Integrated buried heaters for efficient spectral control of air-clad microresonator frequency combs

Integrated heaters are essential in the photonics toolbox, particularly for microresonator frequency tuning through the thermo-refractive effect. Resonators that are fully embedded in a solid cladding (typically SiO2) allow for straightforward lossless integration of heater elements. However, air-clad resonators, which are of great interest for short wavelength dispersion engineering and direct interfacing with atomic/molecular systems, do not usually have similar low loss and efficient heater integration through standard fabrication. Here, we develop a new approach in which the integrated heater is embedded in SiO2 below the waveguiding layer, enabling more efficient heating and more arbitrary routing of the heater traces than possible in a lateral configuration. We incorporate these buried heaters within a stoichiometric Si3N4 process flow that includes high-temperature (>1000 degrees C) annealing. Microring resonators with a 1 THz free spectral range and quality factors near 106 are demonstrated, and the resonant modes are tuned by nearly 1.5 THz, a 5x improvement compared to equivalent devices with lateral heaters. Finally, we demonstrate broadband dissipative Kerr soliton generation in this platform and show how the heaters can be utilized to aid in bringing relevant lock frequencies within a detectable range. (C) 2022 Author(s).

Automated summary

In this study, a new approach was developed to embed integrated heaters in micro-ring resonators, enabling more efficient heating and more arbitrary routing of heater traces. Experimental results showed that micro-ring resonators with buried heaters had a larger tuning range and higher quality factors compared to devices with lateral heaters. Furthermore, the platform was able to generate broadband dissipative Kerr solitons.