Chip-compatible wide-field 3D nanoscopy through tunable spatial frequency shift effect

Spatial frequency shift (SFS) microscopy with evanescent wave illumination shows intriguing advantages, including large field of view (FOV), high speed, and good modularity. However, a missing band in the spatial frequency domain hampers the SFS superresolution microscopy from achieving resolution better than 3 folds of the Abbe diffraction limit. Here, we propose a novel tunable large-SFS microscopy, making the resolution improvement of a linear system no longer restricted by the detection numerical aperture (NA). The complete wide-range detection in the spatial frequency domain is realized by tuning the illumination spatial frequency actively and broadly through an angle modulation between the azimuthal propagating directions of two evanescent waves. The vertical spatial frequency is tuned via a sectional saturation effect, and the reconstructed depth information can be added to the lateral superresolution mask for 3D imaging. A lateral resolution of λ/9, and a vertical localization precision of ∼λ/200 (detection objective NA = 0.9) are realized with a gallium phosphide (GaP) waveguide. Its unlimited resolution enhancing capability is demonstrated by introducing a designed metamaterial chip with an unusual large refractive index. Besides the great resolution enhancement, this method shows better anti-noise capability than classical structured illumination microscopy without SFS tunability. This method is chip-compatible and can potentially provide a mass-producible illumination chip module achieving the fast, large-FOV, and deep-subwavelength 3D nanoscopy.