A Few Words About the Network and Splitters

I want to apologize for the long silence on the blog. As you know, summer is the busy season for fiber installers. Every day it's field work — rooftops, private residential areas. You have to get cables laid out along the routes, splice closures — basically, there's a ton of work and not enough time.

And that's exactly where we are now — we've started building our passive optical network. Every day it's up the ladder, unspooling cable from poles, splicing closures, and coiling it all back up again :) The weather's been cooperating, though spending hours under the sun takes its toll. We're going through water by the bucket. But that's not what I wanted to write about.

The real surprise during the build was splicing standard single‑mode fiber — ITU‑T G.652.D — which is what both the cable and splitter manufacturers specify. For our lines, we're using OKPM‑02‑6×4E3‑(9.0) cable from Moskabel‑Fujikura. This cable has 24 standard single‑mode fibers with an extra low‑loss window — meaning there's practically no excess loss between the 1310 nm and 1550 nm windows, so you can use WDM to increase capacity. For regular networks, this is the most common fiber type. I'm mentioning the 24‑fiber cable as an example — in practice, we use cables ranging from 8 to 144 fibers.

For splitting the optical signal, we bought planar splitters in 2‑way, 4‑way, and 8‑way configurations. Just to recap: planar splitters are made using the same technology as microprocessors — layers are deposited onto a substrate through a mask. Fused splitters, by contrast, are made by fusing two fibers at an X‑shaped intersection. Planar splitters have more stable characteristics — less variation in insertion loss between taps — and most come in a compact housing that's easier to fit inside splice closures. Plus, their passband covers the full PON wavelength range — roughly from 1260 to 1650 nm.

As I mentioned earlier, the first splitter (8‑way) is connectorized, while the downstream subscriber splitter (also 8‑way) is spliced in at the input. During the design and construction phase, we also decided to create subscriber "extensions." That means we put an 8‑way splitter in the subscriber closure, but at that particular location we might only use 4 taps. The remaining taps get spliced to drop cables and routed to a remote group of buildings, where they terminate in a 4‑port enclosure. Inside the enclosure, those four fibers are connected to adapters via pigtails for customer hookups. The reasoning behind this approach was to simplify the connection process and reduce the number of subscriber cables hanging on utility poles. After all, four cables converging on a single pole at the center of a building group looks a lot cleaner than four (or more) parallel cables running the entire last span to the closure.

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