A theoretical study of semiconductor integrated etalon interference lasers - Part I: Waveguiding properties and intermodal coupling analysis

We present a theoretical study of semiconductor interferometric lasers, having a resonator with curved and straight segments, in two parts. In this first part, the wave equation in a curved dielectric waveguide is solved by applying the conformal transformation method to develop design criteria for curved optical waveguides in integrated optics. An intermodal coupling analysis at the junction discontinuity between a curved and straight waveguide is carried out to define a scattering matrix representing lateral mode conversion and internal reflection at the junction. The results of the theoretical analysis reveal two important consequences: 1) an extremely low internal reflection coefficient for the fundamental lateral mode, and 2) an increased internal reflection into higher order lateral modes. This phenomenon leads us to the conclusion that the interferometric effect in integrated etalon interference lasers is caused by the participation of higher order lateral modes into the resonance process.