Distance measurement by the wavelength shift of laser diode light

TLDR

The method is a form of multiwavelength interferometry that uses a single light source. The paper proposes a method to measure distances exceeding the light wavelength using a laser‑diode interferometer. The technique exploits the linear dependence of a laser diode’s wavelength on injection current, causing a sinusoidal phase shift between two beams that is detected by optical heterodyne. Experiments show that the phase‑variation magnitude is proportional to distance and wavelength shift, enabling distances larger than the wavelength to be determined, and confirm the method’s practical applicability.

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.