DCF光纤拉曼放大器的实验研究

DCF(dispersion compensating fibre)光纤具有较高的拉曼增益系数,利用这一点可以用较短长度的DCF光纤制成分立式的光纤拉曼放大器,作为传输线路上的损耗补偿.本文在测量并计算了DCF光纤的拉曼增益系数的基础上,对分立式的DCF放大器的开关增益和噪声指数进行了测量和分析,并将分立式FRA和分布式FRA在开关增益和噪声指数方面做了比较。介绍了用不同的测量方法所造成的实验结果的差异.实验结果表明,放大介质为5 km的DCF光纤所构成的放大器,在抽运功率为800 mW的条件下,最大增益可达14.77dB,3 dB带宽为35 nm,满足作为损耗补偿的要求.     

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。     

Design of Hybrid Optical Amplifiers for High Capacity Optical Transmission

This paper describes our design of a hybrid amplifier composed of a distributed Raman amplifier and erbium‐doped fiber amplifiers for C‐ and L‐bands. We characterize the distributed Raman amplifier by numerical simulation based on the experimentally measured Raman gain coefficient of an ordinary single mode fiber transmission line. In single channel amplification, the crosstalk caused by double Rayleigh scattering was independent of signal input power and simply given as a function of the Raman gain. The double Rayleigh scattering induced power penalty was less than 0.1 dB after 1000 km if the on‐off Raman gain was below 21 dB. For multiple channel amplification, using commercially available pump laser diodes and fiber components, we determined and optimized the conditions of three‐wavelength Raman pumping for an amplification bandwidth of 32 nm for C‐band and 34 nm for L‐band. After analyzing the conventional erbium‐doped fiber amplifier analysis in C‐band, we estimated the performance of the hybrid amplifier for long haul optical transmission. Compared with erbium‐doped fiber amplifiers, the optical signal‐to‐noise ratio was calculated to be higher by more than 3 dB in the optical link using the designed hybrid amplifier.     

双抽运光参量放大的增益特性

在相同条件下(如抽运光功率、信号光功率等),与单抽运相比,双抽运光参量放大(OPA)的增益大,增益带宽宽.由于信号光的增益特性与参量增益系数直接相关,因此,在建立高非线性光纤(HNLF)光参量放大的理论模型的基础上,对相位匹配条件、参量增益以及信号光饱和增益的特性进行了分析讨论,采用有限差分法,对增益饱和的特性进行了模拟.结果表明,参量增益和光纤参数、输入抽运光以及信号光的波长、功率有关,而信号光的饱和增益和输入抽运功率有关.     

G652光纤中背向自发拉曼散射的增益特性

讨论了背向自发Raman散射脉冲在自生分布式G652光纤Raman放大器中传输的增益特性。实验发现，反Stokes Raman（ASR）和Stokes Raman（SR）自生分布式脉冲光纤Raman放大器的阈值抽运峰值功率是25．4W和18．0W。在入射功率为52W时，ASR和SR的增益分别为5．0dB和8．6dB。放大的反Stokes和Stokes背向自发Raman散射光时域反射（OTDR）曲线上放大的阈值时间位置随激发功率的增高前移并具有规律性。放大的ASR背向自发散射强度受光纤温度调制，具有温度效应，已应用于远程分布光纤Raman温度传感器系统。     

Generation of optical phase-conjugate waves and compensation forpulse shape distortion in a single-mode fiber

The generation of optical phase-conjugate waves and the application of optical phase conjugation (OPC) to optical communication systems is described. The method of pulse shape distortion compensation by OPC is outlined including distortion due to both fiber dispersion and the optical Kerr effect. The generation of a forward-going phase-conjugate wave in a third-order nonlinear medium is discussed and that by a nondegenerate forward four-wave mixing in a zero-dispersion single-mode fiber (SMF) is investigated. Suppressing the stimulated Brillouin scattering (SBS) of a pump wave in the fiber prevents saturation of the generation efficiency of the phase-conjugate wave even when the pump power exceeds the SBS threshold. In transmission experiments through a 200-km standard SMF with a 16-Gb/s intensity-modulated signal and a 5-Gb/s continuous-phase FSK (CPFSK) modulated signal, it is shown the applicability of OPC is modulation independent and that OPC effectively compensates for both chromatic dispersion and the optical Kerr effect     

多泵浦喇曼放大器的增益特性分析

提出了用同向泵浦的剩余泵浦功率作为反向泵浦的泵浦功率迭代初值,用Lorentz线型拟合喇曼增益系数,采用简明的数学模型,对比分析了同向、反向多波长泵浦喇曼放大器的增益特性以及信号间的受激喇曼散射对增益的影响.     

用非线性光纤连接的长周期光栅对的光开关特性

提出用一根掺铒光纤连接两个对称的长周期光纤光栅(EDF-LPFG)对构成的新型全光开关.数值模拟了在交叉相位调制下对应于不同抽运功率的信号光的透射谱;还研究了在不同光栅的有效折射率调制幅度和光纤吸收系数下,信号光透射率随抽运光功率的变化.导出了器件的阈值开关功率公式.EDF-LPFG对光开关的阈值开关功率比单LPFG光开关的开关功率降低了5个数量级,不到25 mW.     

光纤参量放大器增益特性的理论与仿真分析

为了优化光纤参量放大器的增益特性,利用理论分析,对FOPA在不同光纤长度、不同泵浦光功率及不同光纤非线性系数下的增益与带宽特性进行了比较与分析。结果表明:使用较长的高非线性光纤、较大的泵浦光、或较大的非线性系数,均可提高FOPA的增益,增益带宽也可随着泵浦光功率和非线性系数的增大而增大。此外,利用仿真模拟对理论分析结果进行了验证。虽然,仿真结果与理论分析结果间略有偏差,但仿真结果依然较好的验证了理论结果的正确性与可行性。     

光纤光参量放大增益特性的研究

分析了光纤光参量放大过程泵浦光与信号光的非线性相互作用，得到信号光增益G_s。进一步分析G_s，获得其增益带宽特性，只有在泵浦波长大于光纤零色散波长时才有增益，带宽约为50nm。     

Raman-amplifier-based submarine transmission systems

The broad bandwidth and low noise figure of a distributed Raman amplifier (DRA) makes it attractive for use in high-capacity, long-haul transmission systems. This paper discusses key technologies for such systems using Raman amplifiers (RAs), such as a method to expand the signal bandwidth for hybrid DRA/EDFAs and all-RAs. The combination of two different types of optical amplifiers enables them to compensate for each other's gain profiles through adjustment of the RA's pump wavelength allocation to reduce the accumulated gain deviation. A variable gain equalization scheme is also described. Furthermore, we have developed a form of dispersion management suitable for a system using DRAs. The overall system performance with this management during a transmission experiment was 1.6 dB better than that with conventional management. Using these techniques, we successfully demonstrated 2.1-Tb/s 7221-km transmission in a system using hybrid DRA/EDFAs and 2.4-Tb/s 7404-km transmission in a system using DRAs.     

Wideband Hybrid Fiber Amplifier Using Er‐Doped Fiber and Raman Medium

In this paper, we report the experimental results of a hybrid wideband fiber amplifier. The amplifying medium is a concatenated hybrid fiber consisting of Er‐doped fiber (EDF) and dispersion compensating fiber (DCF). The gain mechanisms are based on stimulated emission in the EDF and stimulated Raman scattering (SRS) in the DCF. Since we simultaneously use optical amplification by the two processes, the gain bandwidth is easily expanded over 105 nm by a two‐tone pumping scheme. Using an experimental setup constructed with a hybrid structure of EDF‐DCF‐EDF, we analyzed the spectral behavior of amplified spontaneous emission for pumping powers. We achieved an optical gain of over 20 dB in the wavelength range from 1,500 to 1,600 nm under optimized pumping conditions to make the spectral gain shape flat.     

Super-dense WDM transmission technology in the zero-dispersion region employing distributed Raman amplification

This paper describes a practical system design and the transmission performance of high-capacity super-dense-wavelength-division-multiplexing (SD-WDM) transmission in the zero-dispersion region employing distributed Raman amplification (DRA). By combining several semiconductor laser diodes (LDs) of different wavelengths, gain-flattened DRA can be achieved. We quantitatively clarify the relation between the pump power and the maximum input signal power that can be injected into a transmission fiber by taking into account gain saturation due to pump depletion. Based on these analytical results and computer simulations on transmission performance, an SD-WDM transmission experiment is conducted. By employing four-wavelength, backward-pumped DRA and forward-error correction, we successfully demonstrate 1-Tb/s (100 /spl times/ 10 Gb/s) SD-WDM transmission with 25-GHz channel spacing (0.4-b/s/Hz spectral efficiency) in the C-band (zero-dispersion region) over 4 /spl times/ 80 km of dispersion-shifted fiber. These results show that DRA is a powerful technology in realizing high-capacity SD-WDM transmission, particularly in the zero-dispersion region.     

Theoretical investigation of 8 /spl times/ 10-Gb/s WDM signal transmission performance based on gain-equalized SOAs using backward Raman pumping at DCF

We have theoretically investigated 8 /spl times/ 10-Gb/s wavelength-division multiplexing (WDM) signal transmission characteristics based on semiconductor optical amplifiers (SOAs) with equalized gain using discrete Raman amplification (DRA). Gain equalization and low noise figures have been obtained by adjusting the backward Raman pumping power and wavelength at a dispersion compensating fiber (DCF) for each span. Bit-error-rate characteristics were calculated for 8 /spl times/ 10-Gb/s WDM signal transmission over 6 /spl times/ 40-km single-mode fiber (SMF) + DCF links with gain-equalized SOAs using DRAs at DCF. Approximately a 2.5-dB improvement of the receiver sensitivity was achieved by using SOAs and DRAs with optimized Raman pumping. One can easily upgrade the transmission length of a link based on SOAs with an appropriate backward pump laser at each DCF.     

Design of transmission optical fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering

Designed was the transmission fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering (DRBS). Basically the optical signal-to-noise ratio (OSNR) of distributed type Raman amplifier is superior to that of the lumped type Raman amplifier using a high Raman gain fiber such as dispersion compensation fiber. However, much pump power and long length of transmission fiber line are required to acquire a proper gain in the distributed type fiber Raman amplifier. Thus, compositional adjustment on the fiber for optical transmission is of benefit to reduce further the required pump power. In this regard, based on this simulation, the fluorine and germanium co-doped fiber showed a high Raman gain, high OSNR, and low DRBS.     

Optical fibers and amplifiers for WDM systems

The development of optical-fiber amplifiers allowed a dramatic increase in the capacity of optical transmission systems while reducing system costs. Capacity increases are possible because the high output powers afforded by optical-fiber amplifiers support higher bit rates, while their broad bandwidth and slow gain dynamics allow multichannel operation. This benefit comes at the expense of having to manage signal-to-noise ratio degradations due to the accumulation of amplifier noise and dispersion distortions accumulated over the total system link. Furthermore, nonlinear optical effects become significant with the use of high power signals over long lengths of fiber, causing cross talk among the different channels and increasing signal distortions. To fully exploit the potential capacity of wavelength division multiplexing systems, the optical characteristics of the fibers and optical-fiber amplifiers must be optimized. The optical amplifiers should have low noise and flat gain, which can be achieved by using 980-nm pump lasers, optimized fiber glass composition, and gain-flattening filters. The optical fibers should have a small nonzero dispersion and large effective area. Both features can be achieved by optimizing the fiber index profile. This paper summarizes the state of the art in these components and points to directions for future exploration     

级联光纤参量放大器的增益特性分析

首先介绍了级联结构光纤参量放大器的工作原理,即通过两种光纤色散补偿来平坦信号输出增益。其次推导出小信号近似下单泵浦级联光纤参量放大器的信号输出增益表达式,并在此基础上利用Matlab软件对影响增益特性的各个参数进行数值分析。结果表明,级联光纤参量放大器的峰值增益与增益带宽,受到分段数、泵浦光功率、泵浦波长、色散补偿光纤(DCF)长度、高非线性光纤(HNLF)的零色散波长、HNLF长度、HNLF非线性系数和HNLF色散斜率的影响。     

Ultra-Wideband Pulse Generation Based on Cross-Gain Modulation in Fiber Optical Parametric Amplifier

A novel approach to generate ultra-wideband (UWB) monocycle or doublet pulse using cross-gain modulation in fiber optical parametric amplifier is demonstrated in a single experimental setup. The high-speed optical parametric process realizes the signal amplification, idler generation, and pump depletion simultaneously within femtosecond response time in the highly nonlinear fiber. After the combination of the three lightwaves with a suitable time delay between them, UWB pulse is obtained. A selective generation of monocycle or doublet pulse can be made by altering the optical attenuators without changing the wavelengths or the powers of the pump and the signal. In our experiment, high-quality UWB monocycle and doublet pulses with a fractional bandwidth of 115% and 126% were generated.      

多泵浦增益平坦光子晶体拉曼光纤放大器

针对密集波分复用光纤通信系统中拉曼光纤放大器增益及增益谱平坦问题,提出一种采用4个泵浦光的多泵浦方式在光子晶体光纤不同位置处注入两种不同波长泵浦光的组合方式来获得拉曼光纤放大器增益更大、增益谱更加平坦的方法。这种组合方式在拉曼光纤放大器中使得光信号实现了前段放大、后段补偿,从而在拉曼光纤放大器输出端获得高增益和较平坦增益谱。模拟的结果表明:平均增益可达:26.5 dB,增益平坦度为0.046 dB。     

掺钕光纤放大器非线性折射率的分析

利用描述光纤放大器非线性折射率的公式．通过数值模拟的方法模拟了输入信号功率、抽运功率、信号波长以及增益效应和克尔效应等变量对掺钕光纤放大器非线性折射率的影响，结果表明无论是增加抽运光功率或信号光功率，当信号光的波长小于1064nm时．掺钕光纤放大器的非线性折射率的数值在此波段附近所对应的值为正值，大于此值所对应的值为负值；抽运功率较小时增益效应对非线性折射率的影响较大，而抽运功率较大时克尔效应对非线性折射率的影响较大，这主要是增益饱和所导致的结果；当信号光频率一定时，随抽运功率的增加非线性折射率逐渐增加并达到饱和。