Numerical investigation and optimization of a photonic crystal fiber for simultaneous dispersion compensation over S + C + L wavelength bands

In this paper, we numerically investigate and optimize the profile of a photonic crystal fiber (PCF) that can eliminate the residual dispersion from the telecom link as well as can provide identical dispersion compensation over S + C + L bands. A full-vectorial finite element method combined with genetic algorithm is used to optimize the fiber’s profile as well as to accurately determine its modal properties. The optimized PCF exhibits a dispersion of −98.3 ps/nm/km with a variance of ±0.55 ps/nm/km from 1.48 μm to 1.63 μm (i.e., over 150 nm bandwidth) and a zero dispersion slope. Macro-bending loss performance of the designed PCF is also studied and it is found that the fiber shows low bending losses for the smallest feasible bending radius of 5 mm. Further, sensitivity analysis has been carried out for the proposed fiber design and it has been found that a ±2% change in the fiber parameters may lead to a ±8% shift of the dispersion from its nominal value.     

Design of hybrid photonic crystal fiber: Polarization and dispersion properties

A highly birefringent dispersion compensating hybrid photonic crystal fiber is presented. This fiber successfully compensates the chromatic dispersion of standard single mode fiber over E- to L-communication bands. Simulation results reveal that it is possible to obtain a large negative dispersion coefficient of about −1054.4 ps/(nm km) and a relative dispersion slope of 0.0036 nm⁻¹ at the 1550 nm wavelength. The proposed fiber simultaneously provides a high birefringence of order 3.45 × 10⁻² at the 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest. For practical conditions, the sensitivity of the fibers dispersion properties to a ±2% variation around the optimum values is carefully studied and the nonlinearity of the proposed fiber is also reported and discussed. Such fibers are essential for high speed transmission system as a dispersion compensator, sensing applications, fiber loop mirrors as well as maintaining single polarization, and many nonlinear applications such as four-wave mixing, etc.     

1 × 4 coupler based on all solid five-core photonic crystal fibers

An improved 1 × 4 coupler based on all solid multi-core photonic crystal fiber is proposed and analyzed. The expressions to calculate the coupling length and the coupling efficiency are deduced based on the coupled-mode equations firstly. Then a full-vector finite element method (FEM) is used to calculate the coupling length and the coupling efficiency. Next, the propagation characteristics and the performances of the coupler are analyzed through using a full vector beam propagation method (BPM). Research shows that the results derived by FEM agree with that by BPM. The coupling length of the coupler is 4.1 mm at λ = 1.55 μm. A maximum coupling efficiency of 24.96% can be obtained. The coupling ratio is more than 22.5% over a wavelength range of 100 nm. The polarization-dependent loss at λ = 1.55 μm is equal to 0.73 dB. Finally, the influences of the micro-variation of structure parameters and the material refractive index on the working performances of the coupler are investigated.     

Microstructure holey fibers as wideband dispersion compensating media for high speed transmission system

This paper presents a dispersion compensating microstructure holey fiber for wideband transmission system. The finite element method with perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. According to simulation, negative dispersion coefficient of −1455 ps/(nm km) and a relative dispersion slope (RDS) close to that of single mode fiber of about 0.0036 nm⁻¹ is obtained at 1.55 μm. The variation of structural parameters is also studied to evaluate the tolerance of the fabrication. The proposed module can be used in 40 Gb/s dense wavelength division multiplexing (DWDM) systems in optical fiber communication networks.     

Polarization maintaining large nonlinear coefficient photonic crystal fibers using rotational hybrid cladding

In this paper, we present and explore a new hybrid cladding design for improved birefringence and highly nonlinear photonic crystal fibers (PCFs) in a broad range of wavelength bands. The birefringence of the fundamental mode in such a PCF is numerically analyzed using the finite element method (FEM). It is demonstrated that it is possible to design a simple highly nonlinear hybrid PCF (HyPCF) with a nonlinear coefficient of the about 46 W⁻¹ km⁻¹ at a 1.55 μm wavelength. According to simulation, the highest modal birefringence and lowest confinement loss of our proposed structure at the excitation wavelength of λ = 1.55 μm can be achieved at a magnitude of 1.77 × 10⁻² and of the order less than 10² dB/km with only five rings of air-holes in the fiber cladding.     

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.     

Photonic crystal fibers with high and flattened dispersion

We investigate the dispersion property of space filling mode of photonic crystal structures and find a new type of dispersion—structure induced dispersion. By incorporating this new source of dispersion we designed PCF with large normal dispersion ~ 350 ps²/km. Our simulation indicates the dispersion of such fiber changes less than 3% in 1.4-1.7 μm wavelength range and we also show that our design is insensitive to the structure changes.     

液芯高双折射率光子晶体光纤的特性研究

设计了一种纤芯区域由中心椭圆缺陷孔和其横排的上下两侧椭圆孔组成的高双折射率光子晶体光纤,并在其纤芯中心椭圆缺陷孔中填充高折射率液体物质二硫化碳.利用有限元法分析了该光子晶体光纤的双折射率、功率限制因子、模场分布及色散系数特性.研究结果表明:液芯光纤具有较高的纤芯功率限制因子,在波长0.6~1.6μm范围内实现了宽带大负色散系数,在波长1.55μm处光纤双折射率达到了6.8×10-2,即该结构液芯光子晶体光纤同时实现了宽带大负色散和高双折射率特性.通过结构参量容差性分析得到该光纤具有较好的偏振稳定性.