Coherent detection spatial tracking system with automatic alignment in free-space laser communications

Jackie S. C. Fung

doi:10.1117/12.149243

6 August 1993 Coherent detection spatial tracking system with automatic alignment in free-space laser communications

Jackie S. C. Fung

Proceedings Volume 1866, Free-Space Laser Communication Technologies V; (1993) https://doi.org/10.1117/12.149243
Event: OE/LASE'93: Optics, Electro-Optics, and Laser Applications in Scienceand Engineering, 1993, Los Angeles, CA, United States

Abstract

A novel coherent detection spatial tracking with angular span larger than one beamwidth was designed. The coherent detection spatial tracking system had the advantages that it is not susceptible to background radiation and thermal noise, and the azimuth and elevation tracking errors are independent with each other. It was shown that the optics design of the coherent detection spatial tracking system was based on a highly sensitive angular discriminator which was implemented using a Fabry-Perot Etalon. However, it was also shown that the Fabry- Perot Etalon must be rotated with respect to the optical axis of the optical receiver at a certain angle. This angular bias must be maintained at all times. In this paper, the advantages of using electro-optic materials between the two partially reflecting parallel surfaces of the Fabry-Perot Etalon will be investigated. When electrical voltage is applied to the electro-optic material, the optical phase of the electric field of the laser beam will be shifted by an amount proportional to the applied electrical voltage. This optical phase change will alter the nominal angular operating point of the Fabry-Perot Etalon at which the gain of the angular discriminator is maximum. It will be shown that the angular operating point of the Etalon can be easily locked in using a simple feedback loop.

Citation Download Citation

Jackie S. C. Fung "Coherent detection spatial tracking system with automatic alignment in free-space laser communications", Proc. SPIE 1866, Free-Space Laser Communication Technologies V, (6 August 1993); https://doi.org/10.1117/12.149243

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KEYWORDS

Fabry–Perot interferometers

Mode locking

Phase shifts

Signal detection

Feedback loops

Automatic alignment

Electro optics

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