Analysis on diffraction properties of the transmission phase grating

Diffraction properties of the transmission phase grating are analyzed in terms of the Fourier optics theory. The analysis results show that the diffraction intensity distribution of the transmission phase grating is closely related to the optical thickness of the grating and the wavelength of the incident light, and not only determined by the grating's period and slit width. For monochromatic incident light, more than 80% of the diffraction energy will concentrate to the first diffraction order under certain conditions. For white incident light, the energy of the first order of diffraction spectrum may be much higher than other orders. Based on these results, some possible applications of the transmission phase grating are discussed.     

一种用于变压器局部放电在线监测的光纤声发射传感器实验研究

提出了一种光纤声发射传感器并构建传感系统实现变压器局部放电在线监测,利用传感光栅体积小,重量轻,灵敏度高和抗电磁干扰的特点,将传感器置于变压器内部实现局部放电声发射信号的测量。研究了传感光栅实现声发射应力波测量的机理,声发射信号引起传感光栅反射光谱发生漂移,导致特定频点处反射光强发生变化,通过反射光强的变化实现声发射信号的测量。构建声发射传感系统实验模型并提出了一种系统性能优化策略,使系统工作在传感光栅反射光谱上升或下降沿的半峰值频点处,从而保障传感系统具有良好的线性输出特性;研究传感系统工作点稳定技术,设计信号反馈回路自动跟踪反射光谱的漂移,保证系统稳定工作在传感光栅半峰值频点处,消除温度变化对传感系统测量精度的影响。将封装好的传感器用于变压器局部放电现场检测,结果表明,光纤光栅声发射传感器与压电传感器相比具有灵敏度高、动态范围宽等优点,可以实现变压器局部放电在线监测。     

光聚合物中全息光栅的温度依赖性研究

在Polyacrylic Acid(PPA)光聚合物中用双光束相干的方法成功地写入了全息光栅,用He-Ne 激光器作为探测光对光栅的写入过程进行了实时监测.分两种情况重点研究了温度对光栅成栅过程的影响,一是在不同的温度下写入光栅;二是在室温下写入光栅,待光栅强度达到最高时再改变温度来研究温度对光栅的影响.实验中温度的变化范围为25 ℃~100℃.     

双面曝光长周期光纤光栅偏振相关损耗

研究了采用高频CO2激光脉冲通过单面和双面曝光制作出的长周期光纤光栅(LPFG)的偏振相关损耗特性。单面曝光制作的长周期光纤光栅由于光纤横截面折射率改变不均匀,对入射光偏振态有较强的依赖性,主要表现为偏振相关损耗较大;为了降低偏振相关损耗,在制作长周期光纤光栅的过程中采用双面曝光的方法,以使其横截面折射率调制受高频CO2激光曝光改变均匀。实验数据显示,高频CO2激光脉冲制作的普通单面曝光长周期光纤光栅最大偏振相关损耗高达1.24 dB,而采用双面曝光的相同谐振峰值长周期光纤光栅的偏振相关损耗则可降至0.42 dB。因此,双面曝光制作的长周期光纤光栅能较好地克服入射光偏振态的不良影响,从而满足对偏振敏感的光纤通信和传感系统的应用要求。     

取样光纤光栅的多层薄膜分析新方法

将取样光纤光栅看成一个多层薄膜体系,每层膜用界面传输矩阵和膜层传输矩阵表示,将每层的传输矩阵相乘后得到取样光纤光栅的反射谱。数值计算结果表明:取样光纤光栅的总长度、折射率调制深度、占空比、取样周期和啁啾系数等参数都会影响反射谱的峰值和带宽。该模型的精度满足设计要求。     

Numerical Study on Efficient Optical Switching Based on the Nonlinear Phenomenon in a Guided-Mode Resonant Grating with Kerr Medium

Optical switching in a guided-mode resonant grating (GMRG) with a Kerr medium was numerically simulated by the nonlinear finite differential time domain (FDTD) method. The asymmetric resonant grating was adopted to have two resonant reflection peaks for the pump light and the probe light. When the pump light had a wavelength which was slightly longer than the resonant wavelength, the light was suddenly enhanced at a certain intensity because of the nonlinear resonance phenomenon. This resonance is effective in reducing the pump intensity for optical switching. When we assumed the resonant grating of polydiacetylene toluene sulphonate (PTS) with a linear refractive index of 1.88, a third-order susceptibility of 8.5 × 10⊃−0 esu and Q factors of resonant reflection which were ∼800, the pump light of 15 kW/mm⊃ changed transmittance of the probe light from 0 to 80%. 2005 The Optical Society of Japan     

Wavelength stabilized 980 nm uncooled pump laser modules for erbium-doped fiber amplifiers

We review the development of wavelength stabilized 980 nm pump laser modules without active temperature stabilization for applications in erbium-doped fiber amplifiers. Operation over a wide temperature range with an output power exceeding 400 mW at an ambient temperature of 70°C is demonstrated. The overall reliability of uncooled modules is estimated to be well below 500 FIT at all operating conditions. Such devices are made possible by continuous development and steady improvement of the pump laser chip, the optimization of the fiber Bragg grating stabilization scheme, careful design of the module package, and extended reliability analysis on the basis of stress tests as well as field data.     

平面光栅双单色仪的光学系统设计

平面光栅双单色仪是构成光栅衍射效率测试仪的重要组成部分,为了完成光栅衍射效率测试仪的研制,需要对平面光栅双单色仪的光学系统进行设计和模拟。仪器主要由光源、前置单色仪、测量单色仪和探测器组成;结合仪器的实际使用需要,确定了光源、探测器和光路结构,根据仪器的设计要求,分别对前置单色仪和测量单色仪的光学系统进行设计和模拟,给出了各自光学系统的像面点列图和实际光线追迹数据。设计结果保证了仪器光学系统的测量准确性。     

Vibrational relaxation dynamics in transient grating spectroscopy studied by rate equations based on time-dependent correlation function

A modified model, a set of rate equations based on time-dependent correlation function, is used to study vibrational relaxation dynamics in transient grating spectroscopy. The dephasing, the population dynamics, and the vibrational coherence concerning two vibrational states are observed respectively in organic dye IR780 perchlorate molecules doped polyvinyl alcohol matrix. The result shows that in addition to the information concerning system-environment interac- tion and vibrational coherence, the vibrational energy transfer can be described by this modified model.     

变迹-啁啾光栅在瞬态温度测试中的研究与应用

为了快速准确地获取火炮发射时炮管的瞬态温度场信息,设计了基于变迹-啁啾光纤光栅传感器的瞬态测温系统。系统采用啁啾光纤光栅实现对回波光的带宽调制,从而使回波光带宽大幅提高,大大增加了系统带光栅传感器数量及回波光能量。在分析了五种常见变迹函数切趾性能的基础上,系统采用超高斯函数形式完成对回波信号的切趾处理,有效地抑制了由于啁啾调制所造成的旁瓣增大以及光谱抖动,使系统符合瞬态温度测试的设计要求。实验采用调制范围1 532.0～1 548.0 nm的变迹-啁啾光栅传感器,并在炮管上均匀缠绕,共50个测试点位。针对某型火炮发射时炮管的瞬态温度进行测试,实验数据与WRP-130S型高速温度探测器的测试结果比较。实验结果显示,该系统与WRP-130S型探测器测温结果相近,平均误差小于2%,在温降平稳区优于1%。测试结果中,温度-波长数据满足1 ℃约引起0.041 3 nm(均值)的波长偏移。该系统在一次采集过程中可获得50个独立位置的瞬态温度,大大提高了炮管温度场重建的效率。