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In this paper, a large mode area photonic crystal fiber (PCF) based on chalcogenide glass A s 2 S 3 with excellent bending resistance and single-mode operation characteristics is proposed.The guiding properties of the PCF are investigated using the full vector finite element method with perfectly matched layers. Numerical results indicate a single-mode bandwidth of 170 nm, covering the wavelength range from 1.1 to 2.8 μ m. The effective mode area exceeds 720 μ m 2 for a wavelength of 2.0 μ m and a bending radius of 10 cm. The bending radius ranges from 7 to 40 cm, 5 to 30 cm, and 3 to 19 cm at the three commonly used operating wavelengths of 1.31 μ m, 1.55 μ m, and 2.0 μ m, respectively. As a result, the designed chalcogenide PCF is bend insensitive and can maintain stable single-mode operation even at different working wavelengths. Moreover, the proposed PCF is easy to fabricate and has potential for application in high power fiber lasers. [ABSTRACT FROM AUTHOR]

In this paper, we propose a hexagonal photonic crystal fiber (PCF) suitable for broadened mid-infrared supercontinuum generation. The designed PCF has five air-hole rings with three different air holes, arranged in a triangle pattern. The central air hole is filled with G e 10 A s 22 S e 68 and the inner wall of the air hole is coated with A s 2 S 3 . In the mid-infrared wavelength range of 3400 nm to 4500 nm, the supercontinuum bandwidth increases with the increase of the pump wavelength, peak power, and pulse width. When the pump light source with a peak power of 5 kW and the input pulse width is 200 fs, a 10 mm fiber can produce an extremely wide supercontinuum spectrum spanning 6000 nm. In addition, optical parameters including dispersion, confinement loss, effective mode area, and nonlinear coefficients are numerically investigated by the finite element method. The results show that at a wavelength of 4000 nm, the second order dispersion of the fiber is 8.81 × 10 - 27 s 2 m - 1 and the nonlinear coefficient is 972.5 W - 1 km - 1 . The designed photonic crystal fiber is stable, dispersion flat, and can meet the application requirements of obtaining broad supercontinuum spectrum. [ABSTRACT FROM AUTHOR]

This paper reports a double-sided polished microstructured fiber based on the refractive index that simultaneously measures the refractive index and temperature. Two polished planes were introduced into the cladding. A gold film and polydimethylsiloxane are deposited on one side of the plane for temperature measurements, and graphene layers are coated on the surface of the silver film on the other side for refractive index measurements. The finite element method is used to characterize the sensing characteristics of the sensor. The results show that when the liquid refractive index is from 1.36 to 1.4 and the temperature from 70 °C to 110 °C, the maximum sensitivity of the sensor is 15,000 nm/RIU and 8.8 nm/°C, respectively. The double-sided polished structure facilitates the development of multi-parameter measurement sensors for various applications. [ABSTRACT FROM AUTHOR]

To obtain better filtering characteristics and transmission performance, an asymmetric gold-coated photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR) was designed and investigated. The surface plasmon mode is generated by coating gold film to the inner walls of two liquid-filled holes along the y polarization direction. Three air holes with different diameters are introduced near the core which break the symmetry of the primary fiber structure and make the resonance wavelengths of the x polarization and y polarization of the core mode well separated. The filtering performances are evaluated with the finite element method (FEM) based software. The numerical simulation shows that the confinement loss of y polarization is as high as 1375.94 dB/cm at 1.55 µm, while the x polarization loss is only 10.45 dB/cm. Furthermore, the crosstalk (CT) has a maximum of 1186.06 dB in the communication bands when the length of the fiber is 1000 µm. In the range from 1.1 µm to 2 µm, the bandwidth of the filter is approximately 900 nm. The asymmetry of the structure and liquid filling of gold-coated holes enhance the coupling strength of the filter. Meanwhile, the higher confinement loss, crosstalk and wider bandwidth may have useful applications for polarization filters with significance for the design of other filters. [ABSTRACT FROM AUTHOR]

We show that both photonic bandgap guidance and modified total internal reflection can simultaneously occur in a chalcogenide–tellurite photonic crystal fiber (PCF) whose cladding is composed of a high-index array with internal regions being air. The coexistence of these two guidance mechanisms is corroborated by numerical simulations based on a plane wave expansion method and an analytical model. Despite being scalar and for high-index contrast material systems, the analytical model can accurately predict the band structures of the PCF. A PCF with seven ring units removed as the fiber core is designed to guide in the 580–950-nm wavelength range by the photonic bandgap effect and in the 2.0–4.6-μm wavelength range by total internal reflection. Such a PCF can be an interesting platform for nonlinear phenomena occurring across the two guidance regions. [ABSTRACT FROM PUBLISHER]

A photonic crystal fiber is designed with chalcogenide glass As2Se3 as the base material. As2Se3 has a high refractive index and a high nonlinear refractive index; as a result, it has a desired application for strengthening birefringence and nonlinearity. The outer layer of the fiber is a regular decagonal structure composed of four layers of circular air holes, and the inner cladding area is composed of four elliptical air holes arranged in a diamond pattern. The influence of the size of the circular air holes in the fiber cladding, the thickness between each layer, and the size and position of the elliptical air holes in the inner cladding area on the birefringence is analyzed and studied using the full vector finite element method. The results show that the birefringence value of the fundamental mode of the fibers is 0.108 at a wavelength of 1.55 μm, and at the same time, the nonlinear coefficients of the X and Y polarization states are 240 and 197 m − 1 · W − 1, respectively. [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]

This paper proposes a highly sensitive surface plasmon resonance (SPR) refractive index sensor based on the photonic crystal fiber (PCF). The optical properties of the PCF are investigated by modulating the refractive index of a liquid analyte. The finite element method (FEM) is used to calculate and analyze the PCF structure. After optimization, the fiber can achieve high linearity of 0.9931 and an average refractive index sensitivity of up to 14,771.4 nm/RIU over a refractive index range from 1.47 to 1.52, with the maximum wavelength sensitivity of 18,000.5 nm/RIU. The proposed structure can be used in various sensing applications, including biological monitoring, environmental monitoring, and chemical production with the modification and analysis of the proposed structure. [ABSTRACT FROM AUTHOR]

In this work, a surface plasmon resonance (SPR) temperature sensor based on a con-joined-tubular anti-resonance optical fiber (CTF) was theoretically designed and analyzed using the finite element method. The CTF cladding was composed of eight pairs of conjoined tubes, and one or two holes of the tubes were selectively coated with gold to generate the SPR effect. Alcohol was injected into the core of the CTF to work as the sensing medium using vapor deposition. The proposed sensing structure exhibited excellent birefringence and produced more than six resonant peaks in different wavebands of the X and Y polarization. The positions of those resonant peaks were sensitive to temperature change, and the simulated sensitivity was about 3.2–3.6 nm/°C. The multiple working wavebands of the proposed sensing structure could be used for self-verification. Moreover, the influence of structural parameters on sensing performance was analyzed in detail. Possessing features of high sensitivity, good birefringence, multiple measuring wavebands, and self-verification, the proposed CTF-based SPR sensor has great potential in practical applications such as biological research and chemical sensing. [ABSTRACT FROM AUTHOR]

This paper proposes a Photonic Crystal Fiber (PCF) refractive index sensor model based on the surface plasmon resonance effect. The proposed PCF model also uses the full vector finite element method to transfer the structure under the anisotropic Perfect Matching Layer (PML) boundary condition. Numerical calculations were carried out on the sensor characteristics. The calculation results show that the elliptical air hole on the left side of the PCF core is coated with a gold-nano film which serves as a Surface Plasmon Resonance (SPR) sensing channel to detect the refractive index of liquid materials. Compared with other structures, the resonant peak generated by the excited SPR effect from the elliptical sensing channel has a high sensitivity to the change of the refractive index of the liquid to be measured. With the help of this attribute, it is relatively easy to adjust the sensitivity. The refractive index range of this structure is within 1.43–1.49 and the sensitivity is up to 12,719.97 nm·RIU−1. The linearity is good; R2 = 0.99927, which is very suitable for liquid sensing. [ABSTRACT FROM AUTHOR]

In this paper we propose a gold-plated photonic crystal fiber (PCF) refractive index sensor based on surface plasmon resonance (SPR), in which gold is coated on the external surface of PCF for easy fabrication and practical detection. The finite element method (FEM) is used for the performance analysis, and the numerical results show that the thickness of the gold film, the refractive index of the analyte, the radius of the air hole in the first layer, the second layer, and the central air hole can affect the sensing properties of the sensor. By optimizing the sensor structure, the maximum wavelength sensitivity can reach 11000 nm/RIU and the maximum amplitude sensitivity can reach 641 RIU−1. Due to its high sensitivity, the proposed sensor can be used for practical biological and chemical sensing. [ABSTRACT FROM AUTHOR]

In this paper, a surface plasmon resonance refractive index and temperature sensor based on V-cut photonic crystal fiber (PCF) is proposed. The proposed structure is studied and analyzed using the finite element method (FEM). The sensing area is a V-shaped cut groove, and the cases when the cut angle is positive, 0° and negative are discussed and compared. The results show that when the cutting angle is 15°, the optimal sensing performance can be obtained compared with other cutting angle. By optimizing other structural parameters when the cutting angle is 15°, in the refractive index range of 1.34–1.38, the average sensitivity of the refractive index sensor is 10,500 nm/RIU, and the maximum sensitivity is 52,500 nm/RIU. The average sensitivity is 5.57 nm/°C in the range of 85 ℃–145 ℃ as a temperature sensor. Due to the simple structure and high sensitivity of the design, it can be used for real-time monitoring of analytes in medical, biochemical and environmental monitoring. [ABSTRACT FROM AUTHOR]

A photonic crystal fiber is designed with chalcogenide glass As2Se3 as the base material. As2Se3 has a high refractive index and a high nonlinear refractive index; as a result, it has a desired application for strengthening birefringence and nonlinearity. The outer layer of the fiber is a regular decagonal structure composed of four layers of circular air holes, and the inner cladding area is composed of four elliptical air holes arranged in a diamond pattern. The influence of the size of the circular air holes in the fiber cladding, the thickness between each layer, and the size and position of the elliptical air holes in the inner cladding area on the birefringence is analyzed and studied using the full vector finite element method. The results show that the birefringence value of the fundamental mode of the fibers is 0.108 at a wavelength of 1.55 μm, and at the same time, the nonlinear coefficients of the X and Y polarization states are 240 and 197 m − 1 · W − 1, respectively. [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]

• The polarization filter we designed is novel and have a high performance. • The loss peak in Y-polarization is much higher than in X-polarization. • Air-holes except the innermost layer also influence the loss peak well. • The PCF filter can be widely used in system integration. In this study, a novel photonic crystal fiber (PCF) polarization filter has been designed. To resonate the surface plasma mode with the core mode, gold is selectively filled in the air holes. Using numerical simulations based on the finite element method, the influence of structural parameters on the filter is analyzed, and a set of rules for designing the PCF polarization filter is determined. The numerical simulation shows that the peak loss in the y-polarization direction at 1.31 μm reaches 1209.57 dB/cm, whereas the peak loss in the x-polarization is close to zero. Working at 1310 nm in the communication band, a new type of PCF is designed using these characteristics. [ABSTRACT FROM AUTHOR]

The optical and acoustic fields of stimulated Brillouin scattering (SBS) and the interaction between them are investigated in the As 2 S 3 chalcogenide suspended-core microstructured optical fibers (MOFs) by the finite-element method (FEM). The optical and acoustic fundamental modes are analyzed at 1550 nm. The core diameters of the MOFs vary from 1.0 to 6.0 μm. For each case, the holes of the MOFs are filled with different materials such as trichlormethane (CHCL 3 ), alcohol and water. When the core diameter is 6.0, 4.5, 3.0, 2.0 and 1.0 μm, the ratios of difference for optical fields are ∼0.66%, 0.97%, 1.48%, 1.94% and 3.55%, respectively, while the ratios of difference for acoustic fields are ∼0.13%, 0.24%, 0.34%, 0.74% and 29.13%, respectively. The overlap factors between optical and acoustic fields are calculated, which change with the core diameter and the filled material. The results will be helpful to strengthen or suppress the SBS effect in practical applications. [ABSTRACT FROM AUTHOR]

In order to reduce the fiber crosstalk for the space division multiplexing (SDM), this paper proposes a novel multi-core few-mode fiber of composite refractive index profile and dual assistance structure. On the one hand, by adopt dual assistance of air-hole embedment and trench wrapping around all the seven cores, inter-core crosstalk is greatly reduced. On the other hand, a non-circularly symmetrical refractive index (RI) profile is innovatively proposed for the six outer-ring cores, which not only weakens the inter-mode coupling but also has a suppression effect on inter-core crosstalk. The finite element method (FEM) is used to analyze the fiber structure. In the case of transmitting six spatial modes, the minimum inter-mode effective RI difference (Δ n eff) between the linear polarization (LP) modes of the center core and between the spatial modes of the outer-ring core are greater than 0.5 × 10−3, the inter-core crosstalk of the sixth mode LP 02 at 1550 nm is less than -66dB/100km, and the relative core multiplexing factor reaches 29.24. The characteristics of this structure are significantly better than that of current commercial optical fibers, promising broad application prospects in large-capacity SDM optical communication system. [ABSTRACT FROM AUTHOR]

A dual-polarized microstructure fiber sensor is based on surface plasmon resonance, which is arranged of pentagonal lattice to achieve refractive index sensing in the near-infrared spectrum. The gold nanowire-filled fiber sensor exhibits excellent sensing characteristics and improved transmission properties. Finite element method is used for computational analysis and structural optimization for the fiber sensor. When the refractive index of the analyte range from 1.32 to 1.38, dual-polarizd sensing can be implemented as a self-calibration with wavelengths increasing from 700 to 1200 nm. For the proposed sensor, the highest wavelength sensitivity of 10,286 nm/RIU is exhibited with a sensor resolution of 9.72×10−6 RIU, and the corresponding amplitude sensitivity and figure of merit are as high as 544.0 RIU−1 and 146.9. Moreover, the sensing length of at least 1.14 mm ensures accurate detection of optical signals for proposed sensor. Owing to the above advantages, the proposed sensor is suitable for high integration and high precision sensitivity detection. [ABSTRACT FROM AUTHOR]