Study On The Microwave Photonic Filter With Positive And Negative Coefficients And Application In Photonic Generation Of UWB Signal

With the rapid development of modern electronic technology, people’s lives are becoming more and more convenient. At the same time, the available spectrum resources are facing enormous challenges. The changes make the new frequency requirements more stringent. It’s known that processing of microwave signals is easily affected by electronic "bottleneck". The microwave photonic filter based on microwave photonics overcomes this drawback. It can process the microwave or radio frequency (RF) signal in the optical domain. Compared with traditional filter, microwave photonic filter has lots of advantages, such as low loss, high bandwidth, immunity to electromagnetic interference, flexible tunability and reconfigurability. In this paper, microwave photonic filter is introduced from the following aspects:(1) Firstly, the basic concept and the development trend of microwave photonics are briefly introduced. Then we introduce the background, theory, limiting factors of microwave photonic filter. Many approaches have been proposed to realize microwave photonic filters with negative coefficient. The advantages and disadvantages of microwave photonic filter based on Mach Zehnder modulator (MZM) are analyzed.(2) A novel approach to the implementation of microwave photonic filter with positive and negative coefficients based on an unbalanced Mach-Zehnder modulator (MZM) is proposed and analyzed. A microwave signal to be filtered is applied to a single electrode of the unbalanced MZM. Thanks to the unbalance between the two arms of the modulator, a π phase shift is obtained by adjusting the wavelength interval between the adjacent wavelengths, which leads to the generation of the positive and negative coefficients. The theoretical fundamentals of the design are described, which shows that the required unbalanced MZM in the scheme can be well fabricated by the current technology, and the other components including the wavelength multiplexer are also commercially available devices. A multi-tap microwave photonic filter with positive and negative coefficients is numerical simulated. The tunability and reconfigurability of the multi-tap microwave photonic filter are also investigated to verify our approach.(3) By improving the delay structure, a new method to generate UWB signals based on an unbalanced MZM is proposed and analyzed. In order to prove the feasibility of the scheme, we introduce the theory of generating UWB signal using microwave photonic filter firstly. Secondly, by comparing with the present research results, a new structure of generating the first order UWB signal based on unbalanced MZM microwave photonic filter is presented. Finally, the proposed structure is numerical simulated. The feasibility of the proposal is proved from three aspects of principle, structure design and simulation.