Interferometric Distance Meter Using a Frequency-Modulated Laser Diode
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.
KeywordsLaser Diode Phase Noise Beat Frequency Target Distance Optical Feedback
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