Laser Doppler Velocimetry with Small Wavelength Sensitivity Using Planar Lightwave Circuit

Using a semiconductor laser as a lightsource of a laser Doppler velocimeter (LDV) is desirable to reduce the size and the cost of velocity measurement equipment. However, typical inexpensive semiconductor lasers suffer from the problem of instability in lasing wavelength. In this paper, LDVs with small wavelength sensitivity are reviewed. The wavelength sensitivity can be reduced by using arrayed waveguide gratings (AWGs), Mach-Zehnder interferometers (MZIs) or cascaded MZIs. These structures can be formed by planar lightwave circuit (PLC) technology. The principles and the possibility for realizing wavelength-insensitive operation are discussed.