All fiber dynamic gain equalizer based on a fiber grating with rotary refractive index change

An all-fiber dynamic gain equalizer for flattening Er-doped fiber amplifiers based on a long period fiber grating (LPFG) with rotary refractive index change induced by high-frequency CO2 laser pulses is reported, for the first time to our knowledge. Experimental results show that its transverse load sensitivity is up to 0.37dB/(g·mm-1), which is 9 times higher than that of a normal LPFG induced by the same method. In addition, it is found that the strong orientation-dependence of the transverse load sensitivity of the normal LPFG reported previously has been weakened considerably. Therefore, such a dynamic gain equalizer based on the transverse load and temperature characteristics of this novel LPFG provides a much larger adjustable range and makes packaging of the gain equalizer much easier. A demonstration has been carried out to flatten an Er-doped fibre amplifier to ±0.5dB over a 32nm bandwidth.