Ultra-sensitive refractive index gas sensor with functionalized silicon nitride photonic circuits

Abstract

Portable and cost-effective gas sensors are gaining demand for a number of environmental, biomedical, and industrial applications, yet current devices are confined into specialized labs and cannot be extended to general use. Here, we demonstrate a part-per-billion-sensitive refractive index gas sensor on a photonic chip based on silicon nitride waveguides functionalized with a mesoporous silica top-cladding layer. Low-concentration chemical vapors are detected by monitoring the output spectral pattern of an integrated unbalanced Mach-Zehnder interferometer having one coated arm exposed to the gas vapors. We retrieved a limit of detection of 65 ppb, 247 ppb, and 1.6 ppb for acetone, isopropyl alcohol, and ethanol, respectively. Our on-chip refractive index sensor provides, to the best of our knowledge, an unprecedented limit of detection for low gas concentrations based on photonic integrated circuits. As such, our results herald the implementation of compact, portable, and inexpensive devices for on-site and real-time environmental monitoring and medical diagnostics.

Enhanced Refractive Index Sensitivity through Combining a Sol–Gel Adsorbate with a TiO2 Nanoimprinted Metasurface for Gas Sensing

“…Note that sensitivity to isopropanol down to a ppb level has been demonstrated with an integrated Mach−Zehnder interferometer system, coupled to a mesoporous sensitive layer. 41 Despite the complexity of the system and of the signal treatment, a sensitivity of S IPA = 0.06 nm/ppm, lower than the 0.2 nm/ppm demonstrated in this work, was reported.…”

Integrated Nanophotonic Waveguide-Based Devices for IR and Raman Gas Spectroscopy

“…This strategy has become of the utmost importance for highly sensitive transducers with low selectivity or specificity and has been adopted in a number of chemical-sensing devices such as opto-chemical, electro-chemical, plasmonic sensors, and refractive index waveguidebased sensors [92][93][94][95][96]. In the latter case, the analyte either increases the refractive index of the cladding or motivates a change in the thickness of the cladding itself [97][98][99], which is then detected by a phase-sensitive device such as a ring resonator, Mach-Zehnder interferometer, or a Bragg grating [95,97,100]. The advantages of functional cladding have also proven to be highly useful for already selective transducers, such as Raman and IR spectroscopy sensors, as a means to increase the sensitivity by analyte up-concentration and the reduction of the background signal in complex matrices.…”

Sol-Gel Thin Film Processing for Integrated Waveguide Sensors

“…The former one designed a Mach-Zehnder interferometer having one sol-gel coated arm exposed to gas vapors. They were able to retrieve a limit of detection of 65 ppb, 247 ppb, and 1.6 ppb for acetone, isopropyl alcohol, and ethanol, respectively (Antonacci et al, 2020). The latter, implemented a Bragg grating covered with a commercially available hybrid material and was used for developing a temperature sensor (Beneitez et al, 2016).…”