An atomic Faraday beam splitter for light generated from pump degenerate four-wave mixing in a hollow-core photonic crystal fiber

We demonstrate an atomic Faraday dichroic beam splitter suitable to spatially separate signal and idler fields from pump degenerate four-wave mixing in an atomic source. By rotating the plane of polarization of one mode ${90}^{\circ }$ with respect to the other, a subsequent polarizing beam splitter separates the two frequencies, which differ by only 13.6 GHz, and achieves a suppression of $(-26.3\pm 0.1)$ and $(-21.2\pm 0.1)$ dB in the two outputs, with a corresponding transmission of 97 and 99 %. This technique avoids the need to use spatial separation of four-wave mixing modes and thus opens the door for the process efficiency to be enhanced in waveguide experiments. As a proof-of-principle we generate light via four-wave mixing in ${}^{87}$Rb loaded into a hollow-core photonic crystal fiber and interface it with the atomic Faraday dichroic beam splitter.