A novel design of long-period grating filters

A novel LPG structure, step-changed LPG, has been investigated theoretically and experimentally. The step-changed LPGs were fabricated using a two-step UV-beam scanning technique. The spectral characteristics of this type of LPG were simulated by numerically solving the coupled-mode equations and the results obtained from the simulation shown good agreement with the measurement spectra. It has been shown that the spectral profile of such LPG can be tailored by adjusting the step parameters and this property has potential applications in EDFA gain-flattening.