Gain clamped double-pass L-band EDFA with incorporation of FBG at the input end of the optical amplifier

A gain-clamping technique in two-stage double-pass L-band EDFA is demonstrated using a single fiber Bragg grating (FBG). Two types of FBGs, broadband and narrowband, have been used in the gain-clamped system. The gain is clamped at 18.7 and 17.5 dB for the design with narrowband and broadband FBGs, respectively. The measured gain variation in both designs is below ± 0.15 dB. The maximum input-signal-power level for which the gain remains clamped for the narrowband and broadband FBG systems is about -15 and -10 dBm, respectively. However, the existence of a strong laser in the cavity severely reduces the population inversion at the input part of the amplifiers. This causes the noise figure of both designs to increase by 6.4 dB and 3.5 dB for narrowband and broadband FBG system, compared to that of undamped amplifier, at small signal power. These results show that gain clamping can be achieved in a double-pass amplifier by simply adding a single FBG, whereby the broadband system shows a better performance than the narrowband system in terms of input-signal-power dynamics range and noise figure