Nonlinear filtering by use of intensity-dependent polarization rotation in birefringent fibers

We analyze the transmissivity of a nonlinear filter that is based on intensity-dependent polarization rotation in a birefringent fiber. It is shown that the transmissivity of the element depends not only on the intensity of the incident light but also on the time behavior of its amplitude. Such an element can be used as a derivator, an element that transmits only variations in the input pulse. The filter can also be used for obtaining lasers that generate a train of intense noiselike pulses with a broadband spectrum and a short coherence length.     

基于非线性偏振旋转效应的多波长光纤激光器

多波长光纤激光器是未来波分复用光通信系统的理想光源,提出和展示了一个基于非线性偏振旋转效应的多波长光纤激光器,非线性偏振旋转诱导的强度相关非均匀损耗能有效地抑制均匀加宽增益介质掺铒光纤中的模式竞争,从而使光纤激光器在室温下产生稳定的多波长输出,实验实现了最多18个波长的多波长输出.另外,此激光器没有使用传统的滤波器,而是在激光腔内插入一段保偏光纤,保偏光纤与偏振相关隔离器构成一等效Lyot双折射光纤周期性滤波器.利用这种在线型的双折射光纤滤波器简化了光纤激光器的结构,使它更易于集成.还实验研究了多波长输出随抽运功率的演化,发现抽运功率对多波长的均匀性影响很大.     

Observation of elliptical polarization rotation in a long twisted fiber

The intensity-dependent polarization rotation caused by the self-induced nonlinear birefringence in a long twisted fiber is studied numerically and experimentally. By using a 1 km length of twisted fiber, we show that the effect of ellipse rotation accumulates monotonically as if the fiber were perfectly isotropic. Such behavior cannot be observed in a typical nontwisted fiber with randomly varying birefringence and is a unique feature of the twisted fiber, in which the large circular birefringence plays an essential role of preserving the handedness of elliptical polarization. We demonstrate a novel Faraday-mirror configuration to ensure automatic polarization alignment, which is directly applicable to achieving a simple and stable intensity discriminator.     

二次谐波产生的非线性相移的解析研究

给出一种分析二阶非线性级联效应的解析方法，对Ⅱ型二次谐波产生的非线性级联效应进行了详细的理论研究和分析。结果表明倍频晶体中正交输入两个振幅不相等的基波分量时，在近相位匹配下二阶非线性级联效应能够产生大的相移。利用本文的解析方法可以对任意二阶非线性相移产生的过程进行优化，从而以最小的需求输入功率来获得特定的相移。还对由非线性相移诱导的且与光强有关的偏振旋转效应和一种基于偏振旋转效应的全光偏振开关进行了分析和讨论。本文的结果对于建立一种基于Ⅱ型倍频晶体中非线性相移诱导偏振旋转效应的新全固化被动锁模飞秒激光装置具有十分重要的意义。     

具有一般非线性弹性力和广义阻尼力的相对转动非线性系统的周期解问题

讨论了一类相对转动非线性动力系统的周期解问题.首先建立了一类具有一般非线性弹性力、广义阻尼力和强迫周期力项的相对转动非线性动力系统;其次得到了对应自治系统的周期解不存在性结果,以及运用Mawhin重合度理论得到了该模型的周期解存在性结果,推广了已有的结果;最后举例证明本文结果的正确性.     

Coherent soliton pattern formation in a fiber laser

We report the observation of bound states of 350 pulses in a ring fiber laser mode locked by nonlinear rotation of the polarization. The phenomenon is described theoretically using a multiscale approach to the gain dynamics; the fast evolution of a small excess of gain is responsible for the stabilization of a periodic pattern, while the slow evolution of the mean value of gain explains the finite length of the quasiperiodic soliton train.     

Polarization-mixing optical parametric oscillator

We report the experimental realization of a new type of optical parametric oscillator in which oscillation is achieved by polarization rotation in a linear retarder, followed by nonlinear polarization mixing. The mixing is performed by a type II degenerate parametric downconversion in a periodically poled KTP crystal pumped by a 1064 nm pulsed Nd:YAG pump. A single, linearly polarized beam, precisely at the degenerate wavelength is generated. The output spectrum has a narrow linewidth (below the instrumentation bandwidth of 1 nm) and is highly stable with respect to variations in the crystal temperature.     

L-band polarization-controlled multiple dissipative solitons generation in a normal dispersion fiber ring laser

A polarization-controlled multiple dissipative solitons generation in a normal dispersion fiber ring laser operating in L-band is demonstrated. The fiber laser is passively mode-locked with nonlinear polarization rotation (NPR) technique. Depending on the rotations of the PCs, the number of the pulses circulating in the laser cavity can be tuned from 1 to 4. The experimental results suggest that the generation of multiple pulses is caused by the soliton shaping of dispersive waves induced by the variations of spectral filtering effect.     

Multiwavelength fiber laser with fine adjustment, based on nonlinear polarization rotation and birefringence fiber filter

We have proposed and demonstrated a multiwavelength fiber laser based on nonlinear polarization rotation (NPR). The mechanism for stable room-temperature multiwavelength operation contributes to the ability of the intensity-dependent loss in NPR to effectively alleviate mode competition. In addition, through tuning the birefringence fiber filter, the lasing wavelength can be accurately tuned in the free spectrum range of the in-line periodic filter.     

法拉第调制技术在微小旋转角检测中的应用

在外磁场中的碱金属原子蒸汽在光泵浦的作用下变成非线性介质,线偏振光经过这种介质时会变成椭圆偏振光,且椭偏光的主轴相对于入射偏振光的偏振面会产生一个微小的旋转。分析了碱金属原子能级结构和在光泵浦下产生的二向色性及其对探测偏振激光的偏振面旋转情况,并介绍了法拉第调制技术对这种旋转的测量方法,得到探测光强与旋转角的关系表达式,可以实现10^-7 rad量级的小角度检测。     

具时变刚度的相对转动非线性动力系统的周期解问题

建立了一类具有时变刚度,非线性阻尼力和强迫周期力项的相对转动非线性动力系统. 运用Mawhin重合度理论,得到了该模型的周期解存在唯一性结果,推广了已有的结果, 并且列举了具体的例子来说明本文的结果是新的. 关键词： 相对转动非线性动力系统 时变刚度 周期解 存在唯一性     

三光束飞秒激光干涉在GaP,ZnSe表面诱导二维复合纳米-微米周期结构

报道了三光束飞秒激光干涉在GaP和ZnSe晶体表面诱导二维复合纳米-微米周期结构.改变三束光的偏振组合方式,可以得到不同的纳米-微米复合结构.理论计算了相应偏振条件下光场强度分布、椭偏度分布和偏振方向分布.实验和理论计算结果表明,烧蚀斑上的微米长周期结构是由三光束干涉的强度花样决定,短周期纳米结构是由光场的偏振干涉花样决定.这些研究在纳米材料制备、超高密度光存储以及材料特性周期性调制等方面有很大的应用前景.     

基于SOA偏振旋转光开关的性能研究

利用SOA中的偏振主态的概念,理论分析了SOA中的偏振旋转的问题,并以此为基础提出了一种基于SOA中偏振旋转的光开关。这种光开关以SOA和偏振分柬器（Polarization Beam Combiner,PBC）为核心元件,利用光在SOA中的偏振旋转实现了光信号的开关,这种光开关具有开关速度快,功率均衡,易集成等优点,实验得到的开关消光比达到24dB以上,开关速度达到20ns。     

Magnetization-induced third harmonic generation in magnetophotonic microcavities

Magnetization-induced third harmonic generation was experimentally observed in thin films of bismuth-dopedyttrium-iron garnet. The magnitude of magnetization-induced nonlinear optical response was enhanced through building-in a garnet film into a photonic-crystal microcavity. It was shown that the observed magnetization-induced variations in the third-harmonic intensity were caused by the internal homodyne of interfering weak magnetic and strong nonmagnetic polarization components of the cubic nonlinearity of the garnet.     

一类相对转动非线性动力学系统周期解的唯一性与精确周期解

研究了一类具有线性刚度、非线性阻尼力和强迫周期力项的相对转动非线性动力学系统周期解的唯一性和精确周期解.讨论了一类自治系统极限环的唯一性与稳定性.应用定性分析方法,给出了一类相对转动非线性动力学系统具有唯一周期解的必要条件,并在一定条件下得到了系统的一类精确周期解.     

基于非线性光纤环镜的40Gb/s可重构光逻辑门

提出了一种新型的基于非线性光纤环镜(NOLM)的可重构全光逻辑门实现方案。传统的基于NOLM的全光逻辑利用自相位调制效应或交叉相位调制效应,透射传输函数重构的自由度低,可实现的逻辑门种类较少。该方案在传统的结构基础上,分析了NOLM中探测光的偏振态的演化,以及输入光偏振态和环内偏振控制器对NOLM的传输特性的影响。理论分析和数值仿真结果表明在考虑NOLM中的非线性偏振旋转效应的情况下,可以更加自由地构建不同透射传输函数,从而利用单一NOLM结构,仅通过调节偏振控制器,即能够可重构地实现绝大部分基础组合逻辑。实验中,完成了两路40Gb/s的数据信号之间的"非"、"与"、"或"、"或非"、"同或"、"异或"等各种基础组合逻辑,验证了方案的可行性。     

Generation of cavity-birefringence-dependent multi-wavelength bright–dark pulse pair in a figure-eight thulium-doped fiber laser

We experimentally demonstrated a stable multi-wavelength bright–dark pulse pair in a mode-locked thulium-doped fiber laser(TDFL). The nonlinear polarization rotation(NPR) and nonlinear optical loop mirror(NOLM) were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation. By incorporating different lengths of high birefringence polarization-maintaining fiber(PMF), the fiber laser could operate stably in a multi-wavelength emission state. Compared with the absence of the PMF, the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright–dark pulse pair.     

泵浦光强对激光相位共轭波非线性效应的影响

分析了泵浦光强对激光相位共轭谐振腔中探测光场的作用。基于稳定性定理,通过确定系统的Lyapunov指数,数值计算了在不同泵浦光强下的激光相位共轭波的非线性效应。结果显示,泵浦光强是系统的控制参量。调节泵浦光强的数值,系统的动力学性质发生了改变,可以呈现一周期、二周期、四周期以及倍周期分岔、周期并缩和混沌现象。     

Enhancement of photoinduced polarization rotation in azobenzene polymer films

In this paper we demonstrated enhancement of photoinduced polarization rotation for improved transmission of laser light at low input intensities through a crossed polarized system. It is achieved by utilizing two azobenzene doped polymer thin films in tandem. As the input beam propagates through the films, its polarization rotation induced by each film is additive. We obtained polarization rotation of as much as 24° resulting in enhanced transmission compared to a single-film approach. In addition, this novel design is promising for use as a broadband nonlinear transmission system.     

Cubic self-action effects in photonic-crystal microcavities

Third-order nonlinear-optical self-action effects in photonic-crystal microcavities have been studied. Considerable defocusing has been observed in a nonlinear microcavity layer with a thickness much smaller than the wavelength. The polarization self-action effect that is manifested as the significant rotation of the polarization plane of laser radiation resonant to the microcavity mode has been observed. It has been shown that the polarization rotation angle is a linear function of the radiation power density.