Use of a laser diode and an optical fiber for a compact laser-Doppler velocimeter

In order to make an optical-fiber-type laser-Doppler velocimeter (LDV) more compact, we propose the use of a laser diode as the coherent light source. To reduce the optical feedback on the laser source, a polarization-maintaining single-mode fiber was adopted. We have confirmed that the LDV system can be compact and also that it can have a velocity resolution of a few millimeters per second and a signal with a 20-dB signal-to-noise ratio, which are similar to the resolution and signal-to-noise ratio obtained with a He-Ne laser.