Optical integration of a fiber laser Doppler velocimeter

This paper describes an optical integrated circuit (optical IC) for a laser Doppler velocimeter (LDV) in which a polarization-maintaining optical fiber is used to pick up a signal light. To realize more compact and stable heterodyne optics for velocity measurement, a waveguide interferometer including a frequency shifter, a TE/TM mode converter, and a TE/TM mode splitter is integrated on a Z-propagating LiNbO3 substrate 32×7 mm2 in size. In the fabrication of the optical IC, a 3-μm wide waveguide pattern was made by a laser-beam direct writing method. The configuration of the optical IC, properties of key waveguide components, fabrication and velocity measurement characteristics of the optical IC, are described in this paper.