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) rolled-up 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 self-assembled TiO2 RUMRs by incorporating positive thermo-optic 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, which changes at a rate of -33.3 pm/K owing to the negative TOC of TiO2 (−4.9 ±0.5 ×10−5𝑘−1) . By increasing the thickness of SiO2 or Si3N4 as a positive TOC material together with TiO2 the temperature-induced resonant shifts (TIRSs) of TiO2/SiO2 and/or TiO2/Si3N4 RUMRs are theoretically obtained. The TIRS varies between -40 pm/K (-22 pm/K) and about 30 pm/K (22 pm/K) for TiO2/SiO2 (TiO2/Si3N4) RUMRs. It is shown that thermal stability occurs when the thickness of the SiO2 (Si3N4) layer is ~16 nm (12 nm). In the end of this study, for a proof-of-concept, an experiment is demonstrated by fabricating isolated RUMRs (i.e. not coupled to the waveguides) based on TiO2/SiO2 on the flat silicon wafer. In order to study the resonance-temperature-(in-)sensitive, the fabricated devices are excited using He-Cd laser (𝜆=442𝑛𝑚) under different input power via a conventional micro-photoluminescence (μ-PL) setup. The experimental results are represented that by selecting the apricated thickness ratio of TiO2/SiO2, the non-shift (and/or athermalization) of the optical modes is achieved