On the feasibility of Absolute Distance Measurement by using Optical-Feedback into a Superluminescent Diode Cavity

The development of accurate absolute distance interferometers is a long-term research goal. The key impact of this paper is the demonstration of an absolute distance interferometer based on the optical-feedback into a superluminescent diode cavity. Thanks to the optical-feedback, we obtained huge interference fringes even with diffusive targets and without using high-sensitivity and low-noise detectors, but directly exploiting the monitor photodiode enclosed in the same package of the optical source. The low coherence of the optical source makes the system robust to any stray-light along the optical path and thus suitable to work in biological media and dusty industrial environments. The proposed signal processing exploits a zero-crossing approach to determine the absolute target position. Preliminary results show a 95% expanded uncertainty to measuring interval ratio of about 60 ppm over a measuring interval of 50 mm.