FOA CFOS/L cheat sheet

Total internal reflection occurs when light traveling in the core strikes the core-cladding boundary above the critical angle; the refractive index of the core must exceed that of the cladding.

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

Step-index multimode has a uniform core index; graded-index multimode tapers the index toward the cladding to reduce modal dispersion and increase bandwidth.

Single-mode fiber has a small core (about 8-10 um) and a much larger cladding (typically 125 um); multimode cores are commonly 50 um or 62.5 um with 125 um cladding.

Attenuation is expressed in dB/km; loss in dB = 10 x log10(P_in / P_out), and a link's total loss is the sum of fiber, splice, and connector losses.

Operating windows: 850 nm and 1300 nm for multimode, 1310 nm and 1550 nm for single-mode; 1550 nm has the lowest attenuation but bend sensitivity increases.

Dispersion limits bandwidth-distance product; modal dispersion dominates multimode, while chromatic and polarization-mode dispersion dominate single-mode at high rates.

Premises cabling hierarchy runs entrance facility, equipment room, backbone cabling, telecommunications room, horizontal cabling, and work area; the horizontal run is limited to 90 m of cable plus cords.

Outside plant cable uses loose-tube construction with water-blocking gel or dry-blocking yarn; indoor cable uses tight-buffered fibers for direct connectorization.

Plenum-rated cable (CMP/OFNP) uses low-smoke, low-flame-spread materials and may be installed in air-handling spaces; riser (CMR/OFNR) and general-purpose (CM/OFN) ratings apply elsewhere.

Standard single-mode connector polish is UPC (angled 0 degrees, typical return loss better than 50 dB) or APC (8-degree angle, better than 60 dB); APC and UPC must never be mated.

Common premises connectors include SC (square, push-pull), LC (small form factor, 1.25 mm ferrule), and ST (bayonet, 2.5 mm ferrule); MT-based MPO/MTP connectors carry 8 to 24 fibers.

Multimode fiber types are OM1 (62.5/125), OM2 (50/125), OM3 and OM4 (laser-optimized 50/125), and OM5 (wideband 50/125); single-mode is OS1/OS2.

Connector loss budgets typically allow 0.3 dB per mated pair for good field terminations and 0.75 dB or better for worst-case planning; fusion splices are typically 0.1-0.3 dB.

Fiber color code: blue, orange, green, brown, slate, white, red, black, yellow, violet, rose, aqua for fibers 1-12; repeat with tracers for higher counts.

Patch cords must match fiber type and connector polish; hybrid or mode-mismatched cords create high loss and unreliable links.

Pull tension limits: typically 25 lbf (110 N) for tight-buffered indoor cable and up to 600 lbf for outside plant cable; never exceed the manufacturer's rating.

Minimum bend radius during installation is commonly 20x cable diameter and 10x cable diameter after installation for indoor cable; fiber bend radius inside enclosures follows the same rule.

Never exceed a 25 mm (1 in) cable tie or support spacing for horizontal cable and use hook-and-loop or Velcro rather than zip ties on fiber.

Cable trays and J-hooks must support cable continuously; fill ratios and weight limits per the tray manufacturer and local code apply.

Keep fiber and copper separated where practical and maintain separation from power conductors per code; do not run fiber in the same conduit as high-voltage wiring without proper barriers.

Leave a service loop of at least 1 m (3 ft) at each end and in enclosures; slack allows retermination and accommodates future moves.

Firestopping is required wherever a cable penetrates a rated floor or wall; use listed firestop systems and document the installation.

Label both ends of every cable and each fiber strand with a unique identifier before pulling, and record strand assignments in the as-built documentation.

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

Set the reference (one-jumper, two-jumper, or three-jumper method) before testing; the chosen method determines whether connector loss is included in the measured result.

Clean and inspect every connector end-face before mating; use a scope with 200x/400x magnification and dry or wet-dry cleaning per the connector type.

Loss budget = fiber attenuation (dB/km x length) + splice losses + connector losses + a margin (commonly 3 dB for future repairs and aging).

Example: 500 m of OM4 at 3.0 dB/km = 1.5 dB; add 2 connectors at 0.3 dB each and 3 dB margin for a total budget of about 5.1 dB.

Pass/fail criteria come from the standard or the project specification; the calculated loss budget must not be exceeded by the measured insertion loss.

OTDR testing requires launch and receive cables of sufficient length (typically 100 m or more) to measure the near-end and far-end connectors accurately.

Document test results per strand and per link, including wavelength, reference method, instrument serial number, and date, for acceptance and warranty.

Design topologies (point-to-point, star, ring, mesh) based on redundancy, distance, and port count; fiber links are typically point-to-point between active equipment.

Channel length limits: 90 m horizontal cable plus 5 m work-area cord plus 5 m patch cord in the telecommunications room for a 100 m channel.

Backbone distances depend on fiber type and application; OM3/OM4 support 10GBASE-SR to 300/400 m, while OS2 supports 10GBASE-LR to 10 km.

Project phases: requirements and site survey, design and documentation, procurement, installation, testing and acceptance, and closeout with as-builts.

As-built documentation includes cable schedules, strand assignments, rack elevations, test reports, and firestop records; deliver them at project closeout.

Change control: any deviation from the design (routing, connector type, fiber count) requires written approval and an updated drawing before installation.

Use a bill of materials derived from the design and verify quantities against the cable schedule; track serialized equipment and test instruments.

Schedule and risk planning must account for lead times on cable and connectors, permit and inspection windows, and access to occupied spaces.