Long range plasmon assisted all-optical switching at telecommunication wavelengths

We exploit the properties of ultranarrow, Fano-like resonances generated by the coupling of long range surface plasmons with ultrathin (～10?nm), metallic, subwavelength gratings embedded in a nonlinear, cubic material to obtain all-optical switching at telecommunication wavelengths for extremely low input power. We provide an example of a silver metallic grating embedded in a chalcogenide glass (As₂S₃), and we show the concrete possibility to achieve all-optical switching at local field intensities compatible with the photo-darkening threshold of the material.     

Mode-matched Fano resonances for all-optical switching applications

We introduce the concept of mode-matched Fano resonances in one-dimensional, subwavelength, diffraction gratings. These resonances are characterized by an extremely high quality (Q)-factor and lend themselves well for applications to ultra-low power, all-optical switching devices at telecommunication wavelengths. We provide examples of diffraction gratings made of a chalcogenide glass (As₂S₃) where, thanks to the mode-matched Fano resonances, all-optical switching is obtained at local field intensities well below the photo-darkening threshold of the material.     

+1/-1相位掩模板和532nm激光下低损耗As_2S_3硫系光纤布喇格光栅的制备

采用改进型Sagnac干涉光栅写入系统,利用532nm准带隙光曝光源和带+1/-1衍射级的相位掩模板,在两种不同直径的低损耗As_2S_3硫系玻璃光纤上刻写布喇格光栅,并研究曝光期间光栅的动态特性.实验表明,As_2S_3光纤布喇格光栅透射峰值随光纤直径的减小而增强;在曝光过程中,布喇格波长先是较快地向短波长方向移动,随着曝光时间的延长,布喇格波长缓慢地向长波长方向回复.曝光时间为800~1 000s时,在包层直径为140μm的As_2S_3光纤上获得质量良好的布喇格光栅光谱,其透射峰值可达-2.6dB,带宽为0.37nm.对As_2S_3硫系光纤纤芯的光敏性分析结果表明,折射率调制幅度和平均折射率变化随曝光时间分别可达到10-4和10-3数量级.     

双棱镜改变写入Bragg波长的相位掩模技术

将一种可旋转的双棱镜引入到相位掩模技术中以改变光栅的写入Bragg波长.在该系统中,光纤光栅是由来自可旋转双棱镜所形成的波长为248 nm的紫外干涉条纹写入的,其中,相位掩模被用作 1级衍射光的分束器,通过双棱镜的旋转可改变两写入光束的交叉角.为了初始化Bragg波长的参考值,双光栅的顶角由相位掩模的 1级衍射角和双棱镜的折射率确定.因为在～100 nm范围内两光束的非对称旋转对光栅周期的改变是5×10~(-4) nm,双棱镜引入的光栅的闪耀可忽略.当Bragg波长的移位为1 nm时,棱镜最大的旋转角为～1 degree,最小的旋转角是～2.4 min.与Talbot干涉仪中平面镜的旋转角～23 s/nm相比,该相位干涉仪中棱镜的旋转精度降低了2～3个数量级.     

Multi-Wavelength-Switchable Double Clad Yb3+-Doped Fiber Laser Based on Reflectivity Control of Fiber Bragg Gratings by Induced Bend Loss

We propose and demonstrate an all-fiber multi-wavelength switchable double-clad Yb³⁺-doped fiber laser based on the reflectivity cavity control by induced bend loss. The wavelength switching is realized by a variable reflecting mirror that employs a cascaded array of three high reflection (>99%) fiber Bragg gratings at 1064, 1080 and 1096 nm, with a bending controller inserted between each grating. The order of the Bragg gratings is decided according to the gain profile of the Yb³⁺-doped fiber and the induced bending loss allows us to select the Bragg-wavelength laser operation. The laser is capable of switching continuously from one wavelength to another, and slope efficiencies over 50% are obtained at each wavelength.     

An ultrafast all-optical asymmetric Fabry-Pérot switch based on bulk Be-doped InGaAsP grown by He-plasma-assisted epitaxy

We demonstrated ultrafast all-optical switching, using an asymmetric Fabry-Pérot device, based on bulk Be-doped InGaAsP grown by He-plasma-assisted molecular beam epitaxy. We achieved 5 ps switching window (1/e fall time) and a peak contrast ratio of 20 dB at 1.57 μm. High contrast (> 10 dB) was maintained over ～24 nm of bandwidth under switching energy density of 0.5 pJ/μm², and over ～40 nm of bandwidth when switching energy density was increased to 1.4 pJ/μm². The switching operation was independent of data pulse polarization, and could be potentially performed at high repetition rates.     

Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　ＴｈｅｒｅｉｓａｇｒｅａｔｄｅａｌｏｆｉｎｔｅｒｅｓｔｉｎｆｉｂｅｒＢｒａｇｇｇｒａｔｉｎｇｓｄｕｅｔｏｔｈｅｉｒｍａｎｙｉｍｐｏｒｔａｎｔａｐｐｌｉｃａｔｉｏｎｓｉｎｔｈｅｆｉｅｌｄｏｆｔｅｌｅｃｏｍｍｕｎｉｃａｔｉｏｎｓａｎｄｆｉｂｅｒｓｅｎｓｏｒｓ .ＢｅｃａｕｓｅｆｉｂｅｒＢｒａｇｇｇｒａｔｉｎｇｓｅｘｈｉｂｉｔｄｉｓｐｅｒｓｉｏｎｂｏｔｈｉｎｒｅｆｌｅｃｔｉｏｎ ,ｅｓｐｅｃｉａｌｌｙｗｈｅｎｔｈｅ ｇｒａｔｉｎｇｉｓｃｈｉｒｐｅｄ[1] ,ａｎｄｉｎｔｒａｎｓｍ…     

Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

By introducing a convergent lens in the phase mask setup and by tilting appropriately the fiber from the phase mask, a linearly chirped fiber grating with an appropriate chirp can be obtained conveniently. Using this method, two groups of fiber gratings, each of them is composed of 8 overlaped linearly chirped fiber gratings but with different center reflection wavelength separations (～0.8 nm and ～1.6 nm, respectively) are fabricated. Experimental results show that, the compensators based on the two groups of fiber gratings can be used to compensate for the dispersion of 8×2.5 Gb/s transmission over 100 km of standard single-mode fiber for multiple channels in optical time-division multiplexing (OTDM) and densed wavelength division multiplexing (DWDM).     

Large inverse relaxation of photoinduced birefringence in an azobenzene-containing ionic self-assembly complex

Photoinduced anisotropy and polarization holographic recording were investigated in an azobenzene-containing ionic self-assembly complex. The complex film was found to possess large photoinduced dichroism (D～0.36) and photoinduced birefringence (Δn～10^?2). A noteworthy observation was that the photoinduced birefringence did not show any decay, but strongly increased after switching off the pump light at room temperature. The diffracted signals of the polarization holographic gratings, written by two orthogonally linear and circular polarized beams respectively, exhibited similar inverse relaxation behavior as the photoinduced birefringence after switching off the writing lights. A discussion about the mechanism accounting for the abnormal relaxation process of photoinduced birefringence is presented.     

Experimental Study on Optical Limiting and Transient All-optical Switching Properties of a Cubanelike Transition-metal Cluster Compound (n-Bu4N)3[MoAg3BrI3S4]

１ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｒｅｃｅｎｔｙｅａｒｓ,ｔｈｅｐｏｔｅｎｔｉａｌｏｆｒｅｖｅｒｓｅｓａｔｕｒａｂｌｅａｂｓｏｒｐｔｉｏｎ（ＲＳＡ）ｍａｔｅｒｉａｌｓｉｎｏｐｔｉｃａｌｌｉｍｉｔｉｎｇａｎｄｏｐｔｉｃａｌｓｗｉｔｃｈｉｎｇｈａｖｅｇｒａｄ...     

掺铒光纤光栅的开关动力学特征研究

研究在连续光入射下掺饵光纤光栅的开关动力学特征，发展其开关过程有类似于相变的特征。数值结果表明，主动光纤光栅在连续光条件下更适合于脉冲串产生。     

低温辐射计紫外探测器光谱响应度测试技术研究北大核心CSCD

通过研制真空多光路切换组件,结合Y型真空比较通道、探测器真空舱,在保证超高真空环境的前提下,实现激光、紫外连续可调单色光以及真空紫外单色光3个光路的快速切换,从而以低温辐射计为基准,以紫外增强硅陷阱探测器为传递标准,实现波长115 nm~400 nm紫外探测器绝对光谱响应度的测量,实验验证绝对光谱响应度测量不确定度在115 nm~230 nm可达到0.8%~1.5%(k=2),在230 nm~400 nm可达到0.5%~1.0%(k=2)。     

光纤布拉格光栅温度灵敏性的实验研究

在-150～550℃的温度范围内测量了光纤布拉格光栅中心反射波长的温度灵敏性。光栅波长的温度响应是非线性的。通过对试验数据的三次多项式进行拟合分析,结果表明:波长为1500nm左右的光栅具有相同的温度敏感性;波长对温度变化的响应(ΔλB/ΔT)主要是由折射率的变化(dn/dT)引起的,dn/dT随着温度的降低而减小;得到了温度灵敏系数关于温度的二次表达式,并给出了在-150～550℃温度范围内波长变化的快速估算。     

Octave-spanning supercontinuum generation of vortices in an As2S3 ring photonic crystal fiber

We propose As(2)S(3) ring photonic crystal fiber (PCF) for supercontinuum generation of optical vortex modes. Due to the large material index contrast between As(2)S(3) and air holes in the designed ring PCF, there is a two-orders-of-magnitude improvement of the difference between the effective refractive indices of different vortex modes compared with regular ring fiber. The design freedom of PCFs enables a low dispersion (<60 ps/nm/km variation in total) over a 522 nm optical bandwidth. Moreover, the vortex mode has a large nonlinear coefficient of 11.7/W/m at 1550 nm with a small confinement loss of <0.03 dB/m up to 2000 nm. An octave-spanning supercontinuum spectrum of the vortex mode is generated from 1196 to 2418 nm at -20 dB by launching a 120 fs pulse with a 60 W peak power at 1710 nm into a 1 cm long As(2)S(3) ring PCF.     

采用WDM技术的光纤Bragg光栅传感网络

采用绝对测量原理的波长调制技术,光纤Bragg光栅可组成并行、串行和阵列WDM拓扑结构.分析表明,光纤Bragg光栅网络的工作原理类似于一个多宽带平面镜.利用光谱仪可测量上述光纤Bragg光栅网络的反射谱,其中,光源是宽带为～40nm的掺饵光纤放大器.当网络中的光纤Bragg光栅受扰动后,受扰光栅的反射谱发生相应的变化,即Bragg波长发生相应的偏移.结果表明,当事先确定了光纤光栅的波长调制范围,反射的峰值波长能反应光纤光栅传感网络的信息.值得注意的是～3nm的波长调制范围可满足～100℃和～2000με的参量测量.     

用于机械振动实时监测的光纤光栅有源传感装置

把一对中心反射波长分别为1562.11nm和1562.71nm的光纤光栅粘贴在均质、等厚、等腰三角形悬臂梁上下表面作为环形腔光纤激光器端镜，当机械振动激励自由端时，通过观测激光输出脉冲，地施加于自由端的机械振动的频率进行了实时监测；观察两光栅波长漂移量差值的变化，可在0～6.1mm的范围内判断所测振动的振幅。低于100Hz时，实验结果与实际值基本吻合。     

N2O+离子A2Σ+电子态的光解动力学研究

用一束波长为360.55nm的激光，通过N2O分子的（3+1）共振多光子电离（REMPI）过程制备纯净且布居完全处于X2Π(000)态的母体离子N2O+，然后用另一束波长在275—328nm范围内的可调谐激光将制备的N2O+离子激发至预解离电子态A2Σ+.实验发现，由于解离碎片NO+所具有的一定的反冲速度，其TOF质谱峰明显比N2O+母体宽.通过分析NO+碎片TOF质谱峰形状，得到了解离产物的总平均平动能〈ET〉；通过考察〈ET〉随光解能量的变化，发现光解能量在32000cm-1附近约250cm-1的变化 关键词： N2O+离子A2Σ+态 TOF质谱峰 预解离机理     

Sub-micrometer patterns of molecular photo-switches using laser induced molecular implantation techniques (LIMIT)

Using laser induced molecular implantation techniques (LIMIT) in thin polymer films highly space selective patterning of photochromic molecules has been created of 800 nm dimensions. In this way diffraction gratings have been fabricated which operate as photo-switching devices. These transient gratings are permanent molecular implants in a polymer films that can be UV-irradiation activated or thermally deactivated. No further grating writing is required for this transient switching effect once the permanent implantation has been made.