Frequency-domain modal delay measurement for higher-order mode fiber based on stretched pulse interference

Abstract

We propose and demonstrate a novel modal delay measurement technique for a higher-order mode fiber (HOF) based on optical frequency-domain reflectometry (OFDR) using an extremely simple, entirely passive, and ultrafast wavelength sweeping mechanism, namely, dispersion-induced optical pulse stretching. We obtained a high temporal resolution of $\sim 1.12\mathrm{ps}$, which was sufficient for discerning the four excited modes in an HOF with a length of only $\sim 5\mathrm{m}$. The results from our measurements were very consistent with those obtained by using a traditional time-domain measurement method and a conventional OFDR measurement based on a tunable CW laser. Our proposed technique can be also easily adapted to perform conventional time-domain modal delay measurements for very long HOFs.