Design and fabrication of ridge waveguide-based nanobeam cavities for on-chip single-photon sources.

We report on the design of nanohole/nanobeam cavities in ridge waveguides for on-chip, quantum-dot-based single-photon generation. Our design overcomes limitations of a low-refractive-index-contrast material platform in terms of emitter-mode coupling efficiency and yields an outcoupling efficiency of 0.73 to the output ridge waveguide. Importantly, this high coupling efficiency is combined with broadband operation of 9 nm full-width half-maximum. We provide an explicit design procedure for identifying the optimum geometrical parameters according to the developed design. Besides, we fabricate and optically characterize a proof-of-concept waveguide structure. The results of the microphotoluminescence measurements provide evidence for cavity-enhanced spontaneous emission from the quantum dot, thus supporting the potential of our design for on-chip single-photon sources applications.

Open-geometry modal method based on transverse electric and transverse magnetic mode expansion for orthogonal curvilinear coordinates.

A vectorial modal method is presented based on transverse magnetic and transverse electric mode expansion, which significantly simplifies the evaluation of the operator matrix. The method, which features a true open boundary condition, is introduced for an orthogonal curvilinear coordinate system with the specific examples of circular and elliptical geometries presented. We validate the method by considering challenging problems, such as the calculation of spontaneous emission rates, of modal reflection coefficients and of the effect of the emitter spatial misalignment on the spontaneous emission ß factor. Results are compared with literature.