Dispersion-ultra-flattened square-lattice photonic crystal fiber with small effective mode area and low confinement loss

Proposed in this paper is a simple square-lattice photonic crystal fiber (PCF) with nearly zero flattened dispersion (NZFD) over a wide wavelength span. We make a trade-off between the coupling efficiency and the effective mode area in order to obtain relatively low confinement loss and high nonlinearity. Via full-vector finite element method with hybrid edge/node elements, over 1137–1710 nm, the dispersion coefficient is 0.3 ± 0.3 ps/(km nm), the confinement loss is relatively low, in level of 10⁻⁷–10⁻⁴ dB/km and the effective mode area remains 5.88–6.59 μm².     

New nonlinear and dispersion flattened photonic crystal fiber with low confinement loss

A new nonlinear dispersion flattened photonic crystal fiber with low confinement loss is proposed. This fiber has threefold symmetry core. The doped region in the core and the big air-holes in the 1st ring can make high nonlinearity in the PCF. And the small air-holes in the 1st ring and the radial increasing diameters air-holes rings in cladding can be used to achieve the dispersion properties of the PCF. We can achieve the optimized optical properties by carefully selecting the PCFs structure parameters. A PCF with flattened dispersion is obtained. The dispersion is less than 0.8 ps/(nm km) and is larger than −0.7 ps/(nm km) from 1.515 μm to 1.622 μm. The nonlinear coefficient is about 12.6456 W⁻¹ km⁻¹, the fundamental mode area is about 10.2579 μm². The confinement loss is 0.30641 dB/km. This work may be useful for effective design and fabrication of dispersion flattened photonic crystal fibers with high nonlinearities.     

Improved high birefringence photonic crystal fibres with dispersion flattened and single mode operation

A kind of improved high birefringence photonic crystal fibre (PCF) is proposed in this paper. The characteristics of birefringence, dispersion and leakage loss are studied by the multipole method. Numerical results show that the improved PCF possesses the properties of a flat dispersion and single mode operation. Moreover, with the operating wavelength λ = 1.55μm, the modal birefringence increases greatly in comparison with that of the original PCF, and the leakage loss is about 10⁴ times smaller than that of the original PCF because the modification gives rise to the strong confinement of guided modes. It is expected that the improved PCF can be used as high birefringence and dispersion flattened fibres.     

Highly nonlinear dispersion-flattened square photonic crystal fibers with low confinement losses

A new simple structure of an index-guiding highly nonlinear dispersion-flattened square photonic crystal fiber (HNDFSPCF) with low confinement losses is proposed. The results reveal that it is possible to design five-rings HNDF-SPCFs with a flattened dispersion of 0.43 ps/(nm·km), low dispersion slope of -0:02 ps/(nm²·km), low confinement loss of approximately 10³ dB/m, and a large nonlinear coefficient of approximately 35W^-1 km^-1 at 1.55 μm. It is also observed that the confinement loss is less than 10^-1 dB/m in the wavelength range of 1.2 –1.7 μm.     

A broadband ultra flattened chromatic dispersion microstructured fiber for optical communications

A double-cladding microstructured fiber (MF) is proposed in this paper. The inner cladding of this optical fiber is composed of elliptical air holes and silica. The dependence of dispersion on the diameter of the air holes, the pitch, and the axes of the elliptical holes is investigated numerically. The proposed fiber possesses an ultra flattened dispersion curve over a wide wavelength range, and its dispersion value is small. The effective mode area is approaching to 60 μm², and the confinement loss is as low as <0.025 dB/km at 1550 nm. While choosing suitable structure parameters, an ultra dispersion-flattened MF within a broadband from1000 nm to 1900 nm can be achieved. The dispersion fluctuation is 0.6-1.0 ps/(nm·km) in all S, C and L band.     

Multiple defect-core hexagonal photonic crystal fiber with flattened dispersion and polarization maintaining properties

In this paper, we present a dispersion controlling technique with a multiple defect-core hexagonal photonic crystal fiber (MD-HPCF). By omitting air holes in the core region of the conventional HPCF and adjusting the size of air holes around the newly formed core, we can successfully design low flattened dispersion PCF with low confinement loss, as well as high birefringence. The low flattened dispersion feature, as well as the low confinement losses and high birefringence are the main advantages of the proposed PCF structure, making it suitable as chromatic dispersion controller, dispersion compensator, and/or polarization maintaining fiber.     

Design and characterization of single mode circular photonic crystal fiber for broadband dispersion compensation

In this paper, we present a single mode circular photonic crystal fiber (C-PCF) for broadband dispersion compensation covering 1400 to 1610 nm wavelength band over the telecommunication windows. Investigations of guiding properties are carried out using finite element method (FEM) with circular perfectly matched layer boundary condition. Numerical study reveals that a negative dispersion coefficient of about −386.57 to −971.44 ps/(nm km) is possible to obtain over the wavelength ranging from 1400 to 1610 nm with a relative dispersion slope (RDS) of about 0.0036 nm⁻¹ at 1550 nm wavelength. In addition, the single mode behaviour of C-PCF is demonstrated by employing V parameter. According to simulation, it is found that the proposed C-PCF acts as a single mode fiber within 1340 to 1640 nm wavelength. Moreover, effective dispersion, relative dispersion slope, birefringence and confinement loss are also presented and discussed.     

Polarization-maintaining photonic crystal fibers with near-zero flattened dispersion in 1.06 μm waveband for medical applications

In this paper we present the design of a modified hexagonal photonic crystal fiber (PCF) having high birefringence and a near-zero flattened dispersion. Using the finite-difference method (FDM), it is shown that the proposed multiple Gedoped core hexagonal PCF exhibits a high birefringence of order 10⁻³ and a nearly zero flattened dispersion in the optical coherence tomography (OCT) waveband. In addition, the proposed PCF has a confinement loss of less than 10⁻⁸ dB/m at 1.06 μm. PCFs with such properties are considered suitable for both endoscopic OCT and other experimental setups employing 1.06 μm lasers.     

新型矩形点阵光子晶体光纤的高双折射负色散效应

设计了一种新型矩形点阵光子晶体光纤,该光纤纤芯缺失一根空气柱,包层沿光纤长度方向在普通矩形点阵光子晶体光纤中每两列之间隔一行插入一列空气孔而形成正方形网孔结构.采用全矢量有限元法并结合各向异性完美匹配边界条件,对该光纤的色散、双折射和约束损耗进行了数值模拟.结果发现,该光纤具有高双折射负色散效应和较强的模约束能力,约束损耗小于10-2dB·m-1,通过改变光纤结构参数(即空气孔间隔Λ和相对孔间隔d/Λ),可以调节该光纤高双折射负色散工作波长.若调整光纤结构参数Λ=2.0μm,d/Λ=0.4,该光纤在C波段(1.53—1.565μm)呈现负色散并具有负色散斜率,双折射高达10-2,非线性系数接近55km-1W-1.该光纤将在保偏光通信、色散补偿以及基于四波混频的波长转换器设计等方面具有重要的应用.     

Design of large mode area multicore photonic crystal fiber with a flat-top mode

A large mode area multicore photonic crystal fiber with a flattened fundamental mode is proposed in this paper. Another two kinds of single core fibers are also presented as comparison. The modal characteristics such as effective mode area and confinement loss are investigated using the finite element method. Numerical results show that a combination of flattened fundamental mode, large mode area and ultralow loss is obtained in the multicore fiber by introducing higher refractive index in the core region.     

A New Type of Terahertz Waveguides

A new type of THz waveguides, which employs a solid polyethylene rod as the core and polyethylene tubes in a periodic array of square lattice as the cladding, is proposed. Optical properties of this new THz waveguide, especially in dispersion, confinement loss and single mode property, are investigated in detail with the plane wave expansion method and the beam propagation method. Numerical results demonstrate that the new THz waveguide can reach not only low dispersion but also low confinement loss at single mode propagation. Therefore, the square lattice structure is a better candidate as THz waveguides than the triangular ones.     

三种典型结构光子晶体光纤基本特性的比较和分析

应用多极法比较和分析了相同结构参数下的正六边形、正八边形和正十边形光子晶体光纤的色散系数、色散斜率、非线性系数和限制损耗.正六边形光子晶体光纤更适合用于色散补偿和高非线性的研究,在波长0.8 μm处的非线性系数达到了0.37 m^-1·W^-1;正十边形光子晶体光纤更适合用于色散平坦和低限制损耗的研究,在波长0.8 μm处的限制损耗相对正六边形光子晶体光纤减小了约3000个数量级,在1.4—1.65 μm波长范围内,正十边形光纤的色散系数介于-0.07—0.17 p     

Design and analysis of novel highly nonlinear photonic crystal fibers with ultra-flattened chromatic dispersion

The present article describes novel highly nonlinear photonic crystal fibers (HN-PCFs) with flattened chromatic dispersion and low confinement losses. The proposed design has been simulated based on the finite-difference method with anisotropic perfectly matched layers absorbing boundary condition. It is proved that the design novel HN-PCFs is obtained a nonlinear coefficient greater than 45 W⁻¹ km⁻¹ and low dispersion slope −0.009 ps/(nm².km) at 1.55 μm wavelength. In addition, results from numerical simulation show that the ultra-flattened dispersion of 0 ± 0.65 ps/(nm.km) can be obtained in a 1.36-1.62 μm wavelength range with confinement losses lower than 10⁻⁷ dB/m in the same wavelength range. Another advantage of the proposed HN-PCFs is that it possessed modest number of design parameters.     

Dispersion-Flattened Modified Hexagonal Photonic Crystal Fibers with Low Confinement Loss

This paper presents dispersion-flattened modified hexagonal photonic crystal fibers (MH-PCFs) with extremely low confinement loss. The finite difference method (FDM) with an anisotropic perfectly matched boundary layer (PML) is used to investigate the chromatic dispersion and confinement properties. It is demonstrated that it is possible to obtain an ultra-flattened dispersion of 0 ± 0:41 ps/(nm·km) in the wavelength range of 1.35–1.65 mm and an extremely low confinement loss of less than 10⁻⁴ dB/km from a four-ring MH-PCF. Effective single-mode operation of the MH-PCF is confirmed for the entire band of interest.     

Dispersion properties,birefringence and confinement loss of rotational elliptic air-hole photonic crystal fiber

Dispersion properties, birefringence and confinement loss between the circular air-hole photonic crystal fiber (CAHPCF) and rotational elliptical air-hole photonic crystal fiber (REAHPCF) are investigated numerically by means of a plane-wave expansion method and a finite element method. Results show that the performances of REAHPCF on flatter dispersion curve, single mode, high birefringence and low confinement loss is better than that of CAHPCF.     

A new design of low-loss and ultra-flat zero dispersion photonic crystal fiber using hollow ring defect

New hollow ring defect structure is introduced in photonic crystal fiber design for ultra- flat zero dispersion with very low waveguide losses. The hollow ring defect consisted of a central hole surrounded by a doped silica ring provides highly flexible defect engineering capabilities in photonic crystal fibers to achieve precise control of dispersion value and dispersion slope while independently maintaining low waveguide losses, which was not attainable in previous designs. A nearly flat zero dispersion of D=0±0.51 ps/nm km was obtained in the wavelength range of 1.44–1.61 μm with the maximum slope of ?2.7×10^?2 ps/nm² km. The confinement loss was less than 5.75×10^?8 dB/m along with the bending loss of 2.8×10^?6 dB/m for the radius of 10 mm, and splice loss of less than 1.57 dB to conventional single mode fiber at 1.55 μm.     

Dispersion and Confinement Loss Control in Modified Hexagonal Photonic Crystal Fibers

This paper presents a novel technique for the control of chromatic dispersion and confinement loss in hexagonal photonic crystal fibers (H-PCFs). It is demonstrated that it is possible to obtain very low chromatic dispersion of 0 ± 0:38 ps/(nm·km) in the wavelength range of 1.41 to 1.66 μm and confinement loss of less than 0.0001 dB/km from a six ring modified H-PCF (MH-PCF). The higher order dispersion at 1.55 μm is about −0.001 ps/(nm²-km).     

A novel broadband dispersion compensating square-lattice photonic crystal fiber

In this paper we propose a novel square-lattice photonic crystal fiber (SPCF) for dispersion compensation in a wide range of wavelengths. Perfectly matched layer (PML) is considered for the boundary treatment and an efficient compact two dimensional finite-difference frequency-domain (2-D FDFD) method is employed to model square-lattice photonic crystal fibers (SPCF). It has been shown with selecting appropriate parameters for SPCF it is possible to obtain high negative dispersion coefficient, negative dispersion slope over E to L wavelengths, confinement losses less than 10^?5?dB/m and splice losses less than 3.6 dB. The designed SPCF exhibits a relative dispersion slope (RDS) of 3.543 × 10^?3 nm^?1 which is closely matched to the RDS of conventional single mode fibers.     

Characteristics analysis of photonic crystal fiber with rhombus air-core

Aiming at the requirement of low confinement loss and multiple zero dispersion points in fiber-optic sensing systems and optical communication networks, a new type of photonic crystal fiber (PCF) with rhombus air-core is proposed. By using finite element method (FEM), the structural and optical properties of the proposed PCF are analyzed. Simulation results reveal that the proposed PCF has lower confinement loss with 10^?3 dB/m and higher birefringence. Besides, two zero dispersion points can be obtained after optimization. The proposed PCF may have important applications in fiber-optic sensing systems and other aspects.     

Mode field radius of dispersion flattened single mode fibers

We report a comparison between the main definitions of the mode field radius (MFR) in various dispersion flattened single mode fibers. The study shows that the Petermann and gaussian spot sizes for triangular core W-type fiber are larger compared to the fibers with other profiles and similar dispersion properties so as to give minimum splice loss.