Novel technique for the measurement of photonic crystal fiber numerical aperture properties

In this paper, the numerical aperture (NA) of photonic crystal fiber (PCF) is measured by a system with spectrometer, and high-precision results are obtained. The spectrometer can record the light intensity of different wavelengths. It overcomes the limitation that the traditional measurement can only measure the NA in some fixed wavelengths. We get the NA at any wavelength in 500nm∼900nm range, which is determined by light source and spectrometer. Therefore, the parameters related with NA can be better studied, such as: the mode field area, cut-off wavelength and so on. The characterization of PCFs can be better represented too. The measured results are compared with theoretical calculation value, and they agree with each other very well. According to the measured NA, the mode field area of sample fiber is calculated and compared with simulation results calculated by fast-vector-method.