Arbitrary distance measurement without dead zone by chirped pulse spectrally interferometry using a femtosecond optical frequency comb

Abstract

We demonstrate an arbitrary distance measurement method by chirped pulse spectrally interferometry (CPSI) using femtosecond optical frequency comb (OFC). In this paper, the chirped fiber Bragg grating (CFBG) is used to investigate the mapping relationship between displacement and the center frequency of the chirped spectral interferogram. We overcome the direction ambiguity of dispersive interferometry (DPI) ranging and expand the range of distance measurement to 18 cm. Besides, we achieve a full range of dead-zone free ranging by introducing a variable optical delay line (VODL). And through principles simulation and experiment, it is demonstrated that the measurement accuracy is 12 µm in comparison with an incremental He–Ne laser interferometer and the minimum Allen deviation is 52 nm at an average time of 1.76 ms. Similarly, in the experiment with long-distance of ∼30m, the accuracy reaches 20 µm, and 2.51 µm repeatability is achieved under harsh environment.

Enhanced Data-Processing Algorithms for Dispersive Interferometry Using a Femtosecond Laser

“…Hence, research on eliminating the minimum working distance l min is a critical issue in micrometer-order short-range absolute distance measurement. Niu et al made great contributions to analyzing the limitations of dispersive interferometry [ 36 , 37 ]. Based on the Nyquist sampling condition, the resolution of the time delay is determined by the reciprocal of the spectral width, giving rise to the measurement results by dispersive interferometry characterized as a step-like pattern as the target distance increases.…”

Nonmeasurable Range Elimination of Dispersive Interferometry

“…For the light sources mentioned above, their measurable range is significantly constrained when juxtaposed with the extensive measurement dead zone. In addition, white light sources usually have lower coherence, which is also an important factor limiting the DPI measurement range. − In order to expand the DPI measurement range, optical frequency combs (OFCs), as a revolutionary light source with high coherence and ultrawide spectral range, have become ideal light sources for DPI ranging. − In order to eliminate the measurement dead zone, optically down-sampled (frequency selected) methods have been proposed and implemented using Fabry-perot (FP) cavity or virtually imaged phased array (VIPA). , To further enhance the measurement distance and system integration, on-chip soliton microcombs (SMCs) are employed as the light sources for measurement. Their allure stems from their exceptional coherence and ultrahigh repetition rate, which guarantee the system’s ability to perform measurements free of dead zones, given that the spacing of their comb teeth surpasses the resolution of the spectral acquisition equipment. − When amalgamated with other coarse ranging methodologies and homodyne interference techniques, DPI ranging systems can achieve a measurement precision at the nanometer level and a measurement range extending to kilometers. , …”

“…Chirped fiber Bragg grating (CFBG) has also been used to address the issue of interferometric spectral phase. 17 However, in practical measurements, it is necessary to adjust the optical delay line of the reference arm to ensure that the measurement does not fall within the dead zone, which undoubtedly increases the complexity of the measurement.…”

“…Some scholars have used this method to eliminate certain unmeasurable areas. − The current methods of chirped DPI primarily concentrate on oscillations based on the spectral intensity itself. , The main target is to accurately determine the widest interference stripes, but they do not delve into the understanding of the phase of the interference spectrum. Chirped fiber Bragg grating (CFBG) has also been used to address the issue of interferometric spectral phase . However, in practical measurements, it is necessary to adjust the optical delay line of the reference arm to ensure that the measurement does not fall within the dead zone, which undoubtedly increases the complexity of the measurement.…”