Intra-Modal Phase-Sensitive Four-Wave Mixing in a Few-Mode Fiber

Phase-sensitive parametric processes based on four-wave mixing (FWM) in third-order nonlinear media are attractive for the demonstration of numerous functionalities including low-noise amplification, high-sensitivity detection and signal phase quantization with applications to e.g. communication and sensing [1]. Until now, such processes have been demonstrated exclusively in single-mode optical fibers and waveguides. Meanwhile, the exploitation of the spatial (transverse) dimension of waveguides is also being explored for such applications, for instance in order to provide a new multiplexing degree of freedom in telecommunications [2]. One open question is whether the use of phase-sensitive processes can be made compatible with optical fibers and waveguides supporting multiple spatial modes. Some (inter-modal) phase-sensitive processes have been numerically investigated in few-mode fibers (FMFs) [3]. However, to the best of our knowledge, no experimental demonstration of phase-sensitive processes in FMFs has been reported so far. In this work, we demonstrate experimentally intra-modal phase-sensitive FWM, separately in two modes (
$\text{LP}_{01}$
and
$\text{LP}_{11}$
), in a 2-km long step-index FMF [4] supporting 4 LP-modes at 1550 nm.