While optical laser range finders use random signals to determine distance, a laser diode’s fast frequency noise can perform the task. Moreover, this signal can be applied to physical-random number generation. This research describes a method, whereby laser diode’s frequency noise characteristics generate a large number of physical-random numbers and determine the distance to a target  . We tested the random number generating- and distance- measuring capabilities of two types of lasers; a Fabry-Perot-LD and VCSEL: (Vertical Cavity Surface Emitting Laser). With the Fabry-Perot etalon functioning as frequency discriminator, we investigated the physical-random numbers’ characteristics from both Fabry-Perot-LD’s and the VCSEL’s characteristic’s points of view. We verified the generated binary number’s randomness, using NIST FIPS140-2 test, and noted the Random Number Generation (RNG) speed of a FP-LD was 48 Gbit/s, and that of a VCSEL was 159 Gbit/s. When the generation speed of the physical-random number is high, we can increase the sampling rate of our range finders and improve resolution.
While standard laser range finders use modulation signals, such as sharp pulses and periodic signals, to generate fast physical random numbers, our method does away with the modulator, and instead, utilizes laser diodes’ frequency noise and a frequency discriminator, to produce the intensity noise signals that generate fast physical random numbers. Observed through a frequency discriminator, beams having the same intensity noise patterns travel along two different paths, but with a time lag. We measured and calculated their cross-correlation, confirming the degree of difference in their optical paths, up to a distance of 50 m. We improved range resolution by taking advantage of the polynomial approximation of the coefficients around the peak of the correlation waveform.
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.