基于遗传算法的少模光纤放大器增益均衡

根据少模掺铒光纤放大器的放大理论,对四模式复用信号和五模式复用信号进行增益仿真研究。通过遗传算法分别优化三层掺铒的四模式群组少模光纤放大器和四层掺铒的五模式群组少模光纤放大器。仿真优化的结果表明,利用980 nm的两模式复用泵浦并以芯层泵浦前向抽运的方式对1550 nm四模式复用信号进行放大,得到的信号各模式的平均增益为24.48 dB,模间增益差值为0.103 dB;以980 nm三模式复用泵浦并对五模式复用信号进行放大,得到的信号各模式的平均增益为23.31 dB,模间增益差值为0.016 dB。通过优化泵浦模式组合及光纤掺杂结构,提高了四模式群组与五模式群组少模光纤放大器在C波段的增益性能。     

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.     

铋基掺铒光纤放大器宽带放大特性的理论研究

研制了铋酸盐基质掺铒玻璃43Bi2O3-30B2O3-27SiO2,测试分析了玻璃中Er3+离子的光谱性质。结合获得的Er3+离子光谱参数,建立了一个以该铋基掺铒玻璃作为放大器增益介质时Er3+离子跃迁的三能级理论模型,研究了铋基掺铒玻璃光纤放大器(Bi-EDFA)的信号放大特性。研究显示,单波长输入情形下,Bi-EDFA具有大于40dB的信号增益和75nm的3dB波长带宽。同时,相比于硅基掺铒光纤放大器(Si-EDFA),Bi-EDFA具有优异的多波长信号宽带放大和低噪声特性,低噪声系数(~5.5dB)可维持至1610nm波长之外。结果表明,铋基掺铒玻璃光纤放大器是一种单位长度增益极高和宽带放大能力的小型化掺铒光纤放大器,适合于WDM系统的集成化需求。     

基于掺铒光纤/喇曼混合放大的光纤激光器布喇格光栅传感系统

提出了一种提高长距离光纤布喇格光栅信噪比以进行准分布测量的新方法.该方法基于掺铒光纤/喇曼混合放大的光纤激光器结构,掺铒光纤和滤波器构成的环形结构产生激光作为光源,喇曼光纤放大器对布喇格光栅信号进行低噪音的双向放大,置于远处的掺铒光纤利用剩余的泵浦功率产生自发辐射光和放大传感信号,为远处掺铒光纤之后的布喇格光栅传感器提供信号光以及补偿由于长距离传输造成的光纤损耗.实验显示,与使用宽带光源的传感方式相比,系统的性能得到显著提高,仅使用小功率泵浦,分布在50 km光纤上的FBG均获得了超过58 dB的优良信噪比.     

有源循环式光脉冲复制系统的输出特性研究

改进并验证了一种基于有源循环光纤延迟线的模拟光脉冲信号复制技术.实验系统采用低增益掺铒光纤放大器补偿循环损耗.进行了光脉冲信号复制的仿真和实验,在掺铒光纤放大器增益为6.774 dB,光滤波器－3 dB,带宽为0.8 nm时,测得第500个复制光脉冲的信噪比为31 dB.仿真和实验结果表明,选用小增益掺铒光纤放大器可以实现低于3 dB的噪音系数,降低掺铒光纤放大器的放大自发辐射噪音并提高输出脉冲序列的信噪比,有望成为提高光脉冲复制器性能的一种新方法.在系统中插入窄带光滤波器等手段也是改善信噪比的有效措施.     

石英基L波段扩展掺铒光纤及其放大性能

掺铒光纤放大器的增益带宽是限制光纤通信系统传输容量提升的重要因素.受铒离子激发态吸收所限,常规L波段掺铒光纤难以实现更长波段的带宽扩展.本文基于改进的化学气相沉积工艺成功制备了P/Al共掺石英基L波段扩展掺铒光纤,研究了共掺离子对于铒离子4I13/2能级到4I9/2能级激发态吸收的影响.通过分别搭建单级前向泵浦和多级的放大结构,测试了其宽带放大性能.基于前向980 nm泵浦的单级结构,当输入信号功率为–9 dBm,泵浦功率为530 mW时,该光纤在1625.3 nm处增益达10.5 dB,最大噪声指数为5.9 dB.多级放大结构下,该光纤在1625.3 nm处增益可达23.4 dB.实验结果表明P/Al共掺石英基掺铒光纤可以有效抑制铒离子的激发态吸收,为进一步扩展L波段增益带宽提供了强有力的可行方案.     

基于新型长周期光纤光栅的掺铒光纤放大器

报道了基于高频CO₂激光脉冲写入的新型长周期光纤光栅的低噪音掺铒光纤放大器,这种新型长周期光纤光栅是用大约几千Hz的高频CO₂激光脉冲对光纤玻璃热冲击作用而形成的.在铒纤中插入一个长周期光纤光栅,会明显减少掺铒光纤放大器的放大自发辐射(ASE)噪音.报道了两种低噪音掺铒光纤放大器,作为前置放大器和线路放大器,它们的ASE噪音指数分别从4.0 dB减少到3.5 dB和从4.8 dB减少到4.3 dB,并且在作为线放时,其小信号增益从30 dB提高到37 dB,降噪及提高增益效应十分显著.     

基于半导体光放大器的可调谐多波长光纤激光器

报道了一种新型环形腔可调谐多波长光纤激光器，腔内以半导体光放大器为增益介质，利用高双折射光纤构成的高双折射环形镜的滤波特性，在室温下，获得了基本符合ITU-T标准100GHz的17个波长以上的稳定多波长输出.各信道峰值功率差小于6 dB，线宽小于0.102 nm，信噪比大于25 dB.通过调节高双折射环形镜内的偏振控制器状态实现了这一组波长整体在50GHz范围内连续可调谐.并利用实验方法，对该光纤激光器应用于掺铒光纤放大器对多信道放大性能测试的可行性进行了初步探讨.     

带光隔离器的掺铒光纤放大器性能分析

本文通过速率方程对带光隔离器的掺铒光纤放大器(EDFA)的性能进行了理论分析.由于光隔离器有效地抑制了反向传输的放大自发幅射(ASE),从而改善了掺铒光纤放大器的增益、噪音系数和输出功率等性能,分析结果表明光隔离器加在最佳位置时,可使小信号增益提高约5dB,噪音系数降低约1.6dB.     

基于喇曼/掺铒光纤混合放大的长距离布喇格光栅传感器系统

提出了一种提高长距离光纤布喇格光栅信噪比以进行准分布测量的新方法.本方法基于双向喇曼放大和双掺铒光纤结构,喇曼光纤放大器对布喇格光栅信号进行低噪音的双向放大,置于远处的掺铒光纤利用剩余的泵浦功率产生自发辐射光和放大传感信号,为第二段掺铒光纤之后的远处布喇格光栅传感器提供光以及补偿由于长距离传输造成的光纤损耗.实验显示传感器系统的性能得到显著提高.使用功率为240 mW的单个普通泵浦,分布在50 km光纤上的FBG均可获得15 dB的良好信噪比,比混合放大前提高了10 dB.     

Effect of Cascading Amplification Stages on the Performance of Serial Hybrid Fiber Amplifier

Abstract

This study demonstrates simulation and experimental validation of a wideband serial hybrid Raman/erbium-doped fiber amplifier. Two configurations are adopted; in type A, a Raman amplifier is the first stage, and in type B, an erbium-doped fiber amplifier is the first stage. At low input signal power, the average gain level is 20 dB with a flat gain bandwidth of 40 nm for both configurations. The noise figure in type B is dominated by the erbium-doped fiber amplifier and produces lower values and flatter spectra than in type A. The gain of the proposed hybrid amplifiers is affected more by the second amplification stage.     

All-fiber few-mode erbium-doped fiber amplifier supporting six spatial modes

Using the few-mode erbium-doped fiber(FM-EDF) with a simple two-layer erbium-doped structure, we demonstrate an all-fiber FM-EDF amplifier. The gain equalization among the six spatial modes supported by the FM-EDF is achieved when only the pump in the fundamental mode(LP_(01)) is applied. When the signals in six spatial modes are simultaneously amplified, the average modal gain is about 15 dB, and differential modal gain is about 2.5 dB for the signal at 1550 nm.     

1550 nm飞秒脉冲自相似光纤放大仿真模拟EI北大核心CSCD

针对全光纤的超短脉冲掺铒光纤放大器进行了仿真模拟,对正常色散条件下掺铒光纤自相似脉冲放大过程进行了详细分析。在光纤预放大器中,使用高正色散掺铒光纤对脉冲形状进行预整形,将重复频率43 MHz、脉冲宽度600 fs、平均输出功率1.2 mW的孤子型锁模脉冲预整形为抛物线型脉冲,预整形后的脉冲通过光纤主放大器进行功率放大。经两级光纤放大后,1.2 mW的信号光功率放大为102 mW,放大增益19.3 dB。分析了掺铒光纤长度、放大功率对脉冲自相似演化过程的影响。放大后的脉冲经4.4 m长单模光纤将脉冲宽度压缩至53 fs,峰值功率为44.8 kW。     

宽带放大器用碲基掺铒光纤结构参量的设计考虑

利用光波导理论及均匀展宽四能级模型，研究了宽带放大器用阶跃型折射率分布碲基掺铒光纤的结构参量—纤芯半径和相对折射率差的设计考虑.理论研究表明，在单模传输条件下，为获取最大信号增益，宜选择相对折射率差大的碲基掺铒光纤来构建光纤放大器.相对折射率差一定的情况下，在高泵浦功率、小信号输入或光纤长度短于各信道最佳增益长度时，选择纤芯半径大的碲基掺铒光纤可以得到大的信号增益；反之，宜选择纤芯半径小的碲基掺铒光纤.     

Weak laser pulse signal amplification based on a fiber Brillouin amplifier

We propose a high-gain and frequency-selective amplifier for a weak optical signal based on stimulated Brillouin scattering in a single mode fiber. To be able to satisfy the needs of high gain and high signal-to-noise ratio laser pulse amplification, different fiber lengths and core diameters are used to fulfill this experiment. In the experiment, a 430 nW(peak power) pulsed signal is amplified by 70 dB with a signal-to-noise ratio of 14 dB. The small size, high gain, low cost, and low noise of the fiber Brillouin amplifier make it a promising weak signal amplification method for practical applications such as lidar.     

Observation of orbital angular momentum transfer between acoustic and optical vortices in optical fiber

Acousto-optic interaction in optical fiber is examined from the perspective of copropagating optical and acoustic vortex modes. Calculation of the acousto-optic coupling coefficient between different optical modes leads to independent conservation of spin and orbital angular momentum of the interacting photons and phonons. We show that the orbital angular momentum of the acoustic vortex can be transferred to a circularly polarized fundamental optical mode to form a stable optical vortex in the fiber carrying orbital angular momentum. The technique provides a useful way of generating stable optical vortices in the fiber medium.     

Double-pass erbium-doped zirconia fiber amplifier for wide-band and flat-gain operations

The double-pass erbium-doped zirconia fiber amplifier (EDZFA) is proposed and demonstrated to provide a wide-band amplification as well as flat-gain operation in both the C- and L-band regions using only a single-gain medium. The proposed amplifier utilizes an erbium-doped zirconia fiber (EDZF) with erbium ion concentration of 2800 ppm as a gain medium. The medium is fabricated in a ternary glass host, zirconia-yttria-aluminum codoped silica fiber through solution doping technique along with modified chemical vapor deposition (MCVD). Compared to a single-pass operation, the double-pass EDZFA shows a better gain performance. At input signal power of 0 dBm and the optimum EDZF length of 2 m, a flat gain of around 16 dB is achieved by the proposed double-pass amplifier with gain variation of approximately 2.5 dB throughout the wavelength range from 1530 to 1590 nm. However, the noise figure of the double-pass amplifier is slightly higher than that of the single-pass due to inefficient population inversion at the input part of the amplifier.     

Enhanced structure of a double-pass erbium-doped fiber amplifier for multiple wavelength amplifications

We demonstrate an enhanced double-pass erbium-doped fiber amplifier for multichannel amplification. The multichannel selection is formed by combining a demultiplexer and a multiplexer together in the fiber-loop mirror. The structure is able to filter out the amplified spontaneous emission that saturates the amplifier gain in the small signal regime. The maximum average gain of 47.2 dB is obtained with a gain enhancement of 12.8 dB at a ?50-dBm signal power per channel. The noise figure penalty is almost negligible for a signal power per channel of less than ?15 dBm.     

Long-distance fiber Bragg grating sensor system with a high optical signal-to-noise ratio based on a tunable fiber ring laser configuration

A novel tunable fiber ring laser configuration with a combination of bidirectional Raman amplification and dual erbium-doped fiber (EDF) amplification is proposed for realizing high optical signal-to-noise ratio (SNR), long-distance, quasi-distributed fiber Bragg grating (FBG) sensing systems with large capacities and low cost. The hybrid Raman-EDF amplification configuration arranged in the ring laser can enhance the optical SNR of FBG sensor signals significantly owing to the good combination of the high gain of the erbium-doped fiber amplifier (EDFA) and the low noise of the Raman amplification. Such a sensing system can support a large number of FBG sensors because of the use of a tunable fiber Fabry-Perot filter located within the ring laser and spatial division multiplexing for expansion of sensor channels. Experimental results show that an excellent optical SNR of approximately 60 dB has been achieved for a 50 km transmission distance with a low Raman pump power of approximately 170 mW at a wavelength of 1455 nm and a low EDFA pump power of approximately 40 mW at a wavelength of 980 nm, which is the highest optical SNR achieved so far for a 50 km long FBG sensor system, to our knowledge.