FOA CFOS/T flashcards

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

dBm definition

Power relative to 1 milliwatt: dBm = 10 log10(P/1 mW). 0 dBm is 1 mW, −10 dBm is 0.1 mW, and −20 dBm is 10 microwatts.

Reference method one-jumper

Source and meter are joined through a single launch cord to establish reference power; the link under test is then inserted, and the measured difference is the link's insertion loss.

Two-jumper reference

Reference is set through two launch cords, so the reference includes one extra connector compared with the one-jumper method; results differ by roughly one connector loss.

Dead zone pulse width rule

Dead zone scales with pulse width. Short pulses give fine resolution and short dead zones but less range; long pulses reach farther but merge closely spaced events.

Launch and receive fiber

Sacrificial fiber coils placed before and after the link so the OTDR's own connector and dead zone fall outside the link, allowing the near-end connector to be measured.

Gainer splice effect

When two fibers have different backscatter, a splice can read as negative loss in one direction. Bidirectional averaging is required for valid splice loss values.

IOR setting on OTDR

Refractive index of the fiber, typically 1.467–1.470 for single-mode at 1310 nm. An incorrect IOR scales all reported distances proportionally.

Visual fault locator range

A red 635–650 nm laser that scatters at breaks and tight bends. Effective range is roughly 2–5 km in single-mode, limited by fiber attenuation.

VFL blink mode

Pulsed output that makes the target fiber visibly flash, distinguishing it from adjacent fibers when tracing through a bundle or patch panel.

Fiber identifier use

A clamp-on tool that detects traffic or a test tone without disconnecting the fiber, used to identify live fibers safely before any work.

IEC 61300-3-35 zones

Endface acceptance zones: Zone A core must be defect-free; Zone B cladding to 25 µm allows defects ≤3 µm; Zones C and D allow defects ≤10 µm.

Wet then dry cleaning

Apply 99% isopropyl alcohol or cleaning fluid to a lint-free wipe, clean the endface, then dry with a clean wipe to remove residue before inspection.

Inspection magnification

Endface inspection uses roughly 200× for multimode and 400× for single-mode connectors; lower magnification cannot resolve core-zone defects.

Contaminated connector risk

A particle on the core can block a large fraction of the core area, cause high loss, and scratch or crack the glass permanently on mating.

Insertion loss formula

IL in dB equals reference power minus test power, both in dBm: IL = P_ref − P_test, measured at the operating wavelength with clean connectors.

OLTS function

An optical loss test set pairs a stabilized source with a power meter, often at two wavelengths, to measure insertion loss and certify links.

Return loss meter

Measures reflected power at a connector or link, reported in dB. PC connectors are typically ≤−40 dB and APC connectors ≤−60 dB.

Loss budget formula

Allowable loss equals transmitter output minus receiver sensitivity, minus margin. Installed loss must stay below this value at every operating wavelength.

Splitter loss values

Excess loss by ratio: 1:2 about 3.5 dB, 1:4 about 7 dB, 1:8 about 10.5 dB, 1:16 about 14 dB, 1:32 about 17.5 dB.

Attenuation coefficients

Typical values: 850 nm multimode 3.0–3.5 dB/km, 1300 nm multimode 1.0–1.5 dB/km, 1310 nm single-mode 0.35 dB/km, 1550 nm single-mode 0.20–0.25 dB/km.

Chromatic dispersion

Pulse broadening from wavelength-dependent propagation speed, expressed in ps/nm·km. It is compensated optically or electronically in high-rate and DWDM systems.

Polarization mode dispersion

Differential delay between polarization states, expressed in ps/√km and specified as a statistical link value. It limits high-rate transmission over long spans.

PON test wavelengths

GPON uses 1310 nm upstream, 1490 nm downstream, and 1550 nm for video overlay. Test equipment must be filtered to the correct wavelength.

PON OTDR limitation

A standard OTDR cannot test through a live splitter because the pulse is distributed to all subscribers and traffic interferes. A PON-optimized OTDR with a filtered test port is required.

PON power meter

Measures upstream and downstream power simultaneously and must be set for the correct PON technology, since burst-mode upstream power differs from continuous downstream power.

Measurement uncertainty

The range within which the true value lies. A 1.0 dB loss with ±0.3 dB uncertainty means the true loss is likely between 0.7 and 1.3 dB.

Root-sum-square combination

Independent uncertainty contributions combine as the square root of the sum of squares, not by simple addition, giving a smaller and more realistic total uncertainty.

Premises versus outside plant

Premises links are short so connector loss dominates; outside plant spans are long so fiber attenuation and splice loss dominate and require bidirectional OTDR testing.

Test report contents

Record date, technician, instrument model and serial number, calibration due date, wavelength, reference method, test direction, measured value, and acceptance criteria.

OTDR bidirectional testing

Testing a span from both ends and averaging splice losses cancels backscatter differences and the gainer effect, producing valid splice loss values.

Polarity verification

Confirm straight-through or crossover orientation against the as-built documentation using a VFL or fiber identifier before certifying a premises link.

Power meter wavelength setting

The meter must be set to the source wavelength because detector responsivity varies with wavelength; a mismatched setting produces an inaccurate reading.