Showing papers on "Optical communication published in 1991"

All-fiber ring soliton laser mode locked with a nonlinear mirror

Abstract: An amplifying nonlinear-optical fiber loop mirror is used as the gain element in an all-fiber ring laser. The resulting double-loop structure resembles a figure eight. The output of the amplifying nonlinear-optical fiber loop mirror is fed back to the input through an optical isolator to ensure unidirectional operation. The laser produces 2-ps transform-limited pulses. The pulse energy corresponds to that of the fundamental soliton in the fiber used.

Generation of fundamental soliton trains for high-bit-rate optical fiber communication lines

Abstract: The authors present a method for the generation of high-quality soliton trains at a high repetition rate of gigahertz to terahertz range During nonlinear propagation of a continuous-wave (CW) dual-frequency signal through a fiber with effective amplification, a train of practically noninteracting fundamental solitons is formed It is shown that the effective amplification can be achieved as in usual fibers with an actual amplification as well as in fibers with nonuniform parameters along the fiber axis The method is demonstrated experimentally Dual-frequency 25 ps pulses at lambda =155 mu m are reshaped into 02 THz combs of 049 ps solitons in fiber with slowly decreasing dispersion It is also shown that stimulated Brillouin scattering (SBS) can prevent a CW soliton train transmission through optical fibers, and suggests a method for suppression of SBS >

16 Gbit/s all-optical demultiplexing using four-wave mixing

Abstract: A novel, purely optical technique for demultiplexing high-speed time-division multiplexed data is proposed and demonstrated. The technique uses optical fibre nonlinearity induced four-wave mixing with a data signal and a probe signal located at different wavelengths. Using only semiconductor laser light sources, 1:4 demultiplexing of 20 ps long, subpicojoule, 2/sup 15/-1 RZ pulses at a data rate of 16 Gbit/s with less than 1 dB penalty is demonstrated.

Combination cable capable of simultaneous transmission of electrical signals in the radio and microwave frequency range and optical communication signals

Abstract: A compact, flexible, communications cable capable of electrical and optical signal propagation simultaneously is provided. The electrical signal is carried by coaxial inner and outer conductors of metal having suitable conductivity which surround and enclose a centrally disposed optical fiber conductor. The cable allows electrical signal propagation over a bandwidth from about 60 cycle D.C. or A.C. as well as radio frequency and microwave signals up to about 100 gigahertz without appreciable signal loss.

High-speed nondirective optical communication for wireless networks

Abstract: The primary obstacles to high-speed communication, namely, shot noise from ambient light, high-capacitance photodiodes and multipath dispersion, are reviewed, and ways to counter them are demonstrated for a prototypical infrared system. The discussion is limited to the physical-layer issues involved in the design of a single high-speed optical link. The focus is on the downlink (from base station to portable), which is a more challenging problem technically than the uplink for two reasons. First, the complexity of the portable receiver is much more constrained than that of the base station, due to power consumption and cost restrictions. Second, the downlink data rates are likely to be much higher than the uplink rates, because downlink communication will include downloading large executable files and possibly video services, whereas uplink communication will be used for transferring working files and keyboard commands which tend to be much smaller. >

High performance interprocessor communication through optical wavelength division multiple access channels

Abstract: A multiprocessor system with a large number of nodes can be built at low cost by combining the recent advances in high capacity channels available through optical fiber communication. A highly fault tolerant system is created with good performance characteristics at a reduction in system complexity. The system capitalizes on the optical selfrouting characteristic of wavelength division multiple access to improve performance and reduce complexity. This paper examines typical optical multiple access channel implementations and shows that the star-coupled approach is superior due to optical power budget considerations. Star-coupled configurations which exhibit the optical self-routing characteristic are then studied. A hypercube based structure is introduced where optical multiple access channels span the dimensional axes. This severely reduces the required degree since only one 1/0 port is required per dimension, and performance is maintained through the high capacity characteristics of optical communication.

Optical pulse-shaping device and method, and optical communications station and method

Abstract: For use, e.g., in the compensation of frequency dispersion in the course of transmission of an optical signal, a pulse-shaping device is provided with a suitably shaped nonplanar mirror (16). When spatially spread-out frequency components--produced, e.g., by a grating (14)--are reflected from such mirror, a frequency-dependent phase shift is introduced; for example, such phase shift may be a third-order function of frequency. Upon recombination of frequencies, a shaped pulse is obtained. Furthermore, third-order compensation can be used to compress amplified light pulses, e.g. as produced by a semiconductor gain medium (80, 81).

Monolithic, surface-emitting, semiconductor visible lasers and spectrometers for WDM fiber communication systems

Abstract: Proof-of-concept devices to create surface-emitting visible lasers are described and demonstrated. A visible, surface-emitting, solid-state diode laser for InGaAs, InP, and GaAs geometries, as well as for several other devices, is discussed. The use of a multilayer system to enhance the waveguide harmonic mixing over a large bandwidth is demonstrated. The resulting surface-emitted light can then be used to measure frequency differences of multiple optical channels in a fiber communication system. It can also be used for nonblocking switching systems. Since phase is preserved by the harmonic mixing, the device is also usable in coherent communication schemes. Experimental measurements of harmonic generation coefficients for a large Al alloy content in AlGaAs are presented. >

A novel multilevel coherent optical system: 4-quadrature signaling

Abstract: A novel multilevel coherent optical system is proposed. It is based on the exploitation of the property that the electromagnetic field propagating in a single-mode optical fiber can be represented by a four-dimensional vector whose components are the phase and quadrature terms of the two polarization components of the electrical field. This allows a wider use of the resources of the electromagnetic field for information transmission in order to obtain a spectrally efficient modulation format with a limited end. The net performance gain with respect to multilevel amplitude and phase modulation (N-APK) and N-PSK increases with an increase in the number of levels N. For instance, for N=32 the gain is 1.6 and 7.7 dB with respect to N-APK and N-PSK systems. The effect of laser phase noise on the system performance is evaluated. >

Trunk and distribution network application of erbium-doped fiber amplifier

Abstract: Recent research on erbium-doped fiber amplifiers and their applications to trunk and distribution networks is described. Simple methods to estimate amplification performances from only three basic erbium-doped fiber parameters are proposed. It is clarified that optical amplifiers greatly influence the development of future optical communication systems. >

Wavelength-multiplexed optical communication system and optical amplifier used therefor

Abstract: An optical communication system comprises: a plurality of optical communication apparatus for communicating signals by using a plurality of communicating lights having different wavelengths; an optical transmitter for transmitting a controlling light having a different wavelength than any of the plurality of wavelengths; an optical transmission line for interconnecting the optical transmitter and the optical communication apparatus to transmit the communicating lights and the controlling light; an optical amplifier for amplifying the communicating lights and the controlling light transmitted over the optical transmission line; and control circuit for discriminating the controlling light amplified by the optical amplifier from the communicating lights and controlling a gain of the optical amplifier to keep a light intensity of the controlling light at a constant level.

Optical frequency division multiplexing network

Abstract: An optical frequency division multiplexing network includes first optical communication paths connected to terminals, respectively, a second optical communication path connected to the outside and a node composed of a selection unit for selecting signals having optical frequencies to be sent to the plurality of terminals, respectively, from signals transmitted through the second optical communication path in optical frequency division multiplexing, a conversion unit for converting the selected signals into signals having a single optical frequency and an output unit for producing the converted signals to the terminals through the first optical communication paths, respectively.

Optical communications system

Abstract: A line monitoring arrangement of an optical fibre communications system carrying system data signals includes a test sequence generator, an optical transmitter and a correlator. The generator generates a sequence of test pulses, and the optical transmitter repeatedly launches the sequence of test pulses into a first end of a transmission line forming part of the communications system. The correlator correlates signals received at the first end of the transmission line with the sequence of test pulses to identify returned test pulse sequences. The test pulse sequences and system data signals are superimposed onto the transmission line.

Switching system of optical transmission lines for protecting from trouble

Abstract: A system for optical communication between first and second optical terminal stations, containing a plurality of working optical transmission lines each for connecting between the first and second optical terminal stations, a protection optical transmission line. Each of the first and second optical terminal stations contains a plurality of working pieces of optical terminal equipment, connected to the respective working optical transmission lines, a protection piece of optical terminal equipment connected to the protection optical transmission line, and a plurality of bidirectional optical signal paths, provided corresponding to the respective working pieces of optical terminal equipment, and each operative to connect the corresponding working piece of optical terminal equipment to the protection piece of optical terminal equipment.

Time-division optical communications in multiprocessor arrays

Abstract: An optical communication structure for multipro­ ceSsor arrays that exploits the high communication bahdwidth of optical waveguides is proposed. The struc­ turle takes advantage of two properties of optical signal trqnsmissions on waveguides. Namely. unidirectional pfppagation and predictable propagation delays per unit length. Two novel time-division mUltiplexing approaches are proposed for non SIM D environments to obtain a communication bandwidth comparable to that of mes­ sage pipe lining in SIMD environments. Analysis and simulation results are given to evaluate the communica­ tion effectiveness of the system. A clock distribution method is also proposed to address potential synchroni­ zation problems. Finally. feasibility issues with current andfuture technologies are discussed.

Optical coherence multiplexing for interprocessor communications

Abstract: The development of an optical circuit that multiplexes gigabit-per- second electronic data streams into a very broad bandwidth (greater than 10 Gbit/s) optical signal would greatly enhance interprocessor communications in a parallel computer. One possibility that we are investigating is coherence multiplexing. In this method, time delays exceeding the coherence time of the light source are used to achieve multiplexing. We have analyzed the limitations of coherence multiplexing for high-speed data links. For the geometry that we are investigating, the analysis shows that the signal decreases inversely as the square of the number of channels. Noise sources include photon shot noise, excess noise (classical optical field fluctuations) and detector noise. A suitable optical source must have a smooth broad spectrum. Superluminescent diodes or edge emitting diodes are the best candidates. We show how all these factors affect the total information transfer rate. An integrated optical circuit for coherence multiplexing is being designed and built. This device is an array of four Mach-Zehnder interferometers integrated on a lithium niobate substrate. The differential delays will be achieved using proton exchange. Each interferometer will have two sets of electrodes, one for signal modulation and a second for fine adjustments of the delay. 31more » refs., 9 figs.« less

Intermodulation and harmonic distortions of laser diodes with optical feedback

Abstract: Analytical expressions for the second-order harmonic and the third-order intermodulation distortions of laser diodes with optical feedback are derived It is shown theoretically and experimentally that optical feedback from the transmission fiber considerably enhances intermodulation and harmonic distortions of laser diodes Third-order intermodulation distortions up to -15 dBc must be expected for two-tone modulation and low-intensity modulation indexes m approximately=7% per carrier, which affects the performance of subcarrier multiplexed (SCM) communication systems To avoid additional distortions the external feedback level must be two orders of magnitudes lower than the critical external feedback level of the laser diode >

The effect of reflections on the system performance of intensity modulated laser diodes

Abstract: The performance degradation incurred by unwanted external reflections in high-speed digital optical communication systems using intensity-modulated single-longitudinal-mode laser diodes is investigated by numerical simulation of the rate equations. The effects of intensity modulation on the chaotic behavior in the laser output are examined and performance estimates for 0.5, 2.5, and 5 Gb/s systems are made. For example, it is found that to incur less than 0.25-dB power penalty in a 2.5-Gb/s system using a positive-intrinsic-negative photodetector, the reflected light in the laser pigtail should be at least 36 dB below that of the transmitted light. >

Optical communication apparatus using intensity modulation

Abstract: A transmitter unit (100) including a semiconductor laser (101) as a carrier light exciting source, a biasing source (102) for providing the semiconductor laser with a d.c. biasing current, an external modulator (105) for intensity-modulating an output light of the semiconductor laser according to a transmission signal, and means (107; 210; 510; 701, 702, 703, 704) for causing the external modulator to output only the carrier light and either side-band light. Also provided is a receiver unit (150) including a receiver (151) for square-law detecting the carrier light and the side-band light supplied from the transmitter unit to obtain an electric signal, and a linear filter (152) for equalizing this electric signal. The present invention results in an optical communication apparatus capable of easily equalizing dispersion distortion caused in a transmission path (115) having a large dispersion from a light-intensity modulated light signal transmitted therethrough.

Photonic packet switch using semiconductor optical amplifier gates

Abstract: Photonic packet switching using semiconductor optical amplifiers is reported. The optical amplifiers are used as gates to switch the optical packets and also as modulators to provide address header replacement. This eliminates the need for the fibre delay line used in previous photonic packet switching demonstrations, and allows the possibility of packet switch integration onto a single substrate. The photonic packet switch has a crosstalk performance better than 40 dB.

Long-haul coherent optical fiber communication systems using optical amplifiers

Abstract: Studies on long-haul coherent optical fiber communication systems with in-line optical amplifier repeaters are made theoretically and experimentally. By theoretical calculation it was found that coherent systems can achieve wider dynamic range for an amplifier input power as compared with the intensity-modulation direct-detection (IM-DD) systems. The feasibility of such systems using traveling-wave semiconductor laser amplifiers (TWSLAs) and erbium-doped fiber amplifiers (EDFAs) was investigated, and 546 km, 140 Mb/s CPFSK transmission using TWSLAs and 1028-km, 560-Mb/s CPFSK transmission using EDFAs were successfully demonstrated. >

Performance degradation due to four-wave mixing in multichannel coherent optical communications systems

Abstract: Bit-error rate (BER) degradation due to four-wave mixing (FWM), in multichannel coherent optical communications systems, is studied. In particular, analytic expressions for the BER are derived for ASK, PSK, and FSK modulation schemes. The effects of input power, fiber chromatic dispersion, number of channels, and inter-channel spacing on the BER degradation is explicitly shown. The results show that, on the basis of equal peak power per channel, the ASK noncoherent detection scheme has the best performance, while the PSK coherent detection scheme has the poorest performance. For 1.55 μηι 100 channels transmission systems, having 5 GHz inter-channel spacing, the analysis predicts a maximum allowable input power per channel to be 2 dBm for 100 km of conventional single-mode fibers, and only — 9 dBm for 100 km of dispersion-shifted fibers. Finally, these analytical results are found to be in good agreement with recent experimental results.

Optical communications system and method

Abstract: Optical communications systems and methods are disclosed which involve routing optical signals through communications nodes which are controlled such that optical power arriving at input ports is linearly distributed to output ports. Such distribution may be realized by electro-optical, acousto-optical, or electro-mechanical controllable linear divider-combiner devices (401, 405, 411, 415). Preferred systems including optical fiber links can be designed to make maximum use of physically realizable bandwidth, and to achieve high reliability in case of faults.

Recent advances in long-wavelength semiconductor lasers for optical fiber communication

Abstract: A brief history of the semiconductor laser and a short tutorial on its basic operating principles are given. Some key criteria for semiconductor lasers to be used in advanced systems are discussed. Various advanced laser structures (including single-frequency, high-speed and wavelength tunable lasers, laser transmitter optoelectronic integrated circuits, and coherent receiver photonic integrated circuits) are presented together with their performance characteristics. >

Integrable semiconductor optical correlator, parametric spectrometer for communication systems

Abstract: A broadband integrable waveguide correlator and parametric spectrometer is analyzed both theoretically and experimentally. The correlator can measure pulsewidths from subpicosecond to tens of picoseconds centered at wavelengths of 1.06 to 1.7 mu m without any mechanical alignment. The parametric waveguide spectrometer is shown to resolve not only the mode of a 1.3- mu m Fabry-Perot laser diode but also the shift of the modes as a function of bias current. The improvement of these integrable waveguide structures and their possible use in laser stabilization, the defining of fixed frequency channels, and other applications for coherent communication systems are also discussed. >

90 degree optical hybrid for coherent receivers

Abstract: The power losses and noise of the present 90-deg hybrid optical coherent receiver are minimized through the use of a six-port configuration in which channel balancing is furnished by half-wave plates. The 90-deg shift is introduced between orthogonally polarized beam components by a quarter-wave plate, and the output ports are phase-shifted by 180 deg through the sole use of the half-wave plates and polarizing beam splitters.

Optical communication network system and communication method using the same

Abstract: Disclosed is an optical communication network system including a base station (2) for generating a plurality of beams having different wavelengths, an optical transmission line (1a,1b) for transmitting the plurality of beams emitted by the base station (2), an optical transmitter (3,4.....10), connected to the optical transmission line, for selecting one of the plurality of beams transmitted through the optical transmission line and modulating the selected beam in accordance with a signal to be transmitted, and an optical receiver (3,4......10) connected to the optical transmission line, for receiving the signal transmitted using the selected beam. An optical communication method for the above system is also disclosed.

Observation of low-chirp modulation in InGaAs-InAlAs multiple-quantum-well optical modulators under 30 GHz

Abstract: Modulated light spectra were measured in long-wavelength InGaAs-InAlAs multiple-quantum-well intensity modulators under 30-GHz large-signal modulations. The linewidth broadening factor alpha is determined from the relation between the intensity modulation index and the sideband strength relative to the carrier. The minimum alpha value is estimated to be 0.70 at 1.54 mu m, which is almost the same as the lowest value so far reported in a bulk Franz-Keldysh modulator. This is significantly lower than what is obtained from direct-intensity modulation of injection lasers, making this a useful device for application to high-bit-rate long-haul optical communication systems. >