Optical integration of a fiber laser doppler velocimeter

Abstract

Abstract 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 LiNbO 3 substrate 32 × 7 mm 2 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 polarizationmaintaining optical fiber was butt‐coupled to the output waveguide of the optical IC. Using the fabricated optical IC, the Dopplershifted signal light was detected with the signal‐to‐noise ratio of 25 dB in the velocity measurement of a moving mirror. 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.