Thermal tuning of graphene-embedded waveguide filters based on the polymer-silica hybrid structure

Graphene-embedded waveguide filters have been widely used in the areas of polarization and mode filtering because of their characteristics of easy fabrication, high integration, and high extinction ratio. In this article, we propose thermal tuning filters based on a graphene-embedded polymer-silica hybrid waveguide. Compared to previously reported filters, this device can realize the efficient adjustment of the relative position between the optical field and graphene layer by thermal tuning. Consequently, the polarization and mode filtering properties of the filter can be adjusted by thermal tuning. This high-efficiency tuning characteristic is due to the opposite thermo-optic coefficient of the polymer and silica material. Furthermore, a layer with a low refractive index is embedded in the polymer-silica hybrid core to increase the tuning efficiency. The optical absorption, mode properties, and thermal field distributions were simulated. It was found that such single-mode filters could realize E^x ₁₁-pass or E^x ₁₁-stop selection, and the attenuation variation (Δα) was optimized to 32.20 dB cm^-1 (E^x ₁₁ mode) using the top electrode and air trench structure with ΔT = 10 K and P = 48.39 mW in the single-mode waveguide. For the multimode waveguide filters, the attenuation variation (Δα) of the E^x modes (E^x ₁₁, E^x ₁₂, and E^x ₂₁) was also calculated. Such thermal tuning filters were found to be compatible with chemical potential regulation graphene modulators and filters, and they can be applied to broadband photonic integrated circuits and mode division multiplexing systems.