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Fiber Bragg gratings with refractive index direct current component modulation

We propose a simple method for achieving a desirable chirp in the grating based on refractive index direct current component (RIDCC) modulation. The method uses dual-scan technique with an UV beam to obtain an increase of refractive index direct current component in the grating along the grating length. The effect of RIDCC modulation on the group delay characteristic of fiber grating is analyzed and the relationship between the RIDCC modulation and group delay of grating is deduced. Also, the numerical simulation results are given by using coupled mode theory and they agree very well with theoretical values. By controlling the RIDCC modulation function and modulation coefficient, we can realize different group delay profile using the same phase mask. These gratings can be used to compensate dispersion and dispersion slope of transmission fiber in high-speed optical communication systems.