光子晶体光纤中超连续谱产生的理论与实验研究

研究了光子晶体光纤中超连续激光光源的产生机理.利用非线性偏振旋转技术产生的中心波长为1 556.0 nm的飞秒光脉冲作为泵浦光源,在69 m长的高非线性光子晶体光纤中,得到了20 dB带宽约为140 nm的超连续谱;采用实验和数值模拟方法,研究了不同泵浦功率下超连续谱形成的过程.结果表明,在不同的泵浦功率下,超连续谱的形成机理不同,在各种非线性效应的共同作用下,泵浦光脉冲的峰值功率越高,得到超连续谱的带宽越宽,实验与数值模拟结果一致.另外,要想获得平坦的宽带超连续谱,必须选择合适的光纤长度.     

Equilateral pentagon polarization maintaining photonic crystal fibre with low nonlinearity

A new pentagon polarization maintaining photonic crystal fibre with low nonlinearity is introduced. The full vector finite element method was used to investigate the distribution and the effective area of modal field, the nonlinear properties, the effective indices of two orthogonal polarization modes and the birefringence of the new PM-PCF effectively. It is found that the birefringence of the new polarization maintaining photonic crystal fibre can easily achieve the order of 10^-4, and it can obtain higher birefringence, larger effectively mode-field area and lower nonlinearity than traditional hexagonal polarization maintaining photonic crystal fibre with the same hole pitch, same hole diameter, and same ring number. It is important for sensing and communication applications, especially has potential application for fibre optical gyroscope.     

基于光子晶体光纤光脉冲压缩的理论研究

从理论上研究了单根光子晶体光纤的光脉冲压缩,利用较短的具有高非线性系数的光子晶体光纤可以实现较高质量的光脉冲压缩。针对单根光子晶体光纤压缩光脉冲的限制,提出了一种基于光子晶体光纤非线性环路镜中交叉相位调制效应的脉冲压缩方法。理论研究表明,这种脉冲压缩方式可以压缩自身功率较低的信号脉冲,相比于单根光子晶体光纤的方法,可以得到更高压缩质量的脉冲,通过合理选择控制光脉冲的参数,可以有效地抑制基座。     

超短光脉冲在双折射光子晶体光纤中产生超连续谱的偏振特性数值分析

采用矢量耦合非线性薛定谔方程描述了超短光脉冲在双折射光子晶体光纤中的传输过程,并利用分步傅里叶方法求解该方程。数值模拟了中心波长为1550nm的超短光脉冲在不同色散参量的双折射光子晶体光纤中超连续谱的产生及其偏振特性。分析了光纤在不同色散区时,高阶色散和非线性效应对超连续谱及其偏振态的影响。结果表明,当超短光脉冲波长位于近光纤零色散点的反常色散区时,比其在光纤正常色散区和远离光纤零色散点的反常色散区更容易产生宽且平坦的超连续谱,所得到的光谱显示出了复杂的偏振态特性。     

Anisotropy of nonlinear optical transmission at the edge of the photonic band gap of an apodized layered medium

The effect of Kerr nonlinearity on the transmission of laser radiation in a one-dimensional photonic crystal has been investigated by the transfer-matrix method, modified to describe nonlinear effects. The crystal under study is a thin-film multilayer structure with a spatial distribution of the refractive index, which makes it possible to eliminate side bands in the transmission spectrum at each side of the photonic band gap and significantly increase the slope of the transmission curve. The transmission spectrum of such a photonic crystal structure has been studied for two opposite directions of laser radiation propagation. The anisotropy of nonlinear transmission is most pronounced near the edge of the photonic crystal band gap, which lies in the near-IR region. The proposed structure, having strong transmission anisotropy and sufficiently low reflection in the forward direction, can operate as an optical diode (analog of an electron diode).     

Tunable and switchable multi-wavelength Erbium-doped photonic crystal fiber ring laser incorporating a length of highly nonlinear photonic crystal fiber

A tunable and switchable multi-wavelength Erbium-doped photonic crystal fiber ring laser incorporating a length of single-mode highly nonlinear photonic crystal fiber is proposed and demonstrated experimentally. Stable dual-wavelength and triple-wavelength operations at room temperature are achieved by employing the highly nonlinear photonic crystal fiber to induce four-wave mixing effect and a polarization controller to vary the polarization states of propagation lights in the laser cavity. The laser cavity is free from any wavelength selection components. The laser obtains maximal 30 dB signal-to-noise ratio and the peak power fluctuations of lasing lines are less than 1.39 dB.     

非线性光学超构表面

在线性光学范畴内,人们已经通过亚波长尺度的超薄超构表面成功实现了对光的众多新颖特性的调控功能.其主要理念是通过对具有亚波长尺度且空间方向变化的超构功能基元进行特定的排列,从而实现对光的偏振、相位和振幅的有效控制.近来,超构表面上的非线性光学特性也引起了大家的广泛关注.在本综述中,我们对非线性光学超构表面的设计、超构功能单元的材料和对称性选择、非线性手性光学、非线性贝里几何相位和非线性波前整形等内容进行了总结;最后对非线性光学超构表面在调控光与物质的相互作用中面临的挑战和前景进行了展望.     

光子晶体全反射贯穿偏振滤波器的理论研究

 为了研究1维光子晶体中光的全反射贯穿效应及其偏振滤波特性,利用传输矩阵法计算了TE波和TM波在大于全反射角入射1维光子晶体的透射率,发现在透射波中出现了全反射贯穿效应。研究了TE波和TM波的全反射贯穿效应随介质光学厚度和周期数的变化特征,表明：全反射贯穿峰的频率随介质光学厚度的增加而减少,全反射贯穿峰数与周期数相等。且全反射贯穿效应具有优良的偏振滤波特性,利用这些特性可以设计出结构简单、控制方便的1维光子晶体的偏振滤波器。     

The geometric phase in nonlinear frequency conversion

The geometric phase of light has been demonstrated in various platforms of the linear optical regime, raising interest both for fundamental science as well as applications, such as flat optical elements. Recently, the concept of geometric phases has been extended to nonlinear optics, following advances in engineering both bulk nonlinear photonic crystals and nonlinear metasurfaces. These new technologies offer a great promise of applications for nonlinear manipulation of light. In this review, we cover the recent theoretical and experimental advances in the field of geometric phases accompanying nonlinear frequency conversion. We first consider the case of bulk nonlinear photonic crystals, in which the interaction between propagating waves is quasi-phase-matched, with an engineerable geometric phase accumulated by the light. Nonlinear photonic crystals can offer efficient and robust frequency conversion in both the linearized and fully-nonlinear regimes of interaction, and allow for several applications including adiabatic mode conversion, electromagnetic nonreciprocity and novel topological effects for light. We then cover the rapidly-growing field of nonlinear Pancharatnam-Berry metasurfaces, which allow the simultaneous nonlinear generation and shaping of light by using ultrathin optical elements with subwavelength phase and amplitude resolution. We discuss the macroscopic selection rules that depend on the rotational symmetry of the constituent meta-atoms, the order of the harmonic generations, and the change in circular polarization. Continuous geometric phase gradients allow the steering of light beams and shaping of their spatial modes. More complex designs perform nonlinear imaging and multiplex nonlinear holograms, where the functionality is varied according to the generated harmonic order and polarization. Recent advancements in the fabrication of three dimensional nonlinear photonic crystals, as well as the pursuit of quantum light sources based on nonlinear metasurfaces, offer exciting new possibilities for novel nonlinear optical applications based on geometric phases.     

A simple method for fabricating two- and three-dimensional photorefractive photonic lattices microstructures

We demonstrate an approach for easy fabrication of two- and three-dimensional optically induced nonlinear photonic lattices microstructures in photorefractive crystal by applying spatial filter and amplitude mask. The experimental setup of this method is very simple and flexible without complicated optical adjustment system. It can be applied in almost any optical laboratories. Two-dimensional hexagonal, square and three-dimensional hexagonal nonlinear photonic lattices microstructures have been produced in an iron-doped lithium niobate photorefractive crystal. The period of the induced photonic lattices microstructures can be dominated easily. This method is easily extended to generate more complex photonic lattices microstructures in photorefractive crystals, such as quasicrystal lattice.     

V型高双折射光子晶体光纤超连续谱产生的实验研究

高非线性高双折射光子晶体光纤是超连续谱产生的最有效介质之一, 因此本文选取V型光子晶体光纤作为研究对象. 通过多极理论数值模拟的结果, 确定V型光纤具有高双折射、高非线性等特性. 通过实验手段, 发现入射光中心波长和光纤的双折射效应对产生的超连续谱有很大的影响: 当入射光波长处于光子晶体光纤大的反常色散区时, 脉冲相对展得比较宽, 长轴要比短轴方向的超连续谱更宽, 频谱成分更加丰富. 在同一波长下光偏振方向越接近45°时, 超连续谱谱宽范围越大. 随着入射脉冲功率的增加, 超连续谱展得越宽, 但是当功率比较大时会达到功率饱和. 关键词： 光子晶体光纤 高双折射 多极理论 超连续谱     

Terahertz polarization splitter based on an asymmetric dual-core photonic crystal fiber

By employing the liquid crystal refractive index changes induced by applied electric field, a novel terahertz polarization splitter with tunable the operating frequency and bandwidths has been proposed and theoretically analyzed. It possesses an extinction ratio as high as the polarization splitters based on the two-dimensional photonic crystal waveguides. These distinguished features ensure its important applications in the integrated optical systems.     

Enhanced optical nonlinearity near the photonic bandgap edges of a cholesteric liquid crystal

The third-order Kerr nonlinear optical effect of a one-dimensional photonic bandgap structure of a cholesteric liquid crystal is investigated. In a femtosecond nonlinear transmission measurement, nonlinear optical changes in the bandgap edges are observed. From analysis of the dispersion relation, Kerr nonlinear coefficients of nematics, forming the cholesteric liquid crystal, are found to be enhanced by 1-2 orders of magnitude through the photonic bandgap structure.     

Supercontinuum generation by combining clad-pumped Er/Yb co-doped fiber amplifier and highly nonlinear photonic crystal fiber

We present an experimental study on supercontinuum generation by combining a clad-pumped Er/Yb co-doped fiber amplifier (EYDFA) and a highly nonlinear photonic crystal fiber (HNL-PCF). By using the nonlinear polarization rotation technique, a stable femtosecond optical pulse seed signal with a central wavelength of 1556.36 nm and a spectral line width of ∼5.6 nm has been obtained. Then, this pulsed seed signal is amplified by the EYDFA, the amplified pulse, which, with the broaden spectrum, propagates in the HNL-PCF. The 20 dB bandwidth of ∼520 nm from 1230 to 1750 nm is obtained.     

非线性一维光子晶体波导光双稳

利用非线性折射率系数较大且非线性时间响应较快的CdS_xSe_1-x玻璃为材料,设计并制备了非线性一维光子晶体波导光双稳器件,该器件的折射率空间分布呈正弦形式。实验测得双稳开关的阈值功率密度为1.60×10⁵W/cm²,开关时间为63ps。采用时域有限差分方法讨论了光子晶体带隙随入射光强变化而移动的情况,随着入射光功率密度的增加,光子晶体的带隙中心向短波方向移动。同时计算了该器件的双稳特性,理论计算得到双稳开关的阈值功率密度为1.40×10⁵W/cm²,开关时间约为50ps。获得了理论与实验基本一致的结果。     

Intrinsic localized modes in photonic crystal circuits

A discussion of intrinsic localized modes (ILMs) in photonic crystals is given. Emphasis is placed on ILMs in photonic crystal waveguides formed from Kerr nonlinear materials and photonic crystal circuits formed by joining nonlinear photonic crystal waveguides into networks. Work on stationary and propagating ILMs in nonlinear waveguides and waveguide junctions is reviewed. In addition, some discussion is given on the optical bistability of the barrier and junction geometries and on recent results on two-dimensional ILMs in Kerr nonlinear photonic crystals.     

矩形晶格高偏振、低损耗铋锗镓光子晶体光纤的结构设计及性能分析

非对称结构光子晶体光纤应用广泛。其良好的偏振特性、灵活的色散调控能力以及低限制损耗品质,对于优化与改善偏振光纤器件、非线性光学光纤、光通信光纤、光纤传感器等性能发挥着关键的作用。选用高折射率铋锗镓激光玻璃为材料,设计了八边形阵列、矩形晶格排列的光子晶体光纤,纤芯缺陷区包层及外包层均为圆形空气孔。模拟实验数据显示,结构参数为M=0.5,0.6时,在波长为1.55 μm处的双折射系数分别为1.16×10?2和1.33×10?2;在近红外波段短波区,矩形晶格结构光子晶体光纤的色散范围分别在±30 ps·nm?1·km?1之间及?18～32 ps·nm?1·km?1之间。色散斜率较低,曲线具有零色散点,展现了良好的连续谱调控能力;在1.00～1.90 μm波段内,当M=0.5,0.6时,光纤限制损耗稳定在10?7～10?9 dB·km?1之间;在1.55 μm处,限制损耗测量值分别为2.32×10?7和1.62×10?8 dB·km?1。     

Experimental demonstration of 1535-1555-nm simultaneous optical wavelength interchange with a nonlinear photonic crystal

We present results of what is to our knowledge the first experimental demonstration of simultaneous optical wavelength interchange by use of a two-dimensional second-order nonlinear photonic crystal. Fabrication and performance parameters of a 1535-1555-nm wavelength interchange nonlinear photonic crystal fabricated in lithium niobate are discussed.     

基于布里渊动态光栅的高灵敏度静压力传感器设计

设计了一种新型边孔型保偏光子晶体光纤,在包层中对称地引入两个大空气孔,纤芯区域与大空气孔之间仅有一层小空气孔。由平面应变假设将该模型进行二维简化,利用有限元法对该光纤的二维模型进行数值分析,通过计算不同温度和静压力下的双折射频移以研究其温度和静压力传感特性。研究表明,在较大静压力和温度范围内,该保偏光子晶体光纤无需掺杂任何应力材料就可以实现?2.1353 GHz/MPa的静压力灵敏度且具有温度不敏感性,其温度灵敏度仅为+0.1542 MHz/℃。另外,还对该光子晶体光纤的光学特性进行了分析,其满足单模传输条件、具有较小的限制性损耗和较大的有效模场面积。由于具有体积小、与其他光纤兼容度强、静压力灵敏度高、温度不敏感的特性,其在温度变化不定、静压力改变区间较大的环境中静压力精确测量的优势比较明显,较好的光学特性使其在油井、土木的监测应用等方面有着重要参考价值。     

Design and fabrication of two-dimensional photonic crystals with predetermined nonlinear optical properties

By probing the resonances between a photonic band and an external laser field and their nonlinear changes in angle-resolved reflectivity, we show experimental evidence that the nonlinear optical changes in a two-dimensional photonic crystal waveguide with a Kerr nonlinearity are critically dependent on the dispersion nature and the group velocity of the photonic bands. The results agree well with the behavior predicted from band structures, indicating that the design of nonlinear optical properties of material systems is realistically possible by band dispersion and group velocity engineering.