We investigated sensitivity improvement of a dynamic displacement measurement system composed of a phase-modulated fiber optic interferometer and a spatial optical system. We introduced a balanced photodetector to enhance the signal-to-noise ratio of the interference signal. The newly developed system was evaluated by using pseudo vibration made by a phase modulator and was proved to be able to measure the dynamic displacement with a high-frequency vibration of 100 kHz even when the reflected power from a sample was -50 dBm. We also performed experiments using a rubber or a mouse’s ear bone attached to a PZT driven by 100 kHz sinusoidal signal and successfully confirmed that vibration with an amplitude of less than 10 nm was clearly observed even when a reflected optical power was –46.9 dBm.
We developed a phase-modulated optical interferometer based on time-domain analysis using a laser diode with a wavelength of 1.3 μm. Feasibility to measure the vibration of biological soft tissues was assessed by using gelatin sample.
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