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A negative curvature hollow core fiber (NCHCF) refractive index (RI) sensor based on localized surface plasmon resonance (LSPR) is proposed. The gold nanowires are deposited in four cladding tubes in the y-direction, with the core region serving as the analyte channel. The full vector finite element method (FEM) is used to analyze the influence of various structural parameters on this sensor, and the structural parameters are optimized and selected. Ultimately, an average sensitivity of 9356.59 nm/RIU is accomplished within a spacious refractive index detection scope of RI = 1.28–1.43. The sensor attained a maximum sensitivity of 10,220 nm/RIU at RI = 1.36. In the bargain, there is an excellent linear correlation between the resonance wavelength and the refractive index of the analyte, with a value of 0.99901 and a factor of merit (FOM) range of 119.9563–155.9432 RIU−1, achieving a resolution of 10−6 RIU. The sensor has potential applications in various fields such as environmental protection, food safety, and medical diagnostics due to its high sensitivity, spacious detection scope, and positive linear response. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a D-type highly sensitive surface plasmon resonance (SPR)sensor based on multilayer films coated with photonic crystal fiber (PCF). Silver was selected as the plasmon material because its SPR spectrum is sharper than gold. Meanwhile, we used the titania (TiO2) as the second layer film since it could prevent the oxidation of silver and enhance the SPR effect. We simulated the refractive index sensing performances using the finite element method (FEM). This paper optimized the air hole size, polishing depth, silver film thickness, and TiO2 thickness. The multilayer film structure showed a significant improvement in the wavelength sensitivity of the sensor. The result showed that the maximum sensitivity reached 11,000 nm/RIU, which was increased by 139% compared with a single silver film. The sensor was suitable for accurately detecting the medical treatment and organic chemicals because of its high sensitivity and FOM. [ABSTRACT FROM AUTHOR]

A chalcogenide hollow-core anti-resonance fiber (HC-ARF) filter based on surface plasmon resonance (SPR) at 3 μm band is designed. The substrate materials are As40S60 and GeAsS, which are used to create the conditions for the formation of SPR, so as to realize the directional energy coupling in the specific polarization direction of the fiber. The effects of core diameter, capillary radius, and capillary wall thickness on the polarization performance of HC-ARF filter are analyzed by full-vector finite element method (FV-FEM). The numerical results show that the confinement loss of x-polarized fundamental mode (FM) reaches 1917.24 dB/m at the wavelength of 3.02 μm, while that of y-polarized FM is 23.11 dB/m. When the fiber length is 8 mm, the bandwidth with extinction ratio (ER) better than 20 dB covers the wavelength range of 320 nm. In addition, the resonance wavelength can be effectively adjusted by changing the capillary wall thickness. The proposed HC-ARF filter has potential applications in biomedicine, scientific research, and atmospheric detection. [ABSTRACT FROM AUTHOR]

In this paper, a novel phoxonic crystal (PxC) structure composed of silicon, with optimal dual phononic band gap (PNBG) and photonic band gap (PTBG), is presented. Using the finite element analysis method, both the transmission characteristics and dispersion relation of PNBG and PTBG are calculated, and the existence of dual BGs is demonstrated by the means of the analysis of transmission for the PxC structure. The influences of structural parameters on the dual forbidden band characteristics are further explored, the sensitive structure parameters can be determined: the width of elastic beams, the length of square silicon, and the length of square hole. Using the orthogonal test, 25 experimental runs based on 3-factor and 5-level experiment are performed to finish the numerical experimental design and analysis. Four functional relationships can be acquired between the three sensitive parameters and dual BGs. Finally, the unified objective function method is employed to perform the construction of the single objective optimization model for the purpose of obtaining the optimal dual BGs and the corresponding optimal parameter combinations of the PxC structure. Such scheme can be used as the potential optimization way, which may find wide application in the development and design of PxCs. [ABSTRACT FROM AUTHOR]

An ultra-bandwidth and single-mode polarization beam splitter (PBS) of dual hollow-core anti-resonant fiber (DHC-ARF) with circular outer tubes and inner tubes is proposed. Four outer tubes are introduced in the horizontal direction to obtain two hollow cores. The modal coupling is realized through the gap between the two hollow cores. The inner tubes also are inserted into two the outer tubes between the two hollow cores for realizing ultrawide bandwidth in DHC-ARF. To achieve single-mode performance, the high-order modes are coupled with the cladding modes by optimizing the diameter of outer tubes and the inner tubes. The calculation results show that an 11.0 cm long DHC-ARF can be used to develop a PBS with an operating bandwidth of 410 nm, where the polarization extinction ratio is lower than −20 dB. The high-order mode extinction ratio is 625.41, and the loss of fundamental mode is below 1.018 dB/m. • Because the size of elliptical tubes is hard to fabricate, an ultra-bandwidth and single-mode PBS of DHC-ARF completely composed of circular cladding tubes and nested tubes is proposed in the structures. • The influence factors related to bandwidth, the high-order mode extinction ratio and coupling length of PBS based on DHC-ARF are systematically studied by a full-vector finite element method. • The propagation process of light in the optical fiber is also simulated by the light speed propagation method. When the light travels to a certain distance, the two polarized lights will be separated. • Numerical simulation shows an 11.0 cm long DHC-ARF can be used to develop a PBS with an operating bandwidth of 410 nm ranging from 1.35 to 1. 76 μ m , where the polarization extinction ratio reaches −39.0 dB, the high-order mode extinction ratio is 625.41. • The PBS based on DHC-ARF with circular cladding tubes and nested tubes proposed in this paper compares the performance with other existing PBS, this PBS has the widest bandwidth. [ABSTRACT FROM AUTHOR]