Difficulty: Easy & Basic
How does a graded-index multimode core reduce modal pulse spreading?
A Removing cladding
B Adding copper
C Varying core index
D Increasing jacket thickness
Answer: C. Varying core index. Its index profile helps equalize propagation times of different modes.
In a step-index fibre, what changes abruptly at the core boundary?
A Data format
B Supply voltage
C Laser current
D Refractive index
Answer: D. Refractive index. The core and cladding have distinct, approximately uniform indices.
Compared with standard single-mode fibre, multimode fibre generally has what core?
A Larger core
B Smaller core
C No core
D Metal core
Answer: A. Larger core. A larger core supports more guided spatial modes.
What is the unit of numerical aperture?
A Metres
B No unit
C Decibels
D Watts
Answer: B. No unit. Numerical aperture is a dimensionless optical parameter.
Relative to vacuum, light travels through glass at what speed?
A Higher speed
B Lower speed
C Same speed
D Zero speed
Answer: B. Lower speed. Glass has refractive index greater than one, so its phase speed is lower.
For total internal reflection at the core-cladding boundary, the incident angle must exceed what?
A Critical angle
B Acceptance half-angle
C Bend radius
D Polarization angle
Answer: A. Critical angle. Measured from the normal, incidence greater than the critical angle is totally reflected.
What causes reflection at a glass-air connector gap?
A Cable colour
B Higher bit rate
C Index discontinuity
D Receiver gain
Answer: C. Index discontinuity. An abrupt refractive-index change produces Fresnel reflection.
A connector sends some light back toward the source. Which metric concerns this?
A Clock frequency
B Core diameter
C Optical return loss
D Modal bandwidth
Answer: C. Optical return loss. Return loss describes reflected power relative to incident power.
Which measurement compares optical power before and after a component?
A Carrier frequency
B Phase noise
C Core offset
D Insertion loss
Answer: D. Insertion loss. Insertion loss quantifies the power reduction caused by insertion.
A link becomes unreliable after unplugging a connector. What should be checked first?
A Processor clock
B Connector cleanliness
C Battery voltage
D Network password
Answer: B. Connector cleanliness. Contaminated end faces commonly introduce loss or reflection.
In a fibre connector, what aligns and holds the fibre end?
A Ferrule
B Photodiode
C Optical pump
D Laser driver
Answer: A. Ferrule. The ferrule positions the fibre for accurate mating.
What is a pigtail in fibre installation?
A One-ended connector lead
B Two-ended patch lead
C Amplifier module
D Cable strength member
Answer: A. One-ended connector lead. A pigtail has a connector on one end and bare fibre for splicing on the other.
Which cable has connectors on both ends for patching equipment?
A Bare pigtail
B Preform
C Loose tube
D Patch cord
Answer: D. Patch cord. A patch cord provides detachable connections at both ends.
What does a passive optical splitter do?
A Converts light to current
B Divides optical power
C Adds laser gain
D Erases data bits
Answer: B. Divides optical power. It distributes input light among multiple output ports.
Which optical component suppresses light returning toward a laser?
A Power splitter
B Optical isolator
C Patch cord
D Photodiode
Answer: B. Optical isolator. An isolator preferentially passes light in one direction.
After several WDM channels traverse a fibre, what separates them at the receiver?
A Demultiplexer
B Fusion splicer
C Buffer coating
D Clock divider
Answer: A. Demultiplexer. A demultiplexer routes different wavelengths to separate outputs.
At a specified error rate, receiver sensitivity indicates which input limit?
A Maximum fibre length
B Cladding index
C Minimum usable input
D Laser colour
Answer: C. Minimum usable input. It is the lowest optical input level meeting the specified performance.
Excessive optical input can place a receiver in which condition?
A Overload
B Lower attenuation
C Wider core
D Better sensitivity
Answer: A. Overload. Power above the receiver limit can saturate or impair detection.
At 0 dBm, how much optical power is present?
A 0 mW
B 10 mW
C 1 mW
D 1 W
Answer: C. 1 mW. dBm is referenced to one milliwatt.
For two optical powers, a dB figure expresses what?
A Absolute wavelength
B Power ratio
C Cable diameter
D Bit duration
Answer: B. Power ratio. Decibels compare powers on a logarithmic scale.
During cable pulling, which element bears the mechanical load?
A Core glass
B Ferrule
C Photodiode
D Strength member
Answer: D. Strength member. Strength members carry tensile load and protect the glass fibres.
Small pressure-induced distortions along a fibre can produce what?
A Laser gain
B Higher numerical aperture
C Microbending loss
D Zero dispersion
Answer: C. Microbending loss. Local microscopic bends couple guided power into lossy paths.
Which intrinsic process scatters light from tiny glass-density fluctuations?
A Stimulated emission
B Fusion bonding
C Clock recovery
D Rayleigh scattering
Answer: D. Rayleigh scattering. Microscopic index fluctuations scatter a fraction of guided light.
Residual water or other impurities in glass contribute to what?
A Electrical crosstalk
B Improved reflection
C More modes
D Absorption loss
Answer: D. Absorption loss. Impurities absorb light at certain wavelengths.
Why must one avoid looking into the end of an active optical fibre?
A Invisible light hazard
B High voltage inside glass
C Radioactive cladding
D Mechanical rotation
Answer: A. Invisible light hazard. The transmitted light can be invisible and hazardous to eyes.