1 September 1995 Lasers with optical feedback as displacement sensors
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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.
James Arthur Smith, Ulrich W. Rathe, Christian P. Burger, "Lasers with optical feedback as displacement sensors," Optical Engineering 34(9), (1 September 1995). https://doi.org/10.1117/12.212979
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