<title>Integrated optics in laser Doppler metrology</title>

Abstract

The introduction of integrated optical chips (IOC) in laser Doppler metrology allows new types of laser Doppler setups to be constructed. An IOC, which is made of LiNbO<SUB>3</SUB> (by application of APE/annealed proton exchange technology), splits the incoming laser beam into two outgoing measurement beams to build a crossed-beam laser Doppler setup. A special modulator driving routine is applied to achieve electrooptical phase modulation in the IOC and, hence, a mutual frequency shift between the two outlet beams. The advantages of IOCs are: consistent light delivery in optical fibres - from the LD to the IOC and onto the optical head, light splitting and frequency shifting combined in one IOC, and the introduction of a new on-line signal processing routine. Phase modulation allows for a heterodyne signal processing. In terms of signal processing, the IOC modulator is an integral component of a closed-loop arrangement. The detected signal is maintainied at a constant oscillator frequency by changing the modulator frequency in the event of Doppler frequency variation (velocity). Because the setup uses an electronically isolated optical head, length measurement is insensitive to electromagnetic radiation and thermal stress.