基于液体选择填充光子晶体光纤的波分解复用器研究

设计了一种基于液体选择填充三芯光子晶体光纤的1.31/1.55um波分解复用器。中间为缺失一个空气孔的普通二氧化硅纤芯,左右两纤芯填充了不同折射率的液体材料。根据光纤的消逝场耦合的模式理论,不对称相邻波导存在波长相关耦合。不同填充折射率的两纤芯与中间纤芯分别耦合,构成两个不同响应波长的光滤波器。通过选择合适光纤长度,可实现不同波长光的分离。采用全矢量有限元法分析了光纤的传输特性,讨论了填充不同折射率液体时波导间的模式耦合,得到了其匹配波长与耦合长度。基于光束传播法仿真发现,长度为4.88 mm的光纤能实现1.31/1.55 um波长光的解复用。     

Design of large-core single-mode Yb3+-doped photonic crystal fiber

The effective index of the cladding fundamental space-filling mode in photonic crystal fiber (PCF) is simulated by the effective index method. The variation of the effective index with the structure parameters of the fiber is achieved. For the first time, the relations of the V parameter of Yb3+-doped PCF with the refractive index of core and the structure parameters of the fiber are provided. the single-mode characteristics of large-core Yb3+-doped photonic crystal fibers with 7 and 19 missing air holes in the core are analyzed. The large-core single-mode Yb3+-doped photonic crystal fibers with core diameters of 50 μm, 100 μm and 150 μm are designed. The results provide theory instruction for the design and fabrication of fiber.     

Analysis of modal characteristics and thermal effects on photonic crystal fiber laser

In this paper, thermo-optics effects on fiber lasers based on index-guiding photonic crystal fibers (PCFs) are studied. The modal characteristics of the PCF lasers are discussed in terms of the thermal effects. Modal analysis of PCF has been done with help of plane wave expansion and supercell lattice methods. The thermal analysis is performed by obtaining the effective index of fundamental mode and core confinement factor (CCF) when the fiber laser was pumped. The results show that PCF laser structure has negligible modal sensitivity to thermal load in comparison to conventional fiber laser. Analyzing the mode performance of the fiber laser under thermal load shows that the assumed PCF laser at 80 W/m pump power show ∼500° rise in temperature and 0.34% propagation constant variation in fundamental mode index and 0.04% CCF variation in fundamental mode.     

光子晶体光纤分析及其在超连续谱中的应用

通过非线性效应，脉冲激光光谱可以大为扩展，得到应用价值很高的超连续谱（SC），借助光子晶体光纤(PCF)，能方便地产生这种非线性效应。研究了光子晶体光纤的包层等效折射率、归一化频率与PCF结构参数之间的关系,这是PCF实现无尽单模传输的原因。通过类似于阶跃折射率型光纤的理论,得到了光子晶体光纤的折射率和色散的计算模型。依据此模型所做的模拟结果表明,脉冲激光光谱有显著展宽。     

应用等效折射率模型研究光子晶体光纤

应用等效折射率模型研究了光子晶体光纤(PCF)的传播特性.介绍了光子晶体光纤的等效折射率模型.通过求解标量波动方程得到了光子晶体光纤包层基空间填充模的模式折射率,利用阶跃光纤的理论来研究光子晶体光纤的导模特性.应用此模型对不同结构光子晶体光纤包层区的等效折射率与波长的关系进行了讨论.包层区等效折射率与芯子的折射率差随波长的增加而增大,并由此阐述了光子晶体光纤的单模特性.数值分析得到光子晶体光纤的基模的模式折射率,并由此研究了光子晶体光纤的波导色散与结构参量的关系.分析表明,光子晶体光纤的波导色散随空气孔孔距的变化符合Maxwell方程的比例性质.空气孔的相对孔径对波导色散有重要的影响.这些分析表明光子晶体光纤具有可以灵活设计其色散特性的潜在应用前景.     

Study of Raman amplification properties in triangular photonic crystal fibers

The Raman properties of triangular photonic crystal fibers (PCFs) are analyzed in order to design a fiber for Raman amplification with enhanced performances. By casting the Raman intensity propagation equations, the Raman effective area and the Raman gain coefficient are introduced - two meaningful parameters that take into account the overlap between the pump and signal profiles. The behavior of these two parameters is examined in silica PCFs as a function of the geometrical characteristics of the triangular lattice. The numerical results show that a proper design of the hole diameter and the spacing between air holes can minimize the Raman effective area and maximize the Raman gain coefficient. The paper then focuses on PCFs with a germania-doped core. It is found that, for a given PCF cross section and dimension of the doped region, the Raman gain coefficient increases linearly with germania concentration. Moreover, by enlarging the doped region, it is discovered that a PCF with a germania-doped area internally tangent to the first ring of air holes has a maximum Raman gain coefficient. Finally, the calculated values of the Raman gain coefficient are compared with those of other highly nonlinear fibers presented in the literature, showing that a well-designed triangular PCF can significantly improve Raman gain performance.     

低弯曲损耗少模光纤传输特性研究

提出一种采用少模阶跃光纤与单模光纤连接的方法,实现低弯曲损耗传输的新型光纤通信系统。采用有限元法研究了在模场直径相同的情况下少模光纤纤芯半径与折射率差的关系,以及不同参数下光纤的弯曲损耗;采用光束传播法计算了少模光纤的各种模式与普通单模光纤的基模的连接损耗。证明了采用少模光纤可以利用模式间的正交性实现有效的单模传输,并具有低的弯曲损耗和连接损耗。     

Loss characteristics of helical-core fiber

A special optical fiber is investigated,which has a helical core in the cylindrical cladding.The beam propagation method(BPM) is used for analyzing the impacts of the geometric and physical parameters on the properties of mode losses of the helical-core fiber.The propagation loss is 0.32 dB/m for the fundamental mode and the propagation loss is 20.95 dB/m for the LP11 mode in the wavelength range of 1050-1065 nm when the core diameter is 19 μm,the pitch of the core’s helix is 2.66 mm,and the offset of the helix core from the center of the fiber axis is 31 μm.The core diameter of the single-mode helical-core fiber well exceeds that of the conventional large-mode-area fiber.The helical-core fiber can provide the effective large-mode-area single-mode operation without coiling fiber or selecting excitation mode.     

增益导引和折射率导引在大模场单模光纤设计中的应用

传统的大模场光纤是通过设计光纤结构来获得大模场面积的,可以实现的模场面积只能达到几百平方微米。增益导引和折射率导引相结合是实现大模场单模光纤的一种新方法。通过分析增益因子对折射率以及归一化频率的影响,得到了光纤中各阶模式截止条件与纤芯包层折射率差和增益因子的关系。最后以包层折射率为1.5734,纤芯折射率为1.5689,纤芯半径为50μm,10%(原子数分数)重掺杂钕离子的磷酸盐光纤作为模拟计算对象,当波长为1.064μm时,得到其模场直径大于90μm。对于普通光纤,增益导引和负折射率导引相结合的方法对实现大模场单模传输很有前景。     

新型大模场光子晶体光纤传输系统及其传输特性分析

通过在多模光子晶体光纤的两端分别连接一根单模光子晶体光纤,对其选择合适的参数,形成一种可以实现低弯曲损耗、大模场单模传输的光纤传输系统。运用数值仿真,分析了该传输系统在模场面积、弯曲损耗、连接损耗等方面的特性。研究结果表明,多模光子晶体光纤与单模光子晶体光纤所组成的系统可实现有效的单模传输;工作波长为1064nm时,多模光子晶体光纤在直波导状态时的基模模场面积可达1593μm2;在弯曲半径低至10cm时,多模光子晶体光纤仍然可以保持低损耗传输。经过对多模光子晶体光纤结构参数的优化,其与单模光子晶体光纤的连接损耗降低至0.085dB。     

Propagation characteristics of eccentric core fibers using point-matching method

The propagation characteristics of homogeneous single-mode optical fibers with eccentric core are analyzed by a numerical method based on the Improved Point-Matching Method (IPMM). The variation of fundamental mode propagation constant has been computed for various eccentricities with different fiber parameters.     

六角芯高双折射光子晶体光纤

提出了几种六角芯高双折射光子晶体光纤的新型结构,在这些结构中,包层不对称和纤芯不对称都能形成双折射,所有的空气孔都是圆形的,只需调整空气孔的大小、位置就能得到高双折射,这种光纤比椭圆形或矩形空气孔光纤更容易制作.最后,用半矢量平面波法计算模式双折射和波长的关系以及截止波长特性.与全矢量解相比,其带给有效折射率的误差仅约10-5.     

大模场抗弯曲全固态光纤的结构设计

提出了一种具有对称结构的大模场面积和低弯曲损耗的新型结构光纤,运用全矢量有限元法结合完美匹配层边界条件分析了光纤特性。该光纤由纤芯中的梯形折射率环和包层中的多层下陷层组成,仿真结果显示该光纤具有低弯曲损耗大模场单模传输的特性。对比分析了梯形谐振环、矩形谐振环、三角形谐振环结构光纤的弯曲损耗以及电场模式分布,实验结果显示梯形折射率环更具优越性。多层下陷层结构将模场限制在纤芯中,下陷层的数量大于2时模场面积基本上保持不变。研究结果表明,在波长为1 550 nm、弯曲半径为20 cm时,基模(FM)弯曲损耗只有0.056 868 dB/m,而高阶模(HOMs)损耗为3.58 dB/m,有效模场面积可达2 313.67μm²。该光纤对弯曲方向不敏感,在高功率光纤激光器放大器等光通信器件领域具有广阔的发展前景。     

零模间色散三芯光子晶体光纤

为了研究纤芯掺杂低折射率材料后三芯光子晶体光纤中任意两超模之间的模间色散特性,采用全矢量有限元法进行了仿真,取得了模间色散系数、零模间色散波长随纤芯折射率和结构参量变化的数据。结果表明,通过调节纤芯折射率、纤芯直径、空气孔直径以及孔间距这4个结构参量,可以使任意两超模间的模间色散在两个常用波段1.31m和1.55m处为0。该结果对于消除基于模分复用的光纤不同模式间因为模间色散导致的脉冲失真和实现零模间色散的模分复用技术是有帮助的。     

Propagation in Doubly Clad Single-Mode Fibers

General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters inner cladding/core radii ratio and inner cladding/core index differences ratio. LP01, LP11, and LP02 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 µm.     

Design of single-polarization single-mode photonic crystal fiber at 1.30 and 1.55 /spl mu/m

Single-polarization single-mode (SPSM) operation of a highly birefringent (HB) photonic crystal fiber (PCF) is investigated in detail by using a full-vector finite-element method (FEM) with anisotropic perfectly matched layers (PMLs). The cutoff wavelengths of the two linearly polarized principal states can be designed by varying the structure parameters of the PCF. The confinement loss and splice loss to standard single-mode fiber for particular SPSM PCFs are calculated and optimized at both 1.30 and 1.55 /spl mu/m.     

光子晶体光纤模式截止特性的理论分析

"无限单模传输"特性是光子晶体光纤最引人注目的特性,Birks等用有效折射率模型对其进行了合理的解释,但定量分析误差很大,而且由于进行了标量近似,填充比较大时不适用.我们仍采用该法,但作了改进:(1)有效纤芯半径和二阶模截止的归一化频率的选取更准确;(2)采用了全矢量方法.研究了光子晶体光纤的模式截止特性,得到了在不同结构参量下归一化频率与相对波数的依赖关系和二阶模截止的相对波数与结构参量的依赖关系,并由后一关系曲线及其渐近线将光子晶体光纤的工作区域划分为无限单模、单模和多模区域.结果与其它数值方法的结果一致性很好,而且方法较其它方法更为简便.     

Numerical modeling of photonic crystal fibers

Recent progress on numerical modeling methods for photonic crystal fibers (PCFs) such as the effective index approach, basis-function expansion approach, and numerical approach is described. An index-guiding PCF with an array of air holes surrounding the silica core region has special characteristics compared with conventional single-mode fibers (SMFs). Using a full modal vector model, the fundamental characteristics of PCFs such as cutoff wavelength, confinement loss, modal birefringence, and chromatic dispersion are numerically investigated.     

Propagation-mode-controlled fabrication of self-written waveguide in photosensitive polyimide for single-mode operation

We have developed a new fabrication method of single-mode self-written waveguide by controlling the propagation mode in an optical fiber. This method is very appropriate for repeatable fabrication of the single-mode self-written waveguide. Since a Gaussian-like near-field pattern is required for the fabrication of a tiny and uniform waveguide core, the propagation mode in a conventional optical communication fiber was controlled by coupling with an optical fiber having 3-/spl mu/m core, which shows a single-mode operation at visible wavelength region. Single-mode propagation at optical communication wavelength was confirmed for the fabricated self-written waveguide. The evaluated core diameter of the self-written waveguide was /spl sim/9.5 /spl mu/m.     

Fiber Lasers:Emerging in Major Markets

Since its inception,the fiber laser has attracted Since its inception, the fiber laser has attracted users because of its large gain and the ability to produce continuous lasing. The modern fiber laser is pumped by high-power multimode single-emitter diodes or diode bars, typically through a cladding surrounding a single-mode core.This single-mode core is typically 5～12 μm in diameter. The double-clad fiber consists of an inner singlemode core doped with the appropriate rare-earth ions such as neodymium, erbium, ytterbium and thulium.The cladding is made of undoped glass that has a lower index of refraction. The pump light is injected into the cladding and then propagates along the structure, passing through the active core and producing a population inversion.