Optical Intersatellite Links Research Articles

A laser diode transmitter for optical intersatellite communications

AbstractDevelopment of a laser diode (LD) transmitter that has such characteristics as high power, fast frequency response, and good beam profile is essential to a realization of broadband optical intersatellite communications. Both an LD collimator to achieve a good wavefront quality and an LD driver to achieve a fast frequency response are designed for use with an LD operated at a wavelength of 0.83 μm.Also developed is an LD transmitter using an LD collimator and an LD driver. The objective of the LD collimator design was an acceptable degree wavefront aberration with a minimum number of lenses, by applying aspheric lens technology. As a result, a three‐lens configuration for the collimator was obtained. As for the LD driver, two high‐speed LD‐driver GaAs‐ICs are fitted in parallel. Their outputs are combined and fed to an LD. The parallel‐feed configuration enabled a fast frequency response at a high current.For fabrication results, a circularly collimated output beam 5 mm in diameter, with an output power of 60 mW, a transmission rate of 2.5 Gbit/s, and a wavefront aberration of λ/16 was obtained. The result satisfies the system requirements for optical intersatellite link between satellites in low earth orbits.This paper presents an LD transmitter design and data on its test samples, followed by discussions of further improvements.

Applications of Coherent Techniques to Optical Transmission: State of the Art and Perspectives

AbstractThe state of the art and the perspectives of application of coherent techniques to optical‐transmission systems are discussed. After a review of the performance achieved with point‐to‐point single channel transmission systems, different frequency‐division‐multiplexed systems are analyzed for both point‐to‐point transmission and local area network applications. Attention has been devoted to possible applications of coherent optical systems in broadcast and local area networks exploiting both subcarrier and frequency division multiplexing techniques. In conclusion the potentials offered by these systems are considered relatively to space intersatellite optical links.

Optical intersatellite links

Direct communication links between spacecraft will be an important element in the future space communication infrastructure. Optical intersatellite links (OISLs) offer the major advantages over conventional microwave links of low mass, power consumption, size and real estate, and flight-qualified transceivers are now feasible. There are, however, formidable problems in achieving pointing accuracy and stability of the order of a few milionths of a degtree. The Japanese ETS VI experiment, the European Space Agency's ‘SILEX’ experiment and NASA's Laser communication Transceiver are due to fly in the mid-1990s. The article discusses the status of OISL systems and technology and describes the British Aerospace optical multiple access (OMA)system as an example of a lightweight transceiver attractive to spacecraft designers.

Impact of random pointing and tracking errors on the design of coherent and incoherent optical intersatellite communication links

Given the RMS transmitter pointing error and the desired probability of bit error (PBE), it can be shown that an optimal transmitter antenna gain exists which minimizes the required transmitter power. Given the RMS local oscillator tracking error, an optimum receiver antenna gain can be found which optimizes the receiver performance. The impact of pointing and tracking errors on the design of direct-detection pulse-position modulation (PPM) and heterodyne noncoherent frequency-shift keying (NCFSK) systems is then analyzed in terms of constraints on the antenna size and the power penalty incurred. It is shown that in the limit of large spatial tracking errors, the advantage in receiver sensitivity for the heterodyne system is quickly offset by the smaller antenna gain and the higher power penalty due to tracking errors. In contrast, for systems with small spatial tracking errors, the heterodyne system is superior because of the higher receiver sensitivity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Research and development of basic technologies for an optical intersatellite link.

Research and development of basic technologies for an optical intersatellite link.

Resistance of holograms made in Polaroid DMP128 photopolymer to ionizing radiation damage

Because of their light weight and general wave-front-transforming ability, holograms appear potentially useful as beam correctors and collimators for diode-laser arrays in intersatellite optical data links. However, to survive in space a hologram must withstand damage from electrons and protons trapped in the Van Allen belts. We have found that holograms made with Polaroid DMP128 photopolymer on Suprasil-2 can withstand 63-MeV protons up to a total dose of 2 Mrad (Si) and withstand (60)Co gamma rays up to a total dose of 2 Mrad (Si) without loss of diffraction efficiency. It appears that these holograms are sufficiently radiation hard for space application.

Optical ISL tracking considerations in meeting ISDN requirements

AbstractBurst errors in an optical intersatellite link (ISL) are short term (of the order of a millisecond) degradations of the link due to antenna mistracking. These errors degrade the average bit error rate (BER), decrease coding gain, complicate calculations of tracking accuracy, and give rise to concern about the quality of the link for carrying digital signals. After reviewing previous work on these topics, the digital performance of the link is examined in terms of how these considerations affect the ability of an optical ISL to meet ISDN (Integrated Services Digital Network) criteria for an ISL. A link with on‐board regeneration is assumed. Since no allocation has yet been made for an ISL, an allocation of 25 per cent of the degradation permitted for the satellite link by CCITT Rec. G.821 and CCIR Rec. 614 is assumed here. It is found (1) that if the requirement derived from Rec. 614 is met, the requirements derived from Rec. G.821 are also met and (2) that an optical ISL should have little difficulty in meeting these requirements.

Optical intersatellite link with direct detection: The laser diode‐pumped Nd laser option

AbstractFollowing a brief introduction reviewing various laser systems suitable for ISL, a typical link budget for an optical ISL with a Nd laser is calculated. Laser diode pumped Nd lasers are described, and several host materials are considered. Modulation formats and typical receiver performances for direct detection are examined in order to compute the minimum transmitted power required for the proposed link. Results show that laser diode pumped Nd laser systems are competitive for optical ISL.

Identification of requirements for intersatellite links

AbstractThe intersatellite link (ISL) concept has been under evaluation for many years. It has been the subject of various European Space Agency studies, one of which is summarized here.1 The study was aimed at: outlining a reference scenario for satellite communications in the period 1996–2005, when a new satellite generation (Eutelsat III) is expected to be operational in Europe; analysing, within the above scenario, the opportunities for an ISL implementation; performing a deep system analysis of the selected study cases in order to give the requirements for the first ISL generation; evaluating a micro/millimetre wave implementation of the ISL; evaluating an optical implementation of the ISL; evaluating the technical and economic viability of an ISL and suggesting the best technique to be used in the first ISL generation. The main results achieved in this analysis are that: (i) the usefulness of an early implementation of ISL has been demonstrated; (ii) verification of the system aspects in the communications networks using an ISL appears as one of the most important items; (iii) the availability of optical technologies will increase the opportunities offered to ISL implementation. From these results it is shown that a first‐generation (1995–2005) millimetre‐wave ISL would be preferable for future business systems, while a second‐generation (after 2005) optical ISL could extend the ISL field of application. It is also deemed important to have during 1995–2005 an in‐orbit experiment for optical ISL as a necessary step for a subsequent operational system.

Research and development activities of optical ISLS in Japan

AbstractThe current state of research and development activities of optical intersatellite links (ISLs) and related optical devices in Japan, including semiconductor laser diodes, photodiodes, CCDs and modulation/demodulation techniques, is described. Subjects for further research on optical devices and communications are summarized. An optical communication experiment which uses the communications system on board the Engineering Test Satellite‐VI to be launched in Japan in 1992, is outlined.

Performance of optical intersatellite links

AbstractThe performance of optical intersatellite links is described by a model. A significant difference between optical and microwave intersatellite links is the occurrence of so‐called burst errors. The statistics of bit error rate for an optical link are derived from simulations taking into account beam mispointing resulting from satellite motions and tracking channel noise. The effect of coding on the bit error rate is also shown. The mutual tracking system between two optical terminals located on different satellites can become unstable if the noise of the tracking loop exceeds a critical value. The results of tracking simulations are presented.

Principles and design of bidirectional optical isl using GaAlAs laser at λ = O·85 μm and direct detection PPM

AbstractThis paper gives a general introduction to bidirectional optical intersatellite links. The design, principles and link budget are presented, and the four subsystems—transmitter, receiver, optical channel and acquisition/tracking system—are described. GaAlAs semiconductor laser and a silicon avalanche photodiode are used as the optical transmitter and receiver. Pulse polarization position modulation is used to obtain a higher sensitivity. The acquisition/tracking signal is extracted from the top‐modulation data stream. The effect of background noise is analysed, and direct detection and heterodyne detection are compared.

Space coherent optical communication systems--An introduction

Critical technology and system issues for space optical heteroydyne communication systems using GaAlAs lasers are discussed. Heterodyne systems offers 10-20 dB better receiver sensitivities and thus smaller telescope sizes for the same laser power than direct detection systems. Based on present state-of-the-art technologies, it is concluded that an efficient optical intersatellite link can be realized with a few years of development.