Absolute distance measurement method without a non-measurable range and directional ambiguity based on the spectral-domain interferometer using the optical comb of the femtosecond pulse laser

Abstract

With the help of the optical comb of a femtosecond pulse laser, a spectral-domain interferometer has been utilized for measuring absolute distances. Even if the technique can measure distances at a high speed and with good precision, it has two fundamental problems: non-measurable range and directional ambiguity. First, the non-measurable range arises due to the sampling limit of the interference spectra at very short distances or the integer multiple of a double non-ambiguity range. Second, the peak corresponding to the desired distance in the Fourier domain has a directional ambiguity owing to the repeated property of the optical comb. Therefore, due to these two fundamental problems, most previous works never measure the absolute distances by itself in a single operation. In this letter, an interferometric method for measuring arbitrary absolute distances based on a spectral-domain interferometer operating with two reference mirrors is proposed and demonstrated. The two reference mirrors generate two distinguishable signals, primary and secondary, with a predetermined offset, thus solving these fundamental problems clearly. More importantly, as a practical advantage, the simple layout of the proposed method makes it readily applicable to most previous studies.