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The effect of laser wavelength on the photorefractive characteristics of PMDA-DR19 based photorefractive polymeric materials
(1997-09-01)
Chang, CJ
;
Wang, HC
;
Liao, GY
;
Whang, WT
;
Liu, JM
The photoconductivity and photorefractive characteristics of PMDA-DR19-based photoconducting nonlinear optical polymeric films with different compositions were studied using red and green lasers. Contributions of dopants and the host to the photoconductive and photorefractive properties are systematically discussed. The virgin nonlinear optical material PMDA-DR19 was neither photoconductive nor photorefractive in nature. However, it became photoconductive and photorefractive once the charge transport material was incorporated into the PMDA-DR19/PVB polymer film. Films containing more nonlinear optical chromophore exhibited higher diffraction efficiency. Response speed was further elevated when an additional charge generation material was doped in. Diffraction grating was observed under zero electric field and was confirmed due to a photorefractive effect by the two-beam coupling effect. In addition to composition modification, the laser light source was also an important factor in changing the PR response speed. The photorefractive response speed was tremendously improved when films were written and read by two different laser beams, either red/green lasers or green/red lasers. (C) 1997 Elsevier Science Ltd.
2k-grating-assisted self-pumped phase conjugation: Theoretical and experimental studies
(1996-08-01)
Lin, SUH
;
Lian, YW
;
Yeh, PC
;
Hsu, KY
;
Yong, Z
We investigated 2k-grating-assisted self-pumped phase conjugation in photorefractive Ce:BaTiO3 crystals. The phase-conjugation process involves a combination of four-wave mixing and stimulated photorefractive backscattering. An approximation involving separate interaction regions is used to theoretically calculate the reflectivity of phase conjugation as a function of the coupling strength of four-wave mixing and stimulated photorefractive backscattering. Fn our experiments, grating-erasure techniques are employed at the interaction regions to investigate the dependence of phase-conjugate reflectivity on the coupling strength of four-wave mixing and stimulated photorefractive backscattering. The experimental results are in good agreement with the theoretical prediction.
Proposed power-equalized EDFA modules using fiber Bragg gratings with various reflectivities
(1999)
Liaw, SK
;
Ho, KP
;
Hsu, KY
;
Chi, S
;
光電工程學系
We proposed and experimentally demonstrated two power equalized erbium-doped fiber amplifier (EDFA) modules using fiber Bragg gratings (FBGs) with various reflectivities for individual channels. The transmission type power-equalized EDFA module is low-cost for its simple design, while the reflection type power-equalized EDFA module can suppress most of the amplified spontaneous emission noise. Both consist of a bidirectional EDFA, a set of FBG chains with suitable reflectivities, and an optical isolator / optical circulator They can find potential applications in wavelength division multiplexing lightwave transmission systems.
Effect of the sensitizer on the properties of fully functionalized photorefractive epoxy polymers and their performance in the hologram image storage
(1999-06-01)
Chang, CJ
;
Whang, WT
;
Hsu, KY
;
Hsieh, ML
;
材料科學與工程學系
The 3-amino-9-ethyl carbazole (AEC)/Dispersed Orange 3 (DO3)/diglycidyl 1,2 cyclohexanedicarboxylate (DCD) main chain copolymers are synthesized and studied on their photorefractive (PR), photoconductive, and holographic characteristics. They are good hologram recording media because not only the stored hologram exhibits excellent fringe contrast with the resolution at about 20 mu m, but also the image can be stored, erased, and overwritten. The UV/Vis spectra shows that AEC segments may form charge transfer complexes with either DO3 segments or TNF sensitizers. By incorporating the sensitizer or increasing the charge transfer component concentration, the grating growth rate can be speeded up. Applying an electric field on the polymer film containing no sensitizer helps to elevate the grating growth speed, but it shows little influence on the grating growth speed of the films with sensitizers. More nonlinear optical (NLO) segments in the copolymer result in higher diffraction efficiency. The dark decay of the film depends on the dark conductivity. Incorporating sensitizers or more charge transport segments leads to more dark decay because of increasing dark conductivity. The dark decay of the PR properties at elevated temperature can also be evaluated by the thermal stimulated discharge current (TSDC) spectroscopy technique. (C) 1999 John Wiley & Sons, Inc.
Photorefractive Fe : LiNbO3 crystal thin plates for optical information processing
(1999-07-01)
Lin, SH
;
Hsieh, ML
;
Hsu, KY
;
Hsieh, TC
;
Lin, SP
The effects of the donor acceptor concentration ratio in iron-doped Lithium niobate (Fe:LiNbO3) crystal plates on photorefractive response time and on grating diffraction efficiency are studied both theoretically and experimentally. The results provide a useful guide for designing photorefractive plates far optical information-processing applications. Two devices for real-time image recognition have been demonstrated: a photorefractive joint-transform correlator and a VanderLugt correlator. The former emphasizes fast response time, and the latter emphasizes high diffraction efficiency. By appropriate adjustment of the dopant concentration and the ratio of the donor acceptor levels, photorefractive Fe:LiNbO3 crystals that facilitate specific applications have been designed and fabricated. Shift-invariant image correlations have been achieved. (C) 1999 Optical Society of America [S0740-3224(99)01307-7].
Synthesis and relationships between the nonlinear optical and holographic properties of dual functional azocarbazole chromophores based on photorefractive polymers
(1999-08-24)
Chang, CJ
;
Whang, WT
;
Hsu, CC
;
Ding, ZY
;
Hsu, KY
Two kinds of dual functional carbazole-based chromophores are synthesized to enhance the photorefractive (PR) performance of the polymers by attaching the electron-donating and electron-accepting groups with a diazo bridge on the 3- and 6-positions of the N-ethylcarbazole. The electron-donating group is N,N-diethanol aminophenyl. The electron-accepting group is either p-nitrophenyl or 5-nitrothiazole. The peak maximum of the UV/vis absorption spectra of the 5-nitrothiazole-containing chromophore PANTAC at 535 nm is longer than that of the p-nitrophenyl-containing PANPAC at 477 nm. Both chromophores exhibit a large first hyperpolarizability in the hyper-Rayleigh scattering experiment due to the extended chain length. The first hyperpolarizability of PANTAC is 1100 x 10(-30) esu, almost the double of that of PANPAC (590 x 10(-30) esu). The diffraction efficiencies of both polymers are the function of the film thickness and the laser beam wavelength with a maximum eta(max) at a thickness d(max) between 15 and 23 mu m Surprisingly, the PANPAC-based PR polymer reveals a higher maximum diffraction efficiency (eta(max)) and better fringe of the stored holograms than the PANTAC-based PR polymer does. Both the PR polymers written/read by the green/red laser have greater eta(max) values than those written/read by the green/green laser. These phenomena are related to the balance between absorption and transmission of the laser beam through the PR polymer.
Optimal conditions for thermal fixing of volume holograms in Fe : LiNbO3 crystals
(1999-10-10)
Hsieh, CR
;
Lin, SH
;
Hsu, KY
;
Hsieh, TC
;
Chiou, A
We analyze and compare two typical recording and thermal fixing procedures of a volume hologram in a Fe:LiNbO3 crystal (low-high-low procedure and high-low procedure). We consider the kinetics of the recording, compensating, and developing processes by taking into account the ratio of the conductivities between the protons and the electrons as a function of temperature. From the analysis the optimal environmental conditions tin terms of the fixing temperature and the compensation time) for each fixing procedure can be deduced for a crystal with given material parameters. (C) 1999 Optical Society of America.
Modulation transfer function of a liquid crystal spatial light modulator
(1999-11-01)
Hsieh, ML
;
Hsu, KY
;
Paek, EG
;
Wilson, CL
;
光電工程學系
The modulation transfer function (MTF) of a pixelated liquid crystal spatial light modulator (LC-SLM) has been derived as a function of the fill factor. Based on the formula, we have investigated the dependence of the MTF on the orientations and spatial frequency of the input patterns. Furthermore, we have proposed and demonstrated a method for improving the MTF of a LC-SLM. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Performance enhancement of a joint transform correlator using the directionality of a spatial light modulator
(1999-12-01)
Hsieh, ML
;
Paek, EG
;
Wilson, CL
;
Hsu, KY
;
光電工程學系
We observe that conventional electrically addressable spatial light modulators have different transfer functions along the fast (horizontal) and the slow (vertical) directions. We then propose to use the directionality of a spatial light modulator to increase the performance of a joint transform correlator. Our experimental results show that input space-bandwidth product of a joint transform correlator can be significantly increased by recording a hologram so that interference fringes run along the fast (horizontal) direction of a spatial light modulator. (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(99)00412-2].
A hetero-associative memory using phase-multiplexing references
(2000-04-01)
Hsieh, ML
;
Hsu, KY
;
Lin, SH
;
電子物理學系
;
光電工程學系
We present a hetero-associative memory for multiple-associative pairs by using the phase-multiplexing technique. Two methods for reducing the cross-talk between different association pairs are proposed. An optical experiment for the edge-enhancement associative memory is also demonstrated. (C) 2000 Elsevier Science B.V. All rights reserved.

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