Research On Microwave Photonic Filters And Its Applications

With the development of optical fiber communication technology, using the photonic technology to process the microwave and millimeter-wave signal has attracted considerable attention in recent years. A new interdisciplinary area is then produced in this environment. Compared with traditional microwave signal processing, microwave photonic processing functions provide advantages such as low loss, broad bandwidth, immunity to electromagnetic interference, good tunability and reconfigurability. This technique has been widely used in broadband wireless access networks, sensor networks, radar, satellite communications, and warfare systems. Microwave photonic filters are the key component in the system of photonic signal processing of microwave signals. It uses optical fiber and integrated photonic devices to carry out the filtering of clutter and noise from the wanted signal. Microwave photonic filters have already played an important role in Radio-over-fiber (ROF) system and optically controlled phased array antennas and also have the advantage of compatible with current optical fiber communication system. In this thesis, we have presented several studies of microwave photonic filters.(1) The factors that affect the frequency response of microwave photonic filters are summarized and analyzed, including the number of taps, weight coefficients and time delay. Based on Discrete Fourier Transform, the method about how to design the weight coefficients to obtain desired frequency response is analyzed. We also demonstrate a scheme to realize microwave photonic filters with arbitrary frequency response based on XGM and FWM in SOA. The experimental results agree well with theoretical analysis.(2) A novel scheme is proposed to realize all-optical phase shifter, and then microwave photonic filters with complex coefficients based on all-optical phase shifters are demonstrated using two different methods. The two schemes use the XPM in SOA and the demodulation of phase modulated signal respectively. The results show that the tuning range of the proposed filters is a one FSR and half of FSR, respectively.(3) A scheme to realize complex coefficients in microwave photonic filters using FP-SOA is demonstrated. Based on multiple-beam interference, using the change of carrier density in FP-SOA, the filter with large tuning range is obtained. We also propose a novel all-optical phase shifter based on optically Hilbert transform, which can realize phase shift of RF signal in a large bandwidth.(4) The operation principle of optical arbitrary waveform generation is analyzed and described. Begin with the expression of Fourier transform of optical modulated signal, the waveform of output signal can be changed by adjusting the amplitude and phase of each spectral line. In the experiment, we use FWM in SOA to generate spectral comb lines. The amplitude and phase of each line are adjusted by a programmable optical filter. The experimental results show the generated waveform is very similar to that from theoretical calculation.