Access Network

TDM-PON: one fiber, dozens of subscribers. The point-to-multipoint networks that fill most of the access plant start with a single OLT port driving a tree of ONUs through a passive optical splitter — 1:32, 1:64, up to 1:256 — with downstream and upstream on different wavelengths so one fiber carries both directions. Every ONU therefore holds one BOSA, a bidirectional sub-assembly that transmits and receives through the same port; the OLT side pairs a high-power TOSA with a high-sensitivity ROSA/APD. Beside that traffic path, operators hang a monitoring layer on the OLT — a MEMS optical switch plus an OTDR — so one instrument polls the health of every fiber in the plant.

The same PON is moving into the enterprise. Passive Optical LAN (POL) replaces floors of Ethernet switches with a passive ODN, pulling fiber to the desktop and to the room. There is no active electronics in the riser to power, cool or maintain — the fiber plant runs silent from the OLT to every office — which is why greenfield campuses and smart buildings are standardizing on PON instead of three-tier switching.

Three generations share one ODN. GPON (1490 nm down / 1310 nm up), XGS-PON (1577 / 1270 nm) and 50G PON (1342 nm down; upstream 1260–1280, 1290–1310 or 1284–1288 nm) coexist on the same fiber by wavelength — an operator adds a next-generation line card without touching the splitter. That coexistence is a Filter WDM job: thin-film combiners fold the generation bands onto one fiber at the OLT, the same mux/demux discipline our WDM lines build every day, with our IWDM hybrids adding isolator and monitor functions for OLT line cards.

Built for the volume and the elements. A 1:64 split means sixty-four BOSAs per OLT port — access optics ship in the tens of millions. Our TOSA/ROSA/BOSA lines run at that scale with consistent wavelength accuracy and Telcordia GR-1221 / GR-468 qualification, and hermetic receptacles seal the outdoor ONUs, street cabinets and pole-mounted OLTs against humidity and condensation.