Abstract: A ring-type laser including a traveling wave cavity which incorporates at least first and second straight cavity sections and at least one curved cavity section. Corresponding first ends of the straight cavity sections are interconnected at a first light-emitting facet, and second ends of the straight sections are interconnected by the curved waveguide. Additional curved and straight sections can be linked to provide various ring configurations.

Abstract: A controllable, unidirectional ring laser having a reduced length includes at least one curved waveguide section, at least one partially transmitting facet, and a mechanism for producing unidirectional propagation of light within the waveguide cavity. The mechanism includes, in one embodiment, an external reflector which may be either planar or curved, in the path of emitted light from a waveguide facet. In another embodiment of the invention, the reflector is replaced by a source of light directed at the emitting facet of the waveguide, while another embodiment includes the use of an asymmetric element in the cavity. If desired, two unidirectional devices can be used selectively to produce a reversible waveguide.