A long-haul wavelength division multiplexed system using standard single-mode fiber in presence of self-phase modulation

Performance of a long-haul wavelength division multiplexed (WDM) communication system has been evaluated in presence of nonlinear effects using standard single-mode fiber. Different compensation configurations, namely, post-, pre- and bi-end compensation, have been investigated to mitigate the fiber nonlinear effects. Eye-opening degradation due to mutual interplay between self-phase modulation (SPM) and group velocity dispersion for the compensating techniques has been estimated with respect to the transmission length and the residual dispersion in case of WDM system. Maximum threshold power levels at the bit error rate of 10⁻⁹ limited by the SPM effect have been determined. From a comparison among the compensating techniques, bi-end compensation configuration has been found to be the most suitable technique for any fiber length in case of a WDM communication system.     

Timing jitter dependence on data format for ideal dispersion compensated 10 Gbps optical communication systems

Simulations for data formats Return to Zero (RZ), Non-Return to Zero (NRZ), RZ-Soliton, Duobinary and their subcategories have been done with and without ideal dispersion compensation for optical communication systems. The results show that, in general, dispersion compensation improves timing jitter. RZ-Rectangular pulses show the smallest value of jitter without compensation. It has been observed that the RZ-Raised Cosine, and Soliton, give minimum jitter after ideal compensation. It has been reported that the BER performance of optical communication system using Duobinary data format is 10⁻⁸ and 10⁻³⁷ before and after dispersion compensation, respectively. Further the comparative study shows that the timing jitter is the lowest in case of RZ-Soliton (0.0127 ns) after dispersion compensation and 0.0135 ns for RZ-Rectangular data format before dispersion compensation.     

Structural and wavelength dependence of mode power distribution for a broadband dispersion compensating microstructured fiber

Approximate empirical analysis of mode power distribution (MPD) carried by the fundamental mode is newly investigated based on a broadband dispersion compensating microstructured fiber (MF). The fraction of modal power in the core region, η, is defined with the help of extending the applicability of well-established classical optical fiber theories to MFs. In doing so, the influences of structural parameters and wavelength on MPD characteristics of the fundamental mode are systematically analyzed in detail based on simple physically consistent concepts of conventional fibers. As a result, it is shown that for the optimum MF design in Ref. [11] as a multimode fiber, when the number of guiding modes increases, the mode power ratio of the fundamental mode constantly increases from 69.4%; in addition, we find that as wavelength increases within 1.2-1.6 μm, mode power confinement ability of the fundamental mode is lessened for single-mode propagation, whereas for multimode propagation it becomes enhanced.     

Performance limitations of an optical heterodyne CPFSK transmission system due to self-phase modulation

A detailed theoretical analysis is presented to evaluate the combined influence of self-phase modulation (SPM) and group velocity dispersion (GVD) of optical fiber on the bit error rate (BER) performance of a heterodyne optical CPFSK system. The power penalty suffered by the system due to the combined influence of GVD and SPM is evaluated from the BER performance results. It is found that the penalty due to SPM at a BER of 10⁻⁹ is significant when the input power exceeds 7 dBm. Further, the CPFSK system with modulation index of 0.5 is less sensitive to the effects of GVD and SPM compared to the system with a modulation index of 1. The theoretical results are in conformity with the experimental results reported earlier.     

A multi-parameter sensor system using concentric core optical fiber

We, for the first time, report an experimental demonstration of multi-parameter fiber sensor system using the concentric core optical fiber, which can simultaneously determine the stress, the position of stress and the cracks. A high bending-sensitive concentric core optical fiber has been used in a mesh type structure to form the multi-function sensor.     

Suppression of four wave mixing in wavelength division multiplexed system with hybrid modules

In this paper, two different configurations of optical phase conjugator, dispersion compensating fiber and fiber Bragg grating have been investigated. These configurations are further compared with the conventional schemes. Several link configurations have been compared and investigated the potential for inter-subcarrier four wave mixing suppression by means of midway fibers plus hybrid modules. The proposed schemes show improvement in performance by suppressing the four-wave mixing (>40 dBm). It strongly suppresses the four-wave mixing signal by introducing the destructive interference (due to OPC) between the first and second halves of the fiber optic link.     

Cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in dispersion compensated WDM transmission systems

The basic mechanism of cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in a periodically dispersion compensated transmission line has been investigated. Ordinary differential equations have been derived using variational analysis to estimate the phase fluctuation and the analytical result is verified by numerical simulations based on split-step Fourier method. We therefore explore the impact of different dispersion compensation maps on phase fluctuation for 10 Gb/s and 40 Gb/s WDM transmission systems. The effects of initial pulse spacing between channels, channel spacing and residual dispersion on phase shift have been studied. We find that cross-phase modulation induced phase fluctuation can be mitigated by proper adjustment of channel spacing and/or residual dispersion.     

Numerical design of high nonlinear coefficient of microstructure optical fibers

This paper presents a theoretical design of highly nonlinear microstructure optical fiber with dispersion-flat characteristics. The APSS™ 2.3 software based on the finite difference method with perfectly matched boundary conditions is used to simulate the properties of the proposed microstructure optical fiber. According to simulation, the proposed fiber warrants a high nonlinear coefficient of the order 41 W⁻¹ km⁻¹ and a low dispersion of 0.25 ps/nm/km at 1550 nm wavelength. It assumes a dispersion-flat characteristic of 0 ± 0.50 ps/nm/km in a 1450-1620 nm wavelength range centering 1550 nm wavelength with a modest number of design parameters.     

Impacts of dispersion maps on nonlinear distortion in distributed Raman amplified multi-span systems

The influences of dispersion maps on three major nonlinear effects (SPM, XPM and SRS) in distributed Raman amplified fiber transmission systems with periodic dispersion compensation are numerically investigated at identical nonlinear phase shift. The results show that compared with lumped amplification, distributed amplification tends to enhance the SPM/XPM induced penalties provided per span complete DC is used. However, these performance differences can be canceled out by means of optimal dispersion managements. Moreover, distributed Raman amplification can change the optimal dispersion maps for XPM effects. On the other hand, the impacts of SRS crosstalk are mainly determined by wavelength spacing and walk-off parameter, and the effects of dispersion management are quite limited. For a system with properly designed fiber dispersion characteristics, SRS induced waveform distortion can be well suppressed.     

The wavelength accumulation effect of Verdet constant upon an optical current sensor

Verdet constant is one of the prominent parameter showing the magneto-optical property of magneto-optical materials. There will be a wavelength accumulation effect in the systems employing broad-band optical sources, because of the dispersion property of Verdet constant. It is not proved, however, how much this effect can affect the broad-band system up till now. Therefore it is necessary to research into it, because the question whether it is reasonable and feasible to use a monochromatic light model for the describing of broad-band systems is concerned. The dispersion formula of the Verdet constant of ZF-7 glass is calculated first, and then, its wavelength accumulation effect upon an optical current sensor is theoretically analyzed and digitally simulated, in this paper. The results show that the wavelength accumulation effect of the Verdet constant of ZF-7 glass is less enough and the treatment of using monochromatic model to describe broad-band optical current sensing systems is reasonable and feasible, if the wavelength accumulation effects of the other optical parameters of the sensing head are not considered. The results might be a reference to the colleagues working in the optical current sensing techniques area.     

10Gb/s单信道光纤传输系统性能仿真研究

光纤传输系统的优化设计是光纤通信质量的重要保证.本文基于光子传输设计套件(PTDS)软件平台,对光纤传输系统的传输特性作了大量仿真研究,并得出分析了一些重要参量如光纤长度,光纤的损耗和衰减,光功率大小等对光传输系统的影响规律,给出了相应的补偿措施.本文研究结果对优化光纤传输系统有一定的参考价值.     

Analysis of a 2R all-optical regenerator utilizing cascaded four-wave mixing in a highly nonlinear fiber

The properties of an all-optical 2R regenerator based on cascaded four-wave mixing (FWM) in a highly nonlinear fiber (HNLF) are investigated. The regeneration is based on the nonlinear cascaded FWM transfer function and a study of the system's static behavior reveals the operating conditions, under which the transfer function approaches most the ideal, step-like discrimination characteristic function. Numerical simulations for the regenerated temporal satellite wave with different signal and pump powers are investigated, and the optimal transfer function based on different fiber lengths and different injected wavelengths are also demonstrated.     

Numerical reconstruction of an infrared wavefront utilizing an optical phase modulation device

We utilize nitroanisole, that absorbs infrared (IR) radiation as heat, as an optical modulation device based on a thermal process. The nitroanisole exhibits a thermal lens effect, i.e. a temperature dependent refractive index. Hence, the nitroanisole can induce phase modulation to visible light, in direct response to intensity of the incident IR radiation. The proposed method can be used to obtain the phase modulation distribution that corresponds to the IR intensity distribution, i.e. the IR hologram itself, on the nitroanisole by examining the phase map of visible light that is modulated upon passing through the nitroanisole. The IR wavefront can be reconstructed by calculating extracted IR holograms through the Fresnel transform. It is verified that both the amplitude and the phase of the IR wavefront can be reconstructed accurately by proposed method.     

高功率光纤中传输光模式与其波长相关性研究

针对高功率光纤激光模式诊断和光谱诊断的需求,研究了光纤中传输模式的波长相关性,数值计算了光纤中各个模式的模场分布随波长的变化曲线及相应的光束质量,采用双傅里叶变换F~2法实际测量了光纤模式成分与波长的关系曲线.结果表明,光纤中各个模式的模场分布随波长变化,波长越长,模场面积越大;模式的光束质量随波长变化不大,但在截止频率附近明显变差;光纤中各个模式的功率占比与波长有关.     

Effect of radiation-induced mean wavelength shift in optical fibers on the scale factor of an interferometric fiber optic gyroscope at a wavelength of 1300 nm

In order to analyze the effect of wavelength-dependent radiation-induced attenuation (RIA) on the mean trans- mission wavelength in optical fiber and the scale factor of interferometric fiber optic gyroscopes (IFOGs), three types of polarization-maintaining (PM) fibers are tested by using a 60 Co γ-radiation source. The observed different mean wave- length shift (MWS) behaviors for different fibers are interpreted by color-center theory involving dose rate-dependent absorption bands in ultraviolet and visible ranges and total dose-dependent near-infrared absorption bands. To evaluate the mean wavelength variation in a fiber coil and the induced scale factor change for space-borne IFOGs under low radiation doses in a space environment, the influence of dose rate on the mean wavelength is investigated by testing four germanium (Ge) doped fibers and two germanium-phosphorus (Ge-P) codoped fibers irradiated at different dose rates. Experimental results indicate that the Ge-doped fibers show the least mean wavelength shift during irradiation and their mean wavelength of optical signal transmission in fibers will shift to a shorter wavelength in a low-dose-rate radiation environment. Finally, the change in the scale factor of IFOG resulting from the mean wavelength shift is estimated and tested, and it is found that the significant radiation-induced scale factor variation must be considered during the design of space-borne IFOGs.     

Mitigation of phase noise in dispersion compensated quasi-linear optical transmission systems: Analysis

We theoretically investigate the phase noise in quasi-linear optical transmission systems and study the mitigation of phase noise by properly choosing periodic dispersion compensation and amplification. Variational method is used to deduce the analytical formula for calculating the phase fluctuations of a Gaussian pulse. The analytical predictions are then checked against direct simulations by numerically solving the nonlinear Schrödinger equation. We find that stronger dispersion compensation maps can be used to reduce phase noise and it can be further mitigated by modifying the dispersion map appropriately. It is also found that shorter amplifier spacing yields lower phase noise. We also explore the effect of pre-, post- and bi-end dispersion compensation configurations on phase noise with full compensation and check the reduction of phase noise along the fiber link.     

优化二元相位取样光纤布喇格光栅及对色散和色散斜率补偿的应用

利用粒子群算法对二元相位取样光栅的周期相位调制进行优化设计，在此基础上提出了基于二元相位取样光纤布喇格光栅的色散和色散斜率补偿技术.通过光栅周期啁啾可以调整每个信道的带宽，色散量由子光栅长度决定，调整取样函数的啁啾系数可以改变色散斜率，因此可以设计出用于波分复用系统的多信道色散补偿器件.     

基于自相位调制和交叉相位调制的全光开关特性研究

提出一种优化含有掺铒光纤放大器的非线性Sagnac干涉仪全光开关的新方法,建立了基于自相位调制和交叉相位调制两种解析模型,讨论了掺铒光纤放大器的小信号增益和饱和输出功率对开关性能的影响.分析表明掺铒光纤放大器的性能参量对开关所需要的Sagnac环中光子晶体光纤长度产生限制.当采用相同长度的光子晶体光纤时,基于交叉相位调制方式的全光开关与基于自相位调制方式的全光开关相比能够显著降低开关功率.采用分布傅里叶法数值求解非线性薛定谔方程,优化了开关结构,讨论了重复频率为40 GHz脉宽为5 ps的高斯型信号脉冲在开关时沿Sagnac环的传输特性.模拟结果表明,通过合理选择高非线性光子晶体光纤长度和掺铒光纤放大器的性能参量能够实现超低开关功率（＜1 mW）的开关操作.     

Improved dispersion tolerance of an optical duobinary transmitter based on a Mach-Zehnder modulator and an optical delay interferometer

We present a method for improving the dispersion tolerance of an optical duobinary transmitter based on a dual-arm Mach-Zehnder (MZ) modulator and an optical delay interferometer without electrical low-pass filters. Since such a duobinary modulator using a standard 1-bit delay cannot provide high dispersion tolerance, we investigated the impact of the modulator driving voltages and the bit delay in the interferometer to improve the transmitter’s dispersion tolerance.     

基于Fabry-Perot半导体激光器实现全光波长转换及其最优纵模选择

采用Fabry-Perot半导体激光器作为波长转换器件,利用半导体激光器内部的交叉增益调制效应,通过同时将脉冲信号光与连续探测光耦合到半导体激光器,实现了对波长为1552.62nm、重复速率为2.7GHz的光脉冲信号转换到波长为1548.23nm的连续激光,同时实现了脉冲时间抖动的抑制.实验发现,对于确定的半导体激光器及其工作参数,总存在一个固定的纵模,当探测光的波长与该纵模波长一致时可获得最高的波长转换效率和最大的消光比.理论分析了探测光与Fabry-Perot半导体激光器多纵模间的模式选择对波长转换效 关键词： 纵模选择 波长转换 注入锁定 交叉增益调制