Numerical Examination on Transmission Properties of FBG by FDTD Method.

It is important to examine fiber Bragg grating (FBG) for the design of the practical use. Finite difference time domain (FDTD) method is used to examine the transmission properties. FBG is assumed to be two-dimensional periodic structures. Three different grating refractive index shape shows similar reflected frequency, and the square type show the lowest power transmission. Higher grating refractive index value affect in smaller value of transmission amplitude in specific frequency, and the center of transmission frequency drop is slightly shifted to lower value. Correlation between grating period and center of transmission frequency drop is in a nonlinear correlation. Longer total grating length will affect to the lower transmission value, and correlation between them is nearly linear in a certain area. Chirped FBG (CFBG) show a wider broadband reflect compared to the uniform FBG type, with a weaker reflectance. Increasing and decreasing grating period of CFBG show similar transmission characteristic.