Design and fabrication of dual-transmission-band fiber Bragg grating with terahertz wavelength spacing

Phase-shifted chirped fiber Bragg grating (PS-CFBG) with dual π phase shifts was studied theoretically and designed by classic transfer matrix approach. The transmission characteristics of the PS-CFBG with two transmission peaks are only directly dependent on the position of dual π phase shifts. The linewidth of two peaks increase with the chirp rate of the grating, and is not related with the wavelength difference of the peaks. A dual PS-CFBG was fabricated by ultraviolet point-by-point scanning with a ~2.4 nm/cm chirped phase mask. Phase shifts were introduced by controlling half period movement of grating accurately through the piezoelectric ceramic (PZT). The wavelength spacing, extinction ratio, and 3dB linewidth of two transmission peaks are 8nm, 20 dB and 0.08 nm, respectively, which agree with the theoretical design.