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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]

We propose a modified design for a photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR). The air holes are arrayed in diamond lattices, and the diameter of the holes around the gold-coated holes are different that can separate the refractive index of the x-polarization and y-polarization second order surface plasmon polariton (SPP) modes. The influences of structural parameters of the photonic crystal fiber (PCF) on the filter characteristics are studied using the finite element method (FEM). Great changes have taken place in the results of numerical simulation by changing the thickness of the gold film and air hole diameter. Simulation results show that the resonance wavelength is communication wavelength 1550 mm, the loss of the y-polarization mode is 43,126.7 dB/m. When the length of the fiber is 500 μm, extinction ratio is more than 20 dB at the communication wavelength, and bandwidth achieve to 190 nm. It is an important property of PCF polarization filter in production. [ABSTRACT FROM AUTHOR]

A polarization filter is designed at two communication windows of 1310 and 1550 nm based on microstructured optical fiber. The model has four large diameter air holes and two gold-coated air holes. The influence of the geometrical parameters of the photonic crystal fiber on the performance of the polarization filter is analyzed by the finite element method. The numerical simulation shows that when the fiber length is 300 μm, the corresponding extinction ratio is 209.7 dB and 179.8 dB, the bandwidth of extinction ratio (ER) better than 20 dB is 150 nm and 350 nm at the communication wavelength of 1310 nm and 1550 nm. [ABSTRACT FROM AUTHOR]

A polarization filter based on photonic crystal fiber selectively coated with gold film is investigated. The loss spectra and the dispersion characteristics of the designed polarization filter are studied and analyzed by the finite element method. Simulation results show that the loss of core mode is 433.65 dB/cm in y polarization and 2.64 dB/cm in x polarization at the wavelength of 1.55 µm, respectively. The bandwidth of extinction ratio greater than −20 dB is 150 nm. The corresponding wavelength range is from 1.48 µm to 1.63 µm. The position and size of the little air holes along with the thickness of gold film showed influence on the polarization filter properties. And the proposed polarization filter has stable properties of with difference size and position of the little air holes. The designed polarization filter showing excellent properties can be used in polarizations filter in communication transmission. [ABSTRACT FROM AUTHOR]

A kind of polarized filtering photonic crystal fiber (PCF) with nanoscale gold film is studied by using the finite element method. The cross-section structure of the PCF is composed of a hexagonal lattice of air holes in which an air hole is gold coated, and the air-hole layout is modified. By our structure, the loss of x-polarized mode is further larger than the loss of y-polarized mode and the loss peak appears at the wavelength 1.31 μm. The corresponding loss in x-polarized can reach a value of 85,780 dB/m at the resonance wavelength. It can be used for the communication windows of 1.31 μm which can be used for carrying data/voice. When the length of fiber is longer than 30 μm, the extinction ratio is better than 20 dB at the wavelength 1.31 μm. When the length of fiber is longer than 210 μm, the extinction ratio is better than 20 dB with the wavelength ranging from 1.26 to 2 μm. The broadband polarized filtering PCF covering 740 nm is achieved. [ABSTRACT FROM AUTHOR]

A single-polarization photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is proposed. Finite element method is employed in simulating the PCF with gold-coated. The resonance wavelength can be modulated by changing the thickness of gold layer. At the resonance wavelength 1.55 μm, the loss of y-polarized mode is much larger than the loss of x-polarized mode. When the fiber length is set to 2 mm, the value of extinction ratio reaches to −118.7 dB, the y-polarized mode is suppressed and only x-polarized mode can be guided. The fiber is applicable in the production of single-polarization filter. The PCF has a simple structure and a big error tolerance, it has a good practicability. [ABSTRACT FROM AUTHOR]

A polarization filter at the two communication windows of 1.31 and 1.55 μm based on photonic crystal fiber (PCF) coated by nanoscale gold film is proposed. The effects of geometrical parameters of the PCF on the performances of polarization filter are evaluated by finite element method (FEM). Numerical simulations reveal that the polarization filter possesses ultra-short length of 400 μm and high extinction ratios of 41 and −150 dB at the communication wavelengths of 1.31 and 1.55 μm respectively. The bandwidth of extinction ratio (ER) better than 20 dB is 58 nm at the communication window of 1.31 μm. Moreover, the bandwidth of ER better than −20 dB is 164 nm at the communication window of 1.55 μm. [ABSTRACT FROM AUTHOR]

A broadband single-polarization photonic crystal fiber polarized filter based on surface plasmon resonance is proposed based on finite element method. Numerical simulations show the confinement loss of y-PCM (y-polarized core mode) is much higher than that of x-PCM (x-polarized core mode) in the wavelength range 1.20-1.63 μm. The confinement loss of y-polarized mode is 45,240 and 10,200 dB/m at the communication wavelength 1.31 and 1.55 um, respectively, and the corresponding loss of x-polarized mode is just 90 and 80 dB/m. When the fiber length is 3 mm, the bandwidth of extinction ratio better than -20 dB is greater than 430 nm covering almost all the communication wavelength. To our best knowledge, the bandwidth is the widest. The impacts of structural parameters on the resonance characteristics are also discussed. The structure could be further optimized for better result. [ABSTRACT FROM AUTHOR]

In this paper, a novel D-shaped photonic crystal fiber (D-PCF) based on surface plasmon resonance (SPR) is designed, and gold nanowire is used as the SPR active metal. A full-vector finite element method is applied to analyze the polarization filter characteristics. Phase matching between the second-order surface plasmon polariton (SPP) mode and the core-guided modes of x- and y-polarization can be met in two different wavelengths. By adjusting the diameters of the large air holes and the gold nanowire, this designed D-PCF can be used to the polarization filter in two communication bands. The loss of unwanted y-polarization mode can reach 244.9 and 292.8 dB/cm at the wavelength of 1.31 and 1.55 μm, respectively. With a length of 1 mm of the designed D-PCF, the bandwidths with the crosstalk better than 30 dB can reach to 88 and 150 nm, and the crosstalks are 208.4 and 249.5 dB the wavelength of 1.31 and 1.55 μm, respectively. [ABSTRACT FROM AUTHOR]

• A side-polished gold-coated photonic crystal fiber with a offset core is proposed. • The U-shaped air hole arrangement can enhance the leakage of the evanescent field. • The PCF integrates RI sensing and polarization filtering. • The maximum sensitivity within the RI range of 1.35–1.39 is 12,500 nm/RIU. • The proposed PCF polarization filter has bandwidth tunability. The transmission characteristics of a side-polished eccentric photonic crystal fiber (PCF) is studied by using the full-vector finite element method (FV-FEM). The proposed structure is composed of air holes similar to a U-shaped arrangement, and there is a small air hole between the side polishing plane and the core region to enhance the leakage of the evanescent field in the y polarization direction. It integrates refractive index (RI) sensing and polarization filtering. The RI sensing mainly works in the visible light band, while polarization filtering is suitable for the near-infrared band. The maximum sensitivity of the sensor is 12,500 nm/RIU, and the resolution is 8.0 × 10−6 RIU in the detection RI range of 1.35–1.39. By changing the external RI or the thickness of the gold-coated film, the bandwidth-tunable PCF polarization filter with excellent performance can be obtained. Therefore, the design of side-polished PCF will be of great significance to the development of integration and miniaturization of optical devices. [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]

Highlights • The PCF is simple, novel and easy to apply. • The filter can simultaneously achieve polarization filtering effects on the input signals of the 1310 and 1550 nm communication bands. • When the length of the PCF is 0.8 mm, the crosstalk is less than −20 dB or better than 20 dB in the 1550 and 1310 nm bands, the optical bandwidth can reach 220 and 150 nm, respectively. Abstract A photonic crystal fiber (PCF) polarization filter with dual communication bands is proposed in this paper. The polarization characteristics of the double-hole gold-coated PCF are numerically analyzed by utilizing the finite element method (FEM). As we know, the filter can achieve polarization filtering effect on input signals at 1310 nm (y-polarized mode) and 1550 nm (x-polarized mode) bands simultaneously in two orthogonal polarization states. In the above two communication bands, the confinement losses of the unwanted polarization mode can reach 192.7 dB/cm (y-polarized mode) and 427.5 dB/cm (x-polarized mode), whereas other polarization mode losses are very low. Furthermore, when the transmission length of the PCF is 800 μm, x and y polarization mode crosstalk can reach −275.4 and 126.9 dB in the 1550 and 1310 nm bands, respectively. Meanwhile, the crosstalk is less than −20 dB or better than 20 dB, the optical bandwidth can reach 220 and 150 nm, respectively. [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]

In this paper, an asymmetric photonic crystal fiber (PCF) polarization filter near the gold-clad hole based on surface plasmon resonance (SPR) is proposed. The outer walls of the two air holes in the y-direction are coated with a gold film, and the two kinds of cladding air holes are introduced near the coated holes to increase the difference in the coupling strength of x and y polarization modes and SPP modes, thus separating the two polarization states. The finite element method is used to study the characteristics of the polarization filter, and the result shows that the polarization loss in the y-direction is as high as 1565.98 dB/cm at 1. 55 μ m , while the loss in the x-direction is relatively small. When the fiber length is 1 mm, the crosstalk peak reaches 1322.7 dB. From 1 μ m to 2 μ m (range: 1000 nm), the crosstalk is always greater than 20 dB. If four kinds of pores with different sizes are used in the cladding layer, the symmetry around the gold-coated holes will be destroyed, and a better filtering effect can be obtained. The excellent performance of the proposed polarization filter makes it a good candidate material for broadband polarization filters. • Propose a new idea for filter design: improve the asymmetry near the gold-clad hole. • The loss peak in y-polarization is much higher than in x-polarization at communication wavelength 1.55 μ m. • When the fiber length is 1 mm, the crosstalk peak reaches 1322.7 dB. From 1 μ m to 2 μ m, the crosstalk is always greater than 20 dB. • The higher the asymmetry near the gold-plated hole, the better the polarization filtering performance. [ABSTRACT FROM AUTHOR]