Demonstration of a Fiber-Enabled Polarimetric Waveguide Interferometer on a Silicon Nitride Strip Platform With Ultra-High Sensitivity

Integrated photonics is a promising technology for point-of-care sensors. It achieves competitively low limits of detection due to paramount sensitivity. The polarimetric waveguide interferometer is a design that leverages polarization diversity for effective self-referencing. It was shown to be particularly sensitive in both experimental and simulation studies. However, impractical free-space optics or delicate waveguide junctions reduced its feasibility in real-world realizations. We implement a recently devised design relying on a robust in-line polarizer for polarization handling and an optimized strip waveguide geometry on a CMOS-compatible silicon nitride platform. We demonstrate the calibration of such a fiber-enabled polarimetric waveguide interferometer and obtain a superior sensitivity of (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$16 600\pm 30$</tex-math></inline-formula>) rad/RIU in a comparison to competing waveguide geometries. This translates to a limit of detection of (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1.64 \pm 0.06)\times 10^{-6}$</tex-math></inline-formula> RIU with the potential of reaching <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3.8\times 10^{-8}$</tex-math></inline-formula> RIU by achieving peer-level signal-to-noise ratios. Thus, we present a polarimetric waveguide interferometer with a performance on par with the state-of-the-art in refractometric integrated photonic sensors in terms of sensitivity and reinforce the feasibility of deployment due to the robust design.