Punjab PSEB Sr. Sec. NSQF Telecom (Optical Fibre Technician) flashcards

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

Total internal reflection

The confinement mechanism in optical fibre: light in the higher-index core striking the core–cladding boundary above the critical angle reflects back into the core instead of refracting out.

Numerical aperture

NA = √(n1² − n2²), a measure of the fibre's light-gathering cone; its value equals the sine of the maximum acceptance half-angle.

Single-mode fibre core size

About 8–10 µm, small enough to support one propagation mode at 1310 and 1550 nm, which removes modal dispersion and allows long-haul transmission.

Attenuation in decibels

Loss expressed as 10 log10(Pin/Pout); typical single-mode values are about 0.35 dB/km at 1310 nm and 0.20 dB/km at 1550 nm.

Rayleigh scattering loss

Loss from microscopic refractive-index fluctuations frozen into the glass; it scales as 1/λ⁴ and sets the fundamental attenuation floor of silica fibre.

Twelve-fibre colour code

Blue, Orange, Green, Brown, Slate, White, Red, Black, Yellow, Violet, Rose, Aqua; the sequence repeats per tube or group to identify each fibre position.

Loose-tube cable construction

Gel-filled tubes each holding 2–12 fibres, wrapped with strength members and a sheath; suited to outdoor duct and aerial routes with wide temperature range.

Armoured cable purpose

A corrugated steel tape layer that protects fibres from rodent attack and crush; used in direct-burial routes, often with inner and outer jackets.

Bend-insensitive G.657 fibre

A fibre design tolerating much tighter bend radii than G.652.D, preferred for FTTH drop cables and cramped premises wiring where bends are unavoidable.

LSZH jacket

Low-smoke zero-halogen sheath material used indoors; it releases little smoke and no corrosive halogen gas in a fire, unlike PVC.

Cleave angle limit

For single-mode splicing the cleave end face should be within about 0.5° of perpendicular; a poor cleave raises splice loss or causes arc failure.

Bare fibre disposal

Fibre offcuts are sharp and can penetrate skin or eyes; collect them on a dark mat and seal in a sharps container, never in general waste.

VFL safety check

A 650 nm visual fault locator confirms whether a fibre is dark before work; never view a fibre end directly because live infrared sources are invisible.

Fusion splice acceptance loss

Single-mode splices are typically accepted at ≤0.10 dB, and multimode at ≤0.20 dB, measured on the splicer and confirmed by bidirectional OTDR.

APC versus UPC connectors

APC has an 8° angled, typically green end face with ≥60 dB return loss; UPC is flat-polished. Mating APC to UPC causes high loss and damage.

Mechanical splice

A clamp-and-gel splice using index-matching gel; quick for restoration, typically 0.1–0.5 dB loss, higher than a good fusion splice.

Fusion splice sequence

Strip, clean, cleave, load into V-grooves, align, arc fuse, then apply a heat-shrink protector; each step affects final splice loss.

Connector insertion loss limit

A field-installed SC or LC connector is typically accepted at ≤0.3 dB insertion loss, with return loss ≥50 dB for UPC and ≥60 dB for APC.

Pull tension limit

Cable must be pulled below its rated maximum tension, commonly 600–2700 N by design; exceeding it stretches fibre and causes permanent loss.

Installation bend radius

A common rule is 20× cable diameter under load and 10× after installation; tighter bends cause macrobend loss, first visible at 1625 nm.

Direct burial depth

Typically 0.9–1.2 m under roadways with sand bedding and warning tape, shallower in verges; the exact value follows the local utility specification.

Cable blowing installation

Cable is propelled through duct or microduct by air pressure and a feeder, reducing tension and allowing long runs compared with pulling.

OTDR distance formula

Distance d = (c × t)/(2 × IOR), where t is round-trip time and IOR is the group index, about 1.468 for G.652 at 1550 nm.

OTDR pulse width trade-off

Short pulses resolve closely spaced events near the launch; long pulses reach farther but blur nearby events and reduce spatial resolution.

Bidirectional OTDR testing

Measuring a splice from both ends and averaging removes the apparent gain or loss error caused by backscatter differences between the two fibres.

Link loss budget

Total allowed loss equals fibre loss plus connector and splice losses plus a margin, usually about 3 dB, compared with the transceiver's specified budget.

GPON wavelengths

GPON uses 1490 nm downstream, 1310 nm upstream and 1550 nm for video overlay; testing at the wrong wavelength misrepresents live PON loss.

Splitter loss values

Typical insertion loss is about 10.5 dB for 1:8, 13.5 dB for 1:16 and 16.5 dB for 1:32, plus excess loss, and must be included in the FTTH budget.

ONT receive power range

GPON ONTs typically accept about −8 to −27 dBm; a reading outside this range indicates a dirty connector, bend, or excessive splitter loss.

FTTH drop cable handling

Flat 1–2 fibre drop cable with FRP strength members must be clamped, not stapled through, and routed within its bend radius away from electrical cabling.

Baseline OTDR trace

A stored trace per fibre and wavelength taken after commissioning; later faults are found by comparing current traces with this reference.

Splice schedule document

A record mapping each fibre and tube colour to its splice position, closure and port; it must be updated after every splice or re-termination.

Fault ticket content

A record of alarm time, affected services, test results, restoration action and root cause, used for SLA reporting and trend analysis.

NSQF level meaning

A national skills framework level describing responsibility and autonomy, from supervised work at lower levels to independent and supervisory roles higher up.

Technical fault reporting

Reporting with specific data such as fibre ID, wavelength, measured loss in dB and fault distance in metres, rather than general descriptions of poor service.

Contractor cost estimation

Calculating cost per splice or per kilometre from labour, materials and equipment depreciation, then adding margin and taxes before quoting a client.