【作者】 郑宏军；

【导师】 徐静平； 刘山亮；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 鉴于实验条件等因素的限制,以往的脉冲传输与测量实验大多采用自相关技术等测量脉冲时域特性,不能准确得到脉冲的时域波形等特性。又考虑到脉冲通常具有较大的频率啁啾且可以通过预啁啾技术等调节啁啾,利用能够准确测量脉冲时域波形等特性的二次谐波频率分辨光学门(SHG-FROG)技术实验研究了啁啾脉冲在光纤通信系统中的线性和非线性传输特性,并对脉冲传输作了深入系统的理论研究,为光纤通信系统及其关键光电子器件设计和优化提供了重要的理论和实验依据。利用SHG-FROG技术对10 GHz短脉冲线性传输进行了实验研究。结果表明,激光器输出的短脉冲是具有负线性啁啾的近变换极限高斯脉冲,经过12.7 km色散平坦光纤线性传输后仍然为具有负线性啁啾的高斯脉冲,其谱宽在传输过程中基本保持不变,脉宽展宽了3.1倍,啁啾增大了4倍。实验结果、数值计算结果和理论预期一致。在此基础上,采用分步傅里叶方法数值研究了初始啁啾双曲正割脉冲和啁啾双边指数脉冲的线性传输特性,给出了双曲正割脉冲和指数脉冲频谱宽度和时间带宽积随频率啁啾变化的表达式,提供了判断脉冲时域波形的一种有效方法。结果表明,负线性啁啾对两种脉冲时域展宽的影响比正啁啾要大得多。非线性啁啾对双曲正割脉冲和指数脉冲线性传输时域波形变化的影响比线性啁啾更大,非线性啁啾时两脉冲在线性传输过程中都出现时域波形分裂现象,比具有相同啁啾的高斯脉冲时域波形分裂都严重。利用SHG-FROG技术实验研究了10 GHz脉冲演化形成光孤子的规律和特点,并采用分步傅里叶方法数值研究了啁啾孤子脉冲的形成和传输,数值结果与实验数据一致。在此基础上,采用分步傅里叶方法,数值研究了啁啾双边指数脉冲的非线性传输特性。结果表明,脉冲振幅A越大,啁啾参量|C|越小,指数脉冲演化成光孤子所需的的距离越短。在相同传输距离情况下,指数脉冲演化成光孤子所需的最小振幅A比啁啾双曲正割脉冲的大。采用分步傅里叶方法数值研究了线性频率啁啾对高斯光脉冲在凸形色散分布平坦光纤中产生超连续谱的影响,并与啁啾双曲正割脉冲产生超连续谱的情况进行了比较。结果表明,无啁啾高斯光脉冲的超连续谱达到200 nm以上,其特性优于双曲正割脉冲超连续谱特性。获得最佳超连续谱所需光纤长度随啁啾参量C增加而缩短。负啁啾时的超连续谱特性劣于正啁啾时的特性,两种情况下的超连续谱特性均劣于无啁啾时的超连续谱特性,超连续谱特性的劣化程度随啁啾参量|C|的增加而增大。采用分步傅里叶方法数值研究了初始线性频率啁啾对双折射光纤中正交偏振孤子间碰撞特性的影响。研究表明,初始啁啾改变了光孤子在双折射光纤中形成束缚态的阈值δth,正啁啾对光孤子束缚态阈值δth的影响比负啁啾明显。修正了拉曼放大作用下的孤子脉冲传输方程,利用SHG-FROG技术实验研究了拉曼放大对光孤子传输特性的影响,实验数据与采用分步傅里叶方法数值研究结果一致。拉曼放大能够压缩孤子脉冲、补偿光纤损耗,但不改变孤子脉冲的时域波形。在传输光纤长度小于拉曼放大有效光纤长度情况下,拉曼放大能够完全补偿光纤损耗;在传输光纤长度大于拉曼放大有效光纤长度情况下,拉曼放大能够部分补偿光纤损耗。拉曼放大对孤子脉冲的压缩和对光纤损耗的补偿能力与泵浦激光器特性有关,随实验中泵浦功率的增加而增大。光孤子脉冲对拉曼放大泵浦光偏振特性不敏感,与光孤子在光纤中保持均一偏振态的理论一致。由SHG-FROG技术原理导出了超高斯脉冲的自相关特性公式,数值研究了超高斯脉冲的自相关特性及其受锐度参量m、啁啾参量C、脉冲噪声和随机噪声影响的变化规律,并与原脉冲相应参量作了比较,给出了一个有效滤除随机噪声的方法并作了实验验证。更多还原

【Abstract】 Due to limits of experimental conditions, the experiments of pulse propagation and measurement are normally performed by employing the autocorrelation technology so that the temporal waveforms and other characteristics of the pulses can not be exactly determined. The pulses generally have frequency chirp which can be controlled by pre-chirped technology, etc. The second-harmonic generation frequency-resolved optical gating (SHG-FROG) analyzer can be used to exactly measure the pulses characteristics. In this thesis, the linear and nonlinear propagation characteristics of chirped pulses in the optical fiber communication systems are experimentally and theoretically studied by using the SHG-FROG analyzer and the numerical method. As a result, the theoretical and experimental bases are established for design and optimization of optical communication systems and their photoelectric devices.The linear propagation characteristics of 10 GHz short pulse are experimentally studied by employing SHG-FROG analyzer. The pulse from the laser is near transform-limited Gaussian pulse with negative linear chirp. After the pulse propagates over 12.7 km of DFF, the spectral width is almost unchanged, the temporal width is about three times as wide as that of input pulse, the chirp is about four times as large as that of the pulse. The experimental data are consistent with the numerical results and the predictions of the theory.The linear propagation characteristics of the hyperbolic secant pulse and the double-side exponential pulse with initial linear and nonlinear frequency chirp are numerically studied by using the split-step Fourier method (SSFM). It is found that the effect of the negative linear chirp on the two pulses broadening is greater than that of the positive chirp. The effect of the nonlinear chirp on the temporal waveform is greater than that of the linear chirp. The temporal waveform splitting of the two pulses with nonlinear chirp is respectively more obvious than that of Gaussian pulse during linear propagation. Furthermore, the expressions of the spectral width and time-bandwidth product of the two pulses with the linear chirp C are given.The evolution of 10 GHz pulse with frequency chirp into the soliton is experimentally investigated by employing the SHG-FROG analyzer. Formation and propagation of chirped soliton are numerically studied according to the nonlinear propagation theory by using the SSFM. The numerical results are consistent with the experimental data. The nonlinear propagation characteristics of the double-side exponential pulse with initial linear frequency chirp are numerically studied by use of the SSFM. The greater the pulse amplitude A is, the less chirp parameter |C| is, the shorter the propagation distance evolving into a soliton is. The amplitude A of exponential pulse which evolves into a soliton is greater than that of hyperbolic secant pulse at the same propagation distance.The effect of the linear frequency chirp on the supercontinuum spectrum generation of Gaussian pulse is numerically investigated in the dispersion-flatted fiber with convex dispersion profile by using the SSFM. The relevant parameters of the supercontinuum spectrum of Gaussian pulse are compared with those of the hyperbolic secant pulse. The supercontinuum spectrum of the unchirped Gaussian pulse is wider than 200 nm, its characteristics are better than those of the hyperbolic secant pulse. The fiber length corresponding best supercontinuum spectrum decreases with the increase of chirp parameter C. The characteristics of supercontinuum spectrum for negative chirp are worse than those for positive chirp. The characteristics for chirp case are worse than those for unchirped case, gradually become severe with the increase of C.The collision characteristics of the orthogonally polarized solitons with initial linear frequency chirp are numerically studied in a linear birefringent fiber. It is found that initial chirp changes the threshold value of solitons forming into bound state in the birefringent fiber. The effect of initial positive chirp on the threshold value is more obvious than that of negative chirp.The equation of soliton propagation is modified with the Raman amplification. The effects of Raman amplification on propagation characteristics of soliton are experimentally investigated by employing SHG-FROG analyzer. The experimental data are consistent with the numerical results by using the SSFM. Raman amplification can compress the soliton, compensate the fiber loss, while not change the temporal waveform of the soliton. Raman amplification can completely compensate the fiber loss when the propagation distance is less than the effective fiber length of Raman amplification, can partially compensate the fiber loss when the propagation distance is more than the effective fiber length. Compression of the soliton and compensation of the fiber loss increase with the increase of the Raman pumping power. Experimental results show that soliton is not sensitive to the polarization of Raman pumping source. It is consistent with the theory that soliton maintains a high degree polarization in the fiber.The expressions of autocorrelation characteristics of the super-Gaussian pulse are derived form the principle of the SHG-FROG analyzer. The autocorrelation characteristics of the super-Gaussian pulse and their variations affected by the edge sharpness parameter m, linear chirp parameter C, pulse noise and random noise which are compared with the relevant parameter of the pulse, are investigated by using the numerical method. A useful method of filtering the random noise which is validated by the experiment is given.更多还原