Nanoscale Metallo-Dielectric Coherent Light Sources

Compact photonic components are important for the design and fabrication of integrated optical devices and circuits. In the case of light sources, reducing the size can result in improved metrics such as higher packing density and reduced power consumption and also may enhance cavity–emitter interactions such as the Purcell effect. Until recently it was commonly known that the minimum size for a laser is ultimately determined by the free-space wavelength, λ0. For example, as the size of a conventional Fabry–Perot semiconductor laser is scaled down in all three dimensions toward λ0, three effects adversely influence the lasing process. Firstly, the roundtrip path of the optical wave in the gain medium is shortened. Secondly, radiative losses from the end mirrors have an increased effect. Thirdly, the lateral field confinement in the resonator waveguide is reduced, resulting in a smaller overlap of the optical mode with the gain medium. All these effects lead to a significant increase in the lasing threshold. As a result lasing cannot be achieved below a certain size limit. By allowing the laser size to increase in one or two dimensions, it is possible to reduce the physical size of the laser in the remaining dimension(s) to values below this limit. For example, the disk thickness in whispering-gallery-mode (WGM) lasers [1] can be reduced to a fraction of the free-space wavelength [2] but, to compensate for the small thickness, the disk diameter must be increased. It should be noted that, in addition to the optical mechanisms noted above, nonradiative surface recombination can have a non-negligible negative effect on the emitter efficiency and thus needs to be accounted for in the design and analysis of such sources. The ultimate challenge in this respect is concurrent reduction of the resonator size in all three dimensions, and, at the same time, satisfying the requirements for lasing action. The size of an optical cavity can be defined using different metrics, for example, the physical dimensions of the cavity or the size of the optical mode. However, if the goal of size reduction is to increase the integration density (for example, in a