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

The complete bouncing back of light inside a denser medium when it strikes the boundary with a rarer medium at an angle steeper than the critical angle; this effect keeps light guided along an optical fibre core.

The smallest angle of incidence, measured from the normal, at which light travelling in a denser medium is totally reflected at the boundary instead of passing into the rarer medium.

A number showing how much slower light travels in a material than in vacuum; a higher value means denser material and stronger bending of light at the surface.

A measure of the range of angles from which a fibre can accept incoming light; a larger value means easier coupling of light but usually higher dispersion in multimode fibre.

The maximum half-angle of a cone of light that can enter a fibre core and still be guided; it is derived directly from the numerical aperture of the fibre.

An optical fibre with a very small core, about 8 to 10 micrometres, that carries one propagation path; it gives low loss and high bandwidth over long distances such as backbone and FTTH links.

A fibre with a larger core, typically 50 or 62.5 micrometres, that carries many light paths at once; used for short spans inside buildings and data centres because connectors are cheaper and alignment easier.

The loss of optical power as light travels along a fibre, caused by absorption and scattering; it is measured in decibels per kilometre and limits how far a signal can travel without regeneration.

Loss caused by tiny random variations in glass density that scatter light in all directions; it is the dominant loss in single mode fibre at 1310 and 1550 nanometres and cannot be removed.

Extra attenuation around 1385 nanometres caused by hydroxyl ions trapped in the glass; low-water-peak fibre reduces this so the whole band from 1260 to 1625 nanometres can be used.

Spreading of a light pulse as it travels, which blurs adjacent pulses and limits bit rate; it comes from different path lengths or different wavelengths travelling at slightly different speeds.

Pulse spreading caused by a light source containing a range of wavelengths, each travelling at a slightly different speed in the glass; it matters most on long single mode links.

Pulse spreading in multimode fibre because different light paths have different lengths and arrive at slightly different times; it is the main reason multimode is limited to short distances.

A technique that sends several signals at different wavelengths through one fibre at the same time, greatly increasing capacity; coarse and dense versions differ in channel spacing and count.

A logarithmic unit used to express ratios of optical power; in fibre work it describes loss or gain, and a loss of 3 decibels means half the power is gone.

A factory-made assembly containing one or more coated fibres inside loose tubes or tight buffers, plus strength members and an outer sheath that protect the glass from tension, moisture and abrasion.

A cable design in which fibres sit loosely inside gel-filled plastic tubes, allowing them to move slightly and avoid strain; common for outdoor duct and aerial routes.

A cable where each fibre is coated directly with a protective plastic layer, giving a small bend radius and easy handling; used mainly for indoor patch cords and riser wiring.

A cable with a steel tape or wire layer under the outer sheath that resists rodent attack, crushing and accidental digging damage; often used in direct-buried or harsh routes.

A standard sequence of twelve colours, blue, orange, green, brown, slate, white, red, black, yellow, violet, rose and aqua, used to identify fibres and tubes in a cable.

Joining two fibres permanently by cleaning and cleaving their ends, aligning them in a splicer and melting them together with an electric arc; it gives the lowest loss and highest reliability.

A small reusable device that holds two cleaved fibre ends in a precision groove with index-matching gel; quick and tool-light but usually higher loss than fusion splicing.

Scoring and breaking the fibre so it ends in a flat surface square to the axis; a good cleave is essential for low splice loss and reliable connector fitting.

The optical power lost at a joint, expressed in decibels; it rises with core misalignment, poor cleave angle, dirt or a mismatch between the two fibres being joined.

The total power lost when a connector pair or device is inserted into a link, measured as the difference between input and output power and usually kept below half a decibel.

A measure of how much light is reflected back towards the source at a connector or splice; higher values mean better performance, and dirty end faces quickly degrade it.

A connector design in which the two polished ferrules press directly together, removing the air gap; common variants are flat, angled and ultra-polished end faces.

The small precision ceramic or metal tube that holds and centres the bare fibre inside a connector; its hole diameter and concentricity largely decide connector loss.

A short length of fibre with a factory-fitted connector on one end and bare fibre on the other, spliced to a cable fibre to provide a termination point.

A test instrument that sends short light pulses into a fibre and graphs the returning reflections against distance, revealing loss, splice points, connectors and breaks along the route.

A short distance after a strong reflection where the instrument cannot detect weaker events; it is reduced by using shorter pulses and is reported as event or attenuation dead zone.

Light reflected back at a point where the refractive index changes abruptly, such as an air gap or connector; it appears on a trace as a sharp spike and helps locate breaks.

A calibrated instrument that displays received optical power in decibel-milliwatts or microwatts; paired with a light source it is used for end-to-end loss testing.

A small visible red laser tool that injects light into a fibre so breaks, tight bends and damaged connectors glow visibly; useful for quick fault finding over short distances.

The minimum safe curve into which a fibre or cable may be bent without added loss or permanent damage; it is usually stated as a multiple of the cable diameter.

Extra attenuation caused by bending a fibre tighter than its recommended radius, which lets guided light escape the core; it is often visible at 1625 nanometres before other wavelengths.

The customer premises device that converts optical signals from the fibre into electrical Ethernet, telephone and video services, and is the official demarcation point of an FTTH connection.

A passive device that divides one incoming fibre into several outputs, usually in ratios such as 1:8 or 1:32; it is the key building block of a passive optical network.

The equipment at the service provider's exchange or central office that manages the passive optical network, sends downstream traffic to all users and collects upstream bursts from them.

An access network architecture in which optical fibre runs all the way to the customer's living unit, allowing much higher broadband speeds than copper-based connections.

A rack-mounted panel where incoming and outgoing fibre cables are terminated and cross-connected; it gives organised access for testing, re-routing and future expansion.