The authors propose the use of holograms to modify both sides of the substrate of an organic light-emitting diode (OLED) to increase its light output efficiency and to discuss the associated angular, spectral, and near-field effects. A single-source macroscopic phase hologram experiment is used to illustrate the idea. Since the emitted light originates from dynamically varying positions with different directions and has wavelengths longer than the nanometer layer thickness of an OLED, the angular, wavelength, and near-field effects have been analyzed. Diffraction efficiency due to the dynamic density and position variations of the excitons has been discussed. The subwavelength near-field wave propagation effect is described with finite-difference time domain solutions to Maxwell's equations. These effects are not limited to the holographic method, but should exist in other substrate-modification methods proposed for increasing the OLED's external light efficiency.
Following a brief review of OLED structures and emission models, we have proposed a phase holographic method to modify both sides of the substrate of an OLED to increase its output light emission efficiency. The holograms are designed with special masks simulating the emission layer of the OLED. A single source macroscopic phase holographic experiment is used to illustrate the idea. Limitations on diffraction efficiency due to the dynamic density and position variations of the excitons and near-field subwavelength wave propagation phenomena in a real OLED device have been discussed.
A synchronized broad-area laser array (SBLA) can produce a highly coherent light source whose output intensity is proportional to the square of the number of lasers in the array. High contrast optical intensity modulation can be achieved by utilizing the nonlinear response of the total output intensity to the injected light, resulting in fast optical switching. SBLA can be applied to phased array antenna and beam steering. Semiconductor laser array capability provides a unique opportunity not only for free-space adaptive optical communication but also for free-space quantum adaptive optical communications through the atmosphere. In this paper, we propose a paradigm that illustrates how quantum communication (which provides quantum ultra-security) can take advantage of ultrashort pules, high repetition rate, high power density (due to coherent beam coupling), and spatial beam control.
This paper describes experimental results on the injection locking of high-power broad-area semiconductor lasers in a commercially available 19-laser array driven by a common current source. Single-frequency optical spectrum and single lobe far-field pattern are observed as a result of injection locking. We discuss the temporal dynamics, the amplification of the injection light, and the phase coherence between the injection-locked lasers, which are key issues in their applications to free-space laser communication.
The optical limiting characteristics of the methyl-red dye doped nematic liquid crystal (NLC) films have been tested, and an interesting dark spot phenomenon and a dynamic self-action diffraction ring pattern in the far field behind the sample cell have been observed. The time sequence of the dark spot formation and the dynamic self-action diffractino ring apperaance has also been investigated. We found that, with increasing the energy impinging on the sample cell, the dark spot accompanied by a single outer bright ring always appears and lasts until the multiple diffraction rings form. We also found that the dark spot with a single outer bright ring in the far field corresponds to the nonlinear section of the optical limiting characteristic curves of the doped NLC fimls, while the onset of the multiple diffraction rings corresponds to the input damage threshold of the doped NLC film limiters. Our experimental results show that the optical limiter based on the methyl-red dye doped NLC films has a quite low optical limiting threshold and an unusually low clamped output to eye safety. In this paper, we will present how we tested the optical limiting characteristics of the methyl-red dye doped NLC films and what kind of the typical test results we obtained in the experiments. We will theoretically analyze the optical limiting mechanisms of the methyl-red dye doped NLC films. We will also discuss the advantages and some limitations of the methyl-red dye doped NLC films. We will also discuss the advantages and some limitations of the methyl-red dye liquid crystal limiters, and propose several possible solutions to these limitations.
The purpose of this paper is to present a grating-assisted nonlinear limiting method based on the principle of index mismatching and grating diffraction. In addition, various nonlinear organic materials have been tested in the optical limiting system. A few examples with experimental results are presented. Using a YAG nanosecond pulse laser at 532 nm as a simulated threat laser source, we tested the optical limiting characteristics of the methyl-red doped nematic liquid crystal films. In the meantime, we observed some quite interesting optical phenomena, such as self-defocusing diffraction rings, dark spots in the far-field behind the cell. Our experimental results presented in the paper show that the methyl-red doped nematic liquid crystal films posses a good optical limiting performance. When the input energy focused on the cell increases from approximately zero micro Joule to approximately 200 micro Joule, the output energy on the far-field exit plane is kept under 1 micro Joule. We will describe a completed optical limiting system with Q-switched frequency-doubled 12- ns Nd:YAG laser, dual-channel detectors, and computer processing units based on Lab-view software and its design considerations.
Some new techniques and architecture based on the concept of holographic interferometry with the use of photorefractive crystals as real-time recording and reconstruction devices have been developed and employed in the following applications: (1) real-time and adaptive pattern recognition and tracking of moving target; (2) Real-time holographic monitoring and 3D analysis of flow or temperature fields; (3) Optical testing by transversal and longitudinal wavefront shifting interference. Both the theoretical analyses and the preliminary experimented results are presented.
A new photorefractive joint transform correlator architecture using a photorefractive crystal as a reference image storage or sequentially image updating device instead of a joint transform power spectrum recording element is proposed. Three novel and simple methods for moving target recognition and tracking with this architecture are introduced: (1) correlation with single fixed reference image; (2) correlation with a fixed synthetic reference image; (3) adaptive correlation with a sequentially updated reference image. Some specific considerations concerning the recording-erasing property of the crystals and the principle of adaptive tracking are analyzed and discussed. Preliminary experimental studies are made to verify the effectiveness of these methods, the results are in full agreement with our theoretical expectations.
Existence conditions of optical transfer function for discrete imaging systems with focal plane photodetector arrays and aliasing phenomenon due to insufficient sampling intervals are analyzed. A concept of average discrete point spread function based on the characteristics of photodetectors is proposed. A theory of statistical transfer function for discrete imaging systems is suggested.
Recently, a terminal attractor based associative memory (TABAM) with optical implementation techniques was published in Applied Optics (August 10, 1992). Herein perfect convergence and correct retrieval of the TABAM are demonstrated via computer simulation by adaptively setting the threshold values for the dynamic iteration for the unipolar binary neuron states using terminal-attractors and an inner-product approach. The simulations are completed by (1) exhaustive tests with all of the possible combinations of stored and test vectors in small- scale networks, and (2) Monte Carlo simulations with randomly generated stored and test vectors in large scale networks with a M/N ratio equals 4 (M: the number of stored vectors; and N: the number of neurons up to 256). The feasibility of optoelectronic implementation is discussed.
The principle and experimental results of a novel spatial bifurcating optical associative retrieval and pattern recognition technique are presented. A single 2D input image is associated with self-amplification with two output images through holographic diffraction in a photorefractive crystal. In an optical experimental setup utilizing a photorefractive crystal BaTiO3, interesting optical edge enhancement, pattern recognition and auto-associative retrieval phenomena have been demonstrated.
A self-amplified optical pattern recognition technique that utilizes a photorefractive crystal as a real-time volume holographic filter with recording accomplished via laser beams of proper polarization and geometric configuration is described.
In this paper we investigate a feasibility of an opto-electronic implementation of the diffusion neural network for contour detection. The diffusion neural network performs the Gaussian operation efficiently by the diffusion process. We apply this in producing the DOG (Difference of two Gaussian) functions, which can detect the intensity changes of the different spatial frequency components in an image. In the diffusion neural network each neuron has four connections with the four nearest neighbor neurons and a self-decay loop for a 2D image, and the connection weights are fixed-valued. Therefore the diffusion neural network is simpler and more efficient than LOG masking method in hardware or optical implementation. We implement the diffusion neural network opto-electronically using the point spread function of a spatial light modulator. This system is composed of a spatial light modulator, a 2D image sensor array, and a computer. The processing time of the system is very fast. Therefore the system has a potential applicability to the system that requires a real time processing of an image.
A reconfigurable optical interconnection technique via complex amplitude computer generated holograms (CGH) in electrically-addressed spatial light modulators (ESLM) is presented. Several networks including one-to-many (either regular or irregular) and strength-adjustable interconnections can be implemented by the new technique.
A real-time 2-D angular-multiplex beam-array holographic storage and reconstruction technique using electrically-addressed spatial light modulators(E-SLM's) and photorefractive crystals is described. Using a liquid crystal television (LCTV) spatial light modulator (SLM) for beam steering and lithium niobate photorefractive crystal for holographic recording, experimental results of generating large and complicated arrays of laser beams with high diffraction efficiency and good uniformity are presented.
A perfectly convergent, unipolar, neural associative memory system based on nonlinear, dynamical terminal attractors is presented. By adaptively setting the threshold values for the dynamic iteration for the unipolar, binary neuron states with terminal-attractors, the achievement of perfect convergence and correct retrieval has been demonstrated via computer simulation. The simulations are completed by (1) exhaustive tests with all of the possible combinations of stored and test vectors in small-scale networks, and (2) Monte Carlo simulations with randomly generated stored and test vectors in large-scale networks with an M/N ratio equals 4 (M: the number of stored vectors; and N: the number of neurons up to 256). An experiment with exclusive-or logic operation using LCTV SLMs is used to show the feasibility of an optoelectronic implementation of the model. The behavior of terminal attractors in basins of energy space is illustrated through examples.
In general, a decision on any event is made through a sequence of bifurcating selection process. In addition to numerical computation, the binary logic operations of digital electronics may well be used to describe any complicated decision making procedure. In this paper, we show that the single-input-double-output bifurcating principle may be applied to optical information processing. In particular, the massive parallelism and inherent inaccuracy of optics offer a unique representation of human thinking and decision making process. Coherent optical experiments including pattern recognition and dynamic range compression via photorefractive crystals are used to demonstrate the principle of bifurcating optical information processing.
We consider 1-D and 2-D error diffusion (ED), modulated error diffusion, random encoding, and direct quantization computer generated hologram (CGH) encoding schemes. Multilevel (L transmittance levels), macro pixel (N2 CGH pixels per sample) and one CGH pixel per sample, and amplitude and phase encodings are considered. Three diverse applications (matrix-vector processors, spectrum analyzers, and general interconnections for neural nets etc.,) are considered. We find random encoding is best for matrix-vector macro pixels (due to the high local accuracy required, i.e., the fact that one matrix cell maps to one output point), modulated ED (or ED) is best for spectrum analyzers (where good global signal representation is required), and multilevel ED is needed for complex lenses and interconnections (where a very complex global function is required).
A liquid-crystal TV spatial light modulator (LCTV SLM) input device and LCTV nonlinear thresholding element are presently used to accomplish an all-optical implementation of an inner-product neural associative memory. This architecture represents an alternative to the vector-matrix multiplication method of the Hopfield model, which is most often employed by neural network associative memory models. LCTV SLM experimental results are presented and discussed.
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