Supermode analysis of multicore photonic crystal fibers

We reported on the supermode selection of total-internal-reflection photonic crystal fibers (PCFs) with linearly and circularly distributed multicores. The supermode characteristics were investigated using a full-vector finite-element method (FEM). The near and far-field patterns of supermodes supported by the multicore photonic crystal fiber were presented. A Talbot cavity was employed to select the wanted supermode.     

Analytical evaluation of bending loss oscillations in photonic crystal fibers

In this paper we present an analytical formula for bending loss oscillations in photonic crystal fibers (PCFs). We follow the approach originally adopted for conventional double-clad fibers and show that it can be applied to PCFs by substituting the structural parameters of the conventional fiber by their PCF counterparts. We then examine the spectral dependence of the critical bending radius and the position of the first order loss peak as a function of structural parameters of the PCF cladding such as the fill factor and the number of hole rings. Finally, we evaluate the precision of the analytical model by comparing the results to finite element calculations for a selection of PCF geometries.     

Loss-reduced highly birefringent selectively liquid-filled photonic crystal fibers

We have theoretically investigated the birefringence and loss properties of the selectively liquid-filled photonic crystal fibers with the liquid asymmetrically infiltrated into one-line air holes along x-axis. A high birefringence value B = 1.74 × 10⁻³ can be achieved at λ = 1.55 μm. By varying the index of the infiltrating liquid, the birefringence values are shown to be well tuned. In addition, the confinement losses can be efficiently reduced by diminishing the number of liquid holes, which is quite useful for optical devices.     

Analysis of high birefringence photonic crystal fiber with octagonal and squarely lattice

Aiming at the requirement of high birefringence, a new kind of photonic crystal fiber (PCF) with octagonal and squarely lattice is proposed. In this structure, squarely lattices are added in the inner layer to obtain high birefringence. Birefringence and dispersion as a function of wavelength and size of PCF are analyzed by using Finite Element Method (FEM). Simulation results show that this kind of PCF exhibits high birefringence with a magnitude of 10^?3, and one zero dispersion point is obtained simultaneously. In addition, the characteristics of PCF can be tuned by changing the size of fiber.     

Dispersion and polarization properties of elliptical air-hole-containing photonic crystal fibers

In this paper, we investigate the dispersion and polarization properties of photonic crystal fiber with one ring or more rings of elliptical air-holes using plane-wave expansion (PWE) method. By introducing three rings of elliptical air-holes, PCF with ultra-low and ultra-flattened dispersion is designed and a total dispersion curve between ±0.5 ps/nm/km from 1315 to 1855 nm wavelength range is demonstrated. Furthermore, the polarization property of these elliptical air-hole-containing PCFs is analyzed and the variation of the birefringence with the area and ellipticity of the elliptical air-holes are discussed.     

Cladding mode coupling in long-period gratings formed in photonic crystal fibers

We extend the improved effective index method (IEIM) to analyze the cladding mode of the photonic crystal fiber (PCF) and to predict cladding mode coupling in gratings. By introducing a new step-index fiber model for the PCF, the cladding mode coupling between a LP₀₁ core mode and HE₁₁ cladding mode in long-period gratings formed in PCF is accurately predicted by the IEIM. The fiber model works well for the PCF used here not only in predicting resonant mode coupling, but also in analyzing core and low-order cladding modes.     

三角结构三芯光子晶体光纤中的模式耦合特性分析

基于耦合模理论,得出了三角结构三芯光子晶体光纤(TTC-PCF)的耦合模方程.数值模拟研究了该结构中纤芯间的定向耦合特性,分析了光纤结构及入射波长对耦合系数的影响以及入射光振幅比对纤芯间能量耦合特性的影响.结果表明,通过调节入射光振幅比可实现对纤芯间耦合强度的连续调节.对比了耦合模理论与束传播法得到的结果,两者表现出很好的一致性.结合TTC-PCF展现的独特耦合传输性能,讨论了其在耦合强度连续可调光纤定向耦合器和大模场光纤激光器的设计与制备等方面的可能应用前景.     

Optical interleaver based on directional coupler in a 2D photonic crystal slab with triangular lattice of air holes

A small-size optical interleaver based on directional coupler in a 2D photonic crystal slab with triangular lattice of air holes is designed and theoretically simulated using plane wave expansion and finite-difference time-domain method. The interleaver is formed by two parallel and identical photonic crystal slab waveguides which are separated by three rows of air holes. The coupling region is designed below the light line to avoid vertical radiation. The simulated results show that the coupling coefficient is increased and the final length of the interleaver is decreased by enlarging the radius of the middle row of air holes. The transmission properties are analyzed after the interleaver’s structure is optimized, and around 100 GHz channel spacing can be got when the length of the interleaver is chosen as 40.5 μm.     

正方点阵上Fibonacci超元胞声子晶体的带结构

用平面波展开方法研究了水柱体作为填充物, 按照二维Fibonacci排列成超元胞填充在Hg基体中构成的声子晶体的声频带结构. 结果发现, 随着超元胞中准晶格常数的变化, 各个能带均出现三分裂. 对声场分布的研究发现了居间态的存在. 这些现象体现了准周期结构的特征. 关键词： Fibonacci排列 声子晶体 能带结构     

Characteristics analysis of extruded elliptical hole photonic crystal fibers with square air-core

An extruded elliptical hole photonic crystal fibers PCF with square air-core is proposed. By using a full vector finite-element method FV-FEM and anisotropic perfectly matched layers APML, the structure and optical properties of the proposed PCF are analyzed. Simulation results show that the birefringence of the proposed photonic crystal fiber can be up to the order of 10⁻², and has a flattened dispersion from 1.20 μm to 1.80 μm. The proposed PCF may have important application in super-continuum SC generation, dispersion compensation, fiber-optic sensing systems and other aspects.     

Transmission characteristics simulation of an erbium-doped lithium niobate film photonic crystal slab

A photonic crystal slab (PhC slab) which was constructed as a 2D hexagonal lattice with a finite depth was etched into an Er:LiNbO₃ film waveguide. The band diagrams and transmission spectra were simulated by plane wave expansion (PWE) and the finite-difference time-domain (FDTD) method. A high refractive index contrast of 0.5 enables strong light confinement in the vertical direction and a broad band gap. The simulated transmittance spectra indicate that the stop band is determined by lattice constant. The transmission spectra along ΓM of the PhC slab with a lattice constant 500 nm show a 250-nm broad stop band in the wavelength range from 1.33 to 1.58 μm and sharp band edge.     

空芯光子晶体光纤表面模损耗控制的研究

本文研究了纤芯结构对空芯光子晶体光纤光子带隙和传输损耗的影响,得到了适合光纤制备工艺的纤芯结构．首先利用平面波展开法计算了一定占空比三角形结构的空芯光子晶体光纤的带隙结构,给出了在传输波长λ=1．55μm时光纤的结构参数值,并模拟了纤芯直径对带隙位置和大小的影响,得出纤芯直径的取值范围,通过分析泄露损耗特性得出纤芯壁厚的取值．然后根据分析结果设计出了光纤端面图,运用全矢量有限元法模拟出在不同纤芯直径的情况下的模场分布,通过对比分析得出光纤的最佳纤芯半径R为1．6以-1．75A．研究结果表明,选择合适的纤芯结构既能满足空芯光子晶体光纤的光子带隙和损耗特征,又可以适当降低光纤制备工艺的难度．     

Band gap extension in honeycomb lattice two-dimensional plasma photonic crystals in the presence of dissipation

We investigate two types of honeycomb lattice two-dimensional plasma photonic crystals that possess large photonic band gaps in the presence of dissipation. We obtain a clear insight into the band structures and find imaginary parts of the eigenvalue band structure at the symmetry points display discontinuous behaviour when the filling factor of plasma in type-1 structure is low. Further more, we show how the photonic band gaps are affected by the normalized plasma frequency, radius of cylinder, dielectric constant and collision frequency. Our results demonstrate the band gap extension by increasing normalized plasma frequency in both type structures and radius of plasma cylinders in type-1 structure. The width of band gaps could also be enlarged by decreasing dielectric cylinder's radius. The bands shift toward lower frequencies when relative dielectric constant increases in both two types. These results may provide theoretical instructions to design new optoelectronic devices.     

Numerical analysis of a temperature sensor based on the photonic band gap effect in a photonic crystal fiber

In this paper we investigate, by the plane wave expansion method and an analytical model, the temperature effect on the photonic band gap fiber, and we report on a numerical demonstration of a temperature sensor based on the photonic band gap (PBG) shift in a solid core photonic crystal fiber (PCF) infiltrated with a high refractive index oil. The bandwidth and the position of the central wavelength of the band gap are the parameters of interests for our temperature sensing purpose. Simulation results were found to be in excellent agreement with the refractive index scaling law and the highest sensitivity of 3.21?nm/°C was achieved, and it will be even higher than the grating based sensors written in PCFs with similar structure.     

Analysis of photonic crystal fibers infiltrated with nematic liquid crystal

The spectral characteristic of a nematic liquid crystal photonic crystal fiber is analyzed. The locations of the transmission minima in the transmission spectrum can be evaluated by examining the modal cutoffs of specific modes in the liquid crystal inclusion. The selection criteria for these specific modes are based on the fraction of power residing in the core. Explicit expressions for these modal cutoffs are also derived.     

Sensing properties of fiber Bragg gratings in small-core Ge-doped photonic crystal fibers

We report about fiber Bragg gratings (FBGs) inscribed in two different types of small-core Ge-doped photonic crystal fibers with a UV laser. Sensing properties of the FBGs were systematically investigated by means of demonstrating the responses of Bragg wavelengths to temperature, strain, bending, and transverse-loading. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. Moreover, the bending and transverse-loading properties of the FBGs are sensitive to the fiber orientations. The reasonable analyses for these sensing properties also are presented.     

Photonic band gap failure in photonic crystal devices

The photonic crystal is an artificial material with periodic dielectric constant and the key factor to preserve their band features is its periodicity. When the number of periods of photonic crystal is decreased the photonic band gap cannot prevent the light of the corresponding frequencies from propagating in photonic crystal, in another word, photonic band gap will be failure. The minimum periods of photonic crystal device which can keep photonic band gap effective in miniaturization process is analyzed, the transmittance spectrum is calculated by the Finite-difference time-domain algorithm (FDTD) [1], the minimum periods is got in the simulation and the reason which affects the minimum periods is analyzed in this paper.     

Polarization properties of rectangular lattice photonic crystal fiber

In this paper, polarization properties and propagation characteristics of rectangular lattice photonic crystal fibers with elliptical air-holes are investigated by using the full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that the birefringence of the fiber is induced by asymmetries of the cladding. Moreover, by adjusting its structure parameters, such as the hole pitch Λ, and the air-hole elliptical rate η, we find the optimized design parameters of the fiber with high birefringence (the order of 10⁻²) and limited polarization mode dispersion, operating in a single mode region at an appropriate wavelength range.     

Control of photonic band gaps in one-dimensional photonic crystals

The photonic band gaps in one-dimensional photonic crystals (PCs) are theoretically investigated. A new method to broaden the photonic band gaps is introduced. Based on the similar method, a kind of photonic crystals is constructed to generate photonic band gaps with proportioned central frequencies. This technology can be used for designing nonlinear PCs for harmonic generation.     

一维Al/SrF2低温超导体-电介质光子晶体能带结构

基于二流体电子模型和平面波展开法,计算了一维Al/SrF2超导体-电介质光子晶体的能带结构.结果表明:随着超导层厚度的增加,第一光子带隙中心频率和截止频率均发生蓝移,且第一带隙宽度逐渐增加到一个峰值后又逐渐变窄.更重要的是,在低于临界温度的超低温环境中,温度的微小变化,对该类光子晶体的带隙宽度、中心频率以及截止频率均有...