Improved path imbalance measurement of a fiber-optic interferometer based on frequency scanning interferometry

Abstract

We developed a path imbalance measuring system using a reference interferometer with alterable optical path difference (OPD), aiming to eliminate the uncertainties due to synthetic wavelength measurement and remove the requirement of a known and stable reference OPD in frequency scanning interferometry. The path imbalance can be solved by using the phase ratios between the two interferometers produced before and after altering the OPD in the reference interferometer. The results have shown that the measurement uncertainty and the path imbalance are linearly related and a combined relative uncertainty of 4.9 × 10−6 (1σ) in path imbalance measurement over a range from 0.5 m to 50 m is achieved. Besides, we analyzed the contributions to the uncertainty that limit the performance of the system, and we discussed how to obtain a better measurement uncertainty.

Real-Time Measurement and Uncertainty Evaluation of Optical Path Difference in Fiber Optic Interferometer Based on Auxiliary Interferometer

“…Therefore, l l = 803.52 mm, σ ll = 0.03887 mm, l s = 405.05 mm, and σ ls = 0.01667 mm. Using the above phase comparison results, we can recalculate the OPD of the HQLI and its measurement uncertainty by using Equations ( 15) and (16).…”

“…Some schemes are even used for absolute distance measurements or long-distance ranging. Still, they can also be used in OPD measurements, such as white-light interferometry (WLI) [12][13][14], frequency scanning interferometry (FSI) [15,16], and frequency-modulated continuous-wave (FMCW) technology [17,18]. WLI uses white light or broadband light sources to interrogate the optical interferometer and measure the OPD through optical path matching [19], optical spectrum analyzer (OSA) scanning [13,20], or wavelength scanning [14], which has high measurement accuracy.…”

“…For FMCW technology, calculating the OPD from a constant beat frequency is not sufficient in real time [17,22]. The auxiliary interferometer is a simple and effective scheme to ensure the real-time measurement of OPD [16,18,23]. The OPD measurement made by FSI or FMCW technology is based on the auxiliary interferometer, which serves as the benchmark and significantly impacts OPD measurement accuracy.…”

“…In short, the influence of the auxiliary interferometer calibration method on the OPD measurement of the main interferometer under test should be considered to obtain a more accurate OPD measurement. However, the current FSI and FMCW technology based on the auxiliary interferometer rarely analyze the uncertainty contributed by the known OPD calibration method of the auxiliary interferometer [16].…”