Research On Key Technology Of Tunable Microwave Photonic Filter

Microwave Photonic Filter(MPF) has been intensively investigated in the past few years. Among the different types of MPFs, single band-pass MPFs are one of the most important types of MPFs which can find applications in modern radar, communications, and warfare systems.Tunable single band-pass MPF is studied in this thesis. The research background and the working principle of microwave photonic filter are introduced in the chapter1. Then the principle of single band microwave photonic filter is analyzed. And three different methods of achieving single pass-band MPF are introduced. The tunability of these three methods is discussed. A tunable single band-pass MPF based on the optical notch filter is proposed.By analyzing the matrix theory of the Phase-Shift Fiber Bragg Grating(PS-FBG), the notching character of PS-FBG is demonstrated. Thus, PS-FBG can be used as a notch filter in the proposed MPF due to the theory of single band-pass MPF based on notch filter. The equivalent phase modulated(EPM) signal with an adjustable optical carrier power is demonstrated by analyzing the theory of dual-parallel Mach-Zehnder modulator(DP-MZM). The PS-FBG is used as an optical notch filter to remove one sideband of the EPM signal to convert the EPM signal to a single-sideband intensity-modulated signal. At the output of a photodetector, a microwave signal is detected. The entire operation is equivalent to a single band-pass MPF. By analyzing the tune methods and the tunable range of the proposed MPF, we have demonstrated that the tunability is achieved by tuning the wavelength of the optical carrier. The tunable range of the proposed single band-pass MPF is determined by the range of the total reflection bandwidth of the PS-FBG and the location of the notch. The maximum tunable range of the MPF is half of the total reflection bandwidth of the PS-FBG.The relationships between the characters of uniform Fiber Bragg Grating based PS-FBG and the reflection spectrum of the PS-FBG is discussed. And the effects on the frequency response of the proposed MPF are analyzed. While the length of the PS-FBG is 5mm, the location of the phase-shift is in the middle of the PS-FBG, the refractive index modulation depth is4-106 ?, and the phase-shift is ?, a tunable single band-pass MPF is gotten. The single band-pass MPF is a MPF with a pass-band width around 150 MHz and a frequency tunable range of 4.3673 GHz. The tunability of the proposed MPF is achieved by tuning the wavelength of the optical carrier.Due to the limitation of the total reflection bandwidth of the PS-FBG, the proposed tunable sing band-pass MPF has a narrow tunable range. By analyzing the parameters of the chirped Fiber Bragg Grating based PS-FBG(CPS-FBG,), and their effects on the reflection spectrum of the CPS-FBG, a single band-pass MPF with lager tunable range has been gotten. While the central reflection wavelength of CPS-FBG is 1550 nm, the location of the phase-shift is in the middle of the CPS-FBG, the effective refractive index is 1.4466, the phase-shift is 8.0?, the length of the CPS-FBG is 24 cm, the location of the phase-shift is in the middle of the CPS-FBG, the refractive index modulation depth is4102.1-?,and the chirp coefficient is4-107 ?, a single band-pass MPF with lager tunable range is gotten. The single band-pass MPF is a MPF with a pass-band width around 290 MHz and a frequency tunable range of 44.97 GHz. The tunability of the proposed MPF is achieved by tuning the wavelength of the optical carrier.