The International Telecommunication Union (ITU) has issued Recommendation G.983.3 to propose a broadband optical access system with increased service capability by wavelength allocation. This Recommendation designates the 1490 nm wavelength for downstream voice and data signals, 1550 nm wavelength for downstream video signals, and 1310 nm wavelength for upstream voice and data signals.
Many network equipment and component vendors have accepted ITU G.983.3. As such, optical access systems composed of an optical-line terminal (OLT), optical-network terminal (ONT), WDM coupler, and 1 x N splitter are being installed today by many fiber-optic-network operators (see Figure 1).
Figure 1. Optical access systems based on ITU Recommendation G.983.3 include an optical-line terminal, optical-network terminal, WDM coupler, and 1 x N splitter. These broadband systems rely on three transmission wavelengths; the new 1490 nm wavelength is used for downstream voice and data signals.
The fiber-optic test equipment used for these optical access systems must be able to test at all three wavelengths. Fiber-optic-network operators and testing equipment manufacturers are quite familiar with 1310 and 1550 nm transmission wavelengths, but the 1490 nm transmission wavelength presents new challenges for OTDRs.
Many in the industry believe that 1550 nm testing is enough to cover the 1490 nm region. That is generally true for newer fiber that was installed in the late 1990s or more recently, especially the G.652C low water peak fiber. However, this practice is questionable for older fiber deployed in the early '90s, prior to the existence of G.652C when the water peak (E band) was not attracting so much interest. For this reason, many fiber-optic test equipment manufacturers now offer 1490 nm testing functionality on their products developed for PON testing. The main optical tests performed during PON installation include:
End-to-end link characterization
Loss and backreflection characterization of the coupler ports
Bidirectional end-to-end optical return loss (ORL) and optical loss measurement
Re: Is 1490 wavelength testing necessary?
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