Gain characteristics of a dual-pump fiber optical parametric amplifier with Raman effect

We investigate the pump-depleted model of a dual-pump fiber optical parametric amplifier(FOPA) with Raman effect.As bandwidth increases,the gain profile of the distorted FOPA would be impacted seriously.Under the widebands,especially when the pump separation is large,zero dispersion wavelength(ZDW) fluctuation is another factor which can not be neglected.Numerical simulations with these comprehensive factors are mainly analyzed to obtain their influence on gain characteristics.Saturated gain spectrum is also discussed in detail.     

基于光纤光参量放大的多通道全光非归零/归零码转换器

提出了一种基于光纤光参量放大器(FOPA)的多通道全光非归零码(NRZ)/归零码(RZ)调制格式转换的方案.该方案中,非归零码信号与同步的时钟抽运光共同注入到高非线性光纤(HNLF)中,由高非线性光纤构成的参量放大器把非归零码信号转换为归零码信号,同时不改变信号光的波长.多通道的码型转换器以两路10 Gb/s的非归零码进行了实验论证.转换后的归零码信号的信噪比(SNR)高于7.6 dB,其脉冲宽度约为30 ps,并且具有3dB的消光比(ER)提高.根据多通道码型转换器的实现原理,该码型转换器可以应用于40 Gb/s或更高比特率的多通道码型变换操作.     

Noise characteristics of fiber optical parametric amplifiers

We derive an analytical theory for the noise figure of an undepleted and lossless fiber optical parametric amplifier (FOPA). Both the signal and the wavelength converted idler are investigated. Our theory is applicable for both an ideal pump power source, as well as a noisy one. We find that a noisy pump source can severely degrade the performance at high gain due to the stochastic gain-variations the signal and idler will experience. The theory is compared with Monte Carlo simulations of the FOPA and an excellent agreement is obtained. Simulations in the gain-depleted region show the possibility to reach below quantum-limited, phase-insensitive amplification for single channel transmission.     

Noise characteristics of dual-pump fiber-optic parametric amplifiers

The noise figure (NF) properties of an undepleted and lossless dual-pump fiber-optic parametric amplifier (FOPA) are theoretically and numerically investigated. The theoretical study takes into account the noise characteristics of the two pump waves that are considered to have parallel polarization states for gain maximization. It is shown that noisy pump waves degrade the amplifier's NF, especially when the amplifier is operating at high gain values and when the input signal is high. The theoretical observations are validated by Monte Carlo numerical simulations, and the agreement between them is excellent. Finally, a comparative study concerning the noise characteristics of dual-pump and single-pump FOPAs is performed.     

光纤参量放大器的最新进展

从单抽运和双抽运光纤参量放大器两种结构展开论述,着重介绍了光纤参量放大器对信号的放大能力及双抽运光纤参量放大器作为波分复用或密集波分复用系统放大器的可能性和所面临的问题,表明具有高增益和宽带宽的光纤参量放大器有可能成为新一代的光放大器.最后介绍了波长转换器方面的最新进展及双抽运偏振态相互正交时的光纤参量放大器在波长转换方面的独特性能.     

Fiber-optic parametric amplifier in a loop mirror configuration

A configuration of the fiber-optic parametric amplifier (FOPA) using an optical loop mirror is presented and evaluated. Previously presented setups usually suffer a 10-dB loss on the input for the signal wavelength. The setup presented in this letter allows, in principle, virtually lossless combination and separation of pump and signal. In addition, over 30-dB suppression of the pump was achieved in this configuration. Bit-error-rate measurements using the FOPA as preamplifier were compared to a thermal limited receiver. The receiver sensitivity for the FOPA was -30 dBm, which was 10 dB better than the thermally limited receiver.     

Amplitude Regeneration of RZ-DPSK Signals in Single-Pump Fiber-Optic Parametric Amplifiers

The input power tolerance of a single-pump fiber-optic parametric amplifier (FOPA) is experimentally shown to be enhanced for return-to-zero differential phase-shift keying (RZ-DPSK) modulation compared to RZ on–off keying modulation at 40 Gb/s. The improved nonlinear tolerance is exploited to demonstrate amplitude regeneration of a distorted RZ-DPSK signal in a gain-saturated FOPA. An optical signal-to-noise ratio penalty of 3.5 dB after amplitude distortion is shown to be reduced to 0.2 dB after the FOPA, thus clearly demonstrating the regenerative nature of saturated FOPAs for RZ-DPSK modulation.      

采用级连反向泵浦喇曼光纤放大器的长距离光纤传输系统中双重瑞利散射噪声的抑制

给出了反向泵浦喇曼光纤放大器中信号和双重瑞利散射噪声的计算方法,分析了双重瑞利散射噪声的特性,计算了采用光隔离器进行双重瑞利散射噪声抑制时,光隔离器的最佳位置。研究了使用多级反向泵浦喇曼光纤放大器的1080km光纤通信系统的传输特性,比较了信号和双重瑞利散射噪声在加入光隔离器前后沿传输光纤的功率变化。加入光隔离器以后,信号所受的影响不大,但双重瑞利散射噪声能得到有效抑制,可减少约三个数量级。1     

Amplified spontaneous Raman scattering in fiber Raman amplifiers

Amplified spontaneous Raman scattered light power in forward and backward Raman amplifiers is theoretically and experimentally studied under the assumption of the constant Raman gain coefficient in the bandwidth of an optical filter. On the basis of the results, the power ratio of the amplified signal to amplified spontaneous scattering is discussed. As a result, it is clarified that the effect of amplified spontaneous Raman scattering on the signal to noise ratio for backward Raman scattering is larger than for forward Raman scattering.     

基于超长分布式2阶喇曼放大器的光载射频传输

为了提升光载射频传输链路的链路增益以及传输距离,采用了L波段的超长分布式2阶喇曼放大器结构对光信号进行放大。从理论上对分布式2阶喇曼放大器以及光载射频传输链路的原理进行了解释,利用信号光、1阶抽运光、2阶抽运光以及噪声之间的耦合方程组分析了它们之间的关系,并且得到了基于超长分布式2阶喇曼放大器的光载射频传输系统的1阶射频信号增益。通过数值仿真以及系统实验得到了抽运功率大小对超长分布式2阶喇曼放大器的开关增益的影响、光载射频传输系统在0GHz~7GHz范围内的频率响应及其射频增益以及该光载射频传输链路在应用超长分布式2阶喇曼放大器后的相位噪声情况。结果表明,光载射频传输在超长分布式2阶喇曼放大器的作用下获得了28.1dB的链路增益,在距离为80.94km的光链路上实现了近似无损传输,射频信号开关增益与射频信号频率无关。该研究在光载射频链路的长距离传输中有重要的应用价值。     

Effect of a nonlinear photonic Crystal fiber on the noise characterization of a distributed Raman amplifier

The first experimental study of the effect of a nonlinear photonic crystal fiber (PCF) on the noise characteristics of a distributed backward-pumped Raman amplifier is reported. The PCF has a highly nonlinear Raman efficient, and a high Rayleigh scattering parameter. When an optical signal first passes through a 100-m nonlinear PCF followed by a 25-km single-mode fiber, the optical signal-to-noise ratios (OSNRs) of the amplified spontaneous emission and the double Rayleigh scattering (DRS) are improved because the high Raman gain efficiency of the PCF makes the Raman gain of the signal at the beginning of the link increase, and the signal power over the length of the transmission becomes near a constant. However, the improvement of the OSNR of DRS compared with the OSNR of amplifier spontaneous emission is limited by the large Rayleigh scattering in the PCF.     

分布拉曼光纤放大的实验研究

采用符合ITU-T标准的G波段40信道波分复用(WDM)光源对分布式拉曼放大器(DRA)的特性进行了实验研究。对不同抽运方式及不同光纤长度的分布式拉曼放大器性能作了较为详细的报道。在抽运功率相同的条件下，选用50km单模光纤对比研究了不同抽运方式的拉曼放大器增益和噪声。通过对不同光纤长度的分布式拉曼放大器的实验研究发现，在较低抽运功率且输入信号功率较低的情况下，随着光纤长度增加，拉曼增益也增加，有效噪声系数减小。研究了分布式拉曼放大器对波分复用通信系统信噪比的改善，实验发现不同抽运功率下，拉曼放大器对系统信噪比的改善随抽运功率增加而增加，但是不成线性关系，而且最终会出现饱和。     

相对相位噪声对相干光通信系统性能影响

在使用前向抽运喇曼放大器的相干光正交频分复用传输系统中,由于喇曼抽运的强度噪声和交叉相位调制之间相互作用产生相对相位噪声,导致系统性能大幅下降。为了研究此问题,采用数值分析方法进行了理论分析与实验验证,分析了不同的调制格式下,相对相位噪声对相干光正交频分复用系统的影响,并且比较了正交频分复用多载波系统与单载波系统在相同条件下的系统性能,取得了由相对相位噪声所导致的系统损伤程度数据。结果表明,抽运和信号之间相对较大的离散系数有助于抑制相对相位噪声引起的损伤,高阶调制信号比低阶信号对相对相位噪声耐受性低;频谱相同效率时,正交幅度调制格式比相移键控耐受性更好。     

采用喇曼光纤放大器的长距离光纤传输系统中双重瑞利散射噪声的抑制

本文研究了在长距离光纤通信系统中,采用多级喇曼光纤放大器的情况下,双重瑞利散射波的产生和放大过程,提出了采用在喇曼光纤放大器中加入隔离器的办法进行双重瑞利散射噪声抑制。比较信号和双重瑞利散射噪声在入隔离器前后沿传输光纤的功率变化,加入隔离器以后,双重瑞利散射噪声得到了有效地抑制,而信号所受的影响不大。     

原子干涉仪中拉曼激光的相位-频率双调制稳频

为降低拉曼激光的频率噪声,提出了一种相位-频率双调制稳频技术。用光纤电光相位调制器对激光进行调制并产生大失谐边带;用射频信号对光纤相位调制器的微波驱动信号进行频率调制,通过锁相放大法将一个大失谐边带锁到铷原子的饱和吸收谱线上。利用该技术实现了拉曼种子激光的稳频和2 GHz的移频,拉曼激光的线宽大幅压窄到56 kHz,预期拉曼激光频率噪声引起的原子干涉重力仪的单次测量噪声可降低到7×10-9/s2。     

A flexible receiver with fiber optical parametric amplifier in OCDMA-FSO communication system

A new receiver is proposed, which uses the fiber optical parametric amplifier（FOPA） in optical code division multiple access（OCDMA） over free space optic（FSO） communication system. The noise tolerance as the performance index in this receiver is derived. The receiver can not only improve the noise tolerance but also change the pump data conveniently for adapting to the length variation of the coding sequence under a complex and fast-changing weather condition. The influence of different factors on the noise tolerance is analyzed, and a significant improvement of about 18.77 d B for the noise tolerance can be achieved when the pump power and the length of coding sequence are 5 W and 256, respectively.     

Influence of Pump-to-Signal RIN Transfer on Noise Figure in Silicon Raman Amplifiers

The effect of the relative intensity noise (RIN), transferred from the pump to the signal, in 1-cm-long chip scale silicon Raman amplifiers is investigated in the presence of nonlinear losses. We show that due to the short waveguide length, the reduction in fluctuations that normally occurs due to “walk-off” between pump and signal waves in fiber amplifiers is inefficient in chip scale Raman amplifiers. In the counterpropagating pump configuration, which leads to minimum frequency RIN transfer, fluctuations up to 1.5 GHz are transferred from the pump to the signal. As a case study, the noise figure degrades by as much as 11 dB in the silicon waveguide with the free carrier life time of 0.1 ns, when it is pumped with a laser with a RIN value of $-$125 dB/Hz.      

同向抽运喇曼放大器功率转换效率的数值分析

为了对同向抽运光纤喇曼放大器的功率转换效率进行研究,由耦合方程出发,采用龙格-库塔算法的数值模拟方法,详细分析了所有物理因素对同向抽运光纤喇曼放大器功率转换效率的影响. 结果表明,功率转换效率先随着光纤长度的增加而增加,当增加到最大值时保持数值不变;并且功率转换效率也随着初始信号光功率、光纤喇曼增益系数、信号光损耗系数的增加而增加,但随着光纤有效面积、抽运光损耗系数、抽运光与信号光的频率比的增加而减小;功率转换效率和初始抽运光功率呈抛物线曲线关系. 这对同向抽运光纤喇曼放大器功率转换效率的进一步研究以及光纤喇曼放大器的相关研究有一定参考意义.     

Design of double-pass dispersion-compensated Raman amplifiers for improved efficiency: guidelines and optimizations

In this paper, an intensive theoretical and experimental investigation is conducted on the dispersion-compensating Raman amplification module configured in double-pass geometry. An analytical model is developed to study the gain/pump efficiency improvement and the noise performance in a novel double-pass discrete-Raman-amplifier (DCRA) system. This paper demonstrates that the gain and pump efficiency can be improved significantly by using the double-pass configuration and the pump light reflector. The impairments of multipath-interference (MPI) noise due to the Rayleigh scattering and the external reflection are analyzed in order to balance the high gain efficiency and the enhanced MPI noise in the double-pass DCRA. Furthermore, the nonlinear penalty in the DCRA system is investigated and a 10-Gb/s nonreturn-to-zero (NRZ) signal transmission in a 4 /spl times/ 100-km fiber system is simulated. The signal quality and bit-error rate are examined, and the optimization is done with reference to the input signal level and Raman gain; hence, the impact of double-pass DCRA on the dispersion-compensated optical communication systems is explored.     

基于双向二级喇曼抽运的偏振控制研究

为了发展具有实用价值的受激喇曼全光偏振控制方法,根据光纤中受激喇曼散射矢量理论和光纤随机双折射效应设计了基于双向二级喇曼抽运的全光偏振控制方案,构建了偏振吸引理论模型,采用严格数值迭代算法对该偏振控制方案进行了仿真分析,并完成了偏振控制方案最佳工作性能的优化设计。结果表明,当信号光波长为1550nm、功率为0.1mW、一级抽运光和二级抽运光的功率分别为1W和4W、其偏振态都为（0,1,0）、光纤长度为3km时,信号光偏振度可达0.85以上,且信号光强度波动低于35%。该方案有效降低了作用光波功率、减弱了信号光输出强度噪声,并提高了信号光输出偏振度。