A Tellurium Oxide Microcavity Resonator Sensor Integrated On-Chip with a Silicon Waveguide

Abstract

We report on thermal and evanescent field sensing from a tellurium oxide optical microcavity resonator on a silicon photonics platform. The on-chip resonator structure is fabricated using silicon-photonics-compatible processing steps and consists of a silicon-on-insulator waveguide next to a circular trench that is coated in a tellurium oxide film. We characterize the device's sensitivity by both changing the temperature and coating water over the chip and measuring the corresponding shift in the cavity resonance wavelength for different tellurium oxide film thicknesses. We obtain a thermal sensitivity of up to 47 pm/°C and a limit of detection of 2.2 × 10^-3 RIU for a device with an evanescent field sensitivity of 10.6 nm/RIU. These results demonstrate a promising approach to integrating tellurium oxide and other novel microcavity materials into silicon microphotonic circuits for new sensing applications.

Keywords: optical microcavities; photonic sensors; resonators; silicon photonics.

Figure 1

(a) Top view drawing of the resonator sensor showing the pulley-coupled silicon bus waveguide (red) and the TeO₂ microcavity (green). (b) Cross-section schematic of the device through the section indicated by the dashed line in (a), showing the silicon bus waveguide and the TeO₂ resonator layer coated into the trench. (c) Calculated fundamental transverse electric (TE) polarized electric field mode profiles for the TeO₂ resonator and silicon bus waveguide in the region indicated by the dashed line in (b). (d) Focused ion beam (FIB) scanning electron microscope (SEM) cross-section image of a fabricated device showing the realized structure.

Figure 2

Diagram of the optical setup used to characterize the devices.

Figure 3

Resonance spectra measured at temperatures ranging from 20 to 40 °C for the microcavity with a 1100-nm-thick TeO₂ film, showing shifting of the resonance wavelength.

Figure 4

Measured wavelength shift versus temperature for 480-, 900-, and 1100-nm-thick TeO₂ cavities, fitted to have thermal sensitivities of 28, 47, and 30 pm/°C, respectively.

Figure 5

Resonance spectra measured in air (pink) and after covering the chip in water (blue) for (a) 900-nm-thick and (b) 1100-nm-thick TeO₂ resonators.

Figure 6

Measured resonance shift vs. cladding refractive index for a 900-nm-thick TeO₂ microcavity coated in solutions with varying concentrations of glycerol and water.

Figure 7

Cavity resonance modes around 1600 nm measured in air (fit with red line) and after coating the chip in water (fit with blue line) for (a) 900-nm-thick and (b) 1100-nm-thick TeO₂ resonators, demonstrating resonance broadening in water.

Figure 8

Simulated (a) wavelength shift and (b) RIU sensitivity vs. evanescent medium refractive index for cavities with TeO₂ coating thicknesses ranging from 0.5 to 1.1 μm.