Simple optical distance meter using an intermode-beat modulation of a He-Ne laser and an electrical-heterodyne technique

Abstract

A phase measurement distance meter has been devised using a frequency-stabilized intermode optical beat generated from a two-mode He-Ne laser (14-cm-long cavity) and a conventional phase meter. The beat frequency (1096 MHz) is stabilized to within 1 kHz fluctuation by a feedback control system. This frequency was converted to an electrical signal and reduced to 6 MHz by a rf-heterodyne technique in order to match the best frequency response range of the phase meter. Experimental results show that the total distance error of the optical distance meter due to the frequency fluctuation of the laser and the performance of the phase meter is 1 and 19 μm, respectively, for a mirror target located 1 m away from the laser source. Further improvement in the resolution is possible if a better phase meter is used.