Optimal ring lasers with an isolator and reflection from the boundaries of an active element

A theoretical investigation is reported of the characteristics of a mode generated in a laser with a complex coupled resonator consisting of a ring cavity and an isolator, and bounded by the reflecting surfaces of an active layer. It is shown that the mode field always represents a superposition of two counterpropagating waves and the ratio of their intensities K ² is different inside and outside the active medium. Analytic dependences of the threshold gain and of K ² on the resonator parameters are obtained. It is shown that when certain relationships between these parameters are obeyed, single-frequency lasing with extremely good characteristics (including the lowest threshold gain) is possible or a structure in the form of a traveling wave can be established in some part of the resonator cavity, and so on. The range of the resonator parameters ensuring a relatively high lasing stability is determined.