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A novel photonic crystal fiber polarization filter with Au-coated and liquid-filled air holes is designed in this paper. The coupling theory is introduced to explain the complete coupling and incomplete coupling. We can adjust the resonance point to the communication band by optimizing the parameters of the fiber structure. Numerical simulation results demonstrate that the resonance strength can reach 434 dB cm −1 at the communication wavelength of 1.31 μm in x-polarized direction. By filling liquid analyte can help adjust the resonance peak to the proper place. Furthermore, when the fiber length of L equals to 0.1 cm, the crosstalk peak value can reach 353.74 dB at the wavelength of 1.31 μm, and the bandwidth of the crosstalk better than 20 dB can reach 80 nm when the length of the fiber L is 400 μm. These characteristics make it a promising candidate for designing new types of polarization filter devices. [ABSTRACT FROM AUTHOR]

A broadband core shift photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance is proposed in this paper. The fiber is consisted of an asymmetric hexagonal lattice of holes in which a small air hole is coated with gold film and another one large air hole destroyed the structure around the core. The loss of y-polarized core mode is 2232.61 dB/cm at the communication wavelength of 1.55 μm, however, the loss of x-polarized core mode is very weak. When the PCF length is 300 μm, the bandwidth of exceeding 420 nm with extinction ratio better than −20 dB is achieved. To our best knowledge, the bandwidth is the widest. As a consequence, this special fiber filter has a wider range of applications. [ABSTRACT FROM AUTHOR]

In this work, we propose an octagonal photonic crystal fiber (PCF) filter based on tellurite. Selective gold coating in air holes couples the core mode to a surface plasmon mode. The finite element method is used to analyze the structure in the mid-infrared band. The simulated results and analysis show that the losses in the y and x polarization modes at 2.55 µm are 2063.2 and 21 dB/cm, respectively. Therefore, the unwanted y-polarization mode is filtered out. The higher loss ratio optimizes the formant position and intensity of surface plasmon mode and core mode. When the fiber length of the filter is optimized to 500 µm, the extinction ratio of − 102 dB is achieved at 2.55 µm. Consequently, the single polarization transmission with a 500 nm width is realized. When the length of the fiber is greater than 500 µm, it realizes the 1500 nm (2.2–3.7 µm) ultra-wideband filtering. We also analyze the manufacturing feasibility of the proposed PCF and the influence of structural parameters on the limiting loss characteristics. • Introduce a new type of substrate material: TZLB, which breaks the limitation of conventional quartz glass. • The loss of the y-polarization state is much higher than the x-direction. • When the fiber length is 500 µm, the ER reaches −102 dB and the effective filtering range is 2.4‐2.9 μm. • When the fiber length is greater than 500 µm, it achieves the 1500 nm ultra-wideband filtering. [ABSTRACT FROM AUTHOR]

A narrowband dual-polarization filter based on photonic crystal fiber (PCF) with Au-Ag double-layer films is proposed. The cladding of PCF is composed of three layers of air holes, and Au-Ag double-layer films are coated on two symmetrical air holes to excite surface plasmon resonance (SPR) effect. The special mechanism of the Au-Ag double-layer films takes advantage of the narrower full width at half maximum (FWHM) of silver. On the other hand, gold is used to protect the silver from oxidation and improve the stability of the filter, and can also enhance SPR effect. The simulation results show that the dual-polarization filter with double-layer metal films has higher resonance absorption and better spectra than that with the single-layer metal film. When the thickness of the double-layer metal films is 22.5 nm (the thickness of silver film is 18 nm), the confinement loss of dual-polarization filter at 1430 nm is achieved to 64.08 dB/cm (y-pol core mode) and at 1530 nm is achieved to 37.26 dB/cm (x-pol core mode). The wavelength range of crosstalk (CT) greater than 20 dB and less than −20 dB are 1410–1450 nm and 1510–1550 nm for the device length of 10 mm, respectively. The CT is achieved 555.07 dB and −321.54 dB at the wavelength of 1430 nm and 1530 nm, respectively. These characteristics show that the filter has excellent performance, and will become a suitable candidate for a narrowband polarization filter. [ABSTRACT FROM AUTHOR]

In this paper, a dual-polarizated photonic crystal fiber filter (PCF) based on surface plasmon resonance (SPR) was proposed. Its polarization characteristics were numerically researched by finite element method (FEM). The results indicate that the polarization filtering of the filter be able to fulfill in dual communication bands of 1310 and 1550 nm. The confinement loss reaches 80,711.4 dB/m for the x polarization core mode at the wavelength of 1310 nm, while 46,614.5 dB/m for the y polarization core mode at the wavelength of 1550 nm. When the length of PCF is 2.5 mm, the extinction ratios of x and y polarization core modes can achieve 1705.27 and − 883.46 dB, respectively. For the communication windows of 1310 and 1550 nm, the filtering bandwidths can reach to 390 and 350 nm, respectively. These excellent characteristics are beneficial to the design and manufacture of filter devices. • A PCF dual windows polarization filter based on SPR is proposed. The square arrangement of air holes is easy to prepare. • The losses of the filter at dual windows can reach 80,711.4 dB/m and 46,614.5 dB/m. • When L PCF = 2.5 mm, the ER of the two orthogonal modes can reach 1705.27 and − 883.46 dB. The bandwidth can reach 390 nm and 350 nm. [ABSTRACT FROM AUTHOR]