Generalized Polarimetric Dehazing Method Based on Low-Pass Filtering in Frequency Domain.

Polarimetric dehazing methods can significantly enhance the quality of hazy images. However, current methods are not robust enough under different imaging conditions. In this paper, we propose a generalized polarimetric dehazing method based on low-pass filtering in the frequency domain. This method can accurately estimate the polarized state of the scattering light automatically without adjusting bias parameters. Experimental results show the effectiveness and robustness of our proposed method in different hazy weather and scattering underwater environments with different densities. Furthermore, computational efficiency is enhanced more than 70% compared to the polarimetric dehazing method we proposed previously.

Reconfigurable snapshot polarimetric imaging technique through spectral-polarization filtering.

In this Letter, we propose a simple, low-cost, reconfigurable snapshot polarimetric imaging technique for a color camera to measure polarization properties with spectral-polarization filters. Experimental results demonstrate the unique capabilities, such as obtaining circular or elliptical polarized information in a snapshot, that are not available from commercial polarization cameras and other polarization imaging techniques.

High-resolution reconstruction of shortwave infrared polarimetric images using the intensity information of visible images.

Shortwave infrared (SWIR) polarimetric imaging has been found very effective in various applications. However, the low resolution of the SWIR camera severely limits the capacity of this technique. Image reconstruction methods have been developed to improve the spatial resolution, but these methods typically do not consider the polarized information that the images may contain. In this paper, we propose a high-resolution reconstruction method for SWIR images based on the spatial information of visible images without losing polarized information in the SWIR image. Experimental results demonstrate that this method is feasible to reconstruct high-resolution polarized SWIR images. We have also demonstrated its potential application in image fusion.

Efficient light focusing through an MMF based on two-step phase shifting and parallel phase compensating.

Based on a parallel phase compensation scheme, we propose an efficient wavefront shaping method using a spatial light modulator (SLM) for quickly generating a series of focused spots through a multimode fiber (MMF). The compensated phase mask obtained by a two-step phase-shifting technique is loaded to the SLM for generating a focused spot at an arbitrary target position out of the fiber facet. Furthermore, the parallel algorithm we present makes it possible to obtain a series of compensated phase masks, which could be used to generate a series of focused spots at different locations. We experimentally obtained 100 tightly focused spots, with an average focused efficiency of 21.60% and an average focused diameter of 1.9240 µm, and only one-time parallel-compensated phase retrieval is required without multiple iteration optimization.

Chiral long-period gratings: fabrication, highly sensitive torsion sensing, and tunable single-band filtering.

A promising technology for fabricating chiral long-period gratings (CLPGs) is demonstrated using a commercial fusion splicer. The key aspect of this technology is the incorporation of a fully automatic program we designed for the fusion splicer. High-quality CLPGs are successfully fabricated from single-mode fibers, which have very flat surfaces and low insertion loss. We also investigate the tuning characteristics of the transmission spectrum with the mechanical twist rate in CLPGs for torsion sensing application. The torsion sensitivity is improved and the shift in resonance wavelength versus the mechanical twist rate shows an almost perfect linear relationship. In addition, by choosing appropriate fabrication parameters, the fabricated CLPGs can be used as tunable single-band-rejection filters in a broad wavelength range.

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.

Online fabrication scheme of helical long-period fiber grating for liquid-level sensing.

We present a novel online fabrication scheme of helical long-period fiber gratings (H-LPFGs) by directly twisting a standard single-mode fiber (SMF) in a microheater. This is done by taking advantage of the inherent core-cladding eccentricity in SMF. We adopt a fiber optic rotary joint to eliminate the accompanying twisting spiral for real-time spectral monitoring and a stepping mechanical system to accurately control the twisting length in fabrication. As a consequence, low-cost and high-quality H-LPFGs can be readily fabricated. Meanwhile, by using this kind of H-LPFG, we design a simple and low-cost wavelength-interrogated liquid-level sensor with a high sensitivity of 0.1 nm/mm.

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.

Improved multiple-wavelength Brillouin-Raman fiber laser assisted by four-wave mixing with a micro-air cavity.

In this paper, a multiple-wavelength Brillouin-Raman fiber laser (MBRFL) with enhanced performance is presented. This is attributed to the improved Fresnel reflection, thus strengthening four-wave mixing in the fiber laser cavity due to the insertion of a micro-air cavity. As a result, compared with the conventional MBRFL without a micro-air cavity, the thresholds of Brillouin Stokes (BS) lines are observed to be reduced, and more BS lines can be generated. In the experiment, a MBRFL having 40 BS lines is achieved with good stability on laser wavelengths and output power. In view of the fact that more BS lines can be established with a simple scheme and low pump power, our MBRFL promises to be employed as a multiwavelength source for optical communication.

Review of Research Progress on Mo-Si-B Alloys.

Mo-Si-B alloys are a crucial focus for the development of the next generation of ultra-high-temperature structural materials. They have garnered significant attention over the past few decades due to their high melting point and superior strength and oxidation resistance compared to other refractory metal alloys. However, their low fracture toughness at room temperature and poor oxidation resistance at medium temperature are significant barriers limiting the processing and application of Mo-Si-B alloys. Therefore, this review was carried out to compare the effectiveness of doped metallic elements and second-phase particles in solving these problems in detail, in order to provide clear approaches to future research work on Mo-Si-B alloys. It was found that metal doping can enhance the properties of the alloys in several ways. However, their impact on oxidation resistance and fracture toughness at room temperature is limited. Apart from B-rich particles, which significantly improve the high-temperature oxidation resistance of the alloy, the doping of second-phase particles primarily enhances the mechanical properties of the alloys. Additionally, the application of additive manufacturing to Mo-Si-B alloys was discussed, with the observation of high crack density in the alloys prepared using this method. As a result, we suggest a future research direction and the preparation process of oscillatory sintering, which is expected to reduce the porosity of Mo-Si-B alloys, thereby addressing the noted issues.