High-speed range and velocity measurement using frequency scanning interferometry with adaptive delay lines

Range (i.e., absolute distance), displacement and velocity of a moving target have been measured with a Frequency Scanning Interferometer that incorporates a 100,000 scan s-1 VCSEL laser with 100-nm tuning range. An Adaptive Delay Line in the reference beam, consisting of a chain of switchable exponentially-growing optical delays, reduced modulation frequencies to sub-GHz levels. Range, displacement and velocity were determined from the phase of the interference signal; fine alignment and linearization of the scans was achieved from the interferogram of an independent reference interferometer. Sub-nm displacement resolution, sub-100-nm range resolution, and velocity resolution of 12 μm s-1 have been demonstrated over a depth measurement range of 300 mm.