Study On Seven-core Photonic Crystal Fiber For Supercontinuum Generation

The emergence of the photonic crystal fiber provides a new platform for the field of nonlinear optics,high power fiber lasers and optical fiber communications and other fields.Especially in the field of nonlinear optics,multicore photonic crystal fiber can overcome the problems of limited mode field diameter and thermal effects in single-core photonic crystal fiber,and provide a new way for the generation of supercontinuum.In this thesis,we investigate the coupling characteristics,dispersion characteristics and nonlinear characteristics of seven-core photonic crystal fiber.Moreover,the generation of supercontinuum is studied in detail by numerical simulation based on the seven-core photonic crystal fiber.The main achievements are listed as follows:1.The coupled length of seven-core PCF is deduced through the theory of multi-core coupled-mode theory.The influence of the structure parameters of PCF on the coupling characteristics is analyzed by full vector finite element method;And the beam propagation method is also used to simulate the energy coupling process between the cores.The results that the coupling length obtained by the coupled-mode theory and the beam propagation method are in good agreement,which provides a theoretical basis for the rational design of the seven-core PCF structure and characteristic analysis.2.A novel seven-core photonic crystal fiber structure is proposed.The full vector finite element method is used to analyze the dispersion and nonlinear coefficients of seven-core photonic crystal fiber.The results show that the fiber nonlinearity and dispersion curve can be effectively controlled by changing the air hole spacing and the air hole diameter of the cladding.After modifiying the same phase supermode in the seven-core PCF,the nonlinearity of the modified fiber is 68W-1Km-1 and the loss is 4.576×10-6dB/m at the wavelength of 1.55?m,and the dispersion of the fiber structure are all normal in the calculated wavelength range.3.Taking use of the Fourier method of distribution to numerically simulate the spreading process of ultrashort pulse in our fiber.The influence of fiber length,pump wavelength,pulse power and pulse width on spectral broadening is studied.The numerical simulation results show that the characteristics of the generated supercontinuum can be effectively adjusted by choosing the appropriate pulse parameters.Based on the designed seven-core photonic crystal fiber,the supercontinuum of 1.101-1.331?m spectrum is obtained when the fiber length L=5cm,the initial pulse width T0=50fs,the central wavelength 1.55?m and the pulse peak power 40kw-80kw.The results fully show the seven-core photonic crystal fiber with normal dispersion has great potential in generating flat,wide bandwidth supercontinuum.