Multi-wavelength multi-focus Fresnel solar concentrator with square uniform irradiance: design and analysis.

In this paper, a two-step optical design method is proposed to build a superior Fresnel-based photovoltaic concentrator for enhancing light conversion efficiency with the multi-junction solar cell. In the first step, we orthogonally segment a traditional Fresnel concentrator and remove the two normal stripe bands around the horizontal and vertical axes, as well as recombine the resultant four quadrants again. By using such a specific Fresnel concentrator design, a square light pattern can be constructed owing to the off-axis non-rotational symmetric superposition of light. In the second step, as for the response wavelengths of a specific triple-junction solar cell, we further carry out a triple-wavelength and multi-focus design of the above Fresnel concentrator for improving the uniformity of light distribution on the solar cell. To show the validity of this novel design method, a solar concentrator, with typical design parameters including the geometrical concentration ratio of 800× and the F-number of 0.775, is designed and simulated. As a result, theoretical irradiance uniformity up to 87% is obtained. In addition, considering the fact that no second optical element is involved in the concentrator system, our design method inherently has the advantages of good compactness, high efficiency, low cost, and ease for mass-production. We believe that such a concentrator is of great significance to solar cells for high conversion efficiency of light in the concentrator photovoltaic system.

Hybrid phase-amplitude superoscillation element for nonscanning optical superresolution imaging.

In this paper, we report a nonscanning optical superresolution imaging method based on a hybrid phase-amplitude superoscillation element. Using the Chebyshev polynomials as a basis set on the superoscillation waveform, the optimal combination of these, representing the optimal focal -spot in the local field of view, is found by genetic algorithm. Our numerical calculations demonstrate that a subwavelength focal spot with a full width at half-maximum as small as 253 nm is realized, which has more than 30 times improvement in sidelobe suppression ratio, and crucially, a greatly extended needle with continuously shrunken focal spot is yielded, which allows a large imaging tolerance in the axial displacement of the object. We then present our simulated results of the superresolution imaging on sparse point objects and continuous objects, where the practicality and effectiveness of this method are analyzed and discussed in detail.

Far-field super-oscillation imaging based on the super-oscillation elements and PSF feature extraction algorithm.

Suffering from the limited number aperture, a resolution higher than 0.5λ cannot be obtained in conventional far-field optical imaging systems. Recently, research of the optical super-oscillation lens (SOL) has been demonstrated to realize sub-diffractive focusing in both theory and practice successfully. Nevertheless, these systems usually have characteristics of a localized field of view and low-intensity focal spot surrounded by huge sidelobes, which profoundly restricts their application for super-resolution imaging. In this paper, we artificially segment the SOL into two simple-fabrication portions to generate the super-oscillation optical field and realize off-axis far-field imaging. Meanwhile, the point spread function (PSF) feature extraction algorithm is proposed to break the limitation of low core intensity of the PSF and then effectively extract the sub-diffractive structure annihilated by huge sidelobes. Simulations demonstrate its feasibility and reliability in sub-diffraction information recovery, and targets with a resolution of 250 nm are well recovered in the super-oscillation area.

Real-time image haze removal using an aperture-division polarimetric camera.

Polarimetric dehazing methods have been proven to be effective in enhancing the quality of images acquired in turbid media. We report a new full-Stokes polarimetric camera, which is based on the division of aperture structure. We design a kind of automatic polarimetric dehazing algorithm and load it into the field programmable gate array (FPGA) modules of our designed polarimetric camera, achieving a real-time image haze removal with an output rate of 25 fps. We demonstrate that the image quality can be significantly improved together with a good color restoration. This technique might be attractive in a range of real-time outdoor imaging applications, such as navigation, monitoring, and remote sensing.

Polarimetric dehazing method for visibility improvement based on visible and infrared image fusion.

Polarimetric dehazing methods have proven effective in enhancing the quality of chromatic hazy images. Considering that the infrared radiance has a better capacity for traveling through the haze, in this paper we propose a polarimetric dehazing method based on visible and infrared image fusion to improve the visibility of hazy images, especially for dense haze conditions. Experimental results demonstrate that the visibility of hazy images can be effectively enhanced, and the color information can be finely maintained. The visibility of dehazed images can be promoted at least 100%. This kind of dehazing method can be used widely in many dehazing applications.

Polarimetric dehazing method for dense haze removal based on distribution analysis of angle of polarization.

Many dehazing methods have proven to be effective in removing haze out of the hazy image, but few of them are adaptive in handling the dense haze. In this paper, based on the angle of polarization (AOP) distribution analysis we propose a kind of polarimetric dehazing method, which is verified to be capable of enhancing the contrast and the range of visibility of images taken in dense haze substantially. It is found that the estimating precision of the intensity of airlight is a key factor which determines the dehazing quality, and fortunately our method involves a high precision estimation inherently. In the experiments a good dehazing performance is demonstrated, especially for dense haze removal. We find that the visibility can be enhanced at least 74%. Besides, the method can be used not only in dense haze but also in severe sea fog.