We propose a sinusoidal phase-modulating laser diode interferometer for measuring small angular displacement. The interferometer is based on a Fabry-Perot plate. It has a simple structure and is insensitive to external disturbance. Sinusoidal phase-modulating interferometry is used for improving the measurement accuracy. A charge-coupled device (CCD) image sensor is used for measuring the distance between the reflected beams from two faces of the Fabry-Perot plate. From the distance, the initial angle of incidence is calculated. Compared with Michelson interferometers and autocollimators, this interferometer has the advantage of compact size and simple structure. The numerical calculation and experimental results verify the usefulness of this novel interferometer.
In this paper, we proposed a new all fiber laser diode sinusoidal phase-modulating interferometer insensitive to the intensity change of light source. In a laser diode interferometer with a photothermal modulation, intensity modulation of the laser diode is negligible, but the maximum frequency of the photothermal modulation is less than that of injection current modulation. And beam diameter is too large to be used to measure some minute objects such as some components in micro-electro-mechanical system. In this paper, we proposed an all fiber interferometer, in which the effect of the intensity change of the laser diode on measurement is eliminated. The diameter of the light beam is only 0.5 mm. Using this interferometer, we measured displacements of a piezoelectric transducer. The measurement repeatability is less than 1 nanometer.
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