Showing papers on "Photodiode published in 1989"

Improved fiber‐optic interferometer for atomic force microscopy

Abstract: A high‐sensitivity fiber‐optic displacement sensor for atomic force microscopy is described. The sensor is based on the optical interference occurring in the micron‐sized cavity formed between the cleaved end of a single‐mode optical fiber and the microscope cantilever. As a result of using a diode laser light source and all‐fiber construction, the sensor is compact, mechanically robust, and exhibits good low‐frequency noise behavior. Peak‐to‐peak noise in a dc to 1 kHz bandwidth is less than 0.1 A. Images are presented demonstrating atomic resolution of graphite and magnetic force imaging of bits written on a magnetic disk.

20-ps timing resolution with single-photon avalanche diodes

Abstract: Single photon avalanche diodes (SPADs) are avalanche photodiodes specifically designed for reverse bias operation above the breakdown voltage and used for detecting single optical photons. A new silicon epitaxial device structure was designed to give improved timing performance with respect to previous SPADs. Extensive tests were carried out in order to establish the timing resolution of the device in time correlated photon counting (TCPC). The timing resolution of the SPAD in terms of its full‐width at half‐maximum (FWHM) contribution to the overall instrumental response width is 20 ps with the detector cooled to −65 °C, and 28 ps at room temperature. This is the highest resolution so far reported for solid‐state single‐photon detectors. In vacuum tubes, comparable results are obtained only with special microchannel‐plate photomultipliers (MCP‐PMT). Results from time‐resolved photoluminescence measurements in GaAs demonstrate the power of the TCPC technique when used with the new SPAD detector. With the ...

Subassemblies for optoelectronic hybrid integrated circuits

Abstract: Optoelectronic chips, such as Group III-V compound lasers (16) and photodiodes (24, 28), are mounted on a single-crystal silicon base (10), and are optically interconnected to one another by silica waveguides (14, 22, 26) and couplers (20, 23) integrally formed on the base. Integrated circuit chips (40, 42) to provide electronic functions are also mounted on the base. Various schemes for optically coupling and aligning lasers, photodiodes and optical fibers to the waveguides are described. Also described is the use of a single-crystal silicon lid, which serves to provide optical and electrical isolation between chips on the base, as well as a plug-in arrangement in which the edges of the base are adapted to receive parallel guide rods.

High-speed binary optically addressed spatial light modulator

Abstract: We describe the structure and operating characteristics of a high‐speed optically addressed spatial light modulator (OASLM) with a hydrogenated amorphous silicon (a‐Si:H) photosensor and a ferroelectric liquid‐crystal modulator. The photosensor is a p‐i‐n photodiode, which switches the liquid crystal into one of two stable states. Under a write‐light intensity of 6 mW/cm2, the OASLM exhibits a response time of 155 μs, a contrast ratio of 20:1, and a resolution of 40 lp/mm. The writing sensitivity per pixel is 0.1 pJ.

Very high speed GaInAs metal‐semiconductor‐metal photodiode incorporating an AlInAs/GaInAs graded superlattice

Abstract: A lateral structure metal‐semiconductor‐metal photodiode has been fabricated on GaInAs, in which an AlInAs/GaInAs graded superlattice has been incorporated. This photodiode has exhibited a dark current lower than 100 nA, an internal quantum efficiency of greater than 80% at a wavelength of 1.3 μm, and a capacitance of 40 fF, all at the bias voltage of 10 V. The response speed of this photodiode has been characterized by electro‐optic sampling to exhibit a full width at half maximum of 14.7 ps.

Tunneling and dark currents in HgCdTe photodiodes

Abstract: The dc characteristics of front‐illuminated ion‐implanted n+ on bulk p‐type Hg1−xCdxTe with x≊0.22, operating at 77 K, are modeled with three distinct mechanisms that dominate the dark current: In the zero‐ and low‐bias region, diffusion current is the dominant current down to 60 K. For medium reverse bias, at 77 K, trap‐assisted tunneling produces the dark current and dominates the dark current at zero bias below 50 K. For a high reverse bias, bulk band‐to‐band tunneling dominates. By measuring the temperature dependence of the dc characteristics in the temperature range 65–132 K, the mechanisms are studied and the validity of the modeling is confirmed. The 1/f noise phenomena measured at high reverse bias are correlated with the bulk band‐to‐band tunneling current. The electrical profile of the implanted junction is correlated with the origin of the p‐type conductivity and with the dc characteristics.

Stability and quantum efficiency performance of silicon photodiode detectors in the far ultraviolet.

Abstract: Recent improvements in silicon photodiode fabrication technology have resulted in the production of photodiodes which are stable after prolonged exposure to short wavelength radiation and which have efficiencies in the far ultraviolet close to those predicted using a value of 3.63 eV for electron-hole pair production in Si. Quantum efficiency and stability data are presented in the 6-124-eV region for several variations on the basic successful design and on devices with extremely thin silicon dioxide antireflecting/passivating layers. The results indicate that the oxide is dominant in determining many of the performance parameters and that a stable efficient far ultraviolet diode can be fabricated by careful control of the Si-SiO(2) interface quality.

Monolithic integrated coherent receiver on InP substrate

Abstract: The fabrication of a monolithic integrated coherent receiver with a wavelength-tunable DFB laser as local oscillator, a 3-dB waveguide directional coupler for mixing, and p-i-n photodiodes for detection is discussed. Optical heterodyne detection with a clear beat signal was experimentally observed using this monolithic integrated coherent receiver. Since an n-type substrate was used in this device, the two p-i-n photodiodes were not implemented in a balanced mixer configuration. Balanced mixing might be possible if the same structure were fabricated on a semi-insulating substrate. The results obtained suggest the possibility of applying this type of monolithic integrated coherent receiver to optical communication systems. >

Multiplication noise of wide-bandwidth InP/InGaAsP/InGaAs avalanche photodiodes

Abstract: Measurements of InP/InGaAsP/InGaAs separate absorption, grading, and multiplication avalanche photodiode multiplication indicate that at high gains the excess noise factors approach values predicted by the conventional continuum theory. However, at lower gains the noise is suppressed. This is probably an artifact of the very thin multiplication layers which have been used to increase the gain-bandwidth product. From the frequency response of the noise power, a gain-bandwidth product of 60 GHz, which is consistent with the value of 57 GHz obtained directly from bandwidth measurements, is deduced. >

Field-effect transistor self-electrooptic effect device: integrated photodiode, quantum well modulator and transistor

Abstract: The authors propose and demonstrate the integration of a photodiode, a quantum-confined Stark-effect quantum-well optical modulator, and a metal-semiconductor field-effect transistor (MESFET) to make a field-effect transistor self-electrooptic effect device. This integration allows optical inputs and outputs on the surface of a GaAs-integrated circuit chip, compatible with standard MESFET processing. To provide an illustration of feasibility, the authors demonstrate signal amplification with a single MESFET. >

Long and middle wavelength infrared photodiodes fabricated with Hg1−x CdxTe grown by molecular‐beam epitaxy

Abstract: Long and middle wavelength infrared (LWIR, MWIR) p+‐n photodiodes have been fabricated with Hg1−xCdxTe (0.20

Frequency response of InP/InGaAsP/InGaAs avalanche photodiodes

Abstract: A theoretical model for the frequency response of InP/InGaAs avalanche photodiodes (APDs) is presented. Included in the analysis are resistive, capacitive, and inductive parasitics, transit-time factors, hole trapping at the heterojunction interfaces, and the avalanche buildup time. The contributions of the primary electrons, primary holes, and secondary electrons to the transit-time-limited response are considered separately. Using a measurement apparatus which consists of a frequency synthesizer and a spectrum analyzer controlled by a microcomputer, the frequency response of InP/InGaAsP/InGaAs APDs grown by chemical-beam epitaxy are measured. Good agreement with the calculated response has been obtained over a wide range of gains. >

Photodiode and photodiode array on a II-VI material and processes for the production thereof

Abstract: Photodiode and array of photodiodes on II-VI material and their production processes. The photodiodes (48) are formed in a type P, Hg 1-x Cd x Te semiconductor layer (13) with 0≦x≦1 deposited directly on a CdTe insulating substrate (11), having an active zone (37) of type N, a first electrical contact (47) on the semiconductor layer, a second electrical contact (45) on the active zone, and insulant (21) separating the first and second electrical contacts and an insulation or isolation trench (15), whose depth exceeds the thickness of the active zone and surrounding the latter, the first electrical contact (47) being located in the bottom (27) of the trench.

A GaAs MESFET IC for optical multiprocessor networks

Abstract: A GaAs, enhanced/depletion mode, self-aligned, refractory-gate, MESFET chip process and circuit family have been developed for the integration of fiber-optic data link functions (e.g. photodetection, amplification, clock recovery, and deserialization) on a single chip. These authors describe the process and present results on integrating a complete optical receiver, including the photodiode and clock recovery circuits, on one chip. The chip functions use over 2000 devices, and perform at 1-GB/s, while dissipating less than 300 mW of heat. This chip is the most complex high-performance optoelectronic integrated circuit reported to date. >

Wideband frequency-response measurement of optical receivers using optical heterodyne detection

Abstract: Measurements have been carried out using 1.3- mu m distributed-feedback laser diodes (DFB-LDs). The frequency difference of the LDs is continuously varied with temperature changes of a few degrees and the spectral linewidth of one of the LDs is narrowed by optical feedback using a grating. Wideband, highly sensitive measurement has been achieved for a p-i-n photodiode and a Ge avalanche photodiode from DC to 20 GHz. The result is compared with that of the pulse spectrum analysis (PSA) method. Although the finite pulsewidth in the PSA method causes roll-off in the frequency response, the optical heterodyne method has the advantage for very wideband frequency response measurement. The S/N ratio in the optical heterodyne method can be made as high ( approximately 40 dB) as that of the PSA method by narrowing the spectral linewidth of DFB-LDs. >

Initial characterization of a position-sensitive photodiode/BGO detector for PET

Abstract: The authors present initial results for a position-sensitive photodiode/BGO (bismuth germanate) detector for high-resolution, multilayer positron emission tomography (PET). Position sensitivity is achieved by dividing the 3 mm*20 mm rectangular photosensitive area along the diagonal to form two triangular segments. Each segment is individually connected to a low-noise charge amplifier. The photodiodes and crystals are cooled to -100 degrees C to reduce dark current and increase the BGO signal. With an amplifier peaking time of 17 mu s, the sum of the signals (511-keV photopeak) was 3200 electrons with a full width at half maximum (FWHM) of 750 electrons. The ratio of one signal to the sum determined the depth of interaction with a resolution of 11 mm FWHM. >

Spiral silicon drift detectors

Abstract: An advanced large-area silicon photodiode and X-ray detector, called the spiral drift detector, was designed, produced, and tested. The detector has a very small capacitance of about 0.1 pF and a leakage current under 1 nA at room temperature. All electrons generated at the silicon-silicon oxide interface are collected on a guard rather than contributing to the detector leakage current. The decrease of the leakage current reduces the parallel noise of the detector. This decrease and the very small capacitance of the detector anode with a capacitively matched preamplifier may improve the energy resolution of spiral drift detectors operating at room temperature to about 50 electrons RMS. This resolution is in the range attainable at present only by cooled semiconductor detectors. >

GaAs/AlGaAs optical synaptic interconnection device for neural networks

Abstract: A GaAs/AlGaAs optical synaptic interconnection device for neural networks is reported for the first time to our knowledge. This device consists of a light-emitting-diode array, an interconnection matrix, and a photodiode array, which are integrated into a hybrid-layered structure on a GaAs substrate. The device structure and characteristics are reported in detail. The fabricated device can simulate a 32-neuron system. Experimental results of the Hopfield associative memory with three stored vectors are also described.

High‐speed analog spatial light modulator using a hydrogenated amorphous silicon photosensor and an electroclinic liquid crystal

Abstract: A high‐speed optically addressed spatial light modulator is described which uses the electroclinic effect in chiral smectic A liquid crystals with a p‐i‐n photodiode of hydrogenated amorphous silicon (a‐Si:H). The near microsecond response time is a function of the liquid‐crystal mixture and temperature. We present and analyze optical modulation measurements of a device which exhibits a response time of 40 μs at 29 °C and 4 μs at 50 °C. The optical response is continuous and linear with electric field and write‐light intensity, allowing for grey level applications.

Non-imaging laser particle counter

Abstract: A non-imaging particle counter (10) utilizing one or more detectors (25) which directly collect light scattered by particles in a fluid traversing a sensing volume (63). The detectors (25) are non-imaging, non-focusing, optic-less light collection devices, such as large area photodiodes. The detectors (25) are arranged and configured proximate the sensing volume (63), but such that the beam of light (60) is not operatively incident thereon. The beam of light (60) is provided by a laser (50) and is shaped by a focusing/collimating lens (54). The beam of light (60) passes through several apertures (51-53) to reduce stray/background light in the system. The detectors (25) are oriented at an angle with respect to the plane formed by the longitudinal axis of the beam and the flow of fluid, wherein stray light (61) strikes the detectors (25) at an angle greater than the acceptance angle of the detectors (25), while scattered light strikes the detectors (25) at an angle less than the detectors' (25) acceptance angle. A light stop (31) having a Brewster angle for the wavelength of the beam of light (60) is utilized as a beam stop. Further, a coincidence detection circuit (100) provides for reducing spurious counts caused by ionizing emissions and/or other noise.

Slot clock recovery in optical PPM communication systems with avalanche photodiode photodetectors

Abstract: Slot timing recovery in a direct-detection optical PPM communication system can be achieved by processing the photodetector output waveform with a nonlinear device whose output forms the input to a phase-locked loop. The choice of a simple transition detector as the nonlinearity is shown to give satisfactory synchronization performance. The RMS phase error of the recovered slot clock and the effect of slot timing jitter on the bit error probability were directly measured. The experimental system consisted of an AlGaAs laser diode ( lambda =834 nm) and a silicon avalanche photodiode photodetector. The system used Q=4 PPM signaling and operated at a source data rate of 25 Mb/s. The mathematical model developed to compute the RMS phase error of the recovered clock is shown to be in good agreement with results of actual measurements of phase errors. The use of the recovered slot clock in the receiver resulted in no significant degradation in receiver sensitivity compared to a system with perfect slot timing. The system achieved a bit error probability of 10/sup -6/ at a received optical signal energy of 55 detected photons per information bit. >

Status of BGO-avalanche photodiode detectors for spectroscopic and timing measurements

Abstract: Silicon avalanche photodiodes (APD) can be used as photodetectors in combination with scintillation crystals for the detection of radiation. These devi

Method and apparatus for controlling the bias current of a laser diode

Abstract: An apparatus controls the optical output intensity of a laser diode 52 used in an optical communication system The laser diode 52 receives current from a pulse current supply 74 and a bias current supply 72 The optical output intensity of the laser diode 52 is controlled via a closed bias current control loop that includes a photodiode 50, which supplies a signal having a magnitude correlative to the optical output intensity of the laser diode 52 The closed bias current control loop monitors the trough level of the photodiode output to regulate the bias current supply 72 Thus, the output of the photodiode 50 is delivered to a means 56 for detecting the magnitude corresponding to the minimum magnitude of the optical output of the laser diode 52 The voltage corresponding to this detected low level is compared to a preselected voltage level V r and the difference in the two signals is delivered to the bias current supply through an integration circuit 66 Thus, as the optical output intensity of the laser diode 52 shifts with temperature or age degradation, the bias current supply correspondingly increases the current delivered to the laser diode 52 in order to maintain a constant optical output intensity

Optically powered sensor system with improved signal conditioning

Abstract: An optically powered sensor system with improved signal conditioning includes a plurality of sensors connected to a system optical bus that communicates with a system controller. Optical energy is transmitted along the bus for distribution to all sensor in the system with return pulses from the various sensors transmitted on the bus to the system controller. Each sensor includes a photodiode array for converting optical energy transmitted system-wide by the controller into electrical energy for storage in a storage capacitor associated with each sensor. A capacitance probe transducer and a fixed-value reference capacitor are connected to a resettable integrating pulse encoder that produces a series of short-duration pulses having a pulse spacing that is dependent upon the fixed value of the reference and the parameter-affected value of the transducer. The pulses are used to drive an optical source for transmitting optical pulses from the sensor to the system controller.

Signal transmission system for machine tools, inspection machines, and the like

Abstract: Probes (18A,18B,18C) can be interchangably mounted in the spindle (12) of a machine tool. Each probe has an optical signal transmission system, in which an optical signal from a light emitting diode (26) is transmitted to a receiver module 28. Such an arrangement requires a battery in the probe. To conserve battery power, the probe is normally in a stand-by mode, but can be switched on by an optical signal transmitted from the module 28 to a receiving photodiode 32 on the probe. This switch-on signal is modulated at a different frequency for each probe. Each probe contains a filter for the signal received by the photodiode 32, responsive only to the frequency of modulation of its own switch-on signal. Probes which are not intended to be switched on therefore do not react to the switch-on signal of another probe, thus conserving battery power further.

Integrated-optic interferometer position sensor

Abstract: A fully integrated interferometer position/displacement sensor with direction-discrimination capability is discussed. The device is constructed by integrating three kinds of grating components and a pair of photodiodes in a glass waveguide on a silicon substrate and by butt-coupling a single-mode laser diode. Interference signals corresponding to mirror movement were obtained experimentally over a 15-cm range with a 0.39- mu m modulation period. >