Showing papers on "Optical communication published in 1989"

Code division multiple-access techniques in optical fiber networks. II. Systems performance analysis

Abstract: For pt.I see ibid., vol.37, no.8, p.824-33 (1989). In Part I a technique based on optical orthogonal codes was presented to establish a fiber-optic code-division multiple-access (FO-CDMA) communications system. The results are used to derive the bit error rate of the proposed FO-CDMA system as a function of data rate, code length, code weight, number of users, and receiver threshold. The performance characteristics for a variety of system parameters are discussed. A means of reducing the effective multiple-access interference signal by placing an optical hard-limiter at the front end of the desired optical correlator is presented. Performance calculations are shown for the FO-CDMA with an ideal optical hard-limiter, and it is shown that using an optical hard-limiter would, in general, improve system performance. >

Wireless Optical Communication Systems

Abstract: Wireless Optical Communication Systems addresses the problem of designing efficient signaling and provides a link between the areas of communication theory and modem design for amplitude constrained linear optical intensity channel. Topics include historical perspective, channel impairments, amplitude constraints and the characteristics of popular optoelectronic components. A variety of wireless optical channel topologies are presented along with a survey and analysis of present day signalling techniques employed for these channels. The author provides a unifying framework for signalling design which allows the channel constraints to be represented geometrically and permits the use of modem design principles from electrical channels. Modulation schemes are designed using the formalism of lattice codes and a design process for signalling sets is specified. The use of multiple-input/multiple-output (MIMO) wireless optical channels to improve the spectral efficiency of links is explored. The basic spatio-temporal modem design problem is specified and a spatial multiplexing gain is quantified. New spatial discrete multitone modulation is proposed and the unique features are discussed. Based on measurements on an experimental prototype, a channel model is formulated and a realizable spatio-temporal coding scheme is simulated to quantify performance gains. This volume is organized for professional and academic readers engaged in modem design for wireless optical intensity channels. Significant background material is presented on both the properties as well as on fundamental communications principles. Wireless Optical Communication Systems can be used by physicists and experimentalists as an introduction to signalling design as well as communication systems designers.

MPPM: a method for improving the band-utilization efficiency in optical PPM

Abstract: Multiple pulse position modulation (MPPM) is proposed as a modulation method to improve the band-utilization efficiency in optical pulse position modulation (PPM). Optical PPM gives higher transmission efficiency (bit/photon) in optical communications but degrades band-utilization efficiency. The proposed method reduces the required transmission bandwidth in optical PPM to about half with the same transmission efficiency, thus increasing band-utilization efficiency. While in conventional optical PPM, only one optical pulse is transmitted in every signal block, multiple pulses are transmitted using this method. Information is represented by different combinations of the positions of these pulses. The principle of bandwidth reduction applied, the transmission characteristics of the proposed method, and examples of improvement in band-utilization efficiency are also shown. >

Monolithic integrated coherent receiver on InP substrate

Abstract: The fabrication of a monolithic integrated coherent receiver with a wavelength-tunable DFB laser as local oscillator, a 3-dB waveguide directional coupler for mixing, and p-i-n photodiodes for detection is discussed. Optical heterodyne detection with a clear beat signal was experimentally observed using this monolithic integrated coherent receiver. Since an n-type substrate was used in this device, the two p-i-n photodiodes were not implemented in a balanced mixer configuration. Balanced mixing might be possible if the same structure were fabricated on a semi-insulating substrate. The results obtained suggest the possibility of applying this type of monolithic integrated coherent receiver to optical communication systems. >

Devices for wavelength multiplexing and demultiplexing

Abstract: Developments of optical fibre communication systems have until recently concentrated on increasing both the distances between repeaters and the intensity modulation bandwidths for single channel optical transmission. Tremendous achievements have been made in both areas such that, in the latter case, it is electronic component limitations which are starting to restrict the speed of operation of experimental systems. In this context, there is renewed interest in wavelength division multiplexing as a technique to upgrade the transmission bandwidth capacities of existing systems together with the possible future provision of broadband multichannel systems. A critical review of the component technology to enable wavelength division multiplexing is therefore useful at this stage. The major implementations of wavelength multiplexer/demultiplexer devices are discussed and compared with particular emphasis placed on their optical efficiency, spectral stability, crosstalk performance and the number of channels that may be provided. Passive devices ranging from the bulk optic implementations (i.e. prisms, gratings, filters) to integrated waveguide and fibre directional coupler realisations are considered. In addition developments associated with active devices including integrated source and detector arrays, wavelength tunable devices and optical amplifiers which may be employed within wave length multiplexed systems are outlined to provide an insight into possible future directions within the field.

Adaptive polarisation diversity receiver configuration for coherent optical fibre communications

Abstract: We describe an implementation of the polarisation diversity detection technique for coherent heterodyne communications which maintains the total IF amplitude at a constant level, irrespective of fluctuations in the state of polarisation of either the signal or local oscillator optical fields at the output polarisation beam-splitter.

Novel chromatic dispersion measurement method over continuous Gigahertz tuning range

Abstract: A method for the measurement of chromatic dispersion in a single-mode optical fiber is proposed and demonstrated. This method adopts the technique of external modulation of the distributed feedback (DFB) laser output and direct optical frequency sweep range monitoring by coherent heterodyne detection. The method is also applicable to the future optical communication system with narrowband optical elements such as optical amplifiers, whereas measurement is impossible given the present state of the art. >

Angle-tuned etalon filters for optical channel selection in high density wavelength division multiplexed systems

Abstract: Applications are discussed for angle-tuned in-line Fabry-Perot etalons for optical channel selection in a high-density wavelength division multiplexed (WDM) direct-detection fiber system. A typical WDM application (LAMBDANET type) was described. Different demultiplexing techniques and their relative advantages were considered. Design guidelines are given for determining the etalon parameters, the minimum channel spacing and the maximum number of channels for a single etalon and multiple etalons, including stacked identical etalons and stacked nonidentical etalons. Experimental results on using these etalons for optical channel tuning in a multiwavelength WDM optical communication system are presented. >

Optical communication by injection-locking to a signal which modulates an optical carrier

Abstract: An optical communication system is disclosed including an all-optical device whose output modulated optical beam is locked to an input modulated optical beam. In a specific embodiment of the system, the device may be a self-electro-optic effect device (SEED), which is operated as an oscillator by means of an associated tank circuit. Such an embodiment permits recovery of a clock frequency from a bit stream which is input into the device. When the output of the device is directed into an optical decision element, an all-optical regenerator may be realized.

Passive equalization of semiconductor diode laser frequency modulation

Abstract: Optical heterodyne communication systems using direct-frequency-modulated (FM) semiconductor diode lasers often exhibit system degradation because of the nonuniform injection-current-to-FM transfer function present in most semiconductor diode lasers. In a FSK system, a nonuniform FM transfer function causes tone drift which results in increased crosstalk between time slots and a corresponding degradation in system bit-error rate (BER). Using simple passive electrical networks it is possible to equalize the nonuniform FM response and substantially reduce this transfer-function-induced BER degradation. The theory, computer optimation, construction, and test of various equalization networks and their use in realizing an FM-equalized transmitter for a 100-Mb/s binary FSK communication system is described. >

Signal light amplification by stimulated Raman scattering in an N-channel WDM optical fiber communication system

Abstract: The use of forward and backward Raman amplification in an N-channel wavelength-division-multiplexing (WDM) optical-fiber communication system is analyzed. Analytical expressions for the signals, the pumps, and the amplified spontaneous scattered power (ASSP) are presented. The crosstalk among the signal channels is analyzed in terms of system parameters. It is found that the crosstalk is negligible while low pump power is used and becomes significant if high pump power is used. The signal-to-ASSP ratio can be improved by increasing pump power; however, the improvement is small when pump power is already high. A 300-km repeater spacing with more than 20-dB signal-to-ASSP ratio is calculated. >

Polarization diversity optical receiver for coherent optical communication

Abstract: A polarized wave diversity optical receiver for coherent optical communication including: an optical local oscillating circuit (7) for oscillating local oscillating light; a mixing circuit (8) for mixing signal light and the local oscillating light to obtain two polarized components; a detecting circuit (9) for detecting the polarized component to output intermediate frequency signals (e S and e P ); and a frequency control circuit (11) for controlling, in accordance with the intermediate frequency signals (e S and e P ), the oscillating frequency of the optical local oscillating circuit (7). To ensure that the intermediate frequency does not disappear, the frequency control circuit (11) outputs a combined signal of a sum and a difference of the intermediate frequency signals (e S and e P ).

Multiwavelength sources using laser diodes frequency-locked to atomic resonances

Abstract: It is shown that low-cost compact disk AlGaAs laser diodes make it possible to realize manifold optical sources with precise and stable wavelengths when locked to rubidium vapor resonances. Many optical frequency references can be obtained with the use of absorption cells containing a foreign gas or by placing cells in static magnetic fields. The same approach can be used with other wavelengths required by optical fiber communications. >

Experimental spreading and despreading of the optical spectrum

Abstract: An experimental realization of direct-sequence spreading and despreading of the optical spectrum using off-the-shelf electrooptic modulators is reported. This capability is required to implement a fiber-optic network originally devised by G. Foschini and G. Vannucci (1983). The network utilizes spread-spectrum techniques on the optical spectrum, together with coherent signal detection to accommodate a very large number of simultaneous users, for a total throughput measured in hundreds of Gb/s. The results obtained provide confidence that a network built around this idea would perform according to theoretical calculations. Coherent spectral spreading and despreading is thus established as a promising communication technique for fiber-optic systems. >

Programmable optical interconnections with large fan-out capability using the magneto-optic spatial light modulator.

Abstract: We report the use of two-dimensional, binary phase-only diffraction gratings written on a programmable magneto-optic spatial light modulator to interconnect optically an input laser beam to multiple output locations. We show that we can achieve programmable weighted interconnects between the source and two output locations as well as a fan-out capability to as many as 128 separate output locations.

Polarization-insensitive technique for coherent optical communication

Abstract: To exploit the potential advantages of coherent optical communications systems, the polarization states of the received optical signal and the local oscillator waves must be matched. A mismatch may severely degrade detection performance. These mismatches occur because the received signal state of polarization changes with time and along the fiber. We first review several existing techniques for handling this problem, such as polarization-maintaining fibers, polarization-state controllers and polarization-diversity receivers. The insensitive technique reduces the problem of polarization mismatch by forcing the polarization state of either the transmitted signal or local oscillator to vary with time in a non-adaptive manner so that polarization-insensitive performance is obtained. The proposed scheme adopts a completely new approach which uses high-birefringence single-mode fibers to implement polarization switching. These techniques require only a single photodetector and give a fixed level of detection performance, with a power penalty relative to ideal of 3 dB. A specific technique is presented in which polarization-insensitive heterodyne detection is achieved through data-induced polarization switching. The polarization switching is brought about by inserting a passive, birefringent optical device in the path of the transmitted FSK signal.

Terahertz repetition rate optical computing systems, and communication systems and logic elements using cross-phase modulation based optical processors

Abstract: Optical communication systems, optical computing systems and optical logic elements which rely on the phenomina of cross-phase modulation to alter and control, either or simultaneously, the spectral, temporal or/and spatial properties of ultrashort light pulses for processing information with high speed repetition rates. A weak beam of ultrashort light pulses is modulated by an intense beam of ultrashort light pulses by copropagating both beams through a non-linear medium such that cross-phase modulation effects are realized.

Hybrid laser for optical communications, and transmitter, system, and method

Abstract: In the interest of ease of manufacture, hybrid lasers of distributed-Bragg-reflector type are preferred for use as light sources in optical communications. Such lasers are made to operate away from mode instabilities by adjusting a laser parameter such as, e.g., laser temperature, thereby assuring highly error-free transmission. Alternatively, by suitable design of the Bragg reflector it is possible to render mode instability of negligible influence on error rate.

Optoelectronic device for an optical communication system

Abstract: An optoelectronic device for use in an optical communication system is disclosed. The optoelectronic device, coupling to each other the ports of a plurality (e.g. two or three) of optical data transmission lines, comprises: pass-through optical fibers connecting to each other the ports of the optical data transmission lines; receiving optical fibers connecting such ports to the input of an optical-to-electrical transducer; transmitting optical fibers connecting the output of an electrical-to-optical transducer to the above ports; a pulse width fixing circuit, having an input and an output coupled to the output of the optical-to-electrical transducer and the input of the electrical-to-optical transducer, respectively, for regenerating and amplifying the signal and limiting the pulse width of the regenerated signal to a predetermined fixed length; and a pulse width normalizing circuit (second pulse width fixing circuit) to whose output the input of a terminal electronic data processing device is coupled to receive information from the optical signal transmitted through the optical data transmission lines. The output of the terminal data processing device is supplied to the electrical-to-optical transducer.

Equalization in coherent lightwave systems using microwave waveguides

Abstract: The maximum bit rate/ distance product in recent single-frequency laser direct-detection lightwave system experiments has been limited by dispersion. An equalization technique, appropriate for coherent lightwave systems, that uses a microwave waveguide for overcoming the delay dispersion problem is considered. Results show that small low-loss waveguides can be used to greatly reduce dispersion. For example an 8 GHz bandwidth signal transmitted over 68 km of fiber can be equalized by a waveguide with a cross section of 6 mm*3 mm and a length of only 17 cm. With the waveguide equalizer, the dispersion-limited maximum bit rate/distance product for a standard fiber system can be increased to that of a dispersion-shifted fiber system at 1.55 mu m, e.g., a 16-fold increase in maximum bit rate for 100 km transmission. >

Nonlinear distortion due to optical amplifiers in subcarrier-multiplexed lightwave communications systems

Abstract: We show that an optically amplified, subcarrier-modulated lightwave signal suffers both a compression of the optical modulation indices and second-order nonlinear distortion (NLD). Expressions are derived which show that the NLD can seriously degrade performance, unless the lowest subcarrier frequency is larger than several gigahertz. System implications of these effects are discussed.

A heterodyne receiver for coherent optical communication

Abstract: After mixing the signal light and the local oscillation light with a mixing circuit (21), two inter­secting polarization components are divided by a polarization splitter (23) and respective components are subjected to heterodyne detection by optical receivers (24, 25). Thereafter, in an electric signal stage, the intermediate frequency signals outputted from the optical receivers (24, 25) are applied to a 90-degree hybrid coupler (26) and the output signal from one of the output ports is demodulated by a demodulator (27). On the other hand, intermediate frequency signals outputted from the optical receivers (24, 25) are subjected to a subtraction to provide a principal axis angle monitor signal for the signal light. The signal outputted from the output port from the 90-degree hybrid coupler (26) is used to monitor the eiliptic ratio of the signal light and these monitor signals are applied to the polarization control circuit (29). The polarization control circuit drives the polarization operation apparatus (20) based on said monitor signal to control the polarization state (i.e. a principal axis angle and the elliptic ratio) of the signal light to achieve the optimum state.

Fibre Raman amplifier properties for applications to long-distance optical communications

Abstract: This paper reviews recent theoretical and experimental studies on optical amplification by stimulated Raman scattering (Raman amplification) in single-mode optical fibres, and discusses its possible applications to long-distance optical communications. The fibre Raman amplifier can be used as an in-line optical amplifier in both repeaterless and non-regenerative all-optical repeater configurations. In the former application, signal transmission of over 400 km has been predicted theoretically, although high-power pump sources are considered to be required. In the latter configuration, in which optical fibre losses are compensated for by Raman gains, it has been shown that extremely long-distance transmission over more than 1000 km is feasible in terms of signal-to-noise ratio, where the distance achievable is mainly limited by the accumulation of Raman noise. Recent experimental demonstrations including bit-error rate measurements on the Raman amplified signal, and laser-diode pumped amplification, etc., are also reviewed. The results confirm the effectiveness of fibre Raman amplifiers in future long-haul systems.

Principles of Modern Optical Systems

Abstract: Theoretical and applications aspects of optoelectronics technology are examined in an introduction for engineering students and practicing engineers. Chapters are devoted to the fundamental principles of optics and optoelectronics, optical coherence and polarization, semiconductor light sources, optical fibers, nonlinear effects in optical fibers, optical-fiber cables and connectors, and fiber-optic components. Consideration is given to integrated optics, fiber-optic telecommunication systems, fiber sensors and sensor networks, optical remote sensing, optical information processing, guided-wave signal processing, and optical-disk storage systems.

Broadband video distribution over passive optical network using subcarrier multiplexing techniques

Abstract: A 16-channel subcarrier-multiplexed video system has been optimised for operation over a passively split optical network. The system delivers a weighted SNR of 47dB with an optical power budget of 34 dB and a dynamic range of 19dB.

Performance analysis of coherent optical phase-diversity receivers with DPSK modulation

Abstract: The transmission performance of two phase-diversity receiver structures using a six-port fiber coupler is investigated for coherent optical communication systems with differential phase-shift-keying (DPSK) modulation. A general method for evaluating the error probability of phase-diversity DPSK receivers using delay-and-multiply demonstrators is derived. The method is used to show that, in the shot-noise limited case, the performance of the phase-diversity DPSK receivers is close to that achievable with a heterodyne receiver, provided the frequency offset between lasers is less that about 1% of the bit rate. The allowable total laser linewidth is in the range of 0.3-0.4% of the bit rate. >

An optical transmission line for use in an optical communication system

Abstract: A mode scrambler (13) is interconnected between a light source (10) and an optical fiber coupler (1) made of a plurality of graded index multi-mode optical fibers (1F) The mode of the input light signals can be converted to a random pattern mode through the mode scrambler (13), so that a steady excitation state of the input light can be realized, including not only dominant lower modes but also higher modes of the input light signals, resulting in enabling to divide the input light signals without any irregularity of the output light power

16-channel optical FDM distribution/transmission experiment utilising Er3+-doped fibre amplifier

Abstract: A 16-channel optical FDM distribution/transmission experiment at around 1534nm wavelength is demonstrated utilising an Er3+-loped fibre amplifier. 16 intensity-modulated optical signals at 622 Mbit/s were amplified simultaneously at a gain of 15.2–18.5 dB. One of the amplified signals is selected using the waveguide frequency selection switch and directly detected with a receiver sensitivity of −38 dBm (Pa=10−9).

Intersatellite Optical Heterodyne Communication Systems

Abstract: High-capacity intersatellite communication crosslinks will allow more efficient and reliable operation of military and commercial satellite systems. High-speed optical crossl inks can serve as a key building element of an interconnected space-based communication systemfor military applications. A network such as this would provide immediate communication among satellites, eliminating the need for ground-based relay stations and expensive worldwide ground tracking networks, which would greatly improve the efficacy and reduce the vulnerability of existing satellite systems. Crosslinks can also provide connectivty for commercial global satellite communication systems and for deep-space applications. Optical heterodyne communicatiol systems using semiconductor lasers offer small-aperture, modest-weight, low-power, point-to-point crosslink packages, characteristics that are suitable for the envisioned applications. System research and development performed at Lincoln Laboratory permits the implementation of an efficient optical crosslink based on readily available, state-of-the-art devices and technology.