Modified design of photonic crystal fibers with flattened dispersion

We present a modified method to design photonic crystal fibers with flattened dispersion characteristics. By replacing the circular air-holes of the first central ring with elliptic air-holes, we observe a more flattened dispersion curve. Plane-wave expansion (PWE) method is used to analyze the dispersion property in a high-index core PCF. The simulation results are presented, and ultra-low and ultra-flattened dispersion curves over wide wavelength range are demonstrated.     

Achieving both high birefringence and low leakage loss in double-clad photonic crystal fibers

In this paper, a novel double-clad photonic crystal fiber (DC-PCF) is proposed for achieving both high birefringence and low leakage loss. According to numerical simulation of the proposed PCF, the extraordinarily high birefringence (over 2×10⁻²) and low leakage loss of the order of 0.0001 dB/km over a large wavelength range are achieved simultaneously. Single-polarization single-mode (SPSM) operation with low leakage loss is also discussed and can be realized and optimized in the PCF by adopting suitable structure parameters.     

Stimulated emission from two-dimensional nested rectangle photonic crystal fibers

In this paper, we use the theory of spontaneous emission of two-level atoms embedded in photonic crystals. The unavoidable existence of a localized field with a defect mode and its basic properties are confirmed, which enables one to study the inherent laws of spontaneous emission from doped media. We combine the theory of spontaneous emission with numerical simulation for studying stimulated emission in a doped localized field and conditions for increasing the emission. The inherent laws for the cases where transmissivity is larger than unity and the negative imaginary part of the complex refractive index in doped compound lattices appears are also studied. The analysis of two-dimensional nested rectangle photonic crystal fibers (PCFs) with and without active impurities was performed using the finite-difference time-domain (FDTD) method. We find that, when active impurities are introduced into photonic crystal fibers, the negative imaginary part of the complex refractive index appears and the doped mode with high quality factor and great mode density occurs in the photonic forbidden band, thus amplifying substantially the stimulated emission.     

低原子序数材料窄带多层膜的研制

为研制极紫外波段窄带多层膜反射镜,采用低原子序数材料组合设计了30.4 nm波长处Mg/SiC,Si/SiC,Si/B4C和Si/C多层膜反射镜,并与极紫外波段传统的Mo/Si多层膜反射镜进行对比。采用直流磁控溅射技术制备了这些多层膜,在国家同步辐射实验室辐射与计量光束线完成了多层膜反射率测量,测量结果表明:Mg/SiC多层膜的带宽最小,为1.44 nm,且反射率最高,为44%;而Mo/Si多层膜的反射率仅为24%,带宽为3.11 nm。实验结果证明了采用低原子序数材料组成的多层膜的带宽要比常规多层膜窄,该方法可以应用于极紫外波段高分辨研究。     

Highly birefringent photonic crystal fibers with flattened dispersion and low effective mode area

A highly birefringent index-guiding photonic crystal fibers with flattened dispersion and low effective area is proposed by introducing elliptical air holes in the cladding and small holes both in the core area and in the cladding. With the plane wave expansion (PWE) method, the birefringent, dispersion and effective area of the fundamental modes in such photonic crystal fibers are analyzed in detail. The simulation result shows that high birefringence with a magnitude of the order of 10⁻³, flattened chromatic dispersion from 1100 nm to 1800 nm and low effective area (which mean high nonlinearity) are obtained. Furthermore, the influences on the birefringence and dispersion by geometrical parameters have also been discussed and a modest number of design parameters are given.     

Optimization control of modulation-instability gain in photonic crystal fibres with two-zero dispersion wavelengths

We design three kinds of photonic crystal fibres (PCF) with two zero-dispersion wavelengths (ZDWs) using the improved full vector index method (FVIM) and finite-difference frequency domain (FDFD) techniques. Based on these designed fibres, the effect of fibre structure, pump power and wavelength on the modulation instability (MI) gain in the anomalous dispersion region close to the second ZDW of the PCFs is comprehensively analysed in this paper. The analytical results show that an optimal MI gain can be obtained when the optimal pump wavelength (1530~nm) is slightly shorter than the second ZDW (1538~nm) and the optimal pump power is 250~W. Importantly, the total MI gain bandwidth has been increased to 260~nm for the first time, so far as we know, for an optimally-designed fibre with Λ = 1.4~nm and d/Λ = 0.676, and the gain profile became much smoother. The optimal pump wavelength relies on the second ZDW of the PCF whereas the optimal pump power depends on the corporate operation of the optimal fibre structure and optimal pump wavelength, which is important in designing the most appropriate PCF to attain higher broadband and gain amplification.     

Optical sensing with photonic crystal fibers

A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is organized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long‐period gratings and interferometric structures; the fourth one reports applications of these fibers for gas and liquid sensing; finally, the last section focuses on the exploitation of nonlinear effects in photonic crystal fibers for sensing.     

Theoretical study on the photonic band gap in one-dimensional photonic crystals with graded multilayer structure

We theoretically investigate the photonic band gap in one-dimensional photonic crystals with a graded multilayer structure. The proposed structure constitutes an alternating composite layer (metallic nanoparticles embedded in TiO2 film) and an air layer. Regarding the multilayer as a series of capacitance, effective optical properties are derived. The dispersion relation is obtained with the solution of the transfer matrix equation. With a graded structure in the composite layer, numerical results show that the position and width of the photonic band gap can be effectively modulated by varying the number of the graded composite layers, the volume fraction of nanoparticles and the external stimuli.     

Formation of transverse structure of CW light beams in photonic crystal fibers with saturable gain

Transverse beam dynamics in a nonlinear photonic crystal fiber is studied numerically. The field decomposition in terms of Laguerre-Gaussian functions is used to simulate the propagation of a beam along the fiber. Symmetry breakdown due to the competition of transverse modes is demonstrated. Both the few-mode photonic crystal fiber and the endlessly single-mode photonic-crystal fiber are considered. In the photonic crystal fiber with broad gain region, the resulting beam structure is shown to depend strongly upon the initial conditions.     

光子晶体光纤放大器增益特性的实验研究

 采用掺Yb³⁺双包层光子晶体光纤作为放大器的增益介质,在双端泵浦方式下,理论并实验研究了不同信号光时放大器的增益特性。在双端泵浦方式下,泵浦总功率为150.2 W、信号光功率为6 W时,获得了72 W的功率输出,斜率效率达到了60%。实验发现当泵浦总功率超过一定值时,由光纤端面反射形成的振荡腔引起放大器寄生振荡,并由于各种非线性效应出现了自脉动现象,影响了输出功率的进一步提高。     

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．     

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.     

由单负材料组成的含有缺陷层的一维光子晶体结构中的缺陷模

用转移矩阵方法研究了由单负材料组成的含有缺陷层的一维光子晶体的透射特性.研究结果表明:当缺陷层存在时,会在原有光子晶体的禁带中出现缺陷模.缺陷模的位置随杂质层磁导率μ的增加从禁带的高频端向低频端移动;但随杂质层介电常数ε的增加却从禁带的低频端向高频端移动.利用该特性可以实现对光传播的动态调控. 关键词： 单负材料 光子晶体 缺陷模     

胶体晶体微结构光纤传输特性研究

介绍了胶体晶体微结构光纤的结构, 采用时域有限差分法研究了微结构胶体晶体光纤的传输特性. 建立了该结构的FDTD模型, 计算了其透射谱和不同波长的传输场分布. 搭建了光学系统, 测量了实验制备的胶体晶体微结构光纤的透射谱, 并将其与模拟所得透射谱进行比较, 具有良好的一致性. 胶体晶体微结构光纤的传输场分布结果表明, 胶体晶体在不同波长下改变光纤传输场分布.     

加载光子带隙膜系BaF2晶体闪烁光慢成分抑制和抗γ辐照损伤的研究

 根据BaF₂晶体闪烁光快、慢成分波段的不同，设计并制备了用于抑制该晶体闪烁光慢成分的Al₂O₃/MgF₂/Al/MgF₂…光子带隙膜系。实验结果显示：加载光子带隙膜系的BaF₂晶体，其闪烁光快/慢成分比提高80倍以上；经剂量为1×10⁵ Gy的60Co γ射线辐照后，其透射光谱、发射光谱和发光衰减时间谱没有明显的变化,这表明由光子带隙膜系与BaF₂晶体所构成的快闪烁器件不仅可有效避免慢成分的干扰，而且还具有很强的抗γ辐射性能。     

胶体晶体微结构光纤传输特性研究

介绍了胶体晶体微结构光纤的结构, 采用时域有限差分法研究了微结构胶体晶体光纤的传输特性. 建立了该结构的FDTD模型, 计算了其透射谱和不同波长的传输场分布. 搭建了光学系统, 测量了实验制备的胶体晶体微结构光纤的透射谱, 并将其与模拟所得透射谱进行比较, 具有良好的一致性. 胶体晶体微结构光纤的传输场分布结果表明, 胶体晶体在不同波长下改变光纤传输场分布.     

空芯光子晶体光纤光子带隙的测量与数值模拟

用全矢量平面波法计算三角结构光子晶体光纤的带隙. 用透射法测量了自制的空芯光子晶体光纤的透射谱,得到了它在可见光波段透射强度与波长的关系,并在随后的实验中观测到了传光的模场图.通过理论模拟了实验所用的空芯光子晶体光纤的带隙图,与实验结果具有较好的一致性. 关键词： 空芯光子晶体光纤 光子带隙 全矢量平面波法 透射     

基于左手材料的高增益双频带微带天线

左手材料具有平板透镜聚焦效应,突破电磁波的衍射极限实现倏逝波的放大,其覆盖于微带天线上方,可以提高天线增益。设计了一种应用于UHF和WLAN的双频微带天线,通过在接地板上刻蚀己字形弯折缝隙的方法实现双频谐振。为了改善微带天线低频段的增益,设计了一种新型的哑铃型结构双频段左手材料,将其作为微带天线的覆层。测试结果表明,覆层左手材料微带天线的低频段和高频段的峰值增益分别为2.1 dBi和7.4 dBi。     

高双折射纳米结构光子晶体光纤特性研究

设计了一种高双折射高非线性纳米结构光子晶体光纤,利用电磁场散射的多极理论研究了这种光纤的双折射、基模模场、色散以及非线性特性.数值研究发现,加大纤芯及包层空气孔的非对称程度,可使双折射变大,其双折射最大值可达1.918×10-2.通过调节孔节距大小,可将双折射最大值调至所需波长处,孔节距为400nm的纳米光子晶体光纤在800nm波长处非线性系数高达0.2m-1.W-1,同时在750—1000nm的波段有较大的双折射值,高双折射和高非线性在纳米结构光子晶体光纤中实现了完美的结合.对新型纳米光子器件的研制和集成光学的发展具有重要意义.     

Birefringent photonic crystal fibers with zero polarimetric sensitivity to temperature

We designed, fabricated, and characterized birefringent holey fibers with zero polarimetric sensitivity to temperature. The sensitivity measurements were carried out in a wide spectral range of 0.68–1.55 μm in fibers with different hole and pitch values and with birefringence induced by a pair of large holes adjacent to the core. Our results show that zero sensitivity to temperature can be obtained at certain wavelengths for the bare fibers with properly adjusted geometrical parameters. Moreover, the spectral measurements of the sensitivity to temperature are in good agreement with the modeling results for all the investigated fibers.