All fiber dynamic gain equalizer based on a twisted long period grating written by high frequency CO2 laser pulses

A novel dynamic gain equalizer for flattening Er-doped fiber amplifiers based on a twisted long period fiber grating (LPFG) 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 0.34 dB/(g.mm--1) when a 100 mm long fiber with a LPFG in the middle of it is twisted about 20 rad/m, which is 7 times higher than that of a torsion-free LPFG. In addition, it is found that the strong orientation-dependence of the transverse load sensitivity of the torsion-free LPFG reported previously has been weakened considerably. Therefore, such a dynamic gain equalizer based on the unique transverse load characteristics of the twisted 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 ±0.5 dB over a 32 nm bandwidth.