Broadband Gain Flatness Doped Doped Fiber Amplifier Applications

Recent years witness great breakthroughs of Dense Wavelength Division Multiplexing (DWDM) technology and the emergence of new advanced systems for commercial use, the top rate of which has reached 80*10 Gbit/s. The rapid development of DWDM technology is attributed to the introduction of Erbium-doped Fiber Amplifier (EDFA). So far almost all the DWDM systems, whether it is for experimental or commercial purpose, adopt fiber amplifier. During the transmission in optical fibers, DWDM signals will inevitably suffer certain loss and optical dispersion, resulting in the reduced optical signals and widened optical pulses spectra, which require a repeater at a certain distance for amplification and regeneration. The routine solution is the adoption of light/electricity/light repeater, which no longer meets the needs of modern transmission. However the application of fiber amplifier, EDFA in particular, may reduce the loss and optical dispersion caused by the light/electricity conversion. As EDFA becomes more and more applicable, the spreading use of EDFA facilitates the development of digital fiber transmission systems.To ensure the transmission of DWDM systems, EDFA should has adequate bandwidth, flat gain, low noise, and high output power, among which the flatness of gain is a special feature required for EDFA by DWDM systems. In respect of gain and noise, they can be improved by changing the length of fiber, the intensity of Erbium doped, and the pumping scheme.The problems caused by non-flat gain can be overcome by the adoption of gain equalizing technology—using a gain equalizer that has a loss profile reverse to the wavelength gaining profile of the concerned amplifier. Common gain equalizers include standard optical filter, medium multi-layer thin film filter, fiber grating, and planar waveguide. In this paper, long-period fiber grating gain flatten filter (LPFG-GFF) is used for the experiment of flattening the gain by EDFA, which demonstrates the application of LPFG-GFF can greatly improve the gain flatness of EDFA. Besides the application of gain shifting EDFA in the amplification of L-band is also discussed.