Dispersion penalty for 1.3 μm lightwave systems with multimodesemiconductor lasers

The effect of fiber dispersion on the performance of lightwave systems is analyzed for the case where multimode semiconductor lasers operating near the zero-dispersion wavelength of the single-mode fiber are used as sources. Both the intersymbol interference and the mode-partition noise are considered in the discussion of dispersion-induced power penalties. The theory is in agreement with an experiment in which the bit error rate is measured for lasers at various bit rates. The tolerable limits on the deviation of the laser wavelength from the zero-dispersion wavelength are obtained for a 1.3-μm system operating at 1.7 Gb/s. Monte Carlo simulations are used to predict the effect of mode-partition noise on the performance of such high-speed lightwave communication systems     

Single-channel operation in very long nonlinear fibers with opticalamplifiers at zero dispersion

The author investigates, by means of computer simulations, the performance of a very long, single-channel optical fiber system operating very close to the zero-dispersion wavelength of the fiber. Fiber losses are compensated by optical amplifiers. The optical signal is filtered after each amplifier, is passed through a final optical filter prior to square-law detection, and is finally filtered electrically. It is found that such a system does not work well if the fiber dispersion is strictly constant and if the carrier wavelength of the modulated signal coincides with the zero-dispersion wavelength of the fiber. As a result, the optical signal spectrum spreads to many times its initial width so that power is lost in the optical filters and the signal-to-noise ratio is degraded by the need for admitting a wider band of noise to the receiver     

Measurement of nonlinear and chromatic dispersion parameters of optical fibers using modulation instability

We present a simple method for the measurement of Kerr, second- and third-order dispersion coefficients in optical fibers using power and dispersion dependences of modulation instability near the zero-dispersion wavelength. We also complete the analysis by the accurate determination of the zero-dispersion wavelength of the fiber using the phase-matched four wave mixing process which occurs near this specific wavelength.     

Small signal analysis with higher-order dispersion for dispersive optical communication systems

In this paper an improved small-signal analysis has been presented for analyzing the influence of the higher-order dispersion terms on dispersive optical communication systems operating near zero-dispersion wavelength for single mode fiber. A generalized conversion matrix has been reported that gives the transfer function of intensity and phase from the fiber input to fiber output for laser source including the influence of any higher-order dispersion term. In addition, analysis is applicable to evaluate the impact of combined or independent dispersion terms on small-signal frequency response and relative intensity noise (RIN) response of an ultrafast laser diode including noises due to laser spontaneous emission rate and average photon density. These responses are plotted for second-, third-, and fourth-order dispersion terms and their combinations. It is observed that the higher-order dispersion terms have significant impact on frequency and RIN responses at large modulating frequencies and large propagation distances.     

Highly efficient four-wave mixing in an optical fiber with intensity dependent phase matching

Wavelength conversion via four-wave mixing in an optical fiber is investigated under a pump intensity dependent phase-matching condition. To obtain a high conversion gain, we use a fiber with a small mode-field diameter (4.2 /spl mu/m) and a small dispersion slope (0.0307 ps/km/nm/sup 2/). When the signal wavelength is set so that it is 9.2 nm longer than the zero-dispersion wavelength of the fiber, we obtain a wavelength conversion gain of greater than 5 dB over a pump wavelength region of more than 8 nm.     

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。     

Experimental Study on the Role of Chromatic Dispersion in Continuous-Wave Supercontinuum Generation

The influence of chromatic dispersion on continuous-wave (CW)-pumped supercontinuum (SC) generation in kilometer-long standard fibers is experimentally investigated. We perform our study by means of a tunable, high-power fiber ring laser pumping a dispersion-shifted fiber in the wavelength range of small and medium anomalous dispersion. Our results show that, at low input powers, chromatic dispersion plays a dominant role on nonlinear pump spectral broadening, giving rise to a broader spectrum when pumping just above the zero-dispersion wavelength of the fiber. At higher input powers, however, the width of the generated SC spectrum is mostly due to the Raman effect, hence more independent of the value of the chromatic dispersion coefficient. We show that, in this case, the optimum pumping wavelengths for SC generation are not so close to the zero-dispersion wavelength of the fiber as in the previous case. In these conditions, as the chromatic dispersion grows, we can obtain square-shaped and high-power density spectra, which seem extremely promising for applications in optical coherence tomography.      

RMS width of pulses in nonlinear dispersive fibers

An approximate analytical expression for the root means square (RMS) width of pulses propagating in nonlinear, dispersive fibers is derived. This result is useful for predicting how far a pulse can travel before it suffers significant distortion due to the combined influence of the nonlinearity of the refractive index and the dispersive properties of the fiber. This theory applies to pulses operating near the zero-dispersion wavelength where dispersion alone has a negligible influence, but where the combined influence of nonlinear self-phase modulation and dispersion can produce a significant effect     

Grating compensation of third-order fiber dispersion

Subpicosecond optical pulses propagating in single-mode fibers are severely distorted by third-order dispersion even at the fiber's zero-dispersion wavelength (λ₀). Using cross-correlation techniques, the authors measured the broadening of a 100-fs pulse to more than 5 ps after passing through 400 m of fiber near λ₀. The measured asymmetric and oscillatory pulse shape is in agreement with calculations. A grating and telescope apparatus was configured to simultaneously equalize both third- and second-order dispersion for wavelengths slightly longer than λ ₀. Nearly complete compensation has been demonstrated for fiber lengths of 400 m and 3 km of dispersion-shifted fiber at wavelengths of 1560-1580 nm. For the longer fibers, fourth-order dispersion due to the grating becomes important     

光纤零色散波长点附近光孤子传输特征的理论分析

本文利用约化摄动重整化方法研究了光纤零色散波长点附近光孤子传输的特征。研究结果表明,光纤零色散波长点附近,光孤子仍然存在并能够稳定地传输,由于光纤损耗和三阶色散效应的影响,光孤子的振幅按指数规律衰减,标准光孤子分裂成孤子和非孤子两部分。     

光纤损耗对零色散波长附近传输的暗孤子脉冲的影响

利用一种解析的方法研究有损耗的光纤零色散波长附近传输的光脉冲,在正常色散区,得到了稳定的暗孤子解析解,并由此讨论了存在小损耗时暗孤子的形成条件,以及小损耗对暗孤子的中心位置,相位,振幅,频率等参数的影响。     

Chromatic dispersion characterization in short single-mode fibersby spectral scanning of phase difference in a Michelson interferometer

Chromatic dispersion characteristics around zero-dispersion wavelength have been measured in short samples of single-mode fibers by a spectral scanning of the interference signal in a Michelson interferometer. The propagative refractive index is directly obtained from the phase-difference variations with the wavelength between a light beam propagated through the fiber and a reference beam. The optimum operative conditions of the interferometer for obtaining the unequivocal analysis of experimental signals are discussed. The accuracy of the results obtained shows the reliability of the method for a complete dispersion characterization     

Impact of dispersion fluctuations on dual-pump fiber-optic parametric amplifiers

Effects of zero-dispersion wavelength (ZDWL) fluctuations on dual-pump fiber-optic parametric amplifiers are investigated analytically and numerically. It is found that the signal gain varies considerably from fiber to fiber even though each fiber may have the same ZDWL on average. Moreover, the gain spectrum becomes highly nonuniform for a given fiber because of such dispersion fluctuations. Numerical simulations show that this problem can be solved to a large extent by reducing wavelength separation between the two pumps, but only at the expense of a reduced amplifier bandwidth.     

微结构光纤中的相位匹配分析

通过数值计算分析,讨论了微结构光纤（MF）中四波混频（FWM）的相位匹配条件与色散分布的关系.首先,介绍了光纤中四波混频基本理论,并且推导出了符合MF的相位匹配公式.其次,对零色散点分别为一个和两个的MF相位匹配进行了数值分析.最后,通过数值计算对一些实验中出现的四波混频现象进行了解释.     

Soliton technique to characterize single-mode fiber dispersion

Transmitting subpicosecond pulses at moderate powers over a few meters of fiber creates a notch in the pulses' power spectra in the vicinity of the fiber's zero-dispersion wavelength. This is caused by the interaction of nonlinear self-phase modulation and third-order dispersion. This phenomenon can be used to determine the zero-dispersion wavelength of single-mode fibers     

Guided-wave optical equalizer with α-power chirped grating

A theoretical investigation of a guided-wave optical equalizer with an α-power chirped grating is presented. A group delay dispersion of 3700 ps/nm can be obtained at λ=1.55 μm by a chirped grating with α=0.3. It is shown that the chromatic dispersion of 200 km of a fiber whose zero-dispersion wavelength is located at 1.3 μm can be compensated at 1.55 μm to achieve up to 10 GHz signal bandwidth     

Correlation of zero-dispersion wavelength with mode confinement parameters in single-mode fibers; Analysis for simple step, triangular core, and dispersion-shifted models

Studies correlating the zero-dispersion wavelengths of single-mode fibers with various mode confinement parameters are presented. The studies are carried out for simple-step, triangular core, and a fiber design similar to that which has been published by the Corning group. It is found that the latter fiber has markedly improved mode confinement properties at an operating wavelength near 1.55 μm.     

Impact of dispersion fluctuations on the noise properties of fiber optic parametric amplifiers

The effects of zero-dispersion wavelength (ZDWL) fluctuations on the noise characteristics of fiber optical parametric amplifiers (FOPAs) are investigated. The numerical derivation of the noise figure (NF) in terms of the amplifier operating conditions and the magnitude of ZDWL fluctuations is achieved by utilizing a simulation method based on the three-coupled propagation equations. The numerical analysis shows that the average NF of FOPAs is increased compared with the case of uniform dispersion, especially at high-gain operation. Apart from the NF, the gain-to-NF ratio is also evaluated to assess the amplifier performance for a variety of amplifier operating conditions and dispersion profiles.     

Four-wave mixing in an optical fiber in the zero-dispersionwavelength region

Fiber four-wave mixing (FWM) in the zero-dispersion wavelength region is described. The phase-matching characteristics are studied in the wavelength region where the first-order chromatic dispersion is zero. The results show that the phase-matching condition is satisfied and FWM light is efficiently generated at particular combinations of input light wavelengths. It is also shown that the deviation of the zero-dispersion wavelength along the fiber length plays an important role in FWM behavior     

Automatic dispersion equalization for installing high-speed opticaltransmission systems

This paper proposes an optical transmission system with automatic dispersion equalization for exploitation of the fiber capacity without additional installation cost. The system has two operational modes: “measurement-mode” wherein dispersion is measured by phase-to amplitude-modulation conversion, and “data-transmission-mode” for providing telecommunication services. Dispersion equalization is realized by the accompanying use of dispersion compensating devices and wavelength tuning to the zero-dispersion of the optical fibers. Supervisory-channel communication enables remote operation. We demonstrate a simplified system; the dispersion of a 10 Gb/s-1000 km transmission line is successfully equalized in a fully automatic manner. Equalization with the preciseness of 10.1 mn from the zero-dispersion wavelength provides penalty free transmission or better performance with optical input power under the Brillouin threshold