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Silicon microring modulator plays a critical role in energy-efficient optical interconnect and optical computing owing to its ultra-compact footprint and capability for on-chip wavelength-division multiplexing. However, existing silicon microring modulators usually require more than 2 V of driving voltage (V_pp), which is limited by both material properties and device structures. Here, we present a metal-oxide-semiconductor capacitor microring modulator through heterogeneous integration between silicon photonics and titanium-doped indium oxide, which is a high-mobility transparent conductive oxide (TCO) with a strong plasma dispersion effect. The device is co-fabricated by Intel’s photonics fab and our in-house TCO patterning processes, which exhibits a high modulation efficiency of 117 pm/V and consequently can be driven by a very low V_ppof 0.8 V. At a 11 GHz modulation bandwidth where the modulator is limited by the RC bandwidth, we obtained 25 Gb/s clear eye diagrams with energy efficiency of 53 fJ/bit.

Silicon microring resonators (Si-MRRs) play essential roles in on-chip wavelength division multiplexing (WDM) systems due to their ultra-compact size and low energy consumption. However, the resonant wavelength of Si-MRRs is very sensitive to temperature fluctuations and fabrication process variation. Typically, each Si-MRR in the WDM system requires precise wavelength control by free carrier injection using PIN diodes or thermal heaters that consume high power. This work experimentally demonstrates gate-tuning on-chip WDM filters for the first time with large wavelength coverage for the entire channel spacing using a Si-MRR array driven by high mobility titanium-doped indium oxide (ITiO) gates. The integrated Si-MRRs achieve unprecedented wavelength tunability up to 589 pm/V, or V_πL of 0.050 V cm with a high-quality factor of 5200. The on-chip WDM filters, which consist of four cascaded ITiO-driven Si-MRRs, can be continuously tuned across the 1543–1548 nm wavelength range by gate biases with near-zero power consumption.

We demonstrated efficient gate-tuning on-chip wavelength division multiplexing filters using a silicon microring resonator array driven by high-mobility titanium-doped indium oxide gates. It shows extensive wavelength coverage for entire channel spacing over 5 nm.

A novel characterization method is proposed to extract the optical frequency field-effect mobility (${\mu }_{\mathrm{op},\mathrm{FE}}$) of transparent conductive oxide (TCO) materials by a tunable silicon microring resonator with a heterogeneously integrated titanium-doped indium oxide$(\mathrm{ITiO})/{\mathrm{SiO}}_2/\mathrm{silicon}$metal–oxide–semiconductor (MOS) capacitor. By operating the microring in the accumulation mode, the quality factor and resonance wavelength shift are measured and subsequently used to derive the${\mu }_{\mathrm{op},\mathrm{FE}}$in the ultra-thin accumulation layer. Experimental results demonstrate that the${\mu }_{\mathrm{op},\mathrm{FE}}$of ITiO increases from 25.3 to$38.4{\mathrm{cm}}^2\text{⋅}{\mathrm{V}}^{-1}\text{⋅}{\mathrm{s}}^{-1}$with increasing gate voltages, which shows a similar trend as that at the electric frequency.