# Vernier Effect-Enhanced Temperature Sensing Based on On-Chip Spiral Resonant Cavities

## TL;DR

This paper introduces a new on-chip spiral resonant cavity design that enhances temperature sensing using the Vernier effect, achieving significantly higher sensitivity.

## Contribution

A novel on-chip spiral resonant cavity structure that improves the detection range and sensitivity of Vernier effect-based temperature sensing.

## Key findings

- The spiral cavity extends the cavity length to 7.50 m within a limited area, improving the Vernier effect detection.
- Using two cascaded resonant cavities, the sensitivity was improved by a factor of 14.19 compared to a single cavity.
- The free spectral width was reduced to 371.29 MHz, making the Vernier envelope easier to read.

## Abstract

The optical Vernier effect has been widely studied due to its remarkable effect in improving the sensitivity and resolution of optical sensors. This effect relies on the overlapping envelope of two signals with slightly detuned frequencies. In the application of on-chip optical waveguide resonant cavities with whispering gallery modes, due to the on-chip space limitations, the length of the resonant cavity is restricted, resulting in an increased free spectral range. In the case of a small Vernier effect detuning, the required large Vernier envelope period often exceeds the available wavelength range of the detection system. To address this issue, we propose a novel on-chip waveguide structure to optimize the detection range of the cascaded Vernier effect. The proposed spiral resonant cavity extends the cavity length to 7.50 m within a limited area. The free spectral width (27.46 MHz) is comparable in size to the resonant linewidth (9.41 MHz), shrinking the envelope free spectral width to 371.29 MHz, which greatly facilitates the reading of the Vernier effect. Finally, by connecting two resonant cavities with similar cavity lengths in series and utilizing the Vernier effect, temperature sensing was verified. The results show that compared with a single resonant cavity, the sensitivity was improved by a factor of 14.19. This achievement provides a new direction for the development of wide-range and high-sensitivity Vernier sensing technologies.