Research On Sagnac Ring Microwave Photonic Filter Based On Fiber Grating

With the rapid development of optical communication and optical fiber sensing technology, especially the wavelength division multiplexing(WDM) and dense partial multiplexing(DWDM) system have been widely used, the research of comb fiber filters has been a hot research topic in the field of optical fiber communication and optoelectronics. Optical fiber Sagnac loop itself has filtering properties, it has simple structure, low cost, good stability, the advantages of wide tuning range, etc. Fiber Bragg grating has a flexible reflection spectrum bandwidth, small additional loss, small size, low cost and mature technology of compatible with fiber, it is widely used in optical fiber communication and optical fiber sensing in the devices, such as filtering and frequency selective. Fiber grating and Sagnac ring can form a comb filter and achieve all kinds of different filter characteristics.A new design of a microwave photonic filter based on sampled fiber Bragg grating and a Sagnac loop and a new design of a microwave photonic filter based on phase-shifted fiber grating and a Sagnac loop have been proposed and mainly studied, modeled, simulated and optimized in this paper. The influence of various parameters on the spectral characteristics of the filter has been discussed in detail. In this paper, the main innovation points and research content are as follows:(1) The development of microwave photonic filters has been studied in this paper, and the theoretical and numerical studies of general optical fiber Sagnac loop filter have been carried out. Using the transfer matrix method, the structure of optical fiber Sagnac loop has been studied, and the transmission characteristics of a microwave photonic filter based on a fiber Bragg grating and a Sagnac loop has been studied, and MATLAB numerical simulation and analysis have been carried out.(2) First of all, by the use of the Jones matrix method, the detailed theoretical study and numerical simulation of the reflection spectrum of the sampled fiber Bragg grating have been carried on. On this basis, a new scheme of a microwave photonic filter based on a sampled fiber Bragg grating and a Sagnac loop has been proposed. The theoretical analysis model has been established, and the detailed theoretical derivation and the related numerical simulation using MATLAB software have been carried out. The transmission spectrum of a microwave photonic filter based on sampled fiber Bragg grating and a Sagnac loop has been studied emphatically, as well as the effect of the key parameters(optical fiber ring arm length difference, the sampling period, the refractive index modulation depth and duty cycle, etc) of components on the output spectrum of the designed filter. On the basis of a large number of numerical simulation, the optimization of the key parameters, such as the length of the sampled fiber Bragg grating L, optical fiber ring arm length difference DL, the sampling periodP, has been carried out. Six different types of filters were designed, and they have narrow-band comb transmission spectrums with different channels, discrete spectral lines, high reflectivity, and equal interval, and they have good wavelength selectivity and good channel isolation. They can achieve narrow-band filtering for 16 channels of 100 GHz and 8 channels of 200 GHz DWDM system; can be made into dual wavelength fiber laser for the generation of THz wave; and can get a narrow-band peak in the transmission spectrum, which can be applied to the distributed sensing system.(3) A new type of a microwave photonic filter based on phase-shifted fiber Bragg grating and a Sagnac loop has been put forward. The theoretical analysis model was established, and the numerical simulation on MATLAB software platform was carried out by using Jones matrix analysis method. The output spectral characteristics of the structure has been mainly studied, and the effect of some important parameters such as the optical fiber ring arm length difference, the size and location of phase shift and the number of the phase shift on the transmission spectra has been analyzed in detail. The bimodal band-pass comb filters have been achieved, which are approximately symmetric about the center wavelength, and have adjustable channel number and stop-band bandwidth.