【作者】 李泽；

【导师】 章献民； 池灏；

【作者基本信息】 浙江大学 ， 物理电子学， 2012， 博士

【摘要】 微波光子学是一门新兴的交叉学科,其研究范围包括微波信号的光子学发生、微波光子信号处理、基于光子技术的微波频率测量、微波光子传输链路、工作于微波频率的光电子器件、以及光控微波器件等。与传统的微波系统相比,微波光子系统具有带宽大、损耗低、结构紧凑及抗电磁干扰等诸多优点,可以有效的解决“电子瓶颈”的限制。很多在传统微波系统中很难实现的功能都可以利用微波光子技术来实现。因此,微波光子学近年来受到了国际研究人员的广泛关注,被广泛地应用于军事、医疗、通信及航空航天等诸多领域。本文首先介绍了微波光子学的发展历史、主要应用方向及主要器件,然后针对微波光子信号处理中的三个关键问题进行了研究,分别为基于光子学的微波任意波形发生、基于光子学的微波频率测量及光单边带调制和可调谐微波分数阶希尔伯特变换器,论文主要的创新点和学术贡献如下：1、提出并实验论证了两种基于电光调制器和光纤布拉格光栅(FBG)的频率大范围可调谐相位编码微波/毫米波信号发生的方案。实验中分别成功获得了22-27 GHz和40-50 GHz的相位编码射频信号,并使用伪随机二进制序列作为编码信号验证了所得相位编码信号的抗噪声压缩性能,压缩比分别达到了67.5和128。两种方案的频率可调谐范围在理论上分别可以达到12.5-100 GHz和40-110 GHz,如此大的可调谐频率范围使用传统的电子学方法是难以实现的。2、用理论研究和数值仿真的方法详细研究了基于相位调制器的时域脉冲整形(TPS)系统中三阶色散和色散不匹配引起的脉冲失真。首先对基于相位调制器的TPS系统进行了详细的理论分析,然后用数值仿真的方法验证了理论分析的正确性,其中,匹配三阶色散的存在会使系统输出脉冲展宽,且越高阶脉冲展宽就越严重；二阶色散不匹配会对各个输出脉冲引起同样的展宽；三阶色散不匹配则会使输出脉冲产生振荡衰减拖尾。最后,提出了用调制信号预失真技术来补偿三阶色散引起的脉冲展宽的方法,并进行了仿真验证。3、提出并实验论证了三种基于微波频率到功率比映射方法的微波光子瞬时频率测量方案。其中,前两种方案基于微波频率到光功率比映射的方法,实验得到了10 GHz的测量带宽。方案一使用了定标-查表的方法,这种方法对FBG的形状无严格要求,可以消除方案二中由形状误差引起的测量误差,这使得方案一的测量误差在0.08 GHz以内。方案二构造了微波频率到光功率比的线性映射关系,这一方面使得测频系统在最大的测量范围内得到了一个恒定的分辨率,另一方面,与方案一相比,系统在功率比函数斜率较小的低频段的分辨率在理论上得到了提高,但由于方案二对FBG频谱形状的精确度要求较高,因此测量误差在0.2GHz左右。方案三使用了微波频率到微波功率比线性映射的方法,测频范围为0.5-40 GHz,其中一路利用了正弦传递函数的线性段,但由于线性段存在固有误差且功率较低,这使得噪声的影响相对较大,系统的测频误差在0.5 GHz左右。4、用理论分析和数值仿真的方法提出并论证了一种基于光频梳和波分复用器的可重构微波光子信道化接收机。仿真中用两个串联的强度调制器产生了11根均匀谱线,这些谱线被用作11个光载波,而多个信道则是通过使用自由频谱范围(FSR)与相邻光载波的频率间隔稍有不同的多通道光滤波器实现的。仿真中对系统测频精度的可调谐性进行了较详细的分析和论证,对系统的动态范围进行了分析,并证明了使用优化的滤波器可以提高系统的动态范围。5、提出并论证了一种利用基于FBG的光希尔伯特变换器和马赫曾德尔干涉仪结构来实现光单边带调制的新方案。实验中,在6-15GHz工作频率范围得到了约20 dB的边带抑制比,所得到的光单边带信号在标准单模光纤中传输了45.6km,并成功克服了色散引起的射频功率衰减效应。6、提出并实验论证了两种分别基于等间隔和不等间隔抽头微波光子延迟线滤波器的阶数连续可调分数阶希尔伯特变换器(FHT)。其中,基于等间隔抽头微波光子滤波器的FHT利用了偏振调制器互补的相位调制特性和检偏器偏振调制到强度调制转换的特性,成功得到了负抽头,并通过调节中心抽头的系数实现了FHT分数阶的连续调节,实验中通过恒定输出功率掺铒光纤放大器的使用而使得不同阶FHT的频率响应功率波动在3 dB以内。实验演示了0.3-1阶的连续可调谐FHT,且通带内的相位误差小于5°。而基于不等间隔抽头微波光子滤波器的FHT通过正抽头的额外延时而引入了等效的负抽头,系统简单且易调节。实验演示了0.24-1阶的连续可调谐FHT,通带内的相位误差同样小于5°。更多还原

【Abstract】 Microwave photonics is an emerging interdisciplinary subject, the research areas of which include photonic generation, processing and measurement of microwave signals; radio-over-fiber systems; opto-electronic devices processing signals at microwave rates and optical control of microwave devices. Compared with the conventional microwave systems, microwave photonic systems could not only effectively solve the "electronic bottleneck" restrictions, but also lead to some unique advantages, such as large bandwidth, low loss, light weight, and immunity to electromagnetic interference. Microwave photonic technologies could even achieve many functions that are difficult for conventional microwave systems. Therefore, microwave photonics are widely used in many fields, such as military and defense systems, medical treatments, communication systems, and aeronautics & astronautics in recent years.In this thesis, we first give a brief introduction to the historical development, the main application areas and the main devices of microwave photonics. Then, three topics in microwave photonic signal processing area are discussed, which are microwave arbitrary waveform generation, photonic measurement of microwave frequency, optical single-sideband modulation and microwave photonic fractional Hilbert transformers. The major innovations and contributions are as follows:1. Two novel photonic approaches to realizing phase-coded microwave/mm-wave signal generation with large frequency tunability are proposed and demonstrated based on electro-optic modulators and fiber Bragg gratings (FBG). The generation of frequency tunable phase-coded microwave/mm-wave signals with the tuning range of 22-27 GHz and 40-50 GHz are achieved. A pseudo-random binary sequence is used as a phase-coding signal to verify the robustness of the pulse compression technique to noise. A pulse compression ratio of 67.5 or 128 is achieved, respectively. A theoretical frequency tuning range of 12.5-100 GHz or 40-110 GHz is obtained. Such a large tunable frequency range is difficult to achieve using conventional electronic techniques. 2. A thorough analysis on pulse distortions due to the third-order dispersion (TOD) and dispersion mismatches in a phase-modulator-based temporal pulse shaping (TPS) system for the generation of a repetition-rate-multiplied pulse burst is performed. We demonstrate that the profile of a repetition-rate-multiplied pulse burst and the shape of the individual pulses in the pulse burst are distorted due to the TOD and the dispersion mismatches of the dispersive elements. The tolerance of the system to the TOD and the dispersion mismatches when employing an input optical pulse with different pulse width is studied. A technique to use predistortion of the RF modulation signal to tackle the pulse distortions is discussed.3. Three novel photonic approaches to realizing instantaneous microwave frequency measurement based on frequency-to-power mapping are proposed and demonstrated. The first two approaches are based on microwave frequency to optical power mapping, in which a measurement range of 1-10 GHz is realized. The first approach is based on the calibration-look-up-table method, which sets no strict requirements on the shape of the FBG Thus, the measurement error caused by the shape error of the FBG in the second approach could be eliminated, which makes the measurement error of the first approach within 0.08 GHz. In the second approach, a linear power ratio function is constructed, leading to a constant resolution in the maximum measurement range. However, as this approach requires a high accuracy of the FBG spectral shape, the measurement error is about 0.2 GHz. The third approach is based on frequency to microwave power mapping, in which the measurement range is 0.5-40 GHz. However, as the linear segment of the sinusoidal transfer function is used, and there is an inherent error, which makes the impact of noise relatively large, the measurement error of the third approach is about 0.5 GHz.4. A photonic approach to implementing a microwave channelized receiver based on wavelength division multiplexing using an optical comb is proposed. In the approach, a flat optical comb with 11 comb lines is generated using two cascaded Mach-Zehnder modulators. Frequency analysis of a microwave signal with multiple-frequency components is realized by using the optical comb together with an optical etalon with a periodic transfer function, a wavelength division multiplexer (WDM) and a photodetector array. The system is investigated numerically. The reconfigurability of the system realized by tuning the comb-line spacing and the peak positions of the etalon is also evaluated. The improvement of the dynamic range of the system using an optimized periodic filter is also discussed.5. An all-optical approach to realizing optical single sideband (OSSB) modulation based on optical Hilbert transform implemented using an FBG is proposed and demonstrated. In the experiment, an OSSB signal with a frequency from 6 to 15 GHz and a sideband suppression ratio as large as 20 dB is generated. The transmission of the OSSB signal over a single mode fiber of 45.6 km is also studied, and the power fading effect resulted from the chromatic dispersion is eliminated successfully.6. Two approaches to realizing continuously tunable microwave fractional Hilbert transformer (FHT) based on a uniformly-spaced microwave photonic delay-line filter (MPF) and a nonuniformly-spaced MPF are proposed and demonstrated. In the first approach, the MPF with true negative coefficients is realized based on a polarization modulator and polarization-modulation to intensity-modulation conversion in an optical polarizer. The tunability of the fractional order is achieved by tuning the coefficient of the 0th tap. An FHT with a tunable order from 0.3 to 1 is demonstrated. The accuracy of the FHT is evaluated; a phase deviation less than 5°within the passband is achieved. In the second approach, nonuniformly-spaced MPF is used. The advantage of using nonuniform spacing is that an equivalent negative coefficient can be achieved by introducing an additional time delay leading to aπphase shift, corresponding to a negative coefficient. An FHT with a tunable order between 0.24 and 1 is implemented. The accuracy of the FHT is also evaluated and the phase deviation within the passband is also less than 5°.更多还原