Signal enhancement method based on a Fabry-Perot etalon for a self-mixing laser diode

An enhanced self-mixing interference (SMI) method in a laser diode (LD) based on a Fabry-Perot etalon (FPE) is presented. This method uses uncoated fused silica to form a FPE as a narrowband filter in the LD outer cavity, which can tune the laser wavelength to the edge of the FPE transmission spectrum profile to perform intensity demodulation. We compare the SMI signal based on the FPE filter with the conventional SMI signal. The experimental results show that the amplitude of the SMI signal based on the FPE filter is enhanced about 5 times in the range of 1 µm-5 µm; the displacement reconstruction errors are reduced by 30 nm; and the signal quality is significantly improved.