AN ULTRASONIC SENSOR

摘要

An ultrasonic sensor utilising a polarization maintaining optical fibre. The invention comprises a polarization maintaining fibre (4) with a light source (1) to launch into the fibre light beams respectively aligned with each of the principal axes of the fibre and an output detection system (9, 10, 11, 12) to determine phase difference induced between the beams by ultrasonic waves (6) incident upon the fibre. Bias control (15) can be provided to compensate for environmentally induced phase differences. The invention also comprises a polarization maintaining fibre (25) divided into a sensor portion (27) and a lead portion (26). These portions are optically joined together by a 45 DEG joint (28) so that a beam aligned with one principal axis with the lead portion travelling from this portion to the sensor portion is decomposed into two components respectively aligned with each of the two principal axes in the sensor portion. A light source (21) and optics (22) launch a linear polarised beam into the lead portion in alignment with one of the principal axes and a detection system (31, 32, 36, 37) determines phase difference induced by incident ultrasonic waves between the two components passing through the sensor portion.