Browsing by Author "YEH, P"

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CONDITIONAL CONVERGENCE OF PHOTOREFRACTIVE PERCEPTRON LEARNING
(1993-12-15)
HSU, KY
;
LIN, SH
;
YEH, P
;
光電工程學系
;
Department of Photonics
We consider the convergence characteristics of a perceptron learning algorithm, taking into account the decay of photorefractive holograms during the process of interconnection weight changes. As a result of the hologram erasure, the convergence of the learning process is dependent on the exposure time during the weight changes. A mathematical proof of the conditional convergence, as well as computer simulations of the photorefractive perceptrons, is presented and discussed.
EFFECT OF POSITION-DEPENDENT TIME CONSTANT ON PHOTOREFRACTIVE 2-WAVE MIXING
(1992-09-01)
DAI, LK
;
GU, C
;
YEH, P
;
光電工程學系
;
Department of Photonics
The effect of a position-dependent time constant on nondegenerate photorefractive two-wave mixing is analyzed. For codirectional two-wave mixing the results indicate that the bandwidth of the two-wave-mixing gain decreases when the medium becomes lossy and that the photorefractive phase shift depends on the loss of the medium. In contradirectional two-wave mixing the total local intensity strongly depends on the coupling even if the medium is lossless. Thus the bandwidth is dependent on the energy coupling.
INSTABILITIES IN COUPLED PHOTOREFRACTIVE RING CAVITIES AND SELF-PUMPED PHASE CONJUGATORS
(1992-02-01)
DAI, LK
;
GOU, YS
;
GU, C
;
YEH, P
;
光電工程學系
In the preceding paper, we used the mean-field approximation to formulate the time evolution equations for two coupled unidirectional photorefractive ring resonators. Linear stability analysis based upon the steady-state solutions of the mean-field equations showed that the coupled system may become unstable in the unstable off- and steady-state operation regimes. In this paper, we investigate the temporal behavior and nonlinear dynamics of the coupled system. The results indicate that the coupled system exhibits self-pulsation and chaos in the unstable off-state and steady-state operation regimes. The instability is explained in terms of the competition between the nonlinear gain and loss. Numerical results of the transient equations are presented and discussed. The coupling between unidirectional ring resonators is extended to explain the instability in self-pumped phase conjugators.
INSTABILITIES IN COUPLED PHOTOREFRACTIVE RING CAVITIES AND SELF-PUMPED PHASE CONJUGATORS .1. MEAN-FIELD MODEL AND LINEAR-STABILITY ANALYSIS
(1992-01-01)
DAI, LK
;
GOU, YS
;
GU, C
;
YEH, P
;
光電工程學系
We investigate the temporal instabilities of mode intensities in two coupled unidirectional photorefractive ring resonators. The first resonator is driven by an external laser beam via photorefractive two-wave mixing. The internal oscillating beam is then employed to drive the second ring resonator. The second ring resonator provides a nonlinear loss mechanism for the coupled system. Complete spatial-temporal equations for describing the coupled system are derived and mean-field approximation is employed to simplify the transient analysis. The results of linear stability analysis indicate that the coupled system exhibits instability in the off-state and steady-state operation. The instability is explained in terms of competition between nonlinear gain and loss. The results are presented and discussed.
OPTICAL RESTORATION OF PHOTOREFRACTIVE HOLOGRAMS
(1995-11-01)
YEH, P
;
GU, C
;
CHENG, CJ
;
HSU, KY
;
光電工程學系
We consider the possibility of restoration and/or enhancement of decaying holograms in photorefractive media by using a simple optical readout in conjunction with a phase conjugator. The results indicate that extremely weak holograms can be enhanced provided that the two-beam coupling is sufficiently strong. Steady-state photorefractive holograms can be maintained continuously without decay by using a self-enhanced readout scheme. The results also provide an explanation for the formation of mutually pumped phase conjugation in terms of the amplification of an initial noise grating. The results are presented and discussed.
PHOTOREFRACTIVE MODE-COUPLING BETWEEN 2 UNIDIRECTIONAL RING OSCILLATORS
(1991-09-01)
DAI, LK
;
GOU, YS
;
YEH, P
;
GU, C
;
光電工程學系
We consider the coupling between two photorefractive unidirectional ring resonators. The first resonator is driven by an external laser beam via photorefractive two-wave mixing. The internal oscillating beam is then employed to drive the second ring resonator via the same mechanism. Closed form solutions for the oscillation intensities and frequencies are given, and their numerical results are presented and discussed. PACS: 42.65
SHIFT-INVARIANT PHOTOREFRACTIVE JOINT-TRANSFORM CORRELATOR USING FELINBO3 CRYSTAL PLATES
(1993-06-10)
HE, QB
;
YEH, P
;
HU, LJ
;
LIN, SP
;
YEH, TS
We report the results of our experimental investigation on a shift-invariant photorefractive image correlator that uses a thin crystal plate of Fe:LiNbO3, which operates in the Raman-Nath regime of diffraction.
THEORY OF PHASE-CONJUGATE OSCILLATORS .1.
(1990-08-01)
LEE, WS
;
CHI, S
;
YEH, P
;
SAXENA, R
;
光電工程學系
THEORY OF PHASE-CONJUGATE OSCILLATORS .2.
(1991-07-01)
LEE, WS
;
CHI, S
;
YEH, P
;
SAXENA, R
;
光電工程學系
This paper is the second in a series describing propagation of electromagnetic radiation in phase-conjugate oscillators. We apply the formulation developed in the first paper to study the phase-conjugate resonator (PCR) and the Fabry-Perot cavity with an intracavity phase-conjugate mirror (PCM). Our results show that nondegenerate oscillation occurs in the PCR for large parametric gains and fixed separation between the conventional reflector and the PCM. The bandwidth is considerably reduced from that of a PCM alone. In the phase-conjugate oscillator, oscillation will occur at the pump frequency only if there is no separation between the conventional mirrors and the phase-conjugate element and if the nonlinear medium fills the entire Fabry-Perot cavity.