Expanding Capacity through Combined C+L Band Amplifiers

Current transmission systems, based on single-mode fibers, typically use either the C-, or L-band due to the availability of high-performance Erbium-Doped Fibre Amplifers (EDFAs) in these two bands. However, the continuing growth in data transmission (driven primarily by the increased consumption of on-line video1) is generating a great deal of research interest in trying to increasing fiber transmission capacity by spatial-division-multiplexing, either through multiple-core fibers2 or through the use of higher-order modes in a few-mode fiber3. Whilst these techniques may, in time, mature to the point where they are economically viable as a replacement for existing single-mode fiber transmission, it is not yet clear (at least to me) that the issues around practical spatial-division-multiplexing are soluble in a cost-efficient manner.

Recent work by Lynn Nelson and co-workers at AT&T Research4 has revisited the idea of combined C+L band transmission but this time using broadband Raman amplifiers, rather than the twin-EDFA configurations used previously5. Their work used two Finisar “X-Series” WaveShapers (a 4000S/X operating as a signal combiner and a 1000S/X used for gain flattening in a recirculating loop) to demonstrate a capacity of >9 Tb/sec (extendable to >18 Tb/sec) over 6,000km of fiber using standard DP-QPSK transmission. The X-Series WaveShapers have an operating window of >9 THz (73nm) – covering most of the C- and L-band – and so enabled the researchers to maximize the available capacity whilst maintaining excellent gain flatness in the recirculating loop.

WaveShaper 4000STransmission Spectrum of a WaveShaper 4000S X Showing 9 THz 73nm Transmission Window

Finisar WaveShaper 4000S and transmission spectrum of a WaveShaper 4000S/X showing 9 THz (73nm) transmission window Read more »