Fiber optic laser Doppler velocimeter with non-mechanical scanning of spatially encoded points for cross-sectional velocity distribution measurement

Abstract

A fiber-optic laser Doppler velocimeter (LDV) combining non-mechanical scanning and multipoint measurement is proposed for two-dimensional velocity distribution measurement on a cross-sectional plane. The LDV consists of a main body including a tunable laser and LiNbO 3 phase-shifter array, and a probe including diffraction gratings. The phaseshifter array is used to generate spatially encoded measurement points aligned in the transverse direction by multichannel optical serrodyne modulation, and these points are axially scanned with wavelength change. Two-dimensional velocitydistribution measurement is demonstrated using a probe setup with an 8-channel beam array.

Design of low-loss Nb2O5-based grating coupler in scanning differential laser-Doppler integrated probe for cross-sectional velocity distribution measurement

“…Among many applications that are related to velocity distribution measurement, information about the velocity distribution in a 2D cross section of the flow is often required in applications such as fluid flow measurements in pipes. To realize a system with a compact and reliable probe for cross-sectional velocity distribution measurement, we proposed a differential laser Doppler technique using a combination of nonmechanical scanning and simultaneous multipoint measurement using spatial encoding 13 and demonstrated it experimentally using a system based on bulk optics 14 – 17 …”

“…To realize a system with a compact and reliable probe for cross-sectional velocity distribution measurement, we proposed a differential laser Doppler technique using a combination of nonmechanical scanning and simultaneous multipoint measurement using spatial encoding 13 and demonstrated it experimentally using a system based on bulk optics. [14][15][16][17] The use of planar waveguides can provide a compact system in comparison with a system that consists of bulk optics. Photonic integrated circuits based on fluorinated polyimide waveguides on a GaAs substrate 18 or silicon photonics [19][20][21] have been developed for single-point velocity or vibration measurements.…”