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.     

液晶填充碲酸盐光子晶体光纤偏振旋转器

提出一种液晶填充碲酸盐玻璃的柚子型光子晶体光纤偏振旋转器,利用全矢量有限元法,对液晶填充碲酸盐玻璃的柚子型光子晶体光纤的偏振旋转特性进行数值模拟,并分析了光纤结构参数、环境温度、工作波长等对光纤偏振旋转特性的影响.研究结果表明:此种偏振旋转器具有较高的旋转效率、较低的工作串扰和较短的旋转长度,在工作波长为1.55μm、偏振角度为45°时,其值分别达到99.947%、-32.84dB和197μm;另外,随着光纤薄壁厚度的增加,旋转长度随之升高,随着工作波长的变大,旋转长度随之降低,随着温度的增加,旋转长度随之升高.这种新型的光子晶体光纤为偏振旋转器的研发提供了参考.     

Lasing in thulium-doped polarizing photonic crystal fiber

We describe lasing of a thulium-doped polarizing photonic crystal fiber. A 4 m long fiber with 50 μm diameter core, 250 μm diameter cladding, and d/Λ ratio of 0.18 was pumped with a 793 nm diode and produced a polarized output with a polarization extinction ratio (PER) of 15 dB and an M(2) of <1.15. An intracavity polarizer and half-wave plate minimally increased the PER to 16 dB. The output power had 35% slope efficiency relative to the absorbed pump power. The maximum cw output power was limited to 4 W due to the quantum defect heating of the fiber.     

High-power single-polarization and single-transverse-mode fiber laser with an all-fiber cavity and fiber-grating stabilized spectrum

Conventionally, large-mode-area (LMA) fiber lasers use free-space polarizing components to achieve linear polarization output. External components, however, significantly limit laser robustness and power scalability. We demonstrate, to the best of our knowledge, the first high-power all-fiber cavity single-polarization single-transverse-mode LMA fiber laser, without the use of free-space polarizing components. This has been achieved by using tightly coiled high-birefringence 20 microm core LMA fiber. The lasing spectrum at 1085 nm has been stabilized by a fiber grating, spliced at one end of a LMA fiber. Up to 405 W of single-polarization output with a polarization extinction of >19 dB with a narrow spectrum (1.9 nm FWHM) and in a single-transverse mode (M2 < 1.1) has been demonstrated. The simplicity of a monolithic-cavity approach is highly beneficial for a number of applications, including the use of a fiber laser for nonlinear wavelength conversion and for coherent and spectral beam combining.     

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.     

单偏振光子晶体光纤

提出了一种能够在较宽波长范围内保持单偏振的光子晶体光纤,并利用频域有限差分法对其偏振特性进行了数值分析。在孔间距Λ取2.3μm,第一层较大空气孔直径dl取2.4μm,较小空气孔直径ds取1.4μm,包层中其它空气孔的直径d取0.6μm的条件下,这种单偏振光子晶体光纤在1.02-2.0μm波长范围内,保持较高的模式双折射。当较大空气孔直径dl取2.8μm,较小空气孔直径ds取1.4μm时,在1.35-2.0μm波长范围内,仅有一个偏振模能够存在,且波长1.31μm处的模式双折射度达到3.5×10-3。     

中红外高保偏硫系玻璃双芯光子晶体光纤耦合特性研究

设计了一种中红外硫系玻璃双芯光子晶体光纤,利用多极法和模式耦合基本理论研究了这种光纤的耦合特性.数值模拟发现,空气孔间距Λ = 5.4 μm,空气孔半径为r = 1.35 μm,空气填充率d/Λ = 0.5的光纤,在归一化波长λ/Λ = 2.04 μm处双折射可以达到0.551×10^-2,在归一化波长λ/Λ = 0.93 μm处x偏振方向的耦合长度为145.32 μm,y偏振方向的耦合长 关键词： 双芯光子晶体光纤 硫系玻璃 双折射 耦合长度     

Birefringent azopolymer long period fiber gratings induced by 532 nm polarized laser

Based on the photoinduced birefringence in azo materials, the model of the birefringent long period fiber gratings (BLPFGs) has been proposed and the transmission of such birefringent fiber gratings was further simulated by the coupled mode theory. In order to obtain the optimum condition for making birefringent azopolymer optical fiber (APOF) gratings the photoinduced birefringence of azo dye and methyl methacrylate (MMA) copolymers was systematically studied. After photosensitivity study of azo samples, using Teflon technique, azo dye containing single mode polymer optical fiber (POF) was fabricated. Finally, BLPFGs can be fabricated in azopolymer fiber using polarized 532 nm laser. A 120 μm LPFG with a 50% duty cycle has been successfully written within the core of the fiber with 532 nm laser by an amplitude mask method. Under polarized microphotography, the grating was observed when the optical axis was set at 45° with the direction of the first polarizing lens of the polarization microscope.     

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.     

Surface plasmon resonance-induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers

Surface plasmon resonance induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers were proposed and analyzed. The characteristics of the polarization filter were calculated by finite element method(FEM). The gold film was selectively coated on the inner wall of one cladding air hole which was located near the fiber core along the y-axis direction. When the phase of core fundamental mode and surface plasmon polaritons(SPPs) mode matches,the two modes couple with each other intensely. Numerical results show that the resonance wavelength and strength vary with fiber structural parameters and the index of the infilling liquid. The fiber parameters were optimized to achieve specific functions. Under the optimal structure, we realized a dual channel filter at the communication wavelength of 1.31 μm and1.55 μm for y polarization direction and x polarization direction. Then a single channel polarized filter at the communication wavelength of 1.55 μm is also achieved by adjusting the refractive index of the infilling liquid. The proposed polarization filters realized dual channel filtering and single channel filtering simultaneously under the same structure for the first time to the best of our knowledge.     

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。     

Design of passive polarization rotator based on silica photonic crystal fiber

We propose and analyze a novel (to the best of our knowledge) design of a polarization rotator (PR) based on silica photonic crystal fiber. The proposed design has a rectangular core region with a slanted sidewall. The simulation results are obtained using the full vectorial finite difference method as well as the full vectorial finite difference beam propagation method. The numerical results reveal that the suggested PR can provide a nearly 100% polarization conversion ratio with a device length of 3102 μm.     

Mode field diameter preserving fiber tapers

An approach for preserving the mode field diameter (MFD) in fiber tapers is demonstrated. The approach utilizes concentric dual-core fibers, which couple light from an inner core to an outer core through a taper. Fibers with a 6 μm MFD feedthrough and a 15 μm polarization maintaining feedthrough are demonstrated experimentally. Simulations of the MFD in the tapered dual-core fibers are also presented.     

双芯高双折射光子晶体光纤耦合特性研究

设计了一种双芯高双折射光子晶体光纤,采用多极法（multipole method）和光纤的模式耦合理论研究了光纤的双折射、耦合长度以及色散特性.数值研究发现,对于空气孔节距 Λ=1.2　μm,空气孔直径d=1.0　μm的光纤,在1.55　μm处双折射度为1.24×10^-2;对应x偏振模的耦合长度为21.6　μm,对应y偏振模的耦合长度为24.3　μm. 这种具有高保偏度和极短耦合长度的双芯光子晶体光纤对于微型光子器件的研制具有重 关键词： 光子晶体光纤 双芯 双折射 耦合长度     

100 W级全光纤化线偏振单频光纤放大器

报道了一种基于主振荡功率放大结构的全光纤化1064 mm线偏振单频光纤放大器。种子源是一个线宽约为3 kHz的单频光纤激光器。输出功率为50 mW的种子激光经两级掺Yb保偏双包层光纤(光纤纤芯直径分别为10 μm和20 μm)和一级手性耦合纤芯增益光纤放大后,最终获得了输出功率138 W、光束质量M2≤1.2、偏振消光比优于18 dB的高功率单频光纤激光输出。在脉冲调制模式下,获得了峰值功率465 W、脉宽宽度约为500 μs的线偏振单频光纤激光输出。     

2.1 μm可调谐多波长掺钬光纤激光器

为了实现2.1 μm波段光纤激光器输出多波长激光，设计了一种基于光纤Sagnac干涉仪的可调谐多波长掺钬光纤激光器。采用1.9 μm波段掺铥光纤激光器泵浦一段长3 m的掺钬石英光纤，获得2.1 μm波段的光放大；环形腔中，由保偏光纤和偏振控制器构成的光纤Sagnac干涉仪，实现2.1 μm波段周期滤波，获得了2.1 μm波段多波长激光，输出功率1 mW~15 mW可调谐，最多可观测到6个波长的激光输出。通过调节环形腔内偏振控制器，能够实现2.1 μm波段1~6个波长的调谐。     

Er-doped photonic crystal fiber amplifier with 70 W of output power

We report for the first time, to the best of our knowledge, on a large mode area Er-doped photonic crystal fiber laser system. The fiber core had a diameter of 40 μm and NA of <0.04 leading to a mode field diameter of about 31 μm around 1550 nm wavelength. More than 70 W of single-frequency output power at 1556 nm could be extracted using a master-oscillator power-amplifier scheme. Near diffraction limited output beam quality has been verified by measuring the TEM(00) content with a nonconfocal scanning ring cavity.     

128 W单频线偏振光纤放大器特性研究

高功率单频激光在激光雷达、光谱学、精密测量等领域具有广阔的应用前景.采用中心波长为1064 nm、光谱线宽为20 kHz、偏振消光比（PER）高于20 dB的单频线偏振分布式反馈光纤激光器做种子源（尾纤输出功率约为10 mW）,利用种子注入主振荡功率光纤放大技术,通过两级级联放大实现了128 W高功率单频、线偏振、近衍射极限单模连续激光输出.主放大器光-光效率达到83%,PER高于12 dB.采用分段温控技术有效地提高了光纤中的受激布里渊散射（SBS）阈值,实验中未观察到明显的放大自发辐射和SBS现象,进 关键词： 掺Yb光纤放大器 主振荡功率光纤放大 单频 线偏振     

Bismuth-doped silica-based fiber lasers operating between 1389 and 1538 nm with output power of up to 22 W

An efficient CW bismuth fiber laser operating around 1.46 μm with an efficiency of >50% and an output power of >20 W has been developed on a bismuth-doped GeO(2)-SiO(2) fiber. The laser demonstrates weak dependence of the output power on temperature in comparison with bismuth lasers operating near 1.15 and 1.3 μm. The laser generation has been obtained in the range 1.39 to 1.54 μm. The first linearly polarized bismuth-doped fiber laser at 1.46 μm based on a PANDA-type fiber has been demonstrated.     

Effect of multimodal coupling in imaging micro-endoscopic fiber bundle on optical coherence tomography

The effect of higher-order modes in fiber bundle imager-based optical coherence tomography (OCT) has been theoretically modeled using coupled fiber mode analysis ignoring the polarization and core size variation in order to visualize the pure effect of multimodal coupling of the imaging bundle. In this model, the optical imaging fiber couples several higher-order modes in addition to the fundamental one due to its high numerical aperture for achieving light confinement to the single core pixel. Those modes become evident in a distance domain using A-mode (depth) OCT based on a mirror sample experiment where multiple peaks are generated by the spatial convolution and coherence function of the light source. The distance between the peaks corresponding to each mode can be estimated by considering the effective indices of coupled (guided) modes obtained from numerically solving the fiber mode characteristics equations and the fiber length. The results have been compared for various types (fiber dimensions and wavelengths) and lengths of fibers, which have mode separation of 715 μm (1404 μm) and 764 μm (1527 μm) for the measurement and analysis, respectively in a 152.5 mm (305 mm)-long imaging fiber.