  A concept for a low loss all-reflective cavity coupler is experimentally
demonstrated at a wavelength of 1064 nm. A 1450 nm period dielectric reflection
grating with a diffraction efficiency of 0.58 % in the -1st order is used in
2nd order Littrow configuration as a coupler to form a cavity with a finesse of
400. The application of such reflective low-loss cavity couplers in future
generations of gravitational-wave detectors as well as some implementation
issues are discussed.
