Figure 4.

Schematic of different ways to couple light into a symmetric optical microcavity: (a) Angled fiber coupling; (b) Prism coupling. While robust, prism coupling is difficult to achieve for on-chip devices; (c) Tapered optical fiber coupling. The waist of the fiber has been thinned to typically ~500–2000 nm in diameter; (d) Direct illumination in the case where the resonator has internal light emitters such as quantum dots. This enables remote sensing; and (e) Polished half-block coupler. In a half block coupling system, an optical fiber is embedded in a transparent block and mechanically polished until part of the fiber cladding is removed such that light evanesces out.