FOA CFOS/H flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Single-mode fiber core size

SMF has a core of about 8-10 µm and carries one propagation mode at 1310 and 1550 nm, giving low attenuation and long reach for PON and home backbone links.

MMF core and use

Multimode fiber has a 50 or 62.5 µm core, carries many modes, and works with 850 nm VCSELs for short in-home backbone runs, with higher attenuation than SMF.

GPON wavelengths

GPON uses 1310 nm upstream and 1490 nm downstream, with 1550 nm reserved for RF video overlay, so filters and splitters must pass the correct bands.

XGS-PON wavelengths

XGS-PON uses 1270 nm upstream and 1577 nm downstream at 10 Gbit/s symmetric, coexisting with GPON on the same ODN through wavelength-selective coexistence elements.

Splitter insertion loss

Splitter loss is fixed by ratio: about 3.5 dB for 1:2, 7.2 dB for 1:4, 10.5 dB for 1:8 and 17 dB for 1:32, and it applies in both directions.

APC versus UPC polish

APC ferrules are angled 8° and return about -60 dB reflectance, while UPC returns about -50 dB; mating APC to UPC causes high loss and can damage both endfaces.

SC and LC connectors

SC uses a 2.5 mm ferrule with a square push-pull body; LC uses a 1.25 mm ferrule in a small form factor, common at ONTs and high-density panels.

Bend-insensitive fiber G.657

ITU-T G.657.A1 and A2 fiber tolerates tight bends of about 5-10 mm radius, unlike standard G.652.D at about 30 mm, which matters for in-wall and corner routing.

Cable jacket ratings

OFNP plenum cable goes in air-handling spaces, OFNR riser cable in vertical shafts, and LSZH jackets reduce smoke and halogen release in dwellings.

Minimum bend radius rule

Keep at least 10 times the cable outer diameter under load and 20 times unloaded for standard cable; G.657 drop cable allows tighter radii but never below the manufacturer's stated minimum.

Pull tension limit

Indoor drop cable typically rates 50-100 N short-term and 25-50 N long-term; pull on the strength members, never on bare fiber, and avoid jerking.

Fiber slack allowance

Leave 1-3 m of slack at the ONT or outlet and a service loop at the entry point so the link can be re-terminated, re-spliced or moved later.

Fusion splice procedure

Strip and clean the fiber, cleave it squarely, align the ends in the splicer, arc-fuse, then protect the joint with a splice protector sleeve seated in the tray.

Visual fault locator

A VFL is a red laser that makes breaks, tight bends and bad connectors glow; it locates faults but does not measure loss in dB.

OLTS reference method

The reference method sets the zero point: one-cord for a simple link, two-cord for patch cords, three-cord when both ends need a reference connector; record which was used.

OTDR launch cable

A launch cable of 100-300 m lets the OTDR see the near-end connector and first events; set the correct IOR, wavelength and pulse width before testing.

IEC 61300-3-35 zones

This standard defines endface inspection zones (core, cladding, contact, ferrule) and pass/fail criteria for scratches, pits and contamination seen with a video probe.

Loss budget formula

Link loss equals fiber attenuation times length plus connector pairs times connector loss plus splices times splice loss plus splitter loss plus a design margin.

GPON loss classes

GPON Class B+ allows 28 dB optical distribution network loss and Class C+ allows 32 dB; compare the calculated budget against the class before design.

ONT placement rules

Place the ONT near the entry point on a power outlet, with ventilation, access for testing and reasonable Wi-Fi coverage; avoid basements and closed metal enclosures.

As-built documentation

The as-built package holds the topology drawing, cable schedule, loss budget, test reports, equipment serials and labels, and it is the reference for later changes.

Spare fiber per drop

Reserve at least one spare fiber or conduit per drop so a future 10G service or second provider can be added without opening finished walls.

Cleaving quality effect

A square cleave from a clean cleaver gives splice loss near 0.1 dB; a chipped or angled cleave causes high loss or a failed splice and must be re-cleaved.

Polarity test for duplex

Duplex links must be checked A-to-B and B-to-A with a source and meter or VFL pair; reversed polarity shows as no light at the receiver.

Macrobend symptom

A tight bend adds loss that is worse at 1550 nm than at 1310 nm and often disappears when the cable is straightened, which distinguishes it from a bad splice.

OTDR event signatures

A reflective spike indicates a connector, a non-reflective step indicates a splice or bend, and the event distance is compared with the cable schedule to locate it.

Field-installable connector loss

Field-installable connectors typically show 0.5-0.75 dB insertion loss, higher than factory pigtails fusion-spliced at about 0.1-0.3 dB, so budget accordingly.

Firestopping penetration rule

Seal every penetration through fire-rated walls and floors with listed materials and use the jacket rating required by the space to keep the fire separation intact.

Design margin rule

Keep at least 3 dB of margin in the loss budget to cover aging, repairs, temperature variation and connectors added after the initial installation.

Fiber scrap safety

Cleaved fiber scraps are sharps: keep a labeled waste container, wear safety glasses when cleaving, and never leave scraps on floors or in clothing.

Laser eye hazard

Never look into a fiber end or unmated connector; infrared light at 1310 and 1550 nm is invisible and can damage the retina even at modest power.

Acceptance handover gate

Before handover confirm every link passes the loss budget, polarity is correct, labels match the as-built, and signed test reports are delivered to the owner.