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 [1] [2]. 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.
Not so long ago, pseudo random numbers generated by numerical formulae were considered to be adequate for encrypting important data-files, because of the time needed to decode them. With today’s ultra high-speed processors, however, this is no longer true. So, in order to thwart ever-more advanced attempts to breach our system’s protections, cryptologists have devised a method that is considered to be virtually impossible to decode, and uses what is a limitless number of physical random numbers. This research describes a method, whereby laser diode’s frequency noise generate a large quantities of physical random numbers. Using two types of photo detectors (APD and PIN-PD), we tested the abilities of two types of lasers (FP-LD and VCSEL) to generate random numbers. In all instances, an etalon served as frequency discriminator, the examination pass rates were determined using NIST FIPS140-2 test at each bit, and the Random Number Generation (RNG) speed was noted.
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