基于金线填充的双芯光子晶体光纤偏振分束器

提出了一种基于金线填充的双芯光子晶体光纤超短偏振分束器,并进行了有限元分析.金线表面激发的表面等离子激元与双芯光子晶体光纤纤芯模之间的强烈耦合,导致更短的偏振分束器长度和更大的工作带宽.与同类的偏振分束器相比,所提出的偏振分柬器能同时实现较短的长度和较高的消光比.数值结果表明,长度为0.263 mm的偏振分束器,在波长1.55 μm处消光比达-70 dB,-20 dB消光比带宽为124 nm.     

一种新型的基于四孔单元光子晶体光纤的设计与分析

设计了一种基于四孔单元的光子晶体光纤,它可以满足光通信系统中高双折射率、负色散和低限制损耗的要求,比起通常的三角结构光纤有着更高的双折射率,并且结构制作也较简单。采用全矢量有限元法和各项异性完美匹配层法对所设计的光纤进行了仿真研究。仿真结果表明:该光纤在1.55μm波长处可获得10~(-2)数量级的双折射率,在较宽广的波段范围具有大的负色散,限制损耗低于10~(-9)dB/m;该光纤在保偏光纤、单极化单模光纤、色散补偿光纤等方面具有重要的应用。     

Partially liquid-filled hollow-core photonic crystal fiber polarizer

A compact fiber polarizer is demonstrated by the filling of selected air holes of a hollow-core photonic crystal fiber (PCF) with a liquid. The liquid-filling results in an asymmetric waveguide structure, leading to a large polarization dependent loss. A 6 mm long ethanol-filled PCF exhibits a polarization extinction ratio of ～18 dB over a wavelength range from 1480 nm to 1600 nm.     

Theoretical simulation of a polarization splitter based on dual-core soft glass PCF with micron-scale gold wire

A polarization splitter based on dual-core soft glass photonic crystal fiber(PCF) filled with micron-scale gold wire is proposed. The characteristics of the polarization splitter are studied by changing the structural parameters of the PCF and the diameter of the gold wire with the finite element method(FEM). The simulation results reveal that the coupling length ratio of the soft glass-based PCF is close to 2 and the corresponding curve is more flat than that of the silica-based PCF.The broadband bandwidth is 226 nm in which the extinction ratio is lower than-20 d B by the soft glass-based PCF, i.e.,from 1465 nm to 1691 nm which is competitive in the reported polarization splitters, and the bandwidth is just 32 nm by the silica-based PCF. The insertion loss by our polarization splitter is just 0.00248 d B and 0.43 d B at the wavelength of 1.47 μm and 1.55 μm. The birefringence is obviously increased and the coupling length is decreased by filling gold wire into the soft glass-based or the silica-based PCF. Also the birefringence based on the silica-based PCF is much larger than that based on the soft glass-based PCF whether or not the gold wire is introduced. The fabrication tolerance of the polarization splitter is also considered by changing the structural parameters. The polarization splitter possesses broad bandwidth, low insertion loss, simple structure and high fabrication tolerance.     

光子晶体光纤中交叉相位调制光谱展宽特性研究

实验研究了超高速时分复用信号与探测光同向传输,在色散平坦高非线性光子晶体光纤中的交叉相位调制光谱展宽特性,从光谱学的角度分析了信号光波长漂移,泵浦光与信号光总功率及功率比,二者偏振态失配对交叉相位调制光谱展宽效应的影响,探讨了实现偏振不敏感交叉相位调制效应的可行性。研究发现,在36 nm波长范围,总功率大于23 dBm,泵浦光与信号光功率比合理,二者偏振态匹配时交叉相位调制效果最好,交叉相位调制的偏振相关性为11 dB,指出利用色散平坦高非线性光子晶体光纤中的残余双折射,调节泵浦光与光纤双折射主轴成45°,可以实现偏振不敏感交叉相位调制效应,随后的理论模拟和实验结果相一致。研究结果为实现基于交叉相位调制原理工作的超快全光信号处理器件作了充分准备。     

Coupling characteristics of high birefringence dual-core As2S3 rectangular lattice photonic crystal fiber

A type of As2S3 chalcogenide glass mid-infrared dual-core photonic crystal fiber has been proposed.The dualcore photonic crystal fiber(PCF) consists of two asymmetric cores.The high polarization property and the coupling characteristics have been studied by using the finite element method and mode coupling theory.Numerical results show that the birefringence at wavelength λ = 10 μm is up to 0.01386 and the coupling length can reach wavelength λ = 5 μm,261 μm and 271.44 μm for x-polarized mode and y-polarized mode,respectively.It demonstrates that a 6.786-mm-long fiber can exhibit an extinction ratio of better than 10 dB and a bandwidth of 180 nm.     

Generation of a mid-infrared broadband polarized supercontinuum in As₂Se₃ photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber(PCF) is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power(i.e.,37 mW),which indicates that the polarization state is well maintained.     

Equal channel spacing Sagnac filter using high-birefringent photonic crystal fibers

An equal channel spacing Sagnac filter is proposed using a high-birefringent photonic crystal fiber （PCF） with birefringence square to the operation wavelength. A PCF with four smaller central air holes sur-rounded by larger air holes is applied in a Sagnac filter with optimized parameters to achieve equal channel spacing of 0.8 nm. Given that the birefringence of this PCF is square to the operation wavelength, the channel spacing of the proposed filter changes by only 0.03 nm within a wavelength range from 1400 to 1650 nm; this is about one order of magnitude less than that constructed with conventional high-birefringent fibers.     

Photonic crystal fiber polarization filter with two large apertures coated with gold layers

A novel photonic crystal fiber(PCF) polarization filter is designed and fabricated; it consists of two large apertures coated with gold. The asymmetric structure separates the resonance position in the vertical direction well. Due to the metal layer covering, loss is greatly improved. Finite element method is applied for numerical simulation. The influences of varying gold thickness and varying the diameters and the center positions of the larger apertures on filtering performance are evaluated. Theory of coupling between surface plasma and core mode is introduced. By modulating the parameters, we realize a single polarization filter at 1.31 μm and 1.55 μm. The basal mode loss in the y direction can reach 1408.80 dB/cm at 1.31 μm and 1911.22 dB/cm at 1.55 μm respectively, but basal mode loss in the x direction is relatively small, 0.82 dB/cm and 1.87 dB/cm. In addition, two kinds of broadband polarization filters are proposed. If the fiber length is set to 200 μm,the extinction ratio is greater than 20 dB with width of 570 nm and 490 nm. The filter has simple structure and excellent performance.     

A stable and tunable linear polarization single longitudinal mode fiber ring laser

A stable and tunable linear polarization single longitudinal mode fiber ring laser is proposed and demonstrated. A high extinction ratio spatial mode interference filter utilizing two-mode graded-index fiber supresses irregular side modes effectively, the combination of fiber polarizer and polarization maintaining fiber act as a polarization dependent comb filter, and tunable bandpass filter is adopted to select proper lasing wavelength. The power fluctuation and wavelength fluctuation at 1549.88 nm are less than 0.05 dB and 0.02 nm in 1 h, respectively. Only one longitudinal mode appears within a free spectral range of 7.5 GHz, and the degree of polarization in percentage is approximately as high as 99.07%.     

A novel polarization splitter based on dual-core hybrid photonic crystal fibers

Highly birefringent dual-core photonic crystal fibers (PCFs) can be used as a polarization splitter because the orthogonal polarization modes with dissimilar coupling lengths are easily separated from each other. Different from the traditional methods achieving high birefringence, a new highly birefringent hybrid PCF that guides light by both index guiding and bandgap guiding is proposed. Firstly, a novel polarization splitter based on this kind of dual-core hybrid PCF is designed. The transmission modes, coupling lengths for the two orthogonal polarizations and performance of the proposed polarization splitter are investigated and numerically analyzed. The results demonstrate that it is possible to obtain a 4.72-mm-long polarization splitter. The splitting ratio is better than −20 dB in a large wavelength range of 1.53-1.72 μm. Its bandwidth is about 190 nm.     

Generation of a mid-infrared broadband polarized supercontinuum in As2Se3 photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber（PCF） is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power（i.e.,37 mW）,which indicates that the polarization state is well maintained.     

Coupling characteristics of high birefringence dual-core As2S3 rectangular lattice photonic crystal fiber

A type of As₂S₃ chalcogenide glass mid-infrared dual-core photonic crystal fiber has been proposed. The dual-core photonic crystal fiber (PCF) consists of two asymmetric cores. The high polarization property and the coupling characteristics have been studied by using the finite element method and mode coupling theory. Numerical results show that the birefringence at wavelength λ = 10 μm is up to 0.01386 and the coupling length can reach wavelength λ = 5 μm, 261 μm and 271.44 μm for x-polarized mode and y-polarized mode, respectively. It demonstrates that a 6.786-mm-long fiber can exhibit an extinction ratio of better than -10 dB and a bandwidth of 180 nm.     

Switchable multi-wavelength fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer with photonic crystal fiber

Switchable multi-wavelength fiber ring laser with an in-fiber Mach-Zehnder interferometer incorporated into the ring cavity serving as wavelength-selective filter at room temperature is demonstrated. The filter is formed by splicing a section of few-mode photonic crystal fiber (PCF) and two segments of single mode fiber (SMF) with the air-holes on the both sides of PCF intentionally collapsed in the vicinity of the splices. By adjusting the states of the polarization controller (PC) appropriately, the laser can be switched among the stable single-, dual- and triple-wavelength lasing operations by exploiting polarization hole burning (PHB) effect.     

八边形晶格双芯光子晶体光纤偏振分束器

分别以碲玻璃和SF6玻璃作为基质材料,设计制作了一种基于双折射效应的新型八边形晶格双芯光子晶体光纤偏振分束器。应用全矢量有限元法（FEM）分析了碲玻璃和SF6两种双芯光子晶体光纤中结构参数对双折射和相对耦合长度特性的影响,数值模拟了碲玻璃和SF6两种偏振分束器的性能。结果表明：在碲玻璃和SF6两种双芯光子晶体光纤中,增大椭圆率可同时增加结构的双折射和相对耦合长度,与SF6玻璃偏振分束器相比较,碲玻璃偏振分束器具有更高的消光比和更大的带宽,即在工作波长为1.55 μm处,消光比达到最小值-53.46 dB,且消光比小于-20 dB的带宽为120 nm。     

A novel design for single-polarization single-mode photonic crystal fiber at 1550 nm

The present paper proposes a novel design for achieving single-polarization single-mode (SPSM) operation at 1550 nm in photonic crystal fiber (PCF), using a rectangular-lattice PCF with two lines of three central air holes enlarged. The proposed PCF composed entirely of silica material is modeled by a full-vector finite element method with anisotropic perfectly matched layers. Simulations show that single-polarization operation within broad wavelength range can be easily realized with the proposed structure. The wideband SPSM operation features, the low confinement losses, and the small effective mode area are the main advantages of the proposed PCF structure. A SPSM-PCF with confinement loss less than 0.1 dB/km within wavelength range from 1370 to 1610 nm and effective mode area about 4.7 μm2 at 1550 nm is numerically demonstrated.     

新型抗弯曲大模场面积光子晶体光纤

研制出一种新型抗弯曲大模场面积石英光子晶体光纤. 利用光子晶体光纤结构设计的灵活性, 通过规划缺陷的位置及空气孔的尺寸, 实现了大模场面积单模及低弯曲损耗特性.应用建立的实际光子晶体光纤特性分析模型, 研究了研制光纤的模式特性和弯曲特性, 在波长1064 nm处, 平直状态下光纤的模场面积可以达到2812 μm², 基模限制损耗为0.00024 dB/m, 高阶模限制损耗高于1.248 dB/m. 基模和高阶模之间的高传输损耗差, 保证了在获得大模场面积的同时实现单模传输. 弯曲半径和弯曲方向角所带来弯曲损耗变化的研究结果显示, 即使在弯曲半径小到5 cm时, 弯曲损耗也在10^-3 dB/m量级以下, 而且在弯曲半径为30 cm时光纤可承受的弯曲方向角范围扩展至-60°–60°. 研制的光纤具有良好的低弯曲损耗特性, 可有效解决非对称结构所带来的光纤弯曲特性对弯曲方向角敏感的问题. 该光纤在高功率光纤激光器、放大器及高功率传输等技术领域具有重要的应用价值. 关键词： 光子晶体光纤 大模场面积 低弯曲损耗 弯曲方向角     

基于高双折射Sagnac环的可调环形腔掺铒光纤激光器理论与实验研究

报道了一种利用偏振控制器（PC）和保偏光纤（PMF）组成的高双折射Sagnac干涉环实现选频和调谐的环形腔掺铒光纤激光器.理论模拟了PMF和PC对波长的控制作用.实验中调节PC得到了单波长、双波长和多波长激光;并验证了滤波间隔随PMF长度的变化规律.实验中得到了斜率效率20%,3 dB线宽0.016 nm,30 dB线宽0.097 nm,边模抑制比（SMSR）40 dB左右的稳定激光输出. 关键词： 光纤激光器 Sagnac干涉环 环形腔 掺铒光纤     

Switchable multi-wavelength fiber ring laser using a side-leakage photonic crystal fiber based filter

A switchable multi-wavelength fiber ring laser is proposed and experimentally demonstrated with a novel side-leakage photonic crystal fiber (SLPCF) based filter incorporated into the ring cavity at room temperature. Stable multi-wavelength laser operations can be achieved due to the spatial mode beating, polarization hole burning and spectral hole burning effects. By adjusting the polarization controller appropriately, the laser can be switched among the single-, dual- and triple-wavelength lasing oscillations whose signal-to-noise ratio is up to 50 dB. In addition, the lasing wavelength can be also tuned and switched by applying the strain to the filter.     

Highly birefringent octagonal photonic crystal fibers with two zero-dispersion wavelengths

A new highly birefringent octagonal photonic crystal fiber(Hi-Bi OPCF) with a rectangular array of four elliptical airholes in the fiber core region is proposed and analyzed using the full-vector finite element method with anisotropic perfect match layer absorbing boundaries.Numerical results show that the phase birefringence of the photonic crystal fiber(PCF) reaches 3.43×10-2 at the wavelength of 1 550 nm.Moreover,two zero-dispersion wavelengths are achieved in the visible and near infrared wavelength regions for one polarization state but not in the other.