On-chip electro-optic modulator with solution-processed colloidal In₂O₃ nanocrystals

We demonstrate an on-chip electro-optic modulator with colloidal In₂O₃ nanocrystals, which are integrated on a silicon photonic chip with a simple spin-coating process. The modulator has an electrical capacitor-like structure with In₂O₃ and silicon as the two semiconductor electrodes, which are separated by an Al₂O₃ dielectric layer. With the electrical voltage applied to the two semiconductor layers, their carrier densities are changed considerably, and subsequently, the complex refractive indices. As a result, from an In₂O₃-coated silicon microring resonator, the resonance lineshape and central wavelength are modified. The resonance wavelength tunability is 15.7 pm/V, resulting in a modulation depth exceeding 13 dB. A modulation efficiency V_π·L of 0.56 V·cm, a static power consumption of 2.5 pW/nm, and a per-bit power consumption of 2.34 pJ/bit under a driving voltage of 2 V_pp are realized. Our work provides a viable route for CMOS-compatible, high-throughput, and cost-effective solution-based electro-optic modulators for photonic integrated circuits.