Valerie C. Coffey
The component count as well as the cost of existing EDFAs has largely held back penetration of optical amplifiers into application areas that require a large number of amplifiers at a low cost. A new erbium-doped fiber amplifier (EDFA) demonstrated by scientists at the University of Southampton (Southampton, England) and Polaroid Corp. (Norwood, MA) effectively increases amplification by eight times in a compact, low-cost configuration.
The new design approach in adaptive EDFAs combines eight integrated amplifiers, all sharing common pump lasers, in a single package, replacing eight single-port EDFAs and bringing down the amplifier count by nearly one order of magnitude. Furthermore, thanks to the abundance of amplifier capacity, the EDFA can be configured independently, either serially or in parallel, saving cost and increasing network efficiency and reliability.
The new amplifier comprises eight parallel cladding-pumped fiber amplifiers pumped by a compact module with a built-in pump redundancy scheme. Cascading of ports is used to increase output power and bandwidth. The approach incorporates a novel coiled cladding-pumped structure with eight Er/Yb co-doped fibers for signal amplification and two pump fibers coiled together in such a way that pump power penetrates into all eight doped fibers via evanescent field coupling.
The EDFAs offer a 1530- to 1570-nm gain bandwidth with noise below 5 dB (see figure). Each separate amplification channel has a slight signal gain above 30 dB. This is very close to data for conventional, core-pumped amplifiers while the total output power from this type of amplifiers is almost one order of magnitude higher.
The fiber amplifiers have a length of 1.5 m, and possess low crosstalk and small nonlinear signal distortion. The amplifier can thus be used for crosstalk free amplification of WDM signals. To increase gain or saturated power the system can be easily reconfigured by cascading two or more amplifiers, at the same time retaining a very low noise figure. For more information, contact Don Spalinger at don.spalinger@ southamptonphotonics.com.
The performance of individual amplifier fibers is shown by the spectral dependence of signal gain for two arbitrary channels (dashed and solid lines). The gain curves for the other six channels are similar (not shown). The performance is nearly identical to existing independent amplifiers.