Theory of integrated twin-guide lasers

The ITG (integrated twin-guide) laser consists of an active waveguide and an output waveguide which together work as a single or double resonator. This ITG laser may be used as an oscillator of optical integrated circuits. In this paper the gain and loss of a twin-waveguide mode is derived by the perturbation method and the matrix formulation is established for propagation, reflection, and mode conversion. With the aid of this technique, the oscillation condition and efficiency of the ITG laser are derived and its performance characteristics are analyzed in terms of the equivalent reflection factor in an intuitively clear way. Finally the oscillation condition, when the twin waveguides are degenerated, are numerically derived, and selectivity of the wavelength is found. The threshold gain is found to be arbitrarily varied through the coupling factor between the active and output waveguides.