Fig. 1. One-dimensional on-chip topological photonic devices. (a) Silicon waveguide array based on Zak phase^[37]; (b) on-chip topological protection of two-photon states based on Zak phase^[38]; (c) optical directional coupler and beam splitter based on Zak phase^[39]; (d) GaAs nanobeam photonic crystal based on Zak phase^[41]; (e) lithium niobate electro-optic modulators based on Zak phase^[42]; (f) surface plasmon waveguide array based on Floquet phase^[43]

Fig. 2. One-dimensional on-chip topological photonic devices based on topological pumping mechanism. (a) Coupled waveguide array based on topological pumping mechanism^[45]; (b) integer quantized nonlinear Thouless pumping^[48]; (c) directional couplers and mode-order converters based on Thouless pumping mechanism^[50]; (d) asymmetric topological pumping transport in surface plasmon waveguide arrays^[51]; (e) LZ transition in surface plasmon waveguide arrays^[52]; (f) edge state coupling in finite-size optical waveguide arrays using the LZ mechanism^[53]

Fig. 3. Photonic crystal devices based on quantum Hall phase. (a) Unidirectional edge states in gyromagnetic photonic crystals^[6]; (b) self-guided unidirectional edge states in cellular gyromagnetic photonic crystals^[60]; (c) large Chern number in gyromagnetic photonic crystals^[61]; (d) single-mode topological laser in photonic crystals^[62]; (e) antichiral topological edge states in photonic crystals^[63]; (f) unidirectional large-area optical transmission in photonic crystals^[64]

Fig. 4. Photonic crystal devices based on quantum spin Hall phase. (a) Energy-band structure of photonic crystals composed of spin degenerate super-structure materials^[73]; (b) quantum spin Hall effect in uniaxial metacrystal waveguides^[74]; (c) all-dielectric quantum spin Hall photonic crystals^[75]; (d) topological quantum optics interface^[76]; (e) quantum spin Hall effect in all-dielectric bilayer photonic crystal slabs^[77]; (f) quantum spin Hall effect in the visible light frequency range^[78]

Fig. 5. Photonic crystal devices based on quantum valley Hall phase. (a) Energy-band structure of VPC^[81]; (b) quantum valley Hall effect in the optical communication frequency range^[80]; (c) high Q value VPC microring resonator in the optical communication frequency range^[84]; (d) quantum valley Hall effect in the terahertz frequency range^[85]; (e) VPC wavelength division multiplexer in the terahertz frequency range^[86]; (f) electrically pumped terahertz quantum cascade laser based on VPC^[87]; (g) topological beam splitters based on VPC^[88]; (h) asymmetric beam splitter based on VPC^[89]; (i) ultra-compact thermo-optic switch based on VPC^[90]; (j) microring modulator based on VPC^[91]; (k) chiral quantum optical device based on VPC^[92]; (l) all-optical logic gate based on VPC^[93]

Fig. 6. Non-Hermitian topological photonic devices. (a) Parity-time symmetric waveguide array^[95]; (b) non-Hermitian ultrathin metal waveguide array in microwave frequency range^[96]; (c) non-Hermitian Floquet waveguide array^[97]; (d) parity-time symmetric coupled microring resonator^[98]; (e) non-Hermitian topological laser^[99]; (f) non-Hermitian skin effect lasing in one-dimensional microring arrays^[100]

Fig. 7. Synthetic-dimension topological photonic devices. (a) Four-dimensional quantum Hall effect in optical waveguides array^[103]; (b) microring modulator based on the synthetic-dimension^[104]; (c) topological rainbow^[105]; (d) second Chern crystal in the four-dimensional parameter space^[107]; (e) gapless corner modes of photonic crystal slabs within a parameter space^[108]

Fig. 8. Nonlinear topological photonic devices. (a) Nonlinear on-chip optical isolator^[109]; (b) generation of quantum correlated photon pairs in nonlinear two-dimensional microring resonator arrays^[25]; (c) generation of nonlinear third-harmonic waves in a SSH array of silicon nanodisks^[110]; (d) generation of third-harmonic waves in quantum spin Hall photonic crystals^[111]; (e) on-chip topologically protected compressed light generated by the four-wave mixing nonlinear effect^[114]; (f) generation of topologically protected quantum entangled light source^[115]

Fig. 9. Topological photonic devices based on BIC. (a) Realization of guided resonances in photonic crystal slab^[119]; (b) circularly polarized states spawned from BICs under C₂ symmetry breaking^[120]; (c) generation and annihilation of topologically protected BICs topological charge under C₆ symmetry breaking^[121]; (d) realization of unidirectional radiation guided resonances under topologically protected in photonic crystal slab^[122]