Fig. 1. (a) Schematic of the graphene (dark grey) coated nanodisk (light blue) and the corresponding Comsol finite element computational window (light gray). Inset is the horizontal view of the electric field distribution [48]. (b) Q factor and azimuthal mode number as functions of the chemical potential corresponding to 63.2 and 89.4 THz [48]. (c) Schematic of graphene-integrated microdisk cavity [50]. (d) Sensitivity as a function of the chemical potential [50].

Fig. 2. (a) Schematic of the graphene-oxide-coated microring resonator [58]. (b) Transmission spectra under different concentrations of NH3 gas [58]. (c) Conceptual design of a graphene-oxide-layer-incorporated silica capillary resonator [59]. (d) Colored map of the beat note spectra under different concentrations of NH3 gas [59].

Fig. 3. (a) Schematic of the modulator based on a graphene/graphene capacitor integrated with a microring cavity [65]. (b) Transmission spectra and theoretical results as a function of dc voltages [65]. (c) Schematic of the modulator based on a graphene-integrated microring cavity [67]. (d) Transmission spectra under different drive voltages [67]. (e) Schematic of the integration of a graphene/ion-gel heterostructure on a microring cavity [76]. (f) Primary comb lines at different gate voltages [76].

Fig. 4. PL spectra of (a) the ZnO rod and (b) the graphene-covered ZnO rod. Insets are the dark-field optical images and schematics of an individual ZnO rod before and after the cover of graphene under laser excitation. The scale bars correspond to 50 μm [81].

Fig. 5. (a) Schematic of a monolayer WS2 microdisk cavity with a sandwiched structure of Si3N4/WS2/HSQ [102]. (b) PL emission spectra under increasing pump intensity [102]. (c) Monolayer WS2 PL background and cavity emissions as functions of pump intensity [102]. (d) Schematic of the coupled microsphere/microdisk cavity with the integration of MoS2 [103]. (e) PL spectrum after subtracting the background emission (top panel) and the calculated WGM positions (bottom panel) [103]. (f) The integrated intensity and FWHM as functions of excitation power [103].

Fig. 6. (a) Emission spectra at different laser powers of 0.47, 12.3, and 22.8 mW and the corresponding background emission spectra [106]. (b) Normalized background emissions extracted from (a) [106]. (c) SEM image of the as-grown monolayer MoS2 on SiO2 microspheres [107]. (d) PL spectra of the main modes as a function of ethanol concentration [107].

Fig. 7. (a) Axial modes measured before (top panel) and after (bottom panel) gold layer coating on rolled-up tubular microcavities with different lobe positions. Insets are morphologies of microcavities before and after gold layer coating [121]. (b) PL spectra and corresponding morphologies of the bottle-like tube (top panel) and the single-mode tube with periodic hole arrays (bottom panel) [19]. (c) SEM image of the hole array in a rolled-up diamond microcavity. Inset is the schematic of the nanomembrane cross section with patterned holes (right panel) [19]. (d) PL mapping for the rolled-up diamond microcavity. Inset is the magnified PL mapping of the confinement-enhanced mode [19].

Fig. 8. (a) Schematic of the heterogeneous 2D material microcavities based on the rolled-up technology. (b) Scanning transmission microscopy (STEM) image of the cross section of monolayer graphene on the Ge wafer [125]. (c) SEM image of the rolled-up graphene/oxide microtube [125]. (d) and (e) are the electromagnetic field distributions for the enlarged cross section of graphene/oxide layers with s- and p-polarized incident lights [125].