On-Chip Chemical Sensing Using Double-Slot Silicon Waveguide

In this article, we present refractive index measurement using a double-slot silicon waveguide-based Mach–Zehnder interferometer (MZI). We present a double-slot waveguide that offers the best sensitivity and limit of detection (LOD) compared to wire and single-slot waveguides. We demonstrate ultralow loss coupling between a single-mode waveguide and a double-slot waveguide and experimental proof for double-slot excitation. The double-slot waveguide is used to demonstrate a highly sensitive concentration sensor. An unbalanced Mach–Zehnder is used as the sensor device to demonstrate concentrations of potassium chloride (KCl) in deionized water. A sensitivity of 700 nm/RIU and a LOD of
$7.142\times 10^{-{6}}$
RIU are achieved experimentally. To the best of our knowledge, the demonstrated sensitivity is the highest for an ON-chip-guided waveguide sensing scheme. Index Double-slot waveguide, evanescent field, Mach–Zehnder interferometer (MZI), ON-chip, refractive index, sensitivity.