Fig. 1. (a) Optical microscope and scanning electron microscope (SEM) photos of an eight-channel add-drop filter based on second-adiabatic elliptical-MRRs [18]; (b) micrograph of a cascaded MZI (de)multiplexer [20]; (c) optical micrographs of a bidirectional AWG and an MZI-based interleaver [4]; (d) SEM photos of a contradirectional coupler based on an apodized SWG [21].

Fig. 2. (a) SEM photos of a PBS based on grating-assisted contradirectional couplers [36]; (b) SEM photo of a cut-cornered polarization rotator [37]; (c) SEM photo of a PSR based on multimode waveguide and mode converter [38]; (d) micrographs of a PSR employing a nonlinearly tapered double-etched ADC structure [39].

Fig. 3. (a) SEM photo of a three-mode multiplexer based on a shallow-etched MMI [75]; (b) illustration of mode multiplexer using asymmetric Y junctions [68]; (c) micrographs of a 10-channel mode multiplexer based on ADC structures [70]; (d) photos of a 16-channel mode (de)multiplexer (TE0−TE15) using gradient-duty-cycle SWGs [76].

Fig. 4. Various configurations of carrier depletion PN junctions. (a) Lateral PN junction, (b) vertical PN junction, (c) L-shaped PN junction, (d) U-shaped PN junction, (e) interleaved PN junction, and (f) lateral PN junction with doping compensation.

Fig. 5. Schematic of silicon modulator. (a) MZM, (b) MRR modulator.

Fig. 6. (a) High-bandwidth MZM with substrate removed [135], (b) electronic–photonic synergistically designed silicon photonics transmitters [137], (c) lump-segmented silicon transmitter with six lumped phase shifters [138].

Fig. 7. (a) High speed MRM for next generation energy-efficient optical networks beyond 100 Gbaud [147], (b) push-pull silicon dual-ring modulator with enhanced optical modulation amplitude [148], (c) 4×40  Gb/s O-band WDM silicon photonic transmitter based on MRMs [149].

Fig. 8. Structure of the hybrid Si/LN MZM. (a) Schematic of the structure of the whole circuit; (b) schematic of the cross section of the hybrid waveguide; (c) SEM image of the cross section of the LN waveguide; (d) SEM image of the metal electrodes and the optical waveguide; (e) schematic of the VAC; (f) SEM images of the cross sections of the VAC at different positions (A, B, C) and calculated mode distributions associated with the cross sections.

Fig. 9. (a) Cross section (upper) and transverse field profile (lower) of a heterogeneous DFB laser design with an embedded spacer layer [194]. (b) Triple-ring mirror based tunable laser [195]: schematic illustration, SEM image of a Si/III–V taper, coarse tuning spectra showing the tuning range of 110 nm. (c) III–V/Si/SiN4 laser with SiN-based spiral [196]: schematic illustration, cross-section SEM image of the InP/Si gain, comparison of temperature-dependent wavelength shift of the III–V/Si/SiN laser and of a typical one with Si-based mirror.

Fig. 10. (a) Heterogeneous integration allows spectral coverage beyond the 1310 and 1550 nm telecom windows, with the shortest wavelength being 900 nm [198] and the longest wavelength being 4800 nm [199]. (b) Heterogeneous QD laser: schematic image (left) and simulated cross-sectional fundamental transverse-electric (TE) mode electrical field distributions (right). (c) Frequency noise spectrum of a heterogeneous QD laser showing that Lorentzian linewidth of 26 kHz is achieved [200].

Fig. 11. (a) Normal-incidence structure; waveguide-integrated structures: (b) butt-coupling, (c) bottom-up coupling, (d) top-down coupling, (e) side-coupling (top view) schemes.

Fig. 12. (a) Lateral homojunction, (b) lateral heterojunction, (c) vertical heterojunction PIN PDs.

Fig. 13. 100G CWDM-4 QFSP28 transceiver module of Intel.

Fig. 14. 400G DR4 transmitter with 4×100  Gb/s data paths of Intel.

Fig. 15. Chip-on-board 800G silicon photonics transmitter.

Fig. 16. Integrated copackaged optical IO switch package with 16 photonic engines (PEs).

Fig. 17. Monolithic electronic-photonic systems based on a 65 nm transistor bulk CMOS process technology [296].

Fig. 18. Schematic configurations for single-mode networks (first column), multimode networks (second column), and ring-bus networks (third column). (a), (b) The single-mode carriers can be arbitrarily routed by leveraging MRR or Mach–Zehnder switch (MZS) arrays. (c), (d) For multimode operations, the fabrics can be constructed by assembling mode MUXs and a single-mode NoC. (e), (f) The ring-bus NoCs support multiple carriers transferring in a single ring-like bus waveguide, which can be realized by utilizing WDM or MDM technologies. NoC, network on chip; MRR, micro-ring resonator; MZS, Mach–Zehnder switch; MUX, (de)multiplexer; WDM, wavelength-division multiplexing; MDM, mode-division multiplexing; WADM, wavelength add-drop (de)multiplexer; MADM, mode add-drop (de)multiplexer.

Fig. 19. (a) The single-mode NoC based on MRR array [299], under Creative Commons license CC BY. (b) The single-mode NoC based on MZS array [300], under Creative Commons license CC BY. NoC, network on chip; MRR, micro-ring resonator; MZS, Mach–Zehnder switch.

Fig. 20. (a) The multimode NoC based on MRR array [338], under Creative Commons license CC BY. (b) The multimode NoC based on MZS array [339], under Creative Commons license CC BY. NoC, network on chip; MRR, micro-ring resonator; MZS, Mach–Zehnder switch.

Fig. 21. (a) The ring-bus NoC based on WDM [345], under Creative Commons license CC BY. (b) The bus-ring NoC based on MDM [346], under Creative Commons license CC BY. NoC, network on chip; WDM, wavelength-division multiplexing; MDM, mode-division multiplexing.

Table 1. State-of-the-Art Wavelength Multiplexing Devices^a

Table 2. State-of-the-Art Polarization Management Devices

Table 3. State-of-the-Art Mode Multiplexing Devices

Table 4. State-of-the-Art Couplers for Few-Mode Fiber Coupling

Table 5. State-of-the-Art Silicon Modulators

Table 6. State-of-the-Art Waveguide Si-Ge PIN Photodiodes^a

Table 7. State-of-the-Art Si–Ge APDs for High-Speed Optical Communications^a