Article

Parallel interconnection of two 64*32 symmetric selfelectro-optic effect device arrays

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Abstract

The cascaded, parallel operation of two 2-dimensional arrays of 2048 symmetric selfelectro-optic effect devices (S-SEEDs) is demonstrated. Bistable operation of both arrays and cascading of information from each array to the other are shown. The system is compact, tolerant to misalignment, stable and extensible.

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Chapter
Over the last years considerable progress has been made in semiconductor optoelectronics because of the needs of optical telecommunications and the emergence of new fields. Today, semiconductor optical devices are used in fiberoptic systems and for satellite communication, for optical data communication, storage, reading and writing, for optical sensors and measurements, and as solidstate laser pumps. These devices are expected to be more extensively applied in emerging areas such as optical interconnects, optical signal processing and computing or optical memory. This development has been made possible by the greater maturity of material growth and device fabrication techniques, and by an increased knowledge of semiconductor materials and device structures. Ongoing research in this field is reported in the literature and enhanced fabrication tends to make high-yield and low-cost semiconductor devices available.
Chapter
One of the more widely researched optoelectronic devices are the quantum well self-electro-optic effect devices (SEEDs). SEEDs rely on changes in the optical absorption that can be induced by changes in an electric field perpendicular to the thin semiconductor layers in quantum well material. This chapter discusses the concepts of electro-absorption, various configurations of SEEDs, resistor-biased SEEDs, diode-biased SEEDs, symmetric SEEDs, multistate SEEDs (M-SEEDs), logic SEEDs (L-SEED), several types of quantum well modulators and it describes the application of SEEDs to optical signal processing. The basic principle of a SEED is to use the current detected in a photodetector to change the electric field across the quantum well region of the modulators. These devices have optical inputs and optical outputs and are called optical logic devices, even though electrical currents flow within the devices. If the photodetector and modulator are integrated, the SEED can be quite efficient and is one of the lowest energy devices demonstrated for optical processing.
Chapter
Free-space digital optics is a topic based on many disciplines: nonlinear optics, computer and switching network architectural design, semiconductor physics, mechanical design, and, of course, optical system design. Initial work in this area concentrated on the discovery and development of nonlinear optical effects with which to form optical switching devices or logic gates. Progress on the device front stimulated research on switching and computing architectures to capitalize on the potential advantages of free-space digital optics. However, without arrays of practical devices, realistic demonstrations of these architectures were not possible. With the development of batch-fabricated symmetric SEEDs, nonlinear interference filters, and liquid-crystal and magneto-optic spatial light modulators, more complex system experiments became possible.(1–5) The demonstration of these experiments required careful attention to the optical and opto-mechanical system design, in addition to significant device and architectural research.
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Free-space photonic switching systems that optically interconnect large arrays of simple processing elements have already been demonstrated [IEEE Photon. Technol. Lett. 2, 438,600 (1990); Appl. Opt. 31, 5431 (1992); Electron. Lett. 27, 1869 (1991)]. In these system experiments, diffractive optical elements served as critical components that provided functionality not easily assumed by conventional optics. In the latest optical switching network, binary phase gratings were used to generate arrays of uniformintensity beams to illuminate modulators in the processor array. In addition, space-invariant binary phase grating designs were integral in forming the Banyan interconnection network used to link arrays in the system. Here we discuss the function, design, and performance of these diffractive elements.
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Full-text available
The recent evolution of quantum-well self-electrooptic effect devices (SEEDs) for application in free-space optical switching and computing systems is reviewed. Requirements of these systems have stimulated the development of devices usable in large systems of cascaded devices (the symmetric SEED), large two-dimensional arrays of these devices with improved physical performance, logically smarter extensions of these devices (logic-SEEDs), and devices integrating electronic transistors with quantum-well modulators and detectors for both reducing the required optical energies and increasing functionality. This progress and its implications for future developments are summarized
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Photonic technologies are reviewed that could become important components of future telecommunication systems. Photonic devices and systems are divided into two classes according to the function they perform. The first class, relational, refers to devices, that map the input channels to the output channels under external control. The second class, logic, perform some type or combination of Boolean logic functions. Some of the strengths and weaknesses of operating in the photonic domain are presented. Relational devices and their applications are discussed. Optical logic devices and their potential applications are reviewed
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A prototype digital free-space photonic switching fabric consisting of three cascaded 16×8 arrays of symmetric self-electrooptic effect devices (S-SEEDs) is demonstrated. The three stages implement the input interface and one 2×1 node stage of a multistage switching network using crossover interconnections. The devices in the arrays used in this experiment are configured to function as logic gates to implement an array of 2×1 switching nodes. The 128 data inputs to the system are generated by a matrix of 64 fibers and by a laser passing through 8×8 binary phase grating (BPG) beamsplitter. The output power from each fiber is 94 μW. Vignetting in the collection optics results in an output power of less than 1 μW, which limits the first stage switching speed to about 100 kHz (33-kb/s system data rate). The minimum signal power cascaded from one S-SEED array to the next is about 150 μW. If the system speed were limited only by the signal powers between arrays, a data rate of 200 kb/s would be achievable
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A 64*32 array of symmetric self-electrooptic effect devices, each of which can be operated as a memory element or logic gate, is discussed. The required optical switching energies of the devices were approximately 800 fJ and approximately 2.5 pJ at 6 and 15 V bias, respectively, and the fastest switching time measured was approximately 1 ns. Either state of the devices could be held with continuous or pulsed incident optical signals with an average optical incident power per input beam of approximately 200 nW or less than 1 mW for the entire array. Photocurrent and reflectivity were measured for all 2048 devices. Only one device failed to have the negative resistance required for bistability, and only nine of the devices fell outside a band of +or-20% of the mean. Additionally, over 200 devices in the array were operated in parallel using low-power semiconductor laser diodes.< >