Cascaded pumping system and method for distributed Raman amplification in optical fiber telecommunication system

Abstract

A pumping scheme for distributed Raman amplification (DRA) in optical fiber telecommunication systems is disclosed in which pump energy at the wavelength(s) required for DRA of the transmitted optical signal(s) is developed within the transmission fiber from a primary pump source through a series, n, where n >= 1, of Raman conversions resulting from the launch into the fiber of a primary pump source along with low-power seed sources. Alternatively, seed sources can be replaced by reflecting means to return, into the fiber, backward-travelling amplified spontaneous Raman scattered light resulting from high power in the fiber at a wavelength one Raman shift below the desired seed wavelength. The peak Raman gain thus occurs some distance from the primary pump launch terminal and leads to improved amplifier noise performance. Dynamic control of the magnitude and / or the spectral profile of the distributed Raman gain at, or near, a signal launch terminal can also be provided.

Description

technical field [0001] The present invention relates to a fiber optic Raman amplifier and a fiber optic communication system incorporating such an amplifier, and more particularly to a method for pumping a transmission fiber of a fiber optic communication span to generate in the fiber a signal for amplifying transmission along the fiber span Systems and methods for distributed Raman gain. Background technique [0002] Until recently, the amplification of optical signals in fiber optic communication systems has been initially achieved through the use of discrete optical amplifiers, mainly erbium-doped fiber amplifiers (EDFAs). Due to the explosive growth in the need to increase capacity in fiber optic communication systems, there has been interest in repurposing distributed Raman amplification. See for example, P.B. Hansen et al., IEEE Photonics Technology Letters, Vol. 9(2), p. 262, (February 1997). In this scheme, when the signal is transmitted towards a repeater or recei...

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Problems solved by technology

However, this pumping scheme, especially if it is applied to longer spans (eg 125km), requires two relatively expensive, relatively high energy (in the hundreds of mW) sources

This disadvantage is exacerbated in the case of high-capacity WDM systems since the widening of the gain bandwidth requires more such sources

In addition, where the transmitted energy of the signal in the link is at or very close to the limit set by consideration of the reverse nonlinear effects in the fiber, a substantial increase in amplification after the signal is launched can lead to a degradation of link performance due to these nonlinear effects

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