小芯径光子晶体光纤中基于前向受激布里渊散射的超光速传输特性（英文）

理论研究了小芯径光子晶体光纤中基于前向受激布里渊散射的快光.利用前向受激布里渊散射三波耦合方程,通过傅里叶变换,计算小芯径光子晶体光纤中的群折射率和增益系数.用有限元法模拟了声场和光场的分布、信号光时间提前量和展宽因子.小芯径光子晶体光纤中光场与声场可以有效地重叠在纤芯中,增强了它们之间的非线性相互作用,导致强的受激布里渊散射和大的时间提前量.随着信号光传输距离的增加,时间提前量成非线性增长,与此同时,信号光被压缩.随着初始脉冲的增大,脉冲展宽因子逐渐趋于平稳.当传输距离为70 m,初始脉冲宽度为200 ns,泵浦功率为600 mW,计算出时间提前量为21.76 ns和脉冲展宽因子为0.77.     

基于布里渊载波相移的宽带可调谐二倍频微波信号生成

本文提出并实验验证了一种基于光纤中受激布里渊散射效应的光子二倍频微波信号生成技术.利用布里渊增益谱内的强色散特性,对光强度调制器产生的双边带调制信号的载波进行π/2相移,可实现载波与±1阶边带拍频仅生成二倍频微波信号.由于光纤中受激布里渊散射的窄带特性以及仅对双边带调制信号的载波进行相移,不影响调制信号两个边带的幅值和相位,因而生成的二倍频微波信号可实现宽带调谐,调谐范围仅受其他光器件的工作带宽限制.此外,信号光和产生受激布里渊散射的抽运光均来自同一光源,因而不受波长漂移的影响,系统具良好的稳定性.     

基于石英柱模型的光子晶体光纤异常布里渊散射特性的理论研究

通过石英圆柱模型,理论研究了小芯径光子晶体光纤中混合声波模式的色散、模式耦合以及声光相互作用,理论计算出了布里渊散射增益系数谱的双峰结构及其随抽运光波长和温度的演化规律. 理论分析表明光子晶体光纤中布里渊散射增益系数谱的双峰结构源于小芯径光子晶体光纤中混合声波模式之间的模式耦合. 通过温度改变导致的材料参数变化对声波模式色散特性的影响,特别是声波模式耦合点的移动,解释了双峰结构随外界温度的变化规律. 并且,通过理论计算与实验结果的对比讨论了石英圆柱模型的局限性和适用范围. 关键词： 布里渊散射 声光相互作用 模式耦合 光子晶体光纤     

光子晶体光纤中基于受激布里渊散射实现快光的数值模拟研究

为了了解基于光纤受激布里渊散射快光传输系统的一些外在因素对受激布里渊散射快光传输的影响,对该传输过程进行了研究。首先,根据受激布里渊散射过程的"三波耦合方程"进行了理论改进,然后选定了3种光子晶体光纤作为传输介质,通过对比,选出一种光子晶体光纤RB65进行具体分析研究。通过求解"三波耦合方程",对快光受激布里渊散射过程进行了模拟分析,探讨了光纤长度、探测信号脉冲宽度和输入信号功率对传输的影响。结果表明,在保证信号失真相对较小的情况下,取40 m长度光纤、140 ns信号脉宽和174 m W输入信号功率时的快光提前效率最高。     

光子晶体光纤中受激布里渊散射慢光研究

基于受激布里渊散射的慢光在全光通信中具有重要的应用前景。传统的光纤作为慢光介质,具有较低的延迟效率,对光纤长度和抽运功率要求较高,而高非线性光子晶体光纤作为慢光介质应用于慢光系统,可以提高系统的延迟效率。实验选用一段70m长的高非线性光子晶体光纤作为慢光介质,在抽运功率101mW情况下,50ns脉冲信号获得了33dB的布里渊增益,脉冲延迟了30ns,延迟效率达到了0.0046ns/(mW.m),是普通单模光纤的13.7倍。该光纤应用于受激布里渊散射慢光系统可以有效缩短光纤长度和降低对抽运功率的要求,具有潜在的应用前景。     

大功率单频多芯光纤放大器中抑制受激布里渊散射的分析

针对多芯光纤完善了描述抽运光、信号光和Stokes信号的速率方程组.考虑了温差对受激布里渊散射的影响,利用有限元法求解温度分布方程组,分析了前向和后向抽运方式、对流系数、Stokes初始功率、光纤掺杂粒子密度和光纤长度对受激布里渊散射增益的影响.研究表明：后向抽运方式在抑制受激布里渊散射方面具有明显优势;减小对流系数有助于抑制受激布里渊散射;提高光纤掺杂密度能够加强抑制受激布里渊散射,同时也有助于提高光纤放大器的斜率效率.比较了在相同最佳光纤长度条件下,单芯和19芯光纤放大器的最高工作温度和受激布里渊散射 关键词： 光纤放大器 受激布里渊散射 大功率 有限元法     

一种可用于轨道角动量的受激布里渊放大的光子晶体光纤放大器

为了实现高纯度轨道角动量模式的传输和放大,本文提出了一种可用于轨道角动量的受激布里渊放大的光子晶体光纤放大器并对其结构进行了设计.利用有限元法在C波段内对该光子晶体光纤放大器的传输性能进行了系统分析,研究结果表明,该光子晶体光纤放大器可支持66种轨道角动量模式的高纯度传输和放大,其传输的轨道角动量模式的纯度均高于99.4%.通过对不同拓扑荷数的轨道角动量模式的布里渊增益谱进行系统的分析,发现均具有较高的布里渊增益系数(>7×10^-9 m/W),与现有的性能最优的OAM放大器相比提高了4—5个数量级,实现了较高的信号增益.该光子晶体光纤放大器的综合性能显著优于现有基于受激布里渊放大的光纤放大器和掺杂稀土离子的光纤放大器,这使其能够稳定、准确地对OAM模式进行同步放大和长距离传输,为轨道角动量模式激光系统的设计提供了一种可能.     

基于光纤环形腔结构的布里渊频移器设计

为了达到布里渊光时域分析(BOTDA)系统双通道激光源的布里渊频移要求,设计了一个光纤布里渊频移器,放置在其探测脉冲通道,使探测光与另一通道的扫频光具有布里渊频移差(约11.2GHz)。通过分析频移器的输出光谱线宽窄化原理,利用光纤中激发的布里渊增益谱结合一定的环形腔结构形成窄线宽的布里渊斯托克斯光谱输出,且分析了环形腔频移器的受激布里渊散射阈值和光-光转换效率两个性能指标及其影响因素。采用1551nm窄线宽光源,对实际搭建的9km单模光纤布里渊频移器进行了实验验证,结果表明:频移器的受激布里渊散射阈值为2.3mW,布里渊频移对应的波长改变约为0.1nm,此时的定向耦合器耦合比为0.4,光-光转换效率为49%。所设计的光纤布里渊频移器能达到布里渊光时域分析系统光源的技术指标,降低了系统的复杂性和成本。     

一种增益平坦的光子晶体拉曼光纤放大器

为解决传统拉曼放大器增益系数低和增益不平坦的问题,采用级联光子晶体光纤的设计方法设计了一种增益平坦的拉曼光纤放大器.采用受激拉曼散射效应的稳态分析理论,分析了光子晶体光纤的拉曼增益谱,建立了拉曼放大器的理论模型.通过解耦合方程,推导了实现增益平坦的约束条件,发现光纤长度和泵浦功率是影响拉曼光纤放大器增益平坦度的两个参数.仿真结果表明,在1 508～1 544 nm的带宽范围内,实现了一个增益高达21 dB,增益平坦度仅为0.14 dB的光子晶体拉曼光纤放大器,可在光纤通信系统应用中发挥重要作用.     

一种增益平坦的光子晶体拉曼光纤放大器（英文）

为解决传统拉曼放大器增益系数低和增益不平坦的问题,采用级联光子晶体光纤的设计方法设计了一种增益平坦的拉曼光纤放大器.采用受激拉曼散射效应的稳态分析理论,分析了光子晶体光纤的拉曼增益谱,建立了拉曼放大器的理论模型.通过解耦合方程,推导了实现增益平坦的约束条件,发现光纤长度和泵浦功率是影响拉曼光纤放大器增益平坦度的两个参数.仿真结果表明,在1 508~1 544nm的带宽范围内,实现了一个增益高达21dB,增益平坦度仅为0.14dB的光子晶体拉曼光纤放大器,可在光纤通信系统应用中发挥重要作用.     

Threshold reduction of stimulated Brillouin scattering in photonic crystal fiber

A simple configuration for the reduction of stimulated Brillouin scattering threshold in photonic crystal fiber is presented. The threshold reduction is contributed by the bidirectional pumping scheme through the reflection of transmitted Brillouin pump back to the gain medium. The pump recycling scheme has greatly reduced the Brillouin threshold of a 200-m long of photonic crystal fiber from 50 to 30 mW of Brillouin pump power.     

Simple tunable multiwavelength Brillouin/Erbium fiber laser utilizing short-length photonic crystal fiber

We have demonstrated a simple ring cavity tunable multiwavelength Brillouin/Erbium fiber laser (MWBEFL), in which 70 m highly nonlinear photonic crystal fiber (HNL-PCF) is used as the Brillouin gain medium. The fiber laser utilizes recycling mechanism to enhance stimulated Brillouin scattering (SBS). The configuration that consists of only 3 optical components is easy to be integrated and improves the practicality. At the maximum 1480 nm pump power of 110 mW and the Brillouin pump power of 3 dBm, 10 stable output channels with more than 10 dB optical signal to noise ratio (OSNR) and 0.078 nm channel spacing could achieve 10 nm tuning ranges.     

Investigation on threshold power of stimulated Brillouin scattering in photonic crystal fiber

We have developed a theoretical approach to simulate stimulated Brillouin scattering (SBS) generation in photonic crystal fiber (PCF). The threshold condition for the SBS occurrence has been derived as a function of fiber parameters and input pump power. A particular emphasis is given to the influence of the input pump power and fiber length on the Brillouin gain in the PCF. To assess threshold pump power accurately, the pump depletion effect has been included by employing the 1% criterion. This simulation can anticipate the Brillouin threshold gain value precisely. The threshold gain varies from 14 to 18 depending on the PCF length.     

Narrowband optical filter, with a variable transmission spectrum, using stimulated Brillouin scattering in optical fiber

A novel shape-adjustable narrowband optical filter utilizing stimulated Brillouin scattering in an optical fiber is proposed and demonstrated. In this scheme, binary-phase-shift-keying modulation is applied to the pump wave to broaden and shape the Brillouin gain spectrum. By choosing an appropriate modulation data pattern, we realized a flat-top steep-cutoff optical bandpass filter with a 3-dB bandwidth of 1.5 GHz and a 10-dB bandwidth of 2 GHz is realized. In addition, a tunable optical notch filter is also realized by deamplification of the anti-Stokes wave.     

Gain and gain-flatness improved photonic crystal fiber Raman amplifier based on a dual-pass amplification configuration with single pump laser

A gain and gain-flatness improved L-band dual-pass Raman fiber amplifier (RFA) utilizing a photonic crystal fiber (PCF) as gain medium is demonstrated. By introducing complementary gain spectra of typical forward and backward pumping single-pass RFA using the same PCF, we finally achieve average net gain level of 22.5 dB with a ±0.8 dB flattening gain in 20-nm bandwidth from 1595 nm to 1615 nm, which is rare in RFAs with only one single pump and no flattening filter. Compared with the single-pass pump configurations, gain level, flatness and bandwidth are greatly improved by using the dual-pass amplification configuration. The limitation of this configuration caused by multi-path interference (MPI) noise and stimulated Brillouin scattering (SBS) is also discussed.     

Variable single-passband narrowband optical filter based on forward stimulated interpolarization scattering in photonic crystal fiber

A variable transmission spectrum single-passband narrowband optical filter is proposed and experimentally demonstrated. It is based on forward stimulated interpolarization scattering (SIPS) in a photonic crystal fiber by applying a differential quadrature phase-shift keying modulation to the pump wave to broaden and shape the SIPS gain spectrum. By choosing the bit rate of the modulation data pattern, a flat-top steep-cutoff optical bandpass filter with a 3?dB bandwidth of 70?MHz and a 10?dB bandwidth of 90?MHz is realized. In addition, a variable narrowband optical notch filter is also realized by attenuation of the pump wave.     

基于少模光纤的SBS光谱阈值特性分析

受激布里渊散射会影响少模光纤传输系统中的信噪比、传输距离与传输容量,是影响传输系统入纤功率提高的重要因素。对阶跃型少模光纤的受激布里渊散射谱的阈值进行了研究,运用了布里渊散射谱、模式联运谱的数学模型对少模光纤散射特性进行了分析,探讨了少模光纤布里渊散射增益谱、阈值增益系数,以及光纤各参量对少模光纤阈值的影响。分析结果表明：SI-10阶跃型少模光纤中存在五种不同的传播模式,不同模式有各自的传输常数以及有效折射率,各模式相互作用导致模式展宽、增益降低,且布里渊散射谱峰值增益系数为3.9×10-11 m·W-1。阈值增益系数受到光纤传感距离的影响,在相对较短距离传输中阈值急速下降,且其趋势随长度增加渐趋平缓,当光纤长度达到22 km时阈值增益系数趋于常数18.1。少模光纤的阈值因光纤长度的递增而递减,且递减趋势渐缓趋于常数20.5 dBm;少模光纤不同模式受激布里渊散射的阈值也因光纤长度的递增而递减最终趋于常数,且不同模式的阈值因模式阶数的递增而递增;少模光纤的阈值随着光纤衰减系数和纤芯半径的递增而递增,且增加趋势缓慢增大。不同衰减系数的光纤其阈值在不同长度趋于常数,衰减系数越大受激布里渊散射阈值越大越容易趋于一常数。     

High-gain and low-distortion Brillouin amplification based on pump multi-frequency intensity modulation

Using a pump with a multi-line spectrum to broaden the Brillouin gain bandwidth is an effective way to achieve lowdistortion amplification with high gain. Here, we theoretically and experimentally investigate the generation of a broadband Brillouin gain spectrum based on multi-frequency intensity modulation in an optical fiber. The arbitrary bandwidth of the Brillouin gain spectrum of stimulated Brillouin scattering(SBS) can be obtained as expected. In our experiment, a broadband Brillouin gain spectrum with a bandwidth of about 200 MHz is demonstrated. We also achieve a low-distortion amplification of a weak signal, whose maximum magnification is 65 d B for a-68-dBm input power signal.     

On the pre-amplified linear cavity multi-wavelength Brillioun-erbium fiber laser with low SBS threshold highly nonlinear photonic crystal fiber

An efficient multi-wavelength Brillouin-erbium fiber laser utilizing low stimulated Brillouin scattering threshold highly nonlinear photonic crystal fiber (PCF) is presented. A Fabry-Perot pre-amplified Brillouin pump configuration was used which consists of 100 m PCF and 10 m erbium doped fiber (EDF). Up to 28 output channels with SNR of more than 20 dB could be generated with modest pump power.