Showing papers on "Optical communication published in 1976"

Optical Pulse Formats for Fiber Optic Digital Communications

Abstract: Some new optical pulse formats are investigated for solving practical problems in fiber optic communication systems. These pulse formats provide many advantageous features such as error monitoring capability, abundant timing information, uniform optical power utilization, stable detection of optical input, and so forth. It is shown that a modification of Personick's receiver design theory can be used for comparison of various optical pulse formats. The comparison suggests that for state-of-the-art fiber systems with moderate fiber loss and moderate repeater spacing, where no pulse equalization is required, some new classes of 1 binary digit converted to 2 binary digits (1B2B) or 2B3B formats will permit the realization of very simple and reliable repeaters for fiber optic digital transmission. A future low-loss fiber system may permit a very long repeater spacing with the help of equalization. In this case, application of the correlative signal-processing technique is shown to be very promising. Experimental 6.3 Mbit/s and 100 Mbit/s transmissions demonstrate some advantageous features of these optical pulse formats.

Optical access couplers and a comparison of multiterminal fiber communication systems

Abstract: Optical T and multiple T access couplers designed for tapped trunk line multiterminal communication systems that use bundles of multimode fibers as the transmission media have been investigated. The particular coupler designs tested used bent Pyrex rods for bifurcation and scrambling. Coupler throughput losses (not counting packing fraction losses) are 1.5-2.5 dB. The bent rod optical T and multiple T access couplers must be used with high N.A., low packing fraction loss fibers. To avoid the use of a repeater a multiple T or star configuration must be used in a system comprising ten or more terminals.

Optical data communication system

Abstract: An optical communication system is disclosed wherein a multiplicity of stations in a linear, random, or grid arrangement are coupled in a party-line type network in which optical signals originated by a master or responding station are relayed from station to station. Coupling between stations may be accomplished by means of optical lenses, the focal regions of which are coupled to electronic equipments that may be remotely located therefrom. This electronic equipment detects received optical signals, regenerates and retransmits these received optical signals, and originates a responding optical signal to the master station when the received optical signal is addressed to the receiving station.

Light-emitting diodes with a modulation bandwidth of more than 1 GHz

Abstract: The design principle and the fabrication of high-speed l.e.d.s with a 3dB modulation bandwidth in the gigahertz range is described. The modulation characteristic, radiance and spectrum have been measured. The results demonstrate that these l.e.d.s are suited as light generators in optical transmission systems with a bandwidth in excess of 1 GHz.

Ideal light source for an optical communication channel

Abstract: It is shown that, in principle, there exists a light source giving a higher information rate per symbol in an optical communication channel than a single-mode laser Such a source emits a definite number of photons per symbol A possible form for this source is suggested, and the corresponding information rates are compared

Graded-index fiber for multimode optical communication

Abstract: Graded-index fibers, which are the most promising for first-generation optical communication links, are improved for multimode transmission by employing two or more glassy dopants in the core mutually graded with respect to the silica host and to each other to provide simultaneously minimized intermode dispersion at a first-selected wavelength and, in addition, a broader wavelength range of minimized intermode dispersion, or minimized intermode dispersion at a second distinct wavelength pertinent to the multimode transmission, or optimization of another dispersion-related property of said fiber.

Wide-bandwidth high-radiance gallium-arsenide light-emitting diodes for fibre-optic communication

Abstract: High-radiance GaAs l.e.d.s with 3 dB modulation bandwidths exceeding 500 MHz have been fabricated from p-n junction layers prepared with very high zinc acceptor doping levels. This development will permit the use of l.e.d.s in near-gigahertz or gigabit/s optical-fibre communication links.

Optical-fiber impulse-response measurement system

Abstract: This paper describes time-domain instrumentation that was designed to measure impulse response and delay of multimode optical fibers that are being used in an experimental optical communications system at Bell Laboratories. Time-domain data is transformed to frequency-domain by a minicomputer, and the result is displayed as the fiber's baseband frequency response.

Low-loss signal coupler for optical communications and integrated optics

Abstract: A method and means for coupling information or signal power into or out ofiber optics for integrated optical waveguides The coupling consists of selectively doping with impurity ions such as rare earth or transition metal ions which are excited to fluorescence within the waveguide by the frequency of the transmitted carrier wave The fluorescent emission is then detected at right angles to the fiber using conventional photodetectors and amplifiers

Dual channel optical homodyne receiver

Abstract: An improved homodyne receiver for use in wideband optical communications systems is disclosed. The receiver utilizes quadrature demodulation of the optical signal in the manner of a two-phase receiver. A beam-splitting/phase-splitting optical assembly is used to channelize the received and the local oscillator beams to a pair of optical detectors. Squaring amplifiers in the quadrature channels followed by a summing network provide an output signal which is proportional to the square of the modulation of the input signal. This receiver is especially well-suited to the reception of Pulse Code Modulated optical signals.

LASER COMMUNICATIONS IN SPACE: Nd:YAG TECHNOLOGY STATUS

Abstract: The advances made in laser communications technology during the past few years have made it a certainty that operation in space from a satellite will be achieved within this decade. The Air Force began investigating laser communications seriously in 1971 with the formation of the 405B program. The initial requirement was a system operating a t 1000 megabits per second. Various laser systems were evaluated with regard t o the technical feasibility of achieving the required data transfer rate. It was determined that only the C 0 2 laser and the Nd:YAG laser offered the necessary potential. Of the two, only the Nd:YAG laser technology was advanced enough t o support the high data rate. The 405B program was committed in 197 1 to the development of a 1000-megabit-persecond Nd:YAG laser communications system for space use. The 405B program began with technology and component developments and the results were evaluated with regard t o their systems applications. The system development was furthered by considering each component individually, and optimizing each for maximum performance. The 405B program has progressed from purely technological and component development through preliminary subsystem designs, brassboard systems hardware and an engineering-feasibility model (EFM) of the system.' The engineering-feasibility model has been the culmination of all the development work since 197 1. The transmitter package of the model was designed and fabricated to the flight qualification levels of the Defense Meteorological Satellite Program-Block 5 system. The engineering-feasibility model package was tested to the flight hardware acceptance levels. The system and its components survived the thermal and vibration tests without significant degradations. The 1000-Mbps Nd:YAG laser communication system is planned for space launch in 1979. The space flight test is t o include the Air Force 1000-Mbps Nd:YAG laser package, a Navy laser pointing experiment, and a NASA C 0 2 laser package operating at 300-500 Mbps. The laser communications test satellite is t o be launched into a highly elliptical orbit with apogee at a iynchronous altitude and 12-hour period. The satellite apogee is t o be at 100 west longitude and 60 north latitude once every 24 hours. The satellite will be near apogee for 5-6 hours, and the satellite will be simultaneously accessible from the Air Force ground station at Cloudcroft, New Mexico and from the NASA ground station a t Goddard Space Flight Center in Greenbelt, Maryland. The joint DOD-NASA space laser communications experiment will establish the

Measurement of nonlinear distortion in light-emitting diodes

Abstract: The 2nd- and 3rd-order nonlinear distortion levels of light-emitting diodes used for analogue optical communication have been measured and found to be typically -40 and -75 dB, respectively. A method using three independent signal sources was employed in the measurement.

Integrated optical circuits for telecommunications

Abstract: Optical signals can be guided and manipulated in thin films deposited on a substrate. The new technology will allow the implementation of key circuit functions at optical frequencies.

Wideband heterodyne receiver for laser communication system

Abstract: A wideband heterodyne receiver for a laser communication system is disclosed which includes a front end having a cooled photomixer contained in a hermetically sealed spaced quality housing designed for wide bandwidth transmission. The photomixer is coupled through a wideband preamplifier to the receiver back end which includes a frequency tracking network and demodulating equipment. The receiver is capable of tracking a doppler frequency shift of 750 MHz, positive or negative, and has an instantaneous intermediate frequency information bandwidth of 400 MHz. The receiver system is also capable of operating over a wide temperature range and is designed to be suitable for use in outer space communication.

Optical communication system

Abstract: PURPOSE: To prevent the transmission loss of an optical communication system with a simple connection by accomplisying the connection at the transmitting and receiving sides with the use of stub fibers which have larger and smaller diameters than the transmitting optical fiber COPYRIGHT: (C)1978,JPO&Japio

Optical communications forwards scatter compensator

Abstract: Pulse stretching and smearing due to forward scatter of a collimated beam from a light source is eliminated by the use of a multiple field of view detector which divides up the beam in the vicinity of the receiver into segments along the optical path of the beam, inverts the order of the signals from the segments, and delays the signals by predetermined amounts such that pulses from different segments overlap and add, with the delay set to compensate for different path lengths between the transmitter and the receiver due to the intercepting of various segments along the optical path by the fields of view of the individual detectors making up the multiple field of view receiver.

Wide aperture optical communications detector

Abstract: Narrow-band detection of optical signals over a large field of view wherein the selective reflecting power of metallic vapors is employed. A modulated carrier signal to be detected is directed to a Brewster window of an enclosure containing a vapor such as mercury. Only the incident light of interest is reflected through an exit window and detected by means of a photo-multiplier.

Large bandwidth optical communication systems utilizing an incoherent optical source

Abstract: The dispersion of optical signals derived from a spontaneous emitter when coupled into an optical fiber waveguide is substantially reduced by optically coupling a narrow band pass interference filter between the emitter and waveguide. Only a narrow portion of the broad spectral width emission of the emitter is thereby coupled into the waveguide to provide emitter modulation rates limited only by the rise-time of the emitter. In the preferred embodiment, the coupled spectral portion corresponds to the wavelengths of peak emission. Additionally, the filter is a thin film filter deposited onto either the light-exiting face of the emitter or onto the light-receiving end of the fiber waveguide.

Optical communications system

Abstract: PURPOSE:Optical communications system having a surveillance signal circuit for surveillance signal transmission without use of a wavelength or a transmission path different from that for information signal transmission.

Linear charge coupled device detector array for imaging light propagating in an integrated thin-film optical waveguide

Abstract: Device design, fabrication, and operation of a linear charge coupled device (CCD) detector array integrated with a thin film optical waveguide and applications of this structure to integrated optical signal processing and fiber optical communications were discussed A two phase, overlapping-gate CCD is connected in parallel by means of a series of gates to an array of photodiodes The photodiode provides an electrode free surface region so that a highly efficient waveguide detector coupling technique can be implemented A thermally-oxidized layer of SiO2 forms an effective substrate for the optical waveguide

Co2 laser communications

Abstract: Ever since the invention of lasers, optical communication has been one of the major interests in the laser community. There are two well-defined activities, namely, terrestrial telecommunication and the spaceborne data relay link. The formal activity has been evolved around optical fiber transmission.' At this time high purity glass fibers with a graded index profile have yielded excellent optical transmission characteristics with a loss figure as low as 1 dB/km at wavelength 1.06 pm, and pulse dispersion of less than 2 nsec/km. It appears simply a matter of time and economy that optical fibers will be used initially in the intracity network and eventually in intercity telecommunication systems. The other activity concerns wideband data transmission from spacecraft. Two agencies, Air Force and NASA are very active in this area with their respective program plans, which will bring one or more laser relay systems to an operational status in the early 1980s. The mission of the Air Force laser communication system is intended to establish a synchronous-tosynchronous satellite link at a data rate in gigabits. For this purpose the choice at present is the Nd:YAG solid-state laser? NASA, on the other hand, is pushing a CO, laser link3 between a low-altitude earth-sensing satellite to a synchronous satellite. In this case, either digital data (100 to 300 Mbps) or analog data (30 MHz or 6 MHz baseband formats) is sufficient for this mission. This paper concerns mainly the technological status of CO, laser transceiver development directed toward this application. The bulk of this development is being carried out either at the Laser Technology Branch of Goddard Space Flight Center or at industries under NASA sponsorship. FIGURE 1 shows a data relay link between a low-altitude elliptically orbiting earth-sensing satellite (LAS) and the earth through two synchronously orbiting satellites (SOS). The operating characteristics of the communication terminal on LAS must have an optical antenna system that provides at least hemispherical coverage and must have the capability of transmitting wide-band data. The SOS receiving terminal must be capable of tracking and processing the Dopplershifted (nominally f700 MHz) wide-band data and provide a beacon-laser pointing reference for the LAS terminal. Wide-band data relay links are required for a number of future space missions as shown in FIGURE 2. Of these, the low-altitude missions, both manned and unmanned, have the most urgent need for transmission of wide-band data to an earth terminal, and of the most near-term concern is the data recovery from the Earth Observation Satellite (EOS) and the space lab. The EOS will carry instruments such as the synthetic aperture radar (200 Mbps), the high resolution pointable imager (1 20 Mbps), and the thematic mapper (100 Mbps). Advanced multiplexers are under development whose output data stream will exceed 240 Mbps. When other spacecraft instruments and functions are considered, the total data rate requirement for the EOS will range from 300 to 500 Mbps, depending upon the particular complement of instruments on