Showing papers on "Optical communication published in 1993"

Simulation of multipath impulse response for indoor wireless optical channels

Abstract: A recursive method for evaluating the impulse response of an indoor free-space optical channel with Lambertian reflectors is presented. The method, which accounts for multiple reflections of any order, enables accurate analysis of the effects of multipath dispersion on high-speed indoor optical communication systems. A simple algorithm for computer implementation of the technique and computer simulation results for both line-of-sight and diffuse transmitter configurations are also presented. In both cases, it is shown that reflections of multiple order are a significant source of intersymbol interference. Experimental measurements of optical multipath, which help verify the accuracy of the simulations, are discussed. >

A terahertz optical asymmetric demultiplexer (TOAD)

Abstract: A device capable of demultiplexing Tb/s pulse trains that requires less than 1 pJ of switching energy and can be integrated on a chip is presented. The device consists of an optical nonlinear element asymmetrically placed in a short fiber loop. Its switching time is determined by the off-center position of the nonlinear element within the loop, and therefore it can use the strong, slow optical nonlinearities found in semiconductors, which all other fast demultiplexers seek to avoid. The switch's operation at 50 Gb/s is demonstrated, using 600-fJ control pulses. >

Simple measurement of fiber dispersion and of chirp parameter of intensity modulated light emitter

Abstract: We report a novel method to measure two important parameters for optical fiber intensity modulated transmission systems: dispersion of optical fibers and chirp parameter of modulated light emitters. The method is easy, quick, and accurate for chirp parameter in the -10-to-10 range. >

Spectrum-sliced fiber amplifier light source for multichannel WDM applications

Abstract: A potentially inexpensive light source for multichannel WDM applications is proposed The high-power amplified spontaneous emission (ASE) from an erbium-doped fiber amplifier (EDFA), which is already in the single-mode fiber, can be efficiently divided into many channels by using an integrated optic wavelength-division-multiplexing (WDM) demultiplexer This spectrum-sliced ASE can be used as light sources for WDM systems in place of several wavelength-selected DFB lasers To demonstrate the principle, the 40-nm-wide ASE spectrum of an EDFA was sliced using a narrow optical filter (3-dB bandwidth: 13 nm), and the resulting source was used for the transmission of up to 17 Gb/s of data The problem of spontaneous-spontaneous beat noise in these sources is dealt with It is estimated that the total capacity would be about 40 Gb/s, realistically, since the channel spacing should be at least three times the optical bandwidth of each channel to avoid crosstalk >

Eigenvalue communication

Abstract: The authors propose a communication method for a nonlinear and dispersive medium such as an optical fiber that is based on eigenvalues of associated equations for the wave amplitude. In optical communications, the communication distance measured by the carrier wavelength reaches the order of 10/sup 11/-10/sup 13/. As a result, dispersive and nonlinear effects, even if small, contribute significantly to the distortion of signal information contained in waveforms or in frequency spectra. Thus, it is desirable to use other parameters which remain unaltered. The eigenvalues of the associated equation for the nonlinear Schrodinger equation which describes the lightwave envelope in fibers constitute such parameters. Soliton-based communication corresponds to the case of one eigenvalue. >

Integrated solid state light emitting and detecting array and apparatus employing said array.

Abstract: There is provided an integrated semiconductor source-detector matrix (10) in which solid state photonic diodes (12a-12i) are configured as LEDs, disposed on a substrate and coupled to electronic circuits so that the diodes can be individually driven to emit light to detect light as may be desired. Providing an integrated matrix (10) of light source and light sensor units disposed in close proximity results in each unit having nearly coextensive fields of view and illumination (157). Apparatus, such as bar code and optical readers utilizing such a matrix are shown, and are insensitive to the diffusion and laminate effects. In alternate embodiments the matrix (10) is coupled to remote sensors (94) or another similar matrix to provide optical communication and interchange devices having high bandwidth.

Polarisation-independent phase conjugation of lightwave signals

Abstract: The authors propose and demonstrate a technique for phase conjugation of lightwave signals with an efficiency that is independent of the signal polarisation Using either optical fibre or a semiconductor optical amplifier as the nonlinear element, a signal-polarisation dependence of about ±ldB in the conjugation efficiency was obtained

Wavelength division multiplexed optical communication transmitters

Abstract: A wavelength-division-multiplexed transmitter has a single modulator modulating the output of an array of individually actuable semiconductor lasers integrated onto the same substrate as the modulator. An optical combiner integrated onto the same substrate between each of the lasers and the single modulator combines the outputs of the lasers. One or more of the lasers are activated as desired for wavelength division multiplexing.

Time-division optical communications in multiprocessor arrays

Abstract: An optical communication structure is proposed for multiprocessor arrays which exploits the high communication bandwidth of optical waveguides. The structure takes advantage of two properties of optical signal transmissions on waveguides, namely, unidirectional propagation and predictable propagation delays per unit length. Because of these two properties, time-division multiplexing (TDM) of messages has the same effect as message pipelining on optical waveguides. Two TDM approaches are proposed, and the combination of the two is used in the design of the optical communication structure. Analysis and simulation results are given to demonstrate the communication effectiveness of the system. A clock distribution method is proposed to address potential synchronization problems. Feasibility issues with current and future technologies are discussed. >

Stable single-mode erbium fiber-grating laser for digital communication

Abstract: In this paper we report the fabrication of a short, robust, single-mode Er/sup 3+/ fiber-grating laser. This laser is proven by the successful outcome of a long-term bit-error-rate test at the 10/sup -15/ level in a 5- G/s fiber transmission experiment. In the process we present a new pumping geometry, the elucidation of one origin of relaxation oscillations that have plagued previous lasers and the demonstration of a simple electronic feedback scheme for suppressing them. This prototype source shows real promise for use in a high-speed communications system. >

Optical frequency comb generator using phase modulation in amplified circulating loop

Abstract: A method to generate a comb of precisely spaced optical frequencies over a terahertz span is presented. This scheme uses a sinusoidally driven phase modulator and an optical amplifier placed within an optical fiber loop, so that the modulation is enhanced by multiple passes through the loop. By maintaining the loop round-trip gain slightly below unity, a comb of tens to hundreds of frequencies can be generated. If the loop input is derived from a laser locked to an absolute frequency reference, then each of the output frequencies has an absolute accuracy approaching that of the input. >

Wide-angle, high-speed, free-space optical communications system

Abstract: A free-space optical communications system for transmitting data between an aircraft computer system (14) and a ground-based computer system (12). The system includes a pair of corresponding optical transmitters (36) and optical receivers (38) that transmit and receive optical signals transmitted between the two computer systems. Included within each optical transmitter is one or more light-emitting diodes (42) that produce optical signals corresponding to the data to be transmitted. A beam-forming prism (44) is bonded directly to the light-emitting diodes to direct the optical signal uniformly over a target area. The optical receiver includes one or more infrared windows (50) to reduce the amount of ambient light received by the optical receiver. A compound parabolic concentrator (64) collects light transmitted from the optical transmitter and directs the light onto an avalanche photodiode (66), which includes thermal bias compensation. An AC network couples the output signal of the photodiode to a transimpedance amplifier (70). An optional optical shroud (34) surrounds the optical transmitters and receivers to further reduce the amount of ambient light that is received by the optical receivers.

20-nm optical wavelength conversion using nondegenerate four-wave mixing

Abstract: Wavelength conversion of optical signals over 20 nm is demonstrated using highly nondegenerate four-wave mixing in a semiconductor traveling-wave optical amplifier. This technique has the potential for extremely-high-speed operation and allows continuous tuning of both input and output wavelengths over the amplifier gain bandwidth. It is demonstrated that, even for such a large wavelength conversion range, it is possible to obtain conversion efficiencies in excess of -10 dB and high extinction ratios. The feasibility of the technique is demonstrated by system measurements at 622 Mb/s, showing a 1.1-dB power penalty at 10/sup -9/ bit error rate (BER). >

A fiber chromatic dispersion compensation technique with an optical SSB transmission in optical homodyne detection systems

Abstract: A fiber chromatic dispersion compensation technique with optical single-sideband (SSB) transmission in optical homodyne detection systems is described. The chromatic dispersion compensation technique is demonstrated in a 6-Gb/s SSB phase-shift-keying (PSK) homodyne detection system equivalent experiment. A 270-km conventional single-mode fiber is used as a transmission medium at 1.55 mu m, and a microstrip line is used as a delay equalizer. The effect of compensating for the chromatic dispersion with the microstrip line is verified by improvement of eye-opening. >

Tunable liquid-crystal Fabry-Perot interferometer filter for wavelength-division multiplexing communication systems

Abstract: We explain how to obtain the bandwidth and tunable range required for wavelength-division multiplexing communication systems and how to design tunable liquid-crystal Fabry-Perot interferometer filters. The main factors determining the performance are liquid-crystal loss, mirror loss, surface roughness, and parallelism, as well as mirror reflectivity and cavity gap. Experimental results closely agree with the designed performance. Temperature dependence, response time, acceptable input power, and reliability are investigated. Pigtailed polarization-independent filter modules with a Peltier controller are made and are shown to have low polarization dependence ( >

New architectures for optical TDM switching

Abstract: A systematic theoretical study of architectures for optical TDM switching, using lithium niobate optical switches and optical fiber delay lines for storage, is undertaken. The architectures allow the bit rate and wavelength transparency of these devices to be exploited. A technique involving recursive definition and proof is used to define the networks, which are mathematically related to Benes and Waksman networks. This produces architectures that are very different from existing optical TDM networks. They exhibit economical use of components, which reaches the theoretical minimum in some cases. The use of feed-forward rather than feed-back delays give these networks superior crosstalk performance and more uniform attenuation than existing designs. >

Postdistortion circuit for reducing distortion in an optical communications system

Abstract: A postdistortion network for a receiver at a receiver location in an optical transmission system is disclosed. The receiver converts an optical signal carried over an optical transmission link to an RF signal. The postdistortion network includes an input terminal for receiving the RF signal and a distortion generator for generating a distortion signal from the RF signal. An adjusting circuit for adjusts the phase and amplitude of the distortion signal based on distortion at said receiver location. The adjusted distortion signal is combined with the RF signal in order to cancel or substantially suppress distortion in the RF input signal. The present invention permits individual receivers in an optical transmission system to be compensated for distortion which may be unique to that receiver location. A communications system including a predistortion network and a postdistortion network is also disclosed.

All-optical high speed demultiplexing with a semiconductor laser amplifier in a loop mirror configuration

Abstract: A novel, purely optical technique for demultiplexing high speed time-division multiplexed data is demonstrated. The technique uses the SLALOM (semiconductor laser amplifier in a loop mirror) The data rate is not limited by the gain recovery time of the semiconductor laser amplifier. The same technique can also be used for multiplexing. >

Dimensionality in optical fields and signals

Abstract: The spatial chaos in optical fields that result from diffraction of plane waves by random-phase objects with a larger-than-unity phase dispersion is studied. An analog method for evaluating the dimension of chaos in the field is described, and a real-time measuring device that uses this method is proposed. A new method for evaluating the signal-to-noise ratios in optical signals is also proposed.

Semiconductor laser amplifier as optical switching gate

Abstract: The properties of a semiconductor laser amplifier as optical switching gate are investigated. Particular attention is paid to gain, contrast ratio, and switching time of the device. These properties are studied experimentally and theoretically with respect to the injection current, optical input power, and cavity resonances. The experimental arrangements and the theoretical method are described. As an example of the various applications of semiconductor laser amplifier gates, packet switching experiments with self-routing, employing cascaded switching gates, are reported. In a theoretical analysis the restrictions that the properties of semiconductor laser amplifier gates impose on a larger switching system consisting of many such gates are investigated. >

Wavelength conversions ∼1.5 μm by difference frequency generation in periodically domain‐inverted LiNbO3 channel waveguides

Abstract: Wavelength conversions ∼1.5 μm are realized by difference frequency generation in periodically domain‐inverted LiNbO3 channel waveguides for the first time. A wide wavelength conversion bandwidth, which is very important for future wavelength division multiplexing optical communication system, is demonstrated in this kind of devices.

A computer model of non-dispersion-limited stimulated Raman scattering in optical fiber multiple-channel communications

Abstract: The development of a computer model for non-dispersion-limited stimulated Raman scattering (SRS) in optical fiber multiple-channel communication systems is reported. The model takes into account the pump depletion due to SRS and the different attenuation coefficients at different wavelengths of operation. It can calculate the SRS effects in any fiber, provided the Raman gain profile for that fiber is known. Thus, the model is general in nature and can be used for a number of problems. It can be used to calculate the output power of all the channels, given the input of every channel and its operating wavelength. It can also be used, at least in principle, to determine the input power level if a desired level of output power is required. Moreover, it can be used to estimate the optical amplification of a signal due to SRS. This is possible because the governing equations for all of these processes are similar and therefore can be solved using the same approach. >

Pulse time modulation techniques for optical communications: a review

Abstract: The principal factor in realising a high-performance bandwidth-efficient fibre communication system at an acceptable cost is the choice of modulation format on the optical carrier. In this context, pulse time modulation (PTM) techniques represent an attractive alternative to purely digital or analogue methods. The PTM family is reviewed, a classification system is proposed and their potential for use in high-speed fibre systems intended for the transmission of analogue data is examined.

Pump laser control circuit for an optical transmission system

Abstract: An optical transmission system, especially useful in undersea applications, comprises an optical path between two terminals with one or more repeaters (10) located between the terminals for amplifying optical communications signals flowing in the optical path. The repeaters contain optical fiber amplifiers (24,26) driven by pump lasers (40,64). The average optical power produced by the pump lasers is controlled in proportion to the magnitude of electrical line current (30) produced by a controllable constant current source located in one of the terminals. This is achieved by regulator circuits (38,60) which are responsive to a signal related to the magnitude of the line current and signals related to the actual optical output of the pump lasers. The magnitude of the line current may be conveniently set at the terminals so that the lowest bit error rate is achieved in the transmission system. Alternatively, the magnitude of the line current may also be set to some minimum level to achieve an acceptable bit error rate and low pump laser and fiber amplifier aging.

Application of phase conjugate optics to optical systems

Abstract: PROBLEM TO BE SOLVED: To apply phase conjugate optics to various fields such as optical communication, optical measurement, optical information processing and others and to provide a new apparatus applicable for the above usage. SOLUTION: The optical modulator of the optics is equipped with: a light source; an excitation light source; a nonlinear optical medium; a probe light/excitation light supply means to supply probe light from a probe light source together with the excitation light from the excitation light source to a nonlinear optical medium; and a modulating means operationally connected to the excitation light source and modulating the excitation light according to the information signal. Modulated phase conjugate light exits from the nonlinear optical medium. COPYRIGHT: (C)2004,JPO

100 Gbit/s, 50 km, and nonrepeated optical transmission employing all-optical multi/demultiplexing and PLL timing extraction

Abstract: A 16*6.3 Gbit/s, time-and-polarisation division multiplexed optical signal is successfully transmitted through a 50 km dispersion shifted singlemode fibre employing all-optical multi/demultiplexing. A 6.3 GHz timing clock is directly extracted from the multiplexed 100 Gbit/s optical signal by a phase locked loop (PLL) using a travelling-wave laser diode amplifier. A wavelength-tunable modelocked Er/sup 3+/-fibre ring laser and a planar-lightwave-circuit time division multiplexer are newly developed for this experiment. >

New advances on optical components needed for FDM optical networks

Abstract: Two critical components, needed for optical networks based on frequency division multiplexing (FDM) and frequency reuse technologies, are presented. One is a fast tunable laser, yielding 24 discrete frequencies regularly spaced by 40 GHz around 1.53 mu m. The laser can be switched randomly in less than 8 ns among these frequencies. Frequency routing of a 3-Gb/s bit stream in 10-ns packets between ten different destinations has been demonstrated with this laser. The second component is a broadband wavelength shifter capable of switching multigigabit data between optical frequencies in the 1.5- mu m region. The device is tunable and cascadable, provides conversion gain, and is nearly polarization insensitive. Data degradation after wavelength shifting is negligible. Such a device provides the means of reusing the limited set of frequencies given by the lasers and thus of realizing large size networks. >

Liquid crystal devices for optical communication and information processing systems

Abstract: This paper reviews liquid crystal optical devices including tunable filters, photonic switches and spatial light modulators, and examines their application to optical communication and information processing systems. Optical processing has three major advantages: massive parallelism, high speed and broad wavebands. Compared with typical optical materials including silica, semiconductors and inorganic electrooptic crystals used in communication systems, a liquid crystal has a number of outstanding features including its large refractive index change and large polarization rotation power at a low voltage. These features make it possible to develop new optical components.

End-to-end equalization experiments in amplified WDM lightwave systems

Abstract: It is experimentally verified that signal-to-noise ratio equalization in amplified wavelength-multiplexed lightwave systems can be achieved by adjusting input optical signal powers according to a simple algorithm. The experiment involved four channels spaced by 2 nm transmitted through 550 km of fiber with the aid of eight erbium-doped optical amplifiers. >