In this talk, I will present two strategies to realize high-performance metasurfaces. Firstly, by introducing the generalized kerker condition to the plasmonic metasurface, we acquired a circular cross-polarization conversion efficiency higher than 50% in transmission at telecom wavelengths. We also demonstrated a couple of meta-devices with record operating efficiency based on the proposed metasurface. Secondly, I will introduce the Monte Carlo tree search (MCTS) algorithm combined with unsupervised clustering for the inverse design of metasurfaces. With the proposed method, we realized a beam steering metasurface, which is capable of deflecting normally incident light into target directions with minimal sidelobes intensity.
Metasurface enables controlling the light properties at will by structuring sub-wavelength unit elements. Among feasible applications, polarization control plays a vital role in communication, quantum optics, and imaging. Due to the Joule loss issue, the polarization conversion efficiency for the plasmonic metasurfaces operating at NIR region is usually lower than 10% [1]. In this work, we innovate a metasurface design to enhance the polarization conversion efficiency [2]. A S-shaped plasmonic metasurface with a toroidal dipole-quadrupole coupling response is used to push the polarization conversion efficiency to 22.9% that is very close to the theoretical conversion limit 25% [3].
KEYWORDS: Visualization, Current controlled current source, Integral imaging, 3D displays, LCDs, 3D applications, 3D image processing, Image resolution
Depth and resolution are always the trade-off in integral imaging technology. With the dynamic adjustable devices, the two factors of integral imaging can be fully compensated with time-multiplexed addressing. Those dynamic devices can be mechanical or electrical driven. In this presentation, we will mainly focused on discussing various Liquid Crystal devices which can change the focal length, scan and shift the image position, or switched in between 2D/3D mode.
By using the Liquid Crystal devices, dynamic integral imaging have been successfully applied on 3D Display, capturing, and bio-imaging applications.
In this paper, we demonstrate two liquid crystal (LC) lens array devices for 3D microscope and 3D endoscope applications respectively. Compared with the previous 3D biomedical system, the proposed LC lens arrays are not only switchable between 2D and 3D modes, but also are able to adjust focus in both modes. The multi-function liquid crystal lens (MFLC-lens) array with dual layer electrode has diameter 1.42 mm, which is much smaller than the conventional 3D endoscope with double fixed lenses. The hexagonal liquid crystal micro-lens array (HLC-MLA) instead of fixed micro-lens array in 3D light field microscope can extend the effective depth of field from 60 um to 780 um. To achieve the LC lens arrays, a high-resistance layer needs to be coated on the electrodes to generate an ideal gradient electric-field distribution, which can induce a lens-like form of LC molecules. The parameters and characteristics of high-resistance layer are investigated and discussed with an aim to optimize the performance of liquid crystal lens arrays.
In this paper, liquid crystal lens (LC-lens) array was utilized in 3D bio-medical applications including 3D endoscope and light field microscope. Comparing with conventional plastic lens array, which was usually placed in 3D endoscope or light field microscope system to record image disparity, our LC-lens array has higher flexibility of electrically changing its focal length. By using LC-lens array, the working distance and image quality of 3D endoscope and microscope could be enhanced. Furthermore, the 2D/3D switching ability could be achieved if we turn off/on the electrical power on LClens array. In 3D endoscope case, a hexagonal micro LC-lens array with 350um diameter was placed at the front end of a 1mm diameter endoscope. With applying electric field on LC-lens array, the 3D specimen would be recorded as from seven micro-cameras with different disparity. We could calculate 3D construction of specimen with those micro images. In the other hand, if we turn off the electric field on LC-lens array, the conventional high resolution 2D endoscope image would be recorded. In light field microscope case, the LC-lens array was placed in front of the CMOS sensor. The main purpose of LC-lens array is to extend the refocusing distance of light field microscope, which is usually very narrow in focused light field microscope system, by montaging many light field images sequentially focusing on different depth. With adjusting focal length of LC-lens array from 2.4mm to 2.9mm, the refocusing distance was extended from 1mm to 11.3mm. Moreover, we could use a LC wedge to electrically shift the optics axis and increase the resolution of light field.
A plano-convex electrode is presented for a liquid crystal lens array with a hexagonal arrangement, small inactive region, 30μm cell gap and low applying voltage. It uses circular curved electrodes to provide a smooth, controllable applied potential profile across the aperture to manage the phase profile.
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