| Popis: |
An analysis of semiconductor laser structures with adjustable single-mode emission based on a contradirectionally grating coupled twin-waveguide structure consisting of a semitransparent metal (or ITO)/low-index dielectric waveguide on top of a corrugated active laser waveguide is presented. A coupled mode theory, where the coupling coefficients are expressed in terms of field overlap integrals between the unperturbed fields and on-resonant Floquet-fields, is applied to describe the optical fields of the laser resonators with a high degree of accuracy, although the modulation of the refractive index in the grating region is large. At resonance between the laser mode and the surface mode the grating-coupled radiation losses show a sharp drop with a linewidth comparable to the longitudinal Fabry-Perot-mode spacing of the laser cavity, thus preferring a single longitudinal mode. Intermodal discrimination of up to 20 cm -1 and moderate threshold gain of ∼ 50 cm -1 can be obtained. Since the resonance wavelength depends on the optical thickness of the surface waveguide, a simple post-processing adjustment of the emission wavelength with a tuning range in excess of ∼ 15 nm can be achieved. |
