Reflectometric Measurements of Fibre-Based Four-Wave Mixing Systems

A convenient way of achieving polarization-insensitive four-wave mixing in optical fibers is through the use of two orthogonally polarized pumps. However, the interplay between fiber birefringence and the four-wave mixing processes makes polarization insensitivity challenging to achieve. The strict control of the input pumps' states of polarization has been used to minimize polarization sensitivity. Nonetheless, a comprehensive analysis of the complex interplay between birefringence and four-wave mixing, both theoretically and experimentally, is still missing. Here, we adopt an optical time domain reflectometry technique to address this issue by measuring the Rayleigh back-scattered power of the phase-conjugated idler generated by a four-wave mixing process. A system with approximately 50 cm spatial resolution capable of measuring the onset of polarization dependency of orthogonal-pump four-wave mixing systems in the saturation regime is experimentally demonstrated. The obtained results are compared with a detailed fibre model, and close agreement is confirmed. This study will further the understanding of the polarization sensitivity of multi-wave mixing dynamics in optical fibers and support the design of optimized fiber-based parametric devices.