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.     

宽带空芯THz单模单偏振光纤

传统的THz单模单偏振光纤大部分都是基于实芯光纤设计的,增加了THz波的传输损耗。最近几年,也有一些关于空芯THz单模单偏振光纤的报道。但是,他们的带宽太窄,往往只能在单一频率附近工作,影响了单偏振器件在THz范围内的使用价值和技术优势。为了解决这些问题,设计了一种新颖结构的空芯THz单模单偏振器件。它拥有超过0.1 THz的带宽,工作频率范围从1.63 THz到1.73 THz。这种器件对于THz通信网络的建设和应用具有重要意义。     

Broadband single-polarization guidance in hybrid photonic crystal fibers

We present hybrid photonic crystal fibers that provide broadband single-polarization guidance based on two different propagation mechanisms, namely, total internal reflection and the photonic bandgap effect. Experimental results demonstrate polarization dependent loss as high as 26.7 dB and the bandwidth of single-polarization behavior over 225 nm.     

Versatile control of geometric birefringence in elliptical hollow optical fiber

A novel optical fiber fabrication technique was developed by converting the symmetry of the silica substrate into the germanosilicate ring core to efficiently introduce geometric birefringence in an elliptical hollow optical fiber. Due to high ellipticity in the hollow ring core, the fiber provides an extremely high group birefringence of 2.35 x 10(-3) at 1550 nm. Single-mode single-polarization guidance was also experimentally confirmed, with a bandwidth of approximately 35 nm. The generic adiabatic mode conversion capability in the taper also provided a stable fusion splice to conventional single-mode fiber with low loss and high tensile strength.     

All-fiber single polarized Yb-doped fiber laser with a high extinction ratio

We present an all-fiber design for a single polarization Yb-doped fiber laser with all-fiber connections spliced. Single polarization with a high extinction ratio was achieved by the design of a laser cavity consisting of a fiber Bragg grating inscribed on a single-polarization fiber as a high reflective mirror and a piece of end-cleaved single-polarization fiber as an output coupler. The fiber laser operates at 1063.25 nm with an output power of 1.7 W, an optical signal- to-noise ratio of 70 dB and a narrow bandwidth of 54 pm. The laser output has a polarization extinction ratio of 700:1 or 28 dB, and a very stable power output.     

Broadband single-polarization photonic crystal fiber

We demonstrate a single-mode photonic crystal fiber that supports only one polarization state in a 220-nm-broad spectral region centered at 727 nm. The fiber has a mode-field diameter of 15.5 microm and background losses of < 15 dB/km in the single-polarization region. To our knowledge, these are the broadest bandwidth and the largest mode size yet reported for a single-polarization fiber.     

Design and analysis of a photonic crystal fiber with four-hole unit

A novel photonic crystal fiber (PCF) based on a four-hole unit is proposed in order to meet the requirements of high birefringence, negative dispersion and confinement loss in fiber-optic communication. The proposed design has been simulated based on the full vector finite element method (FVFEM) and anisotropic perfectly matched layers (APML). Analysis results show that the proposed PCF can achieve a high birefringence to the order of 10⁻² at the wavelength of 1.55 μm, a large negative dispersion over a wide wavelength range and confinement losses lower than 10⁻⁹ dB/m simultaneously, which has important applications in polarization-maintaining (PM) fibers, single-polarization single-mode (SPSM) fibers, dispersion compensation fibers and so on.     

Performance trade-off of coaxial and fiberoptic cables

In this paper coaxial and fiberoptic cables are traded off by comparing maximum length over which a signal can be transmitted as a function of bandwidth. The calculations verify that coax bandwidth decreases much more rapidly than that of fibers, for unrepeatered length. More specifically, at low and high frequencies, coax bandwidth decreases as 1/L² while optical fiber bandwidth, in the absence of mode mixing, varies at most as 1/L. Curves of unrepeatered length as a function of bandwidth for both coax and fiber are presented under a variety of operating regimes.     

基于光纤四波混频波长转换和色散的慢光实验研究

对基于光纤四波混频（FWM）波长转换和色散的慢光实现进行了详细和系统的实验研究.首先,实验测定了高非线性光纤中FWM带宽约为40 nm,从而确定了慢光的可调谐带宽;接着,在普通单模光纤和色散补偿光纤（DCF）中针对500 MHz正弦信号和100 ps短脉冲信号分别实现了34和198 ns的脉冲延迟,在DCF中还实现了209 ns的脉冲提前.讨论了增大延迟量的方法,指出随着宽带FWM波长转换的实现和大色散光纤的应用有望获得微秒量级的大延迟量,从而为高性能光纤延迟线和全光缓存器等应用提供支持. 关键词： 慢光 四波混频 色散     

Design and analysis of a novel single-mode single-polarization photonic crystal fibre based on polarization-dependent coupling and absorption effect

A novel single-mode single-polarization (SMSP) photonic crystal fibre has been proposed and analysed based on the polarization-dependent coupling and absorption effect via a full-vector finite element method with perfectly matched layers. The numerical results predict that very efficient SMSP operation can be achieved with both high bandwidth and high extinction ratio at low loss penalty. Effects of the fibre structural parameters on the SMSP bandwidth and extinction ratio have been explored, which will provide useful guide for the design and fabrication of the fibre. The results obtained will be instructive for the realization of new SMSP fibres with high performance.     

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。     

Strain dependence of Brillouin frequency, intensity, and bandwidth in polarization-maintaining fibers

The strain dependence of the Brillouin gain-loss spectrum for PANDA, bow-tie, and tiger polarization-maintaining fibers has been studied in the range 0 to 50 degrees C. We found a linear relationship between the strain and the Brillouin frequency, intensity, and bandwidth for PANDA and bow-tie fibers. For PANDA fiber at 20-cm spatial resolution, Brillouin frequency gives 7-micro epsilon uncertainty, which is the highest accuracy among three parameters, whereas the Brillouin bandwidth gives 19-micro epsilon uncertainty.     

Amplification of picosecond pulses and gigahertz signals in bismuth-doped fiber amplifiers

We demonstrate the capability for amplification of picosecond pulses in two bismuth-doped alumosilicate fibers. A spectrally filtered supercontinuum source is used to provide a train of picosecond pulses at discrete wavelengths within the gain bandwidth of bismuth fiber amplifiers. With a 30 m length of active fiber, a small signal gain at 1160 nm of over 20 dB is observed. In addition, we assess the viability of amplification of high repetition rate signals in such amplifiers, applying a 10 GHz modulation to a continuous wave Raman fiber laser operating at 1178 nm, finding that such signals are amplified without noticeable distortion.     

新型空气孔长方形排列单模单偏振光子晶体光纤的数值模拟

提出了一种空气孔长方形排列的单偏振光子晶体光纤结构，并利用基于棱边/节点混合元的带有完全匹配层吸收边界条件的全矢量有限元方法对该结构进行了分析.对设计思路进行了详细说明.通过优化结构参数在理论上获得了波长在1.38—1.61 μm范围内仅有慢轴模且限制损耗低于0.1 dB/km的单模单偏振操作. 关键词： 光子晶体光纤 单偏振 限制损耗 全矢量有限元方法     

基于插入损耗的光纤信号调制器

基于光纤连接的横向偏移造成的插入损耗研制了一种的新型的光纤信号光调制器。调节对接光纤的横向偏移,可以调节对接光纤间的光耦合效率,利用调制信号调制横向偏移可实现对光纤传输光信号的调制。实验中,将调制电信号放大并加载于压电陶瓷使其振荡,由此控制对接光纤的横向偏移与调制信号同步变化,实现了对下一级光纤输出端光强的调制。这种光纤信号调制器主要针对光的振幅调制,实验中获得调制度优于95%,信噪比约为20dB,带宽约为200kHz。具有价格低廉、调制度高的特点,可应用于光纤传输信号的调制及信号斩波等。     

Bandwidth enhancement by differential mode attenuation in multimode photonic crystal Bragg fibers

In multimode bandgap guiding fibers higher-order modes have high radiation losses. Once excited, after a short propagation distance such modes are leaked out of the fiber core. Reduction of the number of excited modes in the fiber core leads to a decrease of intermodal dispersion and a dramatic enhancement of fiber bandwidth. Due to the increase in the propagation loss, bandwidth enhancement by differential mode attenuation also leads to the reduction of the maximal length of a usable fiber span. We demonstrate that by proper design of a photonic crystal reflector long fiber spans of high bandwidth are possible.     

Transmission characteristics of graded-index fibers

The use of graded-index fibers for optical communication systems is now under consideration for numerous civil and military applications, and in these either LED or laser sources can be developed. The bandwidth of the system depends on the source linewidth, the dispersion of refractive index in the fiber, the strength of excitation of the modes by the source, and the extent of mode mixing caused, by example, by microbending. In fibers with refractive-index profiles that have a nearly parabolic dependence upon radius, pulse broadening is a slight, but small departures from an optimum profile can cause a dramatic decrease in bandwidth. It is of considerable importance to predict the bandwidth of fibers from a knowledge of the refractive-index profile and source geometry. The purpose of the first part of this paper is to compare two computational methods by which the propagation characteristics of a fiber, hence the impulse response and system bandwidth, may be determined. In the second part, we shall describe a computer program that determines the excitation of modes in an arbitrarily graded refractive index fiber for a model of laser source.     

Experimental Study of the Intensity Spatial Distribution Uniformity of the Output Field from Multimode Fibers

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All fiber supercontinuum light source using photonic crystal fibers pumped by nanosecond fiber laser pulses

A novel compact supercontinuum (SC) source using the single mode photonic crystal fibers (PCF) pumped with an all fiber MOPA fiber laser is demonstrated experimentally. A bandwidth of 700 nm is achieved by operating the pumping fiber laser at a wavelength of 1064 nm, pulse duration of 10 ns, repetition rate of 50 kHz and peak power of 1 kW. The SC generation is initiated through modulation instability (MI) which breakups the nanosecond pump pulses into picosecond or femtosecond pulses, and further broadened through nonlinear effects of PCF.