Compact and fast vibrational displacement sensor with real-time analog electrical output using self-mixing laser diode

A compact and fast vibrational displacement sensor using a self-mixing laser diode (SM-LD) is proposed, which has an almost real-time analog output voltage. The sensor's output is proportional to an instantaneous displacement, and the r.m.s. amplitude of it becomes an almost real-time electrical output. Being compact, the sensor can be attached to a robot arm and scanned over a device under vibration test in order to measure frequency characteristics of a vibrational amplitude of the device.