Fig. 1. Photonic wire bond and its measurement results^[78]. (a) Scanning electron microscopy (SEM) image of photonic wires between different waveguides on the same chip; (b) SEM image of photonic wires between different chips; (c) characterization of photonic wire loss

Fig. 2. Schematic diagram of the photonic wire platform structure^[80]. (a) Schematic diagram of photonic wire connecting multiple material platforms; (b) SEM image of photonic wires from InP lasers to array of silicon-based electro-optic modulators on chip; (c) SEM image of photonic interconnect from silicon-based electro-optic modulator array chips to low-loss silicon-based AWG chip; (d) SEM image of photonic waveguide from low-loss silicon-based waveguide to multi-core optical fiber

Fig. 3. Laser direct-written three-dimensional integrated optical beam splitter^[84-85]. (a) 632 nm three-dimensional 1×4 beam splitter; (b) losses of the beam splitter at different direct-write energies and different output spacings; (c) SEM image of 1×81 beam splitter; (d) local magnification of Fig. 3(c)

Fig. 4. Process flowchart of a three-dimensional polymer photonic integrated platform, which includes multi-layer polymer waveguides and vertical MMI coupler^[86]

Fig. 5. Three-dimensional polymer OPA^[86]. (a) Schematic diagram of 2×4 port distribution of the OPA, with horizontal spacing of 10 μm and vertical spacing of 7.2 μm at the output ports; (b) SEM image of the fabricated 2×4 port distribution OPA, where L and U represent the switches controlled by the electrodes being on the lower or upper layer; (c) microscope image of the end face of the 2×4 OPA

Fig. 6. Schematic diagrams of 4×4 three-dimensional optical switch structure (left), 16×4 optical switch constructed with a 4×4 unit structure (right upper), interlayer coupler of MMI (right lower)^[87]

Fig. 7. Double-layer optical encryption fluorescent polymer waveguide chip based on optical pulse coding modulation technology^[88]. (a) Normalized photoluminescence spectra of TCBzC and TCNzC luminescent materials; (b) schematic diagram of the three-dimensional structure of multi-layer waveguides; (c) cross-sectional view of the output ports of the multi-layer waveguides; (d) top view of the multi-layer waveguides

Fig. 8. Characteristic analysis of optical response of the dual-layer waveguide device with 405 nm wavelength pumping light excitation^[88]. (a) Top view microscope when coupling 532 nm and 655 nm signal lights with 405 nm wavelength light pumping in; (b) output optical fields of two signal sources (×50); (c)(d) curves of relative gain versus pumping light power intensity variation for 532 nm and 655 nm wavelength signal sources; (e)(f) input/output response square-waves with pulse-code modulation for 532 nm wavelength signal source at 250 Hz frequency; (g)(h) input/output response square-waves with pulse-code modulation for 655 nm wavelength signal source at of 250 Hz frequency

Fig. 9. Schematic diagram of polymer/silica hybrid integrated on-chip amplifier structure^[90]

Fig. 10. Polymer/silica hybrid integrated VOA based on the vertical structure MMI^[91]. (a) Schematic diagram of the structure; (b) cross-section of silica waveguide; (c) cross-sectional diagram of the polymer waveguide

Fig. 11. On-chip three-dimensional integrated electro-optic-thermo-optic optical switch^[92]. (a) Schematic diagram of the three-dimensional structure; (b) top view; (c) end view schematic; (d) SEM image of the vertical coupling structure

Fig. 12. Performance characterization of on-chip three-dimensional integrated electro-optic-thermo-optic optical switch^[92]. (a) Curve of heating power consumption versus optical power; (b) curve of thermo-optic switch response; (c) curve of electro-optic switch response

Fig. 13. SiN/polymer three-dimensional hybrid integrated phase shifter^[93]. (a) Schematic diagram of the structure; (b) top view of the interlayer converter used in the phase shifter; (c) distribution of the optical field at different positions in the z-direction of the phase shifter; (d) relationship curves between the tip width w_tip of the conical waveguide and the length and conversion efficiency of the phase shifter

Fig. 14. SiN/polymer three-dimensional hybrid integrated 1×N OPA^[94]. (a) Schematic diagram of three-dimensional structure; (b) top view of the structure; (c) schematic diagram of the three-dimensional structure of the SiN/polymer hybrid integrated thermo-optic phase shifter; (d) end view schematic of the SiN/polymer three-dimensional hybrid integrated thermo-optic phase shifter