Search

The rigorous vector-based simulation methods for subwavelength diffractive lenses are methods of growing importance. In this paper, we introduce a rigorous vector-based method to compute the electromagnetic propagation. It includes the Finite-Difference Time-Domain (FDTD) for the near field simulation, and the Radiation Spectrum Method (RSM) for the far field propagation. This approach is then proposed to design effective medium cylindrical diffractive lenses. This kind of component, made up of binary features that behave as an effective medium, can achieve an higher diffraction efficiency than conventional diffractive optical elements. The layout design of the component is realised thanks to the FDTD simulation by estimating the phase difference introduced by subwavelength binary gratings. Then, the whole modeling of the component, whose minimum feature size can be smaller than 100 nm, is done with the RSM algorithm. Because of their subwavelength, aperiodic, finite and high spatial frequencies characteristics, these devices conception methods prevent the use of scalar modeling or coupled wave theory. The proposed method overcomes these limitations. First, the principle of the rigorous vector-based method is introduced. Then, we present the design of the subwavelength structures by means of the FDTD method, followed by the design of the subwavelength element. Finally, the simulation method of the subwavelength lens by use of the FDTD method for the near field propagation and the RSM for the far field calculation is also presented. Finally, we discuss the comparison between a subwavelength lens and its multilevel counterpart.

International audience; We propose an iterative algorithm based on our scalar non-paraxial propagator for the design of Fourier Diffractive Optical Elements (DOEs) having features on the order of the illumination wavelength. The simulation results show that our algorithm using iterative Fourier transform and iterative projection obtains higher performance DOEs than a purely scalar paraxial design with the same order of calculation time. Upon verification with the experimental results, we find that our scalar-based design method is valid for DOEs with surprisingly small feature sizes (about half the wavelength) and diffraction angles up to about 37°.

International audience; We present a scalar model to overcome the computation time and sampling interval limitations of the traditional Rayleigh-Sommerfeld formula and Angular Spectrum Method in computing wide-angle diffraction in the far-field. Numerical and experimental results show that our proposed method based on an accurate non-paraxial diffraction step onto a hemisphere and a projection onto a plane accurately predicts the observed non-paraxial far-field diffraction pattern, while its calculation time is much lower than the more rigorous Rayleigh-Sommerfeld integral. The results enable a fast and efficient way to compute far-field non-paraxial diffraction where the conventional Fraunhofer pattern fails to predict correctly.