Showing papers on "Optical communication published in 1971"
TL;DR: In this paper, the information rate of single-mode and multimodal optical communication channels was analyzed, in which a light beam is amplitude modulated at the source by a filter of continuously variable transmittance, and the detector counts the received photons.
Abstract: An optical communication channel is analyzed, in which a light beam is amplitude modulated at the source by a filter of continuously variable transmittance, and the detector counts the received photons. Such a communication channel has intrinsic noise limitations because there is not a one-to-one correspondence between the modulated beam power and the number of counts registered. The information rates achievable with single-mode and multimode lasers are evaluated as functions of the mean number N of detected photons per symbol, for several different input statistics. For large N the information rate increases logarithmically with N. It is shown that, when the symbol length is short, there is a minimum number of independent modes for which the multimode laser gives a greater information rate than the single-mode laser, if the laser power is equally divided among all the modes, and the power per mode is regarded as constant. However, for even moderate numbers of detected photons per symbol, this minimum number of modes is so great that the single-mode laser is to be preferred. When the light beam is derived from a thermal source, the information rate in the channel is, in effect, governed by the same equations as those for the single-mode laser, so long as the detector area is limited to a coherence area.
12 citations
01 Jan 1971
TL;DR: In this article, the performance of a photoconductive (Hg,Cd)Te detector/mixer in a carbon dioxide laser heterodyne communication system is discussed.
Abstract: Discussion of the performance of a photoconductive (Hg,Cd)Te detector/mixer in a carbon dioxide laser heterodyne communication system. The utility of computer simulation of the performance of an optical heterodyne detector/mixer is demonstrated. Certain unusual properties of this device are pointed out that, while having a substantial impact on device performance, have received little previous attention.
1 citations
01 Jan 1971
TL;DR: In this article, basic relationships for atmospheric absorption and scattering are reviewed, after which received signal variations observed on a Datran optical test link are briefly discussed, and detailed expressions for shot-noise and thermal noise limited cases are given.
Abstract: In the design of optical communication links for local distribution, two important aspects, which must be considered, are atmospheric transmission effects and detection techniques used in the receiver.Basic relationships for atmospheric absorption and scattering are reviewed, after which received signal variations observed on a Datran optical test link are briefly discussed.Direct and heterodyne detection techniques are reviewed and detailed expressions for shot-noise and thermal-noise limited cases are given. Shot-noise-limited detection is concluded to be more sensitive but is presently employed less in receivers.
1 citations
20 Aug 1971
TL;DR: It is demonstrated that the data transmitter can extract real-time channelstate information by processing the field received when a pilot tone is sent from the data receiver to the data transmitters.
Abstract: The performance of optical communication links over atmospheric channels is severely limited because of the effects of turbulence. One method of recovering some of the atmospheric fading losses is to match the instantaneous signalling rate to the channel state. We demonstrate that the data transmitter can extract real-time channelstate information by processing the field received when a pilot tone is sent from the data receiver to the data transmitter. Based on these channel measurements, wederive optimal variable-rate techniques, and show that significant improvements in system performance are obtained, particularly at low bit error rates.
1 citations
01 Jan 1971
TL;DR: In this paper, the authors describe a Nd: YAG laser in which solar energy is used directly to produce the population inversion and a specially designed, low-loss LiNbO 3 phase modulator is used to mode lock the laser and produce an output pulse-train which is suitable for use in a pulse-code-modulation optical communication system.
Abstract: The finite lifetime of conventional pump sources and the limited power available in a spacecraft make solar pumping of a space-borne optical communication laser an attractive approach. This paper describes a Nd: YAG laser in which solar energy is used directly to produce the population inversion. Sunlight is collected by a 24-inch diameter mirror and focused into the end of the laser rod. This "end pumping" configuration permits "side pumping" by lamps or light-emitting diodes when the sun is not visible from the satellite. The laser rod is soldered to a heat sink and cooled by direct conductive cooling, a technique which is compatible with spacecraft application. A multi-nlode output of 1.5 watts has been obtained with this laser. A specially-designed, low-loss LiNbO 3 phase modulator is used to mode lock the laser and produce an output pulse-train which is suitable for use in a pulse-code-modulation optical communication system.
1 citations
01 Mar 1971
TL;DR: In this article, a high altitude aircraft test for visible laser communication and analysis of errors in optical communications experiment due to flight path inaccuracies was conducted by using a high-altitude aircraft.
Abstract: High altitude aircraft test for visible laser communication and analysis of errors in optical communications experiment due to flight path inaccuracies
1 citations
01 Nov 1971
TL;DR: In this article, the authors demonstrate that the design and fabrication of an RF subsystem, utilizing coherent demodulation of data, for wideband communications systems is now both feasible and practical.
Abstract: One of the problems inherent in the use of optical communication systems is the exceedingly high Doppler shift which can be expected. With the recent development of stable, linear, octavebandwidth, voltage-tunable oscillators, this problem has been solved. A laboratory tracking receiver which is capable of tracking a 1-GHz frequency shift at rates up to 12 MHz/s with subsequent coherent data demodulation was designed and tested. This work demonstrates that the design and fabrication of an RF subsystem, utilizing coherent demodulation of data, for wideband communications systems is now both feasible and practical.