Interferometric Distance Meter Using a Frequency-Modulated Laser Diode

Abstract

Non-contact, non-incremental, and highly accurate distance measurements over extended ranges are required by a number of industrial applications where compact and robust measuring devices suitable for in-field usage are needed1. Frequency-modulated continuous-wave interferometry (FMCW) can be successfully used for developing non-incremental distance meters. In order to implement a reliable and compact measuring device, the use of laser diodes has been investigated2,3,4. These devices are very appealing due to their compactness, low-cost and ease of modulation. The main limitation to laser diode usage arises from the coherence length of such sources: those available with an extended coherence length are very expensive while the low-cost devices have a short and non-specified coherence. The extension of the coherence length of a laser diode can be obtained by a suitable optical feedback6. In this work, we present a distance measuring device based on both the use of a low-cost laser diode and a suitable optical feedback enabling the system to perform distance measurements over a range greater than 1 m. The main advantages of the proposed system are (i) high accuracy combined with an extended measuring range, (ii) simple optical layout, and (iii) compactness.