Fig. 1. Schematic of the silicon microring resonator (inset: energy conservation for degenerate FWM process).

Fig. 2. (a) Wavelength variations of the refractive index of Si, SiO2, and the calculated effective index for different waveguide widths. (b) Calculated GVD β2 of the silicon waveguide with height of 340 nm and widths of 1050 nm, 1150 nm, and 1250 nm. The inset shows the simulated optical field of the TE0 mode.

Fig. 3. (a) Simulation of normalized FWM CE as a function of cavity length L and power coupling ratio κm2. The blue dashed line represents the critical coupling conditions at each cavity length, the white dashed line represents the selected cavity length, and the blue triangle represents the optimal parameters. (b) Simulated power coupling ratio κm2 of the DC as a function of wavelength for varying width due to different fabrication errors Δw=±10  nm. The inset shows the calculated light propagation profiles. (c) Resonant effect of FWM in a silicon resonator.

Fig. 4. (a) Simulation of the transmission of the high-Q microring resonator. (b) Simulation of normalized FWM CE as a function of signal wavelength.

Fig. 5. (a) SEM image of the fabricated microring resonator and the zoomed-in image of the coupling region. (b) Measured transmission spectrum of the fabricated microring resonator.

Fig. 6. (a) Experimental setup for characterizing the Q-factor of the microring resonator. The insets are: (i) spectrum of the laser source; (ii) ODSB signal spectrum after the MZM; (iii), (iv) ODSB signal spectrum before and after the microring resonator; (v) frequency spectrum response after the PD; (vi) swept RF single output from the VNA. TLS: tunable laser source; PC: polarization controller; MZM: Mach–Zehnder modulator; TDFA: thulium-doped fiber amplifier; VOA: variable optical attenuator; DUT: device under test; TEC: thermoelectric cooler; PD: photodetector; VNA: vector network analyzer; RF AMP: radio frequency amplifier. (b) Measured RF response of the microring resonator with the Lorentz fitting. (c) Measured resonance frequency as a function of temperature variations (31.2°C to 31.7°C by the step of 0.1°C).

Fig. 7. (a) Experimental setup for the measurement of the FWM process. TDFL: thulium-doped fiber laser; TDFA: thulium-doped fiber amplifier; PC: polarization controller; DUT: device under test; TEC: thermoelectric cooler; OSA: optical spectrum analyzer. (b) Normalized FWM spectrum of the microring resonator with the pump and signal light on-resonance. The inset shows the normalized FWM spectrum with maximum CE. (c) Measured FWM CE in the microring resonator (green dots) and the 18-mm-long waveguide (blue dots) as a function of the input pump power in the bus waveguide. The solid curve is the fitting results. (d) Measured FWM CE in the microring resonator as a function of the input signal power in the bus waveguide. (e) Measured FWM CE as a function of signal-idler wavelength separation.

Fig. 8. Summary of experimentally demonstrated FWM CE performances in microring resonators.