Design of phase-shifted long-period grating device and its application as gain-flattening fibre filter

The transmission characteristics of phase- shifted long-period gratings (LPGs) are simulated theoretically by a combination of coupled-mode theory and fundamental-matrix method. It is suggested that a phase-shifted LPG device cascaded with another normal LPG can be used to flatten the gain spectrum of an erbium-doped fibre amplifier (EDFA) with all three gain peaks. The results of simulations have shown that a broadband amplifier with peak-to-peak 0.7 dB gain variation over 36 nm can be practically realized. It proves that such a gain-flattening fibre filter is indeed plausible, and has a potential application in gain-flattening in dense wavelengh-division multiplexed (DWDM) telecommunication systems.