In recent years, infrared thermal polarization imaging technology has emerged as a new method of infrared detection. Its main objective is to detect, identify, and track the differences in infrared polarization characteristics between targets and scenes. Compared to ordinary infrared imaging systems, this technology offers significant advantages for detecting and identifying man-made targets in complex natural backgrounds. Specifically, the division of focal plane (DoFP) polarimeter is currently being extensively researched due to its compact structure, small volume, and real-time imaging capabilities. However, the focal plane array (FPA) of the DoFP polarimeter exhibits varying response gains and bias parameters, while the micro-polarizer array on its surface suffers manufacturing defects, resulting in significant nonuniformity errors that adversely affect resolution accuracy. This paper analyzes the mechanism behind the generation of non-uniformity in the DoFP polarization imaging system and establishes a relationship between the output grayscale of the system and incident irradiance. Additionally, through the use of a mid-infrared polarization radiation source, the proposed method conducts irradiation calibration and polarization parameter calibration to rectify the non-uniformity of the detection image of the system. Based on experimental results, the calibration model significantly enhances the accuracy of polarization detection information for scene targets.
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.
A rotary dual-channel roll and pitch tracking scheme is proposed, and a dual-channel rotation control algorithm is designed to solve the problem of detector front and phase plane rotation, expand the field of view, and improve detection efficiency. The light and miniaturized platform design in space improves the control speed and accuracy. In the strong maneuvering state of the terminal target, the dual-channel infrared tracking reduces the amount of target misses and improves the performance of the control system to precisely hit the target. In this paper, the research results obtained are expounded from the two aspects of the rotary dual-channel system tracking principle and the rotary dual-channel tracking control method. Firstly, the design of the dual-channel rotation control algorithm is introduced; secondly, the dual-channel rotation tracking loop is designed; finally, the research results are verified by experiments, which illustrate the advantages of the rotation-based tracking in fast response, dual-channel interaction and precise guidance.
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.
Head-mounted display (HMD) system is a research hotspot in virtual reality, which has continuous and rapid development in training, medical treatment, aerospace, and entertainment. For the more comfortable immersive experience, the requirements of compact structure, large exit pupil and low F number should be met simultaneously in HMD system. With the use of x-y polynomial surface, an off-axis head-mounted display system with two freeform reflectors is achieved. The HMD system demonstrates a 10 mm exit pupil, a 23°×16° field of view, an f/# number of 3.0 and an eye relief larger than 15 mm. Based on the tolerance analysis of surface figure errors and position location, we present the on-machine measurement and compensation for enhancing machining accuracy, and the frame and mirror integration for high assembling accuracy. Finally, the HMD system was fabricated and the imaging quality was evaluated. In comparison with the results, the effectiveness of the on-machine measurement and compensation are validated, as well as the reliability of tolerance analysis and mechanical structure.
In this paper, a new liquid-crystal microlens array (LCMLA) with patterned ring-electrode arrays (PREAs) is investigated, which has an ability to acquire multiple-mode two-dimensional images with better electrically tunable efficiency than common liquid-crystal devices. The new type of LCMLA can be used to overcome several remarkable disadvantage of conventional liquid-crystal microlens arrays switched and adjusted electrically by relatively complex mechanism. There are two layer electrodes in the LCMLA developed by us. The top electrode layer consists of PREAs with different featured diameter but the same center for each single cell, and the bottom is a plate electrode. When both electrode structures are driven independently by variable AC voltage signal, a gradient electric field distribution could be obtained, which can drive liquid-crystal molecules to reorient themselves along the gradient electric field shaped, so as to demonstrate a satisfactory refractive index distribution. The common experiments are carried out to validate the performances needed. As shown, the focal length of the LCMLA can be adjusted continuously according to the variable voltage signal applied. According to designing, the LCMLA will be integrated continuously with an image sensors to set up a camera with desired performances. The test results indicate that our camera based on the LCMLA can obtain distinct multiple-mode two-dimensional images under the condition of using relatively low driving signal voltage.
When lightwave passes through a metal thin film with a periodic subwavelength hole arrays structure, its transmittance is significantly improved in the partial band compared to other wavelength. Changing the size of the hole, the period or metal material, will make the transmission curve different. Here, we add a layer of dielectric material on the surface of the metal film, such as liquid crystal(LC), by controlling voltage on LC to change the refractive index of this layer, then we can change the transmission curve, and achieve using voltage to move the transmission curve. When there is need for polarization, the holes can be made of a rectangle whose length and width are different or other shapes, for different polarization state of the light, and the film will display different transmission characteristics.
Previous studies have presented the usefulness of typical liquid-crystal Fabry-Perot (LC-FP) infrared filters for spectral imaging detection. Yet, their infrared transmission performances still remain to improve or even rise. In this paper, we propose a new type of electrically tunable LC-FP infrared filter to solve the problem above. The key component of the device is a FP resonant cavity composed of two parallel plane mirrors, in which the zinc selenide (ZnSe) materials with a very high transmittance in the mid-long-wavelength infrared regions are used as the electrode substrates and a layer of nano-aluminum (Al) film, which is directly contacted with liquid-crystal materials, is chosen to make high reflective mirrors as well as the electrodes. Particularly, it should be noted that the directional layer made up of ployimide (PI) used previously is removed. The experiment results indicate that the filter can reduce the absorption of infrared wave remarkably, and thus highlight a road to effectively improve the infrared transmittance ability.
The intense surface plasmons (SPs) can be generated by patterned metal nano-structure arrays, through coupling incident light onto the functioned metal surface, so as to construct highly constrained surface electromagnetic modes. Therefore, a localized micro-nano-field array with a highly compressed surface electron distribution, can also be shaped and even nano-focused over the surface, which will lead to a lot of special physical effects such as anti-reflection effect, and thus indicate many new potential applications in the field of nano-photonics and -optoelectronics. In this paper, several typical patterned sub-wavelength metal nano-structure arrays were designed according to the process, in which common silicon wafer was employed as the substrate material and aluminum as the metal film with different structural size and arrangement circle. In addition, by adjusting the dielectric constant of metal material appropriately, the power control effect on metallic nanostructure was simulated. The key properties such as the excitation intensity of the surface plasmons were studied by simulating the reflectivity characteristic curves and the electric field distribution of the nanostructure excited by incident infrared beams. It is found that the angle of corners, the arrangement cycle and the metal material properties of the patterned nano-structures can be utilized as key factors to control the excitation intensity of surface plasmons.
In this paper, we propose a new device composed of patterned sub-wavelength arrays to investigate surface plasmons (SPs) over sub-wavelength metal nano-structures. The device consists of silicon substrate and sub-wavelength patterns fabricated on a layer of aluminum film with nanometer thickness. Each sub-wavelength pattern formed in aluminum film is composed of a basic nano-square and twelve triangles for shaping single nano-pattern, which are uniformly distributed on the four sides of each square. Reflectance spectra and electric field distribution in infrared region are simulated. Numerical simulation results demonstrate that the device can efficiently lower its reflectance in infrared spectrum, and the response frequency can be controlled by only changing the device parameters such as square side length and then triangle vertex angle. Besides, the simulated electric field distribution of the device shows obviously field localization effect at the edges of aluminum film nano-structure. The electric filed around the tips of aluminum triangles is localized into sub-wavelength scale, so as to be beyond the common diffraction limitation. Our work will help to reveal the interesting properties of SPs device, and also bring new prospect of photonic device.
With rapid advancement of infrared detecting technology in both military and civil domains, the photo-electronic performances of near-infrared detectors have been widely concerned. Currently, near-infrared detectors demonstrate some problems such as low sensitivity, low detectivity, and relatively small array scale. The current studies show that surface plasmons (SPs) stimulated over the surface of metallic nanostructures by incident light can be used to break the diffraction limit and thus concentrate light into sub-wavelength scale, so as to indicate a method to develop a new type of infrared absorber or detector with very large array. In this paper, we present the design and characterization of periodically patterned metallic nanostructures that combine nanometer thickness aluminum film with silicon wafer. Numerical computations show that there are some valleys caused by surface plasmons in the reflection spectrum in the infrared region, and both red shift and blue shift of the reflection spectrum were observed through changing the nanostructural parameters such as angle α and diameters D. Moreover, the strong E-field intensity is located at the sharp corner of the nano-structures.
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