SSE-DCM(C)-C-652(60km)

SSE-DCM(C)-C-652(60km) is a Huawei dispersion compensation module for the OSN 7500, cut to compensate roughly 60 km of G.652 fibre.

What it is actually correcting. Different wavelengths travel through glass at slightly different speeds. A pulse of light is never a single wavelength, so over distance it spreads out until it starts to overlap the pulse behind it and the receiver can no longer tell them apart. That is chromatic dispersion, and it is why an optical span has a reach limit that has nothing to do with how much light arrives. This module winds the spreading back by passing the signal through a path with the opposite dispersion.

Its compensation is 953 to 1009 ps/nm measured at 1545 nm, which is what 60 km of G.652 accumulates. That works out at roughly 16.4 ps/nm per kilometre, and it is worth seeing why that number differs so much between fibre types. Standard G.652 fibre runs around 17 ps/nm/km in the C-band, so a long span accumulates dispersion quickly. Fit a module cut for the wrong fibre type and you will either under-correct or over-correct, and over-correcting degrades the signal just as reliably as leaving it alone.

It is specified for G.652 fibre, which is standard single-mode and by far the most common fibre in the ground. If your span is dispersion-shifted or non-zero dispersion-shifted fibre, this is the wrong module. The fibre type is worth establishing from records or measurement rather than assumption, because it is not visible from the outside and a cable installed decades ago may not be what the current drawings claim.

It operates across 1525 to 1568 nm, which covers the C-band, so it compensates every DWDM channel passing through it rather than a selected one. Compensation is not perfectly flat across that window, so on a system using the full band the channels at the edges are corrected slightly differently from those in the middle. On a long, high-rate system that residual tilt is something the design has to account for.

This is SDH-generation equipment, and SDH is a legacy transport technology. The industry moved to packet and to OTN years ago, and the OSN 7500 is not a platform anyone is designing a new network around in 2026.

That is not the same as saying it is useless. A great deal of SDH is still in service carrying E1 and STM-n circuits that work perfectly well, in utilities, rail, broadcast, defence and government networks where the circuits outlive the fashion in transport technology. If that is what you are maintaining, this keeps it running. If you are being offered SDH for something new, push back.

What we need to get this right. The measured length of the span, the fibre type, and ideally the actual dispersion measurement rather than a calculation from distance, because splices and cable slack mean the optical length is always longer than the map. Tell us the span and what is at each end and we will work out the compensation it needs and whether it belongs in the line or between amplifier stages.

Green Code Technologies supplies Huawei optical transport equipment, including amplification, filtering and compensation. We are a supplier of Huawei alongside HPE, Dell, Cisco, Samsung and Netgear, and we would rather confirm a part against Huawei’s own documentation than sell you the wrong one, which on OSN 7500 equipment is worth doing. Send us the span, the fibre type, the channel plan and the levels at each end and we will come back with a straight answer.