Polarization Stable Hollow Core Fiber Interferometer With Faraday Rotator Mirrors

We report the fabrication of a hollow core fiber (HCF) coupled Faraday rotator mirror component with a total insertion loss below 1.1 dB and demonstrate its use in a polarization-stable all-fiber Michelson interferometer. The signal split into the two interferometer arms is performed using a standard
$2 \times 2$
fused fiber coupler. One of the coupler output ports is permanently and directly connected to the HCF with a low return loss (below −40 dB) and negligible signal coupling into higher-order modes. The demonstrated polarization-insensitive interferometer shows residual peak-to-peak polarization-induced power variations as low as 0.04 dB. The device will be of interest in interferometric applications requiring low thermal sensitivity as the phase drift of light propagating through an HCF is over an order of magnitude less sensitive to temperature than in standard fiber. Moreover, the fiber nonlinearity is almost three orders of magnitude lower in HCFs as compared to standard solid optical fibers.