Photonic Crystal Fiber Polarization Filter Research Articles

A grating-modified broadband D-type photonic crystal fiber polarization filter

In this paper, a D-type grating-modified broadband photonic crystal fiber polarization filter based on surface plasmon resonance is proposed. The asymmetric design of D-type photonic crystal fiber is helpful to achieve single-mode polarization filtering, and grating can increase the coupling between the core mode and the SPP mode and thus increase the constraint loss. From our simulation results, it can be seen that the applicable bandwidth range can easily reach 1 μm. At the communication wavelength of 1750 nm, the calculated constraint losses of x-polarized and y-polarized core modes are 4.2526 dB cm−1 and 1491.8 dB cm−1, respectively, and the crosstalk is up to 1292 dB. The proposed grating-modified of photonic crystal fiber has achieved good filtering effect in the near-infrared band, and even extended to the mid-infrared band.

Design of a broadband dual-cladding PCF polarization filter via triple surface plasmon resonance effects

Photonic crystal fiber (PCF) polarization filters are widely utilized due to high integrity and flexible tunability. However, most filters still face the challenges from intricate structure and limited bandwidth. Here, we propose a dual-cladding PCF polarization filter with a large bandwidth by triple surface plasmon resonance (SPR) effects. Asymmetric Au-filled air holes are arranged in the dual-cladding lattice to excite the triple SPR effects with enhanced birefringence, therefore extending the operating bandwidth. The results show that the triple SPR phenomena occur in the y-polarized direction at resonance wavelengths of 1212.8, 1347.5, and 1567 nm with confinement losses of 946.63, 826.79, and 737.13 dB/cm, respectively. In contrast, the x-polarized direction shows extremely low confinement losses of only 0.20, 1.94, and 2.03 dB/cm. With the fiber length (L) of only 300μm, the filter achieves the maximum crosstalk (CT) of 246.62 dB, and the bandwidth above 20 dB extends to 830 nm. High performance filter based on multiple SPR effects may has the potential applications in optical communication and optical sensing.

A hybrid method for photonic crystal fiber polarization filter based on artificial neural network and genetic algorithms

In this paper, we proposed a design method for photonic crystal fiber polarization filters incorporating the artificial neural network (ANN) and the genetic algorithm (GA) to achieve high-performance polarization filters. The ANN is trained to accurately learn the relationship between the structure parameter and polarization properties of PCFs, and GA is utilized to select the structural parameters with optimal performance. Confinement loss, bandwidth, and resonance wavelength of the polarization filter serve as parameters in the multi-objective optimization process performed by the GA. Numerical results demonstrate that the designed PCF filter has high performance, with a confinement loss of 1995.75 dB/cm for the y polarization core mode at 1.55 μm, and crosstalk and bandwidth of 1720.15 dB and 932 nm, respectively. It indicates that the hybrid design method is a promising and viable approach for the development of optical applications.

Design of high-performance photonic crystal fiber polarization filter by Grey Wolf Optimizer with convolutional neural network

In this paper, a D-shaped photonic crystal fiber polarization filter is optimized using a novel machine learning framework. The framework incorporates the Grey Wolf Optimizer (GWO) and convolutional neural network (CNN) to optimize the optical fiber structure parameters. The designed CNN accurately classifies optical fiber modes, while the GWO selects complex fiber structure parameters. The fitness function conducts multi-objective optimization on the confinement loss and resonance wavelength of the polarization filter. The simulation results show the y-direction confinement loss of the optimized polarization filter is 1111.51 dB/cm at a wavelength of 1.55 µm. At a fiber length of 1000 µm, the crosstalk on the communication band reaches 965.3 dB, with a bandwidth exceeding 1000 µm. Numerical analysis demonstrates that the performance of the designed PCF filter is better than that of the original and also have showed the superiority of the proposed framework, which is a promising avenue for designing other photonic devices.

Optimization of Structural Parameters of PCF Polarization Filter by a Genetic Algorithm

The material and geometry of photonic crystal fiber (PCF) are significant adjustable characteristics, and affect its optical properties. Finding the global optimal fiber is formulated as an optimization problem, and intelligent algorithms are used for the complex objective optimization. This paper presents the optimal structure of PCF for polarization filter determined by the Genetic Algorithm (GA) method, and the fitness function of GA is defined relatedly to the polarization filter optical index crosstalk (CT) and bandwidth. The designed PCF polarization filter has the following characteristics: the CT reaches 1845.3113 dB at 1.55 μm. When the fiber length is limited to 1000 nm, the bandwidth value exceeds 800 nm. Numerical results demonstrate that the performance of the designed PCF filter is better than that of the original and also have proved the GA method is beneficial to the design and fabrication of optical fibers.

High Extinction Ratio and Large Bandwidth PCF Polarization Filter With Gold-Wires Coated by Monocrystalline Silicon

A kind of high extinction ratio (ER) and large bandwidth photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance is proposed. The SPP modes can be inspired by two gold-wires to improve the filter characteristics and the effect of surface plasmon resonance is further enhanced by cladding monocrystalline silicon surrounding gold-wires. An asymmetric structure of leakage channel is introduced in y-pol direction axis which intensifies the energy leakage to external cladding, high polarization extinction ratio is occurred. By using the finite element method (FEM), the structural parameters and optical properties are quantitatively analyzed. Numerical analysis shows that two main adjacent resonance peaks appear in y-pol direction, confinement losses of y-pol core mode at the resonance wavelength of 1519 and 1664 nm are 573.33 and 543.21 dB/cm, while the losses of x-pol core mode are 16.97 and 0.98 dB/cm. When the fiber length L=3 mm, the maximum ER reaches 1449 dB at the wavelength of 1519 nm, and the bandwidth with ER better than 20 dB reaches 405 nm. Hence the proposed PCF with gold-wires coated by monocrystalline silicon would have a widely application in optical fiber communication, optical information processing and other fields.

Surface plasmon resonance (SPR)-based D-shaped photonic crystal fiber polarization filter and refractive index sensor with a hexagonal pore structure

A D-shaped photonic crystal fiber (PCF) polarization filter and sensor with a standard hexagonal arrangement of pores is designed. The effects of geometric parameters, metal film thickness, liquid refractive index, and optical material refractive index on polarization filtering and sensing characteristics are analyzed by the finite element method (FEM). The proposed PCF shows single-polarization filtering in communication window and has ultra-high corresponding bandwidth. At the 1.55 µm communication window band, the confinement loss of the y-polarized core mode is 819.27 dB/cm, while the x-polarized core mode is only 3.45 dB/cm. The crosstalk (CT) reached a maximum of 708.6 dB in the communication bands, and the corresponding bandwidth reaches 1000 µm when the fiber length is 1 mm. Meanwhile, the D-type PCF is widely used in sensing because it avoids filling the gold film and analyte in the internal pores. The change in the thickness of the mental coating from 39 nm to 22 nm provides the proposed PCF with sensing properties. By reducing the refractive index of fiber material, the maximum sensitivity is 10,741 nm/RIU. When the refractive index measurement range of the analyte is specified from 1.33 to 1.36, the average sensitivity reaches 7313 nm/RIU. Good performance enables the proposed compatible filtering and sensing PCF may be used in a wide range of scenarios.

Performance analysis of a photonic crystal fiber polarization filter filled with different materials.

A compact square photonic crystal fiber polarization filter with high performance is proposed. Two larger holes filled with different metal and fluid are designed to break the strict structure symmetry and forming high birefringence. Four small pores are designed to provide a wider channel for the coupling between defect mode and core mode. Its filtering and coupling characteristics are analyzed by the full vector finite element method. In addition, the properties of PCF filled with different materials are compared and discussed. Different metal materials have different dielectric constants, different optical damping, interband transitions, molecular structure, and physicochemical properties, which make their transmission modes and coupling strength different. The results show that the performance of a PCF filter filled with gold and liquid is the best, which is very suitable for an adjustable PCF polarization filter. The calculation results show that the extinction ratio of the designed filter can reach 5383 dB for a device length of 3 mm; the unwanted fiber loss can reach 2073 dB/cm; and the applicable bandwidth of 2000 nm covers almost the whole communication band. The proposed polarization filter shows large unwanted loss, high extinction ratio, wide bandwidth and coordination, which make it a good candidate for excellent optical fiber filter devices.

A Broadband Gold-Coated Photonic Crystal Fiber Polarization Filter with a High Loss Ratio of Both Polarizations at 1550 and 1310 nm

A new kind of gold-coated hexagonal photonic crystal fiber polarization filter is designed in this paper. The filtering properties can be adjusted through varying the structural parameters. With the 25.60 nm gold film thickness, the losses of the respective modes of Y and X-polarized core mode at 1550 nm are 1024.84 and 0.12 dB/cm with the loss ratio of 8540.33 between two polarizations. However, the losses of Y and X-polarized core mode at 1310 nm are 682.14 and 0.03 dB/cm, and the loss ratio is 22,738 with the gold film thickness of 55.30 nm. That indicates that the proposed filter has a higher loss ratio. Moreover, the crosstalk value with the fiber length of 200 μm at 1550 and 1310 nm are 178.01 and 118.49 dB, respectively. The bandwidths with crosstalk value greater than 20 dB are 640 and 180 nm. The designed polarization filter represents good filtering characteristics and allows great fabrication tolerances. Therefore, the designed hexagonal filter can be well applied in the domain of optical fiber communication.

Design of an asymmetric gold-coated photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR)

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.

Research on filtering characteristics of asymmetric photonic crystal fiber based on gold coating

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 1.55μm, 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 1μm to 2μm (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.

Highly efficient modified dual D-shaped PCF polarization filter

In this work, a highly efficient transverse-electric (TE) pass polarizer based on dual D-shaped photonic crystal fiber (PCF) is designed and analyzed. The PCF birefringence between the two polarized modes is efficiently controlled by adjusting the core region. Additionally, the dual D-shaped layers are coated by gold films to enhance the filtering characteristics. Therefore, the surface plasmon (SP) modes at the metal/dielectric interface are strongly coupled to the quasi-transverse-magnetic (TM) core mode with high confinement loss in comparable to the conventional D-shaped PCF. However, no coupling occurs with the quasi-TE core mode. Thus, a TE-pass polarizer is realized with an insertion loss (IL) of −0.39 dB/cm and −0.57 dB/cm at the two-telecommunication wavelengths of 1300 nm and 1550 nm, respectively. Moreover, the reported device has a wide operation bandwidth that extends from λ = 1.2 µm to λ = 1.6 µm where the crosstalk (CT) is less than −21 dB.

Refractive index sensing and filtering characteristics of side-polished and gold-coated photonic crystal fiber with a offset core

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.

Surface plasmon enhanced polarization filter of high birefringence photonic crystal fiber with a partial core based on filled silver nanowire

Abstract A novel kind of near-infrared communication window of photonic crystal fiber (PCF) polarization filter based on filled silver nanowire is proposed in this paper. The silver nanowire is selectively filled in a air hole of the cladding, and the performance of this PCF is analyzed by changing the diameter d2 of the near-core small air holes by finite element method (FEM). It is found that the confinement loss of x-polarization is 10738.726 dB/m, and that of y-polarization is 272.2325 dB/m at the resonance wavelength of 1.24 μm when the diameter d2 = 0.3 μm. Furthermore, when the fiber length is 1 mm, the crosstalks of x and y-polarization are −90.9 dB and 85 dB at the resonance wavelength of 1.24 μm and 1.32 μm, respectively. Thus, it can well realize the function of polarization filtering in two communication bands.

A miniaturized and high-bandwidth polarization filter based on a plasmonic and liquid crystal offset core photonic crystal fiber

Miniaturized and broadband polarization-dependent filters with high crosstalk values are extremely desirable for practical applications in the fields of optical communications and sensing. A miniaturized photonic crystal fiber (PCF) with highly broadband polarization filtering properties is proposed in this paper. Two relatively large air holes coated with a gold film on opposite sides of the liquid crystal-filled offset core are introduced in this PCF structure to produce highly broadband polarization-dependent filtering transmissions. The impacts of the filtering properties with variable structural parameters have been studied based on the finite element method. By altering the gold film thickness (t) to be 18.7 nm and 13.8 nm, the proposed broadband polarization filter offers high resonance peaks of 2041.79 dB/cm and 2342.88 dB/cm for y-polarized mode at the wavelengths of 1.31 μm and 1.55 μm, while the corresponding loss for x-polarized one is 0.10 dB/cm and 0.83 dB/cm, respectively. Moreover, the crosstalk of the 100-μm-long PCF polarization filter with t = 18.7 nm and t = 13.8 nm is up to 177.34 dB and 203.43 dB at 1.31 μm and 1.55 μm, respectively. As the fiber length is 100 μm, the bandwidth with the crosstalk less than − 20 dB can be up to 1200 nm, from 1.2 to 2.4 μm. In addition, the proposed broadband and miniaturized PCF filter is not sensitive to the temperature variation and exhibits stable filtering characteristics with the ± 1% fabrication tolerances.

Design of an ultrabroadband and compact filter based on square-lattice photonic crystal fiber with two large gold-coated air holes

An ultrabroadband and compact square-lattice photonic crystal fiber polarization filter based on surface plasmon resonance is proposed. Four large air holes are introduced near the core to destroy the symmetry of the original fiber structure so that the resonance wavelengths of x- and y-polarized core modes can be well separated. The inner walls of two large air holes along the x polarization direction are coated with gold film to generate the surface plasmon mode. In addition, to further enhance the coupling resonance strength between the core mode and the surface plasmon polariton mode, the six air holes near the gold-coated air holes are replaced by solid glass rods. Then the dispersion characteristics and loss spectrum of the proposed polarization filter are studied by the finite-element method. The results show that when the fiber length of the proposed filter is only 700 μm, ultrawideband y-polarized light transmission with a bandwidth of up to 730 nm in the wavelength range from 0.97 to 1.70 μm can be achieved. The effective filtering range covers all optical fiber communication bands from O to U. Moreover, the filter has excellent structural tolerances. These excellent properties are expected to make it a good candidate for a broadband polarization filter.

A novel gold-coated PCF polarization filter based on surface plasmon resonance

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.

Mid-infrared silicon photonic crystal fiber polarization filter based on surface plasmon resonance effect

In this paper, a novel silicon photonic crystal fiber (Si-PCF) polarization filter based on surface plasmon resonance effect is proposed for the first time. With the full-vector finite-element method, the mode coupling characteristics of the Si-PCF with the gold-coated film between the core mode and surface plasmon polariton mode are investigated, and the confinement losses are analyzed. The confinement losses of the Y-polarized core mode at the three resonant wavelengths 2.84, 3.29, and 4.53μm are 9235.9, 27097.5, and 97818.3 dB/m, respectively. The extinction ratio reaches -391 dB and the insertion loss is less than 1 dB when the Si-PCF length is 4 mm, along with the filter bandwidth of 2.75μm. Moreover, by modifying the fiber structure parameters, the filter bandwidth of the proposed three kinds of Si-PCF polarization filters can cover 2.75 to 7.80μm. It is believed that the proposed Si-PCF polarization filter has important applications in the mid-infrared laser and optical communication systems.

Design of diamond-shape photonic crystal fiber polarization filter based on surface plasma resonance effect**Project supported by the National Natural Science Foundation of China (Grant Nos. 61875238 and 61935007).

A novel plasmonic polarization filter based on the diamond-shape photonic crystal fiber (PCF) is proposed. The resonant coupling characteristics of the PCF polarization filter are investigated by the full-vector finite-element method. By optimizing the geometric parameters of the PCF, when the fiber length is 5 mm, the polarization filter has a bandwidth of 990 nm and an extinction ratio (ER) of lower than –20 dB. Moreover, a single wavelength polarization filter can also be achieved, along with an ER of –279.78 dB at wavelength 1.55 μm. It is believed that the proposed PCF polarization filterwill be very useful in laser and optical communication systems.

High-loss and broadband photonic crystal fiber polarization filter with two large apertures coated with gold layers

A high-loss broadband photonic crystal fiber polarization filter based on surface plasmon resonance is designed. The designed filter has two symmetrical large holes, and the holes are coated with a metal film, which greatly improves the loss. The characteristics of the polarization filter are calculated by the finite element method. The thickness of the metal layer and the arrangement and size of air holes near the core are discussed. The optimum structure of a metal-filled polarization filter in photonic crystal fibers is obtained. By modulating the parameters, the loss of the filter in the $y$y direction at 1.31 µm is 3261.7 dB/cm, while the loss in the $x$x direction is small. If the length of the optical fiber is set to 200 µm, the extinction ratio is greater than 20 dB, and the width is 1 µm, respectively. The filter has a simple structure and excellent performance.