Self-mixing type of phase-locked laser diode interferometer

Abstract

A new type of phase-locked laser diode interferometer that uses self-mixing interference in the optical system is described. The selfmixing interference (SMI) signal is obtained easily by optical feedback, i.e., feeding back the laser beam from the object to the laser diode (LD). The SMI signal can be detected by a photodiode in the package of the LD. Therefore, a beamsplitter, reference mirror, and external photodetector are not required, and an interference signal is obtained using a simple optical system. Although the mechanism of SMI is completely different from that of conventional interference, it is shown that the response of the SMI signal to phase changes is the same as that of conventional interference. We used the phase-locked technique to fix the phase change and demonstrated measurement of absolute distance and displacement.

Locking phenomenon of polarization flipping in He–Ne laser with a phase anisotropy feedback cavity

“…It is used in the fields of velocity [3][4][5], displacement [6][7][8][9], absolute distance [10][11][12], and vibration measurement [13]. Polarization, which is the universal nature of lasers, is also modulated by external feedback.…”

Real-time displacement measurement by use of a coaxial type of laser diode interferometer

“…A lot of sensors that use the SMI have been proposed [2][3][4]. We have also proposed a self-mixing type of LD interferometer that uses phase-locked technique [5]. The coaxial configuration of the self-mixing interferometer enables us to simplify the optical setup.…”

A laser self-mixing interference vibrometer based on current modulation and DSP demodulation

“…Then the reflected light re-enters the laser cavity and mixes with the original light to produce a self-mixing interference effect. The SMI signal which carries the movement information of the irradiated target is suitable for parameter measurement of velocity, distance, vibration and displacement [4][5][6].…”