Design of a temperature sensor based on a valley photonic crystal Mach–Zehnder interferometer

With the development of photonics device integration technology, Mach–Zehnder interferometers (MZIs) are widely applied as sensors because they are extremely sensitive to environmental parameters. Conventional MZI sensors are generally large and unsuitable for high-density integration. MZIs based on photonic crystals (PCs) can significantly improve compactness and are suitable for integration. However, PC MZIs experience substantial optical loss due to scattering. Based on the spin-valley locking effect that can achieve defect-immune unidirectional transmission of topological edge states in valley photonic crystals (VPCs), we propose an MZI sensor based on a VPC structure and apply it in temperature sensing for what we believe is the first time. The interference peaks redshift with an increase in the temperature, which allows accurate sensing of the temperature shift with a high sensitivity of 0.06 nm/K in the temperature range of 100 K–750 K. The ultracompact device has a small footprint of 9.26×7.99µm 2 and a high forward transmittance of 0.88. The design is suitable for the current complementary metal-oxide semiconductor (CMOS) fabrication technique. Thus, it will find broad applications in integrated photonics, optical communication, and integrated temperature sensing.