Ring resonator laser with diffraction grating coupling and axial mode selection

Axial mode selection in ring resonators using diffraction gratings as beam splitters and output couplers is described. Such a ring resonator is suitable for use at high average power levels, especially at infrared wavelengths for which partially transmitting optics are not available. By proper choice of grating blaze angles, the selectivity of the resonator can be adjusted over a wide range of values. The diffraction gratings serve simultaneously as beam splitters to provide axial mode selection, as output couplers, and as wavelength selection elements.