An enhanced refractive index (RI) sensor with combination of long period fiber grating (LPG) and a small core
singlemode fiber (SCSMF) structure is proposed and developed. Since the LPG and SCSMF transmission spectra
experience a blue and red shift respectively as the surrounding RI (SRI) increases, the sensitivity is improved by
measuring the separation between the resonant wavelengths of the LPG and SCSMF structures. Experimental results
show that the sensor has a sensitivity of 1028 nm/SRI unit in the SRI range from 1.422 to 1.429, which is higher than
individual sensitivities of either structure alone used in the experiment.
A novel plasmonic biosensor based on coupled metal-dielectric buffer grating is proposed and analyzed by the rigorous
coupled wave analysis (RCWA) method. The metal-dielectric buffer grating structure offers surface plasmon resonance
suitable for high sensitivity biosensing applications. The calculated FWHW (full width at half maximum) of the
transmission peak is 5 nm and the optical transmission efficiency is significantly enhanced at the resonant wavelength of
800.8 nm by introducing the dielectric buffer grating. The highly concentrated field distribution is sensitive to
surrounding refractive index changes of the metal surface providing a sensitivity of 560 nm/RIU (refractive index unit)
for optical biosensing applications.
We propose a simple ultraviolet (UV) writing technique for the fabrication of buried waveguide devices, which employs a UV lamp as the light source and commercial benzocyclobutene (BCB) and epoxy OPTOCAST 3505 as the core and cladding materials, respectively. We show that the light emitted from the UV lamp can induce a large refractive-index change (up to 0.012) in BCB, while a negligible index change in the epoxy, which makes possible the writing of buried waveguide devices in BCB by exposing an epoxy-clad BCB film to the UV light through a mask. We demonstrate this technique experimentally with straight channel waveguides, Y-junction waveguide branches, and long-period waveguide gratings. The propagation loss of a typical fabricated waveguide is 1.6 dB/cm at 1550 nm and the polarization-dependent loss is 0.4 dB/cm.
There are two approaches to develop reliable photonic devices. One is by the process & materials optimization, and the
other is the reliability assurance during the fabrication, packaging & operation period. These critical issues needed to be
addressed in order to bring commercialization of these devices closer. The development of organic polymers with high
optical quality & high performance has led to a maturing of the polymer photonic device field. The combination of
structural flexibility and toughness in optical polymers also makes it more suitable for vertical integration to realize 3D
and even for all-polymer integrated optics. Packages are usually an integral part of the device. Therefore, fabrication,
packaging and reliability challenges are the well-known potential showstopper to the growth of photonic components. In
this review, the suitability of optical polymer systems, the materials & process optimization issues in fabricating reliable
planner lightwave circuit (PLC) devices, packaging of fiber array & splitter components to integrate fiber-to-waveguide
devices for fiber-to-the-home (FTTH) networks are summarized.
We demonstrate a simple UV-writing technique for the fabrication of buried waveguides using a UV lamp as the source and benzocyclobutene (BCB) and epoxy OPTOCAST 3553 as the waveguide materials. We find that the refractive index of the core material BCB can be increased by as much as 0.01 after UV exposure, while the refractive index of the cladding material epoxy OPTOCAST 3553 is not affected by the UV light. Based on these material properties, buried channel waveguide devices are formed by UV irradiation of an epoxy-clad BCB slab waveguide through a mask. We demonstrate the technique with a straight single-mode waveguide, a Y-junction waveguide branch, and a long-period waveguide grating. The propagation loss of the waveguide fabricated by this technique is 1.8 dB/cm at 1550 nm and the polarization-dependent loss is 0.15 dB/cm.
We propose a polymeric variable optical attenuator using a modified wide angle X-junction structure. The device's size is only one sixth of that using conventional Y-junction structure. A commercial 3D-Beam Propagation Method simulation software was used to optimize and analyze our design, which was then fabricated using benzocyclobutene polyimide. The experimental results well match with the simulation results. The VOA has an attenuation range larger that 34dB for TE polarization by means of thermo-optic tuning. The measured response time was about 100 micro second, which is fast in compared with other thermo-optic device. The compactness of our device makes it very suitable for high density integrated photonics circuits.
The application of Digital Pixel Hologram (DPH) as anti-counterfeiting technology for products such as commercial goods, credit cards, identity cards, paper money banknote etc. is growing important nowadays. It offers many advantages over other anti-counterfeiting tools and this includes high diffraction effect, high resolving power, resistance to photo copying using two-dimensional Xeroxes, potential for mass production of patterns at a very low cost. Recently, we have successfully in fabricating high definition DPH with resolution higher than 2500dpi for the purpose of anti-counterfeiting by applying modern optical diffraction theory to computer pattern generation technique with the assist of electron beam lithography (EBL). In this paper, we introduce five levels of encryption techniques, which can be embedded in the design of such DPHs to further improve its anti-counterfeiting performance with negligible added on cost. The techniques involved, in the ascending order of decryption complexity, are namely Gray-level Encryption, Pattern Encryption, Character Encryption, Image Modification Encryption and Codebook Encryption. A Hong Kong Special Administration Regions (HKSAR) DPH emblem was fabricated at a resolution of 2540dpi using the facilities housed in our Optoelectronics Research Center. This emblem will be used as an illustration to discuss in details about each encryption idea during the conference.
In this paper, we review the inverse WKB method for refractive-index profiling of graded-index planar waveguides with emphasis on the recent developments on profiling of single-mode waveguides.
Long period gratings (LPGs) are fabricated on an ion- exchanged waveguide by the use of direct UV writing. The transmission spectrum of this LPG waveguide is analyzed. An attenuation of 22dB is observed at 1.55 micrometers .
Germanium-doped silica glasses have been fabricated and the UV induced refractive index change have been studied. An order of 10-3 refractive index change has been obtained. With the use of silver ion exchange before UV exposure, much greater refractive index change has been observed. The silver ion exchanged germanium-doped glass has a 10-2 refractive index change when it is exposed to 248 nm excimer laser. This procedure allows the fabrication of integrated optical components in a convenient way.
We report the theoretical performance of a digital switch based on a wide-angle, low-loss asymmetric X-junction we recently proposed. At a full-branching angle of 1.2 degrees, the cross-talk and transmission at the zero-voltage state have been -20 and -0.5 dB, respectively. In the switched state, they are -19.5 and -1.1 dB, respectively.
KEYWORDS: Digital holography, Holograms, Electron beam lithography, Diffraction gratings, Holography, Lithography, Computer programming, Diffraction, Data conversion, Laser systems engineering
A digital pixel cryptogram technology using e-beam holography is described in this paper. The cryptogram is generated by an electronic beam lithography system and it can be applied to fabrication of embossing hologram for anti-counterfeiting and security.
A computer-controlled optical fiber sensor system has been developed for the characterization of ultrasonic transducers in the megahertz range. The sensing element used is a short length of highly birefringent optical fiber. When an ultrasonic wave is incident normally upon the fiber, the birefringence, or the phase difference between the two polarized light waves in the fiber, is modulated. The phase modulation is converted into an intensity-modulated signal by means of polarimetry. To optimize and stabilize the signal against environmental effects such as temperature variations, a liquid-crystal phase retarder, controlled by feedback electronics, is placed in the optical path. Intensity noises arising from the laser source and the fiber leads are also eliminated by using signal processing techniques. The spatial intensity profile of an ultrasonic beam can be determined by scanning the sensing fiber across the ultrasonic beam. Fiber scanning and data acquisition are controlled by a personal computer. In this paper, the principle and the implementation of the sensor system are described. Experimental results obtained from characterizing commercial ultrasonic transducers are presented.
Using Beam Propagation Method (BPM), we show quantitatively how the asymmetry of Y- branches will affect the transmission ratio of the structure in the power dividing or mode splitting operating area. In the mode splitting area, radiation loss will increase due to conversion of fundamental mode to higher order modes. The mode splitting behavior can be retained even with large branching angle if the phase-front accelerator (PFA) design structure is employed.
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