Miniature self-mixing interferometer based on a microsphere superlens for microactuator displacement measurement

A miniature self-mixing interferometer based on microsphere superlens (MSSL) for the displacement measurement of microactuators is proposed. The interferometer is composed of a taper multimode fiber (TMMF) and MSSL with diameter D=5μm. When the MSSL is irradiated by plane wave from the TMMF, the phenomenon of photonic nanojet (PNJ) occurs. The PNJ can focus on the surface of the microactuator. It can also enhance the scattered light from the surface of the microactuator, and enable the scattered light to return to the laser cavity to generate self-mixing interference phenomenon, which can be used to retrieve the displacement detection of the microactuator. Experimental results show that the relative errors are more accurate than 1% by using the proposed method