Showing papers by "Amnon Yariv published in 1991"
Journal Article•
TL;DR: In this article, the possibility of detecting magnetic fields by a magnetostrictive straining of optical fibers is investigated and the effect of shot noise and the limiting sensitivity are considered.
Abstract: The possibility of detecting magnetic fields by a magnetostrictive straining of optical fibers is investigated. The effect of shot noise and the limiting sensitivity are considered.
149 citations
TL;DR: In this paper, a multiple quantum well GaAs/AlGaAs laser with two electrically isolated contacts is passively mode locked in an external cavity at the first through sixth harmonics of the pulse roundtrip frequency of 1.17 GHz to produce pulses shorter than 10 ps.
Abstract: A multiple quantum well GaAs/AlGaAs laser with two electrically isolated contacts is passively mode locked in an external cavity at the first through sixth harmonics of the pulse round‐trip frequency of 1.17 GHz to produce pulses shorter than 10 ps. The repetition rate is switched between harmonics by adjusting the gain section current, and large hysteresis between the different repetition rates is observed, with up to four different repetition rates for the same gain current. The results are compared with small and large signal passive mode‐locking theories by considering modifications to the saturated gain recovery between pulses when the laser operates at different harmonics.
45 citations
TL;DR: In this paper, the spectral properties of grating-assisted directional couplers were studied using an improved coupled mode formulation, and the parameters for the design of these structures, such as the grating period, the coupling length and other structural parameters, were calculated.
Abstract: The spectral properties of grating-assisted directional couplers are studied using an improved coupled mode formulation. Key parameters for the design of these structures, such as the grating period, the coupling length, and other structural parameters, are calculated. The frequency response, the filter bandwidth, and the tuning range are analyzed. The technique is used to examine a specific case of InGaAsP-InP tunable filters, and the results are compared to a prior experiment. >
39 citations
TL;DR: The fixing of a photorefractive grating in KTa(1-x)Nb(x)O(3) is reported and possible mechanisms responsible for the effect are discussed.
Abstract: We report the fixing of a photorefractive grating in KTa1-xNbxO3 . The procedure involves the writing of a photorefractive grating in the cubic phase and the cooling of the sample under an applied field into the rhombohedral phase. We discuss possible mechanisms responsible for the effect.
25 citations
TL;DR: In this article, a monolithic integration of a double barrier AlAs/GaAs resonant tunneling diode and a GaAs/AlGaAs quantum well laser is reported.
Abstract: A monolithic integration of a double barrier AlAs/GaAs resonant tunneling diode and a GaAs/AlGaAs quantum well laser is reported. Negative differential resistance and negative differential optical response are observed at room temperature. The device displays bistable electrical and optical characteristics which are voltage controlled. Operation as a two‐state optical memory is demonstrated.
23 citations
01 Jan 1991
TL;DR: In this paper, a vector-matrix multiplier with simple charge-domain multiply-accumulate units has been implemented, which computes the product of a binary vector and an analog matrix of charge, providing an analog output vector.
Abstract: A mixed analog/digital neural network chip is presented that uses standard 2- mu m CCD/CMOS fabrication. The device incorporates a matrix of charge injection device elements which hold a matrix of charge encoding the synapse strengths. A vector-matrix multiplier with simple charge-domain multiply-accumulate units has been implemented. The device computes the product of a binary vector and an analog matrix of charge, providing an analog output vector. At a clock rate of 1 MHz, the fabricated device computes 64 million binary/analog multiply accumulates per second in a very small area. The matrix refresh time is small compared to the refresh period.<>
21 citations
08 Jul 1991
TL;DR: A vector-matrix multiplier with simple charge-domain multiply-accumulate units has been implemented that computes the product of a binary vector and an analog matrix of charge, providing an analog output vector.
Abstract: A mixed analog/digital neural network chip is presented that uses standard 2- mu m CCD/CMOS fabrication. The device incorporates a matrix of charge injection device elements which hold a matrix of charge encoding the synapse strengths. A vector-matrix multiplier with simple charge-domain multiply-accumulate units has been implemented. The device computes the product of a binary vector and an analog matrix of charge, providing an analog output vector. At a clock rate of 1 MHz, the fabricated device computes 64 million binary/analog multiply accumulates per second in a very small area. The matrix refresh time is small compared to the refresh period. >
19 citations
TL;DR: In this paper, the stability of pulse energy and timing in a passively mode-locked two-section quantum-well laser was measured, and spectral analysis of the 546MHz pulse train revealed rms timing jitter of 5.5 ps above 50 Hz and rms pulse energy fluctuations of < 0.52% above 200 Hz.
Abstract: Stability of pulse energy and timing in a passively mode‐locked two‐section quantum‐well laser is measured. Spectral analysis of the 546‐MHz pulse train reveals rms timing jitter of 5.5 ps above 50 Hz and rms pulse energy fluctuations of <0.52% above 200 Hz.
16 citations
08 Jul 1991
TL;DR: An analog four-quadrant matrix-vector multiplier of low circuit complexity in floating gate CMOS technology, capable of on-chip weight adaptation following an arbitrary incremental outer-product local learning scheme, and with permanent storage of the weights after learning is performed is presented.
Abstract: The authors present an analog four-quadrant matrix-vector multiplier of low circuit complexity in floating gate CMOS technology, capable of on-chip weight adaptation following an arbitrary incremental outer-product local learning scheme, and with permanent storage of the weights after learning is performed. The complete adaptive circuit employs, on average, as few as two transistors per matrix element (C.F. Neugenbauer et al., 1990), allowing a very compact VLSI circuit layout (less than 30 mu m*30 mu m per synapse in standard 2 mu m CMOS technology) suitable for the use in fully interconnected neural network hardware of densities above 256 neurons per cm/sup 2/. With proper biasing techniques, an input linearity region for the multiplier ranging 800 mV at modest current levels are demonstrated. Four-quadrant outer-product weight adaptation, performed locally on-chip by floating gate voltage increments under ultraviolet illumination, has been achieved with floating gate adaptation up to 10 mV/s. >
16 citations
TL;DR: In this article, the authors derived a simple expression for the transparency carrier density as a function of temperature and effective masses to explain the results of the InGaAs laser at 5 K.
Abstract: The operation of ultralow threshold current GaAs and InGaAs quantum well lasers at cryogenic temperatures has been studied. In particular the threshold current Ith and lasing wavelength of GaAs and strained InGaAs lasers have been measured as a function of temperature from 300 down to 5 K. Ith can in both lasers be characterized by a linear function of temperature up to 200 K, with a significantly (2.5×) larger dIth/dT for the GaAs laser. We measured a minimum threshold current of 120 μA for the GaAs laser and 165 μA for the InGaAs laser at 5 K. We derive a simple expression for the transparency carrier density as a function of temperature and effective masses to explain our results.
16 citations
TL;DR: In this article, the authors compared the differential gain of single quantum well and bulk double heterostructure lasers at room temperature and found that only at low temperatures do the quantum well lasers possess higher differential gain than bulk double-heterostructure laser.
Abstract: The differential gain in single quantum well and bulk double heterostructure lasers is compared. In variance with previous predictions, no differential gain enhancement is found in single quantum well structure lasers at room temperature. Only at low temperatures do the quantum well lasers possess higher differential gain than bulk double heterostructure lasers. The results have important implications in the area of high speed phenomena for these devices.
TL;DR: A new type of phase conjugation between counterpropagating beams in photorefractive materials based on diffraction from transmission gratings only is proposed, which may occur spontaneously, with no external seeding, even with wide (frequency) band light sources.
Abstract: We propose and analyze a new type of phase conjugation between counterpropagating beams in photorefractive materials based on diffraction from transmission gratings only. This effect does not require temporal coherence between the counterpropagating beams and may occur spontaneously, with no external seeding, even with wide (frequency) band light sources.
TL;DR: In this paper, the effect of the lateral current confinement on the currentvoltage characteristic of a double-barrier resonant tunneling structure was also studied, and the experimental results were explained by solving the electrostatic potential distribution in the structure using a simple three-layer model.
Abstract: The resonant tunneling effect is optically enhanced in a GaAs/GaAlAs double‐barrier structure that has partial lateral current confinement. The peak current increases and the valley current decreases simultaneously when the device surface is illuminated, due to the increased conductivity of the top layer of the structure. The effect of the lateral current confinement on the current‐voltage characteristic of a double‐barrier resonant tunneling structure was also studied. With increased lateral current confinement, the peak and valley current decrease at a different rate such that the current peak‐to‐valley ratio increases up to three times. The experimental results are explained by solving the electrostatic potential distribution in the structure using a simple three‐layer model.
TL;DR: In this article, photorefractive, absorption, and photoconductivity measurements were made on a KTa1-xNbxO3:CuY sample after a series of reduction and oxidation treatments.
Abstract: We report photorefractive, absorption, and photoconductivity measurements made on a KTa1-xNbxO3:CuY sample after a series of reduction and oxidation treatments. All relevant physical parameters that enter into the Kukhtarev model of the photorefractive effect are determined. Photorefractive measurements are compared with those expected from theory. The oxidation-reduction process is modeled, which permits us to determine the heat treatment that is necessary to produce a given index change and response time. We discuss approaches to optimization of the photorefractive sensitivity.
TL;DR: It is shown that, in spite of the fact that in general, losses spoil phase conjugation, in the important case of paraxial beam propagation, a z-dependent loss can be tolerated and non linear losses and nonlinear dielectrics are also permitted under some fairly general circumstances.
Abstract: Rigorous and approximate conditions that need to be satisfied by a propagation medium to enable phase conjugation to occur are derived. It is shown that, in spite of the fact that in general, losses spoil phase conjugation, in the important case of paraxial beam propagation (along z), a z-dependent loss can be tolerated. In addition, nonlinear losses (gain) and nonlinear dielectrics are also permitted under some fairly general circumstances.
TL;DR: In this paper, a monolithic, laterally coupled semiconductor stripe laser with a tuning range of 14.2 nm has been demonstrated. But the tuning range is not yet known for a single longitudinal mode spectrum.
Abstract: Tunable, single longitudinal mode spectrum of a novel monolithic, laterally coupled semiconductor stripe laser has been demonstrated. A tuning range of 14.2 nm, which is the widest observed so far in a monolithic device, has been achieved.
Patent•
01 Jul 1991TL;DR: In this paper, an optically-coupled high frequency amplifier is described, which includes a laser and a receiver coupled by an optical beam, and a modulator responsive to an input signal for modulating the optical beam generated by the laser.
Abstract: An optically-coupled high frequency amplifier is disclosed herein. The ampliifer of the present invention includes a laser and a receiver coupled by an optical beam. The amplifier further includes a modulator responsive to an input signal for modulating the optical beam generated by the laser. The receiver produces an output signal in response to the modulated optical beam. A specific embodiment of the present invention further includes impedance matching means for increasing the maximum operating frequency of the laser and the receiver.
TL;DR: It is shown that two modes counterpropagating in a single-mode fiber in the presence of random coupling due to refractive-index fluctuations can interfere constructively and give rise to a coherent backscattering process analogous to that associated with back scattering from a disordered medium.
Abstract: We show that two modes counterpropagating in a single-mode fiber in the presence of random coupling due to refractive-index fluctuations can interfere constructively and give rise to a coherent backscattering process analogous to that associated with backscattering from a disordered medium. Both strong- and weak-localization limits are studied and the interplay between localization and radiation losses is analyzed.
TL;DR: Frequency selectivity of a novel type of multielement, multisection laterally coupled semiconductor laser array is studied using the round-trip method and the experimental results show excellent agreement with the theoretical prediction.
Abstract: Frequency selectivity of a novel type of multielement, multisection laterally coupled semiconductor laser array is studied using the round-trip method. It is found that such a structure should lead to a strong frequency selectivity owing to a periodic dependency of the threshold gain on the frequency. A gain-guided two-coupled-cavity device was fabricated. The experimental results show excellent agreement with the theoretical prediction.
TL;DR: In this paper, a circuit model for the OPT was developed to satisfactorily explain the existence of the middle trace and its optical switching, and a new middle trace observed in an optically controlled parallel resonant tunneling (OPT) was demonstrated.
Abstract: Optical switching of a new middle trace observed in an optically controlled parallel resonant tunneling (OPT) device is demonstrated. A circuit model for the OPT is developed. The circuit model satisfactorily explains the existence of the middle trace and its optical switching.
Proceedings Article•
02 Dec 1991TL;DR: A CCD based signal processing IC that computes a fully parallel single quadrant vector-matrix multiplication has been designed and fabricated with a 2µm CCD/CMOS process.
Abstract: A CCD based signal processing IC that computes a fully parallel single quadrant vector-matrix multiplication has been designed and fabricated with a 2µm CCD/CMOS process. The device incorporates an array of Charge Coupled Devices (CCD) which hold an analog matrix of charge encoding the matrix elements. Input vectors are digital with 1 - 8 bit accuracy.
TL;DR: In this article, the authors report on the design, fabrication, and characterization of high-power strained-layer (SL) InGaAs single-quantum-well (SQW) lasers.
Abstract: The authors report on the design, fabrication, and characterization of high-power strained-layer (SL) InGaAs single-quantum-well (SQW) lasers. The lasers emit a 0.980+or-0.002 mu m. They deliver over 100 mW CW optical power at room temperature in a stable single lateral mode with a beam divergence of 15 approximately=20 degrees . The maximum CW output power measured is 265 mW. The lasers have been successfully used as pump sources for an erbium-doped fiber amplifier. >
Patent•
05 Nov 1991
TL;DR: In this article, the authors proposed a method of manufacturing a display screen for use, for example, in large screen television displays, wherein the method comprises the steps of aligning a large plurality of columnar-shaped light emitting diode slivers in an uncured optical epoxy, and then placing orthogonally directed electrodes which are optical transparent on both opposing surfaces of the aligned configuration.
Abstract: A method of manufacturing a display screen for use, for example, in large screen television displays, wherein the method comprises the steps of aligning a large plurality of columnar-shaped light emitting diode slivers in an uncured optical epoxy (Fig. 4 and Fig. 5) by applying an electric field through a mixture of such slivers and epoxy (Fig. 6), curing the epoxy to effectively fix the light emitting diode slivers in that aligned configuration (Fig. 7), and then placing orthogonally directed electrodes which are optical transparent on both opposing surfaces of the aligned configuration (Fig. 9a) for controlling the light being emitted by such diodes. The novel display screen structure (Fig. 10) fabricated in accordance with such method results in a technology which can be easily scaled to large sizes to provide relatively low-cost large screens for televisions.