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

Total internal reflection occurs when light travelling in the core strikes the core–cladding boundary at an angle greater than the critical angle; it then reflects back into the core with negligible loss.

Critical angle: sin θc = n2/n1, where n1 is core refractive index and n2 is cladding refractive index; a larger index difference gives a smaller critical angle and stronger confinement.

Numerical aperture: NA = √(n1² − n2²) ≈ n1√(2Δ), with Δ = (n1 − n2)/n1; NA sets the acceptance cone half-angle, sin θmax = NA.

Single-mode fibre has a core of about 8–10 µm and supports one mode at 1310/1550 nm; multimode fibre has a 50 or 62.5 µm core and carries many modes, causing modal dispersion.

Attenuation is expressed in dB: loss(dB) = 10 log10(Pin/Pout); typical SMF windows are 1310 nm (~0.35 dB/km), 1550 nm (~0.20 dB/km) and 1625 nm for live-fibre testing.

Dispersion limits bandwidth: chromatic dispersion (material plus waveguide) broadens pulses in single-mode fibre, while modal dispersion dominates in multimode; 1310 nm is the zero-dispersion point of standard SMF.

Bending loss has two forms: macrobend loss from visible loops (worst at long wavelengths, so 1625 nm detects it first) and microbend loss from microscopic axis deviations.

Rayleigh scattering, caused by refractive-index fluctuations frozen into the glass, is the fundamental loss floor and scales as 1/λ⁴; it is the main loss at 1310 nm.

Standard 12-fibre colour sequence: Blue, Orange, Green, Brown, Slate (Grey), White, Red, Black, Yellow, Violet, Rose, Aqua; groups of 12 repeat with a tracer or binder colour.

Loose-tube cables house 2–12 fibres per gel-filled tube; the tube colour identifies the group and the fibre colour identifies the position within the group.

Tight-buffered cable has a 900 µm buffer directly on the fibre and is used for patch cords and indoor risers; loose-tube construction suits outdoor duct and aerial routes.

Armoured cable adds a corrugated steel tape for rodent and crush protection; a double-jacket (inner and outer sheath) armoured design is used for direct burial.

Strength members differ by duty: aramid yarn carries tensile load in indoor and patch cables, while FRP or steel central strength members limit contraction and support aerial spans.

Cable jacket material: PE for outdoor UV and moisture resistance, LSZH for indoor fire safety and low smoke, PVC for general indoor use; never run PE indoors where LSZH is specified.

Bend-insensitive (G.657) fibre tolerates tighter radii than G.652.D and is preferred for FTTH drop and premises wiring; minimum bend radius is typically 10× cable diameter under load.

Aerial figure-8 and ADSS cables carry their own strength; ADSS uses aramid yarn and a tracking-resistant sheath because it hangs in the phase field without a messenger wire.

Fusion splicer maintenance sequence: daily arc calibration, electrode check, cleaning of V-grooves and fibre clamps, and mirror/lens cleaning with lint-free wipes and isopropyl alcohol.

Fibre stripper blade sizes must match coating: 250 µm for bare fibre, 900 µm for tight buffer, and a jacket stripper for 2–3 mm cable; wrong blade size causes nicks and splice failure.

Precision cleave angle should be ≤0.5° for single-mode; a bad cleave shows as a high estimated splice loss or an end-face defect on the splicer screen.

Laser safety: never look into a fibre end or connector; use a VFL or fibre identifier to confirm dark fibre, and treat 1310/1550 nm sources as invisible Class 1M/3R hazards.

Bare fibre fragments are a skin and eye hazard: work on a black mat, use tweezers, and dispose of offcuts in a sealed sharps container, never in general waste.

Chemical safety: isopropyl alcohol is flammable and a respiratory irritant, so use it in a ventilated area away from arcs and ignition sources; uncured splice gel or epoxy needs gloves.

Optical power meter and OTDR must be connector-matched: inspect and clean every ferrule with a one-click cleaner before mating, since a single dust particle can add several dB of loss.

Tool calibration records and splicer arc-count logs are quality documents; a splicer with worn electrodes shows rising splice loss and should have electrodes replaced near the rated count.

Fusion splicing steps: strip, clean with alcohol, cleave, load into V-grooves, align (core or cladding), arc fuse, then heat-shrink protect with the splice protector sleeve.

Acceptable single-mode fusion splice loss is typically ≤0.10 dB (often ≤0.05 dB); multimode splices are usually accepted at ≤0.20 dB.

Estimated splice loss from the splicer is a relative arc-based figure; confirm critical splices with an OTDR in both directions and average the two readings.

Mechanical splices use index-matching gel and a clamp; they suit emergency restoration and are typically 0.1–0.5 dB, higher than a good fusion splice.

Connector types: SC (square, push-pull), LC (small form factor, latch), ST (bayonet), FC (threaded); PC, UPC and APC refer to end-face polish, and APC (8° angled) must never be mated with PC/UPC.

Typical insertion loss limits: ≤0.3 dB for a field-installed SC/LC connector and ≥50 dB return loss for UPC, ≥60 dB for APC.

Field-installable connectors may be fusion-pigtail, mechanical splice-on, or epoxy-polish; pigtail splicing gives the most consistent loss and is common in FTTH.

Inspect every end face with a scope against IEC 61300-3-35 zones; scratches or pits in the core zone require re-termination, not cleaning.

Pull tension must stay below the cable's rated maximum (commonly 600–2700 N depending on design); use a swivel and pulling eye and never exceed 80% of rated tension in practice.

Minimum bend radius during installation is typically 20× cable diameter under load and 10× after installation; violation causes macrobend loss visible first at 1625 nm.

Duct installation: use correct duct size (cable OD ≤ 50–60% of duct ID), pre-install a pull rope or use blowing/jetting for long runs, and lubricate for high-friction routes.

Aerial installation: maintain specified sag and ground clearance per local utility rules; use spiral or lashing wire, and leave expansion loops at poles for thermal movement.

Underground direct burial requires sand bedding, warning tape, and a minimum cover depth (often 0.9–1.2 m under roadways, less in verges, per local specification).

Slack coils at joint chambers should be stored with a figure-8 or large loop of at least the minimum bend radius and fixed to a cable bracket, not left loose on the floor.

Blowing/jetting installs cable with air pressure and a feeder; it suits microduct and long duct runs and reduces tension compared with pulling.

Route survey and as-built records (duct occupancy, chamber numbers, cable IDs, splice closures) must be updated after installation to support future fault location.

OTDR distance to event: d = (c × t)/(2 × IOR), where t is the round-trip time and IOR (group index) is typically about 1.468 at 1550 nm for G.652 fibre.

Set OTDR pulse width by range: short pulses (10–30 ns) give fine resolution near the launch, long pulses (1–10 µs) reach far but blur close events; use a launch and receive fibre to see the first and last connectors.

OTDR trace events: reflective spikes are connectors or mechanical splices, non-reflective steps are fusion splices, and a sudden drop to noise floor is a break or high-loss macrobend.

Bidirectional OTDR averaging removes the gainer/ghost effect at splices; report the average of both directions, and remember a splice can show apparent gain in one direction.

Power meter testing: reference the meter (set 0 dB) at the source wavelength, then measure; loss(dB) = source power − measured power, and always record the wavelength used.

Link loss budget: total allowed loss = fibre loss (dB/km × km) + connector losses + splice losses + margin (typically 3 dB); compare with the transceiver's specified budget.

VFL (typically 650 nm red) locates breaks, tight bends and misconnections by visible red glow at the fault; it cannot quantify loss and is not a substitute for an OTDR.

Fault-localisation workflow: confirm with power meter, sweep with OTDR at 1550 and 1625 nm to separate bends from breaks, then compare the event distance with as-built records.

FTTH architecture: OLT in the exchange → feeder fibre → passive optical splitter (commonly 1:8, 1:16, 1:32) → distribution fibre → ONT at the customer premises.

GPON downstream uses 1490 nm and upstream 1310 nm, with 1550 nm reserved for video overlay; XG(S)-PON uses 1577/1270 nm, so test wavelengths must match the PON type.

Splitter 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); include this in the FTTH link budget.

ONT installation: mount the ONT and enclosure, connect the drop cable via SC/APC or LC connector, verify PON LED status, and confirm receive power within the ONT's specified range (often −8 to −27 dBm for GPON).

Drop cable is typically 1–2 fibre, often flat with FRP strength members; it must be routed with bend radius respected and secured with appropriate clamps, not staples through the cable.

Premises cabling should separate fibre from electrical cabling, use LSZH where required, and label the ONT, splitter port and drop cable ID for later maintenance.

ONT activation checks: optical receive level, PON registration/authorisation, Ethernet or Wi-Fi service test, and speed test recorded on the installation sheet.

Customer handover includes explaining LED meanings, the fibre's fragility, and the restriction on moving the ONT or unplugging the drop cable.

Preventive maintenance: periodic OTDR baseline traces, power-level checks, end-face inspection, closure and chamber inspection, and vegetation or clearance checks on aerial routes.

Keep a baseline OTDR trace per fibre and wavelength; faults are identified by comparing the current trace with the baseline, not by absolute loss alone.

Restoration priority: identify the break with OTDR/VFL, isolate and tag the fibre, then splice with a mechanical or fusion splice; temporary mechanical splices are replaced by fusion splices in permanent repair.

Splice closure re-entry requires cleaning, new sealing (heat-shrink or gel), and re-testing the affected fibres after closure to confirm no new loss.

Documentation set: as-built route drawings, fibre allocation/splice schedule, OTDR traces, power meter readings, closure and chamber IDs, and maintenance history.

Fault tickets should record time of alarm, affected services, test results, restoration action, and root cause; this data supports trend analysis and SLA reporting.

Fibre records must be updated whenever a splice or port changes; an out-of-date splice schedule is a leading cause of prolonged restoration.

Spare capacity and fibre allocation discipline (recording used, reserved and spare fibres) reduce restoration time and support future customer provisioning.

NSQF levels map to job roles: Level 4 covers supervised technical work, Level 5 independent skilled work, and higher levels include team or supervisory responsibility.

A job application should match the role's NSQF level and list verifiable skills such as fusion splicing, OTDR testing, FTTH installation, and safety compliance.

Workplace communication: report faults with specific data (fibre ID, wavelength, loss in dB, distance in metres) rather than vague descriptions.

Customer interaction: explain the work, expected downtime and restoration time in plain language, and confirm satisfaction before closing the ticket.

Entrepreneurship basics: estimate cost per splice or per km (labour, materials, equipment depreciation), price with margin, and track GST and invoicing records.

A small OFC contractor needs a written scope, quotation, payment terms, and a safety plan; verbal agreements create disputes over extra work.

Teamwork and escalation: follow the reporting chain, document handovers, and escalate safety or service-affecting issues immediately rather than waiting.

Digital literacy: use spreadsheets for splice schedules and cost sheets, and email or messaging for documented communication with clients and supervisors.