ABSTRACT
Several approaches have been reported for directional discrimination without optical modulators, although these approaches are for one-dimensional velocity measurement. Laser Doppler velocimeters (LDVs) have been widely used to measure the velocity of a fluid flow or rigid object in various studies and industries since the introduction of the concept in 1964. This chapter describes several types of integrated LDVs using planar lightwave circuit (PLC) technology, especially a wavelength-insensitive LDV and a multipoint LDV using arrayed waveguide gratings (AWGs). AWGs have been widely used and deployed as key filtering devices in commercial wavelength-division multiplexing optical communication systems. Passive devices using silica-based PLC have been widely used in optical communication systems because of their reliability, low insertion loss, ease of coupling to optical fibers, integration capacity, and ability to produce optical filters with high accuracy. The chapter also describes techniques for two-dimensional velocity measurement using a simple optical configuration without multiple colors or any optical modulator.
