Traditional mid-infrared optical devices are characterized by complex structures, large volumes, and high prices, which impede the advancement of future multidimensional, multifunctional, and miniaturized integration. However, metasurfaces comprising planar and ultra-thin nanostructures have emerged as a promising alternative. By manipulating the interaction between light and materials at subwavelength scales, metasurfaces exhibit remarkable control over optical fields and offer multifunctional capabilities. Consequently, they provide new avenues for integrating infrared systems in a miniaturized form. In this paper, an efficient metalens based on Pancharatnam-Berry (PB) phase working in the mid-infrared range(3.7μm-4.8μm) is proposed and numerically demonstrated. The proposed metalens enables precise control of incident light phase, thereby converge the incident light into two focal spots within spectral-band ranges: 3.7μm-4.0μm (with a focal length of 150μm) and 4.5μm-4.8μm (with a focal length of 250μm). The bifocal metalens is space division multiplexing designed using alternately arranged a-Si nanobricks, facilitating a high polarization conversion efficiency exceeding 80% and achieving achromatic behavior within the two spectral-band ranges. This work demonstrates the potential application of metalens for addressing complex tasks in infrared optical detection.
Limited by the current technological development level of infrared detectors, it is difficult for the infrared multispectral imaging systems to meet the requirements of practical engineering application indicators such as low structural complexity and high transmittance at the same time. In order to promote the engineering application level of computational imaging technology in the infrared spectrum, this paper proposes a snapshot computational spectral imaging technology scheme based on reflective coding mask; this scheme utilizes the built-in reflective coding mask in traditional imaging system: Firstly, complete the design and molding of the coding mask according to the index requirements, complete the information calibration of the coding mask in the spatial dimension and the spectral dimension by building a high-precision spectral calibration module, and then combine the compressive sensing image restoration algorithm according to the calibration results, finally realize the Imaging and spectral data extraction of targets. Laboratory indoor imaging shows that this scheme can realize broad-spectrum imaging of indoor targets and extraction of multi-spectral information of targets. Compared with the technical scheme of traditional optical filter and grating infrared spectrometer, it has the technical advantages of simple structure and high transmittance.
With the development of computational imaging technology, computational spectral imaging technology based on coding masks has attracted the attention of researchers due to its advantages in obtaining multi-dimensional information. However, the current research on computational spectral imaging technology in the infrared band is relatively scarce. In the research of this paper, in order to solve the problem that the signal-to-noise ratio of the spectral calibration in the infrared spectral calibration of the coding mask is too low, an innovative spectral calibration scheme based on the reflective coding mase is proposed. Firstly, according to the infrared band and spectral resolution index, the mask surface model coding technology is used to design the surface of the mask, according to the above scheme, the reflective mask can be processed, then the spectral modulation of the specific speckle field distribution can be finished base on the corresponding infrared point light source generation module; secondly after completing the spectral calibration of the key points on the encoding mask surface ,the spectral calibration signal reconstruction of the remaining pixels of the encoding mask can be finished base on the improved bilinear interpolation algorithm, this work can greatly save the spectrum calibration time; finally, the effect of the speckle field algorithm base on compressed sensing is used to verify the effect of the spectrum calibration structure. The results show that, compared with the traditional spectrum calibration technology, the high-precision infrared spectrum modulation and calibration technology based on the reflective coding mask used in this paper can greatly improve the signal-to-noise ratio of the spectrum calibration signal and save the time required for the spectrum calibration.
In order to solve the problem of traditional target recognition and tracking algorithms of the multispectral image such as high computation complexity, poor real time performance and low stability under complex scene and great variation of target appearance, a new mosaic image tracking algorithm based on dimension reduction of HOG feature data and multi-scale correlation filter is proposed in this paper. Firstly, in order to reduce the calculation complexity as well as to enhance the detection rate of small target, the 2D multispectral mosaic image data instead of the traditional 3D multispectral image data cubes is used, Then the histogram of oriented gradient (HOG) feature is extracted from the mosaic image data, and the singular value decomposition (SVD) algorithm with improved threshold selection method is adopted to reduce the dimension of the HOG feature matrix. Compared to the method which extracts HOG feature after dimension reduction, the proposed method takes advantage of high recognition precision, simple operation and high real-time performance. Finally, the target tracking is realized based on the dimension-reduced HOG feature with the fast discriminative scale space tracker (fDSST) algorithm which combines the scale filter and the position filter. A multispectral image dataset for target tracking was established, including different target occlusion, motion blur, variation of target scale and target appearance. Target tracking results on the dataset show the proposed algorithm can realize good tracking continuity and stability even if there exist different ground objects, variation in the appearance of the target shape, or target reappearance after occlusion.
Surface plasmon polarizations (SPP) is a nano-scale photon control technology which can converge the spread of oscillation electron driven by incident light. In recent years, SPP has become an advanced research hotspot and has been studied more and more widely. The convergence effect of SPP has extensive applications, such as Schottky barrier detector in which the higher power hotspot, the lower signal-to-noise ratio. In this paper, studies have been done about the interaction of light and matter. Different geometric shapes have been simulated, which were obtained by graphic clipping. Via comparing the power of the hot spot and the minimum location on the transmittance line, we concluded the relationship of the interaction and the structure. It’s found that every absorption peak corresponds a mode of LSPP spread. Therefore, we can design figure to control the spread of the SPP, and achieve fantastic goal. Finally, a typical figure with high power hotspot was given.
Traditional imaging based on common optical lens can only be used to collect intensity information of incident beams, but actually lightwave also carries other mode information about targets and environment, including: spectrum, wavefront, and depth of target, and so on. It is very important to acquire those information mentioned for efficiently detecting and identifying targets in complex background. There is a urgent need to develop new high-performance optical imaging components. The liquid-crystal microlens (LCMs) only by applying spatial electrical field to change optical performance, have demonstrated remarkable advantages comparing conventional lenses, and therefore show a widely application prospect. Because the physical properties of the spatial electric fields between electrode plates in LCMs are directly related to the light-field performances of LCMs, the quality of voltage signal applied to LCMs needs high requirements. In this paper, we design and achieve a new type of digital voltage equipment with a wide adjustable voltage range and high precise voltage to effectively drive and adjust LCMs. More importantly, the device primarily based on field-programmable gate array(FPGA) can generate flexible and stable voltage signals to cooperate with the various functions of LCMs. Our experiments show that through the electronic control system, the LCMs already realize several significant functions including: electrically swing focus, wavefront imaging, electrically tunable spectral imaging and light-field imaging.
In this paper, a polarization difference liquid-crystal microlens array (PD-LCMLA) for three dimensional imaging application through turbid media is fabricated and demonstrated. This device is composed of a twisted nematic liquidcrystal cell (TNLCC), a polarizer and a liquid-crystal microlens array. The polarizer is sandwiched between the TNLCC and LCMLA to help the polarization difference system achieving the orthogonal polarization raw images. The prototyped camera for polarization difference imaging has been constructed by integrating the PD-LCMLA with an image sensor. The orthogonally polarized light-field images are recorded by switching the working state of the TNLCC. Here, by using a special microstructure in conjunction with the polarization-difference algorithm, we demonstrate that the three-dimensional information in the scattering media can be retrieved from the polarization-difference imaging system with an electrically tunable PD-LCMLA. We further investigate the system’s potential function based on the flexible microstructure. The microstructure provides a wide operation range in the manipulation of incident beams and also emerges multiple operation modes for imaging applications, such as conventional planar imaging, polarization imaging mode, and polarization-difference imaging mode. Since the PD-LCMLA demonstrates a very low power consumption, multiple imaging modes and simple manufacturing, this kind of device presents a potential to be used in many other optical and electro-optical systems.
In this paper, a kind of electronically controlled liquid crystal microlens arrays (LCMAs) with non-uniform coil electrodes arrays (NCEAs) is presented. The focal length of the electronically controlled LCMAs can be easily adjusted by applying the appropriate AC signal. The structure of the LCMAs is designed as a NCE array, which can then produce non-uniform electric field to drive liquid crystal molecules. The top electrode is fabricated by depositing an indium-tinoxide (ITO) semiconductor transparent conductive film based on a non-uniform electrode coil, and the bottom electrode is a conventional plate electrode. Due to the design of non-uniform electrode coil array is small, in addition to the traditional lithography process, the etching process we used is dry etching (ICP etching). The simulation results show that, the focal length of the LCMAs with the NCEAs can be tuned easily by applying the appropriate AC signal.
Under the condition of existing intense turbulence, the object's wavefront may be severely distorted. So, the wavefront sensors based on the traditional microlens array (MLA) with a fixed focal length can not be used to measure the wavefront effectively. In order to obtain a larger measurement range and higher measurement accuracy, we propose a liquid-crystal microlens array (LCMLA) with needed ability of swing focus over the focal plane and further adjusting focal length, which is constructed by a dual patterned ITO electrodes. The main structure of the LCMLA is divided into two layers, which are made of glass substrate with ITO transparent electrodes. The top layer of each liquid-crystal microlens consists of four rectangular electrodes, and the bottom layer is a circular electrode. In common optical measurements performed, the operations are carried out such as adding the same signal voltage over four electrodes of each microlens to adjust the focal length of the lens cell and adding a signal voltage with different RMS amplitude to adjust the focus position on the focal plane. Experiments show that the LCMLA developed by us demonstrate a desired focal length adjustable function and dynamic swing ability, so as to indicate that the method can be used not only to measure wavefront but also correct the wavefront with strong distortion.
In this paper, a new kind of symmetrical aluminum (Al) nanotips structure based on localized rather traditional propagating surface plasmon polarizations (SPPs) focusing are designed and fabricated successfully. The simulation results about near-field distribution of electric field and reflectance calculations using finite-difference time-domain (FDTD) simulation theory are exhibited and then the device is fabricated mainly by coating Al films with the thickness of 100 nm on n-type doping silicon (Si), cutting into scale of 15mm×15mm by wafer dicing, electron beam lithography (EBL) exposure and ICP etching. The near-field focusing properties about small spot breaking the diffracting limitation with one order enhancement in the near-tip area of this structure are demonstrated experimentally using scanning nearfield optical microscopy (SNOM), and the comparisons to simulation results are analyzed, so as to reveal a potential application in capturing near-field focusing images quickly by applying exterior voltage signals based on our structure with nanotips.
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