Showing papers on "Optical communication published in 1988"

Optical communications network

Abstract: A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g. telephones in customers' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (14) from a central station (4). The signal is split between several secondary fibers at a first splitter (10) (e.g. array of passive couplers) and between further sets of fibers at a second set of splitters (12). At this stage there are 120 individual fibres to customers' premises (8). Digital speech or data is sent back to the central station by a laser in the customers' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Input power limits of single-mode optical fibers due to stimulated Brillouin scattering in optical communication systems

Abstract: Stimulated Brillouin scattering (SBS) limits the optical power that can be transmitted through a single-mode fiber in long-distance optical communication systems, the authors have investigated SBS gain and threshold characteristics with amplitude-shift-keying (ASK), frequency-shift-keying (FSK), and phase-shift-keying (PSK) modulated lights to estimate the input power limitation set by SBS. It was shown that maximum fiber-input powers or the SBS thresholds for fixed-pattern (1010 . . .) ASK, FSK, and PSK modulated lights are 2, 4, and 2.5 times higher, respectively, than the threshold for unmodulated light. Theoretical predictions were experimentally verified by SBS gain measurements with FSK and PSK modulated lights. The first direct observation of SBS with FSK modulated light pumping is also described. >

A wavelength routing approach to optical communications networks

Abstract: A class of wavelength-routing optical networks is described on the basis of the interconnection of wavelength multiplexed channels. Unlike previously described optical network structures, these networks allow the reuse of wavelengths in different transmission sections and this leads to fewer wavelengths being needed. A choice of structures using a common set of components leads to the opportunity to design a network according to the geographical distribution of the switching nodes. The structures provide for a set of point-to-point interconnections and, with modest numbers of wavelengths, full interconnection between the optoelectronic nodes is possible at the optical level. In bypassing intermediate electronic stages the networks appear to offer good reliability characteristics. Providing the components in an initial network are designed to utilize bandwidth efficiently, the networks could be upgraded to incorporate more channels, optical switching, and other forms of optical processing at the optical nodes. >

A four-channel optical waveguide multi/demultiplexer for 5-GHz spaced optical FDM transmission

Abstract: A four-channel optical waveguide multi/demultiplexer for 5-GHz spaced optical FDM transmission is developed. The multi/demultiplexing principle is first presented, followed by the extinction ratio dependence on the power transfer ratio of the directional couplers, transmission loss of the waveguide, and birefringence of the waveguide. Experimental results are described for waveguides of high-silica glass fabricated on the silicon substrate by combination of flame hydrolysis and reactive ion etching. Their measured characteristics, such as frequency transmittance, loss, extinction ratio, and dependence of polarization and temperature are reported and evaluated. >

Optical communication systems using fabry-perot cavities

Abstract: This invention is a new type of Fabry-Perot cavity, and an optical communication system using such a cavity. The inventive Fabry-Perot cavity comprises both a waveguiding portion (43) and a nonwaveguiding portion (52,53). In this manner, tunable cavities of desirable mid-range length, necessary to obtain required free spectral ranges, may be fabricated with minimal diffraction losses otherwise associated with cavities of such length. The cavity length may be varied using, for example, piezoelectric elements, and the various cavity elements may be aligned and connected, using fiber connector technology.

Ultrafast all-optical switching utilizing the optical Kerr effect in polarization-maintaining single-mode fibers

Abstract: An ultrafast all-optical switching scheme utilizing the optical Kerr effect in two birefringent fibers concatenated with each fast axis crossed is proposed Stable optical Kerr modulation and all-optical demultiplexing of an ultrashort (30 ps) optical pulse train at 197 GHz from a gain-switched distributed-feedback laser diode (DFB LD) have been sufficiently demonstrated using CW mode-locking Nd:YAG laser pulses as a pump Switching speed and required pump powers are studied in terms of fiber bandwidth due to fiber birefringence, and combined effects of chromatic and polarization dispersions on Kerr modulation profiles By utilizing the optical Kerr modulation properties in the presence of dispersions, the nondiagonal yx component of the nonlinear refractive index is also determined to be 034 relative to the diagonal component xx The intrinsic stability and ultimate switching capabilities are discussed >

High-speed data transmission on an optical fiber using a byte-wide WDM system

Abstract: The advantages and problems of using wavelength division multiplexing (WDM) to transmit byte-wide data in parallel through a single-mode optical fiber are studied. The principle problem which is particular to byte-wide transmission is shown to be bit skew caused by group delays of the different transmission wavelengths. The aggregate bit rate of the byte-wide link is shown to be equal to the aggregate bit rate of the serial link for all byte sizes. >

Coherent subcarrier multiplexed optical communication system

Abstract: An optical communication system includes a transmitter for generating a subcarrier multiplexed optical signal, a receiver and an optical fiber for coupling the optical signal from the transmitter to the receiver At the transmitter, an optical carrier is modulated with a composite modulation signal including a plurality of modulated microwave subcarriers to provide the optical signal The receiver includes a local oscillator for generating a local light beam, a detector responsive to the received optical signal and the local light beam for providing a detected signal at an intermediate frequency, and a microwave receiver for demodulating the microwave subcarriers from the detected signal The modulation index of the optical signal produced by each of the modulated microwave subcarriers is selected to permit transmission of a large number of high quality video channels A quadrature detector can be used to eliminate second-order intermodulation products The quadrature detector can also be used to eleiminate optical phase noise

Modulatable narrow‐linewidth semiconductor lasers

Abstract: We find that using the technique of optical feedback locking, to narrow semiconductor linewidths, does not sacrifice the ability to modulate the laser’s frequency via the injection current. The frequency of a laser is stabilized to a separate Fabry–Perot reference cavity using resonant optical feedback and can be modulated efficiently at frequencies related by rational fractions to the free‐spectral range of the reference cavity. This system can provide an array of narrow‐linewidth, frequency‐stable laser lines and shows promise for applications in frequency‐division‐multiplexed coherent communications, as well as laser frequency control and precision measurement systems.

Optical communication system with a stabilized "comb" of frequencies

Abstract: An optical communication system in which a group, or "comb", of intelligence-bearing signals are frequency-division-multiplexed and stabilized using a corresponding "comb" of resonances associated with a Fabry-Perot cavity.

Atmospheric propagation effects relevant to optical communications

Abstract: A number of atmospheric phenomena affect the propagation of light. This article reviews the effects of clear-air turbulence as well as atmospheric turbidity on optical communications. Among the phenomena considered are astronomical and random refraction, scintillation, beam broadening, spatial coherence, angle of arrival, aperture averaging, absorption and scattering, and the effect of opaque clouds. An extensive reference list is also provided for further study, Useful information on the atmospheric propagation of light in resolution to optical deep-space communications to an earth-based receiving station is available, however, further data must be generated before such a link can be designed with committed performance.

Twenty channel FSK subcarrier multiplexed optical communication system for video distribution

Abstract: A two Gbit/s subcarrier multiplexed optical communication system suitable for video distribution is presented where 20 microwave subcarriers are modulated at 100 Mbit/s using a frequency shift keyed format.

400 Mbit/s, 372 km coherent transmission experiment using in-line optical amplifiers

Abstract: We report on an optical transmission experiment using four in-line optical amplifiers. With a net gain of 58,000 (47.7 dB)from the amplifiers, we were able to increase the longest non-regenerated transmission distance to 372 km. The system penalty associated with the amplifiers was only l.5 dB.

Computing the performance of optical receivers with avalanche diode detectors

Abstract: A method is described for exactly computing the probability distribution of the sum of the output of an avalanche diode and Gaussian noise using the Personick-McIntyre model of the random electron multiplication in the diode. A saddlepoint approximation is also presented. Both are incorporated in an optimization procedure for efficiently calculating the minimum input signal strength and the decision level that are needed to attain a preassigned error probability when the diode is embodied in a binary optical communication receiver. >

Multigigabit-per-second optical baseband transmission system

Abstract: Optical transmission baseband technology for multigigabit-per-second transmission is discussed. It is shown that a laser diode direct modulation scheme for multigigabit-per-second transmission is an extremely efficient approach to transform limited pulse transmission. The return to zero (RZ) format is effective for this approach. By the application of multigigabit-per-second monolithic IC technology, an 8-Gb/s optical regenerator and transmission experiment was successfully conducted through dispersive fiber. The experiment suggests that there is no degradation of transmission characteristics through more than 100 km of single-mode fiber within the wavelength region between zero and weak normal dispersion. >

Asymmetrical bidirectional telecommunication system

Abstract: The present invention pertains to an asymmetrical bidirectional optical communication system of the type comprising a central station, a plurality of user stations, and a plurality of bidirectional optical transmission paths, one of which connects the central station and one of the user stations. The central station is provided with a laser for initiating in the optical transmission path the propagation at a wavelength in the 1100-1700 nm window of a single-mode signal. Each user station is provided with a light source which initiates in the optical transmission path the propagation at a wavelength in the 700-950 nm window of a few-mode signal. Each optical transmission path comprises an optical fiber having transmission characteristics such that the single-mode signal propagates with a total dispersion less than 5 ps/km-nm and the few mode signal propagates with a bandwidth greater than 1 GHz-km.

313 km transmission experiment at 1 Gbit/s using optical amplifiers and a low chirp laser

Abstract: The use of four in-line semiconductor laser amplifiers is reported in an optical fibre transmission experiment. Using direct detection at 1 Gbit/s, a transmission distance of 313 km of non-dispersion-shifted fibre was achieved. This is 142 km longer than previous experiments at similar data rates, and is the first time optical amplifiers have been used to improve transmission distance for fibre-optic communication systems.

Photorefractive dynamic optical interconnects

Abstract: We present and demonstrate a set of dynamic optical interconnects which are based on the double phase conjugate mirror with photorefractive wave mixing. These devices are bidirectional, self-adjusting, and controllable in real time. Uses in various interconnection modes are given.

Wideband subcarrier multiplexed optical communication system operating over more than one octave

Abstract: An optical communication system includes an optical transmitter for transmitting a subcarrier multiplexed optical signal through a single mode optical fiber to an optical receiver. The optical transmitter includes a semiconductor laser diode for generating a light beam. The laser diode is preferably a high speed InGaAsP laser diode emitting in a spectral range of 1.3-1.6 micrometers. The light beam is intensity modulated with a composite modulation signal to provide the optical signal for transmission. The composite modulation signal includes multiple modulated microwave carriers that cover a total bandwidth greater than one octave. Harmonics and intermodulation products do not interfere with transmission, and a favorable signal-to-noise ratio or bit error rate is maintained when the bandwidth of the composite modulation signal exceeds one octave.

Optical broadcast network

Abstract: An optical communications network comprises a number of remote stations connected to a node by optical fiber transmission paths interconnected by power dividers, each remote station including an optical transmitter operating at a peak power and a low duty cycle for a short period Typically the optical transmitter is enabled to transmit information for only 10% or less of the total time and for a maximum of 500 ns

Bidirectional optical data communications system

Abstract: A system and method are disclosed for optically communicating data between two data handling units where one of the data units supplies all of the optical power needed for the optical communications between the two data units. In a preferred embodiment a first data unit comprises a first data source, first and second optical sources of optical energy, and a first optical detector, while a second data unit comprises a second data source, a second optical detector and an optical modulator. In a first mode of operation, a first stream of digital data from the first data source pulse modulates the first optical source on and off causing the first optical source to transmit optical pulses to the second optical detector. These optical pulses are converted by the second optical detector back into a representation of the first stream of digital data for use by the second data unit. In a second mode of operation unmodulated optical energy is transmitted from the second optical source in the first data unit to the optical modulator in the second data unit. A second stream of digital data from the second data source is applied to the optical modulator to accordingly modulate the received unmodulated optical energy. Modulated optical pulses from the optical modulator are therefore reflected to the first optical detector. These reflected modulated optical pulses are converted by the first optical detector back into a representation of the second stream of digital data for use by the first data unit.

Wireless optical communication system

Abstract: A wireless optical short-range communication system adapted for use as an intercom system. The system can be used in fast food restaurants and similar commercial institutions. The communication system (Fig. 4) includes a base station (12) to interconnect via optical communication a group of substantially similar physically spaced-apart, remote units (14, 16). Each one of the remote units includes an optical emitter (33, 37) to transmit an optical message-carrying beam to the base station, and an optical receptor (35, 39) to receive an optical message-carrying beam from the base station. The base station includes a receptor (30) for receiving the optical beam transmitted by the optical emitters of all of the remote units, and an optical emitter (28) to relay the received optical beam to the optical receptors of all the remote units. The base station includes a clock arrangement for synchronizing the operation of the system in a time division multiplexing carrier arrangement, by providing individual discrete time slots for the transmission of the signals from the remote units to the base unit, and for the transmission of the signals from the base unit to the remote units.

Laser diode pumped operation of Er3+-doped fibre amplifier

Abstract: Semiconductor laser-diode pumped operation of an erbiumdoped fibre amplifier, exhibiting 6dB gain and operating at 1536nm, is reported. The amplifier was optically pumped at 807 nm using a self-injection-locked semiconductor laser diode array.

Optical functional device of an optical waveguide type

Abstract: The present invention relates to an optical functional device of an optical waveguide type, particularly to an optical waveguide type with an organic nonlinear optical material suitable for the use in the fields of optical communication or optical information processing. In other words, the present invention provides an optical functional device having an organic nonlinear optical material as an optical waveguide embedded into the surface of a substrate and being an organic nonlinear optical material charged into a hollow part which is composed of a channel as a slit provided on the surface of said substrate and a further substrate for covering the upper part of the channel.

Nonlinear interactions in optical amplifiers for multifrequency lightwave systems

Abstract: Nonlinear interactions that occur in an optical amplifier between the carrier density and multiple optical signals, are described using a small-signal analysis. In multifrequency lightwave systems with channel separations less than 1 GHz, the ratio of the signal power to the total intermodulation interference may be less than 25 dB, for total output intensities 10dB below the amplifier saturation intensity.

All-optical regenerator

Abstract: An all-optical regenerator has been demonstrated using two self-electro-optic effect devices (SEED) and a local pump laser. The regenerator's optical signal processing included clock recovery, data retiming and signal amplification. A 2dB optical gain was attained at a 5 kbit/s data rate.

Optical fiber communications system with optical fiber monitoring

Abstract: Optical communications fibers extend from a central office to subscribers' premises for carrying signals in both directions between optical transmitters and receivers. Each subscriber's optical receiver continuously reflects back to its fiber, and then to the central office, about 20 percent of the light which it receives. At the central office the reflected light is monitored in turn for each subscriber, and is correlated with the signal transmitted to that subscriber to provide a signal for optical time domain reflectometry of the respective subscriber's fiber connection.

Comparison Of Optical Technologies For Intersatellite Links In A Global Telecommunications Network

Abstract: Six optical technologies are evaluated for use in a full-duplex tele­ communications link between geostationary INTELSAT satellites. The six tech­ nologies are based upon the carbon dioxide gas laser, the neodymium-doped yttrium aluminum garnet (Nd:YAG) solid-state laser, the indium gallium arse­ nide phosphide (InGaAsP) semiconductor diode laser, and the gallium alumi­ num arsenide (GaAIAs) semiconductor diode laser (three systems). The salient features of the various technologies are described, and their communications performances are analyzed to determine antenna diameter requirements for various modulation formats. The GaAIAs systems, with their small size, high electrical-to-optical conversion efficiency, direct modulation capability, wave­ length selectability, and high reliability are found to be promising technologies for the full-duplex geostationary intersatellite link. Subject terms: optical communications; intersatellite links; satellite communications.

An optical communications network

Abstract: A passive, all optical communications network in which a single optical source in a central station serves many outstations (eg telephones in customer's premises) Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (6) from a central station (4) The signal is split between several secondary fibres at a first splitter (10) (eg array of passive couplers) and between further sets of fibres at a second set of splitters (12) At this stage there are 120 individual fibres to customer's premises (8) Digital speech or data is sent back to the central station by a laser in the customer's premises operating in a low duty-cycle mode The 120 data streams are interleaved at the branching points