【作者】 陈丹；

【导师】 尚韬；

【作者基本信息】 西安电子科技大学 ， 光通信， 2020， 博士

【摘要】 微波光子学技术可用于实现微波信号产生、传输、处理、控制、变频等功能,是下一代无线通信、雷达探测、卫星通信、深空探测、卫星有效载荷以及电子战等领域不可或缺的重要模块;其可广泛用于高频微波信号产生、光纤色散补偿、镜像抑制、多普勒频移(Doppler Frequency Shift,DFS)测量等技术。而随着电子系统业务量的增加,信息传输速率的要求也越来越高,且现在系统越来越向高性能、一体化、多频段信号处理等方向发展。而传统微波链路面临常规低频段频谱资源受限、工作带宽低、传输损耗大、信号隔离度差、抗电磁干扰能力弱等电子瓶颈,使其难以满足未来通信系统的发展。微波光子学链路是将微波信号调制到光信号上,然后,在光域内实现微波信号处理,具有带宽大、频段可调、损耗小、抗电磁干扰能力强等优点,对未来电子领域发展提供较好的研究方向。本文面向未来电子领域的发展,针对目前链路中遇到的技术难点,研究高增益、高线性、高性能的关键技术,具体研究内容如下:(1)针对微波光子链路中高频微波信号产生问题以及天线拉远系统中光纤色散造成信号功率周期性衰减问题,提出了基于Sagnac环和光移相器(Optical Phase Shifter,OPS)的上变频方案,该方案将微波光子混频技术与光纤传输链路相结合,实现了高频微波信号的长距离传输,完成了色散诱导的周期性功率衰减的补偿。在该方法中,通过模拟不同相移、不同光纤长度下的频率响应曲线,可说明本方案的色散补偿性能。仿真结果表明,通过调节OPS的相移角度,可实现上变频微波信号的功率补偿,当相移角度设置为90°时,陷波点处信号功率获得完全补偿,补偿范围约为40dB。同时,频谱分析仪捕获了色散补偿前后的信号频谱图,由此可验证该方案的上变频功能。其中,输入的本振(Local Oscillator,LO)信号频率约为输出射频(Radio Frequency,RF)信号频率的一半,由此说明本方案可减小LO信号的带宽需求,也可降低相位调制器(Phase Modulator,PM)的带宽要求。此外,描绘了60km光纤传输系统的无杂散动态范围(Spurious Free Dynamic Range,SFDR),可知色散补偿后,该系统的SFDR提高了13.54dB左右。随后,对链路稳定性进行分析说明,结果表明,当相位抖动在-30°～30°变化时,输出信号幅度波动仅为1.26dB;当功率分配比在0.3～0.7范围内变化时,输出信号功率波动仅为0.77dB,由此说明了一定程度的相位抖动或轻微的功率分配不平衡,对链路性能影响不大,验证了系统的稳定性。(2)针对微波光子变频链路中的镜像干扰问题,提出了基于Sagnac环的镜像抑制混频方案,并对所提方案进行理论分析和仿真验证。通过观测平衡探测器(Balanced Photodetector,BPD)输出电信号的时域波形,可明显说明该方案的相移功能。另外,通过在电低频90°混合耦合器(Electrical Low-Frequency 90°Hybrid Coupler,90°HC)后连接频谱分析仪和示波器,可获得输出中频(Intermediate Frequency,IF)信号的频谱和时域波形,观察该图可很好的说明所提方案的镜像抑制能力,结果表明镜像IF信号比渴求IF信号功率低57dB左右,即镜像抑制比可达57dB。随后,将所提方案与传统基于并行PM的镜像抑制混频方案相比较,结果表明所提方案获得的渴求IF信号功率比对比链路提高6dB,即所提方案具有较高的转化效率。此外,通过比较不同RF频率或不同IF频率下的镜像抑制比可知,当RF信号在10GHz～40GHz变化时,所得IF信号镜像抑制比均大于45dB;而当输出IF信号频率在0.6GHz～1.2GHz范围内变化时,IF信号镜像抑制比均大于50dB,由此可证明所提方案的宽带处理能力。(3)针对雷达等系统中的多普勒频移测量问题,提出了基于并行相位调制器的DFS信号辨别方法。此方案可通过观察两个光电探测器(Photodetector,PD)输出的DFS信号相位差,来判断DFS的方向;也可通过观察90°混合耦合器的输出频谱图来判断DFS的方向。最终,可同时获得DFS信号的大小和方向。(4)为了进一步优化方案性能,提出了基于Sagnac环和双向相位调制器的DFS测量方案。该方案可实现DFS信号大小和方向的同时辨别;此外,还具有如下优点:(1)Sagnac环的使用,减小了并行链路相位不平衡的影响。(2)上下调制边带的同时利用,提高了频谱利用率。(3)BPD的使用增加了基频信号输出功率,同时可实现直流项、二阶交调失真(Second-order Intermodulation Distortion,IMD2)项和共模噪声的抑制,提高测量精度;其中,仿真测得IMD2信号功率抑制了63.98dB,直流偏移从7.99mV抑制到-0.09mV。同时,仿真模拟了传输信号为16GHz时,±1MHz的DFS信号大小和方向的辨别。更多还原

【Abstract】 Microwave photonics technology,which can realize microwave signal generation,transmission,processing,control,frequency conversion and other functions,is regarded as an indispensable and essential module in the fields of next generation wireless communications,radar detection,satellite communications,deep space exploration,satellite payload,electronic warfare and so on.In addition,it can be widely used in high frequency microwave signal generation,optical fiber dispersion compensation,image rejection,Doppler frequency shift(DFS)measurement,and other technologies.With the increase of business volume of electronic systems,much higher information transmission rate is required,and it is inevitable for modern electronic systems to realize the technique development toward higher performance,integration and multi-band signal processing.However,the traditional microwave links are faced with serious electronic bottlenecks,such as the limited spectrum resources in low frequency band,low bandwidth,high transmission loss,poor signal isolation and weak electromagnetic interference ability,which makes it difficult to meet the development of future communication systems.To this end,the microwave photonics link is proposed,where microwave signal is modulated onto optical wave,and then the microwave signal processing could be realized in the optical domain.Due to the advantages of the microwave photonics link,such as large bandwidth,tunable in broadband,small loss and strong electromagnetic interference ability,it could provide good application prospects for the development of electronic field in the future.In this dissertation,the key technologies of high gain,high linearity and high performance are studied in view of the technical difficulties in microwave photonics link.(1)In order to solve the problems of high frequency microwave signal generation in microwave photonics link and period power fading in antenna remote systems,an upconversion approach based on Sagnac loop and optical phase shifter(OPS)is proposed.In the approach,photonic microwave mixing technology and fiber transmission link are combined to realize long-distance transmission of high-frequency microwave signals,and achieve the period power fading compensation of the signal.The dispersion compensation performance of the scheme is verified by simulating the frequency response curves under different phase shifts and different fiber lengths.The simulation results show that by adjusting the phase shift angle of OPS,the power compensation of the up-converted microwave signal can be realized.When the phase shift angle is set to 90°,the signal power at the notch points can be fully compensated,and the compensation ranges are about 40 dB.The frequency spectra before and after dispersion compensation verify the up-conversion function of the scheme.Among them,the input local oscillator(LO)signal frequencies are about half of the output radio frequency(RF)signal frequencies,which reduces the bandwidth requirement of LO signal and phase modulator(PM).In addition,the spurious free dynamic range(SFDR)of the scheme can be increased by about 13.54 dB after dispersion compensation.Subsequently,the link stability is analyzed and explained.The results show that when the phase jitter changes from-30°to 30°,the output signal amplitude fluctuates only 1.26 dB;when the power distribution ratio changes from 0.3 to 0.7,the output The signal power fluctuation is only 0.77 dB,which shows that a certain degree of phase jitter or slight power distribution imbalance has little effect on the link performance,which verifies the stability of the system.(2)In order to solve the problem of image interference in microwave photonic frequency conversion link,an image rejection approach based on a Sagnac loop is proposed.Meanwhile,the theoretical analysis and simulation verification of the approach are carried out.In the simulation,by observing the time-domain waveforms of the output electrical signals from the balanced photodetectors(BPDs),the phase shift function of the approach can be clearly illustrated.Besides,by connecting the spectrum analyzer and oscilloscope after an electric low-frequency 90°hybrid coupler(90°HC),the spectrums and waveforms of the output intermediate frequency(IF)signal are obtained,and then the image rejection ability can be well explained by observing these figures.The results show that the power of the image IF signal is lower than that of the desired IF signal about 57 dB,that is,the image rejection ratio is 57 dB.Afterwards,compared with the image rejection mixing approach based on parallel PMs,conversion efficiency is improved by about 6 dB.And by obtaining the image rejection ratios at different RF frequencies or different IF frequencies,it can be seen that when the RF signal frequencies change at 10 GHz～40 GHz,the IF signal image rejection ratios are greater than 45 dB;when the output IF signal frequencies change in the range of 0.6 GHz～1.2 GHz,the image rejection ratios are greater than 50 dB.Therefore,the broadband processing ability of the proposed approach can be verified.(3)Aiming at the problem of DFS measurement in radar and other systems,a DFS signal discrimination approach based on parallel PMs is proposed.In this approach,the direction of DFS can be distinguished by comparing the phase difference between the DFS signals from two photodetectors(PD).Meanwhile,the direction of DFS can also be distinguished by observing the output spectrums of 90°HC.(4)In order to further improve the spectrum utilization,a DFS discrimination approach is proposed by using a Sagnac loop and a bidirectional PM.This approach not only can distinguish the value and direction of DFS signal simultaneously,but also has some other advantages.For example,the impact of phase imbalance in parallel link can be reduced effectively by using Sagnac loop,and the spectrum utilization could also be improved through the full utilization of upper and lower sidebands.Meanwhile,using BPD can increase the output power of fundamental frequency signal,and suppress the direct current terms,second-order intermodulation(IMD2)terms and common mode noise.Consequently,the measurement accuracy will be improved.The simulation results show that the power of IMD2 terms is suppressed by 63.98 dB,and the direct current offset is suppressed from 7.99 mV to-0.09 mV.Meanwhile,the discrimination of DFS signal value and direction at ±1 MHz is simulated and analyzed when the transmitted signal is set to 16 GHz.更多还原