Light Amplifying Optical Switch Research Articles

Spice Analysis for the DC Behavior of the Light Amplifying Optical Switch (LAOS)

A heterojunction phototransistor (HPT) is integrated in series with a light-emitting diode to form an optoelectronic device called Light Amplifying Optical Switch. This device has been shown to switch from low current region to high current region at a voltage called breakover voltage. This switching has been attributed to the presence of optical and electrical feedback mechanisms as well as to gain nonlinearity. A circuit model for such device that took into account different factors affecting the switching behavior has been proposed previously. In this paper, a modification to the previously published circuit is made and a spice model is presented for the modified circuit and hence for the LAOS. The spice results presented here are compared to published results and showed a good qualitative agreement. In addition, several factors that affect the switching behavior of such device are analyzed and a good agreement with published results is achieved. The spice model presented here can be very helpful to engineering students in studying optoelectronic circuits and systems that use LAOS.

A new optoelectronic integrated device for light-amplifying optical switch (LAOS)

A new optoelectronic integrated device is proposed for a light-amplifying optical switch (LAOS). The device is composed of an optical field-effect transistor (OPFET) in series with a light source which may be either a double heterostructure light-emitting diode (LED) or laser diode (LD). A quantitative circuit model for the proposed LAOS is presented and theoretical investigation is carried out for developing a current-voltage (I-V) relation for the device. It is shown analytically that switching action takes place from a low current state to a high current state through a region of negative differential resistance (NDR) when a voltage greater than the breakover voltage is applied.

Analysis of transient response of light amplifying optical switch

A simple and accurate analytical model of the transient behaviour of light amplifying optical switch (LAOS) is derived. The model takes into account the effect of feedback currents, Early effect, current gain nonlinearity, and the equivalent circuit. Expressions for the multiplication and switching mode rise times are derived. It is shown that the multiplication mode rise time increases when the feedback coefficient or the Early factor are increased. On the other hand, the switching mode rise time decreases if the feedback coefficient or the Early factor is increased.

A modified model of the light amplifying optical switch (LAOS)

A new analytical circuit model of the light amplifying optical switch (LAOS) is proposed. The static I-V curve, the switching voltage, and the input-output characteristics can be calculated from this model. The model is based on deriving an expression for the nonlinear current gain of the heterojunction phototransistor (HPT). The switching mechanism and the I-V characteristics of the LAGS is studied in the context of optical and/or electrical feedback. The nonlinear current gain of the HPT, and the Early effect are the main factors which are responsible for the thyristor-like characteristics of the LAOS. An external feedback resistor is also added to achieve the appropriate switching condition and build up the feedback mechanism. A bistable system using a LAGS is also studied as well as the device hysteresis width.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

A new physical model of the light amplifying optical switch (LAGS)

A new physical model of determining the static I-V curve of the light amplifying optical switch (LAOS) is derived. The model is based on deriving the currents of the HPT and the feedback current of the LAOS. The feedback currents for optical and/or electrical feedback are determined by solving the continuity equation in the collector and the base of the HPT. A negative resistance region in the I-V curve is obtained and controlled by varying the feedback coefficient of the device and the Early effect coefficient. The main factors affecting the negative resistance region are the feedback coefficient, Early effect, the recombination currents in the emitter-base space-charge region, and the ratio of the collector to base doping. The switching voltage of the device is also calculated for different parameters. >

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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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. >

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. >