Abstract: A super high resolution optical resonator comprising a Fabry-Perot cavity and an intracavity diffraction grating which is operated in a non-zero diffraction order. The diffraction grating is of transmission or reflection type, blazed, single or multiple order. The resonant cavity can comprise two independent mirrors, multiple mirrors, or an optical resonator based on an optical fiber and one or more intracavity diffraction gratings operated in non-zero diffraction order inserted between the two or more mirrors or portions of the fiber, respectively.