Showing papers on "Optical communication published in 1974"

Light source for optical waveguide bundle

Abstract: A source of optical wave energy for an optical communication system. One end of an optical waveguide fiber bundle is disposed in light-receiving relationship with respect to light from a Lambertian-type light source such as a light emitting diode. A spherical bead of transparent material disposed between the diode and the fiber bundle endface provides a rugged and inexpensive optical device that tends to collimate the light emitted from the diode.

Direct-Detection Optical Communication Receivers

Abstract: A model that is sufficiently general to describe the predominant statistical characteristics of the output of many real optical detectors is formulated. This model is used to study the optimum receiver processing for direct-detection optical communication systems. In particular, the structures of detectors and estimators for randomly filtered doubly stochastic Poisson processes observed in additive white Gaussian noise are considered. Representations for the posterior statistics of a vector-valued Markov process that modulates the intensity of the doubly stochastic Poisson process are obtained. Quasi-optimum estimators and detectors are specified in general terms and specialized for several important applications. These include a demodulator for subcarrier angle modulation, a detector structure for binary signaling with known intensities, and a detector structure for binary signaling in the turbulent atmosphere.

Star coupler for single mode fiber communication systems

Abstract: An optical coupler system in which optical communications from separate cers are transmitted over separate lines of a single optical fiber to a coupler which combines the information and transmits the combined information over different single fibers to other communication centers.

Optical communication system source-detector pair

Abstract: A source-detector pair for injecting optical signals into the endface of an optical waveguide bundle and extracting and detecting optical signals emanating from the bundle endface. An optical detector is axially aligned with the waveguide bundle and is separated therefrom by an optical mixer rod. An edge-emitting solid state source is disposed on that side of the detector opposite the mixer rod. Light radiating from the bundle endface is propagated through the mixer rod and impinges upon the detector. Light emitted from the periphery of the source is reflected and propagates past the detector to the mixer rod from which it emerges and illuminates in a relatively uniform fashion the optical waveguide bundle endface.

Optical applications of ferroelectrics

Abstract: Ferroelectric materials have found extensive application in optoelectronic devices for uses in optical communication, memory, display and coherent optical processing. Specific device applications include modulators, beam deflectors, light valves and holographic storage media. These device applications are reviewed with emphasis on progress made since June 1971, and on the competition provided by such technologies as acoustooptics, magnetooptics and liquid crystals.

Broadband data modulation system

Abstract: A broadband data modulation system for the transmission of amplitude and frequency modulation data with a bandwidth up to and greater than 500 MHz. The system involves the multiple heterodyning of microwave signals with infrared or optical signals. The data modulation system utilizes multiple passes of the infrared or optical signal through a crystalline material which also has an acoustic signal forming an acousto-optic grating. Fixed gratings are also imbedded in the crystal so as to aid in the guidance of the infrared or optical signal. The output of the crystal comprises an infrared or optical signal modulated with the desired data, which can be transmitted optically to a transponder, which can in turn convert the last-named infrared or optical signal into a transmitted correspondingly modulated RF signal.

High speed electro-optic waveguide modulator

Abstract: An optical waveguide for transmitting light energy is defined by a channel of diffusant in a selected substrate material. An electrical conductor is positioned proximate to each side of the optical waveguide channel and a source of electrical signals is connected to the electrical conductors to develop an electrical field across the optical waveguide, producing resultant changes in refractive index commensurate with the electrical signals impressed upon the parallel electrical conductors. The changes of refractive index cause changes in polarization of light energy transmitted through that portion of the optical waveguide so that such light energy is phase modulated. In a preferred waveguide electro-optic modulator assembly, polarized light energy transmitted by the optical waveguide may undergo a change of polarization which, when intercepted by a polarization-sensitive filter, will produce an amplitude modulation of the light energy transmitted by the assembly.

Synchronization Using Pulse Edge Tracking in Optical Pulse-Position Modulated Communication Systems

Abstract: A pulse-position modulated (PPM) optical communication system using narrow pulses of light for data transmission requires accurate time synchronization between transmitter and receiver. The presence of signal energy in the form of optical pulses suggests the use of a pulse edge-tracking method of maintaining the necessary timing. In this report the edge-tracking operation in a binary PPM system is examined, taking into account the quantum nature of the optical transmissions. Consideration is given first to "pure" synchronization using a periodic pulsed intensity, then extended to the case where position modulation is present and auxiliary bit decisioning is needed to aid the tracking operation. Performance analysis is made in terms of timing error and its associated statistics. Timing error variances are shown as a function of system signal-to-noise ratio.

Optical communication in free space

Abstract: Two classes of laser communication systems for handling very high data rates across inter-satellite distances are considered that provide for high antenna gains, wide modulation bandwidths, and optical receiver sensitivities. System design considerations are based upon the carbon dioxide laser modulation to accommodate digital or analog information, and the neodymium doped YAG laser pulse for digital modulation.

Low-loss glass for optical transmission

Abstract: Optical losses below the target for an optical-communication system (20 dB/km) are reported for a sodium-borosilicate glass. The glass was prepared in a conventional furnace, and the low loss was obtained by controlling the redox conditions during melting.

Theory, fabrication and performance of some integrated optical devices

Abstract: Recent progress in the fabrication of low attenuation optical fibers raises the attractive possibility of optical communications via these waveguides. Integration of different optical functions on one substrate in the form of optical circuits will form ideal terminals for such a communication network. We shall discuss the theory, fabrication and performance of a few "building stones" of such optical circuits. Optical directional couplers capable of coupling light from one channel to another will be described and their use as switches will be discussed. Distributed feedback for integrated lasers will be analyzed. Laser action in a GaAs waveguide, in which distributed feedback was supplied by corrugations fabricated on the surface, will be described. Longitudinal and transverse mode control of such a laser will also be discussed. We shall conclude with an analysis of nonlinear interactions in thin films, pointing out new methods for phase matching and ways to implement them.

A lithium niobate light modulator for fiber optical communications

Abstract: An electrooptic intensity modulator using lithium niobate has been developed for applications in binary fiber optical digital communications at the wavelength of 1.06 µm. We have shown that many shortcomings generally associated with electro-optic modulators can be surmounted. The modulator was driven by a compact transistor amplifier, temperature dependence of the static birefringence was minimized, and the optical bias was made adjustable by a dc voltage superposed on the signal. The modulator has been operated at 70-Mb/s pulse rate and 100-percent modulation, its extinction ratio is better than 40 to 1 and the optical insertion loss is about 1 dB.

Bit Error Probability for Baseband and Subcarrier Optical Communication Systems

Abstract: Digital baseband and digital subcarrier noncoherent optical communication systems are considered in this paper Expressions are developed for the bit error probability of optical subcarrier systems which use a nonliner polarization modulator and either a one-detector or a two-detector receiver, The expressions are evaluated numerically, and the results are used to compare the one- and two-detector subcarrier systems with the corresponding one- and two-detector baseband systems for a fLxed bit error probability

Method and apparatus for time compression of facsimile transmissions

Abstract: In a facsimile transceiver, a reading or video fiber optic which is connected to a photodetector optically communicates with a document. A leading or look-ahead fiber optic which is also coupled to the same photodetector also optically communicates with the document. When the document is being slowly scanned, the position of optical communication between the reading fiber optic and the document is illuminated through fiber optics associated with the reading fiber optic and signals representing the sensing of dark and light regions are transmitted to a like transceiver. When a predetermined length of time has elapsed since sensing the last dark region, the position of optical communication between the leading fiber optic and the document is illuminated by fiber optics associated with the leading fiber optic and a fast scanning rate is initiated. Sensing of the first dark region by the photodetector via the leading fiber optic reinitiates the slow scanning rate and illumination of the position of the optical communication between the reading fiber optic and the document.

Optical communication and display system

Abstract: The light wave energy of a scanning, intensity-modulated light beam used to provide an optical display or recording of a given scene at a receiving station is the same light wave energy initially employed to optically communicate video information pertaining to this given scene between a transmitting station and the receiving station.

Optical Communications in Space

Abstract: A short history of laser communication developments devoted to space communications is presented, followed by a description of present high data rate (up to 1 Gbps) systems under development, and discussion of the most promising space laser commuication techniques. Critical. components such as the laser, modulator, detector, high speed electronics, and acquisition and tracking system will be discussed.

Laser Communication Technology in Germany

Abstract: A survey of the history and the development of laser communication technology in Germany is given. Fibers, lasers, diodes, and repeaters are treated.

Application of GaAs Lasers and Silicon Avalanche Detectors to Optical Communications

Abstract: Recent advances in the semiconductor laser and photodetector state of the art has led to the development of small low cost, reliable laser transmitter and receiver modules (see Fig. 1). These modules are now being designed into a number of practical communication systems used for a wide variety of applications (see Figs. 2 and 3). These systems have been designed to transmit voice, computer data, and video sivals and offer a number of advantages over previous transmission methods including cost, security, simplicity, bandwidth and licensing requirements. Where atmospheric limitations are either absent or surmountable these optical communication systems offer the communication engineer a viable alternative.

Channel simulation for optical communication systems.

Abstract: A technique is reported for simulating the signal fading that will be experienced by typical optical communication systems. The desired irradiance or amplitude fading statistics can be simulated by incorporating a linearized optical modulator subsystem between the transmitter and receiver. This technique has been implemented in the design and construction of a laboratory channel simulator. The design of the processing electronics is discussed along with the results of tests performed for each mode of operation.

Channel simulation for direct detection optical communication systems

Abstract: A technique is described for simulating the random modulation imposed by atmospheric scintillation and transmitter pointing jitter on a direct-detection optical communication system. The system is capable of providing signal fading statistics which obey log-normal, beta, Rayleigh, Ricean, or chi-square density functions. Experimental tests of the performance of the channel simulator are presented.