Fig. 1. Refractive index and absorption coefficient of single crystal silicon at 1.3 μm wavelength band dependent on concentrations of free electrons and free holes, respectively. (a) Refractive index; (b) absorption coefficient

Fig. 2. Schematics of four operation modes of silicon electro-optical modulators. (a) Carrier injection; (b) carrier depletion; (c) carrier accumulation; (d) DC Kerr effect

Fig. 3. Operation principle of MZI modulator. (a) Relationship curve between output intensity of MZI modulator and phase difference, as well as influence of working point to modulation efficiency; (b) transmission spectra of silicon waveguide MZI with initial arm length differences of 0 μm, 100 μm, and 200 μm (from top to bottom); (c) schematics of optical and electrical signals in modulators with different (upper) and same (lower) propagation speeds, respectively

Fig. 4. Operation principle of a ring resonator modulator. (a) Transmission spectra of a silicon ring resonator at difference refractive index change; (b) relationship between photon lifetime and Q factor of a ring resonator

Fig. 5. High speed electro-optical modulator. (a) Silicon MOS microring modulator and the corresponding eye diagrams at 100 Gbit/s (reprinted with permission from Ref.[39], Springer Nature); (b) EO response of the measurement link of the silicon MOS microring modulator (reprinted with permission from Ref.[39], Springer Nature); (c) slow-light silicon modulator; (d) EO response of the slow-light silicon modulator (upper) and the corresponding eye diagram at 112 Gbit/s (lower) (Figures (c) and (d) are reprinted with permission from Ref.[40] under CC-BY-NC)

Fig. 6. Integrated CMOS–silicon photonics transmitter with 112 Gbaud/s rate. (a) Conceptual diagram of synergistical design with modulator, inductive network, near-end termination impedance, and far-end termination impedance as a whole; (b) driver-modulator integrated transmitter with 2.47 mm phase shifter; (c) EO response of integrated transmitter (reprinted with permission from Ref.［41］ under CC BY 4.0)

Fig. 7. Monolithic integrated optoelectronic chips. (a) structural schematic^[43]; (b) eye diagrams of the 4 transmitter channels in the optical transceiver chip at 64 Gbit/s^[43]; (c) schematic of 3-section microring modulator with wavelength locking and tracing circuit^[44] (reprinted with permission from Ref.[43-44], ©2024, Optica Publishing Group)

Fig. 8. High-linearity silicon electro-optical modulators. (a) Schematic of microring-assisted MZI modulator and optic-electric interfacing (reprinted with permission from Ref.[47], © 2024, IEEE); (b) schematic of slow-light phase shifter based on grating waveguide (upper) and the corresponding mode distribution (lower) (reprinted with permission from Ref.[48], © 2022, Optica Publishing Group); (c) scheme of ultra-high linearity MZI modulation with dual driving; (d) SFDR obtained with the dual driving scheme (Figures (c) and (d) are reprinted with permission from Ref.[49], © 2023, Optica Publishing Group)

Fig. 9. Ultra high extinction ratio electro-optical modulator. (a) Schematic of mode-multiplexing microring modulator; (b) microring transmission spectra at different bias voltages; (c) eye diagrams at 40 Gbit/s PAM4 (upper), 50 Gbit/s PAM4 (middle) and 30 Gbit/s PAM8 (lower) of the microring modulator (Figures (a)-(c) are reprinted with permission from Ref.[55], © 2022, Optica Publishing Group); (d) schematic of coupled-microring modulator; (e) extinction ratios of the modulator at different wavelengths and corresponding filter passbands; (f) measured frequency and location of a vibration signal using a distributed optical fiber sensing system with the coupled microring modulator (Figures (d)-(f) are reprinted with permission from Ref.[13] under CC BY 4.0 license)

Table 1. Typical research progress of silicon electro-optical modulators for high-speed optical interconnect

Table 2. Typical research progress of silicon electro-optical modulators with high linearity

Table 3. Typical research progress of silicon electro-optical modulators with ultra-high extinction ratio