Laser Doppler Velocimeter With Multi-Function Integrated Optic Circuit

Abstract

A miniature fiber-optic Laser Doppler Velocimeter (LDV) is demonstrated which uses a proton-exchanged LiNb03 multi-function integrated optic circuit for signal processing. The system utilizes a high-power (7.5 mW out of the fiber pigtail) 0.8- micron laser diode with short coherence length (approximately 1 cm) as the source and coherence multiplexing techniques to provide a phase-insensitive fiber-optic probe for monitoring moving or vibrating parts. The fiber-optic LDV provides 55 dB signal-to-noise ratio for 3 kHz bandwidth, even when monitoring parts with poor optical surfaces (1 % reflectivity). Operation of the system is demonstrated by monitoring a mirror vibrating at 5.7 kHz with 36.8 nm peak-to-peak deviation. The optical components and all electronic circuitry except for the DC power supply is housed in a 11.5 x 10.5 x 4.2 cm package which weighs 0.6 kg. The entire system operates on a ± 15 V, 300 mA supply. The small size, light weight, low power requirements, and phase-insensitive fiber-optic probe make the fiber-optic LDV appealing for a number of industrial and medical applications.