Fig. 1. Three-dimensional integrated optical waveguide devices based on multi-material systems^[1-6]

Fig. 2. Absorption characteristics of silicon, silicon nitride, and silica materials. Bar area represents optical transparent window of material

Fig. 3. Common structure diagrams and corresponding mode field diagrams of silicon waveguides. (a) Strip waveguide; (b) ridge waveguide; (c) mode field of strip waveguide; (d) mode field of ridge waveguide

Fig. 4. Types of waveguides fabricated by femtosecond laser direct writing technology. (a) Single-line waveguide; (b) double-line waveguide; (c) depressed cladding waveguide

Fig. 5. Three-dimensional interlayer couplers. (a) Evanescent wave coupler; (b) grating coupler; (c) 3D waveguide coupler

Fig. 6. Double-layer interlayer couplers. (a) a-Si-Si interlayer coupler^[27]; (b) Si-Si interlayer coupler^[28]; (c) Si-Si₃N₄ interlayer coupler^[29]; (d) Si-SiN interlayer coupler^[30]; (e) SiO_x-SiO_x interlayer coupler^[31]; (f) a-Si:H-SiN_x interlayer coupler^[32]

Fig. 7. Multi-layer interlayer couplers. (a) c-Si-a-Si interlayer coupler^[33]; (b) a-Si-a-Si-a-Si interlayer coupler^[34]; (c) Si-SiN-SiN interlayer coupler^[35]; (d) Si-SiN-SiN interlayer coupler^[36]; (e) Si-Si₃N₄-Si₃N₄ interlayer coupler^[37]

Fig. 8. Interlayer grating couplers. (a) a-Si-a-Si grating coupler^[38]; (b) a-Si-a-Si grating coupler with metal mirror^[39]; (c) SiN-SiN grating coupler^[40]; (d) Si-SiN_x-SiN_x metamaterial grating coupler^[41]

Fig. 9. Interlayer 3D waveguide couplers. (a) a-Si∶H slope waveguide coupler^[2]; (b) Ge₂₃Sb₇S₇₀ (GSS) slope waveguide coupler^[42]; (c) vertical U-shaped coupler^[43]

Fig. 10. Heterogeneous integrated interlayer couplers. (a) Si-flat TFLN interlayer coupler^[44]; (b) Si-ridge TFLN interlayer coupler^[45]; (c) Si-TFLN hybrid waveguide interlayer coupler^[46]; (d) Si-Ⅲ/V interlayer coupler^[45]

Fig. 11. Heterogeneous integrated interlayer couplers. (a) Strip SiN-flat TFLN interlayer coupler^[47]; (b) ridge SiN-flat TFLN interlayer coupler^[48]; (c) SiN-strip TFLN waveguide interlayer coupler^[49]; (d) SiN-ridge TFLN waveguide interlayer coupler^[50]; (e) SiN-GaAs interlayer coupler^[51]; (f) SiN-a-Si-Ⅲ-V waveguide interlayer coupler^[52]

Fig. 12. Three-dimensional integrated optical transmitters/receivers. (a) 4-channel 2.5D integrated silicon photonic transmitter based on silicon interposer and LTCC^[53]; (b) 2.5D integrated receiver based on 16 nm CMOS FinFET^[54]; (c) 3D integrated CMOS/silicon photonic receiver based on copper pillar^[55]; (d) 25 Gbit/s 3D integrated silicon photonic receiver with high sensitivity^[56]

Fig. 13. Three-dimensional integrated optical transceivers. (a) 2.5D integrated multi-channel optical transceiver based on silicon optical interposer^[57]; (b) silicon photonic coherent transceiver based on LTCC interposer^[58]; (c) 2.5D integrated optical transceiver based on silicon interposer^[59]; (d) 16 channel silicon photonic transceiver with high density and wide bandwidth^[60]; (e) ultra-low power consumption optical I/O transceivers^[61]; (f) hybrid integrated silicon photonic transceiver based on mixed-pitch bumping technology^[62]

Fig. 14. Three-dimensional integrated WDM transceivers. (a) 4-channel WDM transceiver^[63]; (b), (c) 8-channel WDM system based on photonic “bridge” chip^[64]; (d) thermally controlled ring-based 4-channel WDM system^[65]; (e) 3D integrated coarse WDM transceiver based on copper pillar^[66]

Fig. 15. Three-dimensional integrated optical interconnect modules. (a) Tbit/s high density optical interconnects 3D packaging based on silicon photonic active interposer^[67]; (b) silicon photonic modulator driver for >800 Gbit/s optical links^[68]; (c), (d) 3D packaging solution and its variation for photonic engine for 800 G data rate based on double-sided flip chip^[69]

Fig. 16. Polarization multiplexers. (a) Birefringent polarization multiplexer^[70]; (b) polarization beam splitter^[71]; (c) stress-induced polarization beam splitter^[74]; (d) tilt integrated glass slide^[75]

Fig. 17. Mode multiplexers based on directional couplers. (a) Directional coupler with uniform waveguide^[80]; (b) directional coupler with tapered waveguide^[5]; (c) on-chip orbital angular momentum (OAM) mode multiplexing and demultiplexing device^[81]

Fig. 18. Mode multiplexers based on photonic lantern. (a) 16-core 3D photonic lantern^[82]; (b) 57-channel (19×3) mode multiplexer^[84]; (c) 6×6 mode and polarization multiplexing/demultiplexing system^[85]

Fig. 19. Fan-in/fan-out devices. (a) Four-core fiber fan-out device^[6]; (b) 84-core silicon-fiber interconnect device^[87]; (c) 19-core fiber fan-in/fan-out device^[88]

Fig. 20. Applications of femtosecond laser direct writing technology in topological quantum science. (a) Iteration of fractal photonic crystal structure^[92]; (b) photonic realization of anomalous Floquet topological insulator^[93]; (c) schematic diagram of inversion symmetry-broken honeycomb lattice with armchair and zigzag edge domain walls^[95]; (d) directional coupler network for statically disordered eight-step one-dimensional quantum walk^[96]

Fig. 21. A summary and prospect of multi-material system three-dimensional integrated optical waveguide devices