Multi-focus plasmonic lens with metallic nanoslits of variant widths have great potential applications in optical interconnection, integrated optics and nanophotonics. But the design method with simulated annealing algorithm or Yang-Gu algorithm requires complex calculation and multi focuses are limited to be set on the same output plane. In this paper, we propose a design method based on holography. The desired light field distribution and the incident plane wave can be treated as object wave and reference wave, respectively. So the calculation is relative simple and multi focuses can be located in different output plane. Numerical simulation of multi-focus lens design is performed through finite-difference time-domain (FDTD) method and the result confirms the feasibility of our method.

In this paper, a modification method based on a U-Net convolutional neural network is proposed for the precise fabrication of three-dimensional microstructures using laser direct writing lithography (LDWL). In order to build the correspondence between the exposure intensity distribution data imported to the laser direct writing system and the surface profile data of the actual fabricated microstructure, these two kinds of data are used as training tensors of the U-Net convolutional neural network, which is proved to be capable of generating their accurate mapping relations. By employing such mapping relations to modify the initial designed exposure intensity data of the parabolic and saddle concave micro-lens with an aperture of 24µm×24µm, it is demonstrated that their fabrication precision, characterized by the mean squared error (MSE) and the peak signal-to-noise ratio (PSNR) between the fabricated and the designed microstructure, can be improved significantly. Specifically, the MSE of the parabolic and saddle concave micro-lens decreased from 100 to 17 and 151 to 50, respectively, and the PSNR increased from 22dB to 29dB and 20dB to 25dB, respectively. Furthermore, the effect of laser beam shaping using these two kinds of micro-lens has also been improved considerably. This study provides a new solution for the fabrication of high-precision three-dimensional microstructures by LDWL.

Holographic speckle screens with the Gaussian type distribution of scattered light, which are used to increase the viewing angle of the image in projection display systems, result in nonuniform image brightness in different observing positions. In this study, based on Helmholtz-Kirchhoff theory, a dual-beam scattering theory of rough surface is derived. By analyzing the spatial frequency spectrum of the scattered light, it is found that when two laser beams irradiated the ground glass at a certain angle, the resulting speckles recorded on the photoresist can generate a flat-top angular distribution of the scattered light. Speckle screens are fabricated by two light beams at different angles, and the angular intensity distribution of scattered light is measured. The results are in good agreement with the theory. Compared with the Gaussian type diffuser, the energy efficiency of the speckle screen proposed has a 46% increase when the angular luminance uniformity is set to be 80%, which effectively improves the brightness when used in a head up display system.

In this Letter, a contact polarization holographic photoalignment method is proposed. In the holographic recording, a phase mask is contacted with a photoalignment film, making light carrying wavefront information interfere with reference light in the near-field region to realize polarization holographic pattern recording with a sub-micrometer feature size. The relevant theoretical derivation is given, and holographic recording of a 0.4 µm feature-size phase mask is realized. The proposed method can conveniently realize liquid-crystal binary diffractive optical elements with a sub-micrometer feature size. Off-axis diffraction can also be realized by superimposing the grating information by changing the angle between the substrate and the interference light.

Holographic display requires thinner liquid crystal cell for smaller pixels and fast response. In this paper, a continuous geometric phase modulation method realised by electrically tuning a dual in-plane-switching (IPS) LCD is proposed. Firstly, the function of geometric phase modulation and the driving voltage is obtained via numerical simulation. Secondly, a dual IPS liquid crystal cells is designed and fabricated, and by using it, the experimental data is measured. Lastly, the simulation and test results are matched, which show good consistence with each other, and a phase modulation range of near $2\pi$ is achieved. By using the method, the phase modulation quantity is not only independent of the thickness of liquid crystal layer, but can be achieved almost 360° continuous modulation of the geometric phase. This method paves an avenue towards dynamic geometric phase modulation of light, which is meaningful for large field of view and colourful holographic display. Graphical abstract