Label-Free Water Sensors Using Hybrid Polymer–Dielectric Mid-Infrared Optical Waveguides

Abstract

A chip-scale mid-IR water sensor was developed using silicon nitride (SiN) waveguides coated with poly(glycidyl methacrylate) (PGMA). The label-free detection was conducted at λ=2.6-2.7 μm because this spectral region overlaps with the characteristic O-H stretch absorption while being transparent to PGMA and SiN. Through the design of a hybrid waveguide structure, we were able to tailor the mid-IR evanescent wave into the PGMA layer and the surrounding water and, consequently, to enhance the light-analyte interaction. A 7.6 times enhancement of sensitivity is experimentally demonstrated and explained by material integration engineering as well as waveguide mode analysis. Our sensor platform made by polymer-dielectric hybrids can be applied to other regions of the mid-IR spectrum to probe other analytes and can ultimately achieve a multispectral sensor on-a-chip.

High Aspect Ratio Plasmonic Nanotrench Structures with Large Active Surface Area for Label-Free Mid-Infrared Molecular Absorption Sensing

“…2,38 In parallel, mid-IR photonics based on the Si platform is also emerging. 17,18,39 Here we propose the use of hyperbolic metamaterials (HMMs) based on aluminum-doped zinc oxide (AZO) trench structures as a platform for boosting absorption of mid-IR light by molecules in the trenches as illustrated in Figure 1a. AZO exhibits the plasmonic response (that is a negative real part of the permittivity) in the near-and mid-IR wavelength regions between 1.8 and 3.5 μm depending on doping and fabrication schemes.…”

Progress of infrared guided-wave nanophotonic sensors and devices

“…A poly(glycidyl methacrylate) (PGMA) layer was coated on the SiN waveguide for water sensing (Fig. 7e) [148]. A 7.6 times enhancement of sensitivity was experimentally demonstrated as a result of the swelling up of PGMA after exposure to water.…”

“…6d, e). Both the SiN and AlN are leveraged as MIR waveguide materials for biochemical sensing [148,149] while they are also capable of working in the ultra-violet spectrum. It is worth noting that the AlN-on-borosilicate waveguide in [149] possesses flexibility enabled by thinning of the borosilicate substrate.…”

“…c Germanium-on-silicon (Reproduced with permission from [147]). d Silicon nitride-on-insulator (Reproduced with permission from [148]). e Aluminum nitride-on-borosilicate (Reproduced with permission from [149]).…”

“…d Micro-ring resonator (Reproduced with permission from [157]). e Enhancement layer coating (Reproduced with permission from [148]). f Side-trench waveguide (Reproduced with permission from [146]).…”