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Punjab PSEB Sr. Sec. NSQF Telecom (Optical Fibre Technician) study materials
Punjab PSEB Sr. Sec. NSQF Telecom (Optical Fibre Technician) study resources

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

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Question 1Optical Fibre Fundamentals and Principles of Light Transmission

In a step-index multimode optical fibre, what happens to a light ray that strikes the core-cladding boundary at an angle greater than the critical angle?

  1. It is absorbed completely by the core dopants
  2. It is totally internally reflected back into the core Correct answer.
  3. It refracts into the cladding and is lost
  4. It splits equally between core and cladding

Explanation

Total internal reflection occurs when light travelling in the denser core meets the cladding boundary beyond the critical angle, so the ray is reflected back into the core with negligible loss. This confinement is what allows guided propagation along the fibre. Rays below the critical angle refract out and are lost.

Question 2Optical Fibre Fundamentals and Principles of Light Transmission

Which statement correctly describes the relationship between the refractive index of the core and that of the cladding in a standard silica optical fibre?

  1. The core refractive index must equal that of air
  2. The cladding has a higher refractive index than the core
  3. The core has a higher refractive index than the cladding Correct answer.
  4. Core and cladding must have identical refractive indices

Explanation

Guiding requires the light-carrying core to be optically denser than the surrounding cladding so that total internal reflection can occur at the boundary. A lower-index cladding also reduces scattering losses at the interface. If the indices were equal or reversed, light would not be confined.

Question 3Optical Fibre Fundamentals and Principles of Light Transmission

What is the typical cladding diameter of a standard single-mode telecommunication optical fibre?

  1. 250 micrometre
  2. 9 micrometre
  3. 62.5 micrometre
  4. 125 micrometre Correct answer.

Explanation

Standard single-mode fibre has a core of about 8 to 10 micrometres and a cladding of 125 micrometres, which is the mechanical reference for splicing and connector ferrules. The 250 micrometre figure refers to the primary coating diameter, not the cladding.

Question 4Optical Fibre Fundamentals and Principles of Light Transmission

Which wavelength window is most commonly used for long-haul single-mode transmission because of its very low attenuation?

  1. 660 nanometre
  2. 1550 nanometre Correct answer.
  3. 405 nanometre
  4. 850 nanometre

Explanation

The 1550 nanometre window sits near the minimum attenuation of silica fibre, roughly 0.2 dB per kilometre, and also coincides with erbium-doped fibre amplifier gain. This makes it the preferred band for long-haul and DWDM systems. Shorter windows suffer higher loss.

Question 5Optical Fibre Fundamentals and Principles of Light Transmission

A light ray travels from a denser medium into a rarer medium. As the angle of incidence in the denser medium increases towards the critical angle, the angle of refraction in the rarer medium:

  1. Approaches 90 degrees Correct answer.
  2. Remains constant at 45 degrees
  3. Becomes equal to the angle of incidence
  4. Decreases towards zero

Explanation

By Snell's law the refracted ray bends away from the normal when entering a rarer medium, so as incidence rises the refraction angle grows faster and reaches 90 degrees at the critical angle. Beyond that point total internal reflection begins. The refraction angle never exceeds 90 degrees for a transmitted ray.

Question 6Optical Fibre Fundamentals and Principles of Light Transmission

What does the numerical aperture of an optical fibre primarily indicate?

  1. The total attenuation of the fibre per kilometre
  2. The operating wavelength of the transmitter
  3. The ability of the fibre to accept and guide incoming light Correct answer.
  4. The mechanical strength of the primary coating

Explanation

Numerical aperture is defined as the sine of the maximum half-angle of the acceptance cone at the fibre input, so it quantifies light-gathering capability. A larger NA accepts steeper rays but supports more modes. Attenuation, coating strength and wavelength are unrelated parameters.

Question 7Optical Fibre Fundamentals and Principles of Light Transmission

A multimode fibre has a core refractive index of 1.48 and cladding refractive index of 1.46. Using NA equal to the square root of (n1 squared minus n2 squared), the numerical aperture is approximately:

  1. 0.24 Correct answer.
  2. 0.02
  3. 0.48
  4. 1.46

Explanation

Squaring gives 2.1904 minus 2.1316, a difference of 0.0588, and its square root is about 0.242. Numerical aperture therefore lies between zero and one for practical silica fibres. Subtracting the indices directly gives the small index step, not the NA.

Question 8Optical Fibre Fundamentals and Principles of Light Transmission

Why does a graded-index multimode fibre reduce modal dispersion compared with a step-index multimode fibre?

  1. All modes are forced to travel along the central axis
  2. The cladding refractive index is made higher than the core
  3. The core diameter is made much larger to spread the modes
  4. Rays travelling longer paths move faster in lower-index regions near the cladding Correct answer.

Explanation

In a graded-index profile the refractive index falls gradually towards the cladding, so light speed increases away from the axis. Rays that take longer zigzag paths therefore travel faster and arrive closer in time to axial rays, reducing pulse spreading. Step-index fibre has a uniform core speed and hence larger modal dispersion.

Question 9Optical Fibre Fundamentals and Principles of Light Transmission

Which phenomenon is the dominant cause of pulse broadening in long step-index multimode fibre links?

  1. Chromatic dispersion
  2. Rayleigh backscattering
  3. Modal dispersion Correct answer.
  4. Polarisation mode dispersion

Explanation

Different modes in a multimode fibre travel different path lengths at the same wavelength, so they arrive at different times and broaden the pulse; this is modal dispersion. Chromatic and polarisation mode dispersion are far smaller effects in short multimode links. Backscattering causes loss and noise rather than intermodal pulse spreading.

Question 10Optical Fibre Fundamentals and Principles of Light Transmission

What is the main reason single-mode fibre is preferred for very long distance and high bit-rate transmission?

  1. It does not require any protective coating
  2. It operates only in the visible wavelength region
  3. Its core is larger, allowing more light to be launched
  4. Only one spatial mode propagates, so modal dispersion is eliminated Correct answer.

Explanation

With a core small enough that only the fundamental mode is guided, intermodal delay cannot occur, leaving chromatic and polarisation effects as the limiting dispersions. This supports very high bit rates over long spans. Single-mode fibre actually has a smaller core and needs the same external protection as multimode fibre.

Question 11Optical Fibre Fundamentals and Principles of Light Transmission

In a fibre link, a launch condition produces an input power of 1 milliwatt and the output power is 100 microwatts. What is the total loss in decibels?

  1. 10 dB Correct answer.
  2. 100 dB
  3. 0.1 dB
  4. 1 dB

Explanation

Loss in decibels equals ten times the logarithm to base ten of the power ratio. Here the ratio is 1000 divided by 100, giving 10, and ten times log of 10 is 10 dB. A factor of ten in power always corresponds to 10 dB.

Question 12Optical Fibre Fundamentals and Principles of Light Transmission

Which intrinsic attenuation mechanism in silica fibre dominates at wavelengths longer than about 1600 nanometres?

  1. Rayleigh scattering
  2. Microbending loss
  3. Ultraviolet absorption
  4. Infrared absorption Correct answer.

Explanation

At long wavelengths the photon energy approaches vibrational resonances of the silica lattice, producing strong infrared absorption that rises steeply beyond about 1600 nanometres. Rayleigh scattering, by contrast, falls with increasing wavelength. This is why practical silica windows stop near the L-band.

Question 13Optical Fibre Fundamentals and Principles of Light Transmission

Rayleigh scattering loss in an optical fibre varies with wavelength according to which relationship?

  1. Inversely as the fourth power of wavelength Correct answer.
  2. Directly proportional to wavelength
  3. Independent of wavelength
  4. Inversely as the square of wavelength

Explanation

Rayleigh scattering arises from microscopic density and composition fluctuations frozen into the glass, and its coefficient scales as one over wavelength to the fourth power. This steep dependence explains why 850 nanometre links lose far more than 1550 nanometre links. It is the dominant intrinsic loss in the short-wavelength region.

Question 14Optical Fibre Fundamentals and Principles of Light Transmission

Which type of bend loss occurs when the fibre axis is deformed over a scale comparable to the fibre diameter, for example by a rough cable surface?

  1. Splice loss
  2. Microbending loss Correct answer.
  3. Fresnel reflection loss
  4. Macrobending loss

Explanation

Microbending refers to small random axial deformations on the order of the fibre diameter that couple guided light into radiating modes. Macrobending involves large-radius curvature such as coiling. Both are extrinsic losses controlled by cable design and installation practice.

Question 15Optical Fibre Fundamentals and Principles of Light Transmission

A technician coils a single-mode patch cord into several tight loops of small radius. Which effect is most likely to appear?

  1. A shift of the operating wavelength to visible light
  2. Complete removal of chromatic dispersion
  3. Increased attenuation from macrobending loss Correct answer.
  4. A permanent increase in numerical aperture

Explanation

Tight loops create curvature large enough to violate the guiding condition for some of the optical field, so power radiates away and attenuation rises, especially at longer wavelengths. This is macrobending loss and is avoided by respecting minimum bend radius. It does not alter NA or dispersion beneficially.

Question 16Optical Fibre Fundamentals and Principles of Light Transmission

Which statement about the acceptance angle of an optical fibre is correct?

  1. It is the angle at which the fibre end is cleaved
  2. It is the maximum cone half-angle at which launched light is guided Correct answer.
  3. It is fixed at 90 degrees for all telecom fibres
  4. It equals the physical core diameter in micrometres

Explanation

The acceptance angle defines the cone of incident rays that can enter the core and still satisfy total internal reflection, and its sine equals the numerical aperture in air. Rays outside this cone are not guided. It is an optical property unrelated to core diameter or cleave angle.

Question 17Optical Fibre Fundamentals and Principles of Light Transmission

Why is a mode field diameter specified for single-mode fibre rather than a simple core diameter?

  1. The core is too small to measure with any instrument
  2. A portion of the optical power travels in the cladding, so the field extends beyond the core Correct answer.
  3. Single-mode fibre has no defined core region
  4. The mode field diameter equals the coating diameter

Explanation

In single-mode fibre the guided field is not strictly confined to the doped core but decays into the cladding, so the mode field diameter describes the actual power distribution. It is always somewhat larger than the physical core. This matters for splice loss and bend sensitivity.

Question 18Optical Fibre Fundamentals and Principles of Light Transmission

Two single-mode fibres with different mode field diameters are spliced. What is the principal consequence of the mismatch?

  1. Automatic conversion of the link to multimode operation
  2. A change in the cladding refractive index at the joint
  3. Additional splice loss because the field profiles do not overlap perfectly Correct answer.
  4. Elimination of polarisation mode dispersion

Explanation

When the guided fields on either side of a joint have different sizes, part of the light is not coupled into the receiving fibre and is lost, giving mode field diameter mismatch loss. The effect grows with the ratio of the two diameters. Matching fibre types at a splice minimises this loss.

Question 19Optical Fibre Fundamentals and Principles of Light Transmission

What is the main practical reason for using a graded-index profile in multimode fibre for local area networks?

  1. It guarantees single-mode propagation
  2. It removes the need for any cladding layer
  3. It permits operation at 1550 nanometres with zero attenuation
  4. It allows higher bandwidth over the same distance than step-index multimode Correct answer.

Explanation

By equalising arrival times of different modes, the graded-index profile greatly increases the bandwidth-distance product of multimode fibre, which is why it dominates LAN backbones at 850 and 1300 nanometres. It does not eliminate attenuation or change the fibre into single-mode.

Question 20Optical Fibre Fundamentals and Principles of Light Transmission

In a fibre with core index 1.50 and cladding index 1.48, what is the critical angle at the core-cladding interface, to the nearest degree?

  1. 45 degrees
  2. 90 degrees
  3. 9 degrees
  4. 81 degrees Correct answer.

Explanation

The critical angle equals the inverse sine of the cladding index divided by the core index, that is inverse sine of 1.48 over 1.50, which is about 0.9867 and gives roughly 81 degrees. Only rays steeper than this relative to the normal are totally internally reflected. The index difference itself is 0.02, not the angle.

Question 21Optical Fibre Fundamentals and Principles of Light Transmission

A pulse of light contains a spread of wavelengths and travels through single-mode fibre. Which mechanism causes the pulse to broaden in this case?

  1. Modal dispersion
  2. Chromatic dispersion Correct answer.
  3. Connector reflection
  4. Microbending loss

Explanation

Because the refractive index and waveguide properties vary with wavelength, different spectral components of the pulse travel at different group velocities and arrive at different times; this is chromatic dispersion. In single-mode fibre there is no intermodal delay, so chromatic dispersion dominates pulse spreading. It is managed with dispersion-compensating modules or specialised fibre.

Question 22Optical Fibre Fundamentals and Principles of Light Transmission

Which of the following best explains why 1310 nanometres is often chosen for single-mode links that must avoid dispersion compensation?

  1. The fibre becomes multimode at 1310 nanometres
  2. Rayleigh scattering is absent at 1310 nanometres
  3. Chromatic dispersion is close to zero near that wavelength in standard single-mode fibre Correct answer.
  4. Attenuation at 1310 nanometres is lower than at 1550 nanometres

Explanation

Standard single-mode fibre is designed so that material and waveguide dispersion cancel near 1310 nanometres, giving a near-zero dispersion point. This makes it attractive for shorter unrepeatered links where dispersion compensation is uneconomical. Attenuation there is higher than at 1550 nanometres, and Rayleigh scattering is always present.

Question 23Optical Fibre Fundamentals and Principles of Light Transmission

What is the primary function of the primary coating applied immediately over the cladding of an optical fibre?

  1. Setting the operating wavelength of the link
  2. Mechanical protection of the glass surface from microcracks and moisture Correct answer.
  3. Reflecting light back into the core
  4. Increasing the numerical aperture of the fibre

Explanation

Bare silica is strong but fails readily from surface flaws, so an acrylate coating applied during drawing protects the glass from abrasion and moisture ingress and preserves strength. It plays no role in guiding light. Optical parameters such as NA and wavelength are set by the core and cladding design and the transmitter.

Question 24Optical Fibre Fundamentals and Principles of Light Transmission

Compared with multimode fibre, why does single-mode fibre require tighter tolerances during splicing?

  1. Its cladding is a different diameter from all multimode fibre
  2. It carries no light in the cladding region at all
  3. It cannot be fusion spliced and must be glued
  4. Its much smaller core and mode field demand precise alignment to avoid high loss Correct answer.

Explanation

Because the guided mode in single-mode fibre is only about 9 to 10 micrometres across, small lateral offsets or angular misalignments cause a large fraction of the field to miss the receiving core. Multimode fibre has a much larger core and tolerates more misalignment. Modern fusion splicers achieve the required precision automatically.

Question 25Optical Fibre Cables, Types, and Colour Coding

In a loose-tube optical fibre cable, which colour is conventionally assigned to Tube No. 1 in the standard 12-colour fibre/tube sequence used in Indian telecom practice?

  1. Slate
  2. Brown
  3. Blue Correct answer.
  4. Green

Explanation

The standard 12-colour sequence begins with blue, followed by orange, green, brown, slate, white, red, black, yellow, violet, rose and aqua. Tube or fibre No. 1 is therefore always identified by the blue colour. This sequence is the backbone of fibre identification in loose-tube and ribbon cables.

Question 26Optical Fibre Cables, Types, and Colour Coding

A technician counts tubes in a loose-tube cable and identifies position 6 by colour. Which colour marks Tube No. 6 in the standard 12-colour sequence?

  1. Black
  2. White Correct answer.
  3. Yellow
  4. Red

Explanation

Positions 1 to 6 run blue, orange, green, brown, slate and white, so the sixth tube is white. Black is reserved for position eight and red for position seven. Getting this order right prevents splicing errors on multi-tube cables.

Question 27Optical Fibre Cables, Types, and Colour Coding

Which statement best describes the construction of a tight-buffered optical fibre cable?

  1. The fibres are enclosed in a single slotted core with grooves carrying bare glass.
  2. The fibres are sandwiched between two plastic tapes with no individual protection.
  3. Each fibre sits loosely inside a water-blocked gel-filled tube with about 1 mm clearance.
  4. Each fibre is coated directly with a 900 micron buffer that is in contact with the fibre cladding. Correct answer.

Explanation

In a tight-buffered design the 900 micron buffer is extruded directly onto the fibre, giving each fibre its own mechanical protection. This makes the cable flexible and easy to connectorise indoors. Loose-tube and slotted-core designs instead leave the fibre free inside a cavity.

Question 28Optical Fibre Cables, Types, and Colour Coding

A single-mode fibre ribbon cable carries 12 fibres in a colour-coded ribbon. Which colour identifies fibre 11 in the standard 12-colour sequence?

  1. Yellow
  2. Aqua
  3. Rose Correct answer.
  4. Violet

Explanation

The sequence runs blue, orange, green, brown, slate, white, red, black, yellow, violet, rose and aqua. Position 11 is therefore rose and position 12 is aqua. Ribbon mass-splicing depends on this ordering being read correctly.

Question 29Optical Fibre Cables, Types, and Colour Coding

In cables using the tracer or ring marking system, what does a black tracer on a blue fibre indicate?

  1. It identifies fibre number 13 in a cable with more than 12 fibres. Correct answer.
  2. It marks a fibre that must be spliced to the sheath earth.
  3. It marks a spare dark fibre reserved for future use.
  4. It identifies the first fibre of the second tube only.

Explanation

When a cable carries more than 12 fibres, the 12 base colours are repeated and each group is distinguished by a tracer or ring. A blue fibre with a black tracer is therefore fibre 13. This extends the same 12-colour logic to higher fibre counts.

Question 30Optical Fibre Cables, Types, and Colour Coding

A 48-fibre loose-tube cable uses 12-colour tube coding with four fibres per tube. Which tube colour and fibre colour combination identifies fibre 27?

  1. Third tube (green) with blue fibre Correct answer.
  2. Second tube (orange) with white fibre
  3. Third tube (green) with rose fibre
  4. Fourth tube (brown) with blue fibre

Explanation

With four fibres per tube, each tube holds a group of four, so fibres 25 to 28 fall in tube three, which is green. Within that tube the first fibre is blue, giving fibre 27 as the third fibre overall and the blue fibre of the green tube. Counting by tube first and then by fibre position avoids off-by-one errors.

Question 31Optical Fibre Cables, Types, and Colour Coding

Which cable type is most suitable for direct burial in a field without ducting, where the cable must resist soil pressure and moisture?

  1. Flat drop cable with a single steel messenger wire
  2. Indoor tight-buffered riser cable with aramid yarn strength members
  3. Armoured loose-tube cable with steel tape or wire and a moisture barrier Correct answer.
  4. Simplex patch cord with a PVC outer jacket

Explanation

Direct burial demands crush resistance and a moisture barrier, which armouring with steel tape or wire and a water-blocking construction provide. Indoor and patch-cord designs lack the mechanical protection needed underground. Flat drop cable is intended for aerial spans, not buried routes.

Question 32Optical Fibre Cables, Types, and Colour Coding

Why is a gel or water-blocking yarn used inside the loose tubes and the cable core of an outdoor optical fibre cable?

  1. To reduce the bend radius of the finished cable
  2. To increase the optical power launched into the fibre
  3. To provide the tensile strength needed for aerial spans
  4. To prevent water ingress and migration that would otherwise damage the fibres and cause loss Correct answer.

Explanation

Water blocking compounds fill the free space so that any moisture entering a damaged jacket cannot travel along the cable. Water in a loose tube can freeze, expand and stress the fibre, raising attenuation. Strength for aerial spans comes from separate members, not from the gel.

Question 33Optical Fibre Cables, Types, and Colour Coding

An aerial optical fibre cable is being installed on a pole route. Which construction feature most directly allows the cable to carry its own weight between supports?

  1. A gel-filled central tube with 12 fibres
  2. A corrugated steel tape armour under the jacket
  3. A double-layer polyurethane outer jacket
  4. An integrated steel messenger wire or aramid strength member in the cable Correct answer.

Explanation

Self-supporting aerial cable relies on a messenger wire or aramid strength member to take the span load so the fibre does not stretch. The optical fibre itself must never carry tensile load. Jacket material and armour serve other purposes.

Question 34Optical Fibre Cables, Types, and Colour Coding

Which statement correctly distinguishes multimode from single-mode optical fibre cable?

  1. Single-mode has a graded-index core of 62.5 micron and is used for short building links.
  2. Multimode has a smaller core than single-mode and therefore supports longer unrepeated distances.
  3. Multimode has a much larger core, typically 50 or 62.5 micron, and carries many modes; single-mode has a small core around 9 micron and carries one mode. Correct answer.
  4. Multimode uses a 9 micron core and is used mainly for long-haul routes.

Explanation

Multimode fibre has a large core of 50 or 62.5 micron, allowing many light paths and suffering modal dispersion, so it suits short links. Single-mode fibre has a small core near 9 micron and carries a single mode, which supports long distances. Core size is the primary distinguishing construction feature.

Question 35Optical Fibre Cables, Types, and Colour Coding

In an optical fibre cable, what is the function of the central strength member made of FRP?

  1. It takes tensile load and limits contraction and expansion of the cable with temperature Correct answer.
  2. It provides the colour code reference for the first tube
  3. It acts as the earth conductor for the cable sheath
  4. It carries the optical signal between the fibres

Explanation

An FRP central strength member is a dielectric rod that carries tensile load and reduces thermal contraction and expansion of the cable. It keeps the fibres within their safe strain window during installation. FRP is non-conductive, so it cannot serve as an earth conductor.

Question 36Optical Fibre Cables, Types, and Colour Coding

A technician is identifying fibres in a 24-fibre cable that uses 12-colour coding with two tubes of 12 fibres. Which combination correctly identifies fibre 15?

  1. Blue tube, green fibre
  2. Orange tube, blue fibre
  3. Green tube, orange fibre
  4. Orange tube, green fibre Correct answer.

Explanation

Fibres 1 to 12 are in the blue tube and fibres 13 to 24 are in the orange tube. Fibre 13 is the blue fibre of the orange tube, 14 is orange and 15 is green. Reading the tube colour first and then the fibre colour within it gives the correct answer.

Question 37Optical Fibre Cables, Types, and Colour Coding

Which colour combination is used to identify Tube No. 2 and the second fibre within it in a standard colour-coded loose-tube cable?

  1. Green tube and green fibre
  2. Blue tube and orange fibre
  3. Orange tube and blue fibre
  4. Orange tube and orange fibre Correct answer.

Explanation

Tube colours and fibre colours both follow the same 12-colour sequence, so position two is orange in each case. Tube two is orange and its second fibre is orange. The two colour codes are applied independently and then combined.

Question 38Optical Fibre Cables, Types, and Colour Coding

A cable jacket is marked with the letters LSZH. What does this marking indicate about the cable?

  1. The jacket is made of low-density polyethylene for outdoor use
  2. The jacket emits low smoke and no halogen acids when it burns Correct answer.
  3. The cable is suitable for direct burial without armouring
  4. The cable has a low smoke zero halogen rating only for indoor riser use

Explanation

LSZH stands for low smoke zero halogen, meaning the jacket releases limited smoke and no corrosive halogen acids when burned. This is important in buildings where people must escape and where equipment must not be corroded. It is a fire-performance property, not a burial rating.

Question 39Optical Fibre Cables, Types, and Colour Coding

Which construction is typical of an indoor/outdoor tight-buffered distribution cable used inside a building?

  1. Bare 250 micron fibres inside a gel-filled loose tube
  2. Ribbon fibres in a slotted aluminium core with steel armour
  3. A single fibre in a flat jacket with an integral steel messenger
  4. 900 micron tight-buffered fibres with aramid yarn strength members and a flame-retardant jacket Correct answer.

Explanation

Indoor distribution cable uses 900 micron tight-buffered fibres for direct connectorisation, aramid yarn for strength and a flame-retardant jacket for building safety. This design allows field termination without a splice closure. Gel-filled loose tubes and armoured slotted cores are outdoor constructions.

Question 40Optical Fibre Cables, Types, and Colour Coding

A 12-fibre cable uses the standard colour code. A technician must splice fibre 8. Which colour is fibre 8?

  1. Red
  2. White
  3. Black Correct answer.
  4. Slate

Explanation

Counting through the sequence, position 8 is black, after red at position 7 and before yellow at position 9. Black is often confused with slate, which is position 5. Verifying the count before splicing prevents a misconnection.

Question 41Optical Fibre Cables, Types, and Colour Coding

Why are loose tubes in an outdoor cable often stranded around the central strength member in a helical lay rather than laid straight?

  1. The helical lay allows the cable to bend and stretch without straining the fibres and improves flexibility Correct answer.
  2. The helical lay eliminates the need for colour coding of the tubes
  3. The helical lay removes the requirement for a moisture barrier
  4. The helical lay increases the optical power carried by each fibre

Explanation

Stranding the tubes in a helix gives the cable controlled elongation and contraction so the fibres experience less strain when the cable is pulled or bent. It also improves flexibility and crush behaviour. Colour coding and moisture blocking are still required.

Question 42Optical Fibre Cables, Types, and Colour Coding

A field engineer must choose a cable for a 2 km link between two buildings using 1310 nm single-mode optics. Which cable type is the correct choice?

  1. 50/125 micron multimode ribbon cable
  2. 62.5/125 micron multimode tight-buffered indoor cable
  3. Single-mode loose-tube outdoor cable with a dielectric or armoured sheath Correct answer.
  4. Simplex 900 micron multimode patch cord

Explanation

A 2 km span at 1310 nm requires single-mode fibre, whose small core and low dispersion support that distance. Multimode suffers modal dispersion and is normally limited to a few hundred metres in building links. Outdoor routing also calls for a loose-tube cable with a suitable sheath.

Question 43Optical Fibre Cables, Types, and Colour Coding

In a 96-fibre cable built from 12-colour tubes of 8 fibres each, which tube colour and fibre colour identify fibre 73?

  1. Tenth tube (violet) with orange fibre
  2. Eleventh tube (rose) with blue fibre
  3. Ninth tube (yellow) with blue fibre
  4. Tenth tube (violet) with blue fibre Correct answer.

Explanation

With 8 fibres per tube, each tube holds a block of 8, so fibres 73 to 80 fall in tube ten, which is violet. The first fibre of that tube is blue, giving fibre 73 as the blue fibre of the violet tube. Counting in blocks of eight and then checking the tube colour confirms the result.

Question 44Optical Fibre Cables, Types, and Colour Coding

What is the purpose of the rip cord and the outer sheath marking in an optical fibre cable?

  1. The rip cord provides tensile strength, and the marking gives the fibre colour sequence
  2. The rip cord blocks water, and the marking records the date of manufacture only
  3. The rip cord allows the sheath to be opened without damaging the fibres, and the marking identifies the cable and its route Correct answer.
  4. The rip cord earths the sheath, and the marking shows the attenuation of each fibre

Explanation

A rip cord is a strong cord under the jacket that lets a technician slit the sheath cleanly during mid-span access without nicking the fibres. The printed sheath marking carries cable identity, length and route details for records. Neither function relates to tensile strength or fibre attenuation.

Question 45Tools, Equipment, and Safety Practices in OFC Work

Before starting fusion splicing inside a manhole, the technician should first test the atmosphere because the most serious immediate risk in that confined space is:

  1. excessive brightness of the splicing arc
  2. vibration from passing traffic
  3. static charge on the fibre coating
  4. accumulation of toxic or explosive gases and oxygen deficiency Correct answer.

Explanation

Confined spaces such as manholes can collect heavier-than-air gases, methane from sewers, or become oxygen-deficient, which can kill within minutes. A calibrated multi-gas detector is used to test oxygen, combustible gas and toxic gas before entry and continuously during work. Brightness, static and vibration are nuisances that do not cause immediate loss of consciousness.

Question 46Tools, Equipment, and Safety Practices in OFC Work

A technician must strip the 250 micrometre primary coating from a single fibre without nicking the cladding. The correct tool and technique is:

  1. a utility knife drawn along the fibre axis
  2. a precision fibre stripper used with a gentle squeeze and a single straight pull Correct answer.
  3. side-cutting pliers used with a twisting motion
  4. hot tweezers used to melt the coating away

Explanation

Precision strippers have sized holes matched to the coating diameter and remove the acrylate layer cleanly when the fibre is pulled straight. Any twisting, blade scraping or melting introduces nicks and surface flaws that reduce tensile strength and cause breakage or high loss. A nicked fibre usually fails later under bending or temperature cycling.

Question 47Tools, Equipment, and Safety Practices in OFC Work

When cleaving a fibre before splicing, the cleave tool should be used so that the end face is:

  1. left with a long protruding tail for alignment
  2. angled at about 45 degrees to reduce reflection
  3. rounded by melting the tip
  4. flat and perpendicular, with the waste offcut collected safely Correct answer.

Explanation

A good cleave produces a flat, perpendicular mirror end face with minimal hackle or lip, which the splicer needs for low-loss arc fusion. The scrap fibre must be collected in a closed container because it is a sharp, almost invisible eye and skin hazard. An angled, melted or tailed end face will cause high splice loss or arc failure.

Question 48Tools, Equipment, and Safety Practices in OFC Work

Which personal protective equipment is essential when using a high-power optical source for live-fibre testing or OTDR work?

  1. steel-toe boots and a reflective vest only
  2. laser-safety eyewear matched to the source wavelength and an optical power meter for verification Correct answer.
  3. a cotton face mask and cloth gloves
  4. ear defenders and a hard hat only

Explanation

Invisible infrared light from OTDRs and sources can cause permanent retinal damage, and the hazard is not visible to the eye. Appropriate laser-safety eyewear for the wavelength, correct handling of connectors and verification with a power meter before looking into any fibre are standard controls. Ordinary PPE such as masks, gloves or ear defenders gives no protection against optical radiation.

Question 49Tools, Equipment, and Safety Practices in OFC Work

Why must bare fibre offcuts be kept in a sealed container rather than swept into a general bin or left on a bench?

  1. They react chemically with air and release chlorine
  2. They are sharp, springy and nearly invisible, so they can penetrate skin and eyes Correct answer.
  3. They are magnetic and damage the fusion splicer electrodes
  4. They attract moisture that corrodes the splicing machine

Explanation

Cleaved silica fibre is extremely fine and stiff, and can easily pierce skin or lodge in the eye where it is very difficult to remove. The safe practice is to collect offcuts immediately in a closed sharps container and never to blow or brush them off a bench. Fibre is chemically inert, non-magnetic and does not corrode electrodes.

Question 50Tools, Equipment, and Safety Practices in OFC Work

During a fusion splice the splicer reports a high estimated loss and the arc looks dim. The first practical checks should include:

  1. the length of the pigtail jacket
  2. the colour of the splice protector sleeve
  3. the age of the OTDR battery
  4. electrode condition and arc power calibration, plus cleanliness of the fibre end faces Correct answer.

Explanation

A weak or unstable arc usually points to worn electrodes, incorrect arc power settings or dirty fibre ends that disturb the plasma. Checking electrode wear count, cleaning the V-grooves and re-cleaving the fibre are the standard corrective steps. Sleeve colour, jacket length and OTDR battery have no effect on arc behaviour.