ABSTRACT
It has been shown in previous literature that nearly diffraction limited focusing is possible by a doublet metalens up to almost 30 deg. This result indicates that metalenses can work well, even at oblique incidence. Although various meta-atoms have been proposed, as far as we know, there is no report that compares what kind of meta-atom is robust against oblique incidence. Here, we first numerically calculated the incident angle dependence of the three types of meta-atoms. The results show that the waveguide-type structure is the most robust to oblique incidence. Next, we performed rigorous electromagnetic simulations for the cylindrical doublet metalenses to compare the micropost type and waveguide type. These results indicate that a waveguide-type metasurface further improves the off-axis performance of the doublet lens previously introduced.
ABSTRACT
We propose a model-based fringe analysis technique that enables the Fourier transform method to analyze dense fringe patterns with large phase variations. The conventional Fourier-transform method has a limited dynamic range of measurable phase because the Fourier spectra broadened by large phase variations cannot be separated by the spatial carrier frequency. Our model-based iterative technique effectively narrows the broad spectrum and reduces phase errors. Results of simulations and experiments are presented that demonstrate the validity of the proposed spectrum-narrowing technique for high-density fringe patterns.
ABSTRACT
Nyquist sampling theorem in an image calculation with angular spectrum method restricts a propagation distance and a focal length of a lens. In order to avoid these restrictions, we studied suitable expressions for the image computations depending on their conditions. Additionally, a lateral scale in an observation plane can be magnified freely by using a scaled convolution in each expression.
