OPTICAL COMMUNICATIONS EMPLOYING SEMICONDUCTOR LASERS
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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This report discusses the development of optical communications employing semiconductor lasers-both noncoherent and coherent. The large modulation bandwidth obtainable with these devices permits the development of frequency- and pulse-modulation communications systems which overcome scintillation noise produced by the turbulent atmosphere. Emphasis has been placed on the development of communications systems for 98-percent weather capability over short ranges, rather than fairweather capability over long ranges. The development of supporting technology is presented in the areas of semiconductor lasers, fiber optics, optical systems, narrowband optical filters, photomultipliers, and frequency- and pulse-modulation electronic circuitry and components. Measurements of optical signals over a two-mile path under a full variety of weather conditions have permitted a comparative evaluation of AM, FM, and PM systems. The results show clearly the advantage of frequency modulation and pulse modulation. Measurements of pulses transmitted appreciably beyond the limits of visibility in snow and fog indicate a channel bandwidth, limited by scatter-multipaths, but of the order of 200 Mcps. An analysis is presented of multiple-scatter paths and system design considerations for these conditions.
- Lasers and Masers
- Fiber Optics and Integrated Optics
- Non-Radio Communications