Difficulty: Easy & Basic
What physical principle guides light in a conventional optical fibre core?
A Total internal reflection
B Electromagnetic induction
C Thermal conduction
D Acoustic resonance
Answer: A. Total internal reflection. The core and lower-index cladding confine guided light by total internal reflection.
Which fibre region carries most of the guided optical signal?
A Jacket
B Strength member
C Buffer coating
D Core
Answer: D. Core. The central core is the light-guiding region.
Relative to the core, what refractive index does the cladding usually have?
A Higher index
B Equal index
C Lower index
D Zero index
Answer: C. Lower index. A lower-index cladding permits total internal reflection at the boundary.
What protects the glass fibre during handling and cabling?
A Optical amplifier
B Buffer coating
C Photodiode
D Laser cavity
Answer: B. Buffer coating. The polymer coating protects the glass from damage and moisture.
At the transmitting end, what converts electrical data into optical output?
A Optical receiver
B Power meter
C Optical transmitter
D Fibre splice
Answer: C. Optical transmitter. A transmitter modulates a light source with the data.
Which source is commonly used for narrow-spectrum, high-speed optical transmission?
A Photodiode
B Laser diode
C Thermistor
D Resistor
Answer: B. Laser diode. Laser diodes provide a concentrated optical output suitable for high-speed links.
What is another semiconductor light source used in some fibre links?
A ADC
B LED
C Relay
D Capacitor
Answer: B. LED. Light-emitting diodes can launch modulated light into suitable fibres.
Which component converts received light into electrical current?
A Photodiode
B Laser diode
C Fibre jacket
D Optical splitter
Answer: A. Photodiode. A photodiode detects incoming optical power.
How many principal spatial modes does a single-mode fibre guide?
A Two
B Hundreds
C One
D Unlimited
Answer: C. One. Its small core guides one principal spatial mode over its operating band.
What distinguishes multimode fibre from single-mode fibre?
A No cladding
B Only copper conductor
C Multiple guided modes
D No optical source
Answer: C. Multiple guided modes. Several spatial modes can propagate through a multimode core.
Numerical aperture is associated with which fibre property?
A Cable tensile strength
B Receiver voltage
C Splice temperature
D Light acceptance angle
Answer: D. Light acceptance angle. NA characterizes the range of launch angles accepted into guided modes.
In what units is fibre attenuation coefficient commonly stated?
A Watts per metre
B Volts per second
C Bits per pixel
D dB per km
Answer: D. dB per km. Attenuation is often specified as optical loss per kilometre.
What does dispersion do to a transmitted optical pulse?
A Spreads it in time
B Raises supply voltage
C Erases the data
D Shortens fibre length
Answer: A. Spreads it in time. Different propagation delays broaden the pulse.
Which impairment results from different modes taking different paths?
A Connector reflection
B Modal dispersion
C Laser threshold
D Thermal noise
Answer: B. Modal dispersion. Modes arrive at different times, broadening pulses in multimode fibre.
Which wavelength is common for short-reach multimode fibre links?
A 450 nm
B 1310 nm
C 2100 nm
D 850 nm
Answer: D. 850 nm. Many short-reach multimode systems use 850 nm optical sources.
For standard G.652 single-mode fibre, zero chromatic dispersion is near which wavelength?
A 650 nm
B 1310 nm
C 850 nm
D 2000 nm
Answer: B. 1310 nm. ITU-T G.652 specifies a zero-dispersion wavelength around 1310 nm.
Which wavelength region is also widely used for long-haul single-mode links?
A 400 nm
B 650 nm
C 1550 nm
D 850 nm
Answer: C. 1550 nm. The 1550 nm region supports low-loss transmission and optical amplification.
A detachable joint between two fibre ends uses what?
A Fusion splice
B Core preform
C Connector
D Photodiode
Answer: C. Connector. Connectors allow a fibre link to be plugged and unplugged.
What permanently joins two fibre ends by melting glass?
A Patch connector
B WDM filter
C Optical isolator
D Fusion splice
Answer: D. Fusion splice. Fusion splicing aligns and fuses the glass ends.
A tight fibre bend mainly introduces which problem?
A Higher bit rate
B More core modes
C Zero attenuation
D Bend loss
Answer: D. Bend loss. Excessive bending allows guided light to escape.
Which instrument locates a fault using returned backscatter and reflections?
A OTDR
B Voltmeter
C Oscilloscope
D Spectrum analyzer
Answer: A. OTDR. An optical time-domain reflectometer estimates event distance from return time.
Which instrument directly measures received optical power?
A Optical power meter
B Fusion splicer
C Pulse generator
D Network router
Answer: A. Optical power meter. A power meter reports the incident optical power at a test point.
What does wavelength-division multiplexing combine on one fibre?
A Different fibre cores
B Different optical wavelengths
C Only clock pulses
D Copper wire pairs
Answer: B. Different optical wavelengths. WDM carries multiple wavelength channels through one fibre.
Which device boosts an optical signal in the 1550 nm region?
A EDFA
B ADC
C Photodiode
D Copper repeater
Answer: A. EDFA. An erbium-doped fibre amplifier provides optical gain in that region.
What does a link power budget specify?
A Allowable path loss
B Cable colour
C Connector shape
D Processor speed
Answer: A. Allowable path loss. It compares transmitted power and receiver sensitivity to the link’s losses.