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Optical distance measuring system using a laser diode's fast frequency noise as a detection signal

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.