外加电场极化法制备LiNbO3铁电畴反转光栅

在室温下,应用外加电场极化法对z切0．5mm厚的LiNbO3晶体实现了铁电畴反转,并成功地制备了LiNbO3铁电畴反转光栅。     

矩形波导到圆波导模式变换器的优化设计

在圆形槽波导微波毫米波器件中,常遇到矩形一圆形槽波导的模式变换问题,而矩形一圆波导模式变换是矩形一圆形槽波导模式变换的重要组成部分。本文应用有限元方法,首先由分析N端口波导结问题过渡到两端口的矩形一圆波导模式变换器,然后针对现有模式变换器的圆端口面的电场极化方向倾斜的问题利用加圆波导段的方法进行了优化,并设计了一个新的反射微小,结构紧凑和电场极化方向竖直的矩形一圆波导模式变换器．计算结果满足了设计要求。     

波导光电器件的微波有效折射率——器件微波折射率

以波导电光调制器芯片结构为例 ,利用点匹配法计算调制器芯片的电场分布 ,从而计算调制器电极的微波有效折射率 ,由此提出了器件折射率的概念。进一步证明了当光电信号互相匹配时调制带宽可达 10 0GHz。     

外电场周期极化LiNbO3的高压电源设计

分析了周期极化LiNbO3的极化反转过程和特性，进而提出了一种用于外加电场极化法制作周期极化LiNbO3的极化波形，并完成了相应的高压极化电源的设计与制作。电源可产生梯形波、序列脉冲方波以及由两者组合的多种波形，其最高输出电压为15kV，最大输出电流可达到300μA。用其在LiNbO3晶体上进行了多次极化反转实验，取得了很好的效果。     

Ti扩散LiNbO3光波导折射率变化研究

就Ti扩散波导折射率的变化，从弹光效应和电光效应进行了详尽的讨论和分析，结果表明两种效应对折射率变化的贡献在同一数量级；就反转极化Ti扩散波导折射率的变化，从自发极化的角度出发，进行了验证和探讨，结果仍满足Δne＞0和Δno＞0。     

集成光波导微应力传感器研究

在外力作用下,LiNbO3晶体内部产生微应力,引起波导的长度和折射率发生变化,从而使光波导中的光产生相位变化.基于此研究了一种Mach-Zehnder干涉仪型悬臂梁式光波导微应力传感器,分析了它的基本工作原理,并计算出施加外力与相位差之间的线性关系,确定了微应力传感器的灵敏度和量程,最后分析了它的弯曲损耗.     

Ti:LiNbO3光波导在中红外波段的有效折射率研究

应用变分法修正计算表面折射率增量的计算公式 ,并计算Z切Ti:LiNbO3光波导在中红外波长 3 .0、3 .3 9μm导模的有效折射率 ,给出了单模、截止、多模的制备参数。     

分段电极LiNbO3光波导宽带微波电场接收器

采用X切LiNbO3基片,设计并研制了分段电极Mach-Zehnder(M-Z)干涉仪光波导宽带微波电场接收器.其中,电极分段数为10段,器件尺寸为60×6×0.5 mm.研究结果表明,当接收光功率信噪比为5dB时,器件可检测到的最小电场强度小于60 mV/m,并且接收带宽达到10 MHz～3.6 GHz.     

电场辅助离子交换制备玻璃光波导

使用电场辅助离子交换和热离子交换技术在玻璃基片上制作了平板波导。实验结果表明,这两种方法制作的波导的有效折射率分布不同,电场辅助离子交换技术制作的波导有效折射率呈近似阶跃型分布,而热离子交换制作的波导有效折射率分布为渐变型。经数值计算发现,近似阶跃型折射率分布的波导对光场限制得更好,更适用于制作有源光器件和集成光器件。     

入射光偏振方向对LiNbO3晶体近光轴电光调制的影响

分析了在垂直LiNbO3 晶体光轴方向加电压,光沿近光轴方向传播时,入射光偏振方向对电光调制器的影响.通过计算加电场后双折射光程差的变化和偏光振动方向的转动,画出在正交偏振镜下不同起偏方向的锥光干涉图,得到干涉图随起偏方向变化的规律:由偏光振动方向转动引起的消光区域随起偏方向的转动而转动,在起偏和检偏方向上始终消光,在与起偏方向成±45°角方向始终全透光,并且消光线的交点即感应双光轴头不随起偏方向的转动而变化,始终在折射率变大的感应主轴上.     

A novel approach to generate a chirp microwave waveform using temporal pulse shaping technique applicable in remote sensing application

Microwave photonics is a prominent field in which photonic technologies are used to empower and extend the functionalities of microwave system which is a very tough exercise to fulfil directly in microwave domain. A photonic technique to generate a high chirp rate arbitrary microwave waveform using dual-drive LiNbO₃ has been put forward and demonstrated experimentally in this paper. Nowadays in order to increase the Range-Doppler resolution of radar, the chirp microwave waveform is widely used. The Mach-Zehnder modulator (MZM) performs the intensity modulation techniques which can operate on the principle of electro-optic effect. In this paper, the authors used a very simple and straightforward method of producing chirped arbitrary millimetre waveform by change in phase at the two arms of dual-drive LiNbO3 MZM. The generated waveform has the 3 dB bandwidth of 12.6 GHz which exists in extremely high-frequency band applicable in high-frequency microwave radio relay, microwave remote sensing, radar range resolution and millimetre wave scanner. The proposed design is simpler, cost-effective and compact than the previously proposed model of chirped waveform generation using MZM and fibre Bragg grating.     

LiNbO3电光调制器行波电极微波等效折射率的测量

LiNbO3电光调制器的设计中,行波电极的微波等效折射率是一个重要的参数。该文通过自行设计的微波探针架及探针,采用差值的方法,在微波网络分析仪上对样品CPW电极的微波等效折射率进行了测量,分析了实测值与理论计算值的偏差,给出了修正因子,研究了微波等效折射率随频率变化的色散现象,并对这种测量方法进行了误差分析,提出了减小误差的方法。     

The Generation and Propagation of Acoustic Surface Waves at Microwave Frequencies

The generation and propagation of acoustic surface waves is reviewed with particular emphasis on the microwave-frequency range. Theoretical work on optimizing the generation efficiency and the bandwidth of interdigital transducers is compared with recent experimental results. The minimum Iinewidth of 0.9 /spl mu/m which can be produced by optical photolithographic techniques places an upper limit of about 1 GHz on the maximum frequency that can be generated at the fundamental mode. Overtone operation has been used to generate 3 GHz surface waves on LiNbO/sub 3/ but this method has the disadvantage of reduced efficiency plus the complication of volume-wave generation. A better solution for generation above 1 GHz is the fabrication of interdigital transducers by means of electron beam exposure of the photoresist. The surface-wave propagation loss gives a significant contribution to the total insertion loss of delay lines operating at microwave frequencies. Losses of 1.1 dB//spl mu/s and 3.8 dB//spl mu/s at 0.9 GHz and 2 GHz, respectively, have been measured for propagation along the Z-direction of Y-cut LiNbO/sub 3/ by means of a laser deflection method. Larger losses have been observed for quartz. The additional complexities for surface-wave propagation due to the anisotropic single-crystal substrates which are necessary at microwave frequencies are also described.     

非近轴光束下铌酸锂晶体的电光效应

为了研究电场一定时,光束在非近轴条件下铌酸锂晶体的电光效应,采用折射率椭球张量的循环坐标变换方法,理论上推导了光轴正交截面上折射率分布的解析式,讨论了折射率、相位延迟以及透射率与光束入射方向之间的关系,并且进行了实验验证,取得了透过率随光束与光轴夹角α的实验数据。结果表明,y方向加电场时,入射光小角度偏转将引起x方向感应折射率以及光束透射率的明显变化,而y方向的感应折射率不变;光束与光轴的夹角α对铌酸锂晶体电光性能的影响远远大于光矢在x-y平面与x轴正半轴的夹角β对其的影响;x方向加电场时感应折射率同y方向加电场时类似,但此时相位延迟更小,在0°~0.4399°夹角范围内,前者的透过率变化较后者慢,并且在0.45°之后呈现出交替变化的规律,当夹角为0.5°,0.680°等位置时,它们具有相同的透过率。这一结果对利用角度调节以改善铌酸锂晶体的电光性能具有一定的指导意义。     

10 GHz超低抖动光短脉冲源

报道了一种新型的重复频率为10 GHz,脉宽为5.3 ps,抖动为184 fs的高稳定光短脉冲源.将大信号调制半导体激光器产生的10 GHz光脉冲,先送入LiNbO3电光相位调制器增强负啁啾,并使光谱进一步展宽,再通过色散补偿光纤(DCF)压缩脉冲啁啾,可得到光短脉冲.由于大信号调制激光器输出的光脉冲本身具有负啁啾,而通过相位调制器的光脉冲在不同的时间间隔内既有正啁啾也有负啁啾,通过适当调整进入相位调制器的光脉冲时延,使其通过相位调制器后累加产生更大的负啁啾,再利用正色散光纤压缩啁啾,从而得到低抖动且无基座的光短脉冲.     

Photonic Generation of Chirped Microwave Pulses Using Superimposed Chirped Fiber Bragg Gratings

A novel approach to generating linearly chirped microwave pulses in the optical domain based on spectral shaping and linear frequency-to-time mapping is proposed and experimentally demonstrated. In the proposed system, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is spectrum-shaped by an optical filter that consists of two superimposed chirped fiber Bragg gratings (SI-CFBGs) with different chirp rates. The SI-CFBGs form a Fabry-Perot cavity with a cavity length linearly dependent on the resonance wavelength, thus a spectral response with an increased or decreased free spectral range is generated. A chirped microwave pulse with the pulse shape identical to the shaped spectrum is obtained at the output of a high-speed photodetector thanks to the frequency-to-time mapping in a dispersive device. The proposed technique is experimentally demonstrated, a linearly chirped microwave pulse with a central frequency of 15 GHz and a chirp rate of 0.0217 GHz/ps is experimentally generated.     

Automatic chromatic dispersion compensation using alternating chirp signal for installation of high-speed transmission systems

Proposes a simple automatic chromatic dispersion compensation system that can detect the zero-dispersion point of an installed fiber span. This technique realizes high sensitivity without requiring the system to be extensively modified. The alternating chirp signal, which is used as the zero-dispersion-detection signal, has alternating optical frequency shift. It can be generated simply by changing the input signals of multiplexer circuits and shifting the bias voltage of the LiNbO/sub 3/ modulator. This technique is shown to detect the zero-dispersion point in the range of -600 to +600 ps/nm by using the signal modulated at 10 GHz; automatic dispersion compensation is successfully demonstrated in a 20-Gb/s, 400-km transmission experiment in our laboratory. Compensation is also demonstrated in 281-km-installed dispersion-shifted fiber using a 20-GHz alternating chirp signal.     

Chirp behaviour of high-speed GaInAsP/InP optical intensitymodulator

A low chirp characteristic was observed in a high-speed GaInAsP/InP BH optical intensity modulator with a bandwidth of 14 GHz. The maximum chirp was about 0.8 Å under large-signal pulse modulation. This value agrees well with the calculated result using the α_E parameter which was directly evaluated by a change in the complex refractive index     

双频带电磁超材料单元设计及仿真

该文基于谐振型左手理论,提出一种将2种不同的多开口谐振环左手结构单元分别印刷在介质板的正、反面,这种复合结构实现了双频带左手特性。在微波频率范围内采用等效参数（NRW）提取算法,验证了该多开口谐振环的复合结构能实现负的介电常数和磁导率,同时采用LC谐振电路进行分析并解释其产生的机理。数值和仿真结果表明,存在2个介电常数、磁导率和折射率的实部都为负的频带。其负频带频率范围分别为16.5~18.96 GHz和22.8~24 GHz,负双频带带宽为3.66 GHz。由于其带宽性能良好的双负特性,可用于多频带或宽带微波器件的设计。