Abstract

Self-mixing interference in a diode laser has been extensively studied for various applications including velocity measurement, ranging, acoustic sensing and displacement measurement.^[1-4] The self-mixing technique, based on the use of a diode laser shows some advantages in simplicity, compactness and robustness compared with conventional interferometric methods, and it also shows the ability to achieve directional discrimination of the phase movement, but, however, the useful directional information will disappear if the feedback strength from external reflector is weak. In addition, there is an increasing requirement for extended ranging with high accuracy. This can be achieved by using a multi-wavelength interferometer,^[5] but the systems based on this are quite bulky and complicated.

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