An experimental light sensor-based indoor visible light communication (VLC) is presented. Light-emitting diodes (LEDs) primarily used for illumination are employed to transmit wireless optical data over a short distance, while a smartphone’s light sensor is used to receive the data. The light sensor in a smartphone is originally installed to function as a power saving method by adjusting the brightness of the smartphone screen. We propose an efficient and easy-to-use short range VLC based on this light sensor. To compensate for the inherent low sampling rate of the light sensor and also to avoid LED (transmitter) flickering, we propose time shift light intensity modulation. To verify the proposed light sensor VLC, experiments were conducted. The results demonstrate that the data can reliably be transmitted over the VLC link between the LEDs and the smartphone light sensor.

This paper presents the first-time results on design and implementation of a fiber Bragg grating (FBG)-based distributed temperature sensor up to 500°C in a high-voltage and high-electromagnetic interference (EMI) environment. The multiple FBGs at different peak wavelengths were inscribed on a single fiber of length 2 m at the spacing of about 30 cm by controlling the geometrical divergence of a highly coherent UV (255 nm) beam falling on a biprism. The developed multipoint sensor is tested on a high-voltage and high-EMI environment such as a copper bromide (CuBr) laser. The temperature of 200°C to 500°C is monitored online along the operating laser tube length.

The sea level vertical refractive index gradient in the U.S. Standard Atmosphere model is −2.7×10⁻⁸  m⁻¹ at 500 nm. At any particular location, the actual refractive index gradient varies due to turbulence and local weather conditions. An imaging experiment was conducted to measure the temporal variability of this gradient. A tripod mounted digital camera captured images of a distant building every minute. Atmospheric turbulence caused the images to wander quickly, randomly, and statistically isotropically and changes in the average refractive index gradient along the path caused the images to move vertically and more slowly. The temporal variations of the refractive index gradient were estimated from the slow, vertical motion of the building over a period of several days. Comparisons with observational data showed the gradient variations derived from the time-lapse imagery correlated well with solar heating and other weather conditions. The time-lapse imaging approach has the potential to be used as a validation tool for numerical weather models. These validations will benefit directed energy simulation tools and applications.

The optical injection locking (OIL) technique is proposed to reduce the phase noise of a carrier generated for a vertical-cavity surface-emitting laser (VCSEL)-based optoelectronic oscillator. The OIL technique permits the enhancement of the VCSEL direct modulation bandwidth as well as the stabilization of the optical noise of the laser. A 2-km delay line, 10-GHz optical injection-locked VCSEL-based optoelectronic oscillator (OILVBO) was implemented. The internal noise sources of the optoelectronic oscillator components were characterized and analyzed to understand the noise conversion of the system into phase noise in the oscillator carrier. The implemented OILVBO phase noise was −105.7  dBc/Hz at 10 kHz from the carrier; this value agrees well with the performed simulated analysis. From the computed and measured phase noise curves, it is possible to infer the noise processes that take place inside the OILVBO. As a second measurement of the oscillation quality, a time-domain analysis was done through the Allan’s standard deviation measurement, reported for first time for an optoelectronic oscillator using the OIL technique.

We present a simple and cost-effective method for the fabrication of optical elements in the terahertz regime. Caramelized sucrose is used as the refractive medium in the frequency range from 0.1 to 0.4 THz. The absorption coefficient of 7  cm⁻¹ and the high index of refraction of 2.45 at 0.3 THz enables the fabrication of thin optical elements in the near-millimeter wavelength range. The THz beam profiles of the fabricated parabolic lens in focus, evaluated with terahertz pulsed imaging, show the near diffraction limit performance.

A distributed feedback (DFB) fiber laser strain sensor was implemented to measure acoustic emission induced by the hydraulic fracturing process. A study of practical sensor mounting configurations and their characteristics was carried out to find a practical solution. Combining the suitable mounting configuration and ultrahigh strain sensitivity of the DFB fiber laser, the evolution of the hydraulic fracturing process was well monitored. This study shows that fiber lasers can be useful alternatives to piezoelectric sensors in the field of hydraulic fracturing for gas and oil extraction.

Using neighboring cores with different mode propagation constants (indexes) is a well-known way to reduce crosstalk in multicore fiber (MCF). However, in actual field-deployed fiber, random bends can cause a reduction in the difference between the mode indexes of neighboring cores, which consequently increases crosstalk. The level of crosstalk induced by bending in both rectangular cross-section and circular cross-section heterogeneous MCF with cores arranged in a line was investigated. The experimental results obtained indicate that in contrast to circular cross-section MCF, no bending-induced crosstalk occurs in rectangular cross-section MCF wound on the mandrel without special control of cross-section orientation. Thus, to eliminate undesirable bending-induced crosstalk in heterogeneous MCF a rectangular cross-section should be employed.

A simple and compact interferometer for temperature and pressure discrimination is proposed and demonstrated experimentally. It consists of a short section of high-birefringence photonic crystal fiber (Hi-Bi PCF) and a cascaded fiber Bragg grating (FBG). In the Hi-Bi PCF, two orthogonal polarized modes are employed as optical arms to construct, such as a Michelson interferometer. Combined with a cascaded FBG, pressure and temperature measurements are discriminated by a matrix method, and the pressure sensitivity of Hi-Bi PCF is determined to be around 3.65  nm/MPa. The proposed Michelson interferometer is easy-to-fabricate, flexible, and low-cost, which shows great potential in future applications of remote sensing.

This PDF file contains the editorial “Special Section Guest Editorial:Instrumentation and Techniques for Geometrical and Mechanical Quantity Measurement” for OE Vol. 55 Issue 09

From the actual implementation of displacement measurement in the laser synthetic wavelength interferometer, a nonlinear error analysis model was proposed by detecting the simultaneous zero-crossing position errors of two interference signals. By using this model, periodic nonlinear errors resulting from the polarizing leakage induced by the imperfection or misalignment of the polarizing beamsplitter in the basic configuration of the interferometer were analyzed. In order to reduce periodic nonlinear errors, two optimized optical configurations of the interferometer were presented. The simulations and experiments for verifying the performance of three configurations of the interferometer were performed. The experimental results demonstrate that the optimized third configuration has good stability, with a standard deviation of about 0.7 nm.

The coherent fading problem may lead to location error and bad location repeatability in the conventional moving differential method (MDM). A locating method based on the correlation dimension (CDM) in phase-sensitive optical time domain reflectometry is proposed. The CDM of backscattered traces is sensitive to weak vibration and immune to coherent fading, which is suitable to find out the vibration response section and then to calculate the location of the vibration source. Experimental results indicate that, compared with MDM, the standard deviation of location results, which represents location repeatability, can be improved from 25 to 2.1 m through CDM.

This paper studies the challenging problem of object detection using rich image and depth features. An invariant Hough random ferns framework for RGB-D images is proposed here, which primarily consists of a rotation-invariant RGB-D local binary feature, random ferns classifier training, Hough mapping and voting, searches for the maxima, and back projection. In comparison with traditional three-dimensional local feature extraction techniques, this method is effective in reducing the amount of computation required for feature extraction and matching. Moreover, the detection results showed that the proposed method is robust against rotation and scale variations, changes in illumination, and part-occlusions. The authors believe that this method will facilitate the use of perception in fields such as robotics.

High-resolution cameras used for smartphones are comprised of multiple aspheric lenses, a spectral filter, and a semiconductor image sensor, which are packaged together into a single module with tight geometrical tolerances. We investigated the technical possibility of near-infrared low-coherence interferometry for nondestructive geometrical inspection of the complex camera module to examine the inside packaging state. This tomographic scheme enabled us to measure the relative axial position of each inside component and also the lateral surface profile of the image sensor, allowing for comprehensive three-dimensional quality assurance of the whole camera module during the packaging process.

At the present time, there is a need for effective metrological control of the functional parameters of the modern rotary encoders due to their increased production level. This metrological control has to be carried out with high accuracy and high speed of operation. One of the most effective ways of solving this task is the use of dynamic goniometer (DG) jointly with an optical angle encoder and/or ring laser. The article deals with the principles of DG construction and considers the methods and results of DG investigation for the rotary encoder calibration as well as the elimination procedure of various types of DG uncertainties. The article shows that application of the proposed procedure allows to reduce the level of DG uncertainty to 0.2 arcsec, which ensures the uncertainty value of the rotary encoder metrological control by the means of DG to within 0.05 arcsec in a wide range of angular velocities.

We present a small-amplitude, high-frequency vibration measurement system. This system is based on the reflective holographic grating in a crystal of bismuth silicon oxide without applying an external electric field. A quarter-wave plate is applied in the reference beam path, with a polarizer after the crystal, to fulfill the quadrature condition when no electric field is applied to the crystal. A reflection configuration is used to obtain a good overlapping of the interference beams, which increases the beam coupling. The factors that affect the diffraction efficiency, including the signal-to-reference-beam intensity ratio and the recording angle, has been investigated. The experimental results coincide with the theoretical results, and the optimal conditions are obtained. The results of comparisons of our system with the vibrometer TEMPO show that the nanometer vibrations of a piezoelectric transducer can be reliably detected.

Traceability is a fundamental issue for nanoscale dimensional metrology. The lack of traceability in measurements inhibits the comparison of tools from different manufacturers and limits knowledge about the real size of fabricated features. Two approaches for realizing traceability in nanometrology, referred to as a top-down approach and a bottom-up approach, are presented. Following the top-down approach, for instance, realized using metrological atomic force microscopes, the dimension of nanostructures is derived from the displacement of the scanner, which is directly measured by laser interferometers whose optical frequency is calibrated to an iodine frequency-stabilized laser. Thus, the measurement result is directly traceable with an unbroken chain to the International System of Units—the meter. However, to achieve subnanometer measurement accuracy, which is far smaller than the optical wavelength (632.8 nm in this study), the subdivision of the interference fringe is essential for obtaining desired measurement resolution and accuracy. On the contrary, with the bottom-up approach, the dimension of nanostructures is determined using the silicon crystal lattice as an internal ruler. Due to the small dimension of the crystal lattice constant (e.g., d₁₁₁=0.313  nm), the bottom-up approach offers measurements with potential highest accuracy. The crystal lattice constant can be traceably calibrated to the meter by, e.g., a combined optical and x-ray interferometer; thus, the traceability of the bottom-up approach is also ensured. The consistency of the two approaches is experimentally confirmed in this paper.

We present a spatial phase-shift digital speckle patterns interferometry (SPS-DSPI) system with the capability of measuring three-dimensional (3-D) deformations under a dynamic loading condition simultaneously using multiple cameras. The Fourier transform method is utilized to calculate the phase difference. The consistency of different cameras is achieved using digital image correlation (DIC) technology. Calibration and calculation programs are compiled to make sure each subset on the measuring surface is uniform. SPS-DSPI and DIC techniques are combined to provide a direct measurement of the 3-D deformation of the entire surface area simultaneously. The theory, application result, and validation experiment are presented.

A transferable force calibration standard based on a silicon microelectromechanical sensor has been designed, fabricated, and characterized for micrometrology applications. Two essential elements of double-meander springs and full piezoresistive etched <inline-formula< <mml:math display="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML"< <mml:mrow< <mml:mi<p</mml:mi< </mml:mrow< </mml:math< </inline-formula<-silicon-on-insulator Wheatstone bridges (WBs) are integrated to the sensor for enhancing the device’s sensitivity and eliminating the current leakage during an active sensing operation, respectively. The design process is supported by three-dimensional finite element modeling to select the optimal proposed sensors as well as simulating their mechanical and electrical properties in the desired force range (<inline-formula< <mml:math display="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML"< <mml:mrow< <mml:mo form="prefix"<≤</mml:mo< <mml:mn<1000</mml:mn< <mml:mtext<  </mml:mtext< <mml:mi<μ</mml:mi< <mml:mi mathvariant="normal"<N</mml:mi< </mml:mrow< </mml:math< </inline-formula<). To fabricate the microforce sensors, a bulk micromachining technology is used by frequently involving an inductively coupled plasma deep reactive ion etching at cryogenic temperature. Several optical and electrical characterization techniques have been utilized to ensure the quality of the fabricated WBs, where their measured offset voltage can be down to <inline-formula< <mml:math display="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML"< <mml:mrow< <mml:mn<0.03</mml:mn< <mml:mo<±</mml:mo< <mml:mn<0.071</mml:mn< <mml:mtext<  </mml:mtext< <mml:mi<mV</mml:mi< <mml:mo</</mml:mo< <mml:mi mathvariant="normal"<V</mml:mi< </mml:mrow< </mml:math< </inline-formula<. In terms of its linearity, the fabricated device exhibits a small nonlinearity of <inline-formula< <mml:math display="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML"< <mml:mrow< <mml:mo form="prefix"<<</mml:mo< <mml:mn<3</mml:mn< <mml:mo<%</mml:mo< </mml:mrow< </mml:math< </inline-formula<, which leads this sensor to be appropriate for precise microforce standard.

The traditional vibration measurement method usually uses contact sensors, which induce unwanted mass and have limits for moving parts. Currently, using stereo vision for vibration measurement is developing fast because of noncontact and full field. However, for stereo vision, the high-accuracy reconstruction for the vibration motion is a significant challenge and the factors that affect the construction accuracy have not been thoroughly studied. The accuracy analysis of sinusoidal motion reconstruction is important because it can provide guidance for the reconstruction of other vibration motions. The high accuracy reconstruction for sinusoidal motion and the factors that affect the accuracy of the reconstruction are presented. First, the error model of reconstruction using stereo vision considering the delay time, frequency, amplitude, and disparity is established. The accuracy of sinusoidal motion reconstruction in the whole period is analyzed theoretically and experimentally considering subpixel interpolation. Peak identification is essential for the sinusoidal motion reconstruction and has the highest resolution requirement for the reconstruction resolution. This requirement is systematically investigated for the sinusoidal motions with different frequencies and amplitudes. The relationships between the reconstruction resolution and parameters of cameras are analyzed.

The details of a technique to measure solid surface velocity and detect particle movement are presented. This technique is based on the measurements of the frequency change of scattered light of particles crossing the fringes of a nearly Bessel beam formed by an axicon. Experimental results are presented and confirm the theoretical analysis and numerical simulations. Measurements of the movement of wires through the fringes were also performed.

In the reconstruction of the quantitative photoacoustic tomography (QPAT), forward models for both the optical and acoustic problems are usually needed to predict the measurement data from a guess of the distribution of the optical parameters. The diffusion approximation (DA) is the one most often employed as the optical forward model in the QPAT. However, this model usually results in predicted data deviating far from the actual measurements especially in low scattering tissues. To tackle such a problem, we propose a reconstruction method where the modeling error of the DA is modeled and considered in the framework of Bayesian inference. Experimental results show that modeling of the approximation error and considering it in the reconstruction procedure can significantly improve the reconstructed results of the QPAT.

Changes in illumination will result in serious color difference evaluation errors during the dyeing process. A Bagging-based ensemble extreme learning machine (ELM) mechanism hybridized with particle swarm optimization (PSO), namely Bagging–PSO–ELM, is proposed to develop an accurate illumination correction model for dyed fabrics. The model adopts PSO algorithm to optimize the input weights and hidden biases for the ELM neural network called PSO–ELM, which enhances the performance of ELM. Meanwhile, to further increase the prediction accuracy, a Bagging ensemble scheme is used to construct an independent PSO–ELM learning machine by taking bootstrap replicates of the training set. Then, the obtained multiple different PSO–ELM learners are aggregated to establish the prediction model. The proposed prediction model is evaluated with real dyed fabric images and discussed in comparison with several related methods. Experimental results show that the ensemble color constancy method is able to generate a more robust illuminant estimation model with better generalization performance.

To improve the accuracy of fringe projection profilometry for a single deformed pattern, an instantaneous phase retrieval method is proposed using a wavelet ridge section and an adaptive bandpass filter based on dyadic wavelets. First, we present a concept and assumption named wavelet ridge section to depict the instantaneous phases of the deformed fringe signals, which are also degraded by noise, and then introduce a formula to calculate the width of the wavelet ridge section. Furthermore, an adaptive bandpass filter is designed for extracting the wavelet subsignals corresponding to the wavelet ridge sections to reconstruct the analytical signal. Finally, the instantaneous phase of the distorted fringe pattern is effectively retrieved. All parameters of our method are designed to be adaptive for different fringe patterns. Our experiments indicate that the proposed method is effective for measurements and outperforms other existing mainstream wavelet transform profilometry techniques, not only in accuracy but also in noise suppression performance.

An efficient adaptive simultaneous algebraic reconstruction technique (ASART) to calculate optical fiber refractive index profiles is proposed based on phase difference curves obtained by digital holography technique. We develop adaptive relaxation parameter (ARP) on simultaneous algebraic reconstruction technique (SART) to increase the convergence speed and improve the reconstruction accuracy. A formula of ARP is derived mathematically and multilevel scheme (MLS) is used to increase convergence speed in the first iteration. Experimental results show the proposed ASART convergences over 40% faster than SART and achieve significantly higher reconstruction accuracy. Experimental verification shows that ASART is more efficient than SART and filtered back projection in image reconstruction, especially with few projection views. The running time of ASART is much shorter than that of SART, and ASART needs fewer iteration numbers to obtain the same reconstruction effects. In addition, it can be used to measure optical fibers with various diameters that cannot be measured with S14 refractive index profiler (S14).

Human ear recognition has been promoted as a profitable biometric over the past few years. With respect to other modalities, such as the face and iris, that have undergone a significant investigation in the literature, ear pattern is relatively still uncommon. We put forth a sparse coding-induced decision-making for ear recognition. It jointly involves the reconstruction residuals and the respective reconstruction coefficients pertaining to the input features (co-occurrence of adjacent local binary patterns) for a further fusion. We particularly show that combining both components (i.e., the residuals as well as the coefficients) yields better outcomes than the case when either of them is deemed singly. The proposed method has been evaluated on two benchmark datasets, namely IITD1 (125 subject) and IITD2 (221 subjects). The recognition rates of the suggested scheme amount for 99.5% and 98.95% for both datasets, respectively, which suggest that our method decently stands out against reference state-of-the-art methodologies. Furthermore, experiments conclude that the presented scheme manifests a promising robustness under large-scale occlusion scenarios.

This paper presents a motion deblurring method which can obtain both the motion information and the recovered image based on local temporal compressive photography. In this method, video blocks are reconstructed at the corners of the image sensor during a single exposure period. The displacement vector, which will be used to build the prior point spread function (PSF) for image deblurring, is then estimated from the reconstructed videos. With the use of the prior PSF, better recovered images can be obtained with much less iteration. An experiment system is also presented to validate the effectiveness of the proposed method. The experimental results show that the proposed method could provide recovered images of high quality.

In an optical synthetic aperture imaging system, it is necessary to extract edge information of subapertures with complex shape and large gaps, aiming at cophasing of segmented mirrors ultimately. As a measure of image surface irregularities, fractal dimension (FD) was calculated for edge extraction and surface complexity evaluation. The modified differential box-counting (DBC) method was adopted to calculate FD, specifically the window merge replication method was presented to achieve FD estimation with a relatively small scanning window. The subaperture region and interference fringe edge were extracted by using a two-step strategy of preprocessing and postprocessing. Simulations and experiments are conducted to verify the feasibility and accuracy for edge extraction. As well, the capabilities of the proposed method are demonstrated with the results of numerical calculation.

Parallel calculations of large-pixel-count computer-generated holograms (CGHs) are suitable for multiple-graphics processing unit (multi-GPU) cluster systems. However, it is not easy for a multi-GPU cluster system to accomplish fast CGH calculations when CGH transfers between PCs are required. In these cases, the CGH transfer between the PCs becomes a bottleneck. Usually, this problem occurs only in multi-GPU cluster systems with a single spatial light modulator. To overcome this problem, we propose a simple method using the InfiniBand network. The computational speed of the proposed method using 13 GPUs (NVIDIA GeForce GTX TITAN X) was more than 3000 times faster than that of a CPU (Intel Core i7 4770) when the number of three-dimensional (3-D) object points exceeded 20,480. In practice, we achieved ∼40 tera floating point operations per second (TFLOPS) when the number of 3-D object points exceeded 40,960. Our proposed method was able to reconstruct a real-time movie of a 3-D object comprising 95,949 points.

A double-image encryption method is reported using chaotic maps, nonlinear non-DC joint transform correlator (JTC), and fractional Fourier transform (FrFT). The double images are converted into the amplitude and phase of a synthesized function through the application of chaotic pixel scrambling. The synthesized function bonded with a chaotic random phase mask (CRPM) and another different CRPM serve as the input signal of the JTC architecture in the fractional Fourier domain to obtain a real-valued encrypted image. The nonlinear and non-DC operation is also done to improve the security and decrypted image quality. The parameters in joint FrFT correlator and chaotic map serve as the encrypted keys. Numerical simulations have been done to demonstrate the feasibility and validity of this algorithm.

Compared with grayscale patterns in structured light illumination, line stripes, as one binary pattern, are attractive for being more conveniently decoded. However, traditional line scanning typically involves a single line shifting across objects to avoid spatial ambiguities possibly introduced by complex surface geometry of objects. We propose a multiple-line strategy for fast and accurate reconstructing of the three-dimensional surfaces of targets. First, we build a mathematical model for multiline scanning, and second, we derive phase computation from the model along time axis and resolve the issue of ambiguity naturally. Errors of the proposed method are theoretically analyzed, and it shows that the proposed method is immune to nonlinearity and is robust to uncertainty. Experimental results demonstrate that the proposed method is of advantages both in accuracy and time cost.

Optical time domain reflectometry (OTDR) is one of the most successful diagnostic tools for nondestructive attenuation measurement of a fiber link. To achieve better sensitivity, spatial resolution, and avoid dead-zone in conversional OTDR, a single-photon detector has been introduced to form the photon-counting OTDR (ν-OTDR). We have proposed a ν-OTDR system using a gigahertz sinusoidally gated InGaAs/InP single-photon avalanche detector (SPAD). Benefiting from the superior performance of a sinusoidal gated SPAD on dark count probability, gating frequency, and gate duration, our ν-OTDR system has achieved a dynamic range (DR) of 33.4 dB with 1  μs probe pulse width after an equivalent measurement time of 51 s. This obtainable DR corresponds to a sensing length over 150 km. Our system has also obtained a spatial resolution of 5 cm at the end of a 5-km standard single-mode fiber. By employing a sinusoidal gating technique, we have improved the ν-OTDR spatial resolution and significantly reduced the measurement time.

The rhomb-type achromatic prism retarder utilizes the phase difference introduced at the glass–air interface, where the beam of light undergoes total internal reflection. With the proper choice of glass materials and the number of total internal reflection, it is possible to obtain a desired phase difference. The phase difference introduced is also dependent on the angle of incidence of the light beam at the glass–air interface. A small change in angle of incidence causes a considerable change in phase difference. The change in the phase difference introduced with the change in external angle of incidence of the light beam in an achromatic prism-type quarter-wave retarder is studied both theoretically and experimentally. The experimental results obtained are found to be in accordance with the theoretical results.

We propose a multiconjugate adaptive optics (MCAO) system called pupil-transformation MCAO (PT-MCAO) for solar high-angular resolution imaging over a large field of view. The PT-MCAO, consisting of two deformable mirrors (DMs), uses a Shack–Hartmann wavefront sensor located on the telescope pupil to measure the wavefront slopes from several guide stars. The average slopes are used to control the first DM conjugated on the telescope aperture by a solar ground-layer adaptive optics (AO) approach while the remaining slopes are used to control the second DM conjugated on a high altitude by a conventional solar AO via a geometric PT. The PT-MCAO uses a similar hardware configuration as the conventional star-oriented MCAO. However, a distinctive feature of our PT-MCAO is that it avoids the construction of tomography wavefront, which is a time-consuming and complex process for the solar real-time atmospheric turbulence correction. For the PT-MCAO, current widely used and fully understood conventional solar AO closed-loop control algorithms can be directly used to control the two DMs, which greatly reduces the real-time calculation power requirement and makes the PT-MCAO easy to implement. In this publication, we discuss the PT-MCAO methodology, its unique features, and compare its performance with that of the conventional solar star-oriented MCAO systems, which demonstrate that the PT-MCAO can be immediately used for solar high-resolution imaging.

This paper presents an approach to extract accurate color edge information using encoded patterns in hue, saturation, and intensity (HSI) color space. This method is applied to one-shot shape acquisition. Theoretical analysis shows that the hue transition between primary and secondary colors in a color edge is based on light interference and diffraction. We set up a color transition model to illustrate the hue transition on an edge and then define the segmenting position of two stripes. By setting up an adaptive HSI color space, the colors of the stripes and subpixel edges are obtained precisely without a dark laboratory environment, in a low-cost processing algorithm. Since this method does not have any constraints for colors of neighboring stripes, the encoding is an easy procedure. The experimental results show that the edges of dense modulation patterns can be obtained under a complicated environment illumination, and the precision can ensure that the three-dimensional shape of the object is obtained reliably with only one image.

Fast physical random number generators (PRNGs) are essential elements in the development of many modern applications. We numerically demonstrate an extraction scheme to establish an ultrafast PRNG using dual-channel optical-chaos source. Simultaneous suppression of time-delay signature in all observables of the output is verified using autocorrelation-function method. The proposed technique compares the level of the chaotic signal at time t with M levels of its delayed version. The comparators [1-bit analog-to-digital converters (ADCs)] are triggered using a clock subject to an incremental delay. All the delays of the chaotic signal before the ADCs and the relative delays of the clock are mutually incommensurable. The outputs of the ADCs are then combined using parity-check logic to produce physically true random numbers. The randomness quality of the generated random bits is evaluated by the statistical tests of National Institute of Standards and Technology Special Publication 800-22. The results verify that all tests are passed from M=1 to M=39 at sampling rate up to 34.5 GHz, which indicates that the maximum generation rate of random bits is 2.691  Tb/s without employing any preprocessing techniques. This rate, to the best of our knowledge, is higher than any previously reported PRNG.

Design of the controller of an adaptive optical system is very complex because its model is usually with uncertainty. To deal with uncertainty and to improve robust stability, the mixed sensitivity H_∞ control has been introduced to design the controller. In order to testify the validity, wavefront aberration correction capability as well as the robust stability has been compared between the mixed sensitivity H_∞ controller and the classic integral controller. The computer simulation results demonstrate that the system with the mixed sensitivity H_∞ controller, though it cannot guarantee a better correction performance, has greater robust stability than the one with the classic integral controller. That is to say, greater robust stability is achieved at the expense of the correction capability in the system with H_∞ controller. Moreover, the greater the uncertainty is, the more proceeds the mixed sensitivity H_∞ controller will produce. It proves the efficiency of the mixed sensitivity H_∞ controller in dealing with uncertainty in adaptive optics system.

There is a pressing need in the astronomical community for space-suitable multiobject spectrometers (MOSs). Several digital micromirror device (DMD)-based prototype MOSs have been developed for ground-based observatories; however, their main use will come with deployment on a space-based mission. Therefore, the performance of DMDs under exoatmospheric radiation needs to be evaluated. DMDs were rewindowed with 2-μm thick pellicle and tested under accelerated heavy-ion radiation (control electronics shielded from radiation), with a focus on the detection of single-event effects (SEEs) including latch-up events. Testing showed that while DMDs are sensitive to nondestructive ion-induced state changes, all SEEs are cleared with a soft reset (i.e., sending a pattern to the device). The DMDs did not experience single-event induced permanent damage or functional changes that required a hard reset (power cycle), even at high ion fluences. This suggests that the SSE rate burden will be manageable for a DMD-based instrument when exposed to solar particle fluxes and cosmic rays in orbit.

Telescope mirrors determine the imaging quality and the observation ability of the telescopes. Unfortunately, manufacturing highly accurate mirrors remains a bottleneck problem in space optics. One primary cause is the lack of a technique to robustly measure the three-dimensional (3-D) shapes of mirrors for inverse engineering. After centuries of study, researchers developed different techniques for testing the quality of telescope mirrors and proposed different methods for measuring the 3-D shapes of mirrors. Among them, interferometers become popular in evaluating the surface errors of the manufactured mirrors. However, interferometers could not measure some important mirror parameters, e.g., paraxial radius, geometry dimension, and eccentric errors, directly and accurately although these parameters are essential for mirror manufacturing. For those methods that could measure these parameters, their measurement accuracies are far beyond satisfactory. We present a technique for robust measurement of the 3-D shapes of mirrors with single-shot projection. Experimental results show that this technique is significantly more robust than state-of-the-art techniques, which makes it feasible for commercial devices to measure the shapes of mirrors quantitatively and robustly.

Material removal accuracy has a direct impact on the machining precision and efficiency of ion beam figuring. By analyzing the factors suppressing the improvement of material removal accuracy, we conclude that correcting the removal function deviation and reducing the removal material amount during each iterative process could help to improve material removal accuracy. Removal function correcting principle can effectively compensate removal function deviation between actual figuring and simulated processes, while experiments indicate that material removal accuracy decreases with a long machining time, so a small amount of removal material in each iterative process is suggested. However, more clamping and measuring steps will be introduced in this way, which will also generate machining errors and suppress the improvement of material removal accuracy. On this account, a free-measurement iterative process method is put forward to improve material removal accuracy and figuring efficiency by using less measuring and clamping steps. Finally, an experiment on a φ 100-mm Zerodur planar is preformed, which shows that, in similar figuring time, three free-measurement iterative processes could improve the material removal accuracy and the surface error convergence rate by 62.5% and 17.6%, respectively, compared with a single iterative process.

The optical constants of titanium dioxide (TiO₂) have been experimentally determined at energies in the extreme ultraviolet and soft x-ray spectral regions, from 25.5 to 612 eV. Measuring angle-dependent reflectance of amorphous TiO₂ thin films with synchrotron radiation at the BEAR beamline of Synchrotron ELETTRA. The experimental reflectivity profiles were fitted to the Fresnel equations using a genetic algorithm applied to a least-square curve fitting method, obtaining values for δ and β. We compared our measurements with tabulated data. All samples were grown on Si (100) substrates by the electron-beam evaporation technique, with a substrate temperature of 150°C and deposition rates of 0.3 to 0.5  Å/s. Complete films characterization have been carried out with structural (XRD, ellipsometry, and profilometry), compositional (x-ray photoelectron spectroscopy), and morphological (atomic force microscopy) analyses.

We propose to connect a single-mode fiber (SMF) to a dual-concentric cores fiber (DCCF) using an adiabatically tapered microstructured mode converter, and to evaluate the SMF LP₀₁ mode and the DCCF LP₀₁ and LP₀₂ modes selective excitations performances. We theoretically and numerically study this selective excitation method by calculating the effective indices of the propagated modes, the adiabaticity criteria, the coupling loss, and the modes amplitudes along the tapered structure. This study shows that this method is able to achieve excellent selective excitations of the first two linearly polarized modes (LP₀₁ and LP₀₂) among the five guided modes in the DCCF with a negligible loss. The part of the LP₀₁ and LP₀₂ modes from the total power are 99% and 84% corresponding to 0.1 and 0.8 dB losses, respectively.

We prepared an adaptive microlens array (MLA) using a polyvinyl chloride/dibutyl phthalate gel and an indium-tin-oxide (ITO) glass substrate. The gel forms a membrane on the glass substrate and the ITO electrode has a ring array pattern. When the membrane is electrically charged by a DC voltage, the surface of the membrane above each circular electrode in the ring array can be deformed with a convex shape. As a result, the membrane functions as an MLA. By applying a voltage from 20 to ∼65  V to the electrode, the focal length of each microlens can be tuned from 300 to ∼160  μm. The dynamic response time can by reduced largely by changing the polarity of the DC voltage. Due to the advantages of optical isotropy, compact structure, and good stability, our MLA has potential applications in imaging, biometrics, and electronic displays.

Optical digital holographic techniques can be used for nondestructive testing of materials. Digital holographic nondestructive testing essentially measures deformations on the surface of the object. However, there is sufficient sensitivity to detect subsurface and internal defects in metallic and composite specimens. We investigate and discuss the vibration analysis of laminated composite glass-epoxy using time averaging in digital Fresnel holography to visualize the modes of vibration and to test the integrity of the structures of studied materials.

We present a laser beam shaper designed to obtain a homogeneous line beam. A beam shaping system was designed based on cutting and rearranging optics, using two groups of plane parallel plates. The analysis of beam uniformity was performed by use of ray tracing simulation through ZEMAX software and experimental validation. The simulation results show that in the focal plane, a beam width of 1 mm (@95%I_max) and a uniformity of 90.2% are achieved in one direction, and a Gaussian profile with a beam width of 0.06 mm (FWHM) is achieved in the other direction.

A single biconvex microlens is proposed to correct the astigmatism and ellipticity of a laser diode (LD) beam and focus it to a smallest circular spot. The microlens has three different profiles in which one cylindrical input surface is to collimate the beam in the fast-axis (y-axis) direction. Output surface, on the other hand, holds two different parabolic profiles in fast- and slow-axis (x-axis) directions to correct the astigmatism and focus the beam into a smallest circular spot. A simulation software is used to design and optimize those lens profiles. Theoretically, the smallest focused spot size is around 4.24  μm in diameter. The three profiles are then transferred to photo-masks to fabricate the microlens on polycarbonate material using an excimer laser dragging method with alignment accuracy of 1  μm. The machined microlens is assembled with the LD using double-sided optically clear adhesive tape. The experimental focused spot is found to be 16.75  μm in diameter. Circularity of the focused spot is demonstrated by a single-shot exposure test on thin photoresist layer that shows a circular-dot diameter of 7.32  μm. The proposed technique has great potential in applications such as beam pen lithography, fiber coupling, and optical read-write head.

At present, few projection objectives for extreme ultraviolet (EUV) lithography pay attention to correct thermal aberration in optical design phase, which would lead to poor image quality in a practical working environment. We present an aspherical modification method for helping the EUV lithographic objective additionally correct the thermal aberration. Based on the thermal aberration and deformation predicted by integrated optomechanical analysis, the aspherical surfaces in an objective are modified by an iterative algorithm. The modified aspherical surfaces could correct the thermal aberration and maintain the initial high image quality in a practical working environment. A six-mirror EUV lithographic objective with 0.33-numerical aperture is taken as an example to illustrate the presented method. The results show that the thermal aberration can be corrected effectively, and the image quality of the thermally deformed system is improved to the initial design level, which proves the availability of the method.

The probability density function of the intensity of a Hermite–Gaussian (HG) beam is studied. It is assumed that the beam is used in a free-space optics communication link or laser ranging system. In particular, it is assumed that the captured optical radiation pattern assumes an HG beam intensity profile and that the beam is impaired by the residual pointing error cause by the spatial tracking loop responsible for tracking the atmospheric beam wander and platform sway. The mean and variance of the beam profile are also obtained to underscore the impact of spatial jitter on the overall beam profile.

We report efficient coherent beam combining of five kW-class fiber amplifiers seeded with pseudorandom phase-modulated light, using a 1×5 diffractive optical element (DOE). Each fiber amplifier channel was path length matched, actively polarized, and provided approximately 1.2 kW of near diffraction-limited output power (M²<1.1). A low-power sample of the combined beam after the DOE provided an error signal for active phase stabilization. After phase stabilization, the beams were coherently combined via the DOE. Notably, a total output power of ∼5  kW was achieved with 82% combining efficiency and excellent beam quality (M²<1.1). The intrinsic DOE splitter loss was 5%. Additional losses due in part to nonideal polarization, amplified spontaneous emission content, uncorrelated wavefront errors, and fractional beam misalignments contributed to the efficiency reduction. Overall, multi-kW beam combining of pseudorandom-modulated fiber amplifiers was demonstrated for the first time.

The frequency offset estimation (FOE) schemes based on Kalman filter are proposed and investigated in detail via numerical simulation and experiment. The schemes consist of a modulation phase removing stage and Kalman filter estimation stage. In the second stage, the Kalman filters are employed for tracking either differential angles or differential data between two successive symbols. Several implementations of the proposed FOE scheme are compared by employing different modulation removing methods and two Kalman algorithms. The optimal FOE implementation is suggested for different operating conditions including optical signal-to-noise ratio and the number of the available data symbols.

A polarization splitter based on dual-core photonic crystal fiber with a gold layer is proposed. The splitter has a short length of 0.435 mm, and is capable of splitting an incident light into two orthogonal states between 1.48 and 1.72  μm. At the same time, a helpful conclusion is obtained: the variation of the thickness of the gold layer has a weak impact on splitting length and significant influence on the extinction ratio spectra. The polarization splitter can be modulated by changing the thickness of the gold layer.

A high-sensitivity pressure sensor based on wavelength detection technology of fiber Bragg grating (FBG) is proposed in this paper. The FBG pressure sensor can be used to measure downhole pressure of oil and gas wells. An eccentric-pushrod structure is used to improve the sensitivity of the sensor. The effect of adhesive on elastic hysteresis of the sensor is analyzed, and the adhesive with large shear modulus is used to reduce the hysteresis of the sensor. Numerical and experimental results show that this sensor possesses good linearity and repeatability, as well as little elastic hysteresis. The sensitivity of the sensor can reach 230.9  pm/MPa when the measured pressure is in the range of 0 to 20 MPa.

To improve the heat management of high-power diode lasers, a microchannel heat sink is obtained, whose structure is optimized in method of numerical simulation. Following such a design, the microchannel heat sink is fabricated by nickel-based doping rare earth materials by laser three-dimensional (3-D) printing procedure. Since the noncorrosion property of such material has been preliminarily demonstrated by salt spray test, there is no necessity to plate the interior of the laser 3-D printing microchannel heat sink with gold. The coefficient of thermal expansion of such material is 11  ppm/K. The diode laser array (LDA) with 80-W cw output power, 2-mm cavity length, 100-μm emitter width, and 20% fill-factors is mounted on it for the thermal resistance test, and the result is 0.40  K/W. Moreover, the smile effect of the mounted LDA is merely 0.8  μm.

An architecture for flattened and broad spectrum multicarriers is presented by generating 60 comb lines from pulsed laser driven by user-defined bit stream in cascade with three modulators. The proposed scheme is a cost-effective architecture for optical line terminal (OLT) in wavelength division multiplexed passive optical network (WDM-PON) system. The optical frequency comb generator consists of a pulsed laser in cascade with a phase modulator and two Mach–Zehnder modulators driven by an RF source incorporating no phase shifter, filter, or electrical amplifier. Optical frequency comb generation is deployed in the simulation environment at OLT in WDM-PON system supports 1.2-Tbps data rate. With 10-GHz frequency spacing, each frequency tone carries data signal of 20 Gbps-based differential quadrature phase shift keying (DQPSK) in downlink transmission. We adopt DQPSK-based modulation technique in the downlink transmission because it supports 2 bits per symbol, which increases the data rate in WDM-PON system. Furthermore, DQPSK format is tolerant to different types of dispersions and has a high spectral efficiency with less complex configurations. Part of the downlink power is utilized in the uplink transmission; the uplink transmission is based on intensity modulated on-off keying. Minimum power penalties have been observed with excellent eye diagrams and other transmission performances at specified bit error rates.

We report results of supercontinuum generation in highly nonlinear polarization maintaining photonic crystal fiber (PCF) using the first or second harmonics of a subnanosecond passively Q-switched Nd:YAG microlaser. The Nd:YAG microlaser generated 50  μJ energy 300 ps duration pulses at 1064 nm with a kilohertz repetition rate. We demonstrated that we can expand the supercontinuum spectrum to cover the whole visible range and beyond using either first or second harmonics of our pump laser in the case of such pump pulse durations. In the case of a first-harmonic pump (λ_p=1064  nm), the supercontinuum extended from 400 to 1300 nm and in the case of a second-harmonic pump (λ_p=532  nm), it extended from 400 to 900 nm. In addition, we compared the supercontinuum evolution and dependence on pump pulse energy in both cases. We also performed numerical simulations of supercontinuum generation in PCF using an improved approach. The generalized nonlinear Schrödinger equation was modified so that numerical simulations would yield greater accuracy in the case of longer (300 ps) pulses. The simulated supercontinuum spectra display the same qualitative features as that measured in the experiment.

A narrow linewidth (∼8  MHz, instrument limited) CW green laser at 532 nm is demonstrated in linear orthogonally polarized modes resulting in an unidirectional travelling wave cavity using intracavity second-harmonic generation technique with <250-mW output power.

High-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (aluminum, copper, and stainless steel) and Al₂O₃ ceramic at unprecedented processing speeds. This is achieved by using a high-average power picosecond laser in conjunction with a unique, in-house developed polygon mirror-based biaxial scanning system. Therefore, different concepts of polygon scanners are engineered and tested to find the best architecture for high-speed and precision laser beam scanning. In order to identify the optimum conditions for efficient processing when using high-average laser powers, the depths of cavities made in the samples by varying the processing parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. For overlapping pulses of optimum fluence, the removal rate is as high as 27.8  mm³/min for aluminum, 21.4  mm³/min for copper, 15.3  mm³/min for stainless steel, and 129.1  mm³/min for Al₂O₃, when a laser beam of 187 W average laser powers irradiates. On stainless steel, it is demonstrated that the removal rate increases to 23.3  mm³/min when the laser beam is very fast moving. This is thanks to the low pulse overlap as achieved with 800  m/s beam deflection speed; thus, laser beam shielding can be avoided even when irradiating high-repetitive 20-MHz pulses.

We investigate the maximized cross-layer reliability under arbitrary link failure probability in multilayer optical networks. A concept of minimal cross-layer cutset is first defined and a reliability model with arbitrary physical link failure probability is built in the multilayer optical networks. In order to reduce the scale of cutset enumeration, we introduce two metrics to estimate cross-layer reliability, i.e., the minimum cross-layer node reliability and the minimum cross-layer edge reliability (MCER). Furthermore, we develop two linear programming (LP) models and two heuristic algorithms to maximize the cross-layer reliability of multilayer optical networks, i.e., the minimum shared-risk mapping algorithm and the least shared failure probability algorithm. Simulation results show that: (i) the cross-layer reliability of the two proposed algorithms is close to the LP solutions under logical networks with different sizes, which achieves better results in terms of additional resources utilization compared with the shortest path algorithm; (ii) less difference between the results of our proposed algorithms and the results of the shortest path algorithm is accompanied by a small standard deviation of failure probability distribution. Moreover, the superiority of our proposed algorithms becomes more remarkable with the increasing of the standard deviation.

In a metro-access optical network, a bandwidth-allocated algorithm is proposed for traffic-orientated multisubsystem-based virtual passive optical network (MS-VPON) that can implement the syncretism of multiple systems such as time division multiplexing-PON (TDM-PON), wavelength division multiplexing-PON (WDM-PON), and orthogonal frequency division multiplexing-PON (OFDM-PON). VPONs are constructed based on traffic and different VPONs are separated by different types of traffic. The bandwidth-allocated algorithm is modeled with a matrix theory to determine which VPON can be admitted and then a bandwidth is assigned to these VPONs. With the algorithm, the network value can be maximized. Two cases are investigated to demonstrate the effectiveness of the proposed algorithm in the bandwidth-utilized ratio and VPONs’ admission probability.

This paper investigates the efficient estimator of echo data processing to clean the spectrum through the denoising process. The maximum likelihood based on covariance matrix (MLCM) method without a priori knowledge of the spectral width is proposed for denoising the atmospheric signal. This method is applied to simulated and actual data to estimate the spectrum parameters. The probability density function of estimators as an empirical model is used to describe the performance of the estimators. The MLCM method is suggested to be an alternate estimator to precisely obtain the essential spectrum parameters with a lower standard deviation of good estimators and a larger detected range, which is improved by 20%, compared with the maximum likelihood method with a priori knowledge of the spectral width. Moreover, it can reduce the large velocity volatility and the uncertainties of the spectral width in the low signal-to-noise ratio regime. The MLCM method can be applied to obtain the whole wind profiling by the coherent Doppler lidar.

A fast- and low-noise optical receiver using a silicon avalanche photodiode coupled to a very high-frequency preamplifier circuit is developed, characterized, and tested. The gain, bandwidth, and noise of the preamplifier are optimized to the avalanche photodiode performance to achieve detection and amplification without distortion of the fast and weak optical signal. A low noise level at the preamplifier circuit input of only 1.6  nV/Hz^1/2 and a very good linearity from 1 kHz to 280 MHz are achieved. In addition, a good detection performance of the optical receiver is attained: A low-noise equivalent power of only 1.2  pW/Hz^1/2 and a minimum signal-to-noise ratio requirement of only 3 are reached. Furthermore, the maximum detection range of the light detection and ranging remote sensing system, using the developed optical receiver, is estimated.

We report the fabrication and validation of a microfluidic chip for fluorescence detection, which incorporates in the same glass substrate the microfluidic network, the excitation, the filtering, and the collection elements. The device is fabricated in a hybrid approach combining different technologies, such as femtosecond laser micromachining and RF sputtering, to increase their individual capabilities. The validation of the chip demonstrates a good wavelength selective light filtering and a limit of detection of a 600-nM concentration of Oxazine 720 perchlorate dye.

Multibeam, multicolor, large-angle beam-steering is demonstrated in the visible spectral region by imprinting Fresnel zone plates (FZP) on a liquid crystal spatial light modulator. Spectral dispersion, both diffractive and refractive, is observed but does not prevent the use of this technology for beam steering applications. The experimental results show that while diffractive dispersion dominates over refractive dispersion, wavelength-specific FZPs can be rendered to direct those beams on target, either simultaneously or consecutively. Only a slight correction in the FZP positon is necessary to compensate for refractive dispersion. The position, intensity, and wavelength of each beam can be controlled independently.

Lateral diffusion of photon-generated carriers is a critical factor affecting the signal stability and spatial resolution of light-addressable potentiometric sensor (LAPS) array. LAPS with meshed working electrode for rejecting lateral diffusion is presented. Simulation shows that using meshed working electrode can resist the lateral distribution. In an experiment, the inhibition of lateral distribution and the signal stability was studied. Results showed, using the meshed working electrode, the ability to reject the lateral distribution and the signal stability is obviously enhanced. Research in this paper may help to enhance spatial resolution and detection stability of LAPS.

In order to obtain the waveguide of multiple functionalities, we design a coupled system of two unidirectional air waveguides and find it is a system of multiple modes through band calculations. Through numerical simulations, we also find that the mode excitation is dependent on the position of the source. With the same frequency the line source can excite either the even mode or the odd modes in one single waveguide or two waveguide just by changing the positions of the source. Such a system provides us the way to control the excitation of mode and obtain the waveguide modes with special applications.

A birefringent structured side-holes photonic crystal fiber (PCF) with high sensitivity is designed for pressure sensing. Simulation results show that the birefringence and relevant sensitivity are strongly influenced by the air-holes’ sizes and the distance between the fiber core and side-hole. The modal birefringence and the polarimetric pressure sensitivity can be up to 3.943×10⁻³ and −3.67×10⁻⁵  MPa⁻¹ at 1.55  μm, respectively. The proposed side-holes PCF possesses promising applications for pressure sensing.

Metallic film as an indium tin oxide alternative, which shows excellent mechanical flexibility and high conductivity, has the ideal physical properties for flexible organic solar cells (OSCs). However, a bottleneck of metallic film was a lack of transmittance that limits the application in OSCs. We have demonstrated a nanoaperture metallic film fabricated by a template striping method, which can overcome the above-mentioned bottleneck. This metallic film has a random nanoaperture array. The size and shape of the nanoaperture were dependent on master templates. This metallic film with nanoaperture array is not only able to show high conductivity but also possesses tunable localized surface plasmon (LSP) resonance as well. The LSP could be coupled with dipole mode in nanostructure, which can account for the transmission enhancement and efficiently increase the light absorption of active layer in the OSCs. Moreover, this metallic film with nanoaperture array will exhibit particular advantage in flexible OSCs because the backing layer itself is a flexible substrate. The nanoaperture metallic film fabricated by this method as an electrode was a good choice for OSCs.

Europium-doped calcium molybdates (CaMoO₄:Eu³⁺) were successfully synthesized by a high-energy ball milling method. The x-ray diffraction patterns confirmed their powellite structure, and the field emission scanning electron microscope image exhibited the spherical particles with submicron size. The photoluminescence (PL) properties of Eu³⁺ in these phosphors were also studied by analyzing the excitation and emission spectra for the effect of europium concentration. The CaMoO₄:Eu³⁺ PL excitation and PL spectra show charge transfer band and several transition peaks correlated with host lattice band gap and f-f transitions of Eu³⁺, respectively. By sintering Ca_0.95MoO₄:0.05Eu³⁺ phosphor at 1200°C, PL intensity has a maximum value at 618 nm with Commision Internationale de I’Eclairage 1931 (CIE 1931) chromaticity coordinates (0.609, 0.343).

A sandwiched three-port transmission grating with a connection layer under normal incidence is shown. The sandwiched dielectric grating can mainly diffract the identical energies in the ±1st orders and the zeroth diffraction order based on optimized grating parameters by employing rigorous coupled-wave analysis (RCWA) for TE and TM polarizations. On account of optimized parameters, efficiencies more than 32.5% in each diffraction order for two polarizations can be gained under normal incidence. A simplified modal method is used to describe the mechanism of beam propagation and analyze diffraction behavior clearly in the grating. Most importantly, diffraction efficiencies numerically obtained by using RCWA can be in agreement with the rough theoretical analysis on account of the simplified modal method. Therefore, the connection-layer-based sandwiched three-port grating is significant for the further practical manufacture.