Photodetector Circuit Research Articles

The telescope readout electronics for the Gravity Probe B satellite

The pointing and stability requirements for the Gravity Probe B (GP-B) Relativity Mission pose a number of challenges for the star-tracking electronics. Because the telescope-gyroscope assembly operates at 2.8 K, the detector circuit's Si JFETs at the telescope focal plane must-be thermally isolated and heated to at least 50 K through self-heating or with the aid of heating resistors. We have designed a low noise, thermally stable photodetector circuit that meets the GP-B requirements as well as fabricated an isolator to give the required thermal isolation and mechanical stability. Test results of the detector - isolator assembly are presented.

A Pilot Study of the Reliability of the Dynamic Mode of One BTE Work Simulator

This paper presents the results of a study of the reliability of the manual dynamic mode of one BTE Work Simulator. The study was part of an effort to develop a simple method of calibrating the BTE Work Simulator as an evaluation instrument. Weights attached to a 12-in nylon cylinder rotated the shaft of the exercise head against resistance generated by the Work Simulator. A timing device recorded drop times for one complete revolution of the nylon cylinder. The timing device consisted of a digital clock, a photo detector circuit, and a switching circuit. The photo detector recorded one revolution of the cylinder, and the switching circuit started and stopped the clock. Drop times were recorded as fixed weights attached to the nylon cylinder were allowed to drop. The test was repeated a number of times at each combination of weight and exercise level. A minimum of 40 tests were recorded with 4.96-, 10-, 15-, 25-, 30-, and 40-lb weights. This provided accurate measurement of the performance of the Work Simulator in the dynamic mode. Fluctuation in resistance caused drop times for any given weight to vary from - 47% to + 183.7% from the mean. In some cases the resistance fluctuation was sufficient to either prevent the weight from dropping or stop the weight before the cylinder had rotated one revolution. Resistance variation in the dynamic mode of the BTE Work Simulator was found to produce inconsistent performance. Testing that includes other Work Simulators is in progress. J HAND THER 8:199-205, 1995.

Technology development of a high-density 32-channel 16-Gb/s optical data link for optical interconnection applications for the optoelectronic technology consortium (OETC)

A parallel, 32-channel, high density (140 /spl mu/m pitch), 500 Mb/s NRZ, point-to-point, optical data link has been fabricated using existing GaAs IC, silicon optical bench (SiOB), and multichip module (MCM-D) technologies. The main components of the transmitter and the receiver modules are a GaAs-based vertical cavity surface emitting laser (VCSEL) array at 850 mn with its IC driver array chip and an integrated metal-semiconductor-metal (MSM) receiver (photodetector and signal processing circuits) array at 850 nm. The package module uses a modified 164 I/O JEDEC premolded plastic quad flat pack (PQFP) in combination with a polymer film integrated circuit (POLYFIC) chip carrier. The electrical input and output are 500 Mb/s NRZ binary signals. The optical I/O in both modules consists of a directly-connectorized (nonpigtail) fiber array block that plugs into the 32/spl times/1 optical fiber ribbon directly on one side and accepts 32 optical signals from the SEL array or delivers them to the MSM receiver array via a gold-coated 45/spl deg/ polished fiber array mirror. The MACII-32 ribbon cable is an enhanced version of the standard MACII connector ribbon cable. This paper characterizes key components of the optical data link, describes its package design, and discusses preliminary component and optical data link test results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New method of superheterodyne light beating spectroscopy for Brillouin scattering using frequency-tunable lasers.

We have developed a new optical superheterodyne method for light scattering using frequencytunable lasers and succeeded in measuring Brillouin spectra of simple liquids in a wide frequency range, 10 MHz to 3 GHz. Its frequency resolution (\ensuremath{\sim}300 kHz) is determined by the short-time coherency between the two lasers. A great advantage of our method over conventional optical beating methods is that the speed of the photodetector and electric circuits never limits the upper frequency bound. This is realized by the continuous tunability of the laser frequency. The method has a high potential for studying the dynamics in a wide class of condensed matters.

An integrated photodetector-amplifier using a-Si p-i-n photodiodes and poly-Si thin-film transistors

The authors propose a photodetector-amplifier circuit consisting of a bridge photodetector circuit and a CMOS differential amplifier, both monolithically integrated on a transparent substrate. A test circuit was fabricated using a-Si p-i-n photodiodes and poly-Si thin-film transistors on a quartz substrate. A clear effect of the differential amplifier was demonstrated in the test circuit. It is shown that the circuit performance can be controlled by changing the bias current of the differential amplifier. With a relatively low bias current on the order of 10/sup -11/ A, the circuit works digitally with output voltages either close to 0 V or V/sub DD/. The power consumption of the circuit is approximately 60 mu W, which is low enough for use in two-dimensional arrays.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 1.8 Gb/s GaAs optoelectronic universal switch LSI with monolithically integrated photodetector and laser driver

A high-speed monolithic optical interface switch LSI is developed using a GaAs MSM photodetector and large-scale integrated electric circuits. This LSI operates universally as a 1.8 Gb/s optical-input/optical-output four-channel time-division switch, a 1.8 Gb/s optical-input/electrical-output 1:4 demultiplexer, a 2.0 Gb/s electrical-output 4:1 multiplexer, and a 2.8 Gb/s electrical-input/electrical-output 4*4 space-division switch. It uses a new multistage 2*2 switch block with small hardware and high-speed operation. It can be expanded to a 16*16 optical-input/optical-output time-division switch operating at up to 1.8 Gb/s for broadband-ISDN. >

Method for fabricating a simple low-cost position-sensitive photodetector

We describe a very simple method for making a low-cost wide-band position-sensitive photodetector (PSD) and preamplifier circuit. The detector is most suitable for experiments where a laser is used to measure the deflection (linear or angular) of some part of the experimental apparatus. The response of the photodetector is exponential for static beam position changes and linear for oscillating position. The static deflection exponential behavior can be linearized with a logarithmic preamplifier circuit. The detector can also be used as a low-cost laser beam intensity monitor with only a few percent beam loss and approximately 100 dB of dynamic range. We have fabricated PSDs and beam-power monitors capable of operating at wavelengths from 0.2 to 1 μm and by a suitable change of components this range should be extendable from 0.1 up to 22 μm.

Performance implications of mode partition fluctuations in nearly single longitudinal mode lasers

A statistical model of mode partition fluctuations is developed for semiconductor laser diodes with a single dominant lasing mode and one vestigial side mode. It is the basis of a rigorous analysis of the influence of partition fluctuations on the performance of digital lightwave transmission systems. A Gauss quadrature rule is used to evaluate the average probability of error in the presence of mode-partition-dependent shot noise, photodetector multiplication noise, circuit noise, and intersymbol interference. This methodology permits the determination of reliable performance estimates enabling the establishment of permissible degrees of mode partition fluctuations. >

Low noise photodetector circuits using FET's

Photodetector circuits using a photodiode followed by a JFET can provide shot-noise limited performance at low frequencies. The bandwidth of the shot-noise limited performance can be extended into the MHz range using state-of-the-art microwave FET's.