Guiding Properties of a Tapered Photonic Crystal Fiber Compared with Those of a Tapered Single-Mode Fiber

We have fabricated tapered photonic crystal fibers using a fusion splicer and experimentally observed the near-field mode distribution and the beam divergence of it. We have also compared characteristics of the tapered photonic crystal fiber with those of a tapered standard single-mode fiber. Unlike a tapered standard single-mode fiber, the mode field profile of a tapered photonic crystal fiber shows a good confinement of its field within the core region. The numerical apertures of tapered photonic crystal fibers are increased as the diameter of the fiber is decreased.     

Guiding Properties of a Tapered Photonic Crystal Fiber Compared with Those of a Tapered Single-Mode Fiber

We have fabricated tapered photonic crystal fibers using a fusion splicer and experimentally observed the near-field mode distribution and the beam divergence of it. We have also compared characteristics of the tapered photonic crystal fiber with those of a tapered standard single-mode fiber. Unlike a tapered standard single-mode fiber, the mode field profile of a tapered photonic crystal fiber shows a good confinement of its field within the core region. The numerical apertures of tapered photonic crystal fibers are increased as the diameter of the fiber is decreased.     

Excitation of cladding modes in photonic crystal fibers by flexural acoustic waves

We report the excitation by flexural acoustic waves of an individual cladding mode in a single-mode photonic crystal fiber. The propagation constant and the field distributions of the mode have been investigated by use of this technique. The results give the basis for developing a family of acousto-optic devices based on photonic crystal fibers.     

单模低损耗光子晶体光纤的设计及特性分析

设计了几种特殊结构的带隙光子晶体光纤,采用平面波展开法和频域有限差分方法研究了基于不同结构光子晶体光纤的带、模式、色散和色散斜率。由平面波展开法和频域有限差分方法求解麦克斯韦方程组导出本征值方程,可以得到带隙光子晶体光纤中可能存在的不同模式的传播常数、电场分布、本征频率和磁场分布。分别给出了第二圈填充率取三种不同值时带、模式、色散和色散斜率的变化。结果表明,当第二圈填充率改变时其特性有明显的变化。随着填充率从0．75减小到0．45,其二阶模分裂成两个类LP01模,可降低损耗。计算结果对单模和低损耗的光子晶体光纤的设计有参考价值。     

Phase locking and supermode selection in multicore photonic crystal fiber lasers with a large doped area

We report on the laser properties of multicore photonic crystal fiber lasers. A stable phase locking of six- and seven-core structures through evanescent coupling is observed. Effective supermode selection is obtained by using both diffraction losses and the Talbot effect. A pure in-phase supermode is obtained (1.1 times diffraction limited). The laser operating in this mode has a slope efficiency of 70% with up to 44 W of output power. The modal area of the in-phase supermode multicore fiber is 1150 microm2, which makes it, to our knowledge, the single-mode fiber laser with the largest mode field area. In-phase laser action is stable when the fiber is bent.     

基于谐振吸收效应的单模单偏振光子晶体光纤研究

提出了一种基于谐振吸收效应的单模单偏振光子晶体光纤，阐述了其工作原理，并利用全矢量有限元法对其模场分布、限制损耗、工作带宽、消光比等基本特性进行了数值模拟. 数值结果表明这种结构可以获得很高的单模单偏振工作带宽，并能以较低的损耗代价实现极高的消光比.讨论了结构设计参量对光纤性能的影响.研究结果对设计新型的高性能单模单偏振光纤具有一定的指导意义.     

双包层多芯光子晶体光纤自相干合成的数值分析与实验

依据耦合模理论分析了双包层多芯光子晶体光纤的超模模场特性,通过倏逝波对7束光的相位调节,可实现相干合成,激光亮度得到很大提高.利用相干合成原理对双包层多芯光子晶体光纤的出射光相干功率密度进行了分析与测量,对此种结构的光子晶体光纤实现自相干合成提出了理论和实验依据.     

Tapered microstructured fibers for efficient coupling to optical waveguides: a numerical study

We report the possibility of using tapered microstructured fibers to improve the coupling efficiency from a standard single-mode fiber to a photonic crystal waveguide. The tapered microstructured fiber allows for the reduction of the mode mismatch between the output of the standard fiber and the input of the waveguide while maintaining single-mode guidance, which results in an enhanced coupling efficiency. Numerical simulations are conducted in order to optimize the cross section of the microstructured fiber as well as the taper profile. An improvement of more than 4 dB is obtained compared to non-tapered fibers. For further improvement, an elliptical-core tapered microstructured fiber is analyzed. The effect of misalignment between the tapered microstructured fiber and the waveguide is also studied.     

多孔芯光子晶体光纤及其偏振特性

强激光与气体的长距离相互作用能产生许多新奇的物理效应,而自由空间光束的自聚焦、衍射、散射等问题限制了该科技领域的发展。本文提出了一种新型多孔芯光子晶体光纤,纤芯亚波长、低折射率空气孔可以传光,具有宽带、低损耗、单模传输特性。利用倏逝波耦合效应,研究了纤芯亚波长空气孔束缚光的原理。根据光波传输的电磁场理论,分析了低折射率空气孔中的光强增大效应。强光在空气孔中长距离传输,为光与物质的相互作用提供了新条件,可以用于气体传感、非线性光学、高集成光子技术、原子操控等。由于纤芯空气孔可以传光,改变空气孔的大小,直接影响模场分布,进而可以获得很高的结构双折射。通过光纤结构参数的合理设计,分别获得了B=4×10^-2的高双折射、纤芯直径5 μm的大模场高双折射、大模面积单偏振单模特性,在光纤偏振器、光纤滤波器、光开关及光纤传感等领域有广泛的应用前景,为新型光场调控提供了新方法。     

Multimode fiber devices with single-mode performance

A taper transition can couple light between a multimode fiber and several single-mode fibers. If the number of single-mode fibers matches the number of spatial modes in the multimode fiber, the transition can have low loss in both directions. This enables the high performance of single-mode fiber devices to be attained in multimode fibers. We report an experimental proof of concept by using photonic crystal fiber techniques to make the transitions, demonstrating a multimode fiber filter with the transmission spectrum of a single-mode fiber grating.     

Efficient input and output fiber coupling to a photonic crystal waveguide

The efficiency of evanescent coupling between a silica optical fiber taper and a silicon photonic crystal waveguide is studied. A high-reflectivity mirror on the end of the photonic crystal waveguide is used to recollect, in the backward-propagating fiber mode, the optical power that is initially coupled into the photonic crystal waveguide. An outcoupled power in the backward-propagating fiber mode of 88% of the input power is measured, corresponding to a lower bound on the coupler efficiency of 94%.     

新型单模大模场红外硫系玻璃光子晶体光纤设计研究

大模场光子晶体光纤在高功率激光传输、光纤放大器、光纤激光器中的广泛应用, 使其受到研究者的广泛关注.硫系玻璃在红外波段(1–20μm)具有优良透过性能, 且具有折射率高(2.0–3.5)、声子能量低(小于350 cm^-1)、 组分可调等特性, 成为制备红外光纤的理想材料. 本文设计一种基于Ge₂₀Sb₁₅Se₆₅硫系玻璃基质的新型单模传输、低损耗、超大模场面积光子晶体光纤结构, 经理论验证其在λ =10.6 μm处基模限制损耗远低于0.1 dB/m, 高阶限制模损耗大于2 dB/m, 模场面积约为13333 μm². 关键词： 硫系玻璃 大模场面积 红外光子晶体光纤 结构设计     

Highly sensitive miniature photonic crystal fiber refractive index sensor based on mode field excitation

A highly sensitive miniature photonic crystal fiber refractive index sensor based on field mode excitation is presented. The sensor is fabricated by melting one end of a photonic crystal fiber into a rounded tip and splicing and collapsing the other end with a single-mode fiber. The rounded tip is able to induce cladding mode excitation, which resulted in an additional phase delay. Linear response of 262.28 nm/refractive index unit in the refractive index range of 1.337 to 1.395 is obtained for the physical length of a 953 μm sensor. The sensor is also shown to be insensitive to environmental temperature.     

光子晶体光纤模式特征的研究

从基空间填充模出发，将光子晶体光纤的包层等效成均匀介质，从而将光子晶体光纤等效为阶跃折射率光纤。利用等效折射率模型，对光子晶体光纤的模式特征进行了详尽的研究，主要包括模式特性、传输常量、模场分布、功率限制特性、瑞利散射损牦特性、色散特性，等等。并通过功率限制因子这一参量将它与单模光纤进行比较。结果表明，光子晶体光纤单模工作波长范围比较宽，功率限制因子比较高，可用于制作更高抽运效率的光纤放大器。     

Inner cladding influence on mode interaction in symmetry-free photonic crystal fibers under heat load

A further output power scaling of Yb-doped double-cladding photonic crystal fiber lasers, required for practical applications in many industrial fields, is currently prevented by thermal effects, which significantly worsen the beam quality. In this work the mode interaction and, consequently, the single-mode regime of Yb-doped air-silica symmetry-free photonic crystal fibers have been numerically investigated in different heat load conditions using simulation tools based on the finite element method. The effect of the main inner cladding geometric parameters, in particular of the inner cladding dimension, on the guided-mode delocalization has been analyzed, with the aim to identify a design of the large mode area active fiber providing single-mode operation despite the presence of thermal effects. Simulation results have demonstrated that the inner cladding enlargement causes a stronger coupling between core-guided and cladding modes, as well as an increase of the differential overlap between fundamental and first higher-order mode for moderate heat load values. However, the inner cladding influence becomes less important under severe heat load, being the fiber behaviour mainly affected by the thermally-induced refractive index change in the doped core.     

Tunable photonic crystal fiber coupler based on a side-polishing technique

A tunable photonic crystal fiber (PCF) coupler, which couples part of the optical power in one PCF with that in another PCF, has been made by side polishing. We fabricated the PCF coupler by mating two side-polished PCFs. We achieved evanescent field coupling between the core modes of the two PCFs by using side polishing to bring the cores close to each other. By adjusting the mating angle between the two side-polished PCFs we obtained as much as 90% tunability in the coupling ratio. The spectrum of the coupling ratio was almost flat, with small ripples, over a 400-nm wavelength range.     

Photonic Crystal Fiber Attenuator

We propose a novel fiber attenuator based on photonic crystal fibers. The difference in the modal field diameters of a conventional single mode fiber and a photonic crystal fiber was used. A variable optical attenuator was also achieved by applying macro-bending on the PCF part of the proposed attenuator     

All-glass endless single-mode photonic crystal fibers

Endless single-mode fibers, which remain single mode over their entire range of guidance, are, to the best of our knowledge, the first reported unique application of photonic crystal fibers. These endless single-mode fibers are made by omitting a single air hole in a periodic array of small air holes in a background silica glass. The feasibility of all-glass endless single-mode photonic crystal fibers where the air holes are replaced by a glass with vanishingly small refractive index contrast relative to silica is first studied theoretically and then demonstrated experimentally. This new all-glass design enables not only ease and consistency of fabrication but also the convenience to be handled and spliced like conventional fibers.     

光子晶体光纤及在光纤光栅中的应用

从光子晶体光纤(PCF)与普通光纤在光纤结构上的差异出发，简要分析PCF的导光原理与单模特性，并探讨基于PCF的光纤光栅的稳定性，基于聚合物填充多孔光纤的长周期光纤光栅的温度调谐性能，以及纯结构性非光敏纤芯长周期光子晶体光纤光栅的原理。从一个方面说明了光子晶体光纤的潜在应用。     

A colloidal crystal microstructure fiber: fabrication and characterization

A method of fabricating colloidal crystal microstructured fiber is presented. The proposed structure relies on partial etching of the cladding layer of a single-mode fiber and growth of colloidal photonic crystals inside eroded area. The photonic crystal cylindrical annulus embedded in fiber is characterized by optical and scanning electron microscopy. The optical characterization was analyzed by optical transmission spectroscopy. The measurement results show a about 1550-nm band gap. The results also reveal the possibility of cladding cylindrical fibers with three-dimensional photonic crystals.