光纤光栅特性的研究

提出了一种计算光纤光栅的光学特征的方法,即将光纤光栅视为一系列均匀薄膜的膜系,利用每一层薄膜的传输矩阵相乘获得光栅的反射分布,相位响应及时延特性,并以之计算了典型的均匀光栅,线性啁啾光栅和去趾线性啁啾光栅的光学特性,结果表明,这种方法能够能较好地计算光纤栅的光学性质,对光纤光栅的开发有一定的指导意义。     

Mechanism of Bragg Diffraction-Assisted Light Extraction in GaN-based Light-Emitting Diodes Based on a Self-Consistent Model

By introducing the distribution of the light energy density in GaN-based light-emitting diode (LED), the LED model based on the incoherent regime and the light extraction efficiency are investigated. The energy density as a function of the angle of incidence is calculated to demonstrate the mechanism of the lightextraction. The deviation between the tendencies of the transmissivity of the output layer and the extraction efficiency is also demonstrated.     

动态应变场下相移光栅光谱特性及实验研究

光纤传感技术以其抗电磁干扰、高精度、易组网等优势在航空航天及地下工程领域的声发射传感中得到了广泛应用。针对光纤光栅声发射监测系统,目前研究侧重于均匀光纤光栅的动态应变场传感特性,基于相移光纤光栅(phase-shifted fiber Bragg grating, PS-FBG)这一新型光纤光栅器件,重点研究声发射激励产生的动态应变场下相移光纤光栅的光谱特性变化规律。首先利用传输矩阵理论,建立PS-FBG的动态应变传感模型,利用指数衰减的余弦函数模拟声发射激励产生的动态应变场。通过数值仿真,详细研究PS-FBG光谱对动态应变场幅度、采样时刻、衰减系数、声发射频率及波长的响应特性。结果表明,PS-FBG反射谱形状随声发射频率与采样时刻呈现周期性变化,具体表现为透射窗口所对波长产生周期性漂移,而带宽变化不明显;随着动态应变场幅值越大,PS-FBG反射谱的谐振峰向两侧逐渐增多,透射窗口所对波长漂移很小;一定范围内衰减系数对PS-FBG光谱影响较大;而当声发射波长为0.1～2 L时,对PS-FBG光谱产生较大影响,此时光谱畸变较严重,在此范围外,光谱形状不发生明显变化。最后,搭建连续信号激励下的动态应变场实验平台,分析不同幅度a与频率f变化下PS-FBG的光谱特性,实验结果与仿真结果较好吻合。表明PS-FBG光谱对不同声发射激励产生的动态应变场响应不同,呈现一定规律性,该研究为基于相移光纤光栅传感技术的声发射传感提供理论指导。     

动态应力场作用下线性啁啾光栅光谱特性研究

目前柔性结构损伤检测需多个传感器,且需要探测器具有极高的采集频率。光纤光栅具有动态响应快、易实现分布式测量等特点,为解决上述问题提供了有效的途径,提出采用线性啁啾光栅(LCFBG)实现动态应力场探测。首先,用传输矩阵理论建立了LCFBG反射光谱应变传感模型,用衰减正弦函数模拟沿LCFBG分布的动态应力场。通过仿真实验,详细研究了LCFBG反射光谱对不同振幅、不同衰减系数与不同传播速度动态应力场的响应特性。实验结果表明,LCFBG反射光谱的反射率、波长变化与光谱形状均与动态应力场上述参数有关,但是LCFBG反射光谱对动态应力场不同参数的响应规律不同。在一定范围内,LCFBG反射光谱的最大反射率随动态应力场幅值与速度的增大而增大,最终趋于一稳定值,但其随阻尼系数增大而减小。最后,研制了以LCFBG为敏感元件的传感器,并构建了动态应力场实验平台,实验结果与仿真实验数据基本一致。提供了一种通过实时采集LCFBG全光谱信息探测动态应力场的新方法。     

基于准分布式FBG传感器的均质材料内部应变测试的试验研究

采用环氧树脂材料作为试验载体,使用没有任何保护性封装的、运用波分复用技术在同一光纤上刻入三个布拉格光栅的基础FBG传感器,来监测液体树脂流动及固化成型的全过程,并使用固化成型的环氧树脂板进行三点弯曲试验。将所得数据与有限元模拟数值解进行比较,来验证在去除封装、将传感器自身应变影响降到最低的情况下,FBG传感网络是否依然能够有效地反映出试验对象在各种情况下的内部应变。本文给出了FBG光纤光栅在逐级静力荷载加载下材料内部三点弯曲的应变图,并通过数值计算分析了未封装光纤在复合材料内部受力过程中的力学性能。     

A distributed feedback dye laser based on higher order Bragg scattering

A distributed feedback dye laser based on second order Bragg scattering due to a sinusoidal susceptibility modulation is reported. Rhodamine 6G dye solution in three different solvents; methanol, ethanol and benzyl alcohol is pumped by interference fringes produced by two beams from the second harmonic of Nd:YAG laser. Output power is plotted as a function of the pump power. The spectrum of dye laser shows a new type of modulation.     

Spot-scanning beam delivery with laterally-and longitudinally-mixed spot size pencil beams in heavy ion radiotherapy

The three-dimensional(3D) spot-scanning method is one of the most commonly used irradiation methods in charged particle beam radiotherapy.Generally,spot-scanning beam delivery utilizes the same size pencil beam to irradiate the tumor targets.Here we propose a spot-scanning beam delivery method with laterally-and longitudinallymixed size pencil beams for heavy ion radiotherapy.This uses pencil beams with a bigger spot size in the lateral direction and wider mini spread-out Bragg peak(mini-SOBP) to irradiate the inner part of a target volume,and pencil beams with a smaller spot size in the lateral direction and narrower mini-SOBP to irradiate the peripheral part of the target volume.Instead of being controlled by the accelerator,the lateral size of the pencil beam was adjusted by inserting Ta scatterers in the beam delivery line.The longitudinal size of the pencil beam(i.e.the width of the mini-SOBP) was adjusted by tilting mini ridge filters along the beam direction.The new spot-scanning beam delivery using carbon ions was investigated theoretically and compared with traditional spot-scanning beam delivery.Our results show that the new spot-scanning beam delivery has smaller lateral penumbra,steeper distal dose fall-off and the dose homogeneity(1-standard deviation/mean) in the target volume is better than 95%.     

飞秒激光刻写的超短光纤布拉格光栅及其传感特性

为了提高光纤光栅传感器的测量精度及可靠性,实现点式测量,拓宽光纤布拉格光栅(FBG)的应用,本文提出了基于飞秒激光直写扫线技术制备超短FBG。首先,在单模光纤上制备了周期为5.35μm、长度为53.5μm的超短FBG,其温度和应力的灵敏度分别为0.011 nm/℃和1.509 nm/N;然后,用体积分数为4%的氢氟酸对制备超短FBG进行选择性腐蚀,制备出了微通道超短FBG,并研究了它对NaCl溶液的传感特性,其折射率灵敏度为69.11 nm/RIU。结果表明,这种微通道超短FBG具有高重复性、高可靠性、可多参数测量等优点。     

Polarization properties of light reflected from dielectric superlattices

The polarization of the light reflected from a superlattice has been studied theoretically as o function of the angle of incidence and wavelength. The spectral and angular distributions of the ellipticity and azimuth of the polarization of the diffracted light in the vicinity of Bragg resonances have been found. It is shown that near the Brewster angle and on the boundaries of the stophands of the superlattice the effect of an anomalous increase in the ellipticity of the reflected light is manifested. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 199–202, March–April, 2000.     

基于光纤光栅和光纤环形镜的波长选择开关

提出并实验研究了采用压电陶瓷调制的光纤环形镜与光纤光栅结合的新型波长选择性光纤开关,获得了开关动态范围大于16dB、波长选择端口插入损耗小于0.5dB的实验结果.研究表明光纤环形镜干涉臂长的平衡是器件的关键.