We designed, realized and tested a 140 Mbit/s P5K optical homodyne receiver using diode-pumped Nd:YAG ring lasers at X = 1.064im. Phase synchronization between the input signal and the local oscillator laser was achieved using a Costas-type phase-locked ioop. Pre-processing of the optical signals to be synchronized was done with a basically lossless six-port 90° hybrid. Each one of the employed front ends was implemented by means of a transimpedance preamplifier and by two InGaAs photodiodes operating in a balanced manner. We report on the receiver configuration, emphasizing the realization of the optical pre-processing unit and the front ends. Furthermore, we present measurement results characterizing the receiver performance by the bit-error rate dependence on optical input signal power. The total degradation of the receiver sensitivity -as compared to the ideal case of shot-noise limitation - was 5.9dB.

We report the results of a novel method for frequency stabilizing laser diodes based on the resonant Faraday effects. A Faraday cell with crossed Brewster windows comprises the intracavity frequency selective element. In this arrangement a laser pull-in range of 4A was measured and the laser operated at a single frequency with a linewidth less than 6 Mhz.

TRW was awarded a U.S. patent for direct phase modulation of laser diodes. The scheme can replace an electro-optic modulator with an electrical filter, greatly enhancing the practicality of heterodyne or homodyne P5K optical communication systems for satellite and fiber optic applications. The technique is described, simulation results are presented, filter designs are discussed and some experimental work is referenced.

A offset frequency lock system is used for I 0. 6jim laser heterodyne frequency tracking. The system uses digital offset-lock servo loop to realize the offset frequency lock of the tracking laser to the reference one. With computer realtime processing the offset frequency stability of 1 O 1 012is got by nieasurement of Allan variance at different sample times. The tracking range is 45MHz(when offset frequency is 32MHz)and the capture range is about 65MHz. The system shows an excellent anti-interference ability and a high stability.

A beam-steering experiment was carried out to demonstrate the basic behavior of an optical array antenna (OAA) whose subantenna fields are phased, permitting nonmechanical steering of the outgoing laser beam in analogy to the microwave regime. Good correspondence was obtained between the measured far-field intensity patterns and the calculated patterns. The new OAA concept is sufficiently accurate, is quite insensitive against disturbances, and consumes negligible optical power. Steering angles within a range of 1 mrad were obtained. The settling time of a commanded steering angle is about 0.7 ms; it is mainly determined by the response of the phase actuators employed.

A laser transmitter for high bandwidth geosynchronous satellite communications is described. High optical power is achieved by combining semiconductor laser diodes. An active alignment scheme is proposed for achieving the +/- 20 microrad post launch multiple laser angular co-alignment requirement.

This paper describes some of the key parameters that have been considered for the European Satellite Interorbital Link EXperiment (SILEX) optical relay lens design. Particular attention has been given to the specific requirement of transmit/receive beams co-alignment. The method of evaluating co-alignment errors is described and the effect of manufacturing tolerances and environmental long term stability on the co-alignment error investigated.

The effects of phased errors, such as piston errors, tilt errors, and focus errors, on beams combination in synthetic aperture systems (SAS) are analyzed based on the experiments conducted by Hu Zhiping et al. (1989, 1990) on beam control of SAS in vacuum and on a numerical simulation. The physical models of the phase control of different phased errors in SAS are presented, and a computer simulation of the beams control in SAS is performed via the FFT computational methods. The result are presented in form of three-dimensional graphs.

The characteristics of a potassium Faraday anomalous dispersion optical filter operating on the blue and near infrared transitions are calculated. The results show that the filter can be designed to provide high transmission, very narrow pass bandwidth, and low equivalent noise bandwidth. The Faraday anomalous dispersion optical filter (FADOF) provides a narrow pass bandwidth (about GHz) optical filter for laser communications, remote sensing, and lidar. The general theoretical model for the FADOF has been established in our previous paper. In this paper, we have identified the optimum operational conditions for a potassium FADOF operating on the blue and infrared transitions. The signal transmission, bandwidth, and equivalent noise bandwidth (ENBW) are also calculated.

This paper reports observations of a Stark tunable bistable optical device (BOD) (Smith et al., 1977) which uses the interaction between the asQ(6,6) transitions in NH3 gas and the R(18) line of a (C-13)(O-16)2 laser. It is shown that optical bistability can be observed using this laser as the nonlinear element. The effect of Doppler broadening on the Stark bistability is shown via numerical calculations. The observed effect is consistent with results of the theoretical analysis.

Current optoelectronics research and development of high power, high bandwidth laser transmitters, high bandwidth, high sensitivity optical receivers, pointing, acquisition and tracking components, and experimental and theoretical system modeling at the NASA Goddard Space Right Center is reviewed. Program hardware and space flight milestones are presented.

Optical digital receivers are being considered for intersatellite laser communication links. A demonstration system is being designed to operate at 325 MBit/s, using quaternary pulse position modulation (QPPM). Laboratory experiments have been conducted using a 50 MBit/s prototype system. A numerical model has been developed to simulate a QPPM optical receiver. The 50 MBit/s system was simulated to verify the validity of the model. The model was then used to simulate the projected behavior of the 325 MBit/s system. The model predicts a bit error rate of 10.6 at 38 incident photons per bit for 820 nm light.

An unprecedented number of Earth observation and communications spacecraft will be flown in the next decade making much greater demands on the space communication infrastructure. Optical multiple access intersatellite link transceivers capable of maintaining simultaneous communication with a number of low Earth orbiting spacecraft will be an important element. The BAe Optical Multiple Access (OMA) system is based on a lightweight user terminal which offers a similar service to S-band systems but with considerably lower mass, power consumption, volume and real estate. This paper discusses design options for the data relay terminal mounted on the GEO platform. Configurations for 2-access and 8-access transceivers are presented. This includes discussion of terminal configuration options, layout of the optical components to minimize real estate, provision of the beacon source and beacon scanning unit, acquisition times, and measures to ensure that interference between channels is minimized. Mass and power budgets are presented for 2-access and 8-access transceivers and compared with equivalent S-band systems.

This paper presents a preliminary assessment of the impact the resonant laser receiver would have on an end-to-end laser communication system. Link budget calculations are described that determine system performance for an 83,000-km crosslink and 42,000-km communication channels, for which transmitter power and data rate are traded for a fixed 14-cm aperture. The acquisition and fine tracking performance are also assessed to determine such parameters as beacon transmitter power, acquisition scanning and staring methods, modulation formats and detection methods, and detector requirements.

The book discusses the application of optical communication systems to free-space transmission. Particular attention is given to the system requirements (interorbit requirements and orbital constraints); system technologies; the description of optical communication systems, including the direct detection systems and coherent systems; and the sensitivity of detection receivers.

The Laser Crosslink Subsystem (LCS) is a full duplex laser communications terminal in production at McDonnell Douglas Electronics Systems Company. The LCS will provide a data crosslink for geosynchronous satellites. This paper provides an overview of the system design and major elements followed by a brief program history. One LCS is installed on each satellite. The system utilizes a solid state diode pumped Neodymium YAG laser and direct pulse detection to provide 1.28 Mbps data transmission in one direction on the link and 4 Kbps in the other. A single eight inch gimballed telescope provides both the transmit and receive antenna function. After autonomously acquiring, the 200 Hz bandwidth fine tracking system maintains pointing of the 10 microrad optical beam. The LCS began development in 1981. Since then, each of its assemblies has completed-flight qualification testing. The first integrated production unit successfully completed environmental and performance qualification testing in 1990.

A 10.6-micron laser heterodyne receiving system with acoustooptic frequency modulation is described. In this system, the first-order diffraction beams are used as the optical signal modulation beam in the transmitting optical terminal, a 77 K-PV-HgCdTe detector is used as heterodyne reception device in the receiving optical teminal, and the Stark cells are used in the transmission and reception terminals in order to stabilize the frequencies of local and signal laser. With the application of frequency shift key digital modulation, the terminal bit error rate is better than 10 exp -8.

It is well known that coherent detection systems are less susceptible to background radiation and thermal noise than direct detection systems. However, with a diffraction-limited field of view, coherent detection spatial tracking systems have angular span restricted to less than one beam width. Moreover, the azimuth and elevation tracking errors will become coupled when the tracking error increases. In this paper, a novel coherent detection spatial tracking system is designed to overcome the above mentioned problems. The optics design of the new spatial tracking is based on a highly sensitive angular discriminator, which can be implemented using a Fabry-Perot Etalon. The post-detection electronic processor is mainly a phase demodulator. The performance of the new spatial tracking system is presented in terms of the standard deviation of the angular tracking error. It is also shown that two of the four photodetectors used for spatial tracking form a dual-detector coherent receiver for communications. In other words, spatial tracking and communications have been integrated into a single system.

The fabrication of an experimental acquisition, tracking, and pointing (AT&P) subsystem for NASDA's intersatellite laser communication (ILC) system is described, and the methods used in the ILC system are described. The results of tests of the fabricated AT&P system are presented along with a block diagram of the ILC equipment, the main target parameters of the ILC system, and the target specifications of the trial AT&P subsystem.

This paper describes an extended-source spatial acquisition process based on the maximum likelihood criterion for interplanetary optical communications. The objective is to use the sun-lit Earth image as a receiver beacon and point the transmitter laser to the Earth-based receiver to establish a communication path. The process assumes the existence of a reference image. The uncertainties between the reference image and the received image are modeled as additive white Gaussian disturbances. It has been shown that the optimal spatial acquisition requires solving two nonlinear equations to estimate the coordinates of the transceiver from the received camera image in the transformed domain. The optimal solution can be obtained iteratively by solving two linear equations. Numerical results using a sample sun-lit Earth as a reference image demonstrate that sub-pixel resolutions can be achieved in a high disturbance environment. Spatial resolution is quantified by Cramer-Rao lower bounds.

The design of a CCD-based pointing, acquisition, and tracking (PAT) system is discussed together and with the design of a CCD-based tracking loop architecture for a cost-effective PAT system which would be applicable to the full spectrum of lasercom link possibilities. Four separate CCD systems are considered, with sample rates of 30 Hz, 300 Hz, 1 kHz, and 10 kHz; in each case, the CCD architecture is designed to meet a set of performance goals in the presence of host-induced disturbance environments representative of the disturbance environments that might be expected on orbit due to typical spaceborne actuators and vehicle dynamics. The paper describes the PAT base architecture, the performance goals of the CCD, the component analysis models, and the rejection loop designs using the different CCD systems. The results demonstrate that it is possible to increase the system efficiency and decrease its complexity by using a faster sampling CCD rather than relying on inertial measurements to meet tight pointing requirements.

A master oscillator power amplifier (MOPA) configuration has been developed using an anti-reflection-coated AlGaAs semiconductor broad area laser in a reflective amplifier mode. For CW injection, the MOPA produced 340 mW of diffraction-limited power. The semiconductor MOPA configuration also produced peak diffraction-limited powers of 360 mW and 320 mW for quaternary pulse position Q-PPM modulation rates of 50 Mbps and 325 Mbps, respectively, for a peak injected power of 100 mW. Angular beamsteering during modulation was minimized by collimating the injected beam. The diffraction-limited peak power was limited by the frequency chirp of the master oscillator and also by the coupling losses of the injected beam.

A beacon developed and breadboarded by the SPACEBEL Instrumentation in the framework of the ESA Semiconducter Intersatellite Experiment (Silex) is described. The Silex Beacon is a powerful source aboard the GEO terminal, used by the LEO terminal to locate the latter. The paper describes the general architecture of the Silex Beacon and the flight model design and discusses the future developments. The far field pattern obtained by the breadboard is presented.

An algorithm is derived for the design of a collimator for high aspect ratio laser diode arrays. An illustrative design is presented, showing the potential of these high-aspect-ratio, large-emitting-area laser diode arrays in practical transmitting systems.

The multistable output characteristics of an intracavity acoustooptic modulation (IAOM) laser system with a negative feedback device is analyzed based on the behavior of the acoustooptic modulator. Quantitative results with and without active medium are obtained. The bifurcate and chaotic behavior of the IAOM system is discussed in detail.

A ten-meter hexagonally segmented Cassegrain optical telescope is being considered at the Jet Propulsion Laboratory for use as a research and development facility for optical communications technology. The goal of the study is to demonstrate technology which can eventually be used to develop a network of such telescopes to continuously track and communicate with the spacecraft. Hence, the technology has to be economical enough to allow replication for a ground or space based network. As we need to collect signal photons only, the telescope cost can be substantially reduced by accepting lower image quality. An important design consideration for the telescope is its ability to look very close to the sun. The telescope for optical communications must function during the daytime. Indeed, for some planetary missions it may be necessary that the system be capable of looking within a few degrees of the sun. To enable this, a unique sunshade consisting of hexagonal tubes in precise alignment with the mirror segments has been proposed which will also serve as the support for the secondary. Recent progress on the design and analysis of such an optical reception station is discussed here.

A resonant cavity electro-optic phase modulator has been designed and implemented to operate at a data rate of 100 Mbps. The modulator consists of an electro-optic crystal located in a highly resonant cavity. The cavity is electro-optically tuned on and off resonance, and the phase dispersion near the cavity resonance provides the output phase modulation. The performance of the modulator was measured by first heterodyne detecting the signal to an intermediate frequency and then measuring the spectral characteristics using an RF spectrum analyzer. The measured phase shift is shown to be in good agreement with the theoretical predictions.

The design, implementation, and performance evaluation of a 100Mbps binary phase shift keying (BPSK) coherent optical link using frequency stabilized solid state lasers is described. In this demonstration, the transmitted data is binary phase modulated at 100Mbps using an external resonant cavity phase modulator. At the receiving end, the signal is detected using a balanced heterodyne detector. An auxiliary frequency tracking loop (FTL) is used to help the initial frequency acquisition before handing over to the carrier phase tracking loop. The FTL is implemented using a delay line discriminator, and the detected frequency error is fed back to the local oscillator laser to close the tracking loop. Phase coherent reception is achieved by synchronizing the carrier phase using a Costas tracking loop. The demonstration showed that a high data rate phase coherent optical link can be implemented using frequency stabilized solid state lasers.

Spatial acquisition using the sun-lit Earth as a beacon source provides several advantages over active beacon-based systems for deep-space optical communication systems. However, since the angular extend of the Earth image is large compared to the laser beam divergence, the acquisition subsystem must be capable of resolving the image to derive the proper pointing orientation. The algorithms used must be capable of deducing the receiver location given the blurring introduced by the imaging optics and the large Earth albedo fluctuation. Furthermore, because of the complexity of modelling the Earth and the tracking algorithms, an accurate estimate of the algorithm accuracy can only be made via simulation using realistic Earth images. An image simulator was constructed for this purpose, and the results of the simulation runs are reported.

A breadboard sync satellite terminal has been developed incorporating a unique concept of a gimballess multi-access transceiver, which is capable of simultaneously communicating with six independent, asynchronous LEO satellites. The developmental hardware illustrates that low power, weight, and volume is achievable compared to multiple independent gimballed transceivers, while also putting a lesser burden of power, size, and weight on the LEO satellite tranceivers that communicate with the multiple-access transceiver.

Recently, the potential advantages of using single-mode optical fibers within free-space laser communication systems has been recognized. Of particular importance within an optical receiver is the spatial tracking system, which must couple the received signal into a single-mode optical fiber in the presence of environmental disturbances. Because optical beamwidths are small (microrad) and typical disturbances can be large (mrad), this requirement makes the design of the spatial tracking subsystem an important and difficult part of an optical receiver. Previous systems have utilized mechanical techniques for nutating the tip of the receiving fiber to derive tracking information. A new technique, based on using a fixed fiber and an electro-optic beam deflector, is proposed. Design considerations and experimental results are presented.

Spectral properties of commercially available Fabry-Perot and distributed Bragg reflector (DBR) GaAlAs and InGaAs laser diodes operating under deep current modulation are presented. At kHz modulation frequencies spectral widths of commercial diodes are 2.5 nm 15 dB down from the maximum intensity. Structural modifications can narrow this value to 0.4 nm. Prototype DBR devices with maximum output power of 110 mW exhibit extremely narrow CW linewidths of 4 MHz, and are suitable for coherent communication as well as direct detection communication formats.

Performance measurements are reported of a coherent homodyne optical communication receiver that contained an iron doped indium phosphide photorefractive beam combiner, rather than a conventional optical beam splitter. The system attained a bit error probability of 10 exp -6 at received signal powers corresponding to less than 100 detected photons per bit. The system used phase modulated Nd:YAG laser light at a wavelength of 1.06 micron.

Spatial tracking plays a very critical role in designing optical communication systems because of the small angular beamwidth associated with the optical signal. One possible solution for spatial tracking is to use a nutating mirror which dithers the incoming beam at a rate much higher than the mechanical disturbances. A power detector then senses the change in detected power as the signal is reflected off the nutating mirror. This signal is then correlated with the nutator driver signals to obtain estimates of the azimuth and elevation tracking signals to control the fast scanning mirrors. A theoretical analysis is performed for a spatial tracking system using a nutator disturbed by shot noise and mechanical vibrations. Contributions of shot noise and mechanical vibrations to the total tracking error variance are derived. Given the vibration spectrum and the expected signal power, there exists an optimal amplitude for the nutation which optimizes the receiver performance. The expected performance of a nutator based system is estimated based on the choice of nutation amplitude.