摘要
微波光子滤波器以其高带宽,低损耗,抗电磁干扰等优点广泛应用于各种通信领域。光纤光栅由于具备良好的波长选择性能和可控性,在微波光子滤波器中扮演重要角色。品质因数Q (Q-value, Quality Value)是衡量微波光子滤波器的重要指标之一,代表滤波器的选频性能。如何获得高品质因数的微波光子滤波器是当前微波光子领域的研究热点之一
本文重点分析了基于光纤光栅的微波光子滤波器的品质因数,主要工作和创新点如下：
首先,基于光纤光栅波长选择性能的理论模型,分析了基于光纤光栅的微波光子滤波器原理。并重点分析了基于光纤光栅的典型微波光子滤波器的特性,得出影响微波光子滤波器性能的主要因素。
其次,理论分析了高阶微波光子滤波器的通用传输函数中极点和阶次对品质因数Q值的影响,并获得提高高阶微波光子滤波器Q值的有效方法。结论表明提高微波光子滤波器传输函数中的阶数可以提高Q值,并且通过合理设置结构参数使极点趋近于1可以大幅度的提高Q值。
第三,运用信号流程图方法分析基于一阶,二阶和三阶结构的高Q值微波光子滤波器,获得了不同的结构参量对Q值的影响。结论证明了阶数的提高可以增大品质因数,但是同时会受到结构参量的限制。同时提出了一种基于光纤光栅和马赫曾德尔干涉滤波器级联的微波光子滤波器实现高Q值的方法。
第四,提出了一种新型的基于光纤光栅的环状微波光子滤波器结构,并对其传输函数进行了分析。
最后,提出了实现微波光子滤波器的可调谐性和负抽头系数的方法,并分析了基于光源阵列和色散光纤的可调谐微波光子滤波器以及基于电光调制器偏置电压点的负抽头系数平坦微波光子滤波器特性。结果表明增大光源的个数可以提高微波光子滤波器的自由频程FSR (Free Spectrum Range);通过合理设置耦合系数κ和增益g的关系可以使微波光子滤波器达到很好的平坦效果。
Microwave Photonic Filter (MPF) is widely used in kinds of communication domain, thanks to the numerous advantages such as high bandwidth, low loss, and immunity to electromagnetic interference. The FBGs have been considered a good candidate for the microwave filtering because of the excellent property of wavelength choosing and controllability. The Q-value represents the quality of frequency choosing, which is one of the most important factors to measure the character of MPF.
The main work of this paper is to analyze the influence to Q-value of MPF, which is based on the structure of FBGs. The main points are as follows:
1. Analyzing the theory of MPF based on the structure of FBGs, and the character of wavelength filtering of the FBGs is also analyzed. Besides, the factors which influence the quality of MPF are got.
2. The influence of the pole and order to the Q-value in the transform function is been theoretically analyzed. The conclusion is that the Q-value could be improved by increase order of the function. Besides, better results can be got through making the pole of the function approach to the unit circle.
3. The high-Q MPF based on first-order, second-order and third-order of function of MPF are analyzed through the way of signal flow chart. Also, the results prove that increasing the value of order can improve the Q-value, but it is limited by other structure parameters. Moreover, a kind of MPF based on the connected structure between Fiber Bragg Gratings and Mach-Zehnder Interferometer is proposed and analyzed, which has high Q-value.
4. A new structure of MPF is proposed and analyzed through signal flow chart.
5. The new way of implementation in tunable MPF and negative coefficients MPF is discussed. Also, the tunable MPF based on array lasers and dispersion fiber is manipulated. The result shows that increasing the number of laser can improve the Q-value. Besides, the negative coefficients MPF based on two electronic modulators which are driven at different opposing bias points is analyzed, and it proves that the better results can be got when the couple coefficient and gain of EDFA (Erbium-Doped Fiber Amplifier) is set up appropriately.
引文
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