Integrated silicon photonics promises efficient on-chip solutions for chemical and bio-molecule sensing for faster and reliable disease diagnostics. By integrating a sensor with a light source and a detector, a compact lab-on-chip sensing device is possible to realize. To increase the sensing efficiency, slot waveguide geometry is preferable due to the high confinement of the mode within the cover material.
When two different light-paths in a structure interfere with each other, causing the superposition of a Lorenzian response with the background radiation continuum, a Fano lineshape occurs. This sharp resonance leads to a superior refractive index sensing capability.
To develop a compact on-chip Fano-resonant platform for chemical sensing, we used a merged photonic crystal – slot waveguide (MPCSW) structure as the basic building block. It contains slot waveguides merged with Bragg gratings, formed by periodic patterning of the rails. A defect between the two Bragg grating sections forms a resonant cavity. In addition to the enhancement due to the confinement of light in the slot waveguide, the highly dispersive nature of the Bragg grating leads to slow light effect at the resonance. Three MPCSW structures are parallel-coupled to form an on-chip Fano system. By changing the refractive index of the cover material, we found a sensitivity as high as 775 nm/RIU. Moreover, the group index at the resonance of our Fano system is as high as ng = 500, due to the effect of slow light. We obtain vast increase in the refractive index sensitivity of the device.
Arijit Bera, Markku Kuittinen, Seppo Honkanen, and Matthieu Roussey, "Slow-light enhanced sensing with an on-chip Fano system (Conference Presentation)," Proc. SPIE 10106, Integrated Optics: Devices, Materials, and Technologies XXI, 101060V (Presented at SPIE OPTO: February 01, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2251961.5393342283001.
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