Fig. 1. (a) Hexagonal honenycomb lattice of graphene with two atoms (A and B) per unit cell. (b) 3D band structure of graphene. (c) Approximation of the low energy band structure as two cones touching at the Dirac point. (a)–(c) Reproduced with permission^[51]. (d) Transmission of a graphene modulator at different drive voltages and E_f. Reproduced with permission^[56]. (e) Graphene absorption as a function of the wavelength. Reproduced with permission^[58].

Fig. 2. (a) Schematic of a graphene TO modulator integrated in a Si MZI. Reproduced with permission^[59]. (b) Schematic of a graphene TO modulator integrated in a Si microdisk. Reproduced with permission^[60]. (c) Schematic and optical microscope images of the resonant optical switch device integrated with a graphene nanoheater. (d) Normalized output intensity from the through port to the graphene. (c) and (d) Reproduced with permission^[62]. (e) Schematic and (f) layered structure of a graphene-phase-change material reconfigurable silicon photonic device structure. (e) and (f) Reproduced with permission^[64].

Fig. 3. (a) Schematic and (b) dynamic EO response of the graphene-integrated optical waveguide modulator. (a) and (b) Reproduced with permission^[56]. (c) Top: cross-sectional schematic of the SLG EA modulator. Bottom: equivalent electrical circuit of the device. Reproduced with permission^[67]. (d) Schematic of the DLG modulator. Top: perspective view. Bottom: cross-sectional view. Reproduced with permission^[71]. (e) Schematic (top) and transmission spectra (bottom) of the graphene-integrated ring resonator modulator. Reproduced with permission^[74]. (f) 3D (top) and 2D cross-sectional (bottom) schematic of graphene modulator based on metal slot waveguide. Reproduced with permission^[85].

Fig. 4. (a) Optical micrograph, (b) cross section through the dashed line A–A′, and (c) extinction ratio of the graphene-integrated MZI modulator. (a)–(c) Reproduced with permission^[96]. (d) Schematic of the graphene-plasmonic slot waveguide AO modulator and (e) the pump probe measurement. (f) Saturable absorption with picosecond laser pulses in the graphene-loaded (monolayer, bilayer) MIM-WGs and the reference Si-wire WG (without graphene). (d)–(f) Reproduced with permission^[104].

Fig. 5. (a) Schematic of the waveguide-integrated graphene photodetector. (b) Potential profile (black solid line) across the graphene channel. (a) and (b) Reproduced with permission^[111]. (c) Schematic of graphene/silicon-heterostructure waveguide photodetector. Reproduced with permission^[112]. (d) Schematic of the graphene-integrated PG detector. (e) Schematic diagram of the enhanced electric field on the separation of photogenerated carriers in the graphene. (f) Photoswitching characteristics of the device. (d)–(f) Reproduced with permission^[115].

Fig. 6. (a) Measured frequency response of the graphene photodetector based on a slot waveguide plotted in the inset. Reproduced with permission^[121]. (b) Sketch of the Si microring resonator integrated graphene photodetector and (c) its transmission spectra. (b) and (c) Reproduced with permission^[122]. (d) Schematic of the Si-graphene hybrid plasmonic waveguide photodetector. Reproduced with permission^[88]. (e) Schematic of the plasmonic device configuration with graphene and the Si waveguide. Reproduced with permission^[132]. (f) Schematic of the plasmonic photodetector based on graphene and the double-slot structure. Reproduced with permission^[133].

Fig. 7. (a) Atomic structure of the single layers of the TMDCs. (b) Evolution of the band structure of 2H-MoS₂ calculated for samples of decreasing thickness. (a) and (b) Reproduced with permission^[26]. (c) Absorption and (d) photoluminescence spectra of the MoS₂ thin films with average thicknesses ranging from 1.3 to 7.6 nm. (c) and (d) Reproduced with permission^[144].

Fig. 8. (a) Schematic of the hybrid monolayer WSe₂-PCC nanolasers and (b) their PL spectrum. Reproduced with permission^[148]. (c) Schematic image of a monolayer WS₂ microdisk laser and (d) its PL spectrum. (c) and (d) Reproduced with permission^[150]. (e) 3D schematic image of an optically pumped WS₂ disk nanolaser and (f) its emission spectrum. Inset: emission image. Reproduced with permission^[154]. (g) Type-II band alignment and carrier dynamics of the heterobilayer. Reproduced with permission^[158]. (h) 3D schematic image of the heterobilayer-PhCC nanolaser. (i) Cavity lasing emission as compared to the heterobilayer PL background. (h) and (i) Reproduced with permission^[159].

Fig. 9. (a) Design of the waveguide-integrated LED and photodetector. (b) Cross-sectional schematic of the encapsulated bilayer MoTe₂ p–n junction on top of a Si-PhCW. (a) and (b) Reproduced with permission^[155]. (c) Schematic illustration of a vertical MoTe₂-graphene heterostructure detector coupled to a silicon waveguide buried in SiO₂ claddings. (d) Simultaneously measured responsivity and the corresponding EQE as a function of the applied bias voltage. (c) and (d) Reproduced with permission^[166]. (e) Schematic and cross-sectional view of an MRR-integrated MoTe₂ photodetector. (f) Responsivity and EQE as a function of the bias voltage of the device. (e) and (f) Reproduced with permission^[160].

Fig. 10. (a) Puckered honeycomb lattice of the monolayer phosphorene. x and y denote the armchair and zigzag crystal orientations, respectively. (b) Band structures for different few-layer phosphorene systems obtained from HSE06 hybrid functional calculations. Reproduced with permission^[172]. (c) Reflection spectra of the monolayer, bilayer, trilayer, tetralayer, and pentalayer phosphorene. (d) PL spectra of the monolayer, bilayer, and trilayer phosphorene. (a), (c), and (d) Reproduced with permission^[181].

Fig. 11. (a) Schematic and (b) frequency response of the BP photodetector integrated in a Si PIC. Reproduced with permission^[130]. (c) Schematic of the BP photodetector integrated in Si PhCWs. Reproduced with permission^[188]. (d) Schematic of the BP photodetector integrated on a PPC cavity. Reproduced with permission^[189]. (e) Schematic of Au disk-based plasmonic metasurface. Reproduced with permission^[191]. (f) Schematic of the BP photodetector integrated in a ridge LN waveguide. Reproduced with permission^[192].

Fig. 12. (a) Schematic of the structure of the hBN. Reproduced with permission^[197]. (b) Band structures of the monolayer hBN. Reproduced with permission^[31]. (c) Absorption and (d) PL spectra in the hBN grown on sapphire. Reproduced with permission^[202].

Fig. 13. (a) Schematic and (b) high-speed response of the hBN/SLG/hBN photodetector on a buried silicon waveguide. Reproduced with permission^[131]. (c) Schematic cross-section and (d) electro-optical S21 frequency response of an EA modulator with an hBN/HfO₂/hBN dielectric. Reproduced with permission^[209]. (e) Schematic of a twist-controlled Gr/hBN/Gr light-emitting tunnel junction. (f) Evolution of the spectral response for different twist angles θ. (e) and (f) Reproduced with permission^[210].

Fig. 14. (a) Atomic structure of α-/β-In₂Se₃ and (b) their transition process at room temperature. Left: normalized transmission spectra for the hybrid resonator with the α-In₂Se₃ (black), β-In₂Se₃ (red), and retrieved α-state (dark red) In₂Se₃. Right: image and mode profile for the In₂Se₃ on the Si waveguide. (a) and (b) Reproduced with permission^[213]. (c) Sketch and (d) Emission spectra of an MAPbI₃ disc laser integrated on a Si-nitride photonic chip. Reproduced with permission^[216].

Fig. 15. (a) Schematic illustration of the graphene exfoliation technique. Reproduced with permission^[225]. (b) Schematic description of the main liquid exfoliation mechanisms. Reproduced with permission^[228]. (c) Photograph of the dispersion nanosheet solvent. Reproduced with permission^[229]. (d) Schematic of inkjet-printing on a chip. Reproduced with permission^[233]. (e) Schematic of the graphene patterning. Reproduced with permission^[241]. (f) Schematic of the self-release layer (SRL) methodology in combination with a pick-and-place elastomer stamp. Reproduced with permission^[242].