An optical range finder system that relies on laser diodes' frequency noise, instead of intensity or frequency modulations, and its improvement in resolution are reported. The distance to the target is measured by calculating the cross-correlation of two signals reflected from the target and reference mirrors. These two signals are converted from the laser diodes' frequency noise signals by frequency/intensity converters, such as a Fabry-Perot etalon. We obtained the distance to the target by checking time lags between the target and reference beams at the highest correlation coefficient. We also measured the change in the correlation coefficient around the peak sampling point by adjusting the reference-path length, achieving a resolving power of +/- 3 mm. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.