We present a novel waveguide geometry for enhancing and confining light in a nanometer-wide low-index material. Light enhancement and confinement is caused by large discontinuity of the electric field at high-index-contrast interfaces. We show that by use of such a structure the field can be confined in a 50-nm-wide low-index region with a normalized intensity of $20 \mathit{\mu }{\mathrm{m}}^{-2}$. This intensity is approximately 20 times higher than what can be achieved in ${\mathrm{SiO}}_2$ with conventional rectangular waveguides.

We report an experimental demonstration of an integrated biochemical sensor based on a slot-waveguide microring resonator. The microresonator is fabricated on a ${\mathrm{Si}}_3{\mathrm{N}}_4–\mathrm{Si}{\mathrm{O}}_2$ platform and operates at a wavelength of $1.3\mu \mathrm{m}$. The transmission spectrum of the sensor is measured with different ambient refractive indices ranging from $n=1.33$ to 1.42. A linear shift of the resonant wavelength with increasing ambient refractive index of $212\mathrm{nm}$/refractive index units (RIU) is observed. The sensor detects a minimal refractive index variation of $2\times {10}^{-4}\mathrm{RIU}$.

We present the design, fabrication, and characterisation of an array of optical slot-waveguide ring resonator sensors, integrated with microfluidic sample handling in a compact cartridge, for multiplexed real-time label-free biosensing. Multiplexing not only enables high throughput, but also provides reference channels for drift compensation and control experiments. Our use of alignment tolerant surface gratings to couple light into the optical chip enables quick replacement of cartridges in the read-out instrument. Furthermore, our novel use of a dual surface-energy adhesive film to bond a hard plastic shell directly to the PDMS microfluidic network allows for fast and leak-tight assembly of compact cartridges with tightly spaced fluidic interconnects. The high sensitivity of the slot-waveguide resonators, combined with on-chip referencing and physical modelling, yields a volume refractive index detection limit of 5 × 10⁻⁶ refractive index units (RIUs) and a surface mass density detection limit of 0.9 pg mm⁻², to our knowledge the best reported values for integrated planar ring resonators.

We demonstrate label-free molecule detection by using an integrated biosensor based on a ${\mathrm{Si}}_3{\mathrm{N}}_4∕{\mathrm{SiO}}_2$ slot-waveguide microring resonator. Bovine serum albumin (BSA) and anti-BSA molecular binding events on the sensor surface are monitored through the measurement of resonant wavelength shifts with varying biomolecule concentrations. The biosensor exhibited sensitivities of 1.8 and $3.2\mathrm{nm}∕(\mathrm{ng}∕{\mathrm{mm}}^2)$ for the detection of anti-BSA and BSA, respectively. The estimated detection limits are 28 and $16\mathrm{pg}∕{\mathrm{mm}}^2$ for anti-BSA and BSA, respectively, limited by wavelength resolution.

We present an experimental demonstration of fast all-optical switching on a silicon photonic integrated device by employing a strong light-confinement structure to enhance sensitivity to small changes in the refractive index. By use of a control light pulse with energy as low as 40 pJ, the optical transmission of the structure is modulated by more than 97% with a time response of 450 ps.