Spin-Preserving Metasurface-Based Focusing Mirror for Enhancing Light-Matter Interactions

Abstract

We propose a dielectric metasurface mirror that focuses one spin state while diverging the other state and preserves the spin state upon reflection, unlike conventional mirrors. First, we discuss the working principle of the mirror and introduce an earlier version of the design to discuss important potential drawbacks to a metasurface design. Then, we simulate a mirror design that can preserve the spin state up to 99.6%. Overall, the simulations give 81% reflectivity for the desired spin state, half of which is due to material loss. A Fabry Pérot optical cavity formed by a pair of such mirrors would have a finesse of 15 and Q value of 1964. We find the focusing of the mirror to have good quality, with a Strehl ratio of 0.88. We simulate a cavity numerically to find the mode profile after 120 roundtrips. We estimate a mode volume of 725 μm³ for a cavity with length 56μm and mirror size 15μm. Our metasurface design has potential to be used in quantum optics to enhance light-matter interactions and optical nonlinearities. The reflectivity of the mirror can be further enhanced by overcoming material loss, which would allow a high finesse cavity for single spin state to be built. Last, we construct and characterize with broadband polarization tomography a fiber integrated quarter-waveplate formed by misaligning and splicing a short section of polarization maintaining fiber with precise length.