All fiber sinusoidal phase-modulating laser diode interferometer insensitive to the intensity change of the light source

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.