Modal dispersion characterization of few-mode fiber based on electrical spectral interferometry with optical frequency comb

We experimentally demonstrate a novel method based on electrical spectral interferometry with optical frequency comb for characterizing the modal dispersion between the higher-order modes and fundamental mode in a 1-km four-mode few-mode fiber (FMF). In this method, an optical frequency comb (OFC) is used to generate many subwavelengths with the same frequency interval to improve the measurement accuracy and speed. Based on the electrical spectral interferometry, the differential mode group delay (DMGD) and modal dispersion of the tested FMF are obtained by applying the simple FFT processing. The measured DMGD and modal dispersion within the whole C-band are about (3.2032-3.3033) ps/m, (2.5573-4.2085) ps/nm.km and (5.5055-5.7057) ps/m, (−11.2112-−4.1486) ps/nm.km and (11.1111-11.3113) ps/m, (−10.2454-−14.1332) ps/nm.km for LP11, LP21 and LP02 modes respectively. Meanwhile, we achieved a precision of ±0.002 ps/m for DMGD measurement. Compared with previous methods, our method has the advantage of high measurement accuracy, simple configuration and fast speed. The experimental results show that the demonstrated method could be a good solution to the characterization of a long FMF used in large capacity mode-division-multiplexing transmission systems.