Broadband transverse displacement sensing by exploiting the interaction of a focused radially polarized beam with a silicon hollow nanodisk is proposed. The multipolar decomposition analysis indicates that the interference between a longitudinal total electric dipole (TED) moment and a lateral magnetic dipole (MD) moment is dominant in the far-field transverse scattering in the near-infrared region. Within a broadband wavelength range with the width of 155 nm, the longitudinal TED is almost in phase with the lateral MD, and then broadband position sensing based on the sensitivity of scattering directivity to transverse displacement can be achieved.

Subtractive imaging is used to suppress the axial sidelobes and improve the axial resolution of 4pi microscopy with a higher-order radially polarized (RP) Laguerre–Gaussian (LG) beam. A solid-shaped point spread function (PSF) and a doughnut-shaped PSF with a dark spot along the optical axis are generated by tightly focusing a higher-order RP-LG beam and a modulated circularly polarized beam, respectively. By subtracting the two images obtained with those two different PSFs, the axial sidelobes of the subtracted PSF are reduced from 37% to about 10% of the main lobe, and the axial resolution is increased from 0.21λ to 0.15λ.

Specific and highly-sensitive biochemical detection technology is particularly important in global epidemics and has critical applications in life science, medical diagnosis, and pharmaceutics. As a newly developed technology, the THz metamaterial-based sensing method is a promising technique for extremely sensitive biomolecular detection. However, due to the significant resonant peaks generated by THz metamaterials, the characteristic absorption peaks of the analyte are usually masked, making it difficult to distinguish enantiomers and specifically identify target biomolecules. Recently, new ways to overcome this limitation have become possible thanks to the emergence of chiral metasurfaces and the polarization sensing method. Additionally, functionalized metasurfaces modified by antibodies or other nanomaterials are also expected to achieve specific sensing with high sensitivity. In this review, we summarize the main advances in THz metamaterials-based sensing from a historical perspective as well as application in chiral recognition and specific detection. Specifically, we introduce the basic theory and key technology of THz polarization spectrum and chiral sensing for biochemical detection, and immune sensing based on biomolecular interaction is also discussed. We mainly focus on chiral recognition and specific sensing using THz metasurface sensors to cover the most recent advances in the topic, which is expected to break through the limitations of traditional THz absorption spectroscopy and chiral spectroscopy in the visible-infrared band and develop into an irreplaceable method for the characterization of biochemical substances.