Gain Clamped Two-Stage Double-Pass L-Band EDFA with a Single Fibre Bragg Grating

A gain clamping is demonstrated in a two-stage double-pass L-band erbium-doped fibre amplifier (EDFA) by using a single fibre Bragg grating. Two types of the fibre-Bragg-grating (FBG) broadband and narrowband have been used in the gain-clamped system. The combination of the FBG and the optical circulator has created a laser in the cavity for gain clamping. The application of a broadband FBG has improved the amplifier’s efficiency and noise figure compared to the narrowband FBG system. The gain is clamped at about 22.1dB for the amplifier with broadband FBG with gain variation of less than ±0.15dB and the input saturation power P_sat at -8dBm. The gain varies from 19.0 to 25.4dB in the signal wavelength region of 1574nm-1604nm. The noise figure varies from 6.0 to 10.8dB at this wavelength range. The noise figure values are found to improve by as much as 0.3-1.1dB when compared to the unclamped amplifier for signal wavelengths above 1580nm. The high clamped gain and low noise figure are obtained due to the suppression of the backward C-band amplified spontaneous emission. The gain clamped amplifier shows only a small power excursions when three of the four channels are added/dropped. The effects of relaxation oscillation are not seen for the gain-clamped two-stage double-pass L-band EDFA.