FREQUENCY-SHIFT KEYING LASER COMMUNICATION STUDIES.
ARMY ELECTRONICS COMMAND FORT MONMOUTH N J
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A unique optical modulation and detection technique has evolved from an investigation of methods of digital modulation, transmission, and detection in the optical region. In particular a frequency-shift keying laser communication system has been demonstrated and the advantages of such a system have been shown. A detailed theoretical analysis of electromagnetic-wave propagation in an electrooptic crystal of arbitrary orientation was developed. In turn the parameters for an optical modulator capable of frequency-shift keying at a digital rate were determined. Based on this analysis a laboratory communication system incorporating FSK modulation and detection capabilities was built and successfully operated. The transmitter consists of two helium-neon gas lasers operating at wavelengths of 6328 Angstroms and 11523 Angstroms. The two beams are combined and pass through the KDP electro-optic modulator which is driven by a digital voltage of 100 volts peak amplitude. The receiver consists of two photodiodes, each detecting one of the wavelengths. The detected signals are processed by decision circuitry to retrieve the transmitted information. To evaluate the performance of an optical FSK system, error rate measurements were made in a simulated atmospheric type of environment and compared to similar measurements made with an amplitude-modulation communication system. Author
- Lasers and Masers
- Non-Radio Communications