Gain Flattening Filters (GFF’s), also known as gain equalizing filters, are used to flatten or smooth out unequal signal intensities over a number of specified channels in the C-, L- and U-Bands. This unequal signal intensity usually occurs after an amplification stage (e.g., EDFA and/or Raman). GFFs are used in conjunction with gain amplifiers to ensure that the amplified channels all have the same optical gain. GFFs are characterized by their “peak-to-peak error function” (PPEF) which is a measure of how close the GFF transmittance is to the desired target curve and therefore the specified signal flatness.
Iridian’s proprietary design and deposition technologies result in GFFs that outperform traditional gain flattening filters. Iridian’s GFFs vary in complexity from simple parabolic curves to very complex curves possessing high modulation depths and steep slopes. Iridian manufactures custom GFFs with extremely low PPEF values for even the most challenging requirements.
In addition, Iridian also supplies Hybrid-GFFs that can perform additional optical functions. For example, it can block the pump laser providing the optical amplification removing the need for an additional pump wavelength blocking filter. As well, hybrid-GFFs can be designed to pass or block other wavelengths in the 900 to 1700 nm wavelength band.
Iridian has recently developed Premium GFFs that improve EDFA performance and optimize module design.
We have the ability to deftly compensate the EF in GFFs. By designing and producing a filter set with opposite error functions, we can reduce the combined PPEF. Stated differently, we can produce a filter with a precise error function, and then compensate for that error function to cancel it out by using a pair of filters, achieving lower overall PPEF throughout the system.
Some Applications for our GFF filters include: