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Proceedings Paper

Direct Detection vs Heterodyning In Optical Beam Tracking
Author(s): Thomas S. Wei; Robert M. Gagliardi
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Paper Abstract

Optical spatial tracking of a laser beam can be accomplished using quadrant detector error signals obtained from either direct detection or heterodyning. In the direct detection system the received beam is focused directly on the quadrant, and error signals are generated as the beam moves over the detector. In heterodyned systems the received field is mixed with a local laser field on the quadrant detector for error generation. Expressions to evaluate angle error variance due to receiver noise are formulated. The tracking error variance depends on signal-to-noise ratio, quantum efficiency, and the slope of the loop S curve. The loop S curve is derived differently for the two cases, and its specific form is important to the overall performance analysis. Heterodyne detection receivers are less susceptible to background radiation and device noise than direct detection receivers. However, this advantage can be compensated for direct detection system by increasing the received signal power, reducing front end bandwidth, or reducing the number of spatial modes. Design considerations of the laser beam propagating in turbulent atr hphere and multi-mode results are also addressed. Degradation due to heterodyning misalignment is also considered. The results of the study allow direct comparison of both system as possible beacon tracking subsystems. Curves will be shown to relate the key parameter that will determine which method is the most advantageous.

Paper Details

Date Published: 22 April 1988
PDF: 8 pages
Proc. SPIE 0739, Phase Conjugation, Beam Combining, and Diagnostics, (22 April 1988); doi: 10.1117/12.939723
Show Author Affiliations
Thomas S. Wei, University of Southern California (United States)
Robert M. Gagliardi, University of Southern California (United States)

Published in SPIE Proceedings Vol. 0739:
Phase Conjugation, Beam Combining, and Diagnostics
Ira Abramowitz; Robert A. Fisher, Editor(s)

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