Fibre optic modulators for laser velocimetry
Abstract
Techniques for the modulation of optical phase in fiber optic systems are described. This has been achieved using two distinct methods: modulation of the physical properties of the fiber by piezoelectrically applied strain; or through the modulation of the source wavelength, in which a diode laser source is used and wavelength modulation is created through control of the injection current. It is further shown that these phase modulation techniques may be developed to provide control over the state of polarization of the guided beam, and two practical devices are discussed. Control over fiber-guided beams is facilitated by the availability of highly birefringent optical fibers, and the basic waveguiding theory for these is presented together with the results of the experimental investigation of their environmental sensitivities. The application of fiber optic modulators in velocimetry - chiefly for frequency shifting - is described and illustrated by a discussion of two prototype instruments constructed in the laboratories. One of these is capable of measuring two orthogonal velocity components simultaneously, based on a polarization scheme.
- Publication:
-
Laser Anemometry: Advances and Application
- Pub Date:
- 1985
- Bibcode:
- 1985laaa.conf..375J
- Keywords:
-
- Fiber Optics;
- Flow Measurement;
- Laser Anemometers;
- Modulators;
- Optical Fibers;
- Phase Modulation;
- Piezoelectricity;
- Instrumentation and Photography