High-accuracy optical distance meter with a compact femtosecond fiber laser

Recently, femtosecond optical lasers have become popular in several fields of application. Up to now, because the ultrashort laser has been large and complex, it had not been used in practical applications. However, very recently, several types of compact femtosecond lasers have been developed, thanks to the improvement of solid-state laser techniques. In particular, the development ofa palm-top fiber laser has opened the door to real-world applications, such as distance measurements in open fields. A distance meter with a laser is useful because noncontact measurement is possible. Conventionally, continuous-wave lasers have been used for distance measurements, together with intensity modulation or interferometric techniques. The interferometric technique has the advantage that high resolution is possible, but simultaneously, it is too sensitive to environmental fluctuation or vibration. The modulation technique can enable stable measurement, even in an open field, but it requires rather complex setups to achieve high frequency modulation. High-frequency modulation is necessary for realizing high resolution because under most conditions, the measurement resolution is limited by the resolution of the phase meter, and thus higher frequency leads to higher resolution for the same smallest phase unit. The complexity of the setup causes nonlinear error originating from light reflections from the boundary surfaces of the optical components. In this paper, we propose a new high-accuracy optical distance meter with a mode-locked femtosecond laser.