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.

Date Published: 23 February 2018
PDF: 8 pages
Proc. SPIE 10526, Physics and Simulation of Optoelectronic Devices XXVI, 105260W (23 February 2018); doi: 10.1117/12.2288086

Published in SPIE Proceedings Vol. 10526:
Physics and Simulation of Optoelectronic Devices XXVI
Bernd Witzigmann; Marek Osiński; Yasuhiko Arakawa, Editor(s)