FOA CFOS/C cheat sheet

Total internal reflection occurs when light in the core strikes the core-cladding boundary above the critical angle; the critical angle is arcsin(n_cladding / n_core).

Numerical aperture NA = sqrt(n_core^2 - n_cladding^2); NA relates to maximum acceptance angle by sin(theta_max) = NA in air.

Step-index multimode has a uniform core index and high modal dispersion; graded-index multimode tapers the index to equalize path lengths and reduce modal dispersion.

Single-mode fiber carries one mode at 1310 nm and 1550 nm; typical core diameter is 8-10 um with a 125 um cladding.

Standard multimode core/cladding sizes are 50/125 um (OM2-OM5) and 62.5/125 um (OM1); OM3/OM4 are laser-optimized 50 um fibers.

Attenuation is lowest at 1550 nm (about 0.2 dB/km) and higher at 1310 nm (about 0.35 dB/km); 850 nm multimode loss is typically 2.5-3.5 dB/km.

Macrobend loss rises at longer wavelengths and small bend radii; microbend loss comes from random mechanical stress on the fiber axis.

Workforce roles: installer/technician, splicer, tester, inspector/cleaner, designer, and project manager; each maps to separate skill and certification scopes.

Safety: never look into a fiber end or connector; treat all fiber as potentially live and use appropriate eye protection and laser-safety procedures.

ANSI/TIA-568 defines cabling categories: Cat 5e, Cat 6, Cat 6A, and Cat 8 for copper; OM1-OM5 multimode and OS1/OS2 single-mode for fiber.

Maximum horizontal copper channel length is 90 m permanent link plus 10 m of patch cords, totaling 100 m.

Backbone fiber distances depend on fiber type and application; OM4 supports 10GBASE-SR to about 400 m and OS2 supports 10GBASE-LR to 10 km.

TIA-569 covers pathways and spaces; TIA-606 covers administration and labeling; TIA-607 covers bonding and grounding.

Fiber connector types include SC, LC, ST, and MPO/MTP; LC is the common small-form-factor choice for high-density premises links.

Polarity for duplex fiber uses A-to-B (straight) or A-to-A with a crossover; MPO trunk polarity uses Method A, B, or C per TIA-568.

Cable jacket ratings: plenum (CMP) for air-handling spaces, riser (CMR) for vertical shafts, and general-purpose (CM/CMX) elsewhere.

Bend radius rules: typically 10x cable OD during installation and 20x OD under load; follow manufacturer data for installed fiber.

Separation from power: maintain required clearance between communications and electrical pathways per TIA-569 and applicable codes.

Pull tension limits: typical multimode and single-mode premises cable allow about 220-300 N (50-70 lbf) during installation; consult the cable datasheet.

Do not exceed minimum bend radius; kinks and tight loops cause permanent macrobend loss that may not appear until testing.

Support horizontal cable at intervals per TIA-569; avoid stapling or cinching that deforms the fiber or copper pairs.

Leave service loops at both ends; label both ends of every cable using the TIA-606 administration scheme.

Splice trays and enclosures must maintain bend radius and protect splices; fusion splices typically show 0.1 dB or less loss.

Connector termination must be clean and polished; field-installable connectors require a cleave and proper curing or mechanical locking.

Firestopping is required where cables penetrate rated walls or floors; use listed materials and restore the fire rating.

Workmanlike installation: no cable damage, no exposed conductors, proper grounding/bonding, and documentation of as-built pathways.

Installation inspection should verify pathway support, bend radius, labeling, firestopping, and connector cleanliness before testing.

Loss budget: total link loss = sum of fiber attenuation (dB/km x km), connector losses, splice losses, and a safety margin.

Typical connector loss is 0.3-0.75 dB per mated pair; typical fusion splice loss is 0.1-0.3 dB; mechanical splice loss is higher.

Tier 1 testing uses an OLTS (light source and power meter) to measure insertion loss and length; Tier 2 adds an OTDR for event and reflection analysis.

OTDR dead zones: event dead zone limits close-event resolution; attenuation dead zone limits loss measurement of nearby events.

Reference method matters: one-jumper, two-jumper, and three-jumper references produce different loss values; document the method used.

Inspection: use a fiber inspection scope; IEC 61300-3-35 defines pass/fail criteria for connector end-face zones.

Cleaning rule: inspect, clean, and re-inspect every connector before mating; use lint-free wipes and approved cleaning tools.

Never use compressed air or alcohol on connectors unless the manufacturer specifies it; contamination causes high loss and damage.

Test wavelength must match the application (850/1300 nm multimode; 1310/1550 nm single-mode); record all results in a test report.

Design starts with the application requirements: bandwidth, distance, protocol, topology, and environmental conditions.

Choose fiber type by reach: multimode for short building/campus links, single-mode for long-haul and high-bandwidth links.

Link loss budget must include connector pairs, splices, fiber attenuation, and margin; verify computed loss is below the transceiver budget.

Topology options: point-to-point, star, ring, and passive optical LAN (PON) split architectures; each changes loss and component count.

Project phases: requirements, design, procurement, installation, testing/acceptance, and as-built documentation.

Schedule and cost control use work breakdown structure, milestones, and change control; track materials, labor, and test results.

Risk management covers pathway availability, permitting, weather, and material lead times; plan contingencies.

Acceptance criteria should reference the standard used (e.g., TIA-568, IEC 61300-3-35) and include test reports and labeling records.

Documentation deliverables: as-built drawings, cable schedules, test results, and warranty/commissioning records.