电光晶体在MSLM中的应用

本文利用MSLM电光调制理论对几种实用电光晶体的综合电光性能进行了理论分析和比较。讨论了材料固有的铁电相变及自然双折射等特性与器件制作工艺的兼容性问题。结果指出LiNbO₃、LiTaO₃、BSO是目前可以利用的三种各具特点的电光晶体。     

红外光学透镜焦距测量

采用CO₂激光器作为光源,热释电摄像机作为探测器,采集了单缝衍射图像.根据单缝衍射原理,测量了不同焦距的一组红外光学锗透镜的单色焦距,给出了实测结果.讨论了影响测试的主要误差因素.通过计算采样数据的调制传递函数,精确确定被测透镜焦平面的位置.介绍了图像采集系统长度尺寸的精确标定方法.     

重水的冲击压缩性

 用二级轻气炮作为加载装置，测量了重水（D₂O）的冲击压缩线，压力范围为10~43 GPa。用轴对称式电磁感应探头测量冲击波速度，测量精度约1.2%~1.5%。用电探针测量飞片速度，其精度约0.5%。用对比法原理进行测量，标准样品材料为无氧铜。实验发现，重水的冲击波速度随粒子速度变化呈斜率不同的两段直线关系，两线连结处出现拐折。分析认为，这一现象可能由液体D₂O分子在冲击波作用下的离解过程引起。     

CdS0.1Se0.9纳米晶体共振电光效应

采用电吸收谱(EA)的方法研究了在电场作用下,CdS_0.1Se_0.9纳米晶体光学性质的变化.分析了电场效应的物理机制,电场效应是使纳米晶体的吸收谱展宽和移动.第一激发态对外加电场敏感,而其它激发态不敏感.从电吸收谱上得到电光响应信号幅度与外加电场场强的平方成正比,表明纳米晶体的电光效应是 Kerr效应,具有三阶非线性极化率 χ⁽³⁾.     

1.5 μm Ti:LiNbO3电光波导强度调制器

用钛内扩散技术和常规光刻手段,研制出1.5μmLiN_bO₃电光波导强度调制器。它由单模波导非对称Mach-Zehnder干涉仪和三电极共平面波导组成。干涉仪的两个臂长相差波导波长的四分之一,使器件在最佳线性点工作,无需外加电偏压。集总调制和行波调制的理论带宽分别为1GHz和7.8GHz。对于集总器件,测量了调制特性,半波电压为9.5V,调制带宽为0.7GHz。     

亚微米外部电光检测技术

将固浸透镜技术与电光检测技术相结合，建立了具有亚微米空间分辨率的外部电光检测系统，通过使用GaAs半球作外部电光探头，用数值孔径为0.3的显微物镜对波长为1.3μm的探测光束进行聚焦，得到了半峰全宽直径为0.7μm的聚焦光斑，成功测量了微带线上10kHz的正弦波信号，验证了系统的线性响应特性，并得到了6mV/√Hz的电压灵敏度。     

MSLM调制组件的电光性能

对设计并制作的[M_gF₂+(ZrO₂/SiO₂)]膜系·LiNbO₃·ITO/玻璃结构的MSLM用调制组件的综合电光性能进行了实验测定。结果表明,其反射半波电压V_πR为1.2kV±0.1kV,反射率达99%,峰值次级电子发射系数为5.8。用其制作的光导址MSLM具有良好的功能与性能。     

TiO2纳米薄膜微观结构及光学性能研究

用sol-gel法制备了纳米TiO₂薄膜,用原子力显微镜(AFM)观察了薄膜的表面形貌,测量了薄膜的表面粗糙度(RMS)为2.832 nm;用红外光谱(IR)研究了TiO₂薄膜前驱体溶胶的组成; 探讨了TiO₂薄膜的焙烧温度、层数等制备条件对TiO2光催化活性的影响,结果发现在490℃,8层膜的TiO₂活性最高.     

弹光调制测晶体电光系数的数字锁相实现

在弹光调制测晶体电光系数系统中,对弹光调制器工作控制和调制信号数据处理进行了优化设计,并实现一种灵敏度高、测量快速、成本低和系统集成度高的晶体电光系数测量方案.针对弹光调制及调制信号的特点,采用现场可编程门阵列完成弹光调制器的工作控制和测量数据的提取.现场可编程门阵列提供弹光调制器工作电压信号,控制模数转换器的采样频率,同时产生正弦和余弦参考序列来提取直流项、一倍频项的同向分量和正交分量,并输入计算机中求解得出晶体电光系数.对铌酸锂样品进行了测试,实验结果表明系统重复度和灵敏度为0.0016×10~(-12) m/V,测量速率为1ms/数据点.较其他晶体电光系数测量方法,本文方法具有更高的测量灵敏度和更快的测量速率,为实现弹光调制测量晶体电光系数的智能系统奠定了基础.     

光波导F-P干涉型电场和电压传感器

本文报道了 LiNbO₃质子交换光波导 F-P 干涉型电场和电压传感器的结构、制备、工作原理、实验装置与测量结果.用半导体激光器(780nm)作光源,测量了器件对频率在20Hz～1KHz 电场的响应特性,着重测量并得到工频(50Hz)交流电场(幅值为8.3～75V_zms/cm)和电压(20～180V_rms)与调制光输出电压之间的关系曲线.实验研究表明:该器件的线性度为1.4%,电场灵敏度为61.4mV_rms/V_rms/cm,电压灵敏度为25.6mV_rms/V_rms;且具有结构简单、制作容易、几何尺寸小、光传输插入损耗低等优点;稍加完善,可望制成实用化器件.     

钽酸锂、蓝宝石在高压下的光学性质从头算研究

采用量子力学从头算和赝势平面波基组以及非局域广义梯度近似(PP-GGA)方法对两种光学窗口材料(单晶LiTaO3和蓝宝石α-Al2O3)在0~250 GPa静水压力范围内的光学透明性进行了研究.结果表明,随着压力的增加蓝宝石和钽酸锂的最大吸收峰位置均向低波长区移动(蓝移).蓝宝石在0~250 GPa压力下,可见光范围内一直保持其透明性,而LiTaO3则在高压下时就变得不透明了,其原因是钽酸锂的前沿能带闭合而导致其吸收带宽随外界压力的增大变宽所致.     

亚皮秒级时间分辨率的光取样示波器实验样机

利用自行开发的高稳定、低抖动和重复频率可调的“σ”型被动锁模光纤激光器作为高性能光学取样源,与待测的80 Gb/s光脉冲信号同时输入到100 m高非线性光纤中,通过四波混频效应实现了对被测光信号的全光采样。然后利用自行开发的数字信号处理与计算机图形显示软件,精确地重现了被测试的基于RZ码型的80 Gb/s光脉冲信号波形图。同时,还利用该光学取样示波器实验样机系统对重复频率为10 GHz、脉宽为1.8 ps的商用半导体主动锁模激光器的输出波形进行测量,所显示的脉冲宽度值为2.0 ps。这表明开发出的实验样机系统的时间分辨率优于900 fs。     

Sampling of free-space magnetic pulses

We report free-space detection of magnetic pulses via the Faraday effect with shot-noise limited detection. This allows a 10^–8 T / Hz magnetic field resolution. The orthogonal propagation of the optical probe beam and the THz waves demonstrate a 1.3 ps risetime with a 400 GHz frequency bandwidth. The temporal and frequency responses of several crystals are reported with a theoretical response function analysis presented. The dispersion of the magnetic pulse into the sensor crystal is illustrated with a theoretical simulation for comparison. We also contrast the properties of electro-optic sampling with this magneto-optic sampling technique.     

Counterintuitive Gaussian pulse sequence in three-level ladder scheme

In a recent publication we have studied counterintuitive pulse sequence applied to a three level ladder scheme, utilizing rectangular-shaped pulses. In this research we investigate amplification without population inversion in a three level ladder system interacting with two electromagnetic fields, namely, the probe and coupling fields. We take both probe and drive fields in the form of Gaussian shaped pulses. In a counterintuitive sequence scheme, the short probe pulse is introduced prior to the application of the coupling field, in contrast to a regular sequence scheme, where both fields are introduced at the same time. The influence of varying the probe pulse width and time delay between the initiation times of the probe and coupling fields on transient probe gain is investigated. It is found that the system exhibits a kind of memory about previously applied weak probe pulse. This may allow for detection of the past event by applying a strong drive pulse in the future.     

双波长光纤测温仪的工作波长及线宽设计

介绍了一种利用钽酸锂热释电探测器实现的实用化双波长光纤测温仪。测温仪由光学接收系统、信号放大与处理系统及显示系统三部分组成。依照探测器系统的温度分辨率、R(T)～T曲线的线性度及温度灵敏度与各主要技术参数之间的关系,在考虑光路中的选择性吸收气体的影响及探测器的最小可探测功率的基础上,对其工作波长及波长带宽进行了优化设计。分析了仪器的工作波长及波长带宽对温度分辨率及测温灵敏度的影响。结果表明,在测温范围400～1300℃内,当λ1=2 1μm、λ2=2 3μm、Δλ3=20nm时,其测温精度高于0 20%。     

Femtosecond Kerr ellipsometry in polydiacetylene solutions: Two-photon effects

We describe a pump-probe femtosecond Kerr experiment in polydiacetylene solutions (4BCMU, yellow form). The Kerr ellipsometry technique permits a separate determination of the real and of the imaginary part of anisotropic index changes. The wavelength (620 nm) of the pump pulses lies in the transparency region of polydiacetylene while the probe pulses have a broad white spectrum. The largest contribution to the Kerr signal is a quasi-resonant stimulated anti-Stokes Raman absorption. A flat two-photon transition spectrum with 4×10^–3 cm/MW is observed close to 4 eV. The two-photon excited states have a life time close to 12 ps and they present a broad absorption band in the 2 eV range.     

Time-frequency characterization of high-order harmonic pulses

We present energy-resolved cross-correlation measurements of extreme ultraviolet (XUV) pulses generated as high harmonics of femtosecond pulses from a 1 kHz titanium-sapphire laser. The harmonic pulses are probed by a fraction of the fundamental laser pulse at 800 nm, in a noncollinear geometry, allowing us to vary independently the parameters of the harmonic pump and near-infrared probe pulses. We measure the so-called sidebands in the photoelectron spectrum of argon corresponding to the absorption of a harmonic photon plus or minus one probe photon. Spectrally resolving the cross-correlation signal allows us to characterize the time-dependent frequency of the XUV pulse.Received: 20 December 2002, Published online: 24 April 2003PACS: 42.65.Ky Harmonic generation, frequency conversion     

基于周期极化铌酸锂波导的软件同步光采样

随着大于40 Gb/s高速光通信系统的出现, 为了保证光信号传输质量, 需要对光信号进行监测。对于带宽超过传统光电探测器和示波器可测量带宽的高比特率数据光信号, 光采样技术是进行时域测量的重要手段。采用固定频差的方法可以用百兆速率的采样脉冲对高速光信号进行采样, 降低了对采样后电数据处理系统带宽的要求。在对基于周期极化铌酸锂(PPLN)波导中和频效应的采样过程进行建模仿真的基础上, 实现了对Optsim获得的光传输线内10 Gb/s的非归零码(NRZ)和归零码(RZ)信号的采样。采用软件同步算法对采样数据进行处理, 获得信号的眼图, 这一方法可使采样系统对硬件的要求降到最低。与理想与门获得的采样结果进行比较, 对PPLN波导的光采样特性和采样质量进行了分析。     

基于光参量放大的高速实时光取样技术

提出了一种基于光参量放大的高速实时光取样方案. 利用色散介质对光纤锁模激光器产生的窄脉冲源进行色散展宽,从而产生线性啁啾光信号. 将该信号和被取样信号同时送入高非线性光纤,利用高非线性光纤中的参量放大效应,将被取样信号的强度信息调制到线性啁啾光信号上. 在接收端利用不同中心波长的滤波器即可滤出不同时间点的取样信号,从而在光域同时完成了高速实时光取样和取样信号的串-并转换. 是实现高速实时取样技术的一种极具竞争力的实现方案. 实验中,实现了对10 Gb/s非归零码OOK信号的40 GS/s的高速实时取样系统,并转换为4路10 GS/s取样信号输出. 在接收端成功根据4路取样信号恢复出被取样信号波形,验证了该实时光取样方案的可行性. 关键词： 光信号处理 光取样 参量放大 高非线性光纤     

Tunable THz pulse generation by optical rectification of ultrashort laser pulses with tilted pulse fronts

Optical rectification of ultrashort near-IR laser pulses with tilted pulse fronts and pulse energies of a few J in Mg-doped stoichiometric LiNbO₃ cooled to low temperature is a powerful technique for efficient generation of THz pulses. The pulse energy critically depends on the Mg doping (necessary for preventing photorefractive damage) and can be easily increased by a factor of three if the MgO content is reduced. Pulse energies up to 400 pJ at repetition rates of 200 kHz and 3.4% quantum conversion efficiency are achieved at 77 K. At 10 K, changing the tilt angle of the pump pulse front results in continuous tuning of the frequency across the 1.0–4.4 THz range. The temporal pulse shapes measured by electro-optic sampling are in good agreement with the signal calculated by a simple theory. This model predicts tunability on a considerably broader range and narrower spectra even at room temperature if GaSe is used instead of LiNbO₃. The advantages of the velocity matching technique utilizing tilted pulse fronts are analyzed in comparison with quasi-phase-matching in periodically poled LiNbO₃ crystals. The first method provides a ten times higher pulse energy conversion efficiency. PACS 42.65.Ky; 42.70.Mp; 42.72.Ai