A laser diode interferometer that uses an optical fiber is proposed. The laser diode simultaneously functions as a light source,a phase modulator, and a phase compensator. Detection of the vibration and reduction of external disturbance are carried out using a feedback control for the injection current of the laser diode. Thus it can measure vibration accurately in real time with a simple signal processing circuit.The optical fiber not only functions as a flexible probe, enabling us to measure the vibration of an object that cannot be moved onto the optical bench, it also acts as a reference mirror, thereby simplifying the unit construction. The principle of the feedback control in laser diode interferometer is also described in detail. # 1997 social, of Photo-Optical Instrumenta-tion Engineers. S0091-3286(97)01109-4 Subject terms: interferometer; laser diode; optical fiber; feedback control;vibration measurement. Paper 18126 received Dec. 10, 1996; revised manuscript received Apr.1,1997; accepted for publication Apr. 1, 1997. This paper is a revision of a paper presented at the SPIE conference on Laser Interferometry VII, August 1996, Denver, CO. The paper presented there appears (unrefereed) in the Proceedings of SPIE Vol. 2860.
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