【作者】 张阜文；

【导师】 邱昆； 陈福深；

【作者基本信息】 电子科技大学 ， 光学工程， 2004， 博士

【摘要】 传统的无线接收机,随着频段的不同,其接收前端(包括天线、谐振回路和有源电路等)都必须采用不同参数结构和频段的器件。要在零至数千兆的频带范围内实现超宽带无线接收,采用相同的结构和器件是不可能的。本文提出了一种采用光波导电光调制器和电场传感器串接的新型超宽带无线接收方式。其中,利用电场传感器接收空间中的电磁场信号,使得输出光强受控于电磁场信号的电场分量;在此之前,通过光波导电光调制器,实施单频微波光调制。因此,串连的结果导致输出光的双重调制,通过光电探测器后,可以得到完整的宽带载频调制信号。本论文主要工作可概括如下:(一)LiNbO3光波导电光调制器研究1. 采用改进的FD-BPM算法,优化设计了LiNbO3光波导结构,得到了一种低损耗和高消光比的Ti: LiNbO3电光调制器。2. 利用前人提出的微波腔模型,从特征阻抗、微波有效折射率、微波损耗系数和长度四个参数出发,研究了电光调制器电极的不同部分,包括输入/输出端口、锥形区、弯曲段和电光互作用区,对器件传输特性的影响。同时,研究了弯曲段的参数对器件传输性能和损耗系数的影响,以及电光互作用区对器件损耗系数、半波电压和微波有效折射率的影响。并且,就电极弯曲长度对器件传输性能影响做了实验验证,结果表明理论分析与实验结果基本吻合。还分析了电极横向尺寸对传输性能的影响,并对两种计算电光调制器传输特性的方法作了比较。3. 利用有限元法,详细分析和讨论了频域内,不同结构的LiNbO3电光调制器的某些结构参数对特征阻抗的影响。主要包括普通共面波导电极结构、脊型波导结构、不同电极形状的结构、沟道型结构和双驱动电极结构。(二)反转极化LiNbO3光波导及其应用1. 就Ti扩散LiNbO3波导折射率的变化从弹光效应和电光效应进行了详尽的分析。同时,从自发极化的角度出发,对Ti扩散波导反转极化区域折射率的变化,进行了验证和探讨。然后,对无电极M-Z型电场传感器LiNbO3波导折射率的变化从理论和实验两方面作了深入研究。2. 利用波导反转极化原理,从微波有效折射率和微波损耗两方面,对周期反转极化光波导电光调制器的幅频特性和相频特性作了分析和讨论。同时,提出了一种新型的超宽带非周期反转极化LiNbO3波导电光调制器和一种低频率啁啾<WP=9>的宽带电光调制器,并就其性能作了详细分析和讨论。(三)LiNbO3光波导电场传感器研究1. 对分段电极光波导电场传感器作了深入系统的研究。主要包括:波导内电场分布、分段电极电压增益、器件灵敏度、频率响应、热稳定性、系统分析和器件的非线性等。并且,对器件非线性作了详细的计算和讨论,主要从直流偏置点偏移引起的非线性,谐波引起的非线性,交叉调制引起的非线性和干扰信号引起的基波信号功率降低方面作了研究,同时还对器件的线性动态范围作了分析。2. 利用分段电极和天线的组合结构以及反转极化波导原理,提出了一种新型的单片集成光波导电场传感器,它可同时检测电场的x、y和z分量。3. 采用分段的掩埋电极和渐变沟道电极及M-Z型LiNbO3光波导结构,提出了两种新型多量程电场传感器。(四)LiNbO3光波导电场传感器的实验室制作与测试对无电极M-Z型电场传感器和分段电极电场传感器的实验室制作过程做了详细的介绍、分析和总结。主要内容包括:器件掩膜板的设计,LiNbO3晶片的选取,晶片的清洗,蒸Ti,光刻,Ti扩散,质子交换与退火,研磨与抛光,器件的耦合,波导的测试,电极制作,SiO2缓冲层的制作,工艺的改进和器件失效机理分析等。器件的性能测试主要包括直流和交流测试。其中,交流测试包括半无限空间条件下的器件灵敏度和点频响应测试、TEM Cell里的低频响应测试以及微波暗室中的高频响应测试。得到了在5.6mA的光源偏置电流和900MHz的信号频率下,可检测到的最小电压约为0.22 mV。在微波暗室中,在4dB内的频率响应可以达到3.6GHz;并且当信噪比为5dB时,在0.02～3.6GHz的频率范围内,测得器件可接收到的电场强度为60 mV/m左右。同时,对测试结果进行了分析和讨论,并研究了由器件衬底LiNbO3晶体的压电效应引起的谐振效应。(五)新型超宽带集成光波导无线接收的研究建立了集成光波导无线接收的理论模型和等效电路模型,同时进行了系统仿真研究,从理论上证明了两种新型的光波导无线接收方式(即光波导电光调制器和电场传感器串接方式或激光直接调制器与电场传感器的串接方式)是可行的。然后,通过实验有力的验证,得到了与理论分析相一致的结果,从而使得利用集成光波导技术实现的无线接收方式成为现实。更多还原

【Abstract】 A conventional wireless receiver is composed of devices with different parameter structures to obtain various frequency bands. In this dissertation, a novel wireless receiving way with super-broad band by using a waveguide electrooptic modulator and an electric field sensor is investigated theoretically and experimentally. The optical intensity is controlled by an electric field component of the electromagnetic wave received by the E-field sensor after the guided optical wave is modulated by one-frequency microwave signal. Therefore, the connection of the optical modulator and the E-field sensor has brought about wireless receiving of microwave subcarrier with super-broad band. The principal work done in the dissertation is described in the following sections:Ⅰ. Research on LiNbO3 waveguide modulator A LiNbO3 waveguide is optimized with the modified FD-BPM. As a result, a Ti: LiNbO3 modulator with low loss and high extinction ratio has been achieved. Then, with the microwave-cavity model proposed by some scholars, the effects of modulator electrodes composed of different sections (including: input/output, tapers, bends, and active section) on the device transmission performance have been studied in the four aspects, including characteristic impedance, microwave effective index, microwave loss coefficient and electrode length. Also, the electrode bend effects on the device transmission performance and microwave loss coefficient are analyzed, and the influences of the active section on the microwave loss coefficient, half-wave voltage and microwave effective index have both been studied. To test the effect of different bend length on the electric transmission performance, the experiment has been done. As a result, the theoretical analysis is almost agreed with the experiment result. In addition, the influence of electrode transverse size on the transmission performance has been discussed and the comparison of two different methods for calculating device transmission performance is analyzed.Finally, the frequency properties of characteristic impedance of the modulator electrodes are analyzed with Finite Element Method for different structures, such as CPW electrode structure, ridge waveguide structure, structure with different electrode shapes, electrodes on LiNbO3 substrate with channel, and dual-driving electrode structure. Meanwhile, the effect of each structure parameter on the device performance has been discussed. <WP=11>Ⅱ. Reverse-poled LiNbO3 and its applicationThe refractive-index change produced by Ti-diffusion is analyzed using the methods of photoelastic and electro-optical tensor matrixes. It is shown that the two factors contributing to the refractive-index change are in the same level. Also, the refractive-index change in reverse-poled LiNbO3 is validated and discussed based on spontaneous polarization, and the result shows that it satisfies the conditions of Δne >0 and Δno >0. Meanwhile, the refractive-index change in reverse-poled LiNbO3 after proton exchange has been analyzed and concluded. In addition, the refractive-index changes for an E-field sensor in LiNbO3 without electrodes are studied in the two aspects of experiment and theoretical calculation.Then, a periodic phase reversal LiNbO3 modulator with reverse-poled waveguide has been obtained. In order to obtain large broadband, a novel traveling-wave modulator with nonperiodic domain inversions and ridge structure is proposed. The composite structure is designed to achieve velocity matching between the optical wave and the microwave, to get a 50 Ω characteristic impedance and to reduce the loss of the microwave electrodes with finite element method. The calculation results show that the frequency response of the new device is flat up to 350 GHz with interaction length of 1 cm, characteristic impedance of 49Ω, and microwave refractive index of 2.5. In addition, a broadband LiNbO3 modulator with low frequency chirp has been obtained by using the reverse-poled waveguide and ridge structure. The device performance is analyzed and更多还原