(color online) Micro-optical-cavity integrated graphene photodetector. (a) Spectral response of a bi-layer graphene device integrated with a silicon optical cavity. Measurements of responsivity with and without the cavity. Without the cavity, the photoresponse is flat in wavelength and more than an order of magnitude lower than that with the cavity. Inset: Schematic of a graphene microcavity photodetector. Distributed Bragg mirrors form a high-fitness optical cavity. Incident light is trapped in the cavity and passes through the graphene repeatedly. The graphene sheet is shown in red, and the metal contacts are in yellow (from Ref. ^[45]). (b) Top: Schematic of an electrically tunable graphene device integrated with a silicon nanocavity. Bottom: Scanning electron micrographs showing the silicon cavity before (left) and after (right) graphene transfer (from Ref. ^[46]).