Flat FTTH Drop Cable

Preparing a standard modular optical cable for splicing involves several seemingly simple steps:

• Stripping the outer sheath to the required length;
• Removing the aramid yarns;
• Flushing the optical modules with a special compound — D'Gel — to remove the water‑blocking gel;
• Wiping off the remaining D'Gel with purified gasoline;
• Opening the modules and cleaning the optical fibers — usually with gasoline as well.

Modular optical cable with a central strength member.

For an experienced splicer, these operations are routine and take about 5‑10 minutes per cable. A bit trickier is preparing a "loop" entry — feeding the cable into a splice closure without cutting the modules. This usually involves two longitudinal cuts along the sheath on the section to be opened, plus two transverse cuts at the cable anchor points. After that, the sheath comes off like peeling a banana. Cleaning the modules becomes more complicated too, since they're twisted together and it's hard to wipe each one individually to remove all the gel. You also have to be extra careful not to damage the modules — and therefore the fibers inside them. The "loop" entry allows you to significantly reduce the number of splices — unused fibers just pass straight through the closure without being cut. Plus, in my opinion, it improves reliability, since there's less chance of extra loss or fiber breakage at splice points.

It all sounds well thought out and reliable — in theory. In real life, though, working conditions aren't always ideal: rain, wind, freezing temperatures, cramped risers, dusty attics — you name it. And that's when you start wishing for a cable that could be prepped in seconds, without any cleaning solvents. Sometimes cable designers simplify the construction: they use water‑blocking tape instead of gel, a single central module instead of several, experiment with the amount of aramid yarn, the thickness of the central strength member, or the density of the polyethylene sheath. But none of that really hit the spot — I wanted something simpler :)

Apparently, I wasn't the only one thinking this way — and that's how subscriber drop cables for PON connections came about. These were flat, indoor cables, white in color, with the fiber(s) sandwiched between two strength members. Subscriber cables typically use ITU‑T G.657 fiber — bend‑insensitive, with low loss at tight radii. In practice, the cable turned out to be quite easy to work with, even without special tools — just split it in half along the grooves molded into the sheath, and you're ready to handle the fiber itself. Manufacturers didn't stop there and released an outdoor version — black in color. But as it turned out, using this cable outdoors is risky — its tensile strength is too low, even when the glass‑reinforced plastic rods are replaced with steel wire.

Flat FTTH drop cable — design and cross‑section.

At the CSTB exhibition, I finally saw exactly what I was looking for — Fujikura's flat outdoor cable with an additional strength member in the form of a steel wire about 1 mm in diameter. Despite its light weight, this allows spans of up to 50 meters — though that recommendation applies specifically to special anchor clamps for flat cables. For longer spans, the sheath can't take the strain and splits at the attachment point. If you really need a longer span, it's better to carefully separate the steel wire and tie it to a secure anchor point — that way you can go up to 80 meters.

Sheath damage at the attachment point.

Manufacturers, thinking about user convenience, went even further — they developed special connectors that mount directly onto the cable. No extra adapters or distribution boxes needed — you can make a patch cord and plug the cable straight into the equipment. I'm planning to write a separate post about those connectors soon.

SC/APC field‑installable connectors for drop cables.

To sum it up: in my view, flat drop cables — simple and affordable — are perfectly suited for their purpose: connecting endpoints, standalone buildings, shops, and private homes, using any technology, including GPON. But I'd also recommend not cutting corners — go for cable with "bend‑insensitive" G.657 fiber. When you're pulling it through tight channels and conduits, that significantly reduces the risk of micro‑bend losses — which means more reliable data transmission and greater peace of mind for you.

This article is a translation of the original Russian-language post.My journey of learning GPON