Absolute Distance Meter Operating on a Free-Running Mode-Locked Laser for Space Mission

We report a working prototype of absolute distance meter developed for outer-space operation by incorporating a fiber-type modelocked laser. The target distance is measured using a 1 GHz synthetic radio frequency (similar to 0.3 m wavelength) provided by the 20(th) intermode harmonic of a 50 MHz pulse repetition rate. The measurement repeatability is 7 mu m at 1 s averaging with an accuracy of +/- 20 mu m for a 2.5 m target distance. With a 100 Hz update rate, the measurement speed is fast enough to keep track of the target in motion with up to a 1.0 m/s velocity. The prototype is built within a compact volume of A4-size footprint to be feasible for the space mission of satellite-to-satellite distance measurement.