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The dynamic behavior of a neural network is demonstrated by its interconnection weighted matrix. In this paper, we present a Feature Enhanced Interpattern Association (FEIPA) neural network model which is sensitive to special features of reference patterns in the reconstruction. We think of the common part of the stored patterns as redundance and discard its contributions in the associating process. It is equal to enhance the role of special features of the reference pattern in the IWM and in the reconstruction procession. Therefore the IWM of FEIPA is well-distributed and the output before threshold is a little more uniform than that of IPA model. A 2D (8 X 8) optical system is constructed using lenslet array as interconnection to realize the FEIPA model. Digital simulation and experiment results are provided.

In this paper we propose a Feature Enhanced Interpattern Associative (FEIPA) optical neural network. The common part of the stored pattern is regarded as redundance and its contribution in the association process is discarded. Therefore, the output before thresholding is more uniform, and it is more easier for the thresholding performance and increase the iteration speed. Furthermore, the optical implementation is much easier because all the elements of one interconnection matrix are non-negative and unipolar. The theoretical description and the experimental results are presented.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Recently, studies on the photophysical properties of C60 have shown that the population of the first excited singlet state(S1) can be transferred to the first excited triplet state (T1) with a quantum yield higher than 96% by intersystem crossing with a relaxation time about 1ns.

Optical limiting in toluene solution of C60 is first observed by L. W. Tutt and A. Kost,1 which is caused from reverse saturable absorption (RSA) of C60.

In this paper we propose a feature enhanced interpattern associative (FEIPA) optical neural network. The common part of the stored patterns is regarded as redundance and its contribution in the association process is discarded. Therefore, the output before thresholding is more uniform, and hence, it is easier for the thresholding performance and increases the iteration speed. Furthermore, the optical implementation is much easier because all the elements of the interconnection matrix are non-negative and unipolar. The theoretical description and the experimental results are presented.

A high accuracy optical bistable temperature sensor was proposed and proved experimentally by using a fiber-optic Mach-Zehnder interferometer combined with an electro-optic bistable device.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In the past decade, experimental results of transient optical bistabilities in etalons of CdSxSe1-x doped glasses have been presented by many authors[1-3]. Switching speed of ns to ps orders has been obtained. However, there still do not exist a dynamics theory of this transient optical bistability. This paper emphasizes the dependence of the implementation of transient optical bistabilities on the incident pulse width, the media response time, the FP cavity establishing time, and also, the influence of the incident pulse width on the switching speed.

Saturable absorption (SA) in organometallic compounds, such as phthalocyanine (Pc), was extensively studied in 1960’s, the purpose of the research was to find suitable dyes to compress laser pulse. As we know, SA is due to the absorption of the ground state, which can be described by a two-level model or a three-level model[1]. At that time, the excited state absorption, only considered as residual absorption, had not received much attention.

We have measured the nonlinear absorption and nonlinear refractive index changes in ZnSe''ZnS multiple quantum wells at low temperature. The largest change of nonlinear refractive index is 0. 012 and corresponding n2 is 7x1Ocm2IW. The nonlinear mechanism are attributed to exciton band broadening and phase space filling of exciton states. With different excitation wavelengths we have demonstrated the dynamic optical bistabilities in ZnSe/ZnS MQWs.

A rigorous theoretical model for In0.53Ga0.47As/InP single photon avalanche photodiodes operated in the Geiger mode is developed to calculate dark count probabilities over a wide range of temperatures and widths of multiplication layer. Both nonlocal ionization and low field impact ionization in the absorption layer are considered in this model. The calculated results confirm that impact ionization in the absorption and charge layers increases the dark count probability. The primary mechanism of dark counts depends on both device structure and operating conditions. For a 1 µm multiplication width, the dominant mechanism of the dark counts at a temperature above 233 K is the generation–recombination in the absorber while at a temperature below 233 K the tunnelling effect in the multiplication layer begins to dominate.

The excitonic optical nonlinearities in II-VI semiconductor thin films and multiple quantum wells (MQWs) are much complicated than those of GaAs MQWs because the wider band gap and smaller excitons of II-VI semiconductor materials. We report here the observations of dynamic optical bistabilities in ZnSe/ZnS MQWs at low temperature caused by excitonic optical nonlinearity.

We perform optimization of all-optical EDFA-based Sagnac – interferometer switch through an analytical model and numerical simulations by solving nonlinear Schrodinger equations. The effects of the performance of EDFA on the bit rate and the switching power are investigated for all-optical switch based on self-phase or cross-phase modulation. The simulated results show that ultra-low switching power (

The structure of the homologous compounds InMO3(ZnO)m (M=In, Fe, Ga, and Al, m=integer) is considered to be a layered structure, consisting of InO21− layer (In-O) ) interleaved with MZnmOm+11+ layers (M/Zn-O) along the c-axis. In the M/Zn-O layers, the distribution of two kinds of metal atoms is considered to be random fashion from X-ray diffraction analysis. However, in the previous HRTEM study of InFeO3(ZnO)m with m larger than 6, we found a modulated structure, where the image contrast showed a sinusoidal modulation curve present only in the Fe/Zn-O layers. Elemental analysis by EDS clarified that the modulated structure was caused by the ordering of Fe atoms within the Fe/Zn-O layers. In the present study, we try to observe In2O3(ZnO)m compounds, where Fe3+ atoms are replaced by In3+ atoms which have larger ionic radii. We are interested in whether the replacement of Fe3+ by In3+ atoms may cause any structural changes between In2O3(ZnO)m and InFeO3(ZnO)m.The samples were prepared by heating powders of In2O3 and ZnO sealed in Pt tube at 1350 °C for about 3 days and then rapidly cooled down to room temperature. The electron microscope observation was performed by using JEM-2000EX, operated at an accelerating voltage of 200 kV.

An optical limiter was designed and fabricated. The device consists of an organic solution sandwiched between a polymer slab and a transparent relief polymer grating with a triangular groove. At low power the device has a high transmittance because the refractive index of the solution is matched with those of the slab and the grating materials and because the grating does not diffract. However, high power makes the organic solution thermally vaporize and makes the indices of the solution, slab, and grating materials become mismatched, which causes the grating to appear. The incident light is strongly absorbed, scattered, and self-defocused by the organic solution, and the grating suppresses the zero-order diffraction. Thus the transmitted light energy becomes lower than the damage threshold of human eyes or optical sensors. The device is an effective protection for human eyes or optical sensors against broadband pulsed-laser damage.

For what is to our knowledge the first time, the thermal-stress formula in analytical form is derived for the core layer in an optical planar waveguide by the thin-film approximation, which is based on a closed-form solution in multilayered isotropic structures off the edges. This formula indicates that elastic, thermal, and structural parameters can affect the magnitude of the stress. Using the formula, one can remove thermal stress and hence stress-induced birefringence by proper waveguide design.

An amorphous Hf70Cu20Pd10 ternary alloy was prepared and its crystallization process was studied. The crystallization proceeds through two exothermic reactions. Annealing of the specimen at a temperature lower than the onset point of the low-temperature exothermic reaction resulted in the precipitation of an icosahedral quasicrystalline phase. Further annealing at the same temperature caused the phase transformation to Hf2Cu crystalline phase, indicating the metastable character of the icosahedral quasicrystalline phase. In comparison with the crystallization process of other Hf-based amorphous alloys, the effect of Pd addition on the precipitation of the icosahedral quasicrystalline phase was discussed from the point of view of atomic radius.

In the past, four-wave mixing for real-time holography storage based on ground-state absorption at the resonant wavelength has been extensively studied in azo-dye-doped polymer films. We report theoreti- cal and experimental studies on the four-wave mixing based on the excited-state absorption at a nonresonant wavelength using ethyl- orange-doped polyvinyl alcohol films. In our experiments, we use two laser beams: a 632.8-nm He-Ne laser as a nonresonant light source for excited-state four-wave mixing and a 488-nm Ar 1 laser as a preexcited light source to enhance the excited-state absorption. To explain the ex- perimental results, we propose a four-level model for the azo-molecule system. The steady state and dynamic behavior of phase conjugation signal in four-wave mixing are simulated by solving rate equations. The theoretical simulations, which are in accord with the experimental re- sults, show that using the preexcited method, four-wave mixing hologra- phy storage can be realized by using a weak laser beam with a nonreso- nant wavelength based on the excited-state process. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00903-X)

Power spectrum subtraction is introduced into the joint wavelet transform correlator to improve its performance. Because the joint wavelet transform correlator is not a matched recognition, its performance is quite poor when the conventional joint-transform correlator is employed. By subtracting the power spectra of the target image and the reference image, the power spectrum subtraction technique may greatly improve the joint wavelet transform correlator. In comparison with the conventional joint wavelet transform correlator, the new correlator has narrower dc output, bigger space-bandwidth product, stronger wavelet transform output, and greater background-noise resistance. Both theoretical analysis and computer simulation verify its efficiency.

A simple but necessary condition for cascading the multiple stages of an optical fractional Fourier transform with different variable scales is presented. That condition permits more flexibility in the design of optical information-processing systems that use optical fractional Fourier transforms. We have expanded the optical applications of fractional Fourier transforms with adjustable variable scales.

General optical setups that implement the fractional Fourier transforms are proposed by use of the impulse response theory. These architectures are demonstrated to be flexible in practical spatially variant filtering systems that employ cascaded multiple stages of fractional Fourier transforms, because of their capabilities of changing the standard focal length.

The dynamic processes of reverse saturable absorption (RSA) in a solution of C60 are studied in detail by use of rate equations and the light-propagation equation for a five-energy-level model. The RSA experimental results for C60 in toluene solution with a nanosecond–picosecond Nd:YAG laser at 532 nm are consistent with the theoretical simulations. Effects of sample concentration and thickness on RSA and contributions of the singlet and triplet excited states to RSA for various laser-pulse widths and wavelengths are also analyzed. Finally, an all-optical switch based on excited-state nonlinear absorption and the pump-probe technique is implemented.

We have demonstrated a novel optical power limiter which can be used to limit an unstable pulse peak power with temporally smoothing in shape for CO2 laser pulses. The peak power of pulses was limited with 1.1% fluctuation for a 30% change of incident pulse peak power and the frequency of subpulse oscillation on a single pulse was over 30 MHz.

Multiple-valued logic offers many times the logic power and packing desity of binary logic, thus reducing the number of necessary logic gates.1 Recently optical multip1e-va1ued logic has been studied extensively using shadow casting method.2 In this paper we describe a new configuration of optical multiple-valued logic gates using composite bistable laser diode or light emitting diode circuits (BILD or BILED). To our knowledge, this is the first time that optical multip1e-va1ued logic have been obtained using optical bistable device. We have demonstrated four Post logic functions: Complement, Max(x,y), Min(x.y), and Suc(x) using composite BILED circuits. We only take Complement and Max(x,y) for example here.

Integrated optoelectronic logic circuits are promising for use in optical computing. Much attention has been paid to demonstrate binary and multiple-valued optical logic implementation using optoelectronic circuits. In this paper we present what we believe to be the first demonstration of optical binary threshold logic using a modified optoelectronic PD LED bistable circuit (BILED).

Relaxation oscillation can occur in a bistable system when the nonlinearity has two contributions of opposite sign and different time constants.1 Optoelectronic bistable laser diode or light emitting diode (BILD or BILED) circuit is a promising optical logic device.2 Here we present the observation and analysis of optical regenerative pulsation in a system constructed of a liquid crystal switch and BILED circuit. Sine wavelike pulses were obtained in our experiment, and the experimental results show that the oscillation frequencies were stable. The frequency can be adjusted by changing the voltage supply. In our experiment the output from an argon laser is controlled by a LC switch, which is connected to a BILED circuit. The voltage applied across the LC switch is provided by an amplifier, and it is proportional to the output of the BILED circuit. The BILED circuit has two output signals of feedback. One is the light emitted from the LED in the circuit. The other is a part of the laser beam transmitted from the LC switch. As oscillation occurs in the circuit, the laser beam is modulated into a train of pulses by the LC switch.

Gallium nitride powders and zinc oxide powders were each calcined with a few weight percent of copper oxide and/or magnesium oxide either in air or N2. Powder X-ray diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy were performed in order to observe calcination induced structural effects on these wurtzite type semiconductors. We note that our earlier magnetic results on Cu doped GaN are qualitatively consistent with recent first principle calculations [Wu et al., Appl. Phys. Lett. 89 (2006) 62505].

Gallium nitride powders were calcined with copper oxide in either air or N2 and analyzed by means of powder X-ray diffraction (XRD), high-resolution parallel illumination (HRTEM) and scanning probe transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDXS), and electron energy loss spectroscopy (EELS) in order to address the structural and electronic effects of Cu-incorporation into GaN. Gallium oxide and multiple copper oxide phases corresponding to the calcination environment were detected. Significant changes in the lattice parameters and electronic structure of the N2-processed GaN indicate incorporation of both copper and oxygen into the GaN lattice as well as changes in the chemical bonding due to the calcinations process. SQUID magnetometer measurements at 300 K demonstrated ferromagnetism in selected samples.

A design for optoelectronic multiple-value logic circuits that uses bistable laser diodes or light-emitting diodes is reported. In this multiple-valued logic design, an optoelectronic tristable switching circuit, or light-current mirror, in which two bistable light-emitting diodes are connected in parallel serves as the basic logic element. Five ternary logic implementations: Complement. Max(x, y), Min(x, y), Cycle, and Literals, have been demonstrated experimentally. Furthermore, any ternary logic function can be generated with the light-current mirror and the logic primitives.