Showing papers on "Optical communication published in 1986"

Spread spectrum fiber-optic local area network using optical processing

Abstract: Spread spectrum code division multiple access (CDMA) allows asynchronous multiple access to a local area network (LAN) with no waiting. The additional bandwidth required by spread spectrum can be accommodated by using a fiber-optic channel and incoherent optical signal processing. New CDMA sequences are designed specifically for optical processing. It is shown that increasing the number of chips per bit, by using optical processing, allows an increase in capacity of a CDMA LAN. An experiment is performed demonstrating the performance of an optical CDMA LAN, operating at 100 Mbd with three users.

Impact of Laser Phase Noise on Optical Heterodyne Communication Systems

Abstract: The impact of laser phase noise on optical heterodyne communications receivers is analyzed in terms of the system signal-to-noise ratios and error rates. An ASK receiver, three FSK receivers and a DPSK receiver are investigated. The maximum permissible laser linewidth Δν is evaluated for each of these receivers and compared with previously published theoretical and experimental results. It is shown that Δν depends on the system data rate R and on the modulation/demodulation technique chosen. For example, DPSK receivers require at least Δν ^ 0.7% of R while FSK receivers with postdetection frequency discrimination require at least Δν ^ 1.9% of R if the mark-space separation 2 fd is equal to R. At the same time, ASK receivers with envelope postdetection processing, and FSK receivers with large frequency deviation are much more tolerant to phase noise: they only require Av<9%ofR.

Phase modulation to amplitude modulation conversion of CW laser light in optical fibres

Abstract: We have measured the induced amplitude modulation of sinusoidally phase-modulated CW 1.5 ?m laser light propagating in a single-mode fibre. Amplitude modulation approaching 100% was observed for light phase-modulated at 4 GHz and transmitted through 50 km of fibre. PM-AM conversion produces a power penalty in coherent transmission systems.

An experiment on high-speed optical time-division switching

Abstract: An experimental high-speed optical time-division switching system has been realized. The system is able to exchange digitally encoded color video signals at 256-Mbit/s highway speed. Bistable laser diodes and directional coupler switch matrices are adopted as optical memories and optical read/write gates, respectively, in an optical time switch. The bistable laser diode operates as an optical flip-flop circuit which can be set and reset by optical and electrical signals, respectively. 256-Mbit/s highway speed has been realized with sufficient input highway operating margin using the same wavelength as that of bistable laser diodes for an electrooptical converter. Results of this experiment will be helpful data for use in constructing future optical telecommunications networks, where a variety of broad-band services need to be realized.

Balanced dual-detector receiver for optical heterodyne communication at Gbit/s rates

Abstract: A balanced dual-detector receiver which requires low local-oscillator power has been designed and fabricated for optical heterodyne detection at 1·5 ?m wavelength and Gbit/s rates. The receiver consists of two InGaAs PIN photodiodes connected with opposite polarities to a high-impedance GaAs FET amplifier. Frequency response, noise suppression and noise spectrum measurements are reported.

Bidirectional fibre-optical transmission using a multiple-quantum-well (MQW) modulator/detector

Abstract: We demonstrate a simple architecture for bidirectional optical fibre transmission which uses an MQW device as both modulator and photodetector. We achieved transmission of 50 Mbit/s and 600 Mbit/s in both directions over one 3.34 km-long single-mode fibre at 860 nm wavelength. Coherent Rayleigh interference was found to be a limiting factor in single-source bidirectional systems.

Ten-channel coherent optical fibre transmission

Abstract: A laboratory ten-channel coherent fibre-optic broadband transmission system is reported. The frequency-division-multiplexed optical carriers are separated by 6 GHz and are demultiplexed by a tunable heterodyne receiver having a sensitivity of -46 dBm at a bit error rate of 10-9. In this system a maximum number of 64 channels can be installed.

Dispersion penalty analysis for LED/single-mode fiber transmission systems

Abstract: GREAT DEAL of attention has been focused recently on telecommunication systems based on single-mode fiber (SMF) and LED light sources for future deployment in the local network and subscriber loop. These systems combine the advantages of the low loss, large bandwidth, and upgrade potential of single-mode fiber with the high reliability and temperature stability, as well as the low cost of LED’s. Recent experiments have demonstrated the feasibility of LED-SMF ’ systems for transmission rates up to 560 Mbit/s and span lengths (at 140 Mbit/s) up to 50 km [1]-[lo]. Chromatic dispersion is a potential limitation at these bit rates and span lepgths, however, because of the broad spectral widths of LED’s. Even for a practical system of shorter transmission distance, the dispersion penalty remains an important consideration in the power budget since the total power coupled into single-mode fiber is relatively small for LED systems. It is thus important to have realistic estimates of dispersion penalties in LED-SMF system design. Penalties for chromatic dispersion in multimode fiber have been calculated for LED’s based on the assumptions of an optical receiver which has been re-equalized to compensate for the fiber dispersion, and an f receiver noise spectral density [ 111, [12]. In practical systems, however, these assumptions are often not applicable. In this paper we present a new calculation of dispersion penalties arising from intersymbol interference for LED-SMF systems with no re-equalization (the more commonly adopted scheme), and compare the results obtained with a treatment of the re-equalized system which considers both white, andf2 receiver noise spectral densities. Simple approximations of dispersion penalties are derived, and bitrate distance product limits are presented as a useful estimation tool for system feasibility studies. Single-mode fiber transmission experiments at 90, 140, and 560 Mbit/ s have been performed using 1.3- and 1.5-pm LED’s [3][6], and the measured dispersion penalties are compared with the results of the above analysis.

A novel integrated optics wavelength filter in InGaAsP-InP

Abstract: An InGaAsP-InP integrated optics wavelength selective device is proposed and demonstrated. It utilizes coupling between epitaxial layers with different refractive indices and thicknesses. The device is suitable for integration to form, e.g., a monolithic receiver for wavelength division multiplexed optical communication systems. Design considerations are given. The filter bandwidth and center wavelength can be freely chosen, and bandwidths as narrow as 1.5 nm at 1.3 or 1.55 μm center wavelength are shown feasible. Electrical tuning is possible. Experimental filters show that devices can he fabricated with performance in good agreement with theory, The 22-nm -3-dB bandwidth at 1.12-μm center wavelength presently demonstrated is limited by the measurement system.

System limitations due to four-wave mixing in single-mode optical fibres

Abstract: The transmission of a multichannel coherent optical system is limited by four-wave mixing. In a 100-channel monomode fibre link, 5 GHz channel separation, ?20 dB crosstalk level, the input power per channel should be lower than 0 to ?5dBm for a subscriber line (5 km), or ?10dBm for a trunk line (>100 km), employing low-loss dispersion-shifted fibre.

Effect of frequency chirping on the performance of optical communication systems.

Abstract: The effect of frequency chirping on the performance of optical communication systems is analyzed theoretically using a simple but realistic model for the chirped pulses emitted by a directly modulated semiconductor laser. The effect of pulse-edge sharpness is investigated by considering the propagation of super-Gaussian chirped pulses in a dispersive single-mode fiber. The results are presented using the parameter values appropriate for a 1.55-μm optical communication system employing conventional silica fibers and are in qualitative agreement with the reported experimental observations.

Optically controlled integrated optical switch

Abstract: An optically controlled integrated optical switch having a body made up of entirely crystalline silicon. More specifically, the body has a pair of channel waveguides intersecting at an X-like configuration forming therein an intersection crossover region. An electrically controlled optical source is positioned over the crossover region to shine intense, short wavelight on the crossover region in order to generate numerous electron-hole pairs in the waveguide material. These charge carriers alter the refractive index of the intersection region. A controllable current source is used to adjust the optical output power of the optical source. This, in turn, changes the amount of optical cross coupling of light between the intersecting waveguides.

Optical signal receiving apparatus with compensation for peripheral light

Abstract: An improved optical signal receiving apparatus useful in optical communication is provided. Peripheral light can be measured and compared to determine if its intensity is above a certain predetermined level. The apparatus can display an indication when the measured intensity is over the predetermined level, such as through an emission at a predetermined wavelength.

InGaAsP/InP monolithic integrated circuit with lasers and an optical switch

Abstract: InGaAs/InP monolithic integrated circuits composed of a compact carrier-injection optical switch and distributed feedback laser diodes are fabricated. These integrated circuits have a variety of functions, such as monolithic modulators, switches and optical amplifiers for optical communication systems.

A Conceptional Design on Optical Frequency-Division-Multiplexing Distribution Systems with Optical Tunable Filters

Abstract: Optical frequency-division-multiplexing distribution systems providing more than ten frequency multiplexed optical signals separated by on the order of gigahertz, distribute signals to plural receivers, where one of the signals is selected by a frequency selection switch (FS-SW). This paper describes the design of an optical frequency-divisionmultiplexing distribution system. Investigation is made of periodic filters for frequency division multiplexers and FS-SW, and the optical source, as well as single-mode fiber polarization mode dispersion. Preliminary transmission experiments using a bit rate of 450 Mbits/s, fiber length of 13 km, and frequency spacing of 11 GHz are also demonstrated at a 1.5 μm wavelength to show the design's suitability.

Crosstalk in optical amplifiers for two-channel transmission

Abstract: Optical amplifiers for two-channel transmission are investigated. Intensity modulation in one channel causes crosstalk in the other channel via the change of the complex refractive index in the amplifier. The amount of crosstalk is connected with the linewidth enhancement factor α.

Suppression of stimulated brillouin backscattering by psk modulation for high-power optical transmission

Abstract: High-power optical fibre transmission combined with coherent detection offers a significant advantage in terms of length between repeaters. However, nonlinear optical effects limit the level of power into a fibre to a few milliwatts. The paper reports on the initiation and suppression of stimulated Brillouin scattering using phase shift keying at 1320 nm, discusses the effect of signal statistics on the level at which the nonlinear effect appears, and introduces and experimentally confirms an upper bound on the digital sum variation of codes. It emerges that the code requirements for high power, high bit rate, coherent systems can easily be met.

All optical repeater

Abstract: An all-optical device containing saturable gain, saturable loss and unsaturable loss regions which functions to transform weak, distorted optical pulses into uniform standard-shape pulses. The device performs thresholding, amplification and pulse shaping as required from an optical repeater, and may be implemented in semiconductor technology.

Design and fabrication of low-loss and low-crosstalk polarization-maintaining optical fibers

Abstract: Low-loss and low-crosstalk polarization-maintaining optical fibers (called PANDA fibers), which are potentially useful for coherent optical communication systems, have been fabricated based on the optimum design. Transmission loss of 0.22 dB/km, comparable to that of commercially available single-mode fibers, and crosstalk of -27 dB in a 5-km length, corresponding to the polarization-mode-coupling coefficient of 4.0 \times 10^{-7} m-1, have been demonstrated in the 1.56-μm wavelength.

TDMA fibre-optic network with optical processing

Abstract: A fibre-optic network with time-division multiple access (TDMA) is implemented using optical processing. The network is capable of accommodating 50 stations transmitting at 10Mbit/s. Synchronisation is achieved using a central optical source with 2ns pulses. Integrated electro-optic modulators and optical fibre delay lines are used to multiplex the stations.

Coherent optical receiver for 680 Mbit/s using phase diversity

Abstract: A coherent optical receiver using a multiport optical coupler to provide phase diversity is described. By this means, only homodyne bandwidth is required in the signal processing, but with tolerances on the frequency tracking typical of heterodyne systems. Measured sensitivities with limited local-oscillator power are −47.5 dBm at 320 Mbit/s and −42 dBm at 680 Mbit/s. The results at the higher bit rate are strongly influenced by limited receiver module bandwidth.

Rare-earth-doped fiber lasers

Abstract: By virtue of their broad fluorescence linewidth, rare-earth-doped single-mode fiber lasers could allow the construction of tunable sources and broadband optical amplifiers for wavelength division multiplexing long-distance optical communications systems. Similarly, doped-fiber amplifiers could also provide a means of overcoming soliton propagation losses.

Performance of homodyne detection of binary PSK optical signals

Abstract: This study evaluates the performance of an optical receiver for binary phase shift keyed (BPSK) signals in the presence of noise originating from the photodetectors and the phase fluctuations of the optical sources. Analysis of the homodyne detection process shows that the performance is degraded by two effects: One due to the phase error fluctuations of the recovered carrier and the other due to reduction of the energy per bit available for data recovery. The resulting power penalty can be minimized by dividing in an optimal way the received optical signal between the carrier recovery and the data recovery circuits of the receiver. The minimum penalty thus obtained depends on the 3-dB linewidth and on the transmission rate. For example, a penalty of 0.5 dB, relative to the quantum limit of 9 photon bit needed to achieve a BER of 10-9, imposes a minimum transmission rate of about 180 Gbit/s when the optical source has a 3-dB linewidth of 20 MHz.

Optical communication system in the subscriber loop

Abstract: The invention relates to an optical communication system for transmitting subscriber-assigned information in both directions between a center (1) and a plurality of subscribers (3ato 3n), particularly to the subscriber loop of a broadband communication system. In a remote distribution facility which is of either distributed (FIG. 1) or lumped (FIG. 2) design, the optical waveguides (5ato 5n) of a group of subscribers living or working near each other are coupled to a common optical waveguide (4) (or to two common optical waveguides) connected to the center (1). Subscriber-assigned signals to be transmitted from the center to the subscribers are combined into an electric time-division-multiplex signal which is transmitted as an optical signal with a single wavelength (λ o ) to the vicinity of the subscribers and distributed to the latter. From the electric time-division-multiplex signal, each of the subscribers takes only the signal intended for him. The signals to be transmitted from the subscribers to the center are transmitted as optical signals with subscriber-assigned wavelengths (λ l to λ n ) through subscriber-as-signed optical waveguides to the common optical waveguide (4), are coupled into the latter, and are transmitted as a wavelength-division-multiplex signal to the center.

Theoretical limit of repeater spacing in an optical transmission line utilizing Raman amplification

Abstract: The limit of repeater spacing is investigated theoretically for optical transmission lines utilizing stimulated Raman scattering to amplify the signal light. Achievable repeater spacing is numerically estimated on the basis of coupled power equations and measured fiber characteristics for various signal wavelengths and relative index differences. Three types of transmission line configurations are considered, i.e., utilization of forward only, backward only, and bidirectional amplification. In the third case, a transmission distance of more than 400 km is predicted for an input signal light power of 100 μW, a signal wavelength of 1.57 μm, and a pump power of 0.5 W using a fiber with a relative index difference of 1 percent for signal light amplification.

Effect of fiber-far-end reflections on the bit error rate in optical communication with single-frequency semiconductor lasers

Abstract: For a semiconductor laser oscillating predominantly in a single longitudinal mode, the reflection feedback from the far end of an optical fiber generates closely spaced side modes corresponding to the external-cavity longitudinal modes. Using a simple model, it is shown that power fluctuations associated with these feedback-induced side modes can decrease the receiver sensitivity over its shot-noise-limited value for a given bit error rate. Since fiber dispersion plays a minor role, the reflection-induced power penalty is likely to occur for all fiber lengths commonly employed in optical communication systems.

Digital pulse position modulation over optical fibres with avalanche photodiode receivers

Abstract: The question of performance evaluation in digital pulse position modulation (PPM) transmitted over slightly dispersive optical fibres and detected by avalanche photodiodes (APD) is considered. In view of numerical complexity implicit in exact average error probability evaluation, a bound on this probability is derived. Making use of this bound we conclude that optical fibre PPM receivers based on APDs offer some improvement over optical fibre PPM receivers based on PINFETs and a big improvement when compared with PCM receivers.

Ultimate performance of heterodyne/coherent optical fiber communications

Abstract: Research and development of heterodyne/homodyne and coherent optical fiber communications have expanded rapidly because of the expectation for repeater separation elongation and superwide-band frequency-division multiplexing. In this paper, recent progress in heterodyne/coherent optical fiber communications is reviewed with emphasis on theoretical and experimental studies pursuing its ultimate performance. The topics discussed are: the recent and future trend in the system design, the transmitter power limit due to fiber nonlinearity and the resulting repeater separation limit, the laser noise problem, the fiber polarization control and polarization diversity, the possibility of narrow frequency-separation frequency-division multiplexing, and finally, a comparison of heterodyne/coherent and photon-counting communications.

Optical fiber bidirectional transmission system

Abstract: A bidirectional optical communications system is described using a multiple quantum well structure as both a photodetector and light modulator.