Light vector polarization as a fundamental property of lightwave, can be used to effectively distinguish objects in complicated circumstance including surface shape and materials type and transmission medium. As shown, polarization imaging is an advanced information acquirement method which combines the light intensity image and light vector vibration behaviors, which is the direction of electric field of incident lightwaves. A typical microgrid polarimeter with a minimum repeat unit is composed of four pixelated linear polarizer demonstrating different vibration directions. Compared with full polarization information, the polarization image obtained has only one quarter polarization information in each direction. Thus, it will influence the accuracy of other information such as Stokes components, the degree of linear polarization (DoLP), and the angle of polarization (AoP). In this paper we propose a polarization demosaicing network to address the poloarized image demosaicing issue, which are then recovered into the original polarized image. This network aims to improve the accuracy of DoLP and AoP of the targets by adjusting three Stokes components of the network output. We already remove the batch normalization (BN) commonly used in CNN, and thus use a customized loss function to make it suitable for polarization image demosaicing. The experimental results show that network has demonstrated a best peak signal-to-noise ratio (PSNR) and then richer image detail and polarization target information than that of the original image.
As an effective method for collecting light field information and further extending the depth of field, a new imaging technology based on key electrically controlled liquid-crystal microlens array (EC-LCMLA), has been proposed. Compared with common lenses with defined surface profile, the liquid-crystal microlenses can be used to regulate the focal length only through applying different signal voltages to achieve focus tuning or even swing on the observation plane. Generally, the traditional autofocus operations are no longer suitable to EC-LCMLA because the controlling orders for LC structures should be generated through image process. So, an autofocus method, which is used to dynamically adjust the focal length of each imaging unit in the EC-MLA, is proposed for controlled LCMLA in this paper. The method is used to extract the light field information from low-quality image, so as to obtain the key focusing distance of the plane observed by each imaging unit, and then calculate the focal length of the EC-LCMLA without additional sensors. The signal voltage of each liquid-crystal microlens can be adjusted by the driving control unit, which implements an automatic focusing of the LCMLA. The active autofocus therefore is achieved and then all the imaging units in an optimal working state. Based on theoretical analysis and the focusing algorithm constructed by us, the imaging experiments are carried out so as to show a higher performance and then image quality and focusing efficiency of LCMLA. The novel autofocus method highlights a construction of a new kind of plenoptic camera with stronger performances.
In this paper, we propose a novel dual-function infrared liquid-crystal device (DF-ILCD), which can simultaneously perform both tunable focusing and filtering functions through applying alternating current (AC) voltage signals. The key functional micro-structure of the DF-ILCD includes: two paralleled 1-mm-thick ZnSe substrates with 20-nm-thick aluminum (Al) films over their inner surfaces and a periodic repetition microholes over both substrates. The Al films act as both high-reflection films and conductive films. The conventional UV-photolithography and wet-etching process are used to fabricate an arrayed micro-hole with a diameter of 120μm and a period of 336μm over each substrate. The micro-cavity formed between ZnSe substrates has a typical depth of ~12 μm, which is fully filled by a nematic liquid-crystal (LC) materials. Experiments demonstrate that the proposed device exhibit both filtering function based on Fabry–Perot (FP) effect and electrically controlled tunable focusing function generated by the micro-hole electrodes, which is very promising for realizing both the light-field imaging and spectral imaging in the infrared wavelength range.
In this paper, we propose a new type of liquid-crystal cylindrical microlens arrays (LCCMAs) with nonuniform microcoil electrodes (NMEs). The key functional microstructure of the LCCMAs includes two ~500-μm-thick glass substrates with indium-tin-oxide (ITO) films for shaping the top and the bottom electrodes and a thin LC layer with a typical thickness of 20μm. The ITO film of the upper substrate is etched into the shape of nonuniform microcoil by traditional lithography process and inductively coupled plasma etching (ICP etching). By simply adjusting voltage signal applied on the NMEs, the LCCMAs exhibit relatively sharp point spread functions (PSFs) at the focal plane of different spectral beams including red (635-671nm), green (501-561nm) and blue (430-473nm) lasers at relatively low signal voltages (even less than 3Vrms).
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