Generation of free-space spherical focal spots using orthogonally superposed uniform line source antennas

A novel, to our knowledge, method for constructing three-dimensional (3D) spherical focused spots in a 4Pi tight focusing system via the superposition of three orthogonal uniform line source antennas (ULSAs) is proposed and numerically verified. By combining antenna theory with vector diffraction theory, the mapping relationship between the pupil-plane incident field and the tightly focused field in the focal region is analytically derived with high accuracy. Numerical results demonstrate that the superposition of ULSAs along the x , y , and z axes yields a nearly isotropic spherical focused spot, which exhibits approximately circular projections on all orthogonal cross-sections with a consistent full width at half-maximum (FWHM) of ∼0.447 λ . Further analyses demonstrate that such spherical focused spots can be flexibly arranged into 1D, 2D, and 3D arrays with uniform dimensions and negligible crosstalk between adjacent spots. Requiring no iterative optimization or complex phase modulation elements, this method provides a flexible and practical new scheme for the efficient construction of 3D optical fields, holding promising applications in high-precision optical manipulation and related fields.