光子晶体光纤模场直径增加方法

通过加热光子晶体光纤,其包层中空气孔由于表面张力的作用而塌缩减小。理论和实验结果表明,空气孔的塌缩在满足波导的渐变条件下,引入的能量损耗非常小。空气孔的塌缩减小,可以有效地增加光子晶体光纤的模场直径,从而不仅可以提高光耦合的效率和光纤端面的损伤阈值,而且可以降低与其它模场直径不匹配的普通光纤的熔接损耗。     

全固态八边形大模场光子晶体光纤的设计

提出一种新型的全固态八边形大模场低损耗的掺镱石英光子晶体光纤,利用多极法对光纤的结构和特性进行了模拟.这种结构的光子晶体光纤空气孔由掺有少量氧化硼的石英棒代替,简化了制备过程,提高了光纤的热损伤阈值.在波长为1064 μm处,光纤的模场面积可达2000 μm²,还可实现单模传输,而且其弯曲损耗很小,当弯曲半径为5 cm时弯曲损耗小于05 dB/m.这种光纤对光纤激光器和光纤放大器的发展有重要意义. 关键词： 光子晶体光纤 模场面积 弯曲损耗 限制损耗     

基于光纤拉锥模场匹配技术的光子晶体光纤低损耗熔接

光子晶体光纤(PCF)与普通单模光纤(SMF)的低损耗熔接技术是光子晶体光纤走向实用化必须解决的关键技术问题。提出一种基于光纤拉锥模场匹配技术的光子晶体光纤低损耗熔接的新方法,利用熔融拉锥机对模场不匹配的两类PCF进行预处理,结合常规电弧放电熔接技术对三种不同类型的PCF与SMF的熔接损耗进行实验研究。在实验中通过精确控制熔融拉锥机各种参数,实现了不同模场直径PCF和SMF的模场匹配,该方案同时通过优化各种电弧放电参数,使熔接后的损耗降到了0.3dB以下,实现了PCF-SMF之间低损耗、高强度的熔接,满足了不同模场PCF实际应用的要求,具有很好的潜在应用价值。     

光子晶体光纤的全光纤纤芯变形研究

利用有限差分光束传输法分析了全光纤纤芯变形光子晶体光纤中的模场分布以及能量损耗情况.实现了光子晶体光纤的选择性空气孔塌缩,制作了由小纤芯到大纤芯和圆形芯到矩形芯的纤芯变形光子晶体光纤,该光纤在波长1550 nm下以小于0.05 dB的能量损耗实现了光斑的整形.实验结果与模拟结果有很好的一致性. 关键词： 光子晶体光纤 空气孔塌缩 纤芯变形     

大模场面积光子晶体光纤耗散孤子锁模激光器

研制了一种基于掺Yb3+的双包层大模场面积偏振光子晶体光纤的耗散孤子锁模激光器.利用数值模拟分析了光纤激光器中耗散孤子动力学过程,与全正色散锁模激光器相比,脉冲窄化机理更加丰富,半导体可饱和吸收镜(SESAM)的非线性吸收,啁啾脉冲的光谱滤波以及光纤的增益色散同时起作用,这些因素使耗散孤子锁模更加容易实现,并且稳定运行.其中,光谱滤波的耗散过程是稳定锁模机制的主导因素,滤波片能够在频域和时域同时窄化脉冲,并且去除脉冲啁啾,限制脉冲在腔内始终小于1ps.在实验上实现了无色散补偿腔中直接输出脉冲宽度777fs,最高平均功率达到1W,重复频率48·27MHz,对应单脉冲能量20nJ的飞秒激光.     

大模面积平顶模场光子晶体光纤模式分析

通过全矢量有限差分法数值模拟,设计了一种大模面积平顶模场光子晶体光纤。光纤截面上空气孔为三角形格子分布,中心七个空气孔缺失并在其中心引入一低折射率区域。分析了内纤芯大小、空气孔间距和空气孔相对大小等参数变化对内纤芯折射率、基模模面积等特性的影响。给出了工艺上简单易行的平顶模场光子晶体光纤结构,其平顶模面积可达2000μm2。发现增加内纤芯尺寸和导光波长,降低空气孔相对尺寸,可以减少光纤中的高阶模含量。     

自由耦合输出的大模场面积光子晶体光纤锁模激光器

对一种基于高增益掺Yb³⁺大模场面积光子晶体光纤（PCF）的锁模激光器进行了简化线型腔结构的实验和理论研究.实验中直接使用塌陷打磨为0°角的光纤端面作为一端腔镜,利用其端面反馈获得了激光振荡,并进一步利用半导体可饱和吸收镜（SESAM）和光栅对的滤波作用实现了稳定的锁模运转.通过调节滤波程度,使激光器实现了从宽带滤波锁模到窄带滤波锁模的连续可调谐.在宽带滤波锁模的条件下,得到了最大平均输出功率2.2 W,单脉冲能量29.3 nJ,脉冲宽度367 fs的锁模脉冲输出;在窄带滤波锁模的条 关键词： 飞秒激光 光纤激光器 光子晶体光纤 大模场面积光纤     

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     

光子晶体光纤的低损耗电弧熔接方案

提出了一种利用传统电弧熔接机实现光子晶体光纤(PCF)与单模光纤(SMF)低损耗熔接的新方案.方案结合实验测量与理论计算,首先通过改变熔接时间、熔接电流等参量,考察了不同熔接功率对PCF端面气孔结构的影响.由此计算了PCF端面模场分布的相应变化,并根据两光纤端面模场的重叠积分计算了相应的熔接损耗,从而确定出对应低熔接损耗的熔接功率区间.综合考虑熔接强度等要求,反向选取了合理的熔接参量范围,实现了PCF-SMF之间低损耗、高强度的熔接.提出的熔接方案使熔接过程中PCF包层气孔的收缩变化、该变化对两光纤接合匹配度的影响等问题清晰化,克服了以往PCF-SMF熔接中难以设定合理熔接参量的问题,有效地提高了熔接效率和熔接质量.     

微小空气孔传光的光子晶体光纤研究

利用有限元方法对纤芯中心带有一个微小空气孔的光子晶体光纤进行了分析,得到了其模场分布、损耗及色散特性随光纤结构参数及波长的变化规律.根据光的衍射原理及光子晶体光纤的传输特性,对空气孔传光的物理本质进行了解释.得到了微小空气孔低损耗、高强度、单模传输时,光子晶体光纤结构参数及波长的取值范围.设计出了一种优化的光子晶体光纤结构,其模场很好地集中在纤芯微小空气孔中,限制损耗α=5.9×10^-5dB/km,为微小空气孔传光的光子晶体光纤设计及制备提供了理论指导.光在空气孔中高强度、长距离传输,为光与物质相互作用及非线性光纤光学提供了新的条件.     

Study of bending loss and mode field diameter in depressed inner core triple-clad single-mode optical fibers

In this paper, the bending loss and the mode field diameter (MFD) of the R-type depressed inner core triple clad single-mode optical fibers are investigated. The effects of the optical and geometrical parameters on the bending loss and the MFD are examined in these fibers. The simulation results indicate that with increasing of the core radius (a), which is desired from manufacturing point of view, the bending loss and MFD coefficients are decreased. Consequently, the large core radius can be used to optimize the bending loss in the foregoing fibers. In the meantime, simulation outcomes show that the Δ and Q have considerable impact on the bending loss in the RI and RII fibers, respectively. The MFD and bending loss is decreased with increasing of Δ, but the case is inversed for Q. Based on the presented simulations, it is found out that the bending loss strongly depends on the distribution profile of the electric field in the cladding region for a given MFD. In other words, the field amplitude and damping rate in the cladding region determine the fiber bending loss.     

Fusion splicing small-core photonic crystal fibers and single-mode fibers by controlled air hole collapse

A method based on controlled air hole collapse for low-loss fusion splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) was demonstrated. A taper rig was used to control air hole collapse accurately to enlarge the MFDs of PCFs which was then spliced with SMFs using a fusion splicer. An optimum mode field match at the interface of PCF-SMF was achieved and a low-loss with 0.64 dB was obtained from 3.57 dB for a PCF with 4 μm MFD and a SMF with 10.4 μm MFD experimentally.     

Endlessly single-mode operation of highly nonlinear photonic crystal fibers by controlled hole collapse

We report a higher-order mode filter in highly nonlinear photonic crystal fibers (HNPCFs) made by a conventional fiber taper rig based on controlled hole collapse. The air holes of the HNPCFs will become smaller due to the surface stress when they are heated on the taper rig incorporating a simple burner configuration. So the HNPCFs' configuration parameters can be easily changed by controlling the heating time. As is well known, if the relative hole size d/Λ of PCF is less than or equal to 0.4, it will become an endlessly single mode fiber. So we can control the heating time to satisfy the criterion of endlessly single mode operation, the heated section will be a higher-mode filter in HNPCFs. The optical loss of the higher-order mode filter is very low for the fundamental mode, typically less than 0.1 dB.     

光子晶体光纤模式的简并特性研究

应用光子晶体光纤（PCF）的全矢量模型，根据对称性分析，按照最小波导扇面及相应的边界条件，将PCF中的模式进行了分类，并将PCF中的模式类比阶跃光纤来命名. 分析表明，PCF中的模式或者为非简并的，此时能够反映波导结构对称性；或者为简并对，必须二者组合才反映波导结构的对称性. 当简并对中的两个模式都具有与PCF波导结构相同的对称性时，简并将被击破而形成两个非简并模. 关键词： 光子晶体光纤 模式 简并     

Flattened chromatic dispersion in square photonic crystal fibers with low confinement losses

This research presents a simple index-guiding square photonic crystal fibers (SPCFs) that has a silica core surrounded by air hole with two different diameters. It is demonstrated that the designed two-different-size hole-arrayed index-guiding SPCFs has a ultra-flattened chromatic dispersion of 0 ± 0.9 ps/(nm·km) in a wavelength range of 1.34 to 1.61 μm and low confinement loss of less than 10⁻⁷ dB/m in a wavelength range of 1.2 to 1.7 μm. It has also been shown that the proposed SPCFs show reasonable dispersion tolerance.     

Measurements of mode field diameter and effective area of photonic crystal fibers by far-field scanning technique

We have demonstrated that the correction factor k _n = A _eff/(πw ²), where ω = MFD/2 (MFD: mode field diameter), is above 1.20 for photonic crystal fibers (PCFs) with structural parameters in the range of d/Λ ≅ 0.40 to 0.90 (d/Λ ratio of hole diameter d and pitch Λ). By using the far-field scanning (FFS) technique and the finite difference method, the results of experimental measurements and numerical simulations differed by only 0.9 to 3.0% for two types of PCFs. The finding that k _n ≠ 1.0 for PCFs indicates that their electrical field distribution is non-Gaussian and cannot be determined by assuming a conventional step-index distribution for PCFs. It was also found that the ITU-T Petermann II definition is the most suitable for MFD measurements of PCFs with non-Gaussian distribution.     

Mode field diameter and cut-off wavelength measurements of single mode optical fiber standards used in OTDR calibrations

This paper describes determination of the mode field diameter (MFD), and the cut-off wavelength of the single mode optical fiber standards used in OTDR calibrations, which was constructed in Optics Laboratory of National Metrology Institute of Turkey. Measurements of MFD were performed using computer controlled stepper motor unit with far field scanning (FFS) Method. For the same standard fibers, cut-off wavelength measurement was performed employing bend reference method, which is one of the transmitted power techniques. For both measurements, a nitrogen-cooled 5 mm InGaAs radiometer was used to detect optical flux. Detailed uncertainty analyses were presented for the MFD and cut-off measurements. While the total expanded uncertainties in MFD data at 1306.7 nm and 1550 nm were calculated as 0.8% and 1.0% (k=2), respectively, the total expanded uncertainty at determination of cut-off wavelength was found as 0.318% (k=2).     

Dynamic control of mode field diameter and effective area by germanium doping of hexagonal photonic crystal fibers

We demonstrate dynamic control of the effective area (A _eff) of photonic crystal fibers (PCFs) in the range of 18.1–8.22 μm² and the mode field diameter in the range of 4.78–3.42 μm. This control was realized by altering their structural properties and varying the germanium (Ge) doping rate, which changed the refractive index difference (Δn _Ge) between 1.0 and 3.0% relative to the refractive index of the silica cladding. This was achieved by adjusting the Ge doping rate in the core and changing the radius (d _core) of the doped region, i.e., by changing the equivalent refractive index, using numerical calculations. Numerical results were verified by comparison with experimental results for a fabricated Gedoped PCF obtained by far-field scanning based on the ITU-T Petermann II definition. The proposed approach will simultaneously decrease A_eff and achieves high light confinement and high nonlinearity in PCFs. It enables architectonics/controllability of highly nonlinear PCFs with passive optical devices in photonic networks and life science applications.     

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.