Choice 1: the fibre
Single-mode fibre to ITU-T G.652.D is the default for access, metro and long-haul networks: 125 um cladding with a coating of about 242 um, or 200 um in reduced-diameter versions. Bend-insensitive G.657 fibre is used where routes are tight, such as FTTH drops, risers and indoor boxes. G.657.A1 allows a minimum bend radius of 10 mm, A2 and B2 7.5 mm and B3 5 mm, and the A category is compatible with G.652.D, so it can be spliced into the same network. Multimode fibre stays inside buildings and data centres: OM3, OM4 and OM5 are 50/125 um fibres graded by effective modal bandwidth at 850 nm of at least 2,000 MHz.km for OM3 and 4,700 MHz.km for OM4; OM5 adds a 953 nm specification of 2,470 MHz.km for wavelength-division links. For 10G Ethernet over OM4, 400 m is the distance commonly quoted for IEEE 10GBASE-SR.
Attenuation values are given per datasheet for the fibre and cable you order. Where no cable figure is available, older TIA-568 planning values are often used: 3.5 dB/km at 850 nm and 1.5 dB/km at 1300 nm for multimode, 1.0 dB/km indoor and 0.5 dB/km outdoor for single-mode, 0.75 dB per mated connector pair and 0.3 dB per splice. Use the cable maker's spec where available. See optical fibre.
Choice 2: the cable
| Cable type | Construction | Typical cores | Main use |
|---|---|---|---|
| Indoor tight-buffered | 0.9 mm tight buffers, aramid yarn, PVC or LSZH jacket | 2-144 | Risers, floors, equipment rooms |
| Outdoor loose tube | Gel-filled tubes, central strength member, PSP or APL tape, PE sheath | 2-288 | Duct, aerial lashed, armoured for burial |
| ADSS aerial | Loose tubes on a central FRP, aramid strength, PE or AT sheath | Per span design | Pole lines and power line routes |
| FTTH drop | G.657 fibres, FRP or steel strength members, LSZH jacket | 1-2 | Last drop into the premises |
| Patch cords | 2.0 or 3.0 mm jacket, SC or LC | 1-2 | Panels, ONTs, equipment |
The 24-core GYTS reference is about 10 mm in diameter, but weight varies by around 50% between makers, so weight is always taken per datasheet. ADSS must be selected for the span and the weather loading: a cable that suits a 100 m span may only manage about 50 m in heavy ice. Sheath choice between PE and anti-tracking AT depends on the field strength along the line, calculated for the route. In the EU, fibre cable permanently installed in buildings falls under EN 50575 and needs a CPR class; in the US, NEC 770 grades such as OFNR and OFNP apply.
Choice 3: the core count
Count the fibres needed on day one, add spares for repairs and growth, then round up to the nearest standard tube count. Loose tube cables are built from tubes of a fixed fibre count, so a 24-core and a 48-core cable may differ only in the number of tubes, while the jump to a larger tube design can change diameter and drum length. Fibres and tubes are identified by the TIA-598 colour code unless your network uses another scheme, which must be written on the spec sheet. See fibre cable core counts.
Drum length belongs in the same decision. Outdoor and ADSS cable commonly ships on 2 km or 4 km drums and drop cable on 1 km reels, but the right length is the one that matches your splice points, so that crews do not cut short ends off every drum. Give the route lengths or the splice plan and the desk sets the drum plan with the plant before production, with start and end metre marks recorded for every drum.
Choice 4: connectors and polish
SC and LC are the common single-mode connectors; LC dominates in high-density panels. UPC polish suits most data links, while APC is used where back-reflection matters, such as FTTH and video overlays. IEC 61753-1 sets the grades: Grade B random-mated insertion loss averages 0.12 dB or less with 97% of matings at 0.25 dB or less, Grade C averages 0.25 dB or less, and return loss is at least 60 dB for Grade 1 (APC) and 45 dB for Grade 2 (UPC). State the grade you need rather than asking for low loss.
Choice 5: test data
- Attenuation per fibre at the agreed wavelengths, listed by drum and fibre colour.
- OTDR traces for each fibre on each drum, so that splicing crews can compare after installation.
- Insertion and return loss for every patch cord or pigtail, against the IEC 61753-1 grade.
- Drum ledger: drum number, length, start and end metre marks and fibre count, matched to the packing list.
Outdoor cable is commonly built to Telcordia GR-20 and indoor cable to GR-409; ask the plant which reports cover your construction. Fibre and fibre cable are mainly sourced from Wuhan Optics Valley and Qidu in Wujiang. Lead time is set by fibre and tube scheduling and confirmed in writing for each order; see MOQ and lead time.