[en] Diffraction gratings have been considered as input couplers for Fabry-Perot cavities in future gravitational wave detectors. We experimentally demonstrate the use of a triple-suspended, diffractively coupled cavity and examine conventional Pound-Drever-Hall length sensing and control techniques to maintain the required operating condition. Utilizing the diffractively coupled Fabry-Perot cavity, we investigate the effects associated with translational grating motion and observe a unique 1/f slope in the magnitude of the frequency response when monitoring the forward-reflected error signal.