Optical Parallel Processing Research Articles

Surface-Emitting Laser with a Common-Anode Configuration for Application to the Photonic Parallel Memory

A novel structure of a vertical-cavity surface-emitting laser (VCSEL) was proposed and demonstrated. Using a common-anode configuration, lower mesa height and lower electrical resistance were realized. The threshold current was 6 mA for a 10-µm-diameter device under room-temperature pulsed operation. The lasing wavelength was 939 nm. This configuration is suitable for large-scale integration. We also propose an optoelectronic integrated circuit (OEIC) with the common-anode configuration, which consists of a VCSEL and a heterostructure phototransistor (HPT) for optical parallel processing.

High-throughput optical image crossbar switch that uses a point light source array

A high-throughput optical image crossbar switch (OPIX) that uses a point light source array as the switching device is constructed. A prototype OPIX is used to create various switching patterns for two-dimensional images. The newly constructed OPIX is suitable for high-speed operation because it uses point light sources instead of an optical shutter array as the switching device. Since it is based on an imaging system, the OPIX has a large space-bandwidth product. The introduction of OPIX to optical image data buses of parallel optical processing systems is particularly significant.

Optical fractal synthesizer: concept and experimental verification

An application of optical parallel processing in the generation of fractal images is presented. Iterated function systems [M. Barnsley, Fractals Everywhere (Academic, Boston, Mass., 1988), Chap. 3] are the basis of the operation, which can be easily implemented with optical techniques. An optical fractal synthesizer is considered to compute iterated function systems effectively with the advantages of optical processing in data continuity as well as parallelism. As an instance of the optical fractal synthesizer, an experimental system consisting of two optical subsystems for affine transformation and a TV-feedback line is constructed. Several experimental results verify the principle and show the processing capability of the optical fractal synthesizer.

ガラスの研究における最近の話題

The optoelectronics technology will play an important role in the progress of hardware technology. Glasses have long been used as a linear optical material before the discovery of lasers. However, with the availability of very high intensity laser light, the refractive indices of glasses are now known to exhibit reversible changes as a function of intensity (nonlinear optical property NLO). Glassy materials are one of those candidates for photonic switches because of their (1) ease of fabrication, (2) high transparency, (3) fast switching time, and (4) high chemical and thermal stabilities. Main interests in the research are that NLO glass has the potential to become a key material of all-optical switching devices which operate in picosecond or sub-picosecond response time, three orders of magnitude shorter than that of the limit attained by electronic switching devices. Using all-optical switches, optical parallel data processing systems and optical time domain multiplexing transmission systems will be developed in the future. Here, theory and applications of nonlinear optics were reviewed briefly, and the nonlinear optical properties of the glasses doped semiconductor were mentioned. Other optical properties like upconversion, photochromism and photoconduction were also reviewed.

Design considerations of the optical image crossbar switch

Novel types of an optical image crossbar switch based on multiple imaging systems are proposed and demonstrated. The optical systems are based on gometric optics; accordingly, the systems have a large space bandwidth 20 x 20 switching for images with 10(3) x 10(3) pixels is realizable with the proposed optical image crossbar switches. A preliminary experiment is conducted for one of the proposed configurations. The possibility of incorporating the proposed optical switching system into optical parallel processing systems is particularly significant.

Optical content-addressable parallel processor: architecture, algorithms, and design concepts

Associative processing based on content-addressable memories has been argued to be the natural solution for nonnumerical information processing applications. Unfortunately, the implementation requirements of these architectures when one uses conventional electronic technology have been cost prohibitive; therefore associative processors have not been realized. Instead, software methods that emulate the behavior of associative processing have been promoted and mapped onto conventional locationaddressable systems. However, this does not bring about the natural parallelism of associative processing, namely, the ability to access many data words simultaneously. Optics has the advantage over electronics of directly supporting associative processing by providing economic and efficient interconnects, massive parallelism, and high-speed processing. The principles of designing an optical content-addressable parallel processor (OCAPP) for the efficient support of parallel symbolic computing are presented. The architectu re is designed to exploit optics advantages fully in interconnects and high-speed operations. Several parallel search-and-retrieval algorithms are mapped onto an OCAPP to illustrate its capability of supporting parallel symbolic computing. A theoretical performance analysis of these algorithms is presented. This analysis reveals that the execution times of the parallel algorithms presented are independent of the problem size, which makes the OCAPP suitable for applications in which the number of data sets to be operated on is high (e.g., massive parallel processing). A preliminary optical implementation of the architecture with currently available optical components is also presented.

AlGaAs-GaAs pnpn differential optical switch

A differential optical switch based on parallel-connected AlGaAs-GaAs pnpn structures is presented. Continuous input light makes it possible to discriminate between two optical inputs with a power difference of as low as 0.1 nW. The minimum operating energy with pulse inputs was 400 fJ. With the introduction of a storage operation of pnpn structures, the optical S-R flip-flop operation is also demonstrated with a 7.2-pJ optical input energy. The expansibility of the 2-D array is attractive in optical parallel processing systems, especially in optical neural networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Advanced semiconductor lasers

Recent research activities in the field of advanced semiconductor lasers are reviewed with emphasis on highly stable single-wavelength lasers and surface-emitting (SE) lasers for wideband lightwave communication systems and optical parallel information processing. The operational characteristics of DSM (dynamic single-mode) lasers are summarized and requirements for high-performance operation as light sources for high-speed transmission or coherent communications are described. A type of DSM laser called the distributed-reflector (DR) laser is described as an advanced DSM laser which enables high efficiency, high power, and narrow linewidth operations. Specific features and the potential of SE lasers are summarized. Research activities and remaining problems to be solved for a breakthrough in optical parallel information processing are presented. The potential of multidimensional quantum-well structures, such as QW lasers and quantum-box lasers, is discussed in terms of superior characteristics in both stationary and dynamic operations. The present fabrication technologies for realizing high-performance lasers based on multidimensional QW structures are also presented. >

Phase-conjugate Michelson interferometers for all-optical image processing and computing

When the mirrors of a conventional Michelson interferometer are replaced by phase-conjugate mirrors, the resulting interferometer displays dramatically altered behavior which makes it ideally suited to performing important operations in parallel optical image processing and optical computing. The phase-reversing property and real-time response of the phase-conjugate mirrors make this type of interferometer much more immune to spatially uniform and nonuniform phase distortions, both static and dynamic. Phase-conjugate interferometers are remarkably stable, sensitive only to real amplitude disturbances or information in the arms, and they readily display the subtraction, addition, intensity inversion, spatial differentiation and, in certain cases, temporal differentiation of two-dimensional optical images.

Image logic algebra and its optical implementations

A generic language for optical parallel processing image logic algebra (ILA), is proposed. In ILA a neighborhood configuration pattern (NCP) is introduced, and image transformations are defined by the use of NCP operations. The comprehensive relationship of ILA to symbolic substitution, optical array logic, mathematical morphology, and binary image algebra are clarified. Furthermore, an architecture that is suited for ILA and its optical implementations is proposed.

Analog optical processing applying PMMA-modulator-polarizer configurations

Novel applications of PMMA-modulator-polarizer configurations in analog optical processing are described. The PMMA system, consisting of two polarization modulators and two crossed polarizers, can perform addition as well as subtraction and multiplication. Experimental results obtained with a laboratory assembly made up of two photoelastic modulators and a pair of Glan-Thompson prisms confirm the theory. It is concluded that complex structures consisting of a multitude of programmable PMMA processors having high processing speeds can be realized by fiber and integrated optics technology.

Image encipherment based on optical parallel processing using spatial light modulators

All-optical image coding and decoding are demonstrated for image encipherment communication. The optical parallel coder consists of two cascaded bipolar-operational spatial light modulators (BSLMs) that can select positive and negative image readout in response to the electrical pulse polarity. Coding is performed by an exclusive-OR operation, to a key and an input image, while decoding is the same operation performed to a decoding key and an enciphered image. Coding was performed within a 8-ms duration, which is even faster than the conventional television system. Increasing the voltages to the BSLMs two-fold or three-fold and shortening the pulse durations speed up the processing rate.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A New Optical Neuron Device for All-Optical Neural Networks

A new optical neuron device has been developed. The device can perform both summation and thresholding operations in optics, and consists of a PIN a-Si:H photoreceptor, aluminum neuron electrodes and a ferroelectric liquid crystal light modulator. The a-Si:H photoreceptor shows characteristics of an ideal quantum efficiency (η∼1) and a good linearity (γ∼1). The optical neuron device exhibits a response time of ∼30 µs for incident light power of 9 µW and a contrast ratio of 300:1. Using this neuron device, a lenslet array and a memory mask, an all-optical neural network has been constructed. The network demonstrates an associative memory function on purely optical parallel processing without any help from electric computation.

Optical parallel processor for binary images with cascaded bipolar-operational spatial light modulators

An optical parallel processor is implemented for binary images with three cascaded bipolar-operational spatial light modulators that support the reversible readout and storage capabilities of binary images. All 16 Boolean operations are performed in real time according to the electric pulses. The programmable processor will serve for both optical digital signal processing and real-time image processing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Image multiplexer using a planar microlens array

An image multiplexer (IMX) composed of a planar microlens array is proposed for an input device of an optical parallel processing system. Imaging properties were evaluated experimentally and numerically to find a design rule and the limitations of use of the IMX. As a result, it was found that a planar microlens has a relatively good distortion property and low MTF sensitivity for oblique imaging, even if an image height goes to as high as 60% of the lens radius. Furthermore, a compensation method for image shift nonlinearity is proposed. The effective lens number in an array is estimated.

Optical Neuron Computers - Associative Memory and Learning by Optical Parallel Processing -

Optical Neuron Computers - Associative Memory and Learning by Optical Parallel Processing -

Optical flip-flop based on parallel-connected AlGaAs/GaAs pnpn structures

An optical flip-flop using parallel-connected pnpn (thyristor) structures is demonstrated for the first time to our knowledge. We utilize the differential optical switching technique for inverting the state of the flip-flop and the slow dissipation of carriers stored in the gate layers of pnpn structures for retaining the state. The flip-flop operation with 7.2 pJ of optical input energy was attained by using an AlGaAs/GaAs device. The expansibility to monolithic two-dimensional arrays, the high on-off contrast, and the high optical gain of the flip-flop are useful in the design and fabrication of optical parallel processing systems.

Designing massively parallel optical computers: a case study

This paper presents a case study in the design and analysis of a massively parallel optical computer, SPARO, a novel scalable computer intended for symbolic and numeric computing. SPARO was designed for fine-grained parallel processing of combinator graph reduction, a special case of the graph reduction computational model, found most appropriate for parallel optical processing in earlier studies. The architecture consists of a planar array of optical processors that communicate through simple messages (data packets) over an optical interconnection network. A technique called instruction passing is used to realize distributed control of the architecture. Instruction passing can also be used to implement complex structures such as recursion and iteration. Each individual processor in SPARO is a finite state machine that is implemented using symbolic substitution techniques, while gateable interconnects are used to realize data movements between the processors and network. Performance analysis of SPARO reveals that while discrete computing structures can be implemented using optical techniques, massively parallel optical architectures for traditional computational models are currently unable to compete with electronic ones due to the lack of large scale addressable optical memory devices and large scale integratable optical computing elements. However, optical interconnections appear very promising for providing the network throughput necessary for these parallel architectures.

Holographic image storage in iron-doped lithium niobate fibers

Holographic recording on a real-time basis of two-dimensional images in an iron-doped lithium niobate fiber with a 200 μm diameter and 3 mm length is demonstrated for the first time. The erasure time constant as a function of readout beam power, the diffraction efficiency as a function of incident reference angle, and the results of angular-multiple recording of two images are shown. These results suggest that the LN fiber could replace bulk materials for holographic recordings in optical parallel processing.

Arithmetic Fourier-transform calculation using fiber-optical parallel processors

The arithmetic Fourier transform is a number-theoretic method for calculating the Fourier coefficients of continuous-time signals. In this paper we present an efficient realization of the arithmetic Fourier-transform algorithm on an optical parallel processor consisting of fiber-optic tapped delay lines. The performance of the algorithm in the presence of optical errors and noise is analyzed. From the results of numerical experiments on a simple test signal, we observe that the performance of the algorithm is affected minimally by the errors of the optical system.