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Optical Engineering

Lasers with optical feedback as displacement sensors
Author(s): James Arthur Smith; Ulrich W. Rathe; Christian P. Burger
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Paper Abstract

An interferometric displacement sensor with useful properties has been built based on a laser with optical feedback from light that is backscattered by a moving object. Information about the object's motion is encoded in the phase of the backscattered light, which in turn influences the phase and the amplitude of the laser via injection-locking physics. We derive the properties of the amplitude and phase modulation of the laser from standard injection-locking relations augmented by a self-consistency condition. These predictions are then confirmed by experimental results. An off-the-shelf two-mode frequency-stabilized laser is used in two different interferometric configurations. First, the amplitude modulation of the laser is utilized for displacement measurements in a homodyne setup. Second, the phase modulation of the laser is used in a pseudoheterodyne interferometer. In both cases, the backscattered light from the object can be injected into the laser cavity without the help of any focusing optics. Thus the injection-locked sensor combines the advantages of readily available equipment and a straightforward optical setup without need for intricate alignment, and thereby meets two important conditions for industrial applications.

Paper Details

Date Published: 1 September 1995
PDF: 9 pages
Opt. Eng. 34(9) doi: 10.1117/12.212979
Published in: Optical Engineering Volume 34, Issue 9
Show Author Affiliations
James Arthur Smith, Texas Agricultural and Mechanical Univ. (United States)
Ulrich W. Rathe, Ludwig-Maximilians-Univ. (Germany)
Christian P. Burger, Texas Agricultural & Mechanical Univ. (United States)

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