Efficient and compact sol-gel TiO₂ thermo-optic microring resonator modulator

Thermo-optic (TO) modulators play an increasingly important role in wavelength routers, lidar, optical computing, and other reconfigurable photonic systems. Highly efficient TO tunable microring resonators (MRRs) were first demonstrated based on a sol-gel TiO₂ platform in the 1310-nm waveband owing to the synergistic effect between the TiO₂ core and SU-8 cladding with both the negative thermo-optical coefficients. The MRR modulator with SU-8 polymer as the top cladding layer exhibits a thermal tuning efficiency of 33.0 pm/mW, which is more than 14 times higher than that with silica top cladding. Its rise/fall times of 9.4 us/24 us and a Pπ power of 7.22 mW were achieved, indicating a relatively high TO modulator figure of merit among noncrystalline material platforms allowing monolithic integration on different substrates. These results yield a strong promise for applying the sol-gel TiO₂ platform in photonic integrated circuits and suggest a new angle of view to design compact and efficient TO modulators in wearable devices, visible/infrared communication, and biophotonic applications.