distortion model is proposed for bit allocation in three-dimensional video coding. The proposed model separates the view synthesis distortion into two independent terms, and the two terms are modeled respectively by quadratic distortion models. Finally, the optimal quantization parameters for texture and depth can be determined by minimizing the view synthesis distortion under the total bitrate constraint. Experimental results show that compared with a fixed 5:1 method, the proposed method can obtain higher view synthesis rate-distortion performance.

Select this Article OPEN ACCESS		Advanced geometric camera calibration for machine vision Minh Vo, Zhaoyang Wang, Long Luu, and Jun Ma Opt. Eng. 50, 110503 (3 November 2011); http://dx.doi.org/10.1117/1.3647521 Online Publication Date: Nov 03, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In many machine vision applications, a crucial step is to accurately determine the relation between the image of the object and its physical dimension by performing a calibration process. Over time, various calibration techniques have been developed. Nevertheless, the existing methods cannot satisfy the ever-increasing demands for higher accuracy performance. In this letter, an advanced geometric camera calibration technique which employs a frontal image concept and a hyper-precise control point detection scheme with digital image correlation is presented. Simulation and real experimental results have successfully demonstrated the superior of the proposed technique.

Select this Article OPEN ACCESS		Randomized SUSAN edge detector Zhi-Guo Qu, Ping Wang, Ying-Hui Gao, and Peng Wang Opt. Eng. 50, 110502 (3 November 2011); http://dx.doi.org/10.1117/1.3647520 Online Publication Date: Nov 03, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A speed up technique for the SUSAN edge detector based on random sampling is proposed. Instead of sliding the mask pixel by pixel on an image as the SUSAN edge detector does, the proposed scheme places the mask randomly on pixels to find edges in the image; we hereby name it randomized SUSAN edge detector (R-SUSAN). Specifically, the R-SUSAN edge detector adopts three approaches in the framework of random sampling to accelerate a SUSAN edge detector: procedure integration of response computation and nonmaxima suppression, reduction of unnecessary processing for obvious nonedge pixels, and early termination. Experimental results demonstrate the effectiveness of the proposed method.

Select this Article OPEN ACCESS		Assessment approach for image mosaicing algorithms Li-hui Zou, Jie Chen, and Juan Zhang Opt. Eng. 50, 110501 (3 November 2011); http://dx.doi.org/10.1117/1.3646746 Online Publication Date: Nov 03, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In this paper, a novel quantitative assessment approach for image mosaicing algorithms is proposed by evaluating the quality of an output mosaic image and comparing with the input images. Five evaluation indices—entropy, clarity, registration error, peak signal-to-noise ratio, and structural similarity—are calculated and combined with the analytic hierarchy process for comprehensive assessment. This approach can overcome the lack of panoramic image and is easy to implement. Experimental results show the objectivity and the validity of the proposed approach.

Select this Article OPEN ACCESS		Optical refractometer based on multimode interference in a pure silica tube Luís Coelho, Jens Kobelke, Kay Schuster, José L. Santos, and Orlando Frazão Opt. Eng. 50, 100504 (21 October 2011); http://dx.doi.org/10.1117/1.3646393 Online Publication Date: Oct 21, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A multimode interferometer based-fiber optic sensor with a silica tube section aimed to measure refractive index (RI) variations of surrounding liquids is presented. The sensing head is a silica tube section fusion spliced to single mode fibers operating in transmission. In the splice regions tapers were made to allow the light to be guided in the silica tube while the core is formed by air. This configuration permits measurements of refractive index variations with sensitivities of 101.1, 106.29, and 107.97 nm∕RIU considering resonances with different wavelengths. The same resonances were tested with temperature variations with sensitivities achieved of 7.8, 8.7, and 9.3 pm∕ °C, respectively. The spectral variation associated with one degree temperature change corresponds to a refractive index change of ∼8 × 10⁻⁵, proving the low temperature dependence compared with sensitivity to RI variations.

Select this Article OPEN ACCESS		New method for designing narrow-band reflecting filters with application in optical integration Xiaodong Lu and Peide Han Opt. Eng. 50, 100502 (18 October 2011); http://dx.doi.org/10.1117/1.3644932 Online Publication Date: Oct 18, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A method for designing narrow-band reflecting filters has been proposed and it can be easily used to design the reflectance spectrum shapes of multilayer structures by turning the optical thicknesses of layers from regular into irregular. In this paper, we report two design examples of such narrow-band filters by the method and obtain the results of experiment accord with that of theory very well.

Select this Article OPEN ACCESS		Fast data acquisition for three-dimensional shape measurement using fixed-pattern projection and temporal coding Marcus Grosse, Martin Schaffer, Bastian Harendt, and Richard Kowarschik Opt. Eng. 50, 100503 (11 October 2011); http://dx.doi.org/10.1117/1.3646100 Online Publication Date: Oct 11, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The field of image-based shape measurements using structured illumination has been an active research area for several decades now. A lot of different methods are widely used e.g. for industrial inspection, surveillance as well as multimedia purposes. Usually, short measurement times and high correspondence accuracy are mutually exclusive properties, due to the limitations of the used projection technology. Using a standard stereo-photogrammetry approach, as well as a simple, yet powerful structured light projection concept based on a slide-projector, we demonstrate an acquisition rate of more than 700 dense and accurate 3D measurements per second.

Select this Article OPEN ACCESS		Attack propagation of high-powered intrachannel crosstalk in transparent optical networks Zeyu Sun, Yunfeng Peng, and Keping Long Opt. Eng. 50, 100501 (29 September 2011); http://dx.doi.org/10.1117/1.3641411 Online Publication Date: Sep 29, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Transparent optical networks (TON) are becoming increasingly attractive, but transparency introduces security threats, e.g., intrachannel crosstalk attack, to optical networks. In this letter, three attack scenarios, i.e., attack propagation within an optical cross connect (OXC), the secondary attacker traverses successive OXCs and original attacker traverses successive OXCs, are investigated. The scenarios accompanied with gain competition attack are also simulated as comparison. Bit-error-rate (BER), and eye diagram penalties are estimated via VPItransMaker^TM. Our work proved that the attack signal will propagate intrachannel crosstalk attack to successive three OXCs but with limited two stages of optical switches in each OXC. The BER will be somewhat higher in case gain competition attack exists. The results will be useful for future managing, planning, and designing on TONs.

Select this Article OPEN ACCESS		Particle probability hypothesis density filtering for multitarget visual tracking with robust state extraction Jingjing Wu, Shiqiang Hu, and Yang Wang Opt. Eng. 50, 090502 (20 September 2011); http://dx.doi.org/10.1117/1.3638121 Online Publication Date: Sep 20, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Particle probability hypothesis density (PHD) filter-based visual trackers have achieved considerable success in the visual tracking field. But position measurements based on detection may not have enough ability to discriminate an object from clutter, and accurate state extraction cannot be obtained in the original PHD filtering framework, especially when targets can appear, disappear, merge, or split at any time. To meet the limitations, the proposed algorithm combines a color histogram of a target and the temporal dynamics in a unifying framework and a Gaussian mixture model clustering method for efficient state extraction is designed. The proposed tracker can improve the accuracy of state estimation in tracking a variable number of objects.

Select this Article OPEN ACCESS		Scale-adaptive object tracking using color centroids Suk-Ho Lee, Euncheol Choi, and Moon Gi Kang Opt. Eng. 50, 090501 (15 September 2011); http://dx.doi.org/10.1117/1.3633648 Online Publication Date: Sep 15, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose a stable scale-adaptive tracking method that uses the centroids of the target colors in the target localization and scale adaptation. Because of the spatial information inherent in the centroids, a direct relationship can be established between the centroids and the scale of the target region. After the zooming factors are calculated, the unreliable zooming factors are filtered out to produce a reliable zooming factor that determines the new scale of the target.

Select this Article OPEN ACCESS		Design of a bike headlamp based on a power white-light-emitting diode Yi-Chien Lo, Cheng-Chien Chen, Hung-Yu Chou, Kai-Yu Yang, and Ching-Cherng Sun Opt. Eng. 50, 080503 (22 August 2011); http://dx.doi.org/10.1117/1.3615278 Online Publication Date: Aug 22, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In this letter, we present a new design for a light-emitting diode- based bike headlamp. The optical design contains two horizontal reflectors and a light pipe with two horizontal parallel mirrors. The designed illumination pattern in our simulations performs a contrast of 250 in the K-mark regulation, and it was measured to be 21 in the experiment with a not well-finished prototype, which was operated at 1 W. The contrast is higher than 5 as requested in the regulation.

Select this Article OPEN ACCESS		Texture video-assisted motion vector predictor for depth map coding Xiaoxian Liu, Yilin Chang, Zhibin Li, and Junyan Huo Opt. Eng. 50, 080504 (4 August 2011); http://dx.doi.org/10.1117/1.3615644 Online Publication Date: Aug 04, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A texture video-assisted motion vector predictor for depth map coding is proposed in this letter. Based on the analyses of motion similarity between texture videos and their corresponding depth maps, the proposed approach uses the motion vectors of texture videos and the median predictor jointly to determine the optimal predicted motion vector for depth map coding by employing a rate-distortion (R-D) criterion. Experimental results demonstrate that compared with the median predictor utilized in H.264∕AVC, the proposed method can save the maximum and average bit rate as high as 4.89% and 3.68%, respectively, while guaranteeing the quality of synthesized virtual views.

Select this Article OPEN ACCESS		Universal and special keys based on phase-truncated Fourier transform Wan Qin, Xiang Peng, Xiangfeng Meng, and Bruce Gao Opt. Eng. 50, 080501 (28 July 2011); http://dx.doi.org/10.1117/1.3607421 Online Publication Date: Jul 28, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose a novel optical asymmetric cryptosystem based on a phase-truncated Fourier transform. Two decryption keys independent of each other are generated. They are referred to as universal key and special key, respectively. Each of them can be used for decryption independently in absence of the other. The universal key is applicable to decrypt any ciphertext encoded by the same encryption key, but with poor legibility. On the contrary, the special key is adequate for legible decryption, but only valid for one ciphertext corresponding to the specified plaintext. A set of simulation results show the interesting performance of two types of decryption keys.

Select this Article OPEN ACCESS		Retrieval of complex object fields in coherent diffractive imaging using position shift of a phase mask Wen Chen, Chenggen Quan, and Cho Jui Tay Opt. Eng. 50, 080502 (28 July 2011); http://dx.doi.org/10.1117/1.3614472 Online Publication Date: Jul 28, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In this letter, we propose a novel method to quantitatively recover a complex-valued object from diffraction intensity maps. A wavefront modulation is introduced in the optical path, and several diffraction intensity maps are recorded through position shift of a phase mask. A phase retrieval algorithm is further developed, and advantages of the proposed method are discussed.

Select this Article OPEN ACCESS		Densification of silicon carbide using oxy-nitride additives for space-based telescope mirror applications R. Suresh Kumar, Anoop K. Shukla, Sankaranarayanan Babu, Dhenuvakonda Sivakumar, and Ashutosh S. Gandhi Opt. Eng. 50, 070504 (27 July 2011); http://dx.doi.org/10.1117/1.3610987 Online Publication Date: Jul 27, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Densification behavior of alpha silicon carbide (SiC) during vacuum hot pressing was studied up to 1900ºC with sintering additives based on AlN and Y₂O₃ in different proportions. Near theoretical density was obtained with a total sintering additive content of < 4 vol.%. The microstructure of SiC sintered with AlN+Y₂O₃ revealed fine equiaxed grains against the additional elongated grains exhibited by SiC sintered with AlN alone. The SiC having high density exhibited very good strength, elastic modulus, high thermal conductivity, low coefficient of thermal expansion and excellent polishability for telescope mirror applications.

Select this Article OPEN ACCESS		Review of current aided∕automatic target acquisition technology for military target acquisition tasks James A. Ratches Opt. Eng. 50, 072001 (6 July 2011); http://dx.doi.org/10.1117/1.3601879 Online Publication Date: Jul 06, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Aided and automatic target recognition (Ai∕ATR) capability is a critical technology needed by the military services for modern combat. However, the current level of performance that is available is largely deficient compared to the requirements. This is largely due to the difficulty of acquiring targets in realistic environments but has also been due to the difficulty in getting new concepts from, for example, the academic community, due to limitations for distribution of classified data. The difficulty of the performance required has limited the fulfillment of the promise that is so anticipated by the war fighter. We review the metrics, imagery data bases, and sensors associated with Ai∕ATR performance and suggest possible technical approaches that could enable new advancements in military-relevant performance.

Select this Article OPEN ACCESS		Fast mode decision for the H.264∕AVC video coding standard based on frequency domain motion estimation Abdelrahman Abdelazim, Stephen J. Mein, Martin R. Varley, and Djamel Ait-Boudaoud Opt. Eng. 50, 070501 (6 July 2011); http://dx.doi.org/10.1117/1.3597609 Online Publication Date: Jul 06, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The H.264 video coding standard achieves high performance compression and image quality at the expense of increased encoding complexity. Consequently, several fast mode decision and motion estimation techniques have been developed to reduce the computational cost. These approaches successfully reduce the computational time by reducing the image quality and∕or increasing the bitrate. In this paper we propose a novel fast mode decision and motion estimation technique. The algorithm utilizes preprocessing frequency domain motion estimation in order to accurately predict the best mode and the search range. Experimental results show that the proposed algorithm significantly reduces the motion estimation time by up to 97%, while maintaining similar rate distortion performance when compared to the Joint Model software.

Select this Article OPEN ACCESS		Design of a spiral silica photonic crystal fiber for nonlinear applications in visible region Md. Nazmul Hossain, M. Shah Alam, Dihan Md. Nuruddin Hasan, and K. M. Mohsin Opt. Eng. 50, 070503 (6 July 2011); http://dx.doi.org/10.1117/1.3600765 Online Publication Date: Jul 06, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A silica spiral photonic crystal fiber is presented here for tailoring two zero dispersion wavelengths (ZDWs) in the visible region. The proposed fiber has two ZDWs (523.1 and 716.8 nm) along with a very high nonlinearity parameter (1060 W⁻¹ km⁻¹ at 500 nm) around the visible region. The proposed design shows improvement over the group dispersion control and air holes collapsibility of highly air filled hexagonal photonic crystal fiber (HPCF), and low damage threshold of the soft glass photonic crystal fiber. Besides, the low air filling fraction (≈43%) of the proposed design reduces the probability of sustaining higher order modes in the fiber and also ensures easy fabrication due to fewer air holes.

Select this Article OPEN ACCESS		Dye adsorption induced nonvolatile reading of erasable polarization holograms in liquid crystal films Wei-Chia Su, Jhen-Yu Jiang, Hui-Chuan Chen, Yu-Wen Chen, and Sidney S. Yang Opt. Eng. 50, 070502 (6 July 2011); http://dx.doi.org/10.1117/1.3599517 Online Publication Date: Jul 06, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A nonvolatile reading of erasable polarization holograms in dye-doped liquid-crystal films using the same writing wavelength is presented. The recorded hologram can be easily erased with the illumination of one p-polarized wave; nevertheless, it becomes nonvolatile when reading the hologram with one s-polarized wave. We have proven the nonvolatile reading property is induced by dye adsorption on the substrate of the sample.

Select this Article OPEN ACCESS		Laser beam propagation in a flow aligned nematic liquid crystal: analysis on liquid∕light interactions Radhakrishnan Ranjini, Amrutha K. Adiyodi, Murukeshan Vadakke Matham, and Nam-Trung Nguyen Opt. Eng. 50, 050501 (5 May 2011); http://dx.doi.org/10.1117/1.3574767 Online Publication Date: May 05, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The propagation of laser beam in a flow aligned nematic liquid crystal (NLC) and its interaction with liquid are illustrated in this letter. The effect of polarization and scattering on the transmitted power through the NLC under external perturbation flow is demonstrated here. It is found that the flow rate has a significant role in the modulation of refractive index of the medium leading to scattering and change in polarization.

Select this Article OPEN ACCESS		Motion vector coding with contradiction testing Kwanghyun Won, Jungyoup Yang, and Byeungwoo Jeon Opt. Eng. 50, 040502 (28 April 2011); http://dx.doi.org/10.1117/1.3571277 Online Publication Date: Apr 28, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This paper proposes a motion vector coding scheme which uses the optimal predictive motion vector from the surrounding causal motion vectors in the minimum rate-distortion sense. The signaling overhead for the selected predictive motion vector is reduced by a contradiction testing that operates under a predefined criterion at both encoder and decoder for pruning the candidate predictive motion vectors.

Select this Article OPEN ACCESS		Wavefront reconstruction using multiple directional derivatives and Fourier transform Ricardo Legarda-Saenz and Arturo Espinosa-Romero Opt. Eng. 50, 040501 (1 April 2011); http://dx.doi.org/10.1117/1.3560540 Online Publication Date: Apr 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present a Fourier-based regularized method for reconstructing the wavefront from multiple directional derivatives. This method is robust to noise, and is specially suited for deflectometry measurement.

Select this Article OPEN ACCESS		All-optical diode with photonic multilayers based on asymmetric light localization Li Jin, Jun Zhou, Mingyang Yang, Chunhua Xue, and Miao He Opt. Eng. 50, 030503 (16 March 2011); http://dx.doi.org/10.1117/1.3558733 Online Publication Date: Mar 16, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An all-optical diode (AOD) with structure (AB)^m(BA)ⁿ(BBAA)^k is proposed based on asymmetric light localization, and its optical bistability are numerically investigated by the nonlinear transfer matrix method. Research results show that the behavior of the AOD strongly depends on the period number m, n, and k, the transmission direction of the AOD is related to the values of m and n, while k affects the transmission contrast of the AOD. It is a significant reference for the design of all-optical signal processing devices.

Select this Article OPEN ACCESS		Nonlocal oriented method for image denoising Yonghui Gao, Jie Yang, and Lv Guo Opt. Eng. 50, 030502 (10 March 2011); http://dx.doi.org/10.1117/1.3555083 Online Publication Date: Mar 10, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Denoising is expected to improve the image quality and the performance of analysis. Combining the nonlocal-means filter and the mean-shift method, we derive a nonlocal weights estimator considering not only similarity of intensity but also the spatial relationship between image blocks. Filtering is performed in each image block and the center pixel is restored by an oriented filter. Experimental results show the performance of the proposed method in improving the signal-to-noise ratio and preserving local textures.

Select this Article OPEN ACCESS		Adaptive mixed image denoising based on image decomposition Run Liu, Shujun Fu, and Caiming Zhang Opt. Eng. 50, 020502 (25 February 2011); http://dx.doi.org/10.1117/1.3542041 Online Publication Date: Feb 25, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Image denoising while preserving image features is a key problem in image processing and computer vision. This letter proposes an adaptive mixed method for image restoration. First, this method decomposes a given image as the sum of two components: geometric structure and oscillating pattern according to Meyer's theory. Second, a coupled bidirectional diffusion equation is used to restore the structure part, and a nonlocal means filter is used to remove noise in the oscillating part. Experimental results show advantages of this method in feature-preserving denoising.

Select this Article OPEN ACCESS		Light-driven motor Hideki Okamura Opt. Eng. 50, 020503 (22 February 2011); http://dx.doi.org/10.1117/1.3542042 Online Publication Date: Feb 22, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A light-driven motor operated by a single source of light is demonstrated for the first time. The device utilizes a NiTi shape memory alloy (SMA) wire initially trained straight shape. The SMA wire was formed in a loop and put around two wheels. In the experiment a steady and continuous rotation was achieved with a bundled loop of 0.3-mm diameter wire. The rotational speed was proportional to the incident light power and 60 rpm was obtained at 3.6 W of light power. The experimental result was consistent with the theory.

Select this Article OPEN ACCESS		Plastic optical fiber sensor for measuring driver-gripping force Jaehee Park Opt. Eng. 50, 020501 (4 February 2011); http://dx.doi.org/10.1117/1.3542040 Online Publication Date: Feb 04, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This study presents a plastic optical fiber (POF) sensor for measuring the driver's gripping force applied to a steering wheel. This sensor consists of a POF wound around the steering wheel covered with a soft material. The sensing method is based on the bending radiation loss of the POF induced by the driver's gripping force applied to the steering wheel. The bending radiation loss is proportional to the gripping force, and the response time of the POF sensor is about 2 s. The experimental results show that a POF sensor can be effective for monitoring the driver gripping force, and hence driver fatigue.

Select this Article OPEN ACCESS		Performance evaluation of visible-light transceiver for peripheral interface Hongseok Shin, Jinwoo Park, Seoksu Song, Seongbum Park, Kyungwoo Lee, D. K. Jung, and Youngmin Lee Opt. Eng. 50, 010501 (27 January 2011); http://dx.doi.org/10.1117/1.3535588 Online Publication Date: Jan 27, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We examine the practicability of the visible-light communication (VLC) transceiver for bidirectional high-speed and short-range communications. A visible-light peripheral interface could be a novel approach, visualizing the veiled security feature of light by employing visible lights as communication media beyond its intended applications, such as illumination and display. The proposed VLC transceivers are implemented with edge-an emitting laser diode and a silicon photodiode, which is primarily designed to operate in a full duplex mode at 120 Mbit∕s. The shielding method that is employed to reduce the light cross-coupling effect inside the VLC transceiver is proposed and experimentally investigated. The bit error rate performance of the proposed VLC transceiver is examined with respect to the transmission distance and the coverage.

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Letters from Journal of Electronic Imaging

Select this Article OPEN ACCESS		Colorization based on soft segmentation Hyung-Il Koo and Nam-Ik Cho J. Electron. Imaging 20, 010502 (22 March 2011); http://dx.doi.org/10.1117/1.3565470 Online Publication Date: Mar 22, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This paper proposes a new colorization method based on the chrominance blending. The weights for the blending are computed by using the random walker algorithm, which is a soft segmentation technique that provides sharp probability transition on object boundaries. As a result, the proposed method reduces color bleeding and provides improved colorization performances compared to conventional ones.

Select this Article OPEN ACCESS		On the security of ownership watermarking of digital images based on singular value decomposition Huo-Chong Ling, Raphael C.-W. Phan, and Swee-Huay Heng J. Electron. Imaging 20, 010501 (20 January 2011); http://dx.doi.org/10.1117/1.3534865 Online Publication Date: Jan 20, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We show that the two countermeasures proposed in a paper on the security of ownership watermarking of digital images based on singular value decomposition by Loukhaoukha and Chouinard do not solve the false-positive detection problem in contrast to designers’ claim and therefore should not be used for proof of ownership application.

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Letters from Journal of Biomedical Optics

Select this Article OPEN ACCESS		Time-resolved imaging refractometry of microbicidal films using quantitative phase microscopy Matthew T. Rinehart, Tyler K. Drake, Francisco E. Robles, Lisa C. Rohan, David Katz, and Adam Wax J. Biomed. Opt. 16, 120510 (19 December 2011); http://dx.doi.org/10.1117/1.3665439 Online Publication Date: Dec 19, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Quantitative phase microscopy is applied to image temporal changes in the refractive index (RI) distributions of solutions created by microbicidal films undergoing hydration. We present a novel method of using an engineered polydimethylsiloxane structure as a static phase reference to facilitate calibration of the absolute RI across the entire field. We present a study of dynamic structural changes in microbicidal films during hydration and subsequent dissolution. With assumptions about the smoothness of the phase changes induced by these films, we calculate absolute changes in the percentage of film in regions across the field of view.

Select this Article OPEN ACCESS		Simultaneous fluorescence and positron emission tomography for in vivo imaging of small animals Bin Zhang, Shuangquan Liu, Fei Liu, Xiaochun Zhang, Yanyan Xu, Jianwen Luo, Baoci Shan, and Jing Bai J. Biomed. Opt. 16, 120511 (5 December 2011); http://dx.doi.org/10.1117/1.3665438 Online Publication Date: Dec 05, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Simultaneous positron emission tomography (PET) and fluorescence tomography (FT) for in vivo imaging of small animals is proposed by a dual-modality system. This system combines a charge-coupled device-based near-infrared fluorescence imaging with a planar detector pair-based PET. With [¹⁸F]-2-fluoro-2-deoxy-d-glucose radioactive tracer and the protease activated fluorescence probe, on the one hand, the simultaneous metabolic activity and protease activity in tumor region are revealed by the PET and FT, respectively. On the other hand, the protease activity both on the surface layer and the deep tissue of the tumor is provided by the fluorescence reflection imaging and FT, respectively.

Select this Article OPEN ACCESS		Imaging the cellular response to transient shear stress using stroboscopic digital holography Maciej Antkowiak, Yoshihiko Arita, Kishan Dholakia, and Frank Gunn-Moore J. Biomed. Opt. 16, 120508 (16 December 2011); http://dx.doi.org/10.1117/1.3665441 Online Publication Date: Dec 16, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We use stroboscopic quantitative phase microscopy to study cell deformation and the response to cavitation bubbles and transient shear stress resulting from laser-induced breakdown of an optically trapped nanoparticle. A bi-directional transient displacement of cytoplasm is observed during expansion and collapse of the cavitation bubble. In some cases, cell deformation is only observable at the microsecond time scale without any permanent change in cell shape or optical thickness. On a time scale of seconds, the cellular response to shear stress and cytoplasm deformation typically leads to retraction of the cellular edge most exposed to the flow, rounding of the cell body and, in some cases, loss of cellular dry mass. These results give a new insight into the cellular response to cavitation induced shear stress and related plasma membrane permeabilization. This study also demonstrates that laser-induced breakdown of a nanoparticle offers localized cavitation, which interacts with a single cell but without causing cell lysis.

Select this Article OPEN ACCESS		Unsupervised analysis of small animal dynamic Cerenkov luminescence imaging Antonello E. Spinelli and Federico Boschi J. Biomed. Opt. 16, 120507 (1 December 2011); http://dx.doi.org/10.1117/1.3663442 Online Publication Date: Dec 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Clustering analysis (CA) and principal component analysis (PCA) were applied to dynamic Cerenkov luminescence images (dCLI). In order to investigate the performances of the proposed approaches, two distinct dynamic data sets obtained by injecting mice with ³²P-ATP and ¹⁸F-FDG were acquired using the IVIS 200 optical imager. The k-means clustering algorithm has been applied to dCLI and was implemented using interactive data language 8.1. We show that cluster analysis allows us to obtain good agreement between the clustered and the corresponding emission regions like the bladder, the liver, and the tumor. We also show a good correspondence between the time activity curves of the different regions obtained by using CA and manual region of interest analysis on dCLIT and PCA images. We conclude that CA provides an automatic unsupervised method for the analysis of preclinical dynamic Cerenkov luminescence image data.

Select this Article OPEN ACCESS		Development of a noncontact diffuse optical spectroscopy probe for measuring tissue optical properties Sheldon F. Bish, Narasimhan Rajaram, Brandon Nichols, and James W. Tunnell J. Biomed. Opt. 16, 120505 (29 November 2011); http://dx.doi.org/10.1117/1.3662459 Online Publication Date: Nov 29, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Optical reflectance probes are often used as tools to obtain optical spectra from superficial tissues and subsequently determine optical and physiological properties associated with early stage cancer. These probes, when placed directly on the tissue, are known to cause significant pressure-dependent changes in local optical properties. To address this, we fit the probe with an optical device that images the illumination and collection fibers onto the tissue surface, eliminating the influence of contact probe pressure on the sampling area. The noncontact probe addition addresses new optical conditions that may affect its performance such as tissue surface contour, and specular reflections by implementing an autofocusing mechanism and cross polarization. Extracted optical properties of tissue simulating phantoms yield errors of 3.46% in reduced scattering and 8.62% in absorbance. Autofocusing has extended the depth of field from 4 mm to throughout the 12 mm range of autofocus travel, while cross polarization has removed the incidence angle dependent specular reflection component from the collected signal.

Select this Article OPEN ACCESS		Multifocus confocal Raman microspectroscopy for rapid single-particle analysis Lingbo Kong, Pengfei Zhang, Peter Setlow, and Yong-qing Li J. Biomed. Opt. 16, 120503 (23 November 2011); http://dx.doi.org/10.1117/1.3662456 Online Publication Date: Nov 23, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We have developed a multifocus confocal Raman microspectroscopy system that allows simultaneous analyses of ∼80 individual biological or airborne microparticles based on a precise image-guided technique. Multiple individual particles adhered in random positions on a coverslip were illuminated by a multifocus excitation pattern formed by rapidly steering a single laser beam with a pair of galvo-mirrors, and their Raman scatterings were synchronously projected with another galvo-mirror to different rows of a CCD chip for parallel spectroscopic analyses. We show that this technique can be used to rapidly identify single airborne particles or bacteria collected on a slide and to monitor germination dynamics of multiple bacterial spores in real-time.

Select this Article OPEN ACCESS		Measurement of anisotropic reflection of flowing blood using optical coherence tomography Kweon-Ho Nam, Bosu Jeong, In Oh Jung, Hojin Ha, Ki Hean Kim, and Sang Joon Lee J. Biomed. Opt. 16, 120502 (22 November 2011); http://dx.doi.org/10.1117/1.3660299 Online Publication Date: Nov 22, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Light reflectance of blood is a complex phenomenon affected by hematocrit and red blood cell (RBC) aggregation (rouleaux formation). According to the hypothesis that RBC rouleaux are aligned with the direction of blood flow, the spatial alignment of RBC rouleaux, as well as their size and quantity in the blood, may also affect light reflectance. The present study aims to investigate the effect of the spatial alignment and distribution of RBC rouleaux on light reflection using optical coherence tomography (OCT). Blood flow velocity and reflectance profiles in a rat jugular-femoral bypass loop were simultaneously measured using a Doppler swept-source OCT system at various incident angles from −30 to +30 deg. The reflectance profiles of flowing blood show nonmonotonous decay with a local negative peak at the center of the tube. The profiles vary depending on the incident angle. This angular dependence is stronger at a higher angle of incidence. The anisotropic reflectance of flowing blood is consistent with the hypothesis on the spatial alignment of RBC rouleaux.

Select this Article OPEN ACCESS		Quantitative biomarkers of colonic dysplasia based on intrinsic second-harmonic generation signal Shuangmu Zhuo, Xiaoqin Zhu, Guizhu Wu, Jianxin Chen, and Shusen Xie J. Biomed. Opt. 16, 120501 (22 November 2011); http://dx.doi.org/10.1117/1.3659715 Online Publication Date: Nov 22, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Most colorectal cancers arise from dysplastic lesions, such as adenomatous polyps, and these lesions are difficult to be detected by the current endoscopic screening approaches. Here, we present the use of an intrinsic second-harmonic generation (SHG) signal as a novel means to differentiate between normal and dysplastic human colonic tissues. We find that the SHG signal can quantitatively identify collagen change associated with colonic dysplasia that is indiscernible by conventional pathologic techniques. By comparing normal with dysplastic mucosa, there were significant differences in collagen density and collagen fiber direction, providing substantial potential to become quantitative intrinsic biomarkers for in vivo clinical diagnosis of colonic dysplasia.

Select this Article OPEN ACCESS		Measurement of oxygen saturation in small retinal vessels with adaptive optics confocal scanning laser ophthalmoscope Hao Li, Jing Lu, Guohua Shi, and Yudong Zhang J. Biomed. Opt. 16, 110504 (10 November 2011); http://dx.doi.org/10.1117/1.3655354 Online Publication Date: Nov 10, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We have used an adaptive optics confocal scanning laser ophthalmoscope to assess oxygen saturation in small retinal vessels. Images of the vessels with a diameter smaller than 50 μm are recorded at oxygen sensitive and isosbestic wavelengths (680 and 796 nm, respectively). The vessel optical densities (ODs) are determined by a computer algorithm. Then, OD ratios (ODRs), which are inversely proportional to oxygen saturation, are calculated. The results show that arterial ODRs are significantly smaller than venous ODRs, indicating that oxygen saturation in the artery is higher than that in the vein. To the best of our knowledge, this is the first noninvasive measurement of oxygen saturation in small retinal vessels.

Select this Article OPEN ACCESS		In vivo intracardiac optical coherence tomography imaging through percutaneous access: toward image-guided radio-frequency ablation Hui Wang, Wei Kang, Thomas Carrigan, Austin Bishop, Noah Rosenthal, Mauricio Arruda, and Andrew M. Rollins J. Biomed. Opt. 16, 110505 (8 November 2011); http://dx.doi.org/10.1117/1.3656966 Online Publication Date: Nov 08, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Complete catheter-tissue contact and permanent tissue destruction are essential for efficient radio-frequency ablation (RFA) during cardiac arrhythmia treatment. Current methods of monitoring lesion formation are indirect and unreliable. The purpose of this study is to evaluate the feasibility of using optical coherence tomography (OCT) catheter to image endocardial wall in actively beating hearts through percutaneous access. We reported the first in vivo intracardiac OCT imaging through percutaneous access with a thin and flexible OCT catheter. This is a critical step toward image-guided RFA in a clinical setting. A cone-scanning forward-viewing OCT catheter was advanced into beating hearts through percutaneous access in four swine. The OCT catheter was steered by an introducer to touch the endocardial wall. We are able to acquire high quality OCT images in beating hearts, observe the polarization-related artifacts induced by the birefringence of myocardium, and readily evaluate catheter-tissue contact. The observations indicate that OCT could be a promising technique for in vivo guidance of RFA.

Select this Article OPEN ACCESS		Raman spectroscopic characterization and differentiation of seminal plasma Zufang Huang, Xiwen Chen, Yanping Chen, Jinhua Chen, Min Dou, Shangyuan Feng, Haishan Zeng, and Rong Chen J. Biomed. Opt. 16, 110501 (26 October 2011); http://dx.doi.org/10.1117/1.3650310 Online Publication Date: Oct 26, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Raman spectroscopy (RS) was applied for the analysis of seminal plasma in order to detect spectral parameters, which might be used for differentiating the normal and abnormal semen samples. Raman spectra of seminal plasma separated from normal and abnormal semen samples, showed a distinct difference in peak ratios between 1449 and 1418 cm⁻¹ (P < 0.05). More efficient alternative method of using principal component analysis-linear discriminate analysis based on Raman spectroscopic data yielded a diagnostic sensitivity of 73% and specificity of 82%. The results suggest that RS combined with the multivariate analysis method has the potential for differentiating semen samples by examination of the corresponding seminal plasma.

Select this Article OPEN ACCESS		Selective two-photon fluorescence suppression by ultrafast pulse-pair excitation: control by selective one-color stimulated emission Arijit Kumar De, Debjit Roy, and Debabrata Goswami J. Biomed. Opt. 16, 100505 (21 October 2011); http://dx.doi.org/10.1117/1.3645082 Online Publication Date: Oct 21, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Controlling two-photon molecular fluorescence leading to selective fluorophore excitation has been a long sought after goal in fluorescence microscopy. In this letter, we thoroughly explore selective fluorescence suppression through simultaneous two-photon absorption by two different fluorophores followed by selective one-photon stimulated emission for one particular fluorophore. We achieve this by precisely controlling the time delay between two identical ultrafast near infrared laser pulses.

Select this Article OPEN ACCESS		In vivo low-coherence spectroscopic measurements of local hemoglobin absorption spectra in human skin Nienke Bosschaart, Dirk J. Faber, Ton G. van Leeuwen, and Maurice C. G. Aalders J. Biomed. Opt. 16, 100504 (14 October 2011); http://dx.doi.org/10.1117/1.3644497 Online Publication Date: Oct 14, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Localized spectroscopic measurements of optical properties are invaluable for diagnostic applications that involve layered tissue structures, but conventional spectroscopic techniques lack exact control over the size and depth of the probed tissue volume. We show that low-coherence spectroscopy (LCS) overcomes these limitations by measuring local attenuation and absorption coefficient spectra in layered phantoms. In addition, we demonstrate the first in vivo LCS measurements of the human epidermis and dermis only. From the measured absorption in two distinct regions of the dermal microcirculation, we determine total hemoglobin concentration (3.0±0.5 g∕l and 7.8±1.2 g∕l) and oxygen saturation.

Select this Article OPEN ACCESS		Functional photoacoustic microscopy of pH Muhammad Rameez Chatni, Junjie Yao, Amos Danielli, Christopher P. Favazza, Konstantin I. Maslov, and Lihong V. Wang J. Biomed. Opt. 16, 100503 (14 October 2011); http://dx.doi.org/10.1117/1.3644495 Online Publication Date: Oct 14, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract pH is a tightly regulated indicator of metabolic activity. In mammalian systems, an imbalance of pH regulation may result from or result in serious illness. In this paper, we report photoacoustic microscopy (PAM) of a commercially available pH-sensitive fluorescent dye (SNARF-5F carboxylic acid) in tissue phantoms. We demonstrated that PAM is capable of pH imaging in absolute values at tissue depths of up to 2.0 mm, greater than possible with other forms of optical microscopy.

Select this Article OPEN ACCESS		In vivo label-free three-dimensional imaging of zebrafish vasculature with optical projection tomography Andrea Bassi, Luca Fieramonti, Cosimo D’Andrea, Marina Mione, and Gianluca Valentini J. Biomed. Opt. 16, 100502 (3 October 2011); http://dx.doi.org/10.1117/1.3640808 Online Publication Date: Oct 03, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We introduce flow optical projection tomography, an imaging technique capable of visualizing the vasculature of living specimens in 3-D. The method detects the movement of cells in the bloodstream and creates flow maps using a motion-analysis procedure. Then, flow maps obtained from projection taken at several angles are used to reconstruct sections of the circulatory system of the specimen. We therefore demonstrate an in vivo, 3-D optical imaging technique that, without the use of any labeling, is able to reconstruct and visualize the vascular network of transparent and weakly scattering living specimens.

Select this Article OPEN ACCESS		Optical scattering coefficient estimated by optical coherence tomography correlates with collagen content in ovarian tissue Yi Yang, Tianheng Wang, Nrusingh C. Biswal, Xiaohong Wang, Melinda Sanders, Molly Brewer, and Quing Zhu J. Biomed. Opt. 16, 090504 (23 September 2011); http://dx.doi.org/10.1117/1.3625247 Online Publication Date: Sep 23, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Optical scattering coefficient from ex vivo unfixed normal and malignant ovarian tissue was quantitatively extracted by fitting optical coherence tomography (OCT) A-line signals to a single scattering model. 1097 average A-line measurements at a wavelength of 1310 nm were performed at 108 sites obtained from 18 ovaries. The average scattering coefficient obtained from the normal tissue group consisted of 833 measurements from 88 sites was 2.41 mm⁻¹ (±0.59), while the average coefficient obtained from the malignant tissue group consisted of 264 measurements from 20 sites was 1.55 mm⁻¹ (±0.46). The malignant ovarian tissue showed significant lower scattering than the normal group (p < 0.001). The amount of collagen within OCT imaging depth was analyzed from the tissue histological section stained with Sirius Red. The average collagen area fraction (CAF) obtained from the normal tissue group was 48.4% (±12.3%), while the average CAF obtained from the malignant tissue group was 11.4% (±4.7%). A statistical significance of the collagen content was found between the two groups (p < 0.001). These results demonstrated that quantitative measurements of optical scattering coefficient from OCT images could be a potential powerful method for ovarian cancer detection.

Select this Article OPEN ACCESS		Functional photoacoustic imaging to observe regional brain activation induced by cocaine hydrochloride Janggun Jo and Xinmai Yang J. Biomed. Opt. 16, 090506 (13 September 2011); http://dx.doi.org/10.1117/1.3626576 Online Publication Date: Sep 13, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Photoacoustic microscopy (PAM) was used to detect small animal brain activation in response to drug abuse. Cocaine hydrochloride in saline solution was injected into the blood stream of Sprague Dawley rats through tail veins. The rat brain functional change in response to the injection of drug was then monitored by the PAM technique. Images in the coronal view of the rat brain at the locations of 1.2 and 3.4 mm posterior to bregma were obtained. The resulted photoacoustic (PA) images showed the regional changes in the blood volume. Additionally, the regional changes in blood oxygenation were also presented. The results demonstrated that PA imaging is capable of monitoring regional hemodynamic changes induced by drug abuse.

Select this Article OPEN ACCESS		Three-dimensional photoacoustic tomography based on the focal-line concept Jun Xia, Zijian Guo, Konstantin Maslov, Andres Aguirre, Quing Zhu, Christopher Percival, and Lihong V. Wang J. Biomed. Opt. 16, 090505 (2 September 2011); http://dx.doi.org/10.1117/1.3625576 Online Publication Date: Sep 02, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A full ring ultrasonic array-based photoacoustic tomography system was recently developed for small animal brain imaging. The 512-element array is cylindrically focused in the elevational direction, and can acquire a two-dimensional (2D) image in 1.6 s. In this letter, we demonstrate the three-dimensional (3D) imaging capability of this system. A novel 3D reconstruction algorithm was developed based on the focal-line concept. Compared to 3D images acquired simply by stacking a series of 2D images, the 3D focal-line reconstruction method renders images with much less artifacts, and improves the elevational resolution by 30% and the signal-to-noise ratio by two times. The effectiveness of the proposed algorithm was first validated by numerical simulations and then demonstrated with a hair phantom experiment and an ex vivo mouse embryo experiment.

Select this Article OPEN ACCESS		Laser speckle contrast imaging of cerebral blood flow in freely moving animals Peng Miao, Hongyang Lu, Qi Liu, Yao Li, and Shanbao Tong J. Biomed. Opt. 16, 090502 (1 September 2011); http://dx.doi.org/10.1117/1.3625231 Online Publication Date: Sep 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We designed a miniature laser speckle imager that weighs ∼20 g and is 3.1-cm high for full-field high-resolution imaging of cerebral blood flow (CBF) in freely moving animals. Coherent laser light illuminates the cortex through a multimode optical fiber bundle fixed onto the supporting frame of the imager. The reflected lights are then collected by a miniature macrolens system and imaged by a high-resolution CMOS camera at a high frame rate (50 fps). Using this miniature imager, we achieve high spatiotemporal resolution laser speckle contrast imaging of CBF in freely moving animals in real time.

Select this Article OPEN ACCESS		Automatic sound speed selection in photoacoustic image reconstruction using an autofocus approach Bradley E. Treeby, Trond K. Varslot, Edward Z. Zhang, Jan G. Laufer, and Paul C. Beard J. Biomed. Opt. 16, 090501 (1 September 2011); http://dx.doi.org/10.1117/1.3619139 Online Publication Date: Sep 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The reconstruction of images in photoacoustic tomography is reliant on specifying the speed of sound within the propagation medium. However, for in vivo imaging, this value is not normally accurately known. Here, an autofocus approach for automatically selecting the sound speed is proposed. This is based on maximizing the sharpness of the reconstructed image as quantified by a focus function. Several focus functions are investigated, and their performance is discussed. The method is demonstrated using phantom measurements made in a medium with a known sound speed and in vivo measurements of the vasculature in the flank of an adult mouse.

Select this Article OPEN ACCESS		Reflection-mode time-reversed ultrasonically encoded optical focusing into turbid media Puxiang Lai, Xiao Xu, Honglin Liu, Yuta Suzuki, and Lihong V. Wang J. Biomed. Opt. 16, 080505 (11 August 2011); http://dx.doi.org/10.1117/1.3609001 Online Publication Date: Aug 11, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Time-reversed ultrasonically encoded (TRUE) optical focusing was recently proposed to deliver light dynamically to a tight region inside a scattering medium. In this letter, we report the first development of a reflection-mode TRUE optical focusing system. A high numerical aperture light guide is used to transmit the diffusely reflected light from a turbid medium to a phase-conjugate mirror (PCM), which is sensitive only to the ultrasound-tagged light. From the PCM, a phase conjugated wavefront of the tagged light is generated and conveyed by the same light guide back to the turbid medium, subsequently converging to the ultrasonic focal zone. We present experimental results from this system, which has the ability to focus light in a highly scattering medium with a round-trip optical penetration thickness (extinction coefficient multiplied by round-trip depth) as large as 160.

Select this Article OPEN ACCESS		Simultaneous in vivo imaging of melanin and lipofuscin in the retina with photoacoustic ophthalmoscopy and autofluorescence imaging Xiangyang Zhang, Hao F. Zhang, Carmen A. Puliafito, and Shuliang Jiao J. Biomed. Opt. 16, 080504 (5 August 2011); http://dx.doi.org/10.1117/1.3606569 Online Publication Date: Aug 05, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We combined photoacoustic ophthalmoscopy (PAOM) with autofluorescence imaging for simultaneous in vivo imaging of dual molecular contrasts in the retina using a single light source. The dual molecular contrasts come from melanin and lipofuscin in the retinal pigment epithelium (RPE). Melanin and lipofuscin are two types of pigments and are believed to play opposite roles (protective versus exacerbate) in the RPE in the aging process. We have successfully imaged the retina of pigmented and albino rats at different ages. The experimental results showed that multimodal PAOM system can be a potentially powerful tool in the study of age-related degenerative retinal diseases.

Select this Article OPEN ACCESS		Comparative study of the angle-resolved backscattering properties of collagen fibers in bovine tendon and cartilage Deepa K. Kasaragod, Zenghai Lu, and Stephen J. Matcher J. Biomed. Opt. 16, 080501 (5 August 2011); http://dx.doi.org/10.1117/1.3606564 Online Publication Date: Aug 05, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In a biological tissue, light scattering is based on the size and type of scatterers seen as refractive index variations that describe the optical properties shown. In this paper, we have implemented the variable incidence angle technique of multiple angle of illumination experiment on tendon and cartilage samples whose dominant constituents are genetically different types of collagen fibers, type I and type II, respectively. It is found that tendon displays a much greater angular anisotropy in its optical backscattering coefficient than the healthy cartilage. We propose that this is due to a more uniform distribution of fine fibrils than is found in tendon. Rayleigh–Gans approximation is used to give qualitative support to this idea.

Select this Article OPEN ACCESS		Identification of the direction of the neural network activation with a cellular resolution by fast two-photon imaging Xiuli Liu, Tingwei Quan, Shaoqun Zeng, and Xiaohua Lv J. Biomed. Opt. 16, 080506 (1 August 2011); http://dx.doi.org/10.1117/1.3613918 Online Publication Date: Aug 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Spatiotemporal activity patterns in local neural networks are fundamental to understanding how information is processed and stored in brain microcircuits. Currently, imaging techniques are able to map the directional activation of macronetworks across brain areas; however, these strategies still fail to resolve the activation direction for fine microcircuits with cellular spatial resolution. Here, we show the capability to identify the activation direction of a multicell network with a cellular resolution and millisecond precision by using fast two-photon microscopy and cross correlation procedures. As an example, we characterized a directional neuronal network in an epilepsy brain slice to provide different initiation delay among multiple neurons defined at a millisecond scale.

Select this Article OPEN ACCESS		Photoacoustic microscopy of tyrosinase reporter gene in vivo Arie Krumholz, Sarah J. VanVickle-Chavez, Junjie Yao, Timothy P. Fleming, William E. Gillanders, and Lihong V. Wang J. Biomed. Opt. 16, 080503 (1 August 2011); http://dx.doi.org/10.1117/1.3606568 Online Publication Date: Aug 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Photoacoustic tomography is a hybrid modality based on optical absorption excitation and ultrasonic detection. It is sensitive to melanin, one of the primary absorbers in skin. For cells that do not naturally contain melanin, melanin production can be induced by introducing the gene for tyrosinase, the primary enzyme responsible for expression of melanin in melanogenic cells. Optical resolution photoacoustic microscopy was used in the ex vivo study reported here, where the signal from transfected cells increased by more than 10 times over wild-type cells. A subsequent in vivo experiment was conducted to demonstrate the capability of photoacoustic microscopy to spectrally differentiate between tyrosinase-catalyzed melanin and various other absorbers in tissue.

Select this Article OPEN ACCESS		Coregistered photoacoustic-ultrasound imaging applied to brachytherapy Tyler Harrison and Roger J. Zemp J. Biomed. Opt. 16, 080502 (1 August 2011); http://dx.doi.org/10.1117/1.3606566 Online Publication Date: Aug 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Brachytherapy is a form of radiation therapy commonly used in the treatment of prostate cancer wherein sustained radiation doses can be precisely targeted to the tumor area by the implantation of small radioactive seeds around the treatment area. Ultrasound is a popular imaging mode for seed implantation, but the seeds are difficult to distinguish from the tissue structure. In this work, we demonstrate the feasibility of photoacoustic imaging for identifying brachytherapy seeds in a tissue phantom, comparing the received intensity to endogenous contrast. We have found that photoacoustic imaging at 1064 nm can identify brachytherapy seeds uniquely at laser penetration depths of 5 cm in biological tissue at the ANSI limit for human exposure with a contrast-to-noise ratio of 26.5 dB. Our realtime combined photoacoustic-ultrasound imaging approach may be suitable for brachytherapy seed placement and post-placement verification, potentially allowing for realtime dosimetry assessment during implantation.

Select this Article OPEN ACCESS		Detecting apoptosis using dynamic light scattering with optical coherence tomography Golnaz Farhat, Adrian Mariampillai, Victor X. D. Yang, Gregory J. Czarnota, and Michael C. Kolios J. Biomed. Opt. 16, 070505 (18 July 2011); http://dx.doi.org/10.1117/1.3600770 Online Publication Date: Jul 18, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A dynamic light scattering technique is implemented using optical coherence tomography (OCT) to measure the change in intracellular motion as cells undergo apoptosis. Acute myeloid leukemia cells were treated with cisplatin and imaged at a frame rate of 166 Hz using a 1300 nm swept-source OCT system at various times over a period of 48 h. Time correlation analysis of the speckle intensities indicated a significant increase in intracellular motion 24 h after treatment. This rise in intracellular motion correlated with histological findings of irregularly shaped and fragmented cells indicative of cell membrane blebbing and fragmentation.

Select this Article OPEN ACCESS		Method to calibrate phase fluctuation in polarization-sensitive swept-source optical coherence tomography Zenghai Lu, Deepa K. Kasaragod, and Stephen J. Matcher J. Biomed. Opt. 16, 070502 (18 July 2011); http://dx.doi.org/10.1117/1.3597721 Online Publication Date: Jul 18, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present a phase fluctuation calibration method for polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) using continuous polarization modulation. The method uses a low-voltage broadband polarization modulator driven by a synchronized sinusoidal burst waveform rather than an asynchronous waveform, together with the removal of the global phases of the measured Jones matrices by the use of matrix normalization. This makes it possible to average the measured Jones matrices to remove the artifact due to the speckle noise of the signal in the sample without introducing auxiliary optical components into the sample arm. This method was validated on measurements of an equine tendon sample by the PS-SS-OCT system.

Select this Article OPEN ACCESS		Quantification of nanoscale nuclear refractive index changes during the cell cycle Rajan K. Bista, Shikhar Uttam, Pin Wang, Kevin Staton, Serah Choi, Christopher J. Bakkenist, Douglas J. Hartman, Randall E. Brand, and Yang Liu J. Biomed. Opt. 16, 070503 (6 July 2011); http://dx.doi.org/10.1117/1.3597723 Online Publication Date: Jul 06, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Intrigued by our recent finding that the nuclear refractive index is significantly increased in malignant cells and histologically normal cells in clinical histology specimens derived from cancer patients, we sought to identify potential biological mechanisms underlying the observed phenomena. The cell cycle is an ordered series of events that describes the intervals of cell growth, DNA replication, and mitosis that precede cell division. Since abnormal cell cycles and increased proliferation are characteristic of many human cancer cells, we hypothesized that the observed increase in nuclear refractive index could be related to an abundance or accumulation of cells derived from cancer patients at a specific point or phase(s) of the cell cycle. Here we show that changes in nuclear refractive index of fixed cells are seen as synchronized populations of cells that proceed through the cell cycle, and that increased nuclear refractive index is strongly correlated with increased DNA content. We therefore propose that an abundance of cells undergoing DNA replication and mitosis may explain the increase in nuclear refractive index observed in both malignant and histologically normal cells from cancer patients. Our findings suggest that nuclear refractive index may be a novel physical parameter for early cancer detection and risk stratification.

Select this Article OPEN ACCESS		Monte Carlo fluorescence microtomography Alexander X. Cong, Matthias C. Hofmann, Wenxiang Cong, Yong Xu, and Ge Wang J. Biomed. Opt. 16, 070501 (1 July 2011); http://dx.doi.org/10.1117/1.3596171 Online Publication Date: Jul 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Fluorescence microscopy allows real-time monitoring of optical molecular probes for disease characterization, drug development, and tissue regeneration. However, when a biological sample is thicker than 1 mm, intense scattering of light would significantly degrade the spatial resolution of fluorescence microscopy. In this paper, we develop a fluorescence microtomography technique that utilizes the Monte Carlo method to image fluorescence reporters in thick biological samples. This approach is based on an l₀-regularized tomography model and provides an excellent solution. Our studies on biomimetic tissue scaffolds have demonstrated that the proposed approach is capable of localizing and quantifying the distribution of optical molecular probe accurately and reliably.

Select this Article OPEN ACCESS		Towards noncontact skin melanoma selection by multispectral imaging analysis Ilona Kuzmina, Ilze Diebele, Dainis Jakovels, Janis Spigulis, Lauma Valeine, Janis Kapostinsh, and Anna Berzina J. Biomed. Opt. 16, 060502 (9 June 2011); http://dx.doi.org/10.1117/1.3584846 Online Publication Date: Jun 09, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A clinical trial comprising 334 pigmented and vascular lesions has been performed in three Riga clinics by means of multispectral imaging analysis. The imaging system Nuance 2.4 (CRi) and self-developed software for mapping of the main skin chromophores were used. Specific features were observed and analyzed for malignant skin melanomas: notably higher absorbance (especially as the difference of optical density relative to the healthy skin), uneven chromophore distribution over the lesion area, and the possibility to select the “melanoma areas” in the correlation graphs of chromophores. The obtained results indicate clinical potential of this technology for noncontact selection of melanoma from other pigmented and vascular skin lesions.

Select this Article OPEN ACCESS		Novel combined miniature optical coherence tomography ultrasound probe for in vivo intravascular imaging Jiechen Yin, Xiang Li, Joe Jing, Jiawen Li, David Mukai, Sari Mahon, Ahmad Edris, Khiet Hoang, K. Kirk Shung, Matthew Brenner, Jagat Narula, Qifa Zhou, and Zhongping Chen J. Biomed. Opt. 16, 060505 (2 June 2011); http://dx.doi.org/10.1117/1.3589097 Online Publication Date: Jun 02, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We have developed a miniature integrated optical coherence tomography (OCT) ultrasound (US) probing system for intravascular imaging applications. In the OCT probe, the light coming out of a single mode fiber is focused by a gradient-index lens and then reflected by a right-angle prism from the side of the probe into the sample. It was combined with a 35 MHz PMN-PT side-viewing ultrasound transducer to obtain the ultrasound image as well. The OCT and ultrasound probes were integrated as a single probe to obtain OCT and ultrasound images simultaneously. The integrated probe has an outer diameter of 0.69 mm which, to our knowledge, is the smallest integrated OCT-US probe reported. Fast data acquisition and processing was implemented for real-time imaging. In vitro OCT and US images of human coronary artery with pathology, as well as in vivo images of normal rabbit abdominal aorta, were obtained using the integrated OCT-US probe to demonstrate its capability.

Select this Article OPEN ACCESS		Angular high-speed massively parallel detection spectral-domain optical coherence tomography for speckle reduction Yuuki Watanabe, Haruyuki Hasegawa, and Seiya Maeno J. Biomed. Opt. 16, 060504 (1 June 2011); http://dx.doi.org/10.1117/1.3589093 Online Publication Date: Jun 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We demonstrate speckle reduction based on angular compounding using parallel-detection spectral-domain optical coherence tomography (OCT). An ultrahigh-speed two-dimensional complementary metal-oxide semiconductor camera acquired angular and spectral interference fringes (128×1024 pixels) simultaneously at 15,000 frames∕s for a single lateral point. A signal-to-noise ratio improvement of 8 dB was achieved for imaging human skin in vivo by averaging 121 angle-resolved OCT images.

Select this Article OPEN ACCESS		High-speed 1310 nm-band spectral domain optical coherence tomography at 184,000 lines per second Lin An, Guangying Guan, and Ruikang K. Wang J. Biomed. Opt. 16, 060506 (1 June 2011); http://dx.doi.org/10.1117/1.3592492 Online Publication Date: Jun 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose a useful method to boost the imaging speed for spectral domain optical coherence tomography (SDOCT) by multiplying a number of high-speed spectrometers used in the system with selective precise control of data-recording and data-reading phases for spectral cameras employed in each spectrometer. To demonstrate the proposed method, we use two spectrometers built in a 1310 nm-band SDOCT system, each equipped with a high-speed InGaAs line-scan camera capable of 92-kHz line-scan rate, to achieve an unprecedented imaging speed at 184,000 lines∕s. We validate the multiplied imaging speed by measuring Doppler-induced phase shift in the spectrograms using a flow phantom.

Select this Article OPEN ACCESS		Quantitative cell imaging using single beam phase retrieval method Arun Anand, Vani Chhaniwal, and Bahram Javidi J. Biomed. Opt. 16, 060503 (1 June 2011); http://dx.doi.org/10.1117/1.3589090 Online Publication Date: Jun 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Quantitative three-dimensional imaging of cells can provide important information about their morphology as well as their dynamics, which will be useful in studying their behavior under various conditions. There are several microscopic techniques to image unstained, semi-transparent specimens, by converting the phase information into intensity information. But most of the quantitative phase contrast imaging techniques is realized either by using interference of the object wavefront with a known reference beam or using phase shifting interferometry. A two-beam interferometric method is challenging to implement especially with low coherent sources and it also requires a fine adjustment of beams to achieve high contrast fringes. In this letter, the development of a single beam phase retrieval microscopy technique for quantitative phase contrast imaging of cells using multiple intensity samplings of a volume speckle field in the axial direction is described. Single beam illumination with multiple intensity samplings provides fast convergence and a unique solution of the object wavefront. Three-dimensional thickness profiles of different cells such as red blood cells and onion skin cells were reconstructed using this technique with an axial resolution of the order of several nanometers.

Select this Article OPEN ACCESS		Rapid confocal imaging of large areas of excised tissue with strip mosaicing Sanjee Abeytunge, Yongbiao Li, Bjorg Larson, Ricardo Toledo-Crow, and Milind Rajadhyaksha J. Biomed. Opt. 16, 050504 (26 May 2011); http://dx.doi.org/10.1117/1.3582335 Online Publication Date: May 26, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Imaging large areas of tissue rapidly and with high resolution may enable rapid pathology at the bedside. The limited field of view of high-resolution microscopes requires the merging of multiple images that are taken sequentially to cover a large area. This merging or mosaicing of images requires long acquisition and processing times, and produces artifacts. To reduce both time and artifacts, we developed a mosaicing method on a confocal microscope that images morphology in large areas of excised tissue with sub-cellular detail. By acquiring image strips with aspect ratios of 10:1 and higher (instead of the standard ∼1:1) and “stitching” them in software, our method images 10×10 mm² area of tissue in about 3 min. This method, which we call “strip mosaicing,” is currently three times as fast as our previous method.

Select this Article OPEN ACCESS		Multifunctional imaging of human retina and choroid with 1050-nm spectral domain optical coherence tomography at 92-kHz line scan rate Ruikang K. Wang and Lin An J. Biomed. Opt. 16, 050503 (19 May 2011); http://dx.doi.org/10.1117/1.3582159 Online Publication Date: May 19, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The light source at ∼1-μm wavelength is attractive for enhanced imaging depth in retinal optical coherence tomography (OCT). In this paper, we report on a 1050-nm spectral domain OCT system, combined with optical microangiography that operates at a 92-kHz line scan rate for multifunctional imaging of the human eye, delivering the volumetric imaging of microstructure and microvasculature within retina and choroid.

Select this Article OPEN ACCESS		Confocal imaging reveals three-dimensional fine structure difference between ventral and dorsal nerve roots Yuxiang Wu, Tao Sui, Xiaojian Cao, Xiaohua Lv, Shaoqun Zeng, and Peng Sun J. Biomed. Opt. 16, 050502 (10 May 2011); http://dx.doi.org/10.1117/1.3575167 Online Publication Date: May 10, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Peripheral nerve injury repair is one of the most challenging problems in neurosurgery, partially due to lack of knowledge of three-dimensional (3-D) fine structure and organization of peripheral nerves. In this paper, we explored the structures of nerve fibers in ventral and dorsal nerves with a laser scanning confocal microscopy. Thick tissue staining results suggested that nerve fibers have a different 3-D structure in ventral and dorsal nerves, and reconstruction from serial sectioning images showed that in ventral nerves the nerve fibers travel in a winding form, while in dorsal nerves, the nerve fibers form in a parallel cable pattern. These structural differences could help surgeons to differentiate ventral and dorsal nerves in peripheral nerve injury repair, and also facilitate scientists to get a deeper understanding about nerve fiber organization.

Select this Article OPEN ACCESS		Fiber loop ringdown DNA and bacteria sensors Chamini Herath, Chuji Wang, Malik Kaya, and David Chevalier J. Biomed. Opt. 16, 050501 (2 May 2011); http://dx.doi.org/10.1117/1.3572046 Online Publication Date: May 02, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We report a new type of refractive index-based biosensor using a fiber loop ringdown evanescent field (FLRD-EF) sensing scheme, in which the sensing signal is a time constant and detection sensitivity is enhanced by the multipass nature of the ringdown technique. Bulk index-based detections of three different single strand DNAs and one type of bacteria are demonstrated for the FLRD-EF sensors that utilize a partially-etched single mode fiber as the sensor head. Stepwise coating of the sensor head with poly-L-lysine and a probe DNA has enabled surface index-based label-free target DNA sensing. We expect an array of FLRD-EF biosensors to be created, which are superior to counterparts in terms of simplicity, low cost, and high sensitivity.

Select this Article OPEN ACCESS		Quantitative analysis on collagen morphology in aging skin based on multiphoton microscopy Shulian Wu, Hui Li, Hongqin Yang, Xiaoman Zhang, Zhifang Li, and Shufei Xu J. Biomed. Opt. 16, 040502 (14 April 2011); http://dx.doi.org/10.1117/1.3565439 Online Publication Date: Apr 14, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Multiphoton microscopy was employed for monitoring the structure changes of mouse dermis collagen in the intrinsic- or the extrinsic-age-related processes in vivo. The characteristics of textures in different aging skins were uncovered by fast Fourier transform in which the orientation index and bundle packing of collagen were quantitatively analyzed. Some significant differences in collagen-related changes are found in different aging skins, which can be good indicators for the statuses of aging skins. The results are valuable to the study of aging skin and also of interest to biomedical photonics.

Select this Article OPEN ACCESS		Dermal reflectivity determined by optical coherence tomography is an indicator of epidermal hyperplasia and dermal edema within inflamed skin Kevin G. Phillips, Yun Wang, David Levitz, Niloy Choudhury, Emily Swanzey, James Lagowski, Molly Kulesz-Martin, and Steven L. Jacques J. Biomed. Opt. 16, 040503 (4 April 2011); http://dx.doi.org/10.1117/1.3567082 Online Publication Date: Apr 04, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Psoriasis is a common inflammatory skin disease resulting from genetic and environmental alterations of cutaneous immune responses. While numerous therapeutic targets involved in the immunopathogenesis of psoriasis have been identified, the in vivo dynamics of inflammation in psoriasis remain unclear. We undertook in vivo time course focus-tracked optical coherence tomography (OCT) imaging to noninvasively document cutaneous alterations in mouse skin treated topically with Imiquimod (IMQ), an established model of a psoriasis-like disease. Quantitative appraisal of dermal architectural changes was achieved through a two parameter fit of OCT axial scans in the dermis of the form A(x, y, z) = ρ(x, y)exp [ − μ(x, y)z]. Ensemble averaging over 2000 axial scans per mouse in each treatment arm revealed no significant changes in the average dermal attenuation rate, 〈μ〉, however the average local dermal reflectivity 〈ρ〉, decreased significantly following 1, 3, and 6 days of IMQ treatment (p < 0.001) in comparison to vehicle-treated control mice. In contrast, epidermal and dermal thickness changes were only significant when comparing controls and 6-day IMQ treated mice. This suggests that dermal alterations, attributed to collagen fiber bundle enlargement, occur prior to epidermal thickness changes due to hyperplasia and dermal thickness changes due to edema. Dermal reflectivity positively correlated with epidermal hyperplasia (repi2 = 0.78) and dermal edema (rderm2 = 0.86). Our results suggest that dermal reflectivity as measured by OCT can be utilized to quantify a psoriasis-like disease in mice, and thus has the potential to aid in the quantitative assessment of psoriasis in humans.

Select this Article OPEN ACCESS		Contact and contactless diffuse reflectance spectroscopy: potential for recovery monitoring of vascular lesions after intense pulsed light treatment Ilona Kuzmina, Ilze Diebele, Janis Spigulis, Lauma Valeine, Anna Berzina, and Anita Abelite J. Biomed. Opt. 16, 040505 (1 April 2011); http://dx.doi.org/10.1117/1.3569119 Online Publication Date: Apr 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Optical fiber contact probe diffuse reflectance spectroscopy and remote multispectral imaging methods in the spectral range of 400 to 1100 nm were used for skin vascular malformation assessment and recovery tracing after treatment by intense pulsed light. The results confirmed that oxy-hemoglobin relative changes and the optical density difference between lesion and healthy skin in the spectral region 500 to 600 nm may be successfully used for objective appraisal of the therapy effect. Color redness parameter a∗ = 2 is suggested as a diagnostic border to distinguish healthy skin and vascular lesions, and as the indicator of phototreatment efficiency. Valuable diagnostic information on large area (>5 mm) lesions and lesions with uncertain borders can be proved by the multispectral imaging method.

Select this Article OPEN ACCESS		Quantitative microscopy and nanoscopy of sickle red blood cells performed by wide field digital interferometry Natan T. Shaked, Lisa L. Satterwhite, Marilyn J. Telen, George A. Truskey, and Adam Wax J. Biomed. Opt. 16, 030506 (24 March 2011); http://dx.doi.org/10.1117/1.3556717 Online Publication Date: Mar 24, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We have applied wide-field digital interferometry (WFDI) to examine the morphology and dynamics of live red blood cells (RBCs) from individuals who suffer from sickle cell anemia (SCA), a genetic disorder that affects the structure and mechanical properties of RBCs. WFDI is a noncontact, label-free optical microscopy approach that can yield quantitative thickness profiles of RBCs and measurements of their membrane fluctuations at the nanometer scale reflecting their stiffness. We find that RBCs from individuals with SCA are significantly stiffer than those from a healthy control. Moreover, we show that the technique is sensitive enough to distinguish classes of RBCs in SCA, including sickle RBCs with apparently normal morphology, compared to the stiffer crescent-shaped sickle RBCs. We expect that this approach will be useful for diagnosis of SCA and for determining efficacy of therapeutic agents.

Select this Article OPEN ACCESS		Segmental analysis of indocyanine green pharmacokinetics for the reliable diagnosis of functional vascular insufficiency Yujung Kang, Jungsul Lee, Yuri An, Jongwook Jeon, and Chulhee Choi J. Biomed. Opt. 16, 030504 (14 March 2011); http://dx.doi.org/10.1117/1.3556718 Online Publication Date: Mar 14, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Accurate and reliable diagnosis of functional insufficiency of peripheral vasculature is essential since Raynaud phenomenon (RP), most common form of peripheral vascular insufficiency, is commonly associated with systemic vascular disorders. We have previously demonstrated that dynamic imaging of near-infrared fluorophore indocyanine green (ICG) can be a noninvasive and sensitive tool to measure tissue perfusion. In the present study, we demonstrated that combined analysis of multiple parameters, especially onset time and modified T_max which means the time from onset of ICG fluorescence to T_max, can be used as a reliable diagnostic tool for RP. To validate the method, we performed the conventional thermographic analysis combined with cold challenge and rewarming along with ICG dynamic imaging and segmental analysis. A case-control analysis demonstrated that segmental pattern of ICG dynamics in both hands was significantly different between normal and RP case, suggesting the possibility of clinical application of this novel method for the convenient and reliable diagnosis of RP.

Select this Article OPEN ACCESS		Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings Tae Joong Eom, Yeh-Chan Ahn, Chang-Seok Kim, and Zhongping Chen J. Biomed. Opt. 16, 030501 (11 March 2011); http://dx.doi.org/10.1117/1.3552602 Online Publication Date: Mar 11, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present a calibration protocol to obtain the alignment factors of a custom-made spectrometer and the nonlinear fitting function between the measured CCD pixel domain and the wavelength domain to apply to the spectral-domain optical coherence tomography (SD-OCT) using fiber Bragg gratings. We have used five gratings with different center wavelengths covering the broadband source spectral range. All have a narrow spectral bandwidth (0.05 nm) and the same reflectivity (92%) to calibrate and align the custom-made spectrometer. The implemented SD-OCT system following the proposed protocol showed the alignment factors as 44.37 deg incident angle, 53.11 deg diffraction angle, and 70.0-mm focal length. The spectral resolution of 0.187 nm was recalculated from the alignment factors.

Select this Article OPEN ACCESS		Automated identification of epidermal keratinocytes in reflectance confocal microscopy Dan Gareau J. Biomed. Opt. 16, 030502 (9 March 2011); http://dx.doi.org/10.1117/1.3552639 Online Publication Date: Mar 09, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Keratinocytes in skin epidermis, which have bright cytoplasmic contrast and dark nuclear contrast in reflectance confocal microscopy (RCM), were modeled with a simple error function reflectance profile: erf( ). Forty-two example keratinocytes were identified as a training set which characterized the nuclear size a = 8.6±2.8 μm and reflectance gradient b = 3.6±2.1 μm at the nuclear∕cytoplasmic boundary. These mean a and b parameters were used to create a rotationally symmetric erf( ) mask that approximated the mean keratinocyte image. A computer vision algorithm used an erf( ) mask to scan RCM images, identifying the coordinates of keratinocytes. Applying the mask to the confocal data identified the positions of keratinocytes in the epidermis. This simple model may be used to noninvasively evaluate keratinocyte populations as a quantitative morphometric diagnostic in skin cancer detection and evaluation of dermatological cosmetics.

Select this Article OPEN ACCESS		Measurements of wavelength dependent scattering and backscattering coefficients by low-coherence spectroscopy Nienke Bosschaart, Dirk J. Faber, Ton G. van Leeuwen, and Maurice C. G. Aalders J. Biomed. Opt. 16, 030503 (1 March 2011); http://dx.doi.org/10.1117/1.3553005 Online Publication Date: Mar 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Quantitative measurements of scattering properties are invaluable for optical techniques in medicine. However, noninvasive, quantitative measurements of scattering properties over a large wavelength range remain challenging. We introduce low-coherence spectroscopy as a noninvasive method to locally and simultaneously measure scattering μ_s and backscattering μ_b coefficients from 480 to 700 nm with 8 nm spectral resolution. The method is tested on media with varying scattering properties (μ_s = 1 to 34 mm⁻¹ and μ_b = 2.10⁻⁶ to 2.10⁻³ mm⁻¹), containing different sized polystyrene spheres. The results are in excellent agreement with Mie theory.

Select this Article OPEN ACCESS		Processing and rendering of Fourier domain optical coherence tomography images at a line rate over 524 kHz using a graphics processing unit Janarthanan Rasakanthan, Kate Sugden, and Peter H. Tomlins J. Biomed. Opt. 16, 020505 (22 February 2011); http://dx.doi.org/10.1117/1.3548153 Online Publication Date: Feb 22, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In Fourier domain optical coherence tomography (FD-OCT), a large amount of interference data needs to be resampled from the wavelength domain to the wavenumber domain prior to Fourier transformation. We present an approach to optimize this data processing, using a graphics processing unit (GPU) and parallel processing algorithms. We demonstrate an increased processing and rendering rate over that previously reported by using GPU paged memory to render data in the GPU rather than copying back to the CPU. This avoids unnecessary and slow data transfer, enabling a processing and display rate of well over 524,000 A-scan∕s for a single frame. To the best of our knowledge this is the fastest processing demonstrated to date and the first time that FD-OCT processing and rendering has been demonstrated entirely on a GPU.

Select this Article OPEN ACCESS		In-vivo characterization of optical properties of pigmented skin lesions including melanoma using oblique incidence diffuse reflectance spectrometry Alejandro Garcia-Uribe, Elizabeth B. Smith, Jun Zou, Madeleine Duvic, Victor Prieto, and Lihong V. Wang J. Biomed. Opt. 16, 020501 (17 February 2011); http://dx.doi.org/10.1117/1.3536509 Online Publication Date: Feb 17, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In this letter, we report the first use of oblique incidence diffuse reflectance spectrometry to conduct in-vivo measurements of optical properties of three different types of pigmented skin lesions, including melanoma, dysplastic, and common nevi. Both absorption and reduced scattering coefficient spectra were estimated from the spatially resolved diffuse reflectance within the wavelength range of 455–765 nm for 144 pigmented skin lesions including 16 melanomas. The absorption and reduced scattering spectra were found to change with the malignancy of the skin lesions, which were generally higher for the malignant cases than the benign ones. Based on the measurement results, the physiological origin leading to the change of the absorption and scattering properties is also discussed.

Select this Article OPEN ACCESS		Mathematical model that describes the transition from thermal to photochemical damage in retinal pigment epithelial cell culture Clifton D. Clark, III, Michael L. Denton, and Robert J. Thomas J. Biomed. Opt. 16, 020504 (17 February 2011); http://dx.doi.org/10.1117/1.3544504 Online Publication Date: Feb 17, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose a rate process model for describing photochemical damage to retinal cells by short wavelength laser exposures. The rate equation for photochemical damage contains a positive rate that is temperature independent, and a negative (quenching) rate that is temperature dependent. Using the traditional Arrhenius integral to describe thermal damage, we derive damage threshold doses for both thermal and photochemical mechanisms, and show that the model accounts for the sharp transition from thermal to photochemical damage thresholds that have recently been observed in an in-vitro retinal model.

Select this Article OPEN ACCESS		In vivo photoacoustic imaging of osteosarcoma in a rat model Jun Hu, Menglei Yu, Fei Ye, and Da Xing J. Biomed. Opt. 16, 020503 (17 February 2011); http://dx.doi.org/10.1117/1.3544502 Online Publication Date: Feb 17, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Osteosarcoma is one of the most common primary malignant tumors of the bone and the second leading cause of cancer-related deaths in the pediatric age group. Confirmed diagnosis and prompt treatment of osteosarcoma are critical for effective prognosis. In this study, we investigate the application of photoacoustic imaging (PAI) for the detection of osteosarcoma in an animal model. Cross-section images of a normal rat leg and a tumorous rat leg were successfully reconstructed in vivo. Morphological changes and the development of the implanted osteosarcoma were accurately mapped with time-dependent photoacoustic images. Furthermore, we evaluate the use of gold nanorods as contrast agents for imaging osteosarcoma with PAI. This is the first study that uses PAI to detect osteosarcoma in vivo, and the results suggest that PAI has the potential clinical application for detecting osteosarcoma in the early stage.

Select this Article OPEN ACCESS		Drug-loaded biodegradable microspheres for image-guided combinatory epigenetic therapy in cells Ronald X. Xu, Jeff S. Xu, Tao Zuo, Rulong Shen, Tim H. Huang, and Michael F. Tweedle J. Biomed. Opt. 16, 020507 (16 February 2011); http://dx.doi.org/10.1117/1.3548878 Online Publication Date: Feb 16, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We synthesize drug-loaded poly (lactic-co-glycolic acid) (PLGA) microspheres for image-guided combinatory epigenetic therapy in MCF-10A human mammary epithelial cells. LY294002 and Nile Red are encapsulated in microspheres for sustained drug release and fluorescence microscopic imaging. Drug-loaded microspheres target MCF-10A cells through a three-step binding process involving biotinylated antibody, streptavidin, and biotinylated microspheres. LY294002 loaded microspheres and 5-Aza-2-deoxycytidine are applied to MCF-10A cells for combinatory PI3K∕AKT inhibition and deoxyribonucleic acid (DNA) demethylation. Our study implies the technical potential of disease targeting and image-guided combinatory epigenetic therapy using drug-loaded multifunctional biodegradable PLGA microspheres.

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Letters from Journal of Micro/Nanolithography, MEMS, and MOEMS

Select this Article OPEN ACCESS		Analytic form for the power spectral density in one, two, and three dimensions Chris A. Mack J. Micro/Nanolith. MEMS MOEMS 10, 040501 (30 November 2011); http://dx.doi.org/10.1117/1.3663567 Online Publication Date: Nov 30, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Analytical expressions for the power spectral density (PSD) are often useful in stochastic lithography simulation and the metrology of roughness. Using a common stretched exponential correlation function with three parameters (standard deviation, correlation length, and roughness exponent), the PSD can be computed as the Fourier transform of the autocorrelation function. For the special cases of roughness exponent equal to 0.5 and 1, the PSD can be computed analytically for one, two, and three dimensions. In this paper, the analytical results of these calculations are given. The resulting equations can be used when modeling rough lines, surfaces, or volumes.

Select this Article OPEN ACCESS		Fabrication of a needle-type pH sensor by selective electrodeposition Woo-Hyuck Choi and Ian Papautsky J. Micro/Nanolith. MEMS MOEMS 10, 020501 (12 May 2011); http://dx.doi.org/10.1117/1.3580751 Online Publication Date: May 12, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This manuscript reports on the development of a needle-type sensor for in situ on-site measurement of pH. Conventional pH microelectrode sensors are fabricated by pulling glass pipettes and applying ion-selective films at the tip. However, these sensors suffer from low fabrication yields and short sensor lifetime due to disruption or loss of the ion-selective membrane after repeated use. The developed needle-type sensor is fabricated by meniscus etching and takes advantage of the MEMS batch fabrication techniques. The sensor is based on the ion-selective properties of iridium oxide film, which was deposited at the sensor tip by electrodeposition. The sensor exhibited a Nernstian response with sensitivity of ∼62 mV∕pH in the pH 2 to 12 range. The sensor also exhibited a fast 5 s response and a lifetime of ∼2 months when stored in a pH7 buffer solution, which is substantially longer than that of the conventional pulled-pipette sensors.

Select this Article OPEN ACCESS		Fabrication of polynomial 3-D nanostructures in Si with a single-step process Dong Liu, Shakib Morshed, Bo Zhou, Barton C. Prorok, and Soo-Young Lee J. Micro/Nanolith. MEMS MOEMS 10, 010501 (29 March 2011); http://dx.doi.org/10.1117/1.3563601 Online Publication Date: Mar 29, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This work demonstrated the ability to transfer a nanoscale 3-D polynomial structure of arbitrary shape into Si with a single step electron-beam lithography process. The technique involved employing a proximity correction algorithm, PYRAMID, to derive the dose distribution for a given 3-D structure by accounting for the electron scattering effects of the surrounding pixels. The pattern was written into a polymethyl methacrylate (PMMA) resist and then successively transferred into Si via reactive ion etching, where a 1:1 etching ratio between PMMA and Si was achieved. The pattern transferred into Si possessed nanoscale features and matched the desired pattern with high fidelity.

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Letters from Journal of Nanophotonics

Select this Article OPEN ACCESS		Silicon-on-insulator microring resonator defect-based photodetector with 3.5-GHz bandwidth Jason J. Ackert, Marco Fiorentino, Dylan F. Logan, Raymond G. Beausoleil, Paul E. Jessop, and Andrew P. Knights J. Nanophoton. 5, 059507 (13 December 2011); http://dx.doi.org/10.1117/1.3666059 Online Publication Date: Dec 13, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We have devised and fabricated high-speed silicon-on-insulator resonant microring photodiodes. The detectors comprise a p-i-n junction across a silicon rib waveguide microring resonator. Light absorption at 1550 nm is enhanced by implanting the diode intrinsic region with boron ions at 350 keV with a dosage of 1 × 10¹³ cm⁻². We have measured 3-dB bandwidths of 2.4 and 3.5 GHz at 5 and 15 V reverse bias, respectively, and observed an open-eye diagram at 5 gigabit∕s with 5 V bias.

Select this Article OPEN ACCESS		Low-energy single-optical-cycle soliton self-compression in air-silica nanowires Amine Ben Salem, Rim Cherif, and Mourad Zghal J. Nanophoton. 5, 059506 (16 November 2011); http://dx.doi.org/10.1117/1.3662888 Online Publication Date: Nov 16, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We investigated and optimized the process of soliton self-compression in few millimeters-long air-silica nanowires. A 100 fs prechirped input pulse was compressed to a 1.4 fs pulse by pumping at very low energy of 2.5 nJ an air-silica nanowire. More than one octave spanning coherent broadband supercontinuum extending from 260 to 1800 nm was generated.

Select this Article OPEN ACCESS		Ultraviolet electroluminescence from zinc oxide nanorods∕deoxyribonucleic acid hybrid bio light-emitting diode Rohini Bhardwaj Gupta, Swati Nagpal, Swati Arora, Pramod Kumar Bhatnagar, and Parmatma Chandra Mathur J. Nanophoton. 5, 059505 (12 August 2011); http://dx.doi.org/10.1117/1.3618630 Online Publication Date: Aug 12, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Ultraviolet (UV) light-emitting diode using salmon deoxyribonucleic acid (sDNA)-cetyltrimethylammonium complex as an electron blocking layer and zinc oxide (ZnO) nanorods as emissive material was fabricated. UV emission, which was blue shifted up to 335 nm with respect to the band edge emission of 390 nm, was observed. This blue shift was caused due to accumulation of electrons in the conduction band of ZnO because of a high potential barrier existing at the sDNA∕ZnO interface.

Select this Article OPEN ACCESS		Combined atomic force microscopy-Raman mapping of electric field enhancement and surface-enhanced Raman scattering hot-spots for nanosphere lithography substrates Claire S. Sweetenham and Ioan Notingher J. Nanophoton. 5, 059504 (1 June 2011); http://dx.doi.org/10.1117/1.3595345 Online Publication Date: Jun 01, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Surface-enhanced Raman spectroscopy (SERS) substrates formed by nanosphere lithography were investigated for their spatial distribution and magnitude of electric field enhancement. An integrated atomic force microscopy and Raman micro-spectroscopy system was used to establish, with high accuracy, the correlation between the local SERS mappings and substrate topography. Using a monolayer of rhodamine 6G as a probe of the local electric field, the high resolution Raman mappings, showed that the highest electric field enhancement originates from the metallic nanostructures rather than the gaps between them. The enhancement factor of the substrates is calculated from Raman spectra of the substrates covered in a monolayer of p-aminothiophenol and spatial measurements, giving a value on the order of 10⁵. The experimental results were confirmed by theoretical calculations using the finite element method.

Select this Article OPEN ACCESS		Structural optimization of quantum wells used in a 1-μm vertical-external-cavity surface-emitting laser Peng Zhang, Yanrong Song, Teli Dai, and Yiping Liang J. Nanophoton. 5, 059502 (5 April 2011); http://dx.doi.org/10.1117/1.3562569 Online Publication Date: Apr 05, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract On the basis of the analysis of material gain, a comprehensive optimization of quantum wells used in a 1-μm vertical-external-cavity surface-emitting laser was carried out. For a single-well structure, the optimized width lies between 8 and 10 nm, the optimized depth is a quantum well with ∼0.1 Al composition in AlGaAs barrier, and the optimized configurations are graded-index quantum well and quantum well with AlGaAs barrier and a GaAs buffer layer. The optimal width of a double- or triple-well structure lies between 6 and 8 nm. Compared to its single- and triple-well counterparts, double-well structure provides higher gain and has more tolerance to the deviation of laser wavelength.

Select this Article OPEN ACCESS		Enhanced resonance tuning of photonic crystal nanocavities by integration of optimized near-field multitip nanoprobes Xiongyeu Chew, Guangya Zhou, Fook Siong Chau, and Jie Deng J. Nanophoton. 5, 059503 (21 April 2011); http://dx.doi.org/10.1117/1.3582145 Online Publication Date: Apr 21, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A compact and low power control of photonic crystal nanocavity resonance was devised, simulated, and experimentally validated utilizing a hybrid integration of a microelectromechanical systems driven nanoprobe. The experimental results demonstrated a reversible resonance tuning up to 5.4 nm with minimal Q-factor degradation.

Select this Article OPEN ACCESS		Photonic-plasmonic integration through the fusion of photonic crystal cavity and metallic structure Depeng Mao, Ming Li, Wai Y. Leung, Kai-Ming Ho, and Liang Dong J. Nanophoton. 5, 059501 (14 March 2011); http://dx.doi.org/10.1117/1.3562941 Online Publication Date: Mar 14, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A photonic-plasmonic integration scheme was devised to displace the defect-mode field of a photonic crystal (PC) slab cavity from the spatial center to the surface of the slab. The device was constructed by placing an isolated metallic structure on the top surface of a missing-hole defect in the PC. Excitation of the metal's surface plasmon resonance mode by the PC cavity's defect mode was investigated using a three-dimensional plane wave transfer matrix method. It was revealed that using the PC cavity could minimize the background field around the metal, significantly enhancing the field intensity contrast between the metal and surrounding dielectric.

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Letters from Journal of Applied Remote Sensing

Select this Article OPEN ACCESS		Characterization of the Sonoran desert as a radiometric calibration target for Earth observing sensors Amit Angal, Gyanesh Chander, Xiaoxiong Xiong, Taeyoung Choi, and Aisheng Wu J. Appl. Remote Sens. 5, 059502 (22 July 2011); http://dx.doi.org/10.1117/1.3613963 Online Publication Date: Jul 22, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract To provide highly accurate quantitative measurements of the Earth's surface, a comprehensive calibration and validation of the satellite sensors is required. The NASA Moderate Resolution Imaging Spectroradiometer (MODIS) Characterization Support Team, in collaboration with United States Geological Survey, Earth Resources Observation and Science Center, has previously demonstrated the use of African desert sites to monitor the long-term calibration stability of Terra MODIS and Landsat 7 (L7) Enhanced Thematic Mapper plus (ETM+). The current study focuses on evaluating the suitability of the Sonoran Desert test site for post-launch long-term radiometric calibration as well as cross-calibration purposes. Due to the lack of historical and on-going in situ ground measurements, the Sonoran Desert is not usually used for absolute calibration. An in-depth evaluation (spatial, temporal, and spectral stability) of this site using well calibrated L7 ETM+ measurements and local climatology data has been performed. The Sonoran Desert site produced spatial variability of about 3 to 5% in the reflective solar regions, and the temporal variations of the site after correction for view-geometry impacts were generally around 3%. The results demonstrate that, barring the impacts due to occasional precipitation, the Sonoran Desert site can be effectively used for cross-calibration and long-term stability monitoring of satellite sensors, thus, providing a good test site in the western hemisphere.

Select this Article OPEN ACCESS		Coherence-based land cover classification in forested areas of Chattisgarh, Central India, using environmental satellite—advanced synthetic aperture radar data Vyjayanthi Nizalapur, Rangaswamy Madugundu, and Chandra Shekhar Jha J. Appl. Remote Sens. 5, 059501 (14 March 2011); http://dx.doi.org/10.1117/1.3557816 Online Publication Date: Mar 14, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In the present work, the potential of synthetic aperture radar (SAR) interferometric coherence in land cover classification is studied over forested areas of Bilaspur, Chattisgarh, India using Environmental Satellite—Advanced Synthetic Aperture Radar (ENVISAT-ASAR) C-band data. Single look complex (SLC) interferometric pair ASAR data of 24th September 2006 (SLC-1) and 29th October 2006 (SLC-2) covering the study area were acquired and processed to generate backscatter and interferometric coherence images. A false colored composite of coherence, backscatter difference, and mean backscatter was generated and subjected to maximum likelihood classification to delineate major land cover classes of the study area viz., water, barren, agriculture, moist deciduous forest, and sal mixed forests. Accuracy assessment of the classified map is carried out using kappa statistics. Results of the study suggested potential use of ENVISAT-ASAR C-band data in land cover classification of the study area with an overall classification accuracy of 82.5%, average producer's accuracy of 83.69%, and average user's accuracy of 81%. The present study gives a unique scope of SAR data application in land cover classification over the tropical deciduous forest systems of India, which is still waiting for its indigenous SAR system.

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Letters from Journal of Photonics for Energy

Select this Article OPEN ACCESS		Cu₂ZnSnS₄ polycrystalline thin films with large densely packed grains prepared by sol-gel method Minlin Jiang, Yong Li, Rabin Dhakal, Prem Thapaliya, Michael Mastro, Joshua D. Caldwell, Fritz Kub, and Xingzhong Yan J. Photon. Energy 1, 019501 (2 September 2011); http://dx.doi.org/10.1117/1.3628450 Online Publication Date: Sep 02, 2011 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Cu₂ZnSnS₄ (CZTS) was obtained from a sol-gel precursor which consists of copper chloride, zinc chloride, tin chloride, and thiourea. CZTS thin films were prepared by spin-coating the sol-gel precursor followed by annealing in a nitrogen atmosphere. The morphology, composition, and structure of the absorber layer were studied by scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, and Raman scattering. The optical measurement shows the bandgap of these films is ∼1.51 eV, and the optical absorption coefficient is on the order of 10⁴ cm⁻¹. CZTS solar cells with a structure of low-alkali glass∕Mo∕CZTS∕CdS∕i-ZnO∕ZnO:Al∕Al grid were tentatively fabricated. The best solar cell showed a short-circuit current density of 5.06 mA∕cm², an open-circuit voltage of 358 mV, a fill factor of 34.66%, and an efficiency of 0.63% under AM1.5 (100 mW∕cm²) illumination. These results demonstrate the CZTS thin films were successfully deposited by a cheap sol-gel technique.

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