The performance of a system of unstable resonators is addressed. The resonators are coupled to one another through a portion of each output that is mutually shared through reverse (adjoint) waves. The ideal performance of the coupled resonator system is dependent upon operation in a single supermode, insuring that the individual resonator outputs are mutually coherent. A wave optics analysis of two coupled resonators is described. The model considers diffraction effects in Cartesian coordinates and in a single transverse dimension (strip resonator). The sensitivity of coupled resonator performance to the length control of the individual resonators and the strength of coupling between them are evaluated.