A new flame-brush technique is used to fabricate monomode fused couplers for application as hydrostatic pressure sensors, narrowband tunable filters and dissimilar-type fiber lateral splices. Light switching from one output port to the other in the most sensitive case was achieved with a pressure change of 8.8 psi. Wavelength tuning of a 1200 cycle-0.35 rim half period coupler was tuned over a band of 20 nm with a sensitivity of 0.013 nm/psi. Also fused couplers made of dissimilar-type fibers are proposed as lateral splices useful for efficiently exchanging power between the HEll modes of fibers with different normalized frequencies.

The paper reports the development of a high-performance ruggedized single-mode coupler for an operating temperature range of -55°C to +125°C. Test couplers have been subjected to environmental tests recommended for air-borne fiber-optic components for use in data buses in commercial and military aircraft. The design features of the coupler is reported, as well as its optical performance characteristics and environmental test results.

A model for in-line spectral filters using the tapering technique on single-mode fibers is developed. The filters are designed to provide additional isolation to the 1300 nm / 1550 nm demultiplexing fused couplers.

Reliability testing was performed on 3dB couplers manufactured by the Gould Fiber Optics Operation. No significant change in coupler performance was observed during the tests. The maximum change in coupling ratio during repetitive temperature cycling from -40°C to +85°C averaged only 1.6%. Following 250 cycles between -40°C and 85°C, the coupling ratio and polarization sensitivity remained within 0.8% and 0.3%, respectively, of their initial values. The coupling ratio also remained constant to within 1% when measured periodically during a 1500 hour, damp heat test conducted at 65°C and 85% relative humidity. Couplers were also subjected to vibrations from 10-5000 Hz at 9g's and shocks up to 2500g's. During these tests the coupling ratio remained constant to within 1%.

A new type of fiber optic directional coupling device is presented, designed specifically for hard-clad silica ( HCS ) fiber. Typical excess loss of couplers with 50% coupling ratio is 0.15 dB, with devices with this performance specifications being made using different sizes of hard-clad silica fiber. Tests show that the couplers have very stable temperature response, a flat coupling ratio spectrum and high directivity.

In this paper the characteristics of asymmetric, singlemode/multi-mode couplers are presented. The devices are fabricated by fusing a singlemode fiber to a multimode fiber using the fused biconical taper technique. The features of these asymmetric couplers are compared to those predicted by a simple model that is based on the modal capacities of the two fibers.

A fabrication technique for manufacturing fiber directional couplers using plastic optical fiber has been developed. The coupler is manufactured by direct bonding of the uncladded segments of the fibers which enables accurate control of the desired coupling ratio and excess loss. Typical 2x2 couplers have an excess loss less of 0.6dB and 6x6 star couplers had an excess loss less than 2dB. The performance of the devices are found to be relatively stable with temperature over the range of -15 to +65 degree centigrade.

With each passing year, fiber optic technology is being used to solve more communication problems. Optical fibers have extremely wide information bandwidth and are immune to ground loops, EMP, RFI, and EMI. Many military applications are now beginning to utilize optical fibers for interconnections between high speed digital devices, or to interconnect between sensors and signal processing systems.

Fibre-optic polarizing beam splitters are 2x2 port components which cross-couple efficiently one input linear polarization and transmit unaffected the orthogonal one. Such a device is useful in a variety of all-fibre-optic applications such as wavelength multiplexing / demultiplexing, polarization diversity detection schemes, and fibre Raman amplifiers. The configurations reported so far consist of two single-modal low- or high-birefrigence fibres coupled together by either fusion or polishing techniques. Their function relies upon the geometrical form and/or stress-induced birefrigence introduced into the interaction area. The polarization splitting can then be described either by the use of different-coupling- coefficient arguments for the two orthogonal polarizations [1] [2], or by differential beating of the LP0 1 and LP 11 modes excited in the interaction composite region by each of the two orthogonal polarizations [3] [4]. An alternative novel approach to the same problem utilizes the polishing technique to couple the two fibres and Surface Plasmon Waves (SPWs) to achieve polarization separation [5]. A thin metal film incorporated between the two polished surfaces in the interaction area supports SPWs which are inherently TM-polarised. Therefore, in this three-waveguide structure (fibre-thin metal film-fibre) only TM-like-polarized light cross-couples efficiently while the TE-like-polarization is transmitted unaffected. A typical polarization extinction ratio of 35 dB in both arms and a polarization selectivity of 30 dB are achieved.

This paper reports on the design and performance of all-fibre polarizers and polarization beamsplitters utilizing both standard and high birefringence optical fibres. These devices exploit the polarization selective coupling of an optical field to a surface plasmon polariton in a thin metal film. In the case of the polarizer the power coupled into the plasmon is dissipated whereas in the polarization beamsplitter it is further coupled into a second optical fibre. High quality devices have been manufactured and extinct-ion ratios in excess of 50dB and 40dB have been achieved for polarizers and polarizing beamsplitters respectively.

Uniform gain is one of the most important characteristics for a high performance avalanche photodiode (APD). In this paper, we present a review of various APD structures and discuss their performance on gain uniformity. Then we focus-on a high speed planar InP/InGaAsP APD with a reduced junction curvature and low p-type doping which prove to be effective to prevent edge-breakdown and provide gain uniformity. This APD was fabricated by Be + implantation through a photoelectrochemically (PEC) etched InGaAs mask and has a planar structure. A dish-shaped opening was etched by PEC etching in the InGaAs layer, which served as an implant mask. The p-n junction was then formed by a beryllium implant. The dish-shaped depression in the mask layer was replicated in the junction profile in the InP layer. The photoresponse of 1.3 pm wavelength scanned across the diode showed a uniform gain as high as 30 without edge or surface breakdown. The device had a 3 dB bandwidth of > 1.2 GHz and demonstrated a 10-9 bit error rate sensitivity (nP) of -35.5 dBm at a data rate of 1.7 Gb/s. The advantages of this device are the simplicity of the epitaxial material structure and the fact that only a single ion implantation is required to fabricate the device.

A high performance edge emitting 830 nm LED has been mated with SMA and ST fiber optic receptacles using an internal lens to achieve performance comparable to a pigtailed device at substantially lower cost. The absence of a pigtail enhances reliability and simplifies handling during PC board assembly. The design goals included -7 dBm minimum launched power into a 100 micron core fiber at 150 mA drive current, compatibility with existing active device packages, electrical isolation of all pins from the package, and 0° to 50°C operation, typical of commercial Local Area Network (LAN) requirements. These objectives are attained using a cylindrical Graded Index (GRIN) lens bonded into the package, and active alignment of the device during assembly. Where the highest power is required, as in passive star LANs, coupled powers of -3 dBm are easily achieved at 150 mA; alternatively, optical power can be traded for reduced drive current, an attractive property for active star based LANs. The devices exhibit rise times of 4 to 7 ns, with 2 ns available at reduced power output. Repeatability of coupled power for multiple connections of the same or different 100 micron core fibers is typically ±0.5 dB for SMA Type 2 connectors, and ±0.25 dB or less for SMA Type 1 and ST connectors. The devices withstand ten thermal shock cycles (-40° to + 100°C) with no significant change in optical output. Accelerated life testing has demonstrated a MTTF of 2.7 x 107 hours for unpackaged devices, and preliminary results indicate comparable lifetimes for the packaged devices. The paper will discuss the design criteria for optimum coupling in a system consisting of an edge emitting LED, GRIN lens, and connectorized optical fiber; comparison to other lens systems will be made. Data for coupled power versus drive current and fiber size (100 micron, 62.5 micron, 50 micron) will be presented. In addition, results of high pulsed current operation will be given.

The integration of fiberoptic, optoelectronic, and electrical components to form hybrid devices has many advantages to the end user. These include: (i) Elimination of fiber pigtails from the PCB which can either be "snagged" or bent, which in the latter case may incur a loss penalty. (ii) Optimization of system performance by control of the total packaged system. That is, the performance of the transceiver can be optimized because the individual components that make up the device can be selected and/or traded off for given performance requirements. (iii) A compact system can save "real estate" on the PCB and result in lower system costs. (iv) Provides a "user friendly" subsystem that removes the requirement for highly skilled engineers in cross-disciplines. In this paper, details of the integration of single mode lasers, PIN detectors, HCS optical fiber couplers and electronic drive/detector circuitry are presented.

We compare the performance of high speed planar InP/InGaAs separate absorption, grading and multiplication region avalanche photodiodes where the grading layer consists of a single quaternary layer or a chirped superlattice. The devices are grown by atmospheric pressure metal organic vapour phase epitaxy which has been found to produce good quality, low defect density, uniform material on large area (2") slices. Both types of grading layer are found to suppress the slow component of the avalanche photodiodes pulse response while exhibiting low dark currents (1-10nA @ 0.9Vb). The characteristics of the diodes are shown to be uniform over 2" wafers and suitable for use at bit rates up to at least 2.4Gbaud.

Metal-semiconductor-metal (MSM) and pin photodetectors have emerged over the past years as suitable options for large-bandwidth integrated receiver front-ends. In this paper we discuss the inherent bandwidth limitations set by practical constraints of size and quantum efficiency on InP/InGaAs based devices of both types under 1.3 and 1.55 pi m illumination. Large-bandwidth MSM detectors which use a strained GaAs layer between the InGaAs absorption layer and the Ti/Pt/Au contact fingers have been fabricated and tested. Their pulse response will be discussed in detail and compared with theoretical results.

"Optimization of fiber parameters" usually implies that the numerical aperture, the core/clad ratio, or the core profile is modified for the application of interest. While this is generally true, the accompanying assumption is that the materials being used have already been optimized. In this paper, the opposite tack is taken (i.e., the materials have been neither identified nor optimized). The choice of starting materials is critical, and usually understated. Because the proper choice of starting material should include consideration of the mechanical and optical properties, as well as other physical properties, the particular application should require only additional fine tuning.

This paper reviews a worldwide effort to make fiber by sol-gel. Two routes: the all-gel and the hybrid are described. In the latter, a vapor-deposited core member is overclad with gel-silica subsequently to be drawn to fibers. Recently, bodies weighing more than 1 Kg have been cast, dried and consolidated. Taken together these reports suggest that sol-gel processing is approaching the threshold of commercialization.

We present theoretical calculations for chromatic dispersion, splice loss, macrobending loss and microbending loss in single-mode fluoride fibers designed to give optimum performance for future long distance communication systems in the 1.5 to 2.9 μm wavelength region. It is shown that these fibers offer dramatic improvements over silica fibers,even when compared to dispersion-flattened silica fibers.

An optical fiber with a 50um diameter pure silica core and a 55um diameter hard polymeric cladding has been developed and characterized. Optical and mechanical properties are excellent for a fiber of such small diameter. Characteristic dynamic strengths of 523 kpsi are observed with attenuation <50 dB/km at 820nm. The fiber is designed with a small core diameter and high core-to-clad ratio, primarily for use with high resolution and high efficiency optical fiber bundles. The fiber dimensions allow a packing fraction of 0.75 and a maximum core offset of l.5um. The optical and mechanical measurement results are described with a brief description of potential application advantages.

General techniques for the quality control of long lengths of optical fiber for telecommunications applications have been developed during the past 10 years in concert with ongoing handling scenarios that involved cabled versions of the tested fiber. In the present work, we discuss the same quality control techniques, but apply the results to stand-alone fiber (primary or secondary buffer only). Furthermore, by modifying the normal quality control techniques, we have produced a stand-alone fiber that exhibits superior mechanical performance for missile payout applications when compared with standard telecommunications fiber. High quality optical fibers, which were produced to more exacting standards than long-haul telecommunications fibers, were subsequently exposed to high-stress bend tests along multikilometer lengths of the fiber. Mechanical failures during these tests could occur at stresses lower than the required 200 ksi proof test. The fracture surfaces for these failures were examined by normal fractographic techniques. These surfaces clearly showed that mechanical failure occurred at stresses below the proof stress. Furthermore, an appreciable number of these failures were accompanied by damage to the buffer, presumably preceding the mechanical failure. To correct the situation, we introduced changes in both the process and the testing for these fibers. During processing, the fibers were prepared with high quality silica substrate tubing, and all processing was carried out in a clean room environment. Proof testing subsequent to production was changed from a single test at 200 ksi to multiple testing at 100 ksi increments. Testing was further modified to include preinspection of the entire buffer surface for flaws of a serious enough nature to lead to mechanical damage to the underlying glass. The interaction of all of the previously noted changes helped to increase the reliability of the optical fiber for missile payout applications. Fractographs of the failures, proof test data, and identification of the buffer flaws, independent of fiber manufacturer or manufacturing process, will be discussed.

Acknowledgement: The assistance and support of the MICOM Army Missile Command is gratefully appreciated. An analytical tool to investigate the arc fusion splicing of optical fibers is developed. The physical model incorporates heat transfer and thermal, visco elastic strain. The heat transfer equations governing radiation, conduction and convection during arc heating are formulated. The radiation heat flux impinging on the fiber optics is modeled based on reported experimental analysis of a generic type arc discharge. The fusion process considers deformation of the fiber due to thermal, viscous and elastic strain. A Maxwell stress-strain relationship is assumed. The model assumes an initial gap at the beginning of the arc which is closed by a press-stroke during the heating cycle. All physical properties of the fused silica glass fibers are considered as functions of temperature based on available experimental data. A computer algorithm has been developed to solve the system of governing equations and parametric studies carried out. An experiment using a FSM-20 arc fusion splicer manufactured by Fujikura Ltd. was carried out to provide experimental verification of the analytical model. In the experiment a continuous fiber was positioned in the arc and cyclic heating and cooling was carried out. One end of the fiber was clamped and the other was free to move. The fiber was heated for 6 seconds and cooled for 3 minutes for several cycles. At the end of each cooling process, photographs of the deformation of the fiber were taken. The results showed that the fiber necked down on the free end and buldged up on the fixed end. With repeated heating and cooling cycles, the optical fiber eventually necked down to the point that it melted in two. The analytical model was run for the conditions of the experiment. Comparisons of the predicted deformation of the optical fiber with those measured is given. The analytical model displays all of the physical phenomenon of fiber deformation observed in the experiment. The magnitude of the deformation is over predicted in some instances and underpredicted in others. This effect is explained on the basis of unknowns in the model of radiation heat flux and in the variation of density with temperature (i.e., crystal structure changes during heating). It is concluded, however, that the model simulates all the physics correctly, and therefore, provides a meaningful technique for analyzing the significant parameters involved in arc fusion splicing. Plans for further parametric studies are described.

The nonmetallic optical fibers cables have been required in several applications of optoelectronic communication systems. The dielectric fiber lightguide attends the environment characteristics described above and the nonmetallic optical fiber cables meets the optical fiber features (lightwave weight, ground loop free ...). Strength member is the most important component for optical cables. It's responsable to keep the optical fibers free of stress during cable installation. The strength member must not only have a high modulus but must be compatible with the other components of the cable, specially during processing of these materials in cable manufacture. The coefficient of thermal expansion is very important because various plastic materials are typically extruded during cable fabrication, and dimensional changes can cause serious problems during manufacture or subsequent environment temperature extremes if the cable is not properly designed. Cost has been the barrier to using fiber optic links in low and moderate data rate, short and moderate haul applications. KevlarR and F.R.P. are imported materials in Brazil, therefore they are expensive. We have developed a plastic strength member to meet the economic viability of the optoelectronic system. The application of this plastic strength member in tight structure and loose structure are described. The reliability of this composite material as strength member in optical cables as well as the comparison with various imported FRP are shown.

Unlike the multimode era, 1980 to 1984, and the single-mode era, 1984 to 1988, the coming fiber-to-the-home era seems to have its necessary products available and its competitors anxious and ready. Notably-missing in this new market will probably be fusion splicing and Biconic connectors.

A more complete theory of the splice loss for single-mode fibers is presented in this paper. According to the optical waveguide theory and Gaussian beam theory, the optimum analytic relation expression between the step-index fiber parameters and that of its mode field is derived and the calculation formula of the total splice loss is also derived. The total splice loss caused by offset, tilt, end-separation and core diameter non-matching in the same time consists of their four intersection items. The derived formulas can be used to predict and obtain low splice loss for single-mode fibers.

Butt coupling efficiencies reported to date for conventional circular core optical fiber have been low due to the mismatch between the emission profiles of the laser diode and the optical fiber. Attempts to use lenses to increase the coupling efficiency has resulted in the degradation of the laser performance due to external optical feedback from the lenses or from the front end of the fiber. If the fiber is bonded directly to the front facet of the laser, the external optical feedback from the front facet of the fiber is eliminated. A higher coupling efficiency is realized through the use of a non-circular core optical fiber, such as an elliptical core fiber, which more closely matches the highly divergent, elliptically shaped, laser diode emission profile.

A novel method of producing tapers in single-mode fibres by controlled thermal diffusion of the dopant has been developed. Extended biconic tapers have been produced, which have shown a radically improved tolerance to transverse and longitudinal offsets. Mechanical fibre dimensions are maintained during the process. The tapers are appropriate for connection devices, where the improved tolerance to transverse offset will reduce insertion losses or enable the use of cheaper, less accurately machined components. Where free space propagation of light between two fibres is required, the improved tolerance to longitudinal offset removes the need for beam collimation elements. Thin bulk optical devices may be advantageously introduced into the gap. Furthermore, low cost alignment components may be used in the assembly.

A new-type micro-displacement servo stage--lever-type flexure hinge elastic servo stage for the precision alignment of single-mode fibers has been developed. This stage not only processes high displacement resolution(≈0.1μm), small volume(≤40cm), light weight(<0.4kg), but also large movable stroke of ±50p.m. It can realize two-dimension movement on a single layer or plane and the two stages can realize the three-dimension precision alignments of sinule-mode fibers. The structure and design of this stage are presented. Piezoelectric element used as the servo driver of the stage is discussed in detail. The experi ental result shows that the aligntent accuracy of 0.1μm for single-mode fibers has been achieved by the new micro-displacement servo stage.

As fiber optics applications grow in many military areas, many of which are in critical and adverse environments, the need for reliable and easy to field-assemble optical termina-tions has become more essential. A family of multimode "crimp & cleave", no epoxy, no polish, FSMA style fiber optic connectors has been developed (see Fig 1). These connectors are designed to take advantage of the unique properties of Hard Clad Silica (HCS®) fibers. Unlike other crimp and cleave connectors, this system employs a metal crimp applied directly onto the fiber's hard polymeric cladding. This retention mechanism is remarkably stable over a wide range of temperatures and environmental conditions. The connector system is designed for short haul applications in which the field installation time of less than 3 minutes and the environmental reliability are more important than extremely low insertion loss. This paper will describe the connector, MIL-C-83522/15, and the qualification testing done to meet the MIL-C-83522B specification.

The AT&T single-mode ST® connector is a low-loss, low-reflection connector, making it suitable for high-speed, wideband digital transmission. This new connector offers enhanced hardware for easier use and more stable connections. In addition, a new backplane-compatible version is introduced for circuit board applications. The insertion loss of AT&T's single-mode ST connector averages 0.34 dB with a standard deviation of 0.28. The reflection of an AT&T ST connection (product against product) is -42.8 dB average with a worst case of -34.1 dB. The environmental performance of the connector is characterized by very low variations in loss and reflection. The AT&T single-mode ST connector and its backplane version were subjected to a battery of tests whose results are discussed in this paper.

In this paper, an overview of coherent lightwave communications (CLC) was given for the new comer to the field and also to discuss the various components of a CLC system to highlight the papers that were to be presented in the session to follow during the day. The topics covered included: (i) comparison of CLC to direct detection system, (ii) advantages of CLC systems, (iii) modulation formats and their relative advantages, (iv) polarization controllers and polarization preserving fibers, (v) examples of systems demonstrated in the laboratory, (vi) application areas of CLC in long-haul communications, local area networks and space communications. The reader is refered to (i) the many excellent articles in this proceeding, (ii) to the following references, for further details an all aspects of coherent lightwave communications.

Single frequency lasers and frequency tunable lasers are essential components needed for the future generation of optical fiber communication systems and exchange networks. The spectral linewidths of the state-of-the-art distributed feedback lasers are reviewed. Characteristics of frequency tuning of multi-electrode DFB lasers and DBR lasers are discussed.

This paper discusses the impact of state-of-the-art diode laser optical characteristics on the overall performance capabilities of coherent communication systems. In it we explore what the present laboratory device performance represents in terms of system capabilities and what issues remain to be resolved in order to achieve certain goals. The paper deals with the following subjects: ♦Optical performance issues for diode lasers in coherent systems. ♦Reported measurements of key performance parameters. ♦Optical requirements for coherent single channel and (especially) multichannel communications systems. ♦Limitations imposed by diode laser optical performance on multichannel system capabilities. ♦Implications for future developments.

Critical parameter combinations, which govern the reduction of the linewidth and tunability in a DFB laser-based external cavity structure, are determined by a mathematical model. The coupling coefficient, operating point of the DFB laser, refractive index and the external cavity length are found to greatly determine the absolute linewidth of this structure. An optimum continuous tuning range of 55 GHz is predicted. However, the usable tuning range is much smaller as will be seen.

A polarization maintaining single mode fiber birefringent filter which could function as a two channel, three port wavelength selective multiplexer/demultiplexer has been designed, constructed, characterized, and evaluated. A highly accurate and novel procedure was used to measure the wavelength dependence of the beat length of the AT&T rectangular PM fiber used in the prototype filter. In addition, a computer simulation of birefringent filters (based on a new first principle theory of polarized signals in birefringent media) was used as a design tool and found to be in excellent agreement with the spectral response of the prototype filter. The free spectral range of the prototype filter is 326 nm with pass/stop bands of 36 nm and 45 nm about the 1373.2 nm and 1533.3 nm wavelengths, respectively. The insertion loss, which was not optimized, was 4.3 dB. The crosstalk was -11.3 dB and -24.2 dB for the parallel and crossed orientations of the polarizers.

An all-fiber single-sideband frequency shifter has been demonstrated that uses a traveling acoustic wave incident upon a birefringent fiber at an angle to produce phase-matched polarization coupling. The fiber was helically wound on an aluminum cylinder to form a compact device. Conversion efficiency of 75% at 6 MHz has been obtained using 0.4 W of electrical input power. A 3 dB tuning range of 210 KHz was achieved. Sideband and carrier suppressions of 35 and 20 dB, respectively, have been observed.

Coherent optical signals transmitted through a single-mode fiber are highly sensitive to the refractive index changes caused by the fiber axis distortions, stresses and strains. Analysis of the the fiber axis distortions are most conveniently made by periodic perturbations of the fiber axis. Periodic perturbations may enhance periodic birefrengence, thereby, cause an optical signal phase delay[1,2]. Also, it may act as a dispersive filter[3], thus limiting the performances of a high speed optical communication system. Temperature affects the fiber coating, therefore, result in additional phase delay above which is already introduced in the fiber by the cabling process. It also affects the polarization state of the signal transmitted through the fiber.

Design of Fabry-Perot laser-based external cavity structures is presented with particular emphasis on linewidth and tunability. The important design parameters of this structure (ECSL-External Cavity Semiconductor Laser) which affect the linewidth are: optical feedback ratio, reflectivity of the laser facet nearer to the feedback component, frequency detuning of the optical feedback, external cavity length, and feedback bandwidth. We also studied the tuning charac-teristics of external cavity Fabry-Perot semiconductor lasers with strong feedback. It is shown that the gain change mechanism induced by the strong optical feedback in Fabry-Perot cavity is responsible for the spectral tuning. The Fabry-Perot resonator with external cavity can sup-port broad frequency detuning with varying threshold gain. The threshold gain decreases as the diffraction grating is tuned towards longer wavelengths.

The Planar Poincare Chart has been developed as a complete planar equivalence of the Poincare sphere. The four main parameters of the light wave represented by the chart are drawn separately on two parts, so that any orientation of the optical component can be shown on the chart. The Planar Poincare Chart can be used to graphically design and analyze the polarization dependent components, e.g. to predict the polarization change in the birefringent material. Depending on how the chart is projected, different types of birefringent materials can be investigated. Previously the chart for linear and circular birefringent materials has been reported. In a more general case, a chart for elliptical birefringent material is developed where the linear and circular cases can be considered as special cases.

The successful application of an endless polarisation control scheme was demonstrated by its use in a high sensitivity PSK heterodyne optical communication system. The synchronous demodulation of PSK signals was investigated and the practical implementation of a phase locked loop which is able to track the phase noise of optical signals is discussed. A large loop bandwidth is shown to be necessary and a loop filter of modified first order type was found to have advantages over a second order type. A synchronous demodulation system not using a phase locked loop is also proposed.

We report the performance of a 1.4 Gbit/s differential phase shift keying (DPSK) coherent fiber system experiment using a balanced receiver. We show that the detection sensitivity as a function of local oscillator (LO) power follows the same functional dependence as the theoretical prediction.

The polarization modulation technique with two different detection schemes is analyzed. A first experimen-tal test for demonstrating the principle of differential heterodyne detection has been performed. Many computer simulations at high and low bit-rates yield a performance complete equality of the two systems.

An important advantage of coherent lightwave systems is that they can offer access to the vast transmission capacity of single mode fiber by the use of optical frequency division multiplexing.1 The potential of multichannel coherent fiber optic communication systems is increased significantly when the systems employ optical amplifiers as repeaters and/or power boosters.2 One of the main issues concerning such systems is the determination of optimum channel spacing, which would allow maximum channel packing density without system degradation.3 This paper reviews the technical progress and the performance of multichannel coherent lightwave systems. Main technical issues in such systems are first identified4-6 and the mechanism and sources of interchannel crosstalk are discussed.7,8 Then bit-error-rate performance and crosstalk penalty in a multichannel ASK heterodyne system are described. The primary focus is on the laser linewidth effect on channel spacing.9 Some experimental results are compared with the predictions of a theoretical mode1.7,10 This is followed by a discussion on the crosstalk and channel spacing in the presence of optical amplifiers.11-14 Finally, technical areas and issues for further work are identified.

High-capacity intersatellite communication crosslinks will allow more efficient and reliable operation of satellite systems. This paper surveys present and future coherent optical communication technology and its application to intersatellite links.

We describe an all-optical method to transform a weak incident optical beam with constant amplitude and pulsated phase jumps into an amplified optical beam with amplitude modulation. The proposed method uses either the reflected or the transmitted beams by a phase-conjugate mirror. Our analysis assumes that the operation of optical phase conjugation is due to nearly degenerate four-wave mixing where two monochromatic pump fields are mixed in a Kerr-like material with the incident field, producing a transmitted field and a "phase-conjugate" reflected field. Numerical results show that the depth of amplitude modulation decreases with the gain of the phase-conjugate mirror, while the duration of the amplitude pulses increases along with that gain. An original configuration with a single output beam is proposed. The equivalence of the device with coherent detection schemes is discussed.