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.
The Fabry-Perot interferometer (FP) can be used as a kind of filter for obtaining spectral information of targets in several wavelength ranges such as in the visible or infrared regions. So far, the spectral imaging devices based on FP effect mainly include the electrically controlled liquid-crystal filtering structures and the micro-electro-mechanical filtering architectures (MEMS). MEMS are generally micro-structures that integrate micro-sensors for converting incident microbeams into arrayed electronic signals and micro-actuators. The MEMS-FP filter constructed by combining the MEMS and FP functions, can be further integrated into a chip-level imaging spectrometer to achieve spectral imaging operation. The design of distributed Bragg reflectors (DBRs) is an important part to obtain a high transmittance for MEMS-FP structure. Different number of layers of optical film is calculated and compared in this paper and the transmittance can reach 82% and the FWHM is ~ 1nm in the infrared region of 3-5um. Angle of incidence is also considered and the simulation result shows poor robustness. We propose that two liquid-crystal microlens arrays can be mounted on FP arrays to get a high filling-factor and a more flexible range of incident angles.
Metallic micro-nano-structure arrays can be used to induce a collective oscillation of free electrons on the surface of metal films, so as to generate relatively strong surface plasmons (SPs) at the metal and medium interface and further localized light field under the excitation of incident lightwaves. As the oscillating light field propagating along the interface, the field strength can be increased reasonably at the functioned metal surface such as the incident light energy being localized in the sub-wavelength region defined by the functioned micro-nano-structures. The common beam diffraction limit formed during lightwave transmission or process can be broken effectively. Through constructing SPs over the special micro-nano-structures, the infrared reflection characteristics can be changed and then the local light field originated from incident infrared radiation also be enhanced significantly so as to efficiently perform infrared detection. Generally, the reflectivity and light field distribution behaviors of the functioned metal surface can be modulated by changing featured parameters of the metallic micro-nano-structural arrays. In this paper, a metal micro-nano-patterned structures with an arrayed tip is established for compressing the incident light field and then reducing the reflectivity of the metal surface and thus sensing incident light energy. A finite integral method for simulating and analyzing the structural characters such as the distance between tips, the tip sharpness, the thickness of the metal film, is utilized to acquire the reflectivity and field enhancement characteristics. The infrared reflection spectrum and the near-field intensity distribution of the metallic micro-nano-structure are compared and analyzed. The results show that the response frequency and excitation intensity of SPs over the nano-tip array, the intensity and distribution region of the strong light field, can be controlled by matching the structural parameters and layout. The optimization of the metallic micro-nanostructure arrays is conducted so as to lay a solid foundation for further development of the similar technologies.
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.
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.
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