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.
2-D laser Doppler velocimetry without polarization discrimination, wavelength discrimination or frequency-shift discrimination is proposed. In the proposed velocimetry, scattered beams in different directions are monitored with two detection blocks in order to discriminate the direction of velocity. The principle of the proposed velocimetry is described and the discrimination of velocity direction is theoretically analyzed by simulation. The simulation result indicates that the direction of velocity can be discriminated by using the proposed velocimetry as well as the magnitude of velocity.
This chapter describes several types of integrated Laser Doppler velocimeters (LDVs) using the planar lightwave circuit (PLC) technology, especially, a wavelength-insensitive LDV and a multipoint LDV using arrayed waveguide gratings (AWGs). It focuses on two methods for two-dimensional velocity measurement using a simple optical configuration without any optical modulator. LDV have been widely used to measure the velocity of a fluid flow or rigid object in various research and industries since the introduction of the concept in 1964. Several approaches have been reported for directional discrimination without optical modulators, although these approaches are for one-dimensional velocity measurement. The AWG is one of the planar devices. Silica-based PLC technology has been used to fabricate waveguide devices including AWGs. The simulation was performed by assuming to use silica-based materials as the optical circuit. The optical circuit consists of input waveguides, two slab waveguides are waveguide array, and, output waveguides.
