Impact of polarization dependent loss on degree of polarization as feedback signal of polarization mode dispersion

Polarization dependent loss (PDL) has been recognized as a critical issue because various inline optical components may have nonnegligible PDL effect that interacts with polarization mode dispersion (PMD). We investigated the impact of PMD-PDL interaction on degree of polarization (DOP), which is the most commonly used feedback signal in PMD compensation. The simulation results of a 40-Gb/s NRZ code optical transmission system show that the maximum PMD increases from approximately 40 ps to more than 45 ps, while minimum DOP declines from approximately 0.6 to approximately 0.2. The interaction of PMD and PDL also induces residual PMD underestimation of 5-8 ps, which causes degradation of PMD compensation performance.     

Compact first and second order polarization mode dispersion emulator

Polarization mode dispersion (PMD) is becoming major system impairment in high speed and long distance opti- cal fiber transmission systems. Since the PMD-induced pulse spreading is a frequency-dependent statistic pa- rameter and varies randomly over time, it is difficult to be compensated[1-3]. Large length of single mode opti- cal fiber is needed to generate certain amount of PMD in laboratory, and the PMD effect in the fiber varies slightly and slowly over time. Therefore, PMD emula- …     

光纤中受激Brillouin散射动态弛豫振荡特性及其抑制方法

为了避免在高功率光纤放大器和光纤相位共轭镜等实际应用中因受激Brillouin散射（SBS）造成的光纤损伤,根据描述SBS动态弛豫振荡特性的振幅耦合方程,利用有限差分的数值模拟方法研究了光纤中SBS的动态弛豫振荡特性,并对其抑制进行了初步探讨.得到了光纤中SBS弛豫振荡在不同的脉冲上升时间的时空三维图;同时利用方波和脉冲光作抽运光进行了相应实验研究,实验结果与理论模拟结果符合很好.结果表明,增大抽运光脉冲上升时间可以有效抑制因SBS而产生的弛豫振荡,进而避免因其造成的光纤损伤. 关键词： 受激Brillouin散射 动态弛豫振荡特性 有限差分法     

Passive harmonic mode locked all-normal-dispersion Yb-doped fibre lasers

Passive harmonic mode-locking of dissipative solitons is demonstrated in all-normal dispersion Yb-doped fibre lasers.A difference equation model of the mode-locked fibre lasers is adopted to simulate the intra-cavity nonlinear dynamics.Hysteresis phenomena around the mode-locking threshold,and the effect of introducing linear phase bias are discussed.The passive harmonic mode-locking as one kind of multipulsing operations is revealed.Moreover,the simulation shows the bistability between multipulsing and single-pulse or period multiplication.     

基于扭转模腔的全固态单纵模拉曼黄光激光器设计

输出波长在560~590nm的全固态拉曼黄光激光器是近几年兴起的激光器之一。目前,此类激光器内部多模振荡引起的黄光输出谱线单色性较差的问题还没有得到解决。针对这一情况,提出将扭转模腔与拉曼复合腔相结合的新型解决方案,从根本上消除增益介质中空间烧孔效应引起的基频光多模振荡,实现单纵模黄光输出。拉曼复合腔由L型基频光谐振腔与直线型拉曼谐振腔耦合而成,既保证各个非线性变换过程可充分利用腔内的高功率密度,又可相对独立地对不同波长的光路进行优化调节,从而使整个系统实现最佳输出。该设计有助于在全固态拉曼激光器中实现毫瓦量级的单纵模黄光输出,为基于黄激光的生物医疗、钠导星、空间目标识别等系统提供理想的固体黄光光源。     

Artificial spectral filtering in dissipative soliton fiber lasers with invisible bandpass filters

We numerically study the artificial spectral-filtering effect in dissipative soliton fiber lasers without intracavity spectral filters. It is found that in dissipative soliton lasers with real saturable absorbers (SAs), the dynamic spectral filtering of the real SAs serves as an artificial spectral filter and contributes to the pulse shaping. While in the dissi- pative soliton lasers with artificial SAs, such as nonlinear polarization rotation, the spectral filtering introduced by the intracavity polarization-dependent components acts as an artificial spectral filter and shapes the pulses to obtain mode-locking. An investigation of the artificial spectral-filtering effect reveals the operating mechanisms of the dissipative soliton fiber lasers without visible bandpass filters.     

基于光纤四波混频波长转换和色散的慢光实验研究

对基于光纤四波混频（FWM）波长转换和色散的慢光实现进行了详细和系统的实验研究.首先,实验测定了高非线性光纤中FWM带宽约为40 nm,从而确定了慢光的可调谐带宽;接着,在普通单模光纤和色散补偿光纤（DCF）中针对500 MHz正弦信号和100 ps短脉冲信号分别实现了34和198 ns的脉冲延迟,在DCF中还实现了209 ns的脉冲提前.讨论了增大延迟量的方法,指出随着宽带FWM波长转换的实现和大色散光纤的应用有望获得微秒量级的大延迟量,从而为高性能光纤延迟线和全光缓存器等应用提供支持. 关键词： 慢光 四波混频 色散     

Nonreciprocal Coupling in Asymmetric Dual-Core Photonic Crystal Fibres

The photonic crystal fibre with asymmetric dual cores is shown to attain strongly nonreciprocal coupling of the lightwave propagating along the fibre, for the first time to our knowledge. It is found that the coupling properties can be quite different when the incident position is changed. This kind of fibre could have potential for unidirectional coupler applications in fibre-optic local and metropolitan area networks. We also examine the polarization and wavelength dependence of the coupling nonreciprocity in the asymmetric dual-core photonic crystal fibres.     

Frequency Dependence of Polarization Mode Dispersion in a Crystal-Based Polarization Mode Dispersion Compensator

We report the frequency dependence of polarization mode dispersion (PMD) in a PMD compensator based on six cascaded birefringent crystals separated by Faraday rotators. When all crystal axes are aligned, the device can compensate for the first-order PMD. However, if all crystal axes are coupled with arbitrary angles, it can compensate for high-order PMD. The variations of differential group delay and principal state of polarization with optical frequency are analysed. The PMD vector and Stokes components of the device versus wavelength are measured. The theoretical simulations agree well with the experimental results.     

KTa_(1-x)Nb_xO_3:Cu晶体中直流空间电荷场的进一步研究

分别用扩束光和一束写入光对KTa_(1-x)Nb_xO_3:Cu(X=0.32)晶体中的光折变栅进行擦洗,通过不同的擦洗效果,进一步论证了在写入过程中除了形成周期分布的空间电荷场之外,同时还形成了直流空间电荷场.并对直流空间电荷场被擦洗的动态过程进行了详细研究.此外,在写入之前利用一束均匀光照射在外加电场作用下的KTa_(1-x)Nb_xO_3:Cu晶体,研究了直流空间电荷场的形成对衍射信号强度的影响.