一种双模光子晶体光纤模间干涉拍长的研究

保偏光纤的模间干涉拍长是模间干涉式光纤传感器设计中的关键参数,对于决定光纤的调制长度、传感系统的线性度和动态范围以及模间干涉灵敏度都具有重要作用。本文从理论上对保偏光子晶体光纤（PM-PCF）的模传输特性和模间干涉拍长进行了分析,得到PM-PCF中几个线性偏振模的传输特性和LP11偶模的两个正交偏振模截止波长,并得到了...     

一种新型的基于LP01模的双模色散补偿光纤

通过计算机模拟发现在可传输双模的三包层色散补偿光纤中如果抑制ＬＰ０２模，而仅传输ＬＰ０１模时能在一个较窄的带宽内产生大于数千ｐｓ／ｎｍ·ｋｍ的负色散，并且具有较大的模场直径、较小的弯曲损耗和偏振模色散，另外还具有较小的温度波长漂移以及同其它色散补偿光纤一样大小的损耗，是一种非常有前途的新型色散补偿光纤     

High-power Mode Converter of Overmoded Bent Circular Waveguide

Based on the mode coupling theory, a TE₀₁—TM₁₁ mode converter was designed and optimal results were obtained. In this paper, bandwidth of mode converter with axis exponential structure is the largest, and mode converter with axis sinusoidal structure is the most compact in the case of the center frequency is 28GHz and the waveguide radius is 16mm. If the bending angle between input port and output port of mode converter was demanded for 90°, mode converter with axis parabola structure had the characteristics of compact structure, higher mode purity and larger relative bandwidth. Meanwhile, we found that the converter could be also used as TE₁₁ mode transition with transmission efficiency above 99%. But due to bending angle of this structure was restricted, its center frequency and waveguide radius had the obvious corresponding relation.     

光纤弯曲对掺镱光纤激光器光束质量的影响

通过改变F-P腔全光纤激光器中的光纤盘绕半径,对输出激光光束质量进行了研究.搭建了百瓦级全光纤激光器.最大泵浦功率为436 W的条件下,获得了300 W波长1 080 nm的激光输出.光束质量M2=1.13.光-光转换效率为69%.理论分析并计算了20/400 m大模场面积双包层光纤中的两种导波模式LP01模和LP11模沿光纤径向的功率分布和弯曲损耗;利用光纤弯曲选模方法,实验上探究了光纤弯曲半径对输出激光模式及光束质量的影响.实验发现,通过光纤弯曲方式可以有效地消除高阶模式,再经过包层光剥除可以获得更好的光束质量M2=1.06.     

Intermodal interference based refractive index sensor employing elliptical core photonic crystal fiber

A refractive index (RI) sensor based on elliptical core photonic crystal fiber (EC-PCF) has been proposed. The asymmetric elliptical core introduces the polarization-dependent characteristics of the fiber core modes. The performances of intermodal interference between the intrinsic polarization fiber core modes are investigated by contrast in two interferometers based on the Mach-Zehnder (M-Z) and Sagnac interference model. In addition, the RI sensing characteristics of the two interferometers are studied by successively filling the three layers air holes closest to the elliptical core in the cladding. The results show that the M-Z interference between LP01 and LP11 mode in the same polarized direction is featured with the incremental RI sensing sensitivity as the decreasing interference length, and the infilled scope around the elliptical core has a weak correlation with the RI sensing sensitivity. Due to the high birefringence of LP11 mode, the Sagnac interferometer has better RI sensing performance, the maximum RI sensing sensitivity of 12 000 nm/RIU is achieved under the innermost one layer air holes infilled with RI matching liquid of RI=1.39 at the pre-setting EC-PCF length of 12 cm, which is two orders of magnitude higher than the M-Z interferometer with the same fiber length. The series of theoretical optimized analysis would provide guidance for the applications in the field of biochemical sensing.     

熊猫型保偏光纤模间干涉的传感特性研究

分析了熊猫型保偏光纤模间干涉输出光强分布同模间干涉相位差之间的关系,并给出了其分布图;采用有限元法对熊猫型保偏光纤的模传输特性进行了计算,得到了几个低阶模式的传输特性曲线;理论计算了LP01模和LP11模间的干涉拍长。通过实验,验证了熊猫光纤模间干涉输出两个干涉边瓣光强随光纤应力变化呈交替分布的特点以及模间干涉拍长的计算结果。本文的研究为将熊猫型保偏光纤应用到光纤传感器的设计中提供了理论和实验参考。     

Broad-band LP/sub 02/ mode excitation using a fused-type mode-selective coupler

We demonstrate a novel fused-type directional coupler that couples the LP/sub 01/ mode in one fiber and the LP/sub 02/ mode in another using a few-mode fiber. The phase-matching condition was satisfied in the coupler waist by initially etching and prepulling portions of the fibers based on simple numerical calculation. A coupling efficiency of about 70% was maintained over 1515-1595-nm wavelength range, and the mode extinction ratios with LP/sub 01/, LP,/sub 11/, and LP/sub 21/ modes were measured to be 35,20, and 7 dB, respectively.     

光纤激光器高阶模式对相干合成特性影响分析

为了分析光纤激光器中高阶模式对相干合成的影响,采用将光纤激光器的基模以及高阶模式近似表示为拉盖尔-高斯光束的线性叠加的方法,利用拉盖尔-高斯光束的传输特性,得到了当光纤激光器的输出光束包含高阶模式时,激光器阵列相干合成的远场光强分布模型。同时以光纤激光器中输出混合模式为LP01和 LP11以及输出混合模式为LP01和LP02两种情况为例,分析了存在高阶模式的远场相干条纹的峰值功率和条纹对比度。结果表明,当光纤激光器中高阶模式为 LP11模时,远场相干条纹的峰值能量随着LP11模的增加线性下降;当光纤激光器中高阶模式为LP02模时,远场相干条纹的条纹对比度随着 LP02模的增加线性下降。     

Design Considerations of Broadband Dual-Mode Optical Fibers

We propose and present design data for a new type of graded index fiber which has a profile and radius such that only two mode groups (LP/sub 01/ and LP/sub 11/) propagate and both propagate with virtually identical group velocities. This dual-mode fiber has a core diameter approximately twice that of a conventional step index single-mode fiber. For example, a core diameter of 16.3 mu m is attainable with relative index difference Delta=0.3 percent at 1.25-mu m wavelength. Fabrication tolerances securing a group delay difference below 100 ps/km are given by a power-law profile parameter alpha=4.85/spl plusmn/0.25 and a normalized frequency upsilon=4.45/spl plusmn/0.11. The allowable upsilon-value deviation range to keep the group delay difference within 100 ps/km is about five times as large as that of a step-index fiber, in which group delays of two mode groups are matched. Comparison with a multimode graded-index fiber, with respect to group delay characteristics and bending loss of the dual-mode fiber, are also discussed.     

Amplification of high-order azimuthal mode based on a ring-core Yb-doped fiber

In order to increase the number of amplified azimuthal modes in Yb-doped fiber (YDF), a multiple azimuthal modes amplifier based on a ring-core Yb-doped fiber (RC-YDF) was proposed and demonstrated. A home-made RC-YDF which can support 6 azimuthal mode groups was employed to amplify the signal mode at 1 064 nm, using a core pump scheme. The amplification characteristics of 5 high-orderazimuthal linear polarization (HA-LP) mode groups (LP11, LP21,LP31, LP41, LP51) were studied comprehensively. A more than 8 dB gain is obtained for each signal mode with 5 dBm input power, and the associated differential modal gain between all modes is less than 1 dB. The intensity profiles of all modes are stable and well preserved during the process of amplification.     

Observation of polarization property in near-field optical imaging by a polarization-maintaining fiber probe

We fabricated an original near-field scanning optical microscopy (NSOM) fiber probe made of polarization-maintaining and attenuation-reducing (PANDA)-type polarization-maintaining optical fiber, and observed the polarization property of propagation light in a polymer optical waveguide. The distribution of the transmission coefficient in polarization angles through this NSOM probe showed that the linear polarization is maintained in the two crossing directions: the fast and slow axes. The polarization degree parallel to the slow axis decreases from 1000:1 to 2:1 by bending the fiber probe and the decrease is independent of the bending direction. Using this PANDA-type NSOM probe, we investigated the polarization property of periodic intensity modulation. It was found that the intensity modulation was observed clearly with the electric vector parallel to the radius direction of the waveguide, but was observed vaguely with the electric vector perpendicular to the radius direction.     

一种基于三芯光纤的模式复用器/解复用器的设计

提出了一种基于三芯光纤的模式复用器/解复用器,三个纤芯包括两个相同的单模纤芯和一个少模纤芯,在少模纤芯中写入长周期光纤光栅以实现单模纤芯中LP01模与少模纤芯中LP11模间的转换。同时从两个单模纤芯输入LP01模,能激发少模纤芯中两个简并的LP11,a模和LP11,b模。采用光束传播法分析了该模式复用器/解复用器的耦合特性及串扰。数值模拟结果显示,若以少模纤芯中LP11模输出能量大于-1dB的波长范围作为该模式复用器/解复用器的工作带宽,则能够达到23nm,并且少模纤芯中生成的其他模式的输出能量皆比LP11模的输出能量小-21dB以上。该模式复用器/解复用器能够实现对少模光纤的模式复用与解复用,并具有极低的串扰。     

降低模分复用传输中信号串扰的预编码技术

为降低点到多点短距离模分复用传输中的模式串扰,提出了一种基于系数回传的预编码方法.设计了联合控制任意波形发生器(AWG)和示波器(DS0)的控制台,以及连接500 m少模光纤(FMF)的光子灯笼强度调制直接检测(IM-DD)模分复用传输系统,并选用LP01-LP01模式信道和LP11a-LP11b模式信道进行对比实验....     

Rotary propagation characteristics of light in multimode- single mode-multimode fiber structures using ray tracing method

The mode theory is the main way to study the propagation characteristics of light in fiber so far, but it is not suitable for analysis of light in duct. By using ray-tracing method, the rotary propagation characteristics of light in multimode-single mode-multimode (MSM) fiber structures are analyzed in this paper. Firstly, the light ray in fiber can propagate around an inscribed circle, and the central axis of this fiber is the propagation axis. Secondly, the radius of the inscribed circle is decided by both incident angle and incident position, and its variation is between 0 and RM, where RM is the radius of the multimode fiber. Lastly, the bigger the ratio of core and cladding diameter is, the higher the propagation efficiency is.     

消除模间干涉现象的光纤光栅模式转换器

光纤通信技术占据了目前通信传输的主要地位,但基于波分复用技术的单模光纤通信系统目前则面临着严重的信道容量危机,因此基于多模/少模光纤的模分复用技术逐渐得到了人们的重视。模式转换器是模分复用技术中的重要器件之一,而长周期光纤光栅是一种很好的全光纤模式转换器。在利用长周期光纤光栅完成LP01到LP11模式转换的基础上,这种新型的模式转换器利用多模光纤消除了模式间干涉,从而使模式转换的模式纯度更高、稳定性更好,在模式转换效率达到99.5%的同时还可以保证几乎没有模式间干涉现象的产生。同时,这种模式转换器的多种传感特性也良好,其对拉力有着很好的线性灵敏性,可以达到2.83 nm/N和5.66 dB/N,因此此结构在未来的模分复用及传感领域会有重要的作用。     

圆波导TE01-TE11模式转换器设计与实现

基于耦合波理论的基础上,分析了TE01-TE11模式转换器的特性和半径渐变指数,讨论了中心轴线弯曲下的圆波导模式转换器,对中心频率33GHz的波导进行了模拟设计、仿真,在保证带宽的前提下,尽力降低转换器的长度和提高转换效率,最后达到了97．82％的转换效率,带宽达到2GHz。     

Reduced phase error of a fiber optic gyroscope using a polarization maintaining photonic crystal fiber

We report the first measurement of the polarization crosscoupling of a 900-m length of quadrupolar-wound sensing coil for the fiber optic gyroscope (FOG) using polarization maintaining photonic crystal fibers (PM-PCFs). The crosscoupling is analyzed with the Optical Coherence Domain Polarimeter (OCDP). Also the polarization extinction ratio (PER) of the PM-PCF coil is measured. For comparison, a standard panda fiber coil with nearly the same length is examined. The results show that PER of the PM-PCF coil is ～10 dB larger than the panda fiber coil, and polarization crosscoupling in the PM-PCF coil is ～10 dB less than in the panda fiber coil. Moreover, based on measurements, a 4-fold reduction in phase error is demonstrated numerically in a FOG made of the PM-PCF coil, compared to the same gyro operated with a similar coil of panda fiber. These findings have important benefits in a higher measurement precision and stability of FOG.     

E&C跟踪对极化角的影响及解决方法

针对船载卫通站使用线极化卫星通信过程中出现的反极化信号干扰问题,根据不同状态下信号电平变化,发现干扰信号强度与天线跟踪角度有关.结合天线采用的三轴稳定体制结构特点,建立天线转动几何模型,通过不同跟踪模式下天线角度的比较,对其相互关系进行了分析,推导出了该体制下极化角计算公式,据此进行极化补偿,有效解决了EC模式下跟踪线...     

LP01 to LP11 mode convertor based on side-polished small-core single-mode fiber

An all-fiber LP01-LP11 mode convertor based on side-polished small-core single-mode fibers (SMFs) is numerically demonstrated. The linearly polarized incident beam in one arm experiences π shift through a fiber half waveplate, and the side-polished parts merge into an equivalent twin-core fiber (TCF) which spatially shapes the incident LP01 modes to the LP11 mode supported by the step-index few-mode fiber (FMF). Optimum conditions for the highest conversion efficiency are investigated using the beam propagation method (BPM) with an approximate efficiency as high as 96.7%. The proposed scheme can operate within a wide wavelength range from 1.3 μm to1.7 μm with overall conversion efficiency greater than 95%. The effective mode area and coupling loss are also characterized in detail by finite element method (FEM).     

声扭波在单模光纤中的应用

光纤中的基模LP01有两种偏振态,通过在油光纤方面加入声扭波可以引起两个偏振模发生耦合,本文主要介绍了声扭波和振幅和色散关系,同时也发现,采用高阶声扭波可以提高耦合系数的值。