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• A solid-core anti-resonant fiber polarization filter based on SPR is demonstrated and designed with two kinds of chalcogenide glasses, As 38 S 60 and GaAsS. • The filter bandwidth can reach 248 nm and the extinction ratio can reach −377.46 dB when a 4 mm fiber length is coated with a 30 nm gold film. • The filter bandwidth covers the S + C + L optical communication band. • The resonance wavelength can be effectively tuned by changing the wall thickness of the gold-coated cladding tube. Based on surface plasmon resonance (SPR), we proposed a tunable chalcogenide solid-core anti-resonant fiber (SC-ARF) polarization filter. The purpose of introducing the SPR, which is excited by coating the inner wall of the cladding tubes with a gold film, is to achieve a discrepancy between the confinement loss of two polarized fundamental modes (FMs). The full-vector finite element method (FV-FEM) evaluates the impact of fiber core radius, cladding tube radius, cladding tube wall thickness, and gold film thickness on the polarization filter characteristics. The results show that when the thickness of the gold film is 30 nm and the fiber length is 4 mm, the filter bandwidth can simultaneously cover the S + C + L optical communication band and reach 248 nm, and the extinction ratio (ER) value reaches -377.46 dB. Moreover, we also confirmed the tuning effect of the gold-coated cladding tube wall thickness on the resonance wavelength. The proposed fiber polarization filter has potential application value in optical fiber communication and transmission. [ABSTRACT FROM AUTHOR]

A kind of side-leakage photonic crystal fiber (SL-PCF) with external gold-coated film is proposed by introducing a leakage channel in the x polarization direction. The effects of air-holes diameters, gold film thickness, liquid filling, and different metal coating materials on the polarization characteristics of SL-PCF are analyzed using the full vector finite element method (FV-FEM). At resonance wavelengths of 1.41 and 1.59  μm, the losses of x-polarized core mode are 725.74 and 1097.94 dB/cm, while that of y-polarized core mode are only 1.79 and 2.00 dB/cm. When the transmission length of SL-PCF is 1 mm, the bandwidth with extinction ratio better than 20 dB is up to 1410 nm, covering wide wavelengths from 1.09 to 2.5 μm. Moreover, the direction of the polarization filter and its resonance wavelength can be effectively modulated by selectively filling the liquid into the cladding air-holes and changing the coating material.Furthermore, the introduction of side-leakage channel not only increases the mode birefringence, but also enhances the fiber's sensitivity to changes in external pressure, bending, and torque. Therefore, the proposed SL-PCF not only has important applications in fiber polarization filters, but also has broad application prospects in fiber sensors. [ABSTRACT FROM AUTHOR]

Highlights • Single polarization photonic crystal fiber filter proposed. • Proposed filter can be used in communication windows at 1.31 μm and 1.55 μm. • Unwanted polarization mode losses: 251.5 dB/cm at 1.31 μm and 375.3 dB/cm at 1.55 μm. • Bandwidths of 1.31 μm and 1.55 μm reached at 10 nm and 70 nm, respectively. Abstract In this study, we developed a tunable photonic crystal fiber (PCF) polarized filter with a gold coating and liquid filling, which was investigated using the full-vector finite-element method. The gold that selectively filled the cladding air holes acted as a defect mode. When light was transmitted into the core, the energy was transferred from the core mode to the defect mode at a given wavelength and a resonance peak was obtained. Numerical results showed that the proposed PCF could be implemented simultaneously for polarization filtering in the communication windows of 1.31 and 1.55 μm. The confinement losses for the y-polarized mode were 251.5 dB/cm for 1.31 μm and 375.3 dB/cm for 1.55 μm. When the fiber length was 90 μm, the corresponding bandwidths were just less than 20 and 70 nm for 1.31 and 1.55 μm, respectively. The bandwidths are the narrowest obtained and they are conducive to applications in integrated systems. We also studied the effects of structural parameters on the resonance performance. The optical fiber structure could be optimized further to obtain better results. [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]

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]

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 tunable fiber polarization filter by filling different index liquids into the central hole of photonic crystal fiber (PCF) is proposed and demonstrated. The dispersion characteristics and loss spectra of the polarization filter are evaluated by finite element method (FEM). The gold wires are selectively filled into the cladding air holes of the PCF. When the phase matching condition is satisfied, the liquid-core mode couples to surface plasmon polaritons (SPP) mode intensely. The resonance wavelength varies with the change of the structural parameters and liquids. By adjusting the refractive index of the liquid, we realize the polarization filter at the wavelength of 1.31, 1.49, and 1.55 $\mu$m, respectively, under the optimized structural parameters. This is the first time to propose the narrowband polarization filter at the communication wavelength of 1.31 $\mu$m to our best knowledge based on the coupling between liquid-core mode and SPP mode, and the full width half maximum (FWHM) is only 16 nm. The loss of X-polarized mode is 44336 dB/m at $\lambda$ = 1.31 $\mu$m, and the corresponding loss of Y-polarization mode is 224 dB/m. By comparison, we find the birefringence in our structure is further better than that in conventional structure. High birefringence is helpful to separate the resonance wavelength positions of the two orthogonal polarized modes. The result also reveals that resonance loss becomes small with increasing the distance between liquid core and gold wire. [ABSTRACT FROM PUBLISHER]

• A polarization filter based on hollow-core anti-resonant fiber with tellurite glass as the base material was designed. • By varying the structure, a single-mode single-polarization fiber with a bandwidth of 30nm near 1550nm was achieved. • Through the Surface Plasmon Resonance (SPR) effect, a polarization filter with a bandwidth of 390 nm was realized near 1550 nm. Hollow-core anti-resonant fiber (HC-ARF) with unique light propagation through air present a promising avenue for advanced applications of polarization filters based on HC-ARF. This paper proposes a single-mode and single-polarization filters (SMSPF) around 1550 nm based on HC-ARF with tellurite glass as the substrate material. The polarization filtering characteristics of the HC-ARF with varying wall thickness and gold wire filling are simulated and analyzed using the finite element method. A single-mode single-polarization (SMSP) HC-ARF with a continuous bandwidth of 30 nm is obtained, and a polarization filter with low polarization loss and a high filtering bandwidth of 390 nm is achieved through the surface plasmon resonance (SPR) effect. [ABSTRACT FROM AUTHOR]

A novel polarization filter based on photonic crystal fiber with two open-ring channels is proposed. The optical device is compatible with both broadband filtering and sensing. The calculation results show that the loss of the y-polarized core mode is as high as 1147.79 dB/cm at a communication wavelength of 1.55 μm, while the loss of the x-polarized core mode is only 1.86 dB/cm. When the length of PCF is 800 μm, the optical bandwidth of crosstalk greater than 20 dB can reach 790 nm at the wavelength band of 1.55 μm, and the corresponding crosstalk peak is 796.4 dB. In addition, the simulation results show that the proposed PCF is applied in the field of sensing as long as the thickness of the gold film is changed from 22.5 nm to 40 nm. Further, when the refractive index of the tested material varies from 1.32 to 1.37, the average sensitivities of 3057 nm/RIU and 1000 nm/ RIU are obtained in x- and y-polarized modes, respectively. [ABSTRACT FROM AUTHOR]