【作者】 瞿鹏飞；

【导师】 陈维友；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 微波光子移相器(MWPPS)是一种在光域中对微波信号进行相位处理的光子器件。它随着微波光子学以及光载射频通讯(RoF)的兴起而日益在军事和卫星通信领域受到人们的重视。该器件是光控相控阵系统中的关键器件,主要用于对相控阵系统中的各天线阵元提供合适的相位反馈,产生光波束形成网络,完成系统的探测扫描任务。由于MWPPS在本质上属于微波和光子学的交叉领域。因而它可以借助微波和光子领域的双重优势,用更丰富、更灵活的手段对电学移相器无法处理的高频微波信号进行相位调谐。本文首先详细阐明了MWPPS在相控阵系统中的概念、功能、优缺点及设计原则,并对MWPPS的发展现状进行了深入了解。正文主要分为理论研究和实验研究两个方面。理论上对两类工作在毫米波段的集成MWPPS进行了设计；实验中则结合实际条件,对工作频率为10GHz的分立型、集成化的两类矢量和MWPPS进行了详细研究。在理论工作中作者结合边带调制技术,首次成功设计了一种基于SOI脊形波导的在线式集成MWPPS。该器件在单一波导内集成了F-P腔窄带滤波器、布拉格反射器以及热光型光学相位调制区,通过F-P腔窄带滤波器对双边带光载微波信号滤波、布拉格反射镜对透射边带的反射和PMR对透射边带的相位调节,通过外部调谐,在折射率变化为0～10×10-3的范围内,可实现对输入的任何双边带光载微波信号超过360°的连续相位调节,调节精度约6.92°/℃。该器件在同类中的优势在于其具有超大的工作带宽,适用于从38GHz到1.9THz的所有可用的高频波段。且器件具有相位调谐量不随工作频率变化、输出功率恒定的特性。另外,作者首次提出了基于集成光波导模式的正交矢量和技术,解决了传统矢量和MWPPS无法集成化的难题。文中详细的论证了该技术在克服合成信号的功率不稳定性和集成化两方面的可行性。器件以SOI亚微米矩形波导为基础,设计了基于对称定向耦合器(SDC)的光功率分配器、光开关单元：以非对称定向耦合器(ADC)为基础成功设计了0th to 1st MOCM和0th to 2nd MOCM两种模式转换复用器。利用SOI亚微米波导较大的模间色散特性,在约4617μm的波导传输中可实现1st和2nd以及0th和2nd模式间6.25ps和18.75ps的相对延时。通过对光功率分配器的调节以及对光开关的切换操作,在调谐区折射率变化为0～15×10-3范围内,可实现40GHz微波信号精度为1.64°/℃、360°全范围相位调谐。在实验方面作者首先论证了基于宽带光源矢量和MWPPS的可行性,然后对工作频率为10GHz的分立矢量和MWPPS进行了研究。构建了四分支结构的矢量和MWPPS,通过对四分支的两两组合,并用衰减器调谐各分支的光功率,每种组合可获得90°的相位调谐,一共可实现360°的全范围调谐。器件输出功率的最大波动约3dB,扫频波动约3.6dB；为了简化四分支系统的复杂结构,作者采用光强度调制器在不同偏压下的反相特性,构建了两分支结构,实验结果表明,简化结构减小了对光功率衰减量的要求。在两种不同的偏置电压下,MWPPS只需较小的光功率变化即可实现共近360°的相位变化。但信号输出功率最大波动可达到20dB。作为对宽带光源的补充,作者还提出了一种基于多载波调制的矢量和MWPPS,作者对波长为1530nm和1560nm载波复用,双载波被调制器同时调制后通过52m长的光纤的色散引入约25ps的相对延时,通过调谐输出光功率,这一构造可实现10GHz光载微波信号90°的相位调谐,输出功率最大波动7dB。最后结合分立系统的研究成果,作者首次提出并制作了一种基于宽带光源的SOI脊型波导的非对称Mach-Zehnder结构集成VSM-MWPPS,结合调制器的反相特性可实现微波信号近360°的相位调谐。宽带光源的使用解决了片上VSM-MWPPS光载微波信号合成时微波信号功率和相位的不稳定性问题,而调制器反相特性的利用则简化了器件结构。研究中作者采用小截面SOI脊型波导对工作频率为10GHz的VSM-MWPPS各个功能模块,即分路器、合路器、衰减单元以及延时线进行了设计,并以此为依据在SOI硅片上进行了器件制作。在实验中,重点对器件制作的关键工艺ICP的主要参数进行了对比研究,得到了理想的刻蚀条件。最后对器件进行了基本性能测试。结果表明,器件直波导的传输损耗约7.6dB/cm,端面耦合损耗约为5.5dB/端面。波导的有效折射率约为3.42558,群折射率约3.5893,两波导延时线之间的相对延时差约48ps,在10 GHz工作频率下,相位差约172.8°。在2 GHz带宽内扫频,输出功率波动约2 dB。更多还原

【Abstract】 Microwave photonic phase shifter (MWPPS) is a photonic device which is used to tune the phase of a microwave signal in optical domain. It have drawn much attention in both military and satellite communications due to the advantage of compact size, light weight, high operating frequency and large simultaneous band. It plays an important role in optically controlled phased-array antenna (OCPAA) for optical beam forming network (OBFN). And it can overcome the electronic-bottleneck and tune the phase of high frequency signal in millimeter-wave band even in～THz domain by taking advantage of microwave and photonics.In this dissertation, OCPAA was firstly introduced and then the basic concept, functionality and design rule of the MWPPS were elaborated in detail. The main body of this dissertation can be divided into two parts. In the first part, two different kinds of millimeter-wave band MWPPS, i.e., sideband-modulation based MWPPS and orthogonal vector sum method (VSM) based MWPPS, were theoretically demonstrated. The second part is the experimental study of two VSM-MWPPSs, i.e., discrete MWPPS and integrated MWPPS.In chapter 2, a tunable wide band microwave photonic phase shifter based on sideband technology was designed in SOI waveguide for the first time. This MWPPS consists of a Fabry-Perot (F-P) filter, a phase modulation region (PMR), and distributed Bragg reflectors (DBRs). Firstly, the two sidebands-based microwave signals in optical domain were separated by the F-P filter Then the reflector was designed to～100% reflect the transmitted wave came from the F-P filter. Finally, the PMR was set in the middle to modulate the phase of the transmitted wave by thermo-optics effect. For this device, it was demonstrated that the linear microwave phase shift of 0～2πcould be achieved in an ultra-wide band (38 GHz～1.9 THz) by a refractive index (RI) variation of 0～10×10-3.The tuning resolution was about 6.92°/℃.The phase response is frequency-independent and its output power is constant.In chapter 3, for the first time to our knowledge, orthogonal VSM was proposed to transfer the traditional bulk VSM MWPPS to integrated one which is very important for large-scale OCPAA. This integrated VSM MWPPS consists of a 1×2 variable optical power splitter (VOPS), an optical switch (OS), two mode order convertor-multiplexers (MOCMs) and fixed time delay lines (FTDLs).The 1×2 VOPS and OS were successfully designed in SOI rectangular waveguides based on symmetrical directional coupler (SDC). And the 0th to 1st and 0th to 2nd MOCMs were designed based on asymmetrical directional coupler (ADC). Finally, the fixed time delay of 6.25 ps and 18.75 ps were achieved in a distance of 4617μm due to the large group velocity difference between different modes in SOI multimode waveguides. By operating the VOPS and OS, the microwave phase shift of 0～2πcould be achieved by a refractive index (RI) variation of 0～15×10-3 for 40 GHz signal. The corresponding tuning resolution was about 1.64°/℃.In chapter 4, the discrete MWPPSs for 10 GHz were experimentally studied. Firstly, the feasibility of broadband source based VSM-MWPPS was studied. Then, four-branch structure VSM-MWPPS was constructed and measured. By combining two adjacent branch while keeping the other branches in off-state, the phase shift of 0～π/2 can be achieved. The phase shift of 0～2πcan be realized by four combinations. The corresponding maximum power variation in each combination is about 3 dB. The maximum power variation in frequency-sweep is about 3.6 dB.The two-branch structure VSM-MWPPS was then constructed to simplify the four-branch structure. The fixed time delay between the two branches is 48ps. The measured phase shift of this device ranged from 0 to 175°. By combining the reversal characteristic of the Mach-Zehnder LiNbO3 intensity modulator, the phase shift of 180°to 355°was achieved. The total phase shift range is near 360°. The maximum power variation is less than 20 dBAt the end of this chapter, multicarrier-modulation based VSM-MWPPS was constructed which can be used in long haul OCPAA systems. Two carriers of the wavelengths of 1530 nm and 1560 nm were multiplexed and then modulated by a 10 GHz microwave signal. A 52 m-long SMF-28 fiber was used to introduce a time delay of 25 ps between the two carriers due to the dispersion in SMF-28 fiber. Finally, a measured phase shift of 0 to 90°was achieved by tuning the optical power of the carriers. The maximum power variation is about 7 dB.In chapter 5, for the first time to our knowledge, an integrated asymmetrical Mach-Zehnder structure VSM-MWPPS for 10 GHz based on broadband optical source was designed in small cross-section SOI rib waveguides and then studied experimentally.0 to near 360°phase shift can be achieved by using the reverseal characteristic of the intensity modulator. Four sub-components, i.e., Y-branch power splitter, waveguide true time delay lines, waveguide variable optical attenuators and Y-branch power combiner were integrated in SOI rib waveguides. In experiment, the masks of the device and the electrode were firstly fabricated. Then the Inductively coupled plasma (ICP) processing, which is a key technology for fabricating SOI rib waveguides, was studied in detail. The optimum conditions of ICP etching were obtained. And the device was also fabricated.Finally, some important parameters of the integrated VSM-MWPPS were measured: the propagation loss is about 7.6 dB/cm, the coupling loss is about 5.5 dB/cut, the pure bending loss is about 2 dB/90°, the effective refractive index is about 3.42558, the group index is about 3.5893, the group delay between the two delay lines is about 48 ps, the corresponding fixed phase difference between the two branches is about 172.8°for 10 GHz MW signal, and the maximum power variation at frequency-sweep state is about 2.2 dB.更多还原