Abstract
Ring resonators with TiO2 core confinement factors from 0.07 to 0.42 are fabricated and measured for thermal sensitivity achieving -2.9 pm/K thermal drift in the best case. Materials used are CMOS compatible (TiO2, SiO2 and Si3N4) on a Si substrate. The under discussed role of stress in thermo-optic behavior is clearly observed when contrasting waveguides buried in SiO2 to those with etched sidewalls revealed to air. Multiphysics simulations are conducted to provide a theoretical explanation of this phenomenon in contrast to the more widely reported theories on thermo-optic behavior dominated by confinement factor.
Highlights
Thermal stability is an important topic in integrated photonics research
We have shown that TSO effects are important to performance of TiO2 core waveguides most strongly indicated by reduction of the thermo-optic coefficient (TOC) by more than two orders of magnitude
We clarified the theoretical framework for this phenomenon with derivations of three models of ring resonator thermal drift
Summary
Thermal stability is an important topic in integrated photonics research. The need for athermal structures is clear for photonics applications from low-cost communications links in data centers, passive optical networks, microwave photonic filters, and sensors. The current solutions use single channels, coarse wavelength division multiplexing (CWDM), temperature stabilizing feedback loops, or a power hungry thermo-electric cooler (TEC). This is an active research area with a number of solutions to address the thermal stability challenge by designing intrinsically athermal structures. Titania (TiO2) has been suggested as a CMOS compatible alternative material to polymers for enabling athermal waveguides in photonic integrated circuits [8]. The reason for this is its strong negative material thermo-optic coefficient (TOC) dn dT.
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