Altermalization rolled-up TiO2 microtube ring resonator for both visible and telecom photonics

One important concern in integrated optics is thermal heating which leads to the unwanted wavelength shift in the integrated system. This shift oftentimes is not suitable for some important applications e.g. optical filtering and switching and etc.. To this end, one needs to fabricate the athermal optical devices instead of the conventional optical devices in the integrated system. In this work, for the first time a hybrid TiO2-SiO2 and or (TiO2-Si3N4) rolledup microtube ring resonator (RUMRs) with a temperature insensitive resonance (i.e. athermal) is theoretically and experimentally demonstrated. In the first part of this paper, the thermal stability of optical filters based on selfassembled TiO2 RUMRs by incorporating positive thermooptic coefficient (TOC) materials (e.g. SiO2 and/or Si3N4) is investigated. The influence of the TOC, refractive index, and thickness of the positive TOC materials on the filtering performance of the TiO2 RUMRs are theoretically studied. The results illustrate that an increase in temperature leads to a blue-shift in resonant wavelength of the RUMR-based optical filter.