Finisar's Hybrid Raman-EDFA module enables cost-effective deployment of ultra-long haul networks as well as the extension of existing long-haul, regional and metro networks, without the need for 3R O-E-O regeneration. The Hybrid module consists of a counter-propagating Raman pump unit and a variable gain (VG) EDFA. These two elements are integrated to provide exceptionally low noise figure and excellent gain flatness - two imperative parameters for ultra-long haul systems. The module can support up to 3 Raman/EDFA pumps in various configurations.
Since the module’s first stage is a Raman pre-amplifier which has a negative effective noise figure, the overall combination of the Raman pre-amplifier and VG EDFA has a very low effective noise figure. This allows the link reach to be extended 3 to 4 times, in comparison to a system based on traditional EDFAs. The Hybrid control circuitry operates in advanced AGC mode, in which the actual Raman gain is automatically measured and then complemented using the EDFA gain. The required total gain is therefore constantly maintained. This fast AGC control circuitry also provides excellent transient suppression, allowing the amplifier to keep the gain constant also in cases where there are fast and large changes in the input power (regardless of ASE produced by the Raman pump).
The module also incorporates laser safety mechanisms, ensuring that both the Hybrid Raman-EDFA module itself and the network in which it is installed can be classified as Class 1M products with respect to laser safety.