Diffractively coupled Fabry-Perot resonator with power-recycling.

We demonstrate the optical coupling of two cavities without light transmission through a substrate. As the all-reflective coupling component, we use a dielectric low-efficiency 3-port diffraction grating. In contrast to a conventional transmissive coupling component, such an all-reflective coupler avoids all thermal effects that are associated with light absorption in the substrate. An all-reflective scheme for cavity coupling is of interest in the field of gravitational wave detection. In such detectors light that is resonantly enhanced inside the so-called power-recycling cavity is coupled to (kilometre-scale) Fabry-Perot resonators representing the arms of a Michelson interferometer. We realized such an all-reflective coupling in a table-top experiment. Our findings are in qualitative agreement with the theoretical model incorporating the characteristics of the 3-port grating used, and therefore encourage the application of all-reflective cavity couplers in future gravitational wave detectors.