利用光纤光栅对实现双波长增益控制掺饵光纤放大器特性的实验研究

控制激光的弛豫振荡和空间烧孔现象的存在，对全光增益控制掺饵光纤放大器(EDFA)的性能产生劣化影响。采用一种新颖简单的利用两对光纤光栅对形成谐振腔结构，实现双波长增益控制掺饵光纤放大器。由两个不同波长的激光共同承担增益控制的任务，降低了控制激光引起的空间烧孔现象和瞬态输出变化。在动态工作条件下，双波长激光增益控制掺饵光纤放大器显示出优越的特性，适用范围扩展为普通单波长增益控制掺饵光纤放大器的两倍，能够适应0—43kHz的上下载频率。     

基于高双折射光纤布拉格光栅的自动增益控制掺铒光纤放大器

掺铒光纤非均匀展宽引起的空间烧孔现象导致单波长激光并不能完全控制放大器增益,提出了一种新颖的自动增益控制掺铒光纤放大器的结构:即采用高双折射光纤布拉格光栅产生抽运光,其写制光栅的波峰对应的波长分别为1549.3 nm和1549.83 nm,波长间隔为0.53 nm。通过调整偏振控制器,就实现了单激光或双激光的增益控制。这种设计增益控制范围为40 nm(1530~1570 nm),当输入功率在-40~-15 dBm的动态范围内,双激光增益控制的掺铒光纤放大器的平均增益和噪声系数分别约为22.22 dB和8.69 dB,而它们的漂移分别被钳制在0.69 dB和1.51 dB。系统性能测试表明:双激光控制掺饵光纤放大器在稳定性方面比单激光有着明显的优势。     

新型双波长激光增益控制掺铒光纤放大器

掺铒光纤非均匀展宽引起的空间烧孔现象导致单波长激光并不能完全控制放大器增益。提出了一种新颖简单的结构，利用自由光谱范围为26．7nm的法布里－珀罗可调谐滤波器和由长周期光纤光栅制成的波长选择性可调谐的衰减器，有效地调整不同波长处的腔内损耗，可以实现不同强度的双波长激射。由两个不同波长的激光共同承担增益控制的任务，降低了控制激光引起的空间烧孔，同时双波长激射有效地抑制了信号光的弛豫振荡。     

一种增益可调掺铒光纤放大器的研究

在所设计的增益可调掺铒光纤放大器中,采用可编程控制器PC机控制可变直流电压源引发压电陶瓷的电致伸缩效应,导致光纤布拉格光栅的Bragg波长发生漂移,实现被调制参数的变化.分析了双光纤光栅受到压电陶瓷电致伸缩效应时的反射谱变化规律和增益可调掺铒光纤放大器的放大特性.由该放大器的增益与输入信号功率的关系得出小的波长间隔,增益较小,但控制范围较大;大的波长间隔,增益较大,但控制范围较小的结论.在输入宽带光源时,得到两光纤布拉格光栅在不同中心波长之差时的掺铒光纤放大器的增益特性.     

掺铒孔辅助导光光纤的特性研究与优化设计

掺铒孔辅助导光光纤是由掺铒的高折射率纤芯、低折射率包层和少量的空气孔组成. 采用有限元法分析了掺铒孔辅助导光光纤的模式特性；给出了数值计算截止波长和模场直径的方法；提出了改进的平均粒子数反转度迭代算法来数值计算掺铒光纤放大器的增益和噪声系数. 研究空气孔对掺铒孔辅助导光光纤的截止波长、模场直径和放大器的增益系数的影响. 发现：减小相对孔芯距的值，可使截止波长向短波长移动，减小模场直径的值；当孔的相对大小较大时，截止波长、模场直径和增益的最大值基本上不随孔的相对大小的增大而改变. 最后，综合考虑掺铒光纤基模和二阶模的截止波长、与普通单模光纤的熔接损耗、放大器的增益和噪声系数等因素，优化设计了掺铒孔辅助导光光纤的四个结构参量——纤芯半径、纤芯与包层的折射率差、相对孔芯距和孔的相对大小. 关键词： 孔辅助导光光纤 掺铒光纤 光纤放大器 有限元法     

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.     

掺铒光纤Sagnac环掺铒光纤放大器增益平坦特性

在通信领域,特别是波分复用方面,为了同时调整多通道增益和实现多波长光纤激光器大范围稳定的光波输出,本文提出了一种未泵浦掺铒光纤Sagnac环透射端掺铒光纤放大器增益平坦特性研究方案,其由Sagnac环自身谐振模式、未泵浦掺铒光纤的吸收特性和由环中双折射拍长引起的谐振模式3者共同作用。通过调节Sagnac环中的偏振控制器,使得掺铒光纤放大器(EDFA)增益光谱在非泵浦掺铒光纤Sagnac环透射端可以被部分或者全部平坦化。实验结果表明:在透射端14 nm的波长范围内,部分增益光谱的平坦度为±0.145 dB;整个C波段光谱36.5 nm的波长范围内,增益光谱的完全平坦度为±1.225 dB。该增益谱平坦方案结构简单,输出光谱平坦度好,有望用于波分复用系统和多波长激光器中。     

915nm泵浦混合掺铒/铒镱共掺双包层光纤放大器

研究了一种混合掺铒/铒镱共掺光纤放大器,用掺铒光纤放大器作为输入信号的预放大器,用铒镱共掺双包层光纤放大器作为主放大器。掺铒光纤放大器采用20m长掺铒光纤作为增益介质,采用最大输出功率318mW的单模半导体激光器二极管作为泵浦源,预放大器获得的最大输出功率是113mW。铒镱共掺光纤放大器采用14m长铒镱共掺双包层光纤作为增益介质,采用2个915nm多模半导体激光二极管作为泵浦源,在输入信号功率为10mW、信号波长1555nm时,混合光纤放大器获得了最大输出功率为32.04dBm,即1.6W,与此相应的混合光纤放大器的光-光转换效率为18.5%。     

一种基于新型长周期光纤光栅的动态增益均衡器

报道了一种用高频CO²激光脉冲写出的长周期光纤光栅的温度特性和弯曲特性.实验表明,这种长周期光纤光栅的波长漂移随温度的变化呈线性关系,它的透射峰幅值变化随弯曲量的变化也呈线性关系.基于这两种线性关系,通过控制新型长周期光纤光栅的谐振峰位置和幅度,动态平坦了一组掺铒光纤放大器增益谱线.实验结果表明在C波段32nm范围内掺铒光纤放大器增益谱线平坦度可动态调整为±0.7dB.     

L波段掺铒光纤放大器的自发辐射谱与增益的研究

利用Giles模型对L波段掺铒光纤放大器小信号增益特性进行了数值模拟,模拟结果表明最佳铒纤长度并不是一定值,它随输入信号波长的不同而改变,较短的波长对应较短的光纤长度;在数值模拟、分析的基础上,分别采用7m和9m的L波段铒光纤构成长波段掺铒光纤放大器,通过实验测量,分析比较了它们的自发辐射谱以及增益和噪声指数,得到了光纤长度对L波段增益谱、噪声指数和自发辐射谱的影响规律;最后,辅以C波段掺铒光纤放大器加以分析,指出了适合于放大L波段信号的最佳自发辐射谱型。     

Dynamic-channel-equalizer using in-line channel power monitor and electronic variable optical attenuator

We propose and demonstrate a polarization-insensitive dynamic-channel-equalizer (DCE) for compensating erbium-doped-fiber-amplifier (EDFA) amplified signals after dynamic optical add/drop. The DCE can be monolithically integrated on silicon-on-insulator (SOI) platform and is potentially low cost and compact. The DCE can compensate complicated gain slope shape, which may be generated in cascaded EDFAs or deliberate channel add/drop, based on individual channel equalization. Fifteen-decibel receiver sensitivity improvement at 10 Gb/s bit-error-rate (BER) measurement of 10⁻⁹ was achieved in the compensated channel by removing cross-gain-modulation generated by neighboring channel add/drop.     

Modeling Gain Dynamics in EDFAs: Space-Resolved Versus Lumped Models

We present a detailed comparison of dynamic space- and frequency-resolved and lumped erbium-doped fiber amplifier (EDFA) models. The space- and frequency-resolved models are based on an iterative solution of propagation equations for pump, multiple signals, and spectral components of forward and backward propagating amplified spontaneous powers and rate equations for pump, metastable, and ground energy level population densities of erbium ion. In contrast to space-resolved models, the lumped model solves a single ordinary differential equation for time evolution of the length-averaged metastable level population and is therefore substantially less computer time consuming. Both the space, and frequency-resolved and the lumped models give almost identical results when used for an analysis of surviving channel power excursions in concatenated EDFAs fed by multiwavelength signal and add/drop scenarios. For a statistical analysis of output power and signal-tonoise ratio fluctuations in EDFA cascades fed by burst-mode packet traffic, only lumped models can be used.     

Modeling Gain Dynamics in EDFAs: Space-Resolved Versus Lumped Models

We present a detailed comparison of dynamic space- and frequency-resolved and lumped erbium-doped fiber amplifier (EDFA) models. The space- and frequency-resolved models are based on an iterative solution of propagation equations for pump, multiple signals, and spectral components of forward and backward propagating amplified spontaneous powers and rate equations for pump, metastable, and ground energy level population densities of erbium ion. In contrast to space-resolved models, the lumped model solves a single ordinary differential equation for time evolution of the length-averaged metastable level population and is therefore substantially less computer time consuming. Both the space, and frequency-resolved and the lumped models give almost identical results when used for an analysis of surviving channel power excursions in concatenated EDFAs fed by multiwavelength signal and add/drop scenarios. For a statistical analysis of output power and signal-tonoise ratio fluctuations in EDFA cascades fed by burst-mode packet traffic, only lumped models can be used.     

Performance Degradation due to Cascaded Erbium Doped Fiber Amplifier Power Transients in Wavelength Routed Optical Networking

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Performance Degradation due to Cascaded Erbium-Doped Fiber Amplifier Power Transients in Wavelength Routed Optical Networking

We have investigated the fast power transient effect of the cascaded erbium-doped fiber amplifiers (EDFA) in wavelength routed optical networks. The bit error ratio (BER) degradation of surviving channel was measured at the different adding/dropping frequencies of the disturbed channels. The result show that, for low channel-adding/dropping frequency closed to EDFA transient rate, the transmission performances of the surviving channels are impaired severely.     

Impact of the all-optical gain-clamping technique on the transience characteristics of cascaded discrete fiber Raman amplifiers

We theoretically analyse the dynamic response of amplifier cascades involving combinations of unclamped and gain-clamped discrete fiber Raman amplifiers (DFRAs) in the worst possible case of power transients. We consider a 64-channel system in which all of the channels except one (i.e. the surviving channel) are modulated to simulate channel add/drop. We vary the number and the position of the gain-clamped DFRAs in the cascade to determine whether a cascade in which only a few amplifiers are gain-clamped (referred to as a mixed cascade) can be as effective as a cascade comprising all gain-clamped amplifiers for controlling the power transients within tolerable limits (for example, 1 dB). We take into account the location of the surviving channel and the operational regime of the amplifiers. Our results show that the location of the gain-clamped DFRAs in a mixed cascade affects the transient characteristics and that it is possible to control the transients within tolerable limits.     

Tunable add/drop channel coupler based on an acousto-optic tunable filter and a tapered fiber

We report a tunable add/drop channel coupler based on an acousto-optic tunable filter and a tapered fiber. The coupling efficiency and central wavelength of the add/drop channel coupler are tunable by simply tuning the power and frequency of the driving radio frequency signal. Further possible improvements on the configuration are also discussed.     

Development of an Automatic Gain Controller Card or Next Generation EDFAs

This paper describes a low cost automatic gain controller card that provides fast transient gain control to maintain the power of the surviving channels when the number of input channels to an erbium-doped fiber amplifier (EDFA)changes rapidly.     

Design and analysis of two-dimensional photonic crystals channel filter

A novel three-port channel add/drop filter consisting of two waveguides and two cavities is proposed. One is used for a resonant tunneling-based channel add/drop operation from the bus waveguide to the add/drop waveguide, while the other is used to realize the wavelength-selective reflection feedback in the bus waveguide. By means of coupled mode theory in time, the conditions to achieve 100% add efficiency are derived thoroughly. Based on these theoretical analysis, the channel add filter and some other multi-channel filters are designed in two-dimensional photonic crystals (2D PCs) with square lattice of dielectric rods in air. The numerical results by using the finite-difference time-domain (FDTD) method demonstrate almost complete channel add/drop tunneling at resonance via the three-port systems.