Showing papers on "Optical communication published in 1977"

Digital frequency-translated, plural-channel vestigial sideband television communication system

Abstract: A television communication system distributes plural VSB digitally encoded TV channels via an optical transmission link to one or more distribution terminals. At the headend the frequency band of each of the VSB signals is shifted down to baseband and transmitted in digital format. At each station along the network, the digitized baseband VSB television signal is converted into analog format and then reshifted through an up-converter to its original IF band so as to be compatible with the television receiver circuitry of the subscribers served by the distribution station. Advantageously, the present invention may employ optical communication techniques for coupling the digitally encoded frequency-shifted VSB television signals between stations. To maintain signal strength and quality, repeater units may be located in the optical communication link. Each repeater converts an incoming optical signal to an electrical signal for amplification and then reconverts the improved electrical signal back into optical form for further transmission along the link.

Wide‐band electro‐optical tuning of semiconductor lasers

Abstract: A semiconductor laser having a narrow emission bandwidth (<1 A) with center wavelength electronically tunable over a large spectral range is demonstrated for the first time. This electro‐optically tunable infrared semiconductor laser source should have interesting applications in, for example, optical communications systems, optical radar, and spectroscopy.

Receiver design for optical fiber systems

Abstract: This paper is a tutorial review of the theory and practice of receiver design for optical fiber communication systems. Topics discussed include fundamental limitations on performance; design and performance limitations of laboratory receivers; and practical design trade-offs and their effects on the performance of real system receivers.

Secure optical communication components, method, and system

Abstract: A transmitter of information to be communicated in secure form is optically coupled to a composite optical fiber at one end, the fiber being connected to a receiver of the secure information at the other end. The composite optical fiber has cores including a central core for carrying the secure information, one or more guard signal cores, a cladding matrix surrounding all the cores, and a metallic or other nontransmissive film surrounding the central core but not the guard cores. A guard signal optical transmitter section is coupled to the guard cores for jamming any leakage of secure information through the film, and a guard signal receiver section is provided at the other end of the fiber for monitoring purposes. The optical transmitter apparatus employs pulse code modulation (PCM) and sends related security bits in the guard and secure signals. The optical receiver apparatus features amplitude monitoring and a comparison of the related security bits and provides a warning when unexpected changes indicative of tampering are observed.

Acoustooptic modulator for optical fiber waveguides

Abstract: An acoustooptic modulator is disclosed in which light may be modulated while propagating through an optical fiber waveguide through the use of focussed acoustic waves. The modulator is formed by encircling a portion of the optical fiber waveguide in an optical communications system with an acoustic transducer. Due to the encircling of a portion of the waveguide by the transducer, the acoustic waves which are generated in the optical fiber waveguide material are focussed inwardly to the center so that the energy densities where acoustooptic modulation occurs are high. Therefore, the acoustic driving powers and modulation efficiencies are highly favorable.

CO 2 laser communication systems for near-earth space applications

Abstract: Projects of the growth of earth-sensing systems for the latter half of the 1980's show a data transmission requirement of 300 Mbit/s and above Mission constraints and objectives lead to the conclusion that the most efficient technique to return the data from a sensing satellite to a ground station is through a geosynchronous data relay satellite Of the two links that are involved (sensing satellite to relay satellite and relay satellite to ground), a laser system is most attractive for the space-to-space link A five-year program was conducted which has shown the basic technical feasibility of accomplishing this link with a CO 2 laser system operating at a wavelength near 10 µm The system uses a mercury-cadmium-telluride infrared mixer cooled to approximately 100 K by a radiative cooler The laser local oscillator and coupling-modulated laser transmitter use conductively cooled beryllium oxide construction The optical antenna used for transmission and reception has a gain of nominally 92 dB with a 3-dB beamwidth of 80 µr Tracking jitter is less than ten µr and signal acquisition occurs in less than 1 min The receiver subsystem has a sensitivity of 10-19W/Hz, accommodates a 300-Mbit/s data rate, and can track Doppler frequency variations over a ±700-MHz range

Method and apparatus for manufacturing optical communication cables

Abstract: A cabling technique for assembling an optical communication cable having a helically twisted stacked array of optical fiber ribbons and an extruded cable jacket to which helically stranded longitudinal strength members are tightly coupled.

White light optical processing and holography.

Abstract: A method is described wherein optical processing and holography using transparencies are performed using point source white light. The method is coherent, in that the optical systems are linear in amplitude rather than intensity. Perfect wavelength compensation is achieved, with no restriction on the source spectral width.

Fibre Optic Communication Systems

Abstract: The basic requirements for practical optical communication systems are reviewed. The construction and performance of some of the key constituents such as the fibre, cable, sources, connectors and splices are discussed. Particular emphasis is placed on the special properties of optical communication systems such as the economic advantage of wideband trunk communication, the immunity to electrical interference, and the high strength to weight ratio of the transmission medium. Details of a repeated 140 Mbit/s field demonstration over a 9 km route between Hitchin and Stevenage are given to illustrate the features of a comprehensive optical communication system.

Low loss optical data terminal device for multimode fiber guide optical communication systems

Abstract: The active data terminal device employs an array of multiple mode optical fiber guides as input-output devices, each abutted against a flat input-output focal face of an electro-optically active plate provided with opposed deflection modulation electrodes. Opposite the input-output focal face is a cylindrical mirror surface for refocusing the multiple-mode light from any predetermined input fiber guide into a second one of the array of fiber guides as selected by the voltage applied to the electrode pair.

Spatial-multiplex, spatial-diversity optical communication scheme

Abstract: An optical communications system for coding, transmitting, receiving, and coding digital message signals is described. A beam from a coherent optical source, such as a laser, is transmitted through an aperture in which there is disposed a random phase screen, e.g., ground glass. One or more isometric bar gratings containing the coded message data in a particular amplitude distribution pattern are disposed adjacent to the ground glass in the optical transmission path. The ground glass, phase screen, introduces a random coding to the message bit. At the receiver a plurality of point detectors sense the signals to facilitate subsequent decoding of the message.

Method and apparatus for distortion reduction in optical communication systems

Abstract: An optical transmitter suitable for analog transmission in optic fiber communication systems utilizes two matched light emitting diodes to achieve distortion reduction

Light emitting device for optical communications

Abstract: A high-speed, light emitting device which utilizes a solid state source for generating light for use in fiber optical communications. The source is an active, narrow band gap layer of semiconductive material between heterojunctions formed with a p+ -type material on one side of an n+ -type material on the other side. A mirror on the back of the source reflects light toward an optical fiber abutting the substrate on the front of the source. A side mirror traverses the edge of the active layer at an angle of about 45° and reflects light traveling parallel to the active layer toward the optical fiber. Contacts are coupled to the semiconductor material for applying an electrical signal across the active layer to generate light. In a preferred embodiment, the active layer is GaAsSb joined to GaAlAsSb and the substrate is GaAs.

Multiplexer at 5 Gbit/s for fibre-optical communication systems

Abstract: A 5 Cbit/s multiplexer using a step-recovery diode, microstrip transmission delay lines and fast p-i-n diode switches has been investigated. The signal/distortion ratio is 12 dB, where most of the distortion is due to an imperfect input signal. The overall multiplexer seems to be simple enough to be adopted in highcapacity optical-fibre communication systems.

Averaged threshold receiver for direct detection of optical communications through the lognormal atmospheric channel.

Abstract: An averaged threshold receiver is developed for an optical communication system consisting of a symmetric binary, pulse-code modulated transmitter, a lognormal channel, and an array of independent photocounting detectors. When compared to previously described receivers, it is shown to be a much simpler structure to implement and to provide generally lower bit error rates. Probability of error curves demonstrating this improved performance are presented for various combinations of turbulence strength, background radiation level, SNR, number of diversity channels, and, in the newly developed processor, number of bits used for threshold averaging.

Multiplexed optical communication system

Abstract: The system permits the multiplex telecommunication through the medium of an optical carrier wave. The system comprises a source of coherent light whose optical spectrum is dispersed in an optical device comprising a pair of diffraction gratings. A plurality of light modulators are disposed in the path of the spread out beams and controlled by electric signals which carry items of information. Output optical means collect the modulated spectral components.

Phase Compensation Receivers for Optical Communication

Abstract: Phase compensation receivers are investigated in the context of optical communication, with particular emphasis on low visibility channels. It is shown that phase compensation can be viewed as a reduction of the number of spatial modes in the signal field so that an improvement in communication performance can be realized by a receiver which exploits the spatial coherence of the compressed signal mode. The phase compensation receiver structure separates nicely into configurations for measuring the phase of the signal field across the aperture and the required processors to obtain the phase compensation control from the measurements. The optimum phase control, which is chosen to spatially concentrate the signal power in the focal plane, is shown to be the minimum-mean-squared-error estimate of the aperture field phase, when the estimation error is "small enough." The phase observation-estimator structures are placed in an idealized phase compensated receiver. Minimum signal power requirements for adequate phase estimation performance are established. Communication performance, in terms of the parameters that describe the low visibility channel, is examined for both compenstated and uncompensated receivers. Depending on the system used, and for phase coherence times in the tens of milliseconds, phase compensation is most appealing for signaling rates from the middle kilobit to low megabit per second range; the resulting improvement in communication performance made possible by phase compensation is as much as 40-60 dB in optical power relative to an uncompensated receiver.

Optical communication at the source bandwidth limit.

Abstract: The possible limiting components on optical communication bandwidth are the source, the modulator, the propagation medium, and the detector. It is easy to show that the source bandwidth is the fundamental limit. The possibility of source bandwidth limited communication is demonstrated theoretically and experimentally. The basic principles involved are readily extendable to more practical partial approaches to this limit.

Optical communication system utilizing light emitting diode

Abstract: In an optical communication system, wherein light intensity modulation with no carrier is performed using a light emitting diode with linear relation of the drive signal current vs. optical output power over a range which changes with frequency of the drive signal, the input signal is modulated for relatively larger amplification of frequencies higher than a predetermined frequency, above the thermal response frequency of the light emitting diode, than for frequencies lower than the predetermined frequency.

Method for transmitting two-dimensional information and system for effecting same

Abstract: A method is disclosed for transmitting two-dimensional information about an object with the aid of a two-dimensional reference signal and a two-dimensional useful signal through an optical communication line. The two-dimensional useful signal is formed by two-dimensional spatial modulation of a coherent light flux. The two-dimensional reference signal is displaced with respect to the two-dimensional useful signal by a time interval which is not in excess of the time instability interval of the communication line. A hologram is recorded at the output of the communication line, of the two-dimensional useful signal matched in time and space with the two-dimensional reference signal. A Fourier hologram can be made of the two-dimensional useful signal and the two-dimensional reference signal in relation to the two-dimensional reference signal, which, when reproduced, makes it possible to obtain the undistorted two-dimensional information that has been transmitted. In addition, a system is disclosed for transmitting two-dimensional information at optical frequencies in accordance with the above method.

Laser equipment for optical communication

Abstract: PURPOSE:To avoid the thermal impairment for the semiconductor laser by securing a cut-off state for the bias current flowing to the semiconductor laser when the peripheral temperature exceeds the prescribed effective temperature

Automatic fusion welding connector of glass fiber core wires for optical communication

Abstract: PURPOSE:To perform adjustment of light incidence rapidly and easily by measuring, comparing and processing the power of incident light thereby controlling the movement of an adjusting table

Glasfaser-Bussysteme zur Signalübertragung in Bordnetzen

Abstract: To transmit electrical control, test, and actuator signals on board, presently conventional multi-wire communication links are used. Signal multiplexing has not been a common technique up to now. The enormous growth of electronic devices on board imposes stringent requirements on data transmission. Signal multiplexing, which is a common technique in telecommunications, has been studied for on board application. It is shown, that a time division multiplex data bus system with fibre optic signal transmission has the best performance characteristics. Bus structures using standard interfaces present flexibility and growth capability. Fibre optics offer reduced weight, large transmission capacity, and immunity to electromagnetic interference. Für die Dokumentation: Bordnetz / Datenübertragung / Bussystem / Glasfaser

Optical communication device

Abstract: PURPOSE:To reduce the transmission distortion as well as to increase the economical performance with use of one unit of optical receiver, by transmitting one unit of the information per one unit of the optical transmitter

Star repeaters for fiber optic links

Abstract: A star repeater combines the functions of a passive star coupler and a signal regenerating amplifier. By more effectively utilizing the light power radiated by a light emitting diode, the star repeater can, when used with small diameter channels, couple as much power to all receivers of a multiterminal link as would be coupled to the single receiver of a simple point-to-point link.

Fiber for optical transmission

Abstract: PURPOSE:To provide an optical transmission fibber which can have electric characteristics of low loss and wide transmission range for optical communication by giving a preset relationship to the distribution of refractory index of the active portion of the fiber.

Enhanced Faraday effect and its application to optical communication.

Abstract: This paper shows that the enhanced Faraday effect of optical resonance lines can be applied to optical communication. A secure optical communication system was designed and successfully tested. It used the integrated enhanced Faraday effect at low fields to produce polarization modulation and the high dispersion of the enhanced effect at high fields to scramble and unscramble the transmitted messages.