• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.379-381
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• 1994

Volume holograms recorded in photorefractive materials can find important applications in optical memories and optical computing systems. One problem with a photorefractive hologram is that it gets erased by the readout light. Nondestructive readout can be achieved by hologram fixing, and several fixing methods have been reported. Fixing is accomplished by thermally activated motion of an unknown ionic defect, which neutralizes the electronic space-charge patterns. At room temperature the ionic patterns are stabilized. When the electrons are partially redistributed by light, a net space-charge pattern appears, and tile fixed hologram can be read out. In this paper, theoretical modeling and some experimental results are presented for thermal fixing of volume phase holograms in photorefractive $LiNbO_3$:Fe. Thermal fixing can be done during or after recording and depends on fixing temperature ($100{\sim}200^{\circ}C$ range) and grating length. Fixed Slating can be erased completely at the temperature over $300^{\circ}C$. Theoretical modeling shows weil the compensation of electronic Slating by ionic grating and is in good agreement with experimental results. In experiments the dependence of thermal fixing on temperatures and grating lengths is investigated.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1832-1834
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• 2001

A new method of all optical packet header recognition scheme using a photorefractive hologram filter is presented. Wavelength encoded packet that has the header of a specific wavelength is assumed and the photorefractive filter can detect the wavelength. Concatenated electronics drives the optical switch to route the $\lambda$-encoded optical packet. The delay time at the switched signals are measured and compared with the original data stream.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.1051-1058
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• 1998

We propose a bandpass filter using wavelength selectivity as variation of writing beam incident angle in photorefractive crystal. From TWM(Two-Wave Mixing) experiment, optimal diffraction properties are induced, and bandpass filter for selection wavelength transmission bandwidth are taken by change of writing beam incident angle.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.9
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• pp.1108-1114
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• 1988

Usng the P.Yeh's analytic method, we derive the condition for oscillation of a linear phase conjugate oscillator which consists of photorefractive medium and two conventional mirrors. From this general oscillation condition, we obtain the threshold oscillation conditon of a single phase conjugate resonator and the self-oscillation condition of photorefractive medium, then in special case (phase shift =90\ulcorner: no external dc electric field), oscillation conditions of the linear phase conjugate oscillator for any cavity length are derived. The results indicate that, unlike in a phase conjugate oscillator with Kerr-like medium, oscillation cannot occur at special cavity length for given couplinyg strengths.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2001.05a
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• pp.64-76
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• 2001

In this paper, A simple image hologram encryption and decryption technique based on the principle of interference are proposed. The technique using the photorefractive material for getting a stable interference pattern is also proposed. And combine these two techniques, I would like to implement a stable optical information security system. In the encrypting process, I would generate binary phase hologram which can reconstruct original image perfectly, and regard this hologram as original image to be encrypted image. And then the hologram is encrypted as randomly generated binary phase image. Reference image is also generated from the encrypted image by applying interference rule. In the decrypting process, I can get a interference intensity by interfering the reference image and the encrypted image in the interferometer. and transform inferference intensity information into phase information. I recover original image by inverse Fourier transforming the phase information. In this process, the intensity information generated by interference of two images is very sensitive to external vibrations. So, I would like to get a stable interference using the characteristic of SPPCM(self pumped phase conjugate mirror) in photorefractive materials, especially BaTiO₃.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.267-274
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• 2002

In this paper, the real-time color pattern recognition system is experimented by optical approach using the SLM(TH LCD) and a photorefractive material. In the implemented system, the character patterns to recognize are controlled of an SLM, and a 10mm thick LiNbO$_3$ crystal having high angular selectivity and photorefractive effect is used for recording materials. The shape and color informations of the red or green color patterns are excellently discriminated at independent positions by real-time processing, as the results obtained by proposed optical architecture.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.10
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• pp.1571-1575
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• 1989

Nonlinear beam coupling phenomena in photorefractive materials are analyzed as a function of the input beam intensities. Signal beam saturation and pump beam depletion are shown to be the intensity-dependent functions of these materials. Utilizing these phenomena in a photorefractive BaTiO3 crystal, optical logic processors such as AND, OR, NOT, etc., are implemented.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.11
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• pp.48-53
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• 1997

Volume hologram was recorded using reference beam form optical fiber taper. A singel mode fiber was chemically etced to make a taper structure, and we showed experimentally that the referencing by the irregular beam pattern from this taper structure could increase the storage density of photorefractive volume hologram. The spatial selectivity of the volume hologram with this method was increased by two times compared to the normal single mode fiber referencing case. A theoretical analysis with randomly phased plane model also confirmed the results.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.206-207
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• 2001

The photorefractive (PR) effect in liquid crystals sandwiched between photoconductive polymer layers was first studied by Ono et al. They reported that the PR effect vanished at steady state If there were not insulating layers because no charge trapping occurred in the photoconductive poly(N-vinylcarbazole) (PVK) layers. However we observed a significant PR effect in the polymer layered liquid crystal (PLLC) system where a liquid crystal layer doped with fullerene is sandwiched between two photoconductive PVK layers. (omitted)

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.666-669
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• 1993

The space charge fields, including intermode apace charge fields in photorefractive material with two impurities are obtained for the small light intensity at large modulation depth, and their implication of high-capacity volume holographic interconnection are presented. In the following data regions the effect of intermode space charge fields are suppresed and the criteria for optimal implementation of volume holographic interconnections are satisfied.