High-Sensitivity Polarization-Independent Biochemical Sensor Based on Silicon-on-Insulator Cross-Slot Waveguide

Slot waveguides reported so far are strongly polarization dependent. The concept of a novel cross-slot waveguide (WG) is presented here, which contains both vertical and horizontal slots and supports the power enhancement in the slot region for both the quasi-TE and quasi-TM polarizations. This WG can be fabricated by exploiting well developed CMOS technology. For the unpolarized operating light, the cross-slot WG is optimized to have the maximum total slot confinement factors for the two polarizations. As for a polarization-independent design, confinement in slot for each polarization can reach 39.4% when the silicon core width and height are set to around 223 and 216 nm, respectively. It is shown here that a biochemical sensor employing a cross-slot-WG exhibits a significantly better sensitivity, compared to either a vertical-slot-WG or a horizontal-slot-WG-based biochemical sensor. As an example, when both the vertical slot width and horizontal slot height are set to 100 nm, its sensitivity is almost double compared with a simple vertical or horizontal slot with 100 nm gap.