Hollow-Core Fiber (HCF) has attracted great interest from researchers because of its high damage threshold and small nonlinearity compared with solid-core fiber. However, how to reduce the loss of HCF has always been an urgent problem to be solved. Aiming to solve the problem, we propose a novel Hollow-Core Negative Curvature Fiber (HC-NCF) with an elliptical nested tube and a circular nested tube. The structure of this HC-NCF is relatively simple, which greatly reduces the difficulty of fabrication. Finite element modeling has been used to simulate and calculate the Confinement Loss (CL) and Bending Loss (BL) of the fiber with different nested tube structures. Results show that the CL of the LP01 mode is as low as 6.48×10-6 dB/km at the interesting wavelength of 1.06 μm. It exhibits a minimum CL of 5.28×10-6 dB/km at 1.01 μm with maintaining a loss of less than 0.003 dB/km over 1020 nm (0.77 μm to 1.79 μm) bandwidth. In addition, we proposed the HC-NCF has been confirmed to have better-bending resistance. Within a bending radius of 5–40 cm, the HC-NCF has a BL below 3.75×10-4 dB/km at a 10 cm bending radius; the BL is below 1.03×10-5 dB/km at a 40 cm bending radius.
Image restoration has attracted the attention of many scientists due to the image is degraded by the bad weather (such as haze, smog, fog). Clear images provide a means for security surveillance, remote sensing and various military application to understand objective facts. Many dehaze methods have been proposed by the experts for image restoration, especially for image dehaze. The dark channel prior dehaze method is a typical image restoration method based on atmospheric physical model. This method is a kind of statistics of outdoor haze-free images, and it is a simple but effective remove haze from a single input image. However, this method fails to restore the sky region of degraded image, and it has a high computational cost associated with soft matting algorithm. To overcome these problems, we propose an image restoration method based on quadtree decomposition to restore the images degraded by scattering media. The proposed method uses the quadtree decomposition to find the sky region for the atmospheric light estimation. The transmission of sky region is improved by the proposed method to obtain an accurate global transmission of degraded image. The degraded image can be quickly restored by our proposed method without halo effect or color distortion. The proposed method will be helpful to the security surveillance, remote sensing and various military application et al.
There is a strong demand for beam steering aiming to reposition an optical beam in various fields of applications, such as optical communications, light detection and ranging, microscopies, displays. In this paper, we present a beam steering method actuated by a hydraulic polymer elastic membrane. A thick polydimethylsiloxane (PDMS) membrane is placed underneath a thin PDMS membrane. The beam steering angle can be varied adaptively through inputting different hydraulic pressure. The thin PDMS membrane deforms significantly and the thick PDMS membrane deforms slightly since there is enough thickness difference between thick and thin PDMS membrane when the liquid pressure is applied. The model of the adaptive beam steering method is built and some simulation experiments are carried out by COMSOL Multiphysics software. The effects of some model parameters are analyzed. The parameters include the thickness ratio, the distance between the thick PDMS membrane and the acrylic frame, the length of the thick PDMS membrane, and liquid pressure are studied. We can find that the linearity of the effective refractive surface increases with the increase of thickness ratio and decreases when the thick PDMS membrane is close to the acrylic frame. The beam steering angle increases with increasing of the liquid pressure. We also find that there is a tradeoff between the length of the thick PDMS membrane and the range of the beam steering angle. The results show that the appropriate thickness ratio of the thick and thin PDMS membrane is 7:1. The beam steering angle is 0°~33.46° when the liquid pressure is 0 kPa~8 kPa. The length of the thick PDMS membrane is 7.5 mm. This paper can be used to design an adaptive beam steering device actuated by the hydraulic pressure.
A novel approach based on the isomerous structure is proposed to improve the performances of liquid crystal optical phased array. Inspired by a space-variant structure, a series of kinoforms are sent to the spatial light modulator to produce space-variant beam steering. The mathematical model of the proposed is deduced and the key parameters are studied. Simulations and experiments are carried out to test the models. Simulations agree well with the experiments, which shows the correctness of the theory. The results are of interested to the integrated, low-cost, and stable beam steering system.
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