Fast estimation method of feedback factor based on the derivative of the self-mixing signal.

The self-mixing (SM) technique has been a promising optical measurement technique for a few decades. The estimation of the optical feedback factor is the key to SM displacement measurement with a better resolution than half a wavelength. But this estimation is extremely complex and tricky, and thus leads to its time-consuming nature, which is one of the important causes that increases the cost and labor for the development of a self-mixing sensor.