Using multi-beam interferometry, a photonic structure with a graded intensity distribution is designed and obtained experimentally. Based on the structure, we choose different exposure thresholds and background materials to design a graded photonic crystal (GPC) lens with a graded air hole diameter. The transmission and focusing characteristics of the GPC lens with bismuth silicate crystal (BSO) and polymethyl methacrylate (PMMA) as background materials are investigated in the visible-light band. Comparatively speaking, the graded photonic crystal lens of BSO with a large refractive index had better performance. In addition, the focal intensity does not decrease significantly with increasing the angle of incidence. The focus point intensity remains above 93% of parallel incidence for both lenses.
A dielectric elliptic cylinder is chosen as a nanostructure unit to design unusual deflecting metasurface and multifunctional metalens. Based on Pancharatnam–Berry (PB) phase principle, the abrupt phase change is investigated by adjusting the rotation angle of the nanostructure unit. The relationship between abrupt phase change and rotation angle is optimized. Using this relationship, we have designed different metasurface elements working in the visible-light range. The designed metasurfaces can arbitrarily control the phase of the light wave, and also convert the incident left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light into each other. One of the designed structures is a deflecting metasurface, which can deflect incident LCP and RCP light by the same angle while the bending directions are different. By cascading multiple gradient phase metasurfaces, an innovative type of multiplex beam splitter is constructed. The other is a metalens that can converge the incident LCP light and diverge the incident RCP light. In addition, two types of bifocal metalenses are dexterously designed using alternately arranged nanostructures, which can arbitrarily control two focal lengths of each metalens. This is promising for developing nano-integrated elements and interconnection.
A D-shaped fiber surface plasmon resonance (SPR) sensor based on a Hi-Bi photonic crystal fiber (PCF) is investigated with finite element method. Through changing the size of the air holes beside the fiber core, it is found that the Hi-Bi structure can enhance the plasmon resonance at mid-infrared wavelength. The effect of the two fiber core side holes as well as the different gold film thickness on plasmon resonance is numerically investigated. A high and sharp loss peak is achieved, which indicates that the sensor should have high accuracy. The sensitivity of this D-shaped PCF sensor is obtained to be 8920nm/RIU in the range of 1.37 to 1.39 and the power sensitivity is 154 dB/(cm·RIU) in the range of 1.33 to 1.36. Particularly, near 1.36, with the detection limit of 0.1 nm the resolving power of the sensor is lower than 10-4 RIU with a figure of merit of 28.6.
We propose a multi-fiber holographic interferometry for fabricate double-periodic Graded Photonic Crystal (GPC) structures over large areas. This experimental system consists of an ultraviolet laser, Single-Mode Optical Fiber Splitters (SMOFS), fiber holder and focus lens. This method simplifies the system configuration by leaving out the spatial light modulator. Holographic GPC structures have been designed by using multi-fiber interference in this paper. The interference pattern is controlled by the number and position of the beams. The simulation results show that the gradient trend in the interference graph can be accurately adjusted through the above method. Experiment results were obtained and recorded for multi-fiber interfering system. The simulated interference patterns are verified experimentally through a microscopic camera. A good consistence has been observed between the theoretical and experimental results. This proposed method is possible to develop a new technique for fabrication of GPC lens or lens array.
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