FTTH Components, Hardware and Optical Distribution Networks
What this domain tests
Questions here ask you to identify hardware, pick the right part for a given location, and know which component choices change the optical budget. You need the active elements, the splitter family, outside-plant hardware and premises hardware, plus connector polish.
Active elements and splitters
- OLT – chassis with uplink and PON line cards, one PON port per ODN.
- ONT/ONU – subscriber unit providing Ethernet, VoIP, IPTV or RF video and Wi-Fi.
- Splitter – planar lightwave circuit (PLC) is the PON standard: broadband, thermally stable, available to 1:64. Fused biconic taper (FBT) splitters are cheap at 1:2 and 1:4 but wavelength-sensitive.
- WDM coupler – combines the 1550 nm video overlay with the 1490/1310 nm PON wavelengths.
Outside-plant hardware
An FDH or fiber distribution cabinet holds the splitter, splice trays and a parking lot for unused connectors. Splice closures come as dome, inline or butt types; below grade you may use pedestals or handholes. Multiport drop terminals (4, 8 or 12 ports) carry hardened SC/APC adapters. Cable is ADSS or lashed to strand aerially, and pulled through conduit or innerduct underground.
Premises hardware
Flat drop cable (about 2 × 3 mm, LSZH jacket, dielectric strength members, G.657 bend-insensitive fiber), SC/APC connectors with green bodies for PON ports, LC/APC for high-density panels, an ONT enclosure or NID at the demarcation point, riser cable and MDU boxes, pigtails, splice trays, adapters and patch panels.
Polish matters
APC is an 8° angled polish giving return loss of 60 dB or better; UPC gives 50 dB or better. Mate like with like: an APC plug in a UPC adapter produces high loss, high reflectance and can damage the ferrule.
Worked example
Compare one 1:32 splitter at the FDH with a cascade of 1:8 at the FDH plus 1:4 near the premises. Splitter loss is 17.0 dB against 10.5 + 7.2 = 17.7 dB, and the second splitter adds a splice (0.1 dB) and a connector pair (0.5 dB), so the cascade costs about 1.3 dB more. It cuts distribution fiber count by four, which is usually worth the loss in suburban MDU work but not on a long rural reach.
Traps
Forgetting PLC excess loss; specifying FBT for 1:32; mixing APC and UPC; using indoor-rated drop cable on a facade; bending cable tighter than the splice tray rating; and assuming preterminated assemblies can be re-routed like field-terminated cable.