Highly-Sensitive Unbalanced MZI Gas Sensor Assisted With a Temperature-Reference Ring Resonator

In this paper we study the gas sensing performance of a compact silicon photonics Mach-Zehnder interferometer (MZI) with a coiled sensing arm. A partially exposed sensor was fabricated using deep UV lithography, with a process resolution of 248 nm. Testing with inert gases, He and N₂, resulted in a measured sensitivity and limit of detection of~\!1458 nm/RIU and~8.5×10-5RIU, respectively, in a sensing volume of 1.852 picoliters. The temperature sensitivity of the sensor was 166 pm/^∘C and the inclusion of a cladded ring-resonator, post-MZI, allowed resolving the temperature drift due to gas flow. In order to further enhance the overlap of the optical mode with the measurand and thus the sensitivity, a suspended MZI was designed and simulated with an expected sensitivity of~5500 nm/RIU, for wavelengths around 1550 nm and a temperature of 300 K.