Experimental And Theoretical Investigation On Numerical Aperture And Mode Field Diameter Of Pcf

With the improvement of the numerical methods used in photonic crystal fiber analysis and the maturity of the fabrication technology, the application prospects of photonic crystal fiber have been continuously expanding and the practical process of photonic crystal fiber has been improved. Now, the fabrication technology of photonic crystal fiber has been greatly improved, a variety of photonic crystal fibers with complex structure have can be drawn out. However, all the theoretical studies shoud be proved its correctness by experiments. In this paper, the numerical aperture and mode field diameter of photonic crystal fiber are studied, including numerical simulation and experimental measurement.Firstly, it describes the actuality of the measurement of photonic crystal fiber and the advatage and disadvatage of traditional measurement method of numerical aperture and mode field diameter. Then it proposes using spectrometer to measure the numerical aperture of photonic crystal fiber and investigates the impact of the wavelength, the diameter of air-hole and the pitch on numerical aperture with wavelengh at 500~1 100 nm,and the measurement results are compared with simulation results. According to the measured numerical aperture, the parameters of fiber related with wavelength can be better studied, such as: the non-linearity coefficient, macro-bending loss, the effective mode area, cut-off wavelength and so on.Secondly, according to studying the traditional measurement method of numerical aperture and mode field diamete, it proposes the scheme to measure the mode field diameter of photonic crystal fiber based on lateral displacement method and spot method, then set up the experimental arrangement. By measuring three kinds of photonic crystal fiber which are fabricated by our laboratory, the mode field distribution of photonic crystal fiber can be received. The mode field distribution is observed by CCD. The mode field distribution is transformed into a three-dimensional light intensity distribution map by matlab program.Finally, a novel octagonal Yb3+-doped photonic crystal fiber with large mode area is proposed based on the flexible design feature of photnic crystal fiber. The properties of photonic crystal fiber are investigated by multipole method. This fiber is meaningful for the development of fiber lasers and fiber amplifiers.