Application of the Vernier method with the phase shift time of flight technique for optical metrology

The phase shift (PS) continuous wave time of flight (PS CW TOF) method is an optical measuring technique that can be used to obtain high accuracy absolute and relative distance measurements. Optical systems based on this method can be applied as a simple and low-cost metrology solution for application in an industrial and scientific context.

A PS CW TOF range finder determines a source-target distance by comparing the phase difference of a continuously modulated signal in its source and when it is detected. Due to the cyclical properties of the phase angle, the position information is contained within an ambiguity interval. There are several established techniques that can be used to remove the ambiguity in this method, they usually rely in increasing the unambiguous range, using auxiliary measuring techniques or multiple modulation frequencies.

In this work, we present a Vernier approach applied to the dual-frequency PS CW TOF method to remove the ambiguity in a phase measurement. We validate the proposed methodology by constructing an experimental setup based on heterodyne down conversion to perform distance measurements in a [0, 5] m range. This technique allowed reaching an expanded uncertainty in the distance measurement of ≈ 530 μ m with k = 2 with a modulation frequency of 1.825 GHz.