Broad working bandwidth and "endlessly" single-mode guidance within hybrid silicon photonics.

The successes of nonlinear photonics and hybrid silicon photonics with a growing variety of functional materials entail ever-enlarging bandwidths. It is best exemplified by parametric comb frequency generation. Such operation challenges the dielectric channel waveguide as the basis for guidance, because of the adverse advent of higher order modes at short wavelengths. Surprisingly, the popular mechanism of endlessly single-mode guidance [Opt. Lett.22, 961 (1997).] operating in photonic crystal fibers has not been transposed within silicon photonics yet. We outline here the strategy and potential of this approach within planar and hybrid silicon photonics, whereby in-plane and vertical confinement are shown to be amenable to near-single-mode behavior in the typical silicon band, i.e., λ=1.1 µm to ∼5 µm.

Resonant waveguide sensing made robust by on-chip peak tracking through image correlation.

We demonstrate a solution to make resonant-waveguide-grating sensing both robust and simpler to optically assess, in the spirit of biochips. Instead of varying wavelength or angle to track the resonant condition, the grating itself has a step-wise variation with typically few tens of neighboring "micropads." An image capture with incoherent monochromatic light delivers spatial intensity sequences from these micropads. Sensitivity and robustness are discussed using correlation techniques on a realistic model (Fano shapes with noise and local distortion contributions). We confirm through fluid refractive index sensing experiments an improvement over the step-wise maximum position tracking by more than 2 orders of magnitude, demonstrating sensitivity down to 2 × 10(-5) RIU, giving high potential development for bioarray imaging.

2D label-free imaging of resonant grating biochips in ultraviolet.

2D images of label-free biochips exploiting resonant waveguide grating (RWG) are presented. They indicate sensitivities on the order of 1 pg/mm2 for proteins in air, and hence 10 pg/mm2 in water can be safely expected. A 320x256 pixels Aluminum-Gallium-Nitride-based sensor array is used, with an intrinsic narrow spectral window centered at 280 nm. The additional role of characteristic biological layer absorption at this wavelength is calculated, and regimes revealing its impact are discussed. Experimentally, the resonance of a chip coated with protein is revealed and the sensitivity evaluated through angular spectroscopy and imaging. In addition to a sensitivity similar to surface plasmon resonance (SPR), the RWGs resonance can be flexibly tailored to gain spatial, biochemical, or spectral sensitivity.