Distributed Raman fiber amplifier for S-band

The dense wavelength division multiplexing (DWDM) systems are demanded continuously to increase the channel capacity and transmitting distance due to rapid growth of the data and internet traffic. It means broadening of available bandwidth and increasing its amplifying span is necessary. Now days WDM transmission is using up the entire gain band of Erbium-doped fiber amplifier (EDFA) i.e. C-band and L-band. Even though the entire band of the EDFA is fully utilized and very high spectral efficiency was obtained through soliton technology, demands from internet still seem to keep on growing recklessly. Infact EDFA-based WDM transmission technology has been hitting the upper limit of transmission capacity [1-3]. Erbium-doped fiber amplifiers are lumped amplifiers in which gain is lumped at a point of the transmission line. The distributed amplifier such as Raman fiber amplifier keeps the optical signal level over a long distance along the transmission line. The Raman fiber amplifier offer gain at any wavelength so long as a suitable pump laser can be found at appropriate wavelength. This characteristic is helpful in broadening the available bandwidth. Raman fiber amplifier has some outstanding advantages, such as the seamless gain over wide bandwidth, remarkable noise reduction, extension in the span length and better nonlinear impairments of transmission systems [3-5]. Raman amplifiers use stimulated Raman scattering in silica glass fiber, which is inelastic scattering of a photon with a molecule. The interaction between the incident photon and molecule will cause the molecule to vibrate, resulting in the frequency down shift or stokes shift of the photon for the sake of energy conservation. Quantum mechanically this process is described in Fig. 1.