F.R. Beyette

Optoelectronic data filter for selection and projection

Database processing, like the majority of nonnumerical applications, exhibits a high degree of functional parallelism but does not require complex operations; therefore it is amenable to optical solutions. The architecture of an optoelectronic filter that is capable of performing selection and projection operations on a two-dimensional data array in a relational database environment is presented. The system receives input from a parallel optical memory, one page at a time, and performs logic operations by using optoelectronic smart pixels based on heterostructure phototransistors and vertical-cavity surfaceemitting lasers. Combinations of AND and XOR gates are used to realize row-lcolumn masking and comparisons of input data against user-supplied search arguments. The main goal of the filter is to reduce the effective data rate between the highly parallel optical storage and the low input data rate conventional electronic computer, thus efficiently interfacing currently available photonic and electronic technologies.

Electrical and optical feedback in an InGaAs/InP light-amplifying optical switch (LAOS)

A circuit model for optical and electrical feedback has been developed to investigate the cause of negative differential resistance (NDR) switching in a series connected heterojunction phototransistor (HPT) light-emitting diode (LED) device. The model considers optical feedback from the light generated in the LED, electrical feedback from the holes thermally emitted over the LED cladding layer, nonlinear gain of the HPT, the Early effect, and leakage resistance. The analysis shows that either electrical or optical feedback can be the dominant cause for the NDR, depending upon their relative strengths. The NDR observed in the devices was caused primarily by electrical feedback since the optical feedback is weak. For low input power, avalanche breakdown appears to initiate the NDR in the devices although avalanching alone cannot cause NDR. >

Smart pixels using the light amplifying optical switch (LAOS)

A light amplifying optical switch (LAOS), a vertically integrated heterojunction phototransistor (HPT) and light emitting diode (LED) that has latching thyristor type current-voltage characteristics, is described. Since the HPT is designed to have high optical gain, it can be incorporated in a circuit with the LAOS to fabricate high-performance optical logic gates such as a NOR, NAND, AND, or a gated latch. The methods for implementing these gates, experimental results for large mesa devices, and the performance of the gates are discussed. Logic gates that use either one or two wavelengths of input light are demonstrated. The present logic gates are shown to have output contrast ratios from 4 to 30, and operate at frequencies up to 300 kHz. Increasing this performance by improving processing techniques and reducing mesa size is discussed. >

Optoelectronic exclusive-OR using hybrid integration of phototransistors and vertical cavity surface emitting lasers

Heterojunction phototransistors and surface-emitting lasers were used to demonstrate two new optoelectronic circuits that implement the exclusive-OR (XOR) function. One of the circuits also determines which of the two inputs is greater than the other. The XOR gates have high ON/OFF contrast ratios (>28:1) and optical gate gain approximately=3.<<ETX>>

Optoelectronic parallel processing with surface-emitting lasers and free-space interconnects

Parallel optoelectronic processing that uses smart pixel arrays and free space interconnections may provide an attractive alternative to applications that exhibit a large degree of functional parallelism and require massive input/output data rates. Two fine-grain parallel architectures based on two-dimensional arrays of processing elements are discussed in this paper. The logic complexity of the smart pixels ranges from two-input AND and XOR gates for a database filter to multiple-input multiple-output compare-and-exchange modules for a recirculating bitonic sorting unit. Both systems use vertical-cavity surface-emitting lasers as light sources but light detection and logic are implemented differently. The data filter uses GaAs-based phototransistors while the sorting unit requires silicon detectors and CMOS circuitry for its more complex logic. The free-space one-to-one interconnection patterns required between processing planes can be realized with either refractive or diffractive optics and their simplicity and regularity permit easy scale-up. >

Switching light with light

The basic characteristics of the light amplifying optical switch (LAOS) are explained. The LAOS, as compared to its electronic counterparts, will substantially reduce the interconnect time between components, chips, PC boards, and machines. The use of the LAOS to implement optical logic circuits with multiple input stages that invert and restore the input signal is discussed. Applications to image and signal processing are examined. Future uses are considered.<<ETX>>

Integrated optical NOR gate

A two-input optical NOR gate structure is proposed and demonstrated. The NOR gate is fabricated from a vertically integrated heterojunction phototransistor and light emitting diode InGaAs-InP structure grown by gas source molecular beam epitaxy. Operation up to 500 kHz is demonstrated for devices fabricated with 250- mu m*250- mu m mesas. Analysis indicates that operation at frequencies up to 50-100 MHz is possible for smaller mesa areas. ON/OFF optical contrast ratios as high as 30 were measured.<<ETX>>

Bitonic sorting using an optoelectronic recirculating architecture

An optoelectronic bitonic sorter based on a recirculating architecture is presented. The data are input inword parallel-bit parallel fashion and processed by two smart pixel arrays made up of bitwise compare-and-exchange modules. Along with the logic design, the control and synchronization of the bitwise compare-and-exchange modules are discussed. Finally, the capacity, hardware requirements, response time, and throughput of the recirculating bitonic sorter are compared with a pipeline implementation. The proposed recirculating architecture is shown to require less hardware than the pipelined systems. However, the decrease in hardware results in a decrease in system throughput.

Optical digital comparison unit for equal-to, less-than, and greater-than determination

A number of nonnumerical processing applications, including database management, full text search, and pattern recognition rely heavily on digital comparisons. The development of massive-capacity optical memories coupled with the high speed and parallelism of optics have led to the investigation of optical techniques for nonnumerical processing. This paper proposes a system design for an optical comparator capable of performing multiple equal-to, less-than, and greater-than comparisons between pairs of binary words. The comparator consists of three two-dimensional arrays of optical elements based on a new optical logic device called the light-amplifying optical switch. The first two stages contain inverters, NOR gates, and flip-flops, while the third stage is a custom-designed winner-takes-all network. With a compact design and with small high-speed devices a comparator with 2.5 × 10(4) pixels could theoretically attain a processing rate of approximately 4 × 10(10) 16-bit word comparisons/s.

Optoelectronic exclusive-OR (XOR) gate

An optoelectronic circuit that implements the exclusive-OR (XOR) logic function is described. The circuit uses two unmatched heterojunction phototransistors and a light amplifying optical switch (LAOS) monolithically integrated on an InGaAs/InP wafer grown by gas-source molecular beam epitaxy. The circuit was operated from DC up to the limit of the probe stand (90 kHz). The ease of operation and high ON/OFF contrast ratio (>50) make this XOR gate ideal for applications that require optical binary comparison or addition.<<ETX>>