Enhanced fractional Fourier lens with isotropic transformation media

By manipulating the principal stretches during a two-step space mapping within the framework of transformation optics, the input spatial frequency bandwidth of a conventional Fourier lens can be extended based on an isotropic transformation material. Isotropy is important for easy fabrication, low loss, and broadband application; moreover, it suggests a route for realizing Fourier transforms of continuous fractional order with enhanced input spatial frequency bandwidth.