Laser-diode interferometer; Practice and application

Laser diodes (LDs) have been served as light sources of a phase-measuring interferometer through the wavelength tunability of LDs by controlling their currents. Laser-diode interferometers based on a heterodyne technique are reviewed with their practice and application. A two-wavelength laser-diode interferometer is elaborately demonstrated with current control of dual LDs in opposite directions to extend the range of interferometric measurements. The wavelength is controlled by the laser injection current and is stepwise or rampwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. A feedback interferometer with electronics is used to lock the interferometer on a preset phase shift to ensure the measurement accuracy. The interferometric techniques with laser diodes have been applied to an optical radar such as a single detection of multiplexed phase objects and to a distance measurement.