Non-contact surface grating coupling for arrays of atom–photonic devices

For future atom-photonic devices, the incoupling method is expected to become the main bottleneck in the scal ing of the number of devices, as current devices use side-coupling, which is restricted to the sample edges. This paper describes how light from above is coupled directly from free space into a freestanding membrane of 220 nm thin silicon nitrite (Si3N4) with surface grating couplers. The design for these couplers is modeled, captured in an elegant design formula, and experimentally tested. A coupling efficiency of 12% makes experimental coupling to an array of atom-photonic devices possible. The elegant design formula makes grating design straightforward for all-dielectric materials and wavelengths. For this formula, determination of the correct effective index of t he specific waveguide mode inside the grating layer is essential.