Figure 1.

Single-molecule epi-fluorescence sensing by metalens on the chip. (a) Scheme of the epi-fluorescence sensing of diffusing single molecules. The metalens dimensions are designated as follows: metalens size (D_metalens), taper length (L_taper), narrow single-mode waveguide width (w₁), wide waveguide width (w₂), waveguide height (w_h), thickness of the upper cladding layer of SOG (h_SOG). The metalens focal length is approximately 7 µm, while the height and diameter of the cylindrical meta-atoms amount to 500 nm and 200 nm, respectively. The taper shape follows a relation: $y=\alpha \cdot {\left({\displaystyle \raisebox{1ex}{$L_{taper}$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}-x\right)}^m+{\displaystyle \raisebox{1ex}{$w_2$}\!\left/ \!\raisebox{-1ex}{$2$}\right.},$ where $\alpha ={\displaystyle \raisebox{1ex}{$w_1-w_2$}\!\left/ \!\raisebox{-1ex}{$2L_{taper}^m$}\right.}$, with m being 1.15 and x belonging to the range from −L_taper/2 to L_taper/2. (b) The meta-atom position produces a phase map focusing on two wavelengths. The phase profiles of the metalenses are represented along the propagation direction of light in the waveguide. (c) Segmentation of the metalens into two zones to generate foci at two wavelengths. (d) Coupling strength of modes of meta-atom and waveguide in a broad wavelength range. (e) Near-field transmission of the meta-atoms. The white line corresponds to the meta-atom height selected for designing integrated metalenses.