S.A. Feld

Transverse-mode dynamics in vertical-cavity surface-emitting lasers excited by fast electrical pulses

Summary form only given. With modulation bandwidth of 10-15 GHz, vertical-cavity surface-emitting lasers (VCSELs) have become a suitable choice for optical interconnects. However, the presence of higher order modes in the cavity can cause rapid variations of the spectral, spatial and noise characteristics of the laser beam that can affect the gigahertz performance of these devices. Herein we present measurements of the response of VCSELs excited by 0.8-1-ns pulses that show the importance of mode competition and spatial hole burning in the dynamics in VCSELs.

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. >

Fabrication of a Fabry-Pe/spl acute/rot cavity in a microfluidic channel using thermocompressive gold bonding of glass substrates

This paper presents a simple, low-cost, and reliable process for the fabrication of a microfluidic Fabry-Pe/spl acute/rot cavity in a Pyrex glass substrate. The microfluidic channels were etched in HF solution on a glass substrate using a Cr/Au/photoresist etching mask resulting in a channel bottom roughness of 1.309 nm. An effective thermocompressive gold-gold bonding technique was used to bond the photolithographically etched glass substrates inside a 350/spl deg/C oven in a 10/sup -3/ torr vacuum. Pressure was applied to the glass pieces by using two aluminum blocks with intermediate copper sheets. This method takes advantage of using Cr/Au layers both as a wet etching mask and as intermediate bonding layers, requiring only one lithography step for the entire process. The fabrication method is also compatible with the incorporation of dielectric mirror coatings in the channels to form a high-finesse Fabry-Pe/spl acute/rot cavity. A parallelism of 0.095 degrees was measured, and a finesse as high as 30 was obtained using an LED. The microfluidic cavity developed here can be used in electrophoresis and intracavity spectroscopy experiments.

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. >

Linewidth and α‐factor in AlGaAs/GaAs vertical cavity surface emitting lasers

Measurements of the α‐factor, the linewidth‐power product, and the differential gain in AlGaAs/GaAs vertical cavity surface emitting lasers are presented. The linewidth power product of 95 MHz mW which results in the α‐factor of 3.7 is obtained. The α‐factor as a ratio of the refractive index and gain derivatives with respect to the carrier density is also estimated. From the small signal modulation measurements of the resonance frequency, a differential gain of 3.7×1016 cm2 is obtained. The estimate of differential effective index is made difficult by an anomalously strong dependence of the emission wavelength on injection current.

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.