Diffraction symmetry of binary Fourier elements with feature sizes on the order of the illumination wavelength and effects of fabrication errors.

When building spot array binary Fourier diffractive optical elements (DOEs) having feature sizes on the order of the wavelength, we noticed remarkable variations in the experimental diffraction efficiency compared to the simulation results. Even with the use of high-cost electron beam lithography and rigorous Fourier modal method simulations, there appear to be no publications, to the best of our knowledge, showing close agreement in diffraction efficiency between the simulation and experimental results. In this Letter, we show that the diffraction symmetry of binary Fourier DOEs can be an efficient and consistent metric for evaluating the limit of the thin-element approximation and the effects of fabrication errors.

Smart multifunction diffractive lens experimental validation for future PV cell applications.

Recently, diffractive optical elements (DOE's) have attracted more attention for applications to third generation PV cells. Some DOE types can provide multiple functions such as spectrum splitting and beam concentration (SSBC) simultaneously. An off-axis diffractive lens has been designed and its ability to achieve the SSBC proved experimentally. This lens can be used to separate the solar spectrum in the Vis-NIR range into two bands with a low concentration factor, and about 70% optical efficiency. It is expected that this kind of lens can be integrated with the lateral multijunction PV cells to build an effective compact solar system.

Iterative scalar nonparaxial algorithm for the design of Fourier phase elements.

We propose an iterative algorithm based on our scalar nonparaxial 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°.

Computationally efficient scalar nonparaxial modeling of optical wave propagation in the far-field.

We present a scalar model to overcome the computation time and sampling interval limitations of the traditional Rayleigh-Sommerfeld (RS) 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 nonparaxial diffraction step onto a hemisphere and a projection onto a plane accurately predicts the observed nonparaxial far-field diffraction pattern, while its calculation time is much lower than the more rigorous RS integral. The results enable a fast and efficient way to compute far-field nonparaxial diffraction when the conventional Fraunhofer pattern fails to predict correctly.