具有非均匀零色散波长光纤中的四波混频

提出了一种分析具有非均匀零色散波长光纤中四波混频(FWM)的简便方法,导出了多段不同零色散波长组成的光纤中和零色散波长连续变化的光纤中四波混频效率的计算公式.实例计算结果表明,光纤中零色散波长分布的不均匀,会影响四波混频效率,特别是在抽运光和检测光波长间隔较大时,影响尤为显著. 关键词： 四波混频 相位匹配 零色散波长     

低串扰的多波长光纤光栅色散补偿器

分析了光纤光栅色散补偿系统中的串扰，并比较了几种常用的多波长光纤光栅色散补偿器的串扰特性，结合串联的窄带光纤光栅和取样光纤光栅的优点，提出一种抑制光纤光栅色散补偿系统串扰的方法.它通过在邻近信道间引入随机时延差，既能改善取样光纤光栅的线性串扰特性，又能抑制交叉相位调制效应和四波混频等非线性串扰.使用该方法可以得到具有低串扰的多波长光纤光栅色散补偿器.     

DWDM系统非简并四波混频串扰的分析

考虑到DWDM系统中的比特序列的随机性、信道间脉冲走离效应等多种因素的影响,完善了归零调制格式下的四波混频效率的计算方法,给出了相应的非简并四波混频噪声标准差的计算公式,并利用该公式进行实例分析,计算结果表明,当占空比和信道间隔变小时,不同信道内的随机比特序列的相对初始时延及光纤色散值的取值组合对四波混频效率的影响变得更大,为保证系统的低色散和低四波混频串扰特性,必须对这些量取值组合进行优化. 关键词： 非简并四波混频 脉冲走离 密集波分复用     

基于光纤四波混频效应的新型组播方法

组播是波长路由光通信网络中的一项重要功能.提出并实验实现了基于高非线性光纤四波混频效应的全光组播方法,将一束载有数据的输入信号光和一束抽运光一起入射到一段高非线性光纤中,通过两个简并四波混频过程产生了两个携带该数据信息的闲频光,从而实现了单一信号的两信道组播,同时抽运光也会受到数据信息的调制.该方法的优点在于组播的实现只需要单一的抽运光源,而不需要再提供其他输入光,结构简单,组播光信号功率均匀、波长可调,并且具有进一步增加组播信道的能力. 关键词： 组播 四波混频 高非线性光纤     

非均匀零色散波长光纤中的四波混频效率

本文讨论了光纤零色散波长的离散对光纤中四波混频效率的影响,导出了多段均匀零色散波长光纤输出的四波混频光波强度的表达式,进而对该式进行了推广,导出了一般情况下的表达式.最后我们对几种具体情形进行了计算.计算结果表明当光纤的零色散波长存在漂移时,光纤中四波混频效率显著降低.而且光纤零色散波长漂移的幅度和分布规律以及泵浦光波长的选取对光纤四波混频效率也有重要影响.     

光子晶体光纤四波混频光谱中相位匹配特性的研究

与传统光纤不同,光子晶体光纤可以具有多个零色散波长,在四波混频光谱中,具有更丰富的相位匹配特性。目前很多文献报道了光子晶体光纤非线性光学特性的实验结果,但对其产生机理及光谱的变化规律缺乏详细的理论分析。为此对光纤中四波混频原理进行了分析,给出了高增益的相位匹配条件。利用多极法计算了光子晶体光纤的非线性系数及色散特性。对具有多个零色散波长光子晶体光纤的相位失配特性进行了分析,得到了相位匹配波长随泵浦波长及泵浦功率的变化规律。给出了相位匹配曲线,分析了不同色散曲线的相位匹配波长特点,两个零色散波长光子晶体光纤,在四波混频光谱中将激发出四个新的波长。实验得到了两个零色散波长光子晶体光纤的四波混频光谱,与理论分析一致,验证了相位匹配理论的可靠性。多个零色散波长光纤,能产生丰富的相位匹配曲线,会出现更多的四波混频波长,可以有效的控制光孤子及超短脉冲的四波混频及共振散射产生的光谱特性。为光子晶体光纤中基于四波混频的波长变换及超连续谱的研究提供了理论指导。     

基于光子晶体光纤四波混频效应的波长转换研究

研究了光子晶体光纤中的四波混频效应及其波长转换.采用长度为25 m的高非线性色散平坦光子晶体光纤,当泵浦功率为19.8 dBm时,得到100 nm的转换带宽和-20 dB的最大转换效率.实验结果表明,当信号功率低于四波混频阈值时,两路不同波长的信号同时输入产生的四波混频效应互不影响.     

基于光子晶体光纤四波混频效应的波长转换研究

研究了光子晶体光纤中的四波混频效应及其波长转换.采用长度为25 m的高非线性色散平坦光子晶体光纤,当泵浦功率为19.8 dBm时,得到100 nm的转换带宽和－20 dB的最大转换效率.实验结果表明,当信号功率低于四波混频阈值时,两路不同波长的信号同时输入产生的四波混频效应互不影响.     

色散管理波分复用系统中的简并四波混频噪声

建立了强度调制色散管理波分复用的简并四波混频噪声标准差的理论计算模型,此理论模型考虑到了两种随机因素的影响:各信道内的比特流的随机性及脉冲初始相位的随机性.信道间的脉冲走离效应使色散管理光纤链路中的脉冲碰撞位置的分布比较复杂,这些碰撞位置又会对四波混频噪声标准差的值产生较大影响,所建立的理论模型充分考虑到了这种碰撞位置的影响.利用这个理论模型进行了相关计算,计算结果表明,优化的色散管理方案在保证脉冲稳定传输的同时,能获得较小的四波混频噪声标准差;当系统选择较小的占空比时,优化各信道脉冲的相对初始时延能较大程度地减小四波混频效应的不利影响.     

基于光子晶体光纤中多抽运四波混频效应的新型光层组播技术

光层组播是未来透明光子网络中一项重要的全光信号处理功能,提出并实验证实了一种基于色散平坦高非线性光子晶体光纤中多抽运四波混频效应的光层组播方法,将一束信号光与两束连续抽运光同时输入高非线性光子晶体光纤中,通过多抽运四波混频过程,产生四个携带该数据信息的闲频光,从而实现了单一信号的四信道光层组播功能,组播信道波长在35.2 nm范围可调谐,组播信道最大间距4.4 THz,最大转换效率-22 dB,最优Q因子为5.3,该方法的特点在于基于光纤中的四波混频效应工作,因而具有对调制格式和比特率透明的 关键词： 光层组播 多抽运四波混频 光子晶体光纤     

Extended Method of Fast Allocation of USC’s for Millimeter-Wave DWDM-ROF Transmission Over ZDSF

Four-wave mixing (FWM) may happen efficiently and introduce crosstalk at the signal channels in dense-wavelength-division- multiplexing (DWDM) systems employing zero-dispersion-shifted fiber (ZDSF). This paper presents extended method of fast allocation of unequally spaced channels (USCs) to minimize FWM crosstalk in millimeter-wave (MMW) DWDM radio-over-fiber (ROF) systems. When all of the MMW sub-carriers are at same frequency, by spacing the channels unequally using the extended method, all FWM products except the ones bound to be generated at the signal frequencies, can be excluded from the signal channels. While when the MMW sub-carriers are allowed to be different in frequencies, all of the FWM products can be excluded from the signal channels by spacing the channels unequally. Transmission of 622 Mbit/s BPSK data over 40 kilometers ZDSF, with and without wavelength interleaving, are simulated, for both schemes with equally and unequally spaced channels. Results comparison shows that the link performances can be clearly improved, when the channels are unequally spaced using the extended method.     

Effects of frequency and polarization allocations on FDM lightwave transmission systems

In long-haul frequency-division-multiplexing (FDM) lightwave transmission systems, transmission characteristics are degraded by four-wave mixing (FWM) generated in optical fibers. To overcome this problem in equally spaced (ES) allocation, modified repeated unequally spaced (RUS) allocations such as equally spaced RUS (ERUS) and unequally spaced RUS (URUS) allocations have been already examined. Also, it has been shown that FWM noises are decreased by arranging the polarization states of the channels. In this paper, dependence of FWM noises on frequency allocations and polarization allocations is investigated. It is revealed that FWM noises are decreased in ES, RUS, ERUS, and URUS with alternating polarization allocations of the channels, and FWM noises are drastically reduced when light polarizations are perpendicularly crossed at both sides of the zero dispersion frequency.     

Optimum algorithm for WDM channel allocation for reducing four-wave mixing effects

A novel channel allocation method, based on optical Golomb ruler (OGR), that allows reduction of the FWM effect while maintaining bandwidth efficiency along with the algorithms has been presented in this paper. Very high-capacity, long-haul optical communication systems can be designed by wavelength division multiplexing (WDM) of high-bit-rate channels and by using erbium-doped fiber amplifiers (EDFAs) to periodically compensate the fiber loss. In such all-optical systems, the effects of chromatic dispersion and nonlinearities accumulate during light propagation, imposing limits on the achievable performance. Chromatic dispersion at 1.55 pm can be effectively reduced by using dispersion-shifted fiber (DSF). The use of very-low-dispersion fiber, however, enhances the efficiency of generation of four-wave mixing (FWM) waves by reducing the phase mismatch naturally provided by the fiber dispersion. For this reason, crosstalk due to FWM is the dominant nonlinear effect in long-haul WDM systems using DSFs. To reduce four-wave-mixing crosstalk in high capacity long-haul repeater less WDM light wave systems, the use of the channel allocation method that involves unequal spaced channels has been proposed.     

A comparative study of modified PUSCA and paired PUSCA strategies in WDM system

In G.653 compliant fiber, four-wave mixing (FWM) is a dominant non-linear effect. Performance of optical wavelength division multiplexing (WDM) network based on G.653 fiber is affected by the generated FWM components. The paper aims to discuss the methods used to reduce the number of FWM components and make efficient utilization of bandwidth. We have earlier proposed two methods (a) modified periodically unequally spaced channel allocation (modified PUSCA) and (b) paired PUSCA. In this paper, we have compared both the methods by considering the ratio of increase in weighted average signal to FWM noise ratio to increase in bandwidth as a figure of merit. Further, the performance of paired PUSCA scheme on G.653 fiber has been compared with equally spaced channel allocation (ESCA) scheme on G.652 fiber in which FWM is not a dominant non-linear effect. We demonstrate that paired PUSCA on G.653 fiber performs better than ESCA on G.652 fiber when the number of channels is less than 30.     

A bandwidth-efficient channel allocation scheme for mitigating FWM in ultra-dense WDM-PON

In this paper, we investigate four-wave mixing (FWM) effects in the ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) system and propose an efficient channel allocation scheme to mitigate the FWM impact. This scheme is formed by grouping signal channels into several blocks with different channel spacing. Through numerical analysis and simulations, our proposed scheme is verified to be able to reduce the FWM effects and have higher bandwidth efficiency than the traditional unequal channel allocation scheme. The simulation results also demonstrate that our proposed scheme can achieve nearly 4 dB increases in optical power budget of the UDWDM-PON systems at the BER of 1e−3, in comparison with the equal spaced channel scheme.     

Effects of frequency/polarization allocations and the zero-dispersion frequency on FDM lightwave transmission systems

In long-haul frequency-division-multiplexing lightwave transmission systems, transmission characteristics are degraded by four-wave mixing (FWM) generated in optical fibers. To overcome this problem, several FWM suppression techniques have been reported. In this paper, dependence of FWM noises on frequency allocations, polarization allocations, and the zero-dispersion frequency is investigated. It is revealed that FWM noises are drastically decreased in frequency allocations such as equally spaced, repeated unequally spaced (RUS), equally spaced RUS, and unequally spaced RUS allocations by arranging polarization allocations of the channels with an increase in a separation between the channel frequencies and the zero-dispersion frequency.     

Reduction of FWM noise in WDM-based QKD systems using interleaved and unequally spaced channels

To extensively deploy quantum key distribution(QKD) systems, copropagating with classical channels on the same fiber using wavelength division multiplexing(WDM) technology becomes a critical issue. We propose a user-based channel-interleaving WDM scheme with unequal frequency spacing(UFS-i WDM) to reduce the impairment on the quantum channels induced by four-wave mixing(FWM), and theoretically analyze its impact on quantum bit error rate(QBER). Numerical simulation results show that a UFS-i WDM can significantly reduce the FWM noise and improve QBER compared with the corresponding WDM scheme with equal frequency spacing(EFS), especially in the case of nonzero dispersion shifted fiber.     

Novel Strategies for Reducing FWM Using Modified Repeated Unequally Spaced Channel Allocation

Four-wave mixing (FWM) is a dominant nonlinear effect present in optical wavelength division multiplexing (WDM) networks employing dispersion-shifted fiber. The method of placing the carrier at unequally spaced frequencies to reduce the FWM effect in these networks is known. A modification to this method with periodic unequally spaced channel allocation repeated base unit structures has been suggested that leads to a much better bandwidth utilization with lesser number of FWM components. A figure of merit, defined as the ratio of decrease in number of FWM components generated to increase in bandwidth, has been used as a metric of performance.     

All-optical wavelength multicasting based on cascaded four-wave mixing with a single pump in highly nonlinear fibers

We theoretically present and experimentally demonstrate all-optical wavelength multicasting based on cascaded four-wave mixing (FWM) in highly nonlinear fibers only using a single pump. The cascaded FWM effect is analyzed based on the sum amplitude method, which overcomes the limitation of the number of analyzed idlers, and the performance of the wavelength multicasting is evaluated. By using a continuous wave pump and a pulse train as the signal, multiple-order idlers are experimentally generated and the patterns of 6 multicasting channels are measured. Regardless of the dynamic region of the tunable filter, this method has the potential to realize more multicasting channels, especially when higher pump and signal powers are used.