Wavelength-Tunable Laser-Diode Interferometer |
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Authors: | Yukihiro Ishii |
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Institution: | (1) University of Industrial Technology, Department of Electronics, Sagamihara, 4-1-1, Hashimotodai, Sagamihara 229-1196, Japan |
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Abstract: | Laser diodes (LDs) have been applied to a phase-measuring interferometer through the wavelength tunability of LDs by controlling their currents. Laser-diode interferometers based on a heterodyne technique are reviewed. A two-wavelength laser-diode interferometer is demonstrated with current control of dual LDs in opposite directions. A synthetic wavelength makes it possible 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. The optical output is demodulated with a phase-extraction algorithm. Systematic phase errors caused by the LD-power variation and by the difference between the beat frequency and ramp frequency are analyzed. A feedback interferometer with electronics is used to eliminate the phase error by locking the interferometer on a preset phase. Typical experimental results are shown. |
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Keywords: | laser diode wavelength tunability phase measurement phase-shifting method heterodyne interferometer feedback control two-wavelength interferometer systematic phase errors |
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