A diffraction grating with periodically arranged protrusions and grooves at a relatively narrow pitch and improved diffraction efficiency is disclosed. The multilayer film stack can be formed by vapor deposition techniques such as chemical vapor deposition or atomic layer deposition. The memory stores information of the set power saving mode and the set power saving mode items in association with the specified power saving mode type. If it is determined that the client cannot support the preferred authentication technique, then one of the other authentication techniques is used to authenticate the client.