Distance measurement by the wavelength shift of laser diode light

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Abstract
This paper proposes a method for measuring distance larger than the wavelength of light with an interferometer using a laser diode. This method uses the fact that the wavelength of the emitted light of a laser diode varies in proportion to the diode’s injection current. The phase difference between the two interfering beams varies due to the sinusoidal variation of wavelength. The variation of the phase difference is detected by the optical heterodyne method. The magnitude of the variation is proportional to the measuring distance and the light wavelength shift. If the wavelength shift is known, a distance larger than the wavelength can be obtained from measurement of the phase variation. This method is a kind of multiwavelength interferometry using a single light source. We have done some fundamental experiments with this method and have confirmed its applicability to practical applications.