How GFFs And WDMs Serve Optical Fiber Amplifiers

EDFA modules are commonly used in fiber optic communication systems to recover the optical signal after it has been transmitted over a certain distance. Traditionally, electronic amplification was used for this task, transferring the optical signal to an electrical signal, amplifying that signal, and then transferring the updated electrical signal back to an optical one.

However, EDFA modules (passive amplifiers) use an erbium-doped fiber to eliminate the need for transferring a signal from optical to electrical and back again. The optical signal is amplified within the fiber by a laser operating at a wavelength of 980 nm or 1480 nm, used to excite the erbium atoms, which then emit large numbers of photons when triggered by the much weaker incoming optical signal at the same wavelengths as the incoming signal. This results in an amplified version of the input signal at the output of the EDFA.

Most telecom wavelengths operate in the C-band (1520-1570 nm) or the L-band (1570-1620 nm), and the pump laser acting upon the signal will disrupt that precise wavelength – particularly problematic in a fiber accepting multiple communication channels.

In traditional EDFA modules, a pair of filter components is applied to correct the EDFA’s output signal. A GFF is used to “flatten,” or even out, the outgoing amplified signal. This filter operates in tandem with a 980 nm-blocking (or 1480 nm-blocking) wavelength-division multiplexer (WDM), the latter used to minimize interference cause by the pump laser.

What is a Hybrid Gain Flattening Filter, and what Advantages Does it Offer?

A Hybrid GFF, which combines the functionality of both a WDM and the GFF on one component. Specifically, a Hybrid GFF can block the pump laser from light in the range of approximately 980 nm or 1480 nm while providing gain flattening for signal light amplification — without the need for an additional pump wavelength blocking filter.

Moreover, a Hybrid GFF can be designed to pass or block other wavelengths in the 900 nm to 1700 nm band.

It’s vital to note that neither a base GFF nor a WDM is a trivial component from a design and manufacturing standpoint. So, combining them into a single component that costs less than two separate filters – while accepting no compromise in single-band or multiband performance – is no mean feat.

The most obvious benefit of Hybrid GFF is substantial cost savings; a Hybrid GFF costs barely more than a base GFF while offering the functionality of two components. In addition to eliminating the cost of a separate WDM, use of a Hybrid GFF reduces system design complexity by cutting out a now-unnecessary element.

Related, eliminating the separate WDM leads to more compact dimensions for the EDFAs and other optical amplifiers overall, whether you’re trying to reduce equipment size or accomplish more within the same space.

In terms of quantifiable performance metrics, Hybrid GFFs excel, as well.