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。     

110 W double-ended ytterbium-doped fiber superfluorescent source with M2 = 1.6

High-power operation of a broadband superfluorescent fiber source has been achieved via the process of amplified spontaneous emission (ASE) in a double-clad Yb-doped multimode-offset-core fiber by using a novel fiber-end termination geometry to suppress lasing. The fiber was cladding pumped by a high-power diode source at 976 nm and yielded a maximum ASE output of 63 and 47 W from the two ends of the fiber, respectively. The maximum combined ASE output was 110 W with slope efficiency with respect to launched pump power of up to 68%. The wavelength spectrum of the ASE source spanned the range from approximately 1032 to 1120 nm, and the bandwidth (FWHM) of the emission spectrum was 40 nm. The output beam was slightly multimode with a beam-quality factor (M2) of 1.6. The prospects for further improvement in performance are considered.     

Enhancement of pump conversion efficiency in preamplified L-band erbium-doped fiber amplifiers

A new configuration of L-band erbium-doped fiber amplifiers (EDFAs) is presented here. The system contains a double-pass L-band EDFA and an optical preamplifier. Different from conventional preamplified double-pass L-band EDFA systems in which only the forward ASE of the preamplifier is re-used as an auxiliary pump, the new system recycles the backward ASE of the preamplifier as well. Two kinds of main L-band EDFAs are studied, both of which include a section of un-pumped erbium-doped fiber placed in a loop reflector. An improvement of up to 110% in pump conversion efficiency is demonstrated with the proposed recycling of the backward ASE, with respect to the system without recycling.     

Role of aggregation in the amplified spontaneous emission of [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] in solution and films

The amplified spontaneous emission (ASE) spectra of the conjugated polymer [2-methoxy-5-(2′- ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is investigated under different conditions such as thin film and solution, solvent type and concentration. Results indicate that aggregation has a pronounced effect on ASE spectra. In solution form, as concentration was increased and thus the proportion of aggregates, a decrease in the ASE emission bandwidth and a red shift of the ASE peak was observed. For the thin film samples, the ASE spectra show two emission bands which were assigned to the first and second vibronic transition of the polymer chains.     

Induced modulational instability in EDFAs in the presence of higher-order nonlinear and dispersive effects

We derive the dispersion equation for erbium doped fiber amplifiers (EDFAs), assuming the supplementary effects of time-derivative nonlinearities including intrapulse Raman scattering and self-steepening incorporated with third order dispersion and product of gain and square of dipole relaxation time parameter, in the extended form of nonlinear Schrödinger equation and investigate their impacts on gain and cut-off frequency of modulational instability (MI) in EDFAs. Also, the influences of those effects on instability of steady-state amplitude, in the form of generation of terahertz pulse train of femtosecond solitons from a weak-modulated signal by induced MI, are numerically simulated and discussed within EDFAs in normalized form.     

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.     

掺铒光纤放大器的理论模拟与全局分析

基于Giles模型并考虑了ASE噪音,对各种泵浦方式下的掺铒光纤放大器(EDFA)进行了数值模拟.提出了一种新的分析方法(增益噪音指数全局分析法),直观有效地分析了EDFA的增益和噪音指数与掺铒光纤长度和泵浦功率的依赖关系,并对各种EDFA的性能作了全面的比较.     

Impact of optical modulation formats on SPM-limited fiber transmission in 10 and 40 Gb/s optimum dispersion-managed lightwave systems

In this paper, 10 and 40 Gb/s optical systems have been investigated for nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ) and RZ-differential phase-shift-keying (RZ-DPSK) data formats. For the range of the optical signal power from −5 to 15 dBm, a maximum self-phase modulation (SPM)-limited transmission distance L_SPM is determined with eye-opening penalty (EOP) >1 dB .The observations are based on the modeling and numerical simulation of optimum dispersion-managed transmission link. Transmission over distances of the order of several hundreds of kilometers has been shown with and without amplified spontaneous emission (ASE) noise of the in-line erbium-doped fiber amplifiers (EDFAs).     

双向掺铒光纤放大器的特性分析

讨论了双向掺铒光纤放大器的结构方案,利用考虑放大的自发辐和北员耗影响的双向掺铒光纤放大器稳态放大速率方程模型分析的增益与掺铒光纤长度、输入信号光功率、帛运光功率及抽运方式等参数之间的关系,研究了单向和双向等功率抽运下正反向噪声系数随正反向信号光输入功率的变化行为。     

Modeling and optimizing of low-repetition-rate high-energy pulse amplification in high-concentration erbium-doped fiber amplifiers

Starting from the modeling of isolated ions and ion-pairs, a closed form rate and power evolution equations for pulse amplification in high-concentration erbium-doped fiber amplifiers (EDFAs) are constructed. According to the equations, the effects of ion-pairs on the performance of a high-concentration EDFA in steady state including upper-state population, ASE powers without input signal are analyzed numerically. Furthermore, the effects of ion-pairs on the dynamic characteristics of low-repetition-rate pulse amplification in the EDFA including the storied energy, output pulse energy and evolution of pulse waveform distortion are systematically studied by using the finite-difference method. The results show that the presence of the ion-pairs deteriorates amplifier performance, such as the upper-state population, ASE power, storied energy, output pulse energy, and saturated gain, etc. For the high-concentration EDFA, the optimum fiber length should be modified to achieve a better performance. The relations between the evolution of pulse waveform distortion or output pulse energy and the input pulse peak power are also discussed. The results can provide important guide for the design and optimization of the low-repetition-rate pulse amplification in high-concentration EDFAs.     

Study on optimum fiber length for maximum gain in C- and L-band EDFAs

We study the optimum fiber length for maximum gain of C- and L-band Erbium Doped Fiber Amplifiers (EDFAs) with fixed pump power. We show that the dependence of the optimum length on the wavelength and power of the signal is stronger in the L than in the C band and validate our findings trough distributed gain measurements. We also show that the predictions of the transcendental power equation model, which neglects the Amplified Spontaneous Emission (ASE), give accurate results for the optimum length even of L-band EDFAs, fact not obvious a priori because of the key rule played by the ASE as a pump source in amplifiers operating in this region.     

Broadband amplified spontaneous emission from an Er(3+)-Tm(3+)-codoped silica fiber

A new type of amplified spontaneous emission (ASE) based on an Er-Tm-codoped silica fiber is reported. When the fiber was pumped at 980 nm, the emission yielded a 3-dB bandwidth over 90 nm (1460-1550 nm) without any external filters, which is twice larger than that produced by conventional Er-doped fiber ASE sources. We believe that the superposition of two ASE bands, one from Er ions near 1530 nm and the other from Tm ions near 1450 nm, results in the broad bandwidth. Temperature-dependent ASE powers and fiber-length-dependent spectra strongly suggest that photon-assisted energy transfer between the sensitizing ion, Er, and the acceptor ion, Tm, plays an important role in changes in the bandwidth's size.     

The temperature dependency of EDFAs in the 1480 nm pumping configuration

A theoretical study of the temperature-dependent gain and noise figure effects on erbium-doped fiber amplifiers (EDFAs) pumped at 1480 nm is investigated, solving the propagation equations related to two level systems. The solution of these equations is based on the population and temperature difference among amplification levels. The temperature-dependent propagation equation considered is used to determine the gain and noise figure effects on EDFAs. The population difference depends on pump and signal powers, Boltzmann factor K_B, cross-sections, noise figure (NF) and Er³⁺ concentration. The temperature-dependent gain and noise figure effect the EDFA length are numerically obtained for the temperature range of −20 °C to +60 °C. All of the analyses consist of the amplified spontaneous emission (ASE) effect.     

基于长周期光纤光栅滤波器的掺铒光纤放大器理论和实验研究

从理论和实验上研究了带有高频二氧化碳激光写入的低成本长周期光纤光栅（LPFG）掺铒光纤放大器（EDFA）.结果表明,单波长和多波长EDFA的性能都可以通过在掺铒光纤（EDF）中插入长周期光纤光栅用作自发辐射噪声（ASE）滤波器或增益平坦器来提高性能.优化设计了带LPFG噪声滤波器的线放EDFA,与没有LPFG噪声滤波器相比,线放的噪声和小信号增益分别被减小和提高了约0.5 dB和7 dB。通过在多波长EDFA的EDF中插入一个LPFG增益平坦滤波器的方法,获得了1.5 dB的增益平坦度,与没有LPFG平坦器相比,EDFA的噪声被减小了0.1 dB,增益被提高了1 dB.     

铋基掺铒光纤放大器中放大自发辐射处理研究

分别设计了一个带光隔离器和一个带光环形器的复合型宽带铋基掺铒光纤放大器(Bi-EDFA),理论上研究了Bi-EDFA中对于后向传输放大自发辐射(ASE)的处理对放大器性能的影响。研究表明,在C+L波段多波长信号同时输入情形下,通过在铋基掺铒光纤中插入一个光隔离器抑制后向传输的ASE,可以提高放大器各波长信号增益,降低噪声系数。利用一个光环形器引导后向传输的ASE去泵浦一段未抽运的低掺杂铋基掺铒光纤,可以显著地提高放大器长波段信号增益,而噪声系数只是略有增加,理论研究与报道的实验结果达到了比较好的一致。研究结果对于新型宽带Bi-EDFA的设计和应用具有一定实际指导意义。     

A high flattening C + L band broadband source based on single pump and the same erbium-doped fiber

In order to realize a high flattening C + L band amplified spontaneous emission (ASE) light output, a broadband source using just one 976 nm laser diode (LD) and two stages erbium-doped fibers (EDF) with the same concentration is proposed theoretically and demonstrated experimentally, and the theoretical analysis and experimental verification are presented in details. Firstly, based on the energy level of Er³⁺, the methods of realizing C + L band ASE output is presented. Then, the system configuration is designed. One 976 nm LD is used for pumping, and the pump light, which is divided into two parts by one coupler, is pumped into two EDFs by wavelength division multiplexer (WDM). A fiber loop mirror (FLM) is used to improve working efficiency. Meanwhile, an optical isolator is used to avoid the effect of reflected wavelength from output facet. Finally, based on the mathematical model of the ASE gain, the length of EDF is discussed as well. In the experiment, by optimizing the length of EDF1 and EDF2, a 0.12 m EDF1 and 16 m EDF2 are adopted. In the end, the flatness of the spectra from 1540 nm to 1610 nm is ±0.91 dB, and the flatness is ±1.65 dB during 1520–1610 nm without any filter. The high flattening C + L band ASE output is achieved by just one 976 nm LD, which can optimize system and reduce the cost as well.     

Amplified spontaneous emission properties of a single mode Er3+-doped tellurite fiber

Spectral characteristics of the amplified spontaneous emission(ASE)from a novel single mode Er3+ doped tellurite fiber with D-type cladding is reported in this letter.When pumped at 980 nm,an ASE source that has nearly a 100-nm flat FWHM bandwidth is obtained with a fiber length of 30-60 cm. Variation of ASE spectra with pump powers and fiber lengths are measured.Output power up to 2.0 mW is obtained with a launched pump power of 660 mW.     

Tapered fiber amplifier with high gain and output power

We present a high-power ytterbium fiber amplifier based on active tapered double-clad fiber (T-DCF) and capable of high single-pass gain. The T-DCF power amplifier seeded with a 320 mW narrow-band signal generates up to 110 W of average output power corresponding to more than 25 dB gain. The amplifier exhibits near-diffraction-limited beam quality (M ² = 1.06) at the highest output power, which was limited by the available pump power. With a broadband seed source, the amplifier produced a gain of nearly 40 dB obtained for low-signal limit of the seed. The high output power combined with high gain is achieved owing to amplified spontaneous emission (ASE) filtering and increased stimulated Brillouin scattering (SBS) threshold inherent to the axially non-uniform geometry. The amplifier operates efficiently with a wide range of input seed powers thus providing the basis for one-stage tapered amplifier which combines the functions of preamplifier and power amplifier and can be a competitive alternative to multi-stage design.     

Effect of injection of C-band ASE on L-band erbium-doped fiber amplifier

The effect of injecting conventional band (C-band) amplified spontaneous emission on the performance of long-wavelength band erbium-doped fiber amplifier (L-band EDFA) is demonstrated. It uses a circulator and broadband fiber Bragg grating (FBG) to route C-band ASE from a C-band EDFA. Injection of a small amount of ASE (attenuation of 20 dB or above) improves the small signal gain with a negligible noise figure penalty compared to that of an amplifier without the ASE injection. A maximum gain improvement of 3.5 dB is obtained at an attenuation of 20 dB. At very large amounts of ASE injection (attenuation of 0 dB), the gain of the amplifier is clamped at 15.2 dB from ?40 to ?10 dBm with a gain variation of less than 0.3 dB. The saturation power is also increased from ?8 dBm (for without ASE injection) to 2 dBm (VOA=0 dB) with a slight noise figure penalty. These results show that the ASE injection technique can be used either for gain improvement or for gain clamping in L-band EDFA.     

Amplification enhancement of L-band erbium-doped fiber amplifiers by reflection scheme

A reflection L-band erbium-doped fiber amplifier (EDFA), which can effectively suppress and completely exploit the backward C-band amplified spontaneous emission (ASE) with a feedback reflection loop, is presented in this paper. The mechanism of the backward ASE secondary pumping effect is experimentally investigated in detail. Our experimental results have shown that, for a given input pump power, compared to the end-pumped EDFA, the gain and output power of the reflection EDFA can be improved considerably without paying much noise penalty. When the EDFA operates with flattened gain spectra, the gain is improved by about 7 dB with an extra noise penalty of about 1.2 dB, where the saturation output power is increased by 2.5–3.2 dB and which may also be made independent of the input signal power.