Optical distance measuring method using fast frequency noise characteristics of a laser diode

Abstract

While standard laser range finders use modulation signals, such as sharp pulses, the method we devised employs laser diode's frequency noise, and a frequency discriminator, to produce the intensity noise signal, which we use to generate fast physical random numbers. Observed through a frequency discriminator, beams traveling along two different paths share intensity noise patterns, i.e., the same fast physical random numbers, but with a time lag. We compared the two, and calculated their cross-correlation. By sweeping their time lags, we confirmed the length of the two optical paths, up to 50m.