Showing papers on "Optical communication published in 1995"

Optical duobinary transmission system with no receiver sensitivity degradation

Abstract: This Letter proposes a novel optical duobinary transmission system with no receiver sensitivity degradation. The transmitter yields a narrowband optical signal, and the receiver configuration is as simple as a binary IM-DD receiver. The feasibility of the proposed system is experimentally confirmed at 2.5, 5 and 10 Gbit/s.

Modulation analysis for wireless infrared communications

Abstract: The channel model for indoor wireless optical communication links is unusual in that it combines the intensity-modulation constraints of the Poisson photon-counting channel with the multipath dispersion, bandwidth constraints, and additive white Gaussian noise of the conventional radio channel. In this paper we examine the performance of several modulation schemes on the indoor wireless optical channel. Modulation schemes having low duty cycle, such as pulse-position modulation (PPM), offer improved power efficiency at the expense of decreased bandwidth efficiency. We compare the power and bandwidth efficiency of several forms of PPM, including multiple PPM, overlapping PPM, convolutional coded PPM, and trellis coded OPPM. We also examine the differences between the wireless infrared communications channel and the quantum-limited photon-counting channel.

Direct detection of optical digital transmission based on polarization shift keying modulation

Abstract: Receiver structures for the direct detection of binary and multilevel digital optical modulation schemes employing the modulation of the state of polarization of light, or polarization shift keying (POLSK), are proposed and accurately analyzed, in the presence of optical amplifier ASE noise and electrical receiver noise. A comprehensive set of results shows that the performance of the binary system is approximately 3 dB better than IM/DD (on peak optical power), and stays so for a wide range of optical filter bandwidths. As a somewhat unexpected result, the multilevel schemes show a lower sensitivity to the use of a wide optical filter than the binary one. As a consequence, transmitting 3 b/symbol on a cubic constellation on the Poincare sphere brings about virtually no penalty, whereas transmitting 2 b/symbol has a better performance than binary transmission, for even relatively low values of the optical filter bandwidth. A clear explanation of this phenomenon has been found. These results suggest that narrow-bandwidth and therefore low-dispersion, multilevel, POLSK transmission could be performed with no penalty. Together with the low excitation of nonlinear effects in the fiber that polarization modulation seems to ensure, these results make POLSK schemes look promising for very-long-haul transmission. >

Card-shaped optical data link device

Abstract: A card-shaped optical data link device is utilized for transmitting and receiveing data in optical communications using an exisiting card slot of a computer, electronic devices etc. The card-shaped optical data link device of the present invention comprises an electric connector, electric signal processor 20 electrically connected to the electric connector, a optical transmission module 30, an optical reception module 30A electrically connected to the electric signal processor 20, an optical connector 50 for supporting the optical transmission module 30 and the optical reception module 30A, a frame 11 for supporting the electric connector and the optical connector 50 at a position opposing to the electric connector, and a pair of panels 12 for sandwiching the frame 11 and constituting an envelope with the frame 11. The electric connector, the electric signal processor, the optical transmission module 30, the optical reception module 30A and the optical connector 50 are located within the envelope.

Optical communication system

Abstract: PURPOSE:To simultaneously operate plural communication systems while using the same communication medium by allocating different wavelengths to the communication protocol units of information to be transferred inside the same medium for optical transmission. CONSTITUTION:As optical frequency divided and multiplexed optical signals, optical signals at frequencies fa-fc are propagated inside an optical fiber 10. On the other hand, concerning nine optical communication nodes 21-29 performing the communication while being connected to the optical fiber 10, the optical communication nodes 21, 24 and 27 perform the communication according to a communication protocol A, the optical communication nodes 22, 25 and 28 perform the communication according to a communication protocol B, and the optical communication nodes 23, 26 and 29 perform the communication according to a communication protocol C. Concerning these optical communication protocols, the optical signals frequency-divided into three ranger are allocated to three communication protocols A-C existent inside the system, and the respective optical communication nodes 21-29 perform the communication while using the optical signals at the frequencies fa-fc allocated to the communication protocols to which their nodes themselves belong.

Ultrafast polarization‐discriminating Mach‐Zehnder all‐optical switch

Abstract: We propose a polarization‐discriminating Mach‐Zehnder (PDMZ) all‐optical switch The switching speed of this PDMZ all‐optical switch is not limited by the slow relaxation time of highly efficient incoherent nonlinearities We demonstrate a squarelike modulation characteristic, which is necessary in most switching applications, at a switching speed (on‐off time) of 40 ps We also demonstrate ultrafast switching at a detector limited speed of ∼8 ps

All-optical parallel-to-serial conversion by holographic spatial-to-temporal frequency encoding.

Abstract: Optical processors that perform parallel-to-serial and serial-to-parallel data conversion are introduced and experimentally demonstrated for long-distance optical communication networks.

A novel technique for double sideband suppressed carrier modulation of optical fields

Abstract: We present a simple and efficient technique to produce double sideband suppressed carrier (DSBSC) modulation for coherent analog optical communications. When operating a Mach-Zehnder electro-optic modulator at the appropriate bias point the carrier exits one of the output ports while the information carrying sidebands exit the other output port. The absence of a strong carrier component in the DSBSC output allows the use of an optical amplifier immediately following the modulator where the light signals are still relatively strong hence preserving the high S/N. In our experiments using heterodyne detection at 1319 nm, we show a -28-dB carrier suppression using a commercial M-Z modulator. >

Optical communications networks

Abstract: An optical communications network includes a plurality of passive optical networks (PONs) connected in a ring in PON address order, in which communication channels between terminals are wavelength multiplexed. Each optical link between adjacent PONs includes a tunable wavelength filter, and a common wavelength allocation database is arranged dynamically to select wavelengths for a connection and to provide corresponding control signals to the appropriate filters such that the allocated wavelengths for a connection can pass over only the transmission path between the terminals. Thus the same wavelengths can be re-used for another connection whose transmission path does not overlap with any existing transmission path involving those wavelengths.

Ultra-high-speed OTDM networks using semiconductor amplifier-based processing nodes

Abstract: The use of semiconductor amplifiers in high speed communications systems is reviewed. Processing of signals at 10 Gb/s in a 40-Gb/s OTDM network is demonstrated using nonlinear loop mirror configurations, and mode locked ring lasers. Particular attention is paid to the role of carrier density modulation, long believed to be a detrimental effect, and its useful exploitation. >

Expandable wavelength division multiplexed optical communications systems

Abstract: The present invention provides wavelength division multiplexed optical communication systems configured for expansion with additional optical signal channels. In one embodiment, the WDM system comprises N source lasers for producing N optical signal channels, each channel having a unique wavelength where N is a whole number greater than or equal to 2. An optical multiplexer module having N+x inputs, where x is a whole number greater than or equal to 1, optically communicates with each of the N source lasers. The N+x input ports of the multiplexer are configured such that the N input ports are optically coupled to the N source lasers and the x input ports are supplemental ports not optically coupled to the N source lasers. An optical transmission path optically communicates with the multiplexer for carrying a multiplexed optical signal comprising the N optical signal channels. N optical channel selecting modules are provided, each selecting module including a Bragg grating configured to select a unique optical channel wavelength. An optical splitter module optically communicates with the optical transmission path and the optical channel selecting modules. The optical splitter includes N+y output ports, where y is a whole number greater than or equal to 1. The N+y output ports are configured such that each of the N output ports is optically coupled to one of the N optical channel selecting modules and the y output ports are supplemental ports not optically coupled to the N optical channel selecting modules.

Experimental study of a model digital space optical communication system with new quantum devices

Abstract: We report a digital space optical communication system with new features both in the transmitting and in the receiving ends. The diode laser source is stabilized to within ±100 kHz by locking its frequency to the transmission peak of a Faraday anomalous dispersion optical filter (FADOF). The optical filter in the receiver uses two FADOF’s that are linked to eliminate the multipeak structure and achieve a single-peak bandwidth of ~1 GHz. The detection sensitivity of this system is 23 times higher than that of a system with a traditional interference filter.

Characterisation and modelling of artificial light interference in optical wireless communication systems

Abstract: Wireless indoor infrared transmission systems are affected by noise and interference induced by natural and artificial ambient light. While the shot noise induced on the receiver photodiode by steady ambient light has been extensively described and included in system models, the interference produced by artificial light has only been mentioned as a source of degradation and quite simple descriptions have been presented. This paper presents a characterisation (through extensive measurements) of the interference produced by artificial light and proposes a simple model to describe it. These measurements show that artificial light can introduce significant in-band components for systems operating at bit rates up to several Mbit/s. Therefore it is essential to include it as part of the optical wireless indoor channel. The measurements show that fluorescent lamps driven by solid state ballasts produce the wider band interfering signals, and are then expected to be the more important source of degradation in optical wireless systems.

Coherent Optical Communications Systems

Abstract: Theory of Optical Communications. Fiber Devices for Optical Communication Systems. Integrated Devices for Optical Communication Systems. Direct Detection Optical Communication Systems. Coherent Systems: Structure and Ideal Performance. Performance Degradation Sources in Coherent Optical Systems. Multilevel Coherent Optical Systems. Multichannel Optical Systems. Present--Day Systems Implementations. Appendices. Index.

Transmission and reception module for a bidirectional optical communication and signal transmission

Abstract: A transmission and reception module for a bidirectional optical communication and signal transmission includes a light transmitter having a first lens coupling optical element, and a light receiver. A fiber connection has a second lens coupling optical element for a common optical waveguide. A beam splitter is disposed in a free beam path. A common housing surrounds the foregoing. The light transmitter, the beam splitter and the fiber connection as well as the light receiver which is orthogonal thereto, are disposed axially symmetrically. An optical axis of the first lens coupling optical element is axially offset from an optical axis of the light transmitter, an optical axis of the second lens coupling optical element is axially offset from the optical axis of the fiber connection, the end surface of the fiber connection, given optimal coupling-in of light, has an angle of inclination relative to its optical axis, and the beam splitter is inclined relative to an axis of symmetry of the configuration, such that backreflected radiation strikes neither a radiation-active part of the light transmitter nor a radiation-sensitive part of the light receiver.

Optical wavelength converters

Abstract: Devices and techniques for shifting the frequency/wavelength of an optical carrier wave are reviewed, with particular reference to applications in wavelength/frequency division multiplexed optical communication systems. Considered first are devices which make use of semiconductor laser amplifiers or oscillators. Some of these techniques come close to satisfying the requirements for a suitable wavelength shifter, though none appear to offer the potential for a transparent network independent of data modulation format. A second main category, using nonlinear optical materials, promises to satisfy the requirements for frequency translation in a network which is fully transparent to the modulation format. However, the conversion efficiencies currently available appear too low for cost-effective communication systems engineering so that further advances in nonlinear optical materials/techniques are still required. It seems likely that guided wave techniques will provide the best means of improving the efficiency by increasing the interaction length and the optical intensity for a given power. Schematic examples of such a converter are discussed. All of the existing techniques have some deficiencies compared to an ideal system so that wavelength conversion for optical communication systems is still a problem in search of a good solution.

Optical frequency conversions in nonlinear medium with periodically modulated linear and nonlinear optical parameters

Abstract: A new method considering both linear and nonlinear optical parameter modulation and propagation loss is proposed to treat second-order nonlinear optical interactions in nonlinear media having periodic structures. Mathematical expressions are derived for difference frequency generation (DFG) and compared with those for second-harmonic generation (SHG). Wavelength conversions around 1.55 /spl mu/m, which are very interesting in optical communication systems, are studied for semiconductor DFG devices with periodic structures. Semiconductor (e.g., AlGaAs) DFG devices of standard device lengths (several mm) and pump light intensities (10/sup 5/ kW/cm/sup 2/) are shown capable of practical level conversion efficiencies (/spl sim/10%) and extremely wide bandwidths (/spl ges/100 nm). Effects of propagation loss in DFG devices are also examined. >

Oscillation polarization selective semiconductor laser and optical communication system using the same

Abstract: An oscillation polarization selective semiconductor laser that switches oscillation polarization modes between two different polarization modes includes a laser structure on a substrate. An active layer of the laser structure includes plural sets of quantum wells and barriers. The structure of at least one set of quantum wells and the barriers is different from the other sets so that the gain spectra generated in the active layer for induced mutually perpendicular propagation modes are selectively controlled by controlling the carrier density injected into the active layer. The oscillation polarization selective semiconductor laser may be used as a light source in optical communication systems.

Amplified telecommunication system for wavelength-division multiplexing transmissions capable of limiting variations in the output power

Abstract: An optical telecommunication system comprising means (37, 38, 39, 40) for generating optical signals of different wavelengths, an optical-fibre line with amplifying means (45, 45', 45'', 45'''), a pre-amplifier (47), and receiving means (54, 55, 56, 57), wherein the pre-amplifier (47) comprises an optical waveguide (5,7,9) doped with a rare earth material, differential-attenuation means (8) located at a first position along the doped waveguide and capable of causing an attenuation in the signal band which is greater than the attenuation caused at the pumping wavelength, and filtering means (6) located at a second position and adapted to attenuate by a value higher than a predetermined minimum, the spontaneous emission in a wavelength band contiguous with the signal band. The position and attenuation of the differential-attenuation means and filtering means and the wavelength band are selected in a functional relation with respect to each other in order to limit the output power variations from the pre-amplifier.

Digital free-space optical interconnections: a comparison of transmitter technologies

Abstract: We investigate the performance of free-space optical interconnection systems at the technology level. Specifically, three optical transmitter technologies, lead-lanthanum-zirconate-titanate and multiple-quantum-well modulators and vertical-cavity surface-emitting lasers, are evaluated. System performance is measured in terms of the achievable areal data throughput and the energy required per transmitted bit. It is shown that lead-lanthanum-zirconate-titanate modulator and vertical-cavity surface-emitting laser technologies are well suited for applications in which a large fan-out per transmitter is required but the total number of transmitters is relatively small. Multiple-quantum-well modulators, however, are good candidates for applications in which many transmitters with a limited fan-out are needed.

Optoelectronic smart pixel array for a reconfigurable intelligent optical interconnect

Abstract: A packaged smart pixel array for a reconfigurable intelligent optical interconnect is described. The smart pixel array (298) comprises an optical-to-electronic optical I/O channel 68 input means, an electronic-to-optical optical I/O channel 68 output means, an electrical channel input means (134), an electrical channel output means (114), a data switching means (110) for switching data from optical channel input means to electrical channel output means, a data switching means (130) for switching data from electrical channel input means and optical channel input means to optical channel output means and a packaging means (300) which packages all these means onto a single package with identifiable input and output port means. The smart pixel array makes possible the realization of a reconfigurable optical interconnect which implements multiple reconfigurable optical communication channels.

Digital signal regeneration with side-injection-light-controlled bistable laser diode as a wavelength converter

Abstract: Digital optical signal regeneration with a SILC-BLD markedly improves the bit error rate of degraded optical signals. The extinction improved from 3 dB to 17 dB and intensity fluctuation was suppressed from 3 dB to 0 dB. This diode can not only regenerate the signal but also converts the signal wavelength at the same time without wavelength filters or isolators. >

Optical communications and interconnection networks having opto-electronic switches and direct optical routers

Abstract: A multiple wavelength optical network includes a plurality of nodes, each of which can receive and transmit multiple wavelengths. The nodes include at least one fixed wavelength switched optical coupler and at least one direct coupler, so that the signals of high volume and other users can pass directly through the nodes without interruption. Wavelengths can be reused, even when there is a direct connection, by saturating a series of amplifiers in a direct coupler to erase the information signal from the carrier. The carrier signal is not interrupted, and can be remodulated immediately with another information signal.

Optical fiber amplifier

Abstract: An optical fiber amplifier used for optical communication, and provided with a pumping light source (1), a first wave combining means (2) for combining signal light with pumping, a first light amplifying fiber (3) through which the combined light is passed, a wave separator (4) provided on the output side of the first optical amplifying fiber so as to separate the wave-combined light into signal light and excitation light, an optical element (5) disposed in a path through which the separated signal light passes, a second wave combining means (7) for combining the signal light with the pumping light again, and a second light amplifying fiber (8) through which this combined light is passed. The optical element (5) includes at least either a dispersion compensation fiber or an optical filter.

Performance evaluation of an optical multi-carrier network using wavelength converters based on FWM in semiconductor optical amplifiers

Abstract: An analysis of the transmission performance of optical multi-carrier network layer employing wavelength converters based on four wave mixing in semiconductor travelling wave amplifiers is presented. The all-optical wavelength conversion proposed here would allow the network to fulfil the requirement of flexibility, maintaining the transparency of the optical layer. Analytical results, obtained by an accurate model of the transmission through the network, are reported for two different photonic switching approaches. One is based on a combination of wavelength choice and space switching, while the other one relates to a switching completely in the wavelength domain. In both the cases the results assess satisfactory transmission performances. >

Picosecond-accuracy all-optical bit phase sensing using a nonlinear optical loop mirror

Abstract: We demonstrate picosecond-accuracy bit phase comparison using a nonlinear optical loop mirror. We use this all-optical bit phase comparator to synchronize an external cavity modelocked diode laser operating at 10-GHz to a soliton compression source operating at 10-GHz using an electrooptic phase lock loop. We believe this is the first demonstration of soliton compression source synchronization. The holding range of the phase lock loop is /spl plusmn/20 MHz, and is limited by the modelocking bandwidth of the external cavity laser. Clock acquisition time is dominated by the latency of the nonlinear optical loop mirror. >

Spatial optical CDMA

Abstract: A method for optical signaling is investigated that allows multiple transmitters to simultaneously use the same noncoherent receiving aperture. The signaling is based on the properties of laser speckle interference patterns. Capacity for an interference limited system is explored for a correlation receiver based on random coding. A synchronization scheme is presented that allows a practical implementation of the proposed optical multiple access system. >

Fiber-optic access system for subscriber optical communication

Abstract: A fiber-optic access system for subscriber optical communication adopting star type topology in an optical fiber network includes a central office, a plurality of optical network units, an optical interface, and a signal recognition/reproduction and clock extraction IC. The optical interface is provided in the central office and includes an array optical transmission module as a package unit accommodating a plurality of light sources and a plurality of output fiber terminals, and an array optical reception module as a package unit accommodating a plurality of optical sensors and a plurality of input fiber terminals. The signal recognition/reproduction and clock extraction IC is provided to each channel of the array optical reception module. The access system provided is of a scale comparable to that of a central office side optical interface of PDS and wide band characteristics comparable to those of a single star type system.

Data encoded optical pulse generator

Abstract: The apparatus and method according to the present invention includes a semiconductor laser-modulator which is used to simultaneously generate optical pulses and encode data. The optical data output from the laser-modulator are soliton pulses in RZ format suitable for transmission in long distance optical communications.

Optimum amplitude- and frequency-modulation in an optical communication system based on dispersion supported transmission

Abstract: It is shown theoretically that the presence of amplitude modulation is necessary for optimum performance of a dispersion supported transmission system. For 10 Gbit/s nonregenerated transmission at lambda =1.5 mu m over more than 300 km standard singlemode fibre, an amplitude modulation index of 0.5 compared to 0.01 is expected to increase the receiver sensitivity by 7-14 dB.