Optical integrated circuit for a fiber laser doppler velocimeter

In this paper, we propose and demonstrate a new optical integrated circuit (optical IC) pigtailed with a polarization-maintaining fiber for the laser Doppler velocimeter. In this optical IC, a waveguide frequency shifter, a TE/TM mode converter, and a mode splitter are integrated in -propagation Ti-diffused LiNbO3as well as a waveguide interferometer. Since the optical IC is as long as 32 mm, the waveguide patterning has been made with m accuracy by a laser-beam lithographic system recently developed. Using the fabricated optical IC, the velocity of a moving object has been successfully heterodyne-detected with the signal-to-noise ratio of 25 dB.