基于二氧化钛的片上集成微腔及应用研究

高Q值光学微腔在集成光子回路中起到越来越重要的作用。然而，传统硅基微腔受到双光子吸收的影响而高Q值氮化硅微腔的量产受到应力的限制。因此，能够与CMOS技术和电子元器件同时兼容的二氧化钛材料及器件开始受到人们的关注。然而，二氧化钛基集成光子回路的研究处于起步阶段，加工工艺尚不成熟，制备的波导、微腔等器件存在非常大的传输损耗，无法支撑高Q值的谐振模式及相关的非线性应用。基于课题组过去的技术积累，本项目将对片上集成的二氧化钛微腔进行研究。通过模场控制和对关键加工工艺的优化，我们将大幅减少器件的表面损耗，把二氧化钛微腔Q值提高到2-3×10^5以上，并研究微腔与波导系统的高效耦合。同时，也将研究二氧化钛片上系统与传统光纤系统的耦合，最终实现可与现有光通信系统兼容的高Q值片上二氧化钛微腔光子回路，并探索其在非线性器件及传感器件中的应用。

High-Q microcavities have been key elements for on-chip integrated photonic circuits. In additional to their linear applications, the nonlinear optical phenomena in high-Q microcavities have also attracted intensive research attention. A large number of nonlinear optical devices have been developed with high-Q microcavities, e.g. frequency comb. However, the current systems face severe challenge in mass-manufacturable on-chip photonic circuits. The SiO2 microcavities including microspheres, microtoroids, and microdisk are not CMOS compatible. The conventional Si microcavities are limited by their large two-photon absorption at the telecommunication wavelength. The Si3N4 microcavities can support higher Q factors of 10^6 or higher. However, the corresponding wafer must be grown with LPCVD. The tension within the film usually breaks it into small pieces, strongly hindering the possible mass-fabrication. ..In past decade, TiO2 based photonic devices have attracted considerable research attention due to their several intrinsic advantages, e.g. higher refractive index, higher nonlinearity, CMOS compatibility, and compatible with electric circuits. A lot of TiO2 photonic devices such as waveguide, M-Z interferometer, microring resonator, and metasurfaces et al. While distinguished performances have been achieved, these photonic devices are only on their infant stages and are significantly limited by their top-down nanofabrication techniques. The scattering loss is more than 4 dB/cm in waveguide and the Q factor is below 10,0000, which is not high enough for nonlinear applications...In this research, we start to challenge the status of the TiO2 nanophotonics. Based on our research backgrounds on TiO2 metasurfaces and Si photonic chips, we will optimize the on-chip integrated TiO2 mcirocavities to realize the high Q factors around 2-3×10^5 and even higher. From the aspect of optical design, we will optimize the polarization, thickness, width of waveguide and resonators to reduce the scattering at the side surface. In case of nanofabrication, we will optimize the reactive ion etching (RIE) process to reduce the surface roughness and further average out the surface roughness by an additional atomic layer deposition (ALD) process. Based on our high Q factors, we will also demonstrate the potential applications of TiO2 microcavities in nanoparticle sensing and nonlinear optical process such as full wave mixing...Overall, owing to their large nonlinearity and CMOS compatible mass-fabrication, the improvement in Q factors can pave a significant step towards real applications of on-chip integrated nonlinear photonic circuits.