From the physical cable to the loss budget, the full optical network and, for passive optical networks, the split ratio and the optics that have to close.
The discipline
A fibre link either has the loss budget to close or it does not, and the difference is usually a few tenths of a dB spread across every connector pair, every splice and every kilometre of cable. The budget itself is a single sum: the power the transmitter launches, minus every loss between the two ends, checked against what the receiver needs, with margin left for ageing and repair.
Choosing the cable is a different question. The glass inside a loose tube cable and an ADSS cable of the same count is usually the same G.652.D single mode fibre. What separates them is whether the cable can hold its own weight across a pole span, survive the trench, fit the duct already in the ground and meet the fire rating the building needs.
Passive optical networks add a splitter that can take 17 to 23 dB on its own at high split ratios, and a sizing problem on top. Subscribers per port is a cascade from splitter to ONT to access point, and bandwidth, the ONT port limit or the split ratio can each be the cap. Both the optics and the sizing have to close.
The tools below go from the physical cable to the loss budget and the full network design, then, for PON, the sizing and the optical check.
The workflow
Filter a real manufacturer catalogue on fibre count, installation method, armour, sheath, temperature and duct clearance. Aerial ADSS spans are checked against the datasheet sag and tension table, and every cable that fails shows the reason it failed.
Do it withFibre Optic Cable Selector Free Open the tool →Enter the fibre segments, an IEC 61753-1 connector inventory, fusion and mechanical splices and an optional ITU-T G.671 splitter, and read the total link loss against the design margin, the link ORL and a multimode reach check in one view.
Do it withFibre Optic Connector and Splice Loss Calculator Free Open the tool →Drag transmitters, spans, splitters, WDM mux, ROADMs and amplifiers onto a node graph. Every change reruns a bidirectional link budget per path with OSNR, chromatic dispersion and the ITU-T PON budget class each design satisfies, plus an OTDR trace view per node.
Do it withFibre Optic System Designer Pro Open the tool →Walk the cascade from subscriber target to ONTs, PON ports, line cards and OLT shelves for GPON, XG-PON, XGS-PON or NG-PON2, with the binding constraint named and distribution points sized separately because partly filled splitters cannot be shared between them.
Do it withPON Split Ratio Planner Free Open the tool →Run the downstream and upstream loss waterfalls against the ITU-T class budget, with G.671 splitter loss, FEC gain and the ONT receive window, and rank every standard split ratio for feasibility on the plant you have.
Do it withPON Optical Budget Calculator Free Open the tool →Loss figures default to typical datasheet values. Replace them with the figures for the parts you install and confirm the link with an OTDR and a light source and power meter test.
From other disciplines
Further reading
Free tools are free on a Standard account, with no time limit. Pro tools are included in the 14-day trial on every new account. No credit card.
