Showing papers on "Optical communication published in 1996"

Optical communication system which determines the spectrum of a wavelength division multiplexed signal and performs various processes in accordance with the determined spectrum

Abstract: An optical communication system for transmitting wavelength division multiplexed (WDM) signal light through an optical fiber. The optical communication system includes a decoupling unit and a monitoring unit. The decoupling unit decouples a portion of the WDM signal light from the optical fiber as a monitoring signal. The monitoring unit determines the spectrum of the WDM signal light from the monitoring signal and performs control processing in accordance with the determined spectrum. Control processing includes performing at least one of the following: (1) controlling light sources to maintain a constant wavelength of each light signal in the WDM signal light, (b) determining a noise figure of an optical amplifier which amplifies the WDM signal light, (c) controlling the optical amplifier to achieve a desired noise figure, (d) detecting a signal-to-noise ratio of the WDM signal light, (e) detecting a true signal power of the WDM signal light, (f) maintaining the true signal power to be at a constant level, (g) counting the number of channels in the WDM signal light, (h) equalizing the gain of an optical amplifier to maintain a flat gain, (i) selecting a light source from among redundant light sources for providing a light signal on a respective channel of the WDM signal light, or (j) selecting a respective channel of the WDM signal light for signal enhancement.

Indoor ambient light noise and its effect on wireless optical links

Abstract: Knowledge of ambient optical noise is essential for designers of free space optical links, for designing resilient circuits. An experimental characterisation of the most commonly encountered ambient optical radiation is presented. The study includes tungsten filament sources, low and high frequency fluorescent lights, IR headphones, TV remote controls and daylight. Practical means to reduce their influence on the performance of the links are also given. The results are also valuable for setting a standard way of comparing wireless IR links, based on testing their performance under such ambient noise.

Transmission performance of high bit rate spectrum-sliced WDM systems

Abstract: We simulate transmission of a spectrum-sliced WDM channel operating at high bit rates (e.g., 622 to 2488 Mb/s). We calculate the bit error rate using the non-Gaussian statistics of thermal light sources that are commonly used in spectrum slicing and account for the effects of fiber dispersion. We evaluate the tradeoff in optical slice linewidth between signal-to-excess optical noise ratio and dispersion penalty in spectrum-sliced WDM systems, and determine the channel slicewidth that minimizes transmission penalty for a given link length and bit rate. We compare our simulations against the measured performance of a 1244 Mb/s channel over 20 km of fiber. The results in this paper provide useful information for the design of spectrum-sliced WDM networks.

Adaptive optics and ground-to-space laser communications

Abstract: The relationships between laser communication system parameters and adaptive optics system parameters are addressed. Improvement in optical signal propagation between space-based receivers and ground-based transmitters is possible with adaptive optics systems that compensate for a few degrees of freedom. Beginning with the relationship between optical signal fade and surge and the atmospheric log-amplitude variance and coupling to expressions that combine adaptive optics systems performance with the reduction in log-amplitude variance, system level examinations of the effects of adaptive optics can be done. Examples are given that show the advantageous reduction in signal fade and surge when adaptive optics are built into the optical system.

Transparent optical self-healing-ring communication network

Abstract: An optical self-healing-ring communication network is described which includes: a first optical communication line, forming a closed optical path; at least two add/drop nodes for optical signals, optically connected along the line; a second optical communication line forming a closed optical path and optically connected to the optical-signal add/drop nodes. Defined in the network are first and second mutually opposite. travel directions of the optical signals, with respect to the position of the optical-signal add/drop nodes. At least one of said nodes further comprises selection means, controlled by the optical signals, for the selective dropping of the optical signals from one of the communication lines. At least one of the optical-signal add/drop nodes further includes means for the simultaneous input of at least one optical signal in the first direction along the first communication line and in the second direction along the second communication line.

Wavelength selective optical couplers

Abstract: A wavelength selective optical fiber coupler having various applications in the field of optical communications is disclosed. The coupler is composed of dissimilar waveguides in close proximity. A light induced, permanent index of refraction grating is recorded in the coupler waist. The grating filters and transfers energy within a particular range of wavelengths from a first waveguide to a second waveguide. Transversely asymmetric gratings provide an efficient means of energy transfer. The coupler can be used to combine or multiplex a plurality of lasers operating at slightly different wavelengths into a single fiber. Other embodiments such as a dispersion compensator and gain flattening filter are disclosed.

Wireless infrared communication links using multi-beam transmitters and imaging receivers

Abstract: We discuss two modifications to the design of wireless infrared links that can yield dramatic performance improvements. In nondirected, non-line-of-sight (non-LOS) links, replacement of the diffuse transmitter by one that projects multiple narrow beams can reduce the path loss, typically increasing the link SNR by about 20 dB. In both non-directed, LOS and non-directed, non-LOS links, replacement of the non-imaging receiver by one employing an imaging light concentrator and a segmented photodetector can reduce the received ambient light noise and multipath distortion. This can yield SNR improvements of tens of decibels.

Modeling of four-wave mixing and gain peaking in amplified WDM optical communication systems and networks

Abstract: A theoretical model is presented for analyzing the propagation of densely spaced WDM optical signals through a cascade of erbium-doped fiber amplifiers and single-mode optical fibers with nonuniform chromatic dispersion. By combining a numerical solution for the EDFA and an analytical expression for FWM components generated through the cascade, the model allows a realistic system analysis which includes gain peaking effect, amplified spontaneous emission accumulation and the effect of dispersion management on the four-wave mixing efficiency. The FWM power distribution at the end of the multi-amplifier transmission link is computed taking into account the phase relation between FWM light amplitudes generated within different sections of the link. The transmission of many WDM channels, evenly spaced around 1547.5 nm, has been analyzed for various dispersion management techniques and propagation distances. Numerical results point out the importance of such a model for a realistic design of WDM optical communication systems and networks. A proper choice of chromatic dispersion, amplifier characteristics, span length, input signal powers and wavelengths, combined with the use of gain equalizing filters, allows to maximize the transmission distance ensuring acceptable signal-to-noise ratio (SNR) and limited SNR variation among channels.

Principles and Applications of Optical Communications

Abstract: I Overview 1 Introduction to Optical Communications 2 From Point-to-Point Links to Networking II Basic Point-to-Point Communication Blocks 3 Light Sources 4 Optical Fibers 5 Photo Detectors 6 Noise in Optical Communications 7 Incoherent Detection III Networking 8 Time Domain Multiple Access (SONET, FDDI, B-ISDN, etc.) 9 Frequency Domain Multiple Access 10 Subcarrier Multiplexing 11 Photonic Switching IV Signal Processing 12 Direct Modulation 13 External Modulation 14 DFB Modulation 15 Coherent Detection 16 Line Coding and Timing Recovery 17 Optical Amplification 18 Soliton Transmission

An optical communications system having distributed intelligence

Abstract: The invention is embodied in a distributed intelligence optical fiber communications system capable of fully automated and continuous monitoring and testing of the optical fibers and their connections within the optical fiber distribution frames therein. In particular, it is an optical communications system having an optical distribution frame including interconnection modules having actively intelligent microcontrollers thereon. Also, the distribution frame includes inventive electrical and optical interconnection fabrics between the distributed intelligence located on the interconnection modules and a host located outside of the distribution frame. The distributed intelligence interconnection modules allow monitoring, testing and/or related activities of the overall optical communications system to be performed locally at the interconnection modules. Also, when used in combination with the electrical and optical interconnection fabrics, the inventive modules substantially reduce optical fiber routing and enable more effective monitoring and testing operations to be performed, while maintaining compatibility with existing conventional cross-connect, switching and network architectures.

Optical communication system compensating for chromatic dispersion and phase conjugate light generator for use therewith

Abstract: An optical communication system compensating for chromatic dispersion and a phase conjugate light generator for use therewith. The system includes an optical transmitter which receives an input signal and transmits signal light over an optical transmission line which is then input to a phase conjugate light generation unit. The phase conjugate light generation unit generates phase conjugate light corresponding to the signal light and outputs the phase conjugate light to an optical receiver which reproduces a demodulated signal corresponding to the input signal. The system compensates for chromatic dispersion by having the phase conjugate light generator generate phase conjugate light corresponding to signal light received over a first optical transmission line and then transmitting the generated phase conjugate light over a second optical transmission line.

Performance of infrared transmission systems under ambient light interference

Abstract: Optical transmission systems are mainly impaired by the shot noise induced by ambient light, the transmitted optical power limitations (high path losses), the channel bandwidth limitations owing to multipath dispersion and the interference produced by artificial light sources. Several modulation and encoding schemes have been proposed for this channel and their performance has been studied and presented by several authors while neglecting the effects of the artificial light interference. The work reported extends the previous analysis by taking into account the optical power penalty induced by artificial light interference. An analytical approach is used to estimate this. In practical systems, the effect of the interference is usually mitigated using electrical highpass filters. In the paper the combined effect of interference and highpass filter is evaluated. The presented results show that the interference produced by fluorescent lamps driven by electronic ballasts induce high power penalties in OOK and L-PPM systems, even when electrical highpass filtering is used, for data rates up to 10 Mbit/s. For the interference produced by incandescent lamps and fluorescent lamps driven by conventional ballasts, the power penalty induced in OOK systems can be effectively reduced using highpass filtering, while PPM is very tolerant to that interference even without any highpass filtering. The major conclusion is that artificial light interference have to he considered both in system design and performance evaluation.

Method of and device for driving optical modulator, and optical communications system

Abstract: A device and a method for driving an electro-absorption optical modulator for receiving carrier light emitted from a light source and outputting signal light subjected to intensity modulation according to the absorption of the carrier light. A bias circuit generates a bias voltage determined so that the optical modulator has a given chirping parameter. A driving circuit generates a modulating signal corresponding to an input signal, superimposes the modulating signal on the bias voltage, and supplies the superimposed signal to the optical modulator. A control circuit controls at least one parameter selected from a parameter group including the amplitude and duty of the modulating signal and the power of the carrier light, based on the bias voltage. It can be possible to provide a method of and a device for driving an optical modulator capable of arbitrarily setting a chirping parameter.

Optical communication system

Abstract: A discontinuous ring is formed by separate bidirectional optical communication links, with possibly different transmission speeds, synchronous or asynchronous transmission, and ratios of working to protection channels, each linking a pair of terminals in different nodes of a communication system. To protect protection-switched traffic on a communication link from a link failure, it is routed around the ring via the protection channel of the other communication links. To this end, an optical switch is provided between the protection channel of each link and the associated terminals in each node, and is controlled differently in nodes adjacent the link failure and in nodes not adjacent the link failure to route the protection-switched traffic accordingly. Rapid protection switching is facilitated by controlling the optical switches using wavelength detectors directionally coupled to the protection channel at each node.

Wavelength selective optical devices

Abstract: Wavelength selective devices and subsystems having various applications in the field of optical communications are disclosed. These devices and subsystems are composed of bidirectional grating assisted mode couplers (9). The high add/drop efficiency and low loss of this coupler enable low loss wavelength selective elements such as optical switches (62), amplifiers (63), routers (5), and sources to be fabricated. The grating assisted mode coupler (23) can be wavelength tuned by modifying the optical properties of the coupler interaction region. A programmable, wavelength selective router (5) composed of multiple grating assisted mode couplers is also disclosed.

WDM Optical communication systems with remodulators and remodulating channel selectors

Abstract: The present invention provides a WDM optical communication system with remodulators at the transmission input and remodulating channel selectors adjacent the optical receivers, providing complete control over the interfaces with optical transmission equipment. In an exemplary embodiment, the WDM system includes optical transmitters which input transmitted optical signals into optical remodulators. The optical remodulators place the information from each of the transmitted signals onto separate optical channels in the WDM system channel plan. The optical channels are multiplexed onto an optical waveguide. At the receive end, remodulating channel selectors each receive a portion of the WDM optical signal, select a particular optical channel, and place the information from the selected channel onto a newly-generated optical signal. This newly-generated optical signal is output to a receiver or to a further WDM optical system.

Optical transceiver and optical communications network for both of optical fiber transmission and free space transmission

Abstract: A cable network is constituted such that interconnectable, passive 4-terminal star couplers are connected to each other via optical fiber cables and a bi-directional optical relay amplifier. Cells each constituted by using free space transmission light are integrated by the cable network. An optical signal transmitted from or directed to a mobile station in a cell is linked to the cable network via an optical relay amplifier, which provides interface between free space transmission light and guided light. Even in a case where a barrier interposed between two mobile stations prevents a direct communication between those stations, a collision between those stations can be detected by a collision detection proxy server having functions of collision detection according to the principle of code transition rule violation and jamming signal transmission. A communication between those stations can be realized by connecting, to the cable network, a relay proxy server having a packet relay and transmitting function.

Design and performance of an optical path cross-connect system based on wavelength path concept

Abstract: This paper describes the system design and performance of an optical path cross-connect (OPXC) system based on wavelength path concept. The (OPXC) is designed to offer 16 sets of input and output fiber ports with each fiber transporting eight multiwavelength signals for optical paths. Each optical path has a capacity of 2.5 Gb/s. Consequently, the total system throughput is 8/spl times/16/spl times/2.5=320 Gb/s and the OPXC features high modularity and expandability for switch components. By exploiting planar lightwave circuit (PLC) technologies, four sets of (8/spl times/16) delivery-and-coupling-type optical switches (DC-switches) are developed for the 320 Gb/s throughput OPXC system. The DC-switch offers the average insertion-loss of 12.6 dB and ON/OFF ratio of 42.1 dB. The PLC arrayed-waveguide gratings are confirmed to successfully demultiplex the eight directly modulated signals, multiplexed at a spacing of 1 nm, with a crosstalk of under -25 dB. Eight wavelength-division multiplexing signals, directly modulated at 2.5 Gb/s, are confirmed to be transported over 330 km via a cross-connection node in the test-bed system that simulates five-node network. The experimental performances demonstrated In this paper ensures full scale implementation of the proposed optical path cross-connect system with 320 Gb/s throughput and high integrity.

Comparison of the performance of optically amplified transmission systems

Abstract: In this paper, we show a comparison among the performance of single- and multichannel optical systems considering NRZ and soliton signals. The results have been obtained by means of numerical simulations, taking into consideration the chromatic dispersion, the Kerr nonlinearity, the fiber loss, and the ASE noise of the optical amplifiers. The performance of IM-DD and coherent asynchronous ASK systems have been evaluated in terms of the Q factor. We have considered the propagation in links encompassing conventional step-index fibers, DS fibers and in links with two different dispersion management techniques in which the chromatic dispersion is varied along the propagation distance both in randomly and in deterministically way. The effects of the in-line filtering process are mainly investigated in soliton propagation.

Reconfigurable device for insertion-extraction of wavelengths

Abstract: This device includes optical add-drop multiplexers (M1 to M2) each having a band-pass filter. An optical switch (C1) has outputs connected to the multiplexers. An optical coupling (C2) has inputs connected to the multiplexers. The device is useful in optical communications.

System for an optical domain

Abstract: A transmission-based restoration system and method restores a failure of an optical pipe within an optical domain. Restoration occurs in the same domain in which the failed optical pipe is located. First and second optical pipe rings and a first plurality of optical switch platforms are deployed within a domain. The first optical pipe ring carries optical communication signals in first and second opposing directions around the first optical pipe ring. The second optical pipe ring carries optical communication signals in first and second opposing directions around the second optical pipe ring. Each optical switch platform is connected to the first optical pipe ring and the second optical pipe ring for switching the optical communication signals between the first and second optical pipe rings. When the first and second optical pipe rings both fail between adjacent first and second optical switch platforms, the first optical switch platform switches the optical communication signals carried in the first direction in the optical pipe ring to be carried in the second direction in the second optical pipe ring. The second optical switch platform switches the optical communication signals carried in the second direction in the first optical pipe ring to be carried in the first direction in the second optical pipe ring. Preemptive traffic, multiple domain switches, and redundant configurations are used.

Wavelength-division multiplexing optical communication apparatus and method therefor

Abstract: A wavelength division-multiplexing optical communication apparatus and method includes a plurality of modulators for respectively modulating the intensity of a plurality of light rays, each having a different wavelength from one another, with a data signal from a signal source, a wavelength division-multiplexer for combining the light from the modulators, fiber optics for transmitting light from the wavelength division multiple and a wavelength division-multiplexed light receiver for separating the light from the transmission path fiber optics by wavelength (and receiving the separated light, respectively. The light modulators control or select a magnitude of the phase modulation caused at the time of intensity modulation, and the modulator for each light wavelength is separately controlled and selected for the operating point, so as to cause a phase modulation component which minimizes the waveform distortion after transmission through the transmission path fiber optics. Hence, the apparatus is not limited in its wavelength range or transmission distance caused by waveform distortion due to the wavelength dependency of dispersion of transmission path.

40 Gbit/s demultiplexing experiment with 10 GHz all-optical clock recovery using a modelocked semiconductor laser

Abstract: A 40 Gbit/s time-division multiplexed signal was demultiplexed to 10 Gbit/s using a single modelocked semiconductor laser as the clock source. The pulses of the laser directly control an all-optical switch for demultiplexing.

Low-loss polarization-insensitive InP-InGaAsP optical space switches for fiber optical communication

Abstract: High-performance InP-InGaAsP optical space switches are reported, which in monolithic four switch arrangements reach fiber-to-fiber losses as low as 5 dB. Polarization insensitivity is within /spl plusmn/0.5 dB. On-off ratios throughout the 1.53-1.56 /spl mu/m wavelength range exceed 15 dB. Switch rearrangement times are below 200 ps.

Bidirectional optical telecommunication system comprising a bidirectional optical amplifier

Abstract: A bidirectional optical amplifier, comprising a unidirectional optical amplifying unit having one amplification wavelength band; two input/output ports for at least two optical signals having opposite propagation directions, the signals having a first and a second wavelength respectively, which are distinct from each other and included in the amplification wavelength band; two first and two second wavelength-selective optical couplers, respectively having a first wavelength pass-band including said first wavelength and a second wavelength pass-band including said second wavelength, the first and second wavelength pass-bands being non-overlapping, wherein the amplifying unit is connected between two opposite nodes of an optical bridge circuit, and wherein at the nodes of said bridge circuit the first and second selective optical couplers are present and are disposed symmetrically with respect to the amplifying unit and to the input/output ports of the optical signals.

Optical amplifier and optical communication system employing the same

Abstract: An optical amplifier having an optical amplifying medium, a pump light source outputting pump light, a first optical coupler for supplying the pump light to the optical amplifying medium, a probe light source for outputting probe light having a wavelength included in an amplification band, a second optical coupler for supplying the probe light to the optical amplifying medium, detectors for detecting the powers of input signal light and the probe light, respectively, and control unit for controlling the power of the probe light according to outputs from the detectors. This structure makes it possible to provide an optical amplifier which can reduce the wavelength dependence of gain.

Optical transmitter, optical communication system and optical communication method

Abstract: An optical transmitter comprises a first unit for generating an optical signal having a bandwidth given by a main signal, a second unit modulating the optical signal according to a control signal to extend the bandwidth of the optical signal, a third unit extracting backward light including SBS(stimulated Brillouin scattering) light generated in an optical fiber transmission line, and a fourth unit performing feedback control so that the power of the SBS light becomes substantially constant. Through the structure of the optical transmitter good transmission characteristics of a main signal are obtained and the suppression of the SBS is allowed.

Scanning heterodyne acousto-optical interferometers

Abstract: Compact, high performance, scanning heterodyne optical interferometers for interferometric phase-based measurement and a host of other applications are introduced. An in-line, almost common-path optical interferometer design offers robustness to externally induced phase noise via mechanical vibrations, thermal effects, and other environmental effects. Several instrument designs are disclosed for both transmissive and reflective interferometry. These interferometers use acousto-optic devices or Bragg cells to implement rapid (e.g., <50 μs/scan spot) optical scanning of a test medium. Although the read optical beam scans a given test region, the double Bragg diffraction optical design of the instrument makes the final interfering output beams stationary on the two high speed photo-detectors used for radio frequency signal generation via heterodyne detection. One photo detector acts as the fixed phase reference, while another fixed photo detector picks up the test medium phase information as the optical beam scans the test region. High speed two dimensional optical scanning of a test medium is possible by using a fixed one dimensional output high speed detector array, or via the use of high speed non-mechanical electro-optic deflectors. Also, the invention can be embodied in a coherent wide bandwidth optical transmitter using fast optical scanning of spatial codes for encrypted coherently coded coherent optical fiber transmission. This coherent system for complex optical code reading and transmission is reversible in nature, and can be used for both transmit-receive coded coherent optical communications.

System-level comparison of optical and rf technologies for space-to-space and space-to-ground communication links circa 2000

Abstract: Rf and optical communication conceptual terminal designs; size, weight, and power requirements; and development costs are compared for three representative 1-Gbps links Year 2000 technology is assumed for the designs of LEO-to-GEO, LEO-to-LEO, and LEO-to- Ground terminals based on 32-GHz rf, 60-GHz rf, AlGaAs optical, and InGaAsP/EDFA optical technologies The optical technologies exhibit advantages in the areas of antenna size, terminal weight, and recurring cost at the 1-Gbps data rate

Circuit and method of testing for silent faults in a bi-directional optical communication system

Abstract: In optical communications systems crosstalk can result in what is termed silent failure. In silent failure, a faulty transmitter appears to function correctly because a receiver in communication therewith is receiving a signal induced by crosstalk. The invention overcomes this problem by tapping the received signal and monitoring it external to the receiver in order to ensure adequate signal levels for a received signal. A microcontroller disables the failed circuit and in an embodiment switches the communication functions to a stand-by circuit.