What is the 'Critical Angle' in an optical fibre?
- Optimal launch speed
- Breaking point tension
- Maximum bend radius
- Total reflection limit
Explanation: The critical angle is the minimum angle of incidence at which light is totally reflected back into the core.
In optical fibre terminology, what does the acronym 'DWDM' stand for?
- Direct Wave Digital Mode
- Dual Wide Data Monitoring
- Digital Waveform Delay Module
- Dense Wavelength Division Multiplexing
Explanation: DWDM is a technology that puts data from different sources together on an optical fibre, with each signal carried on its own separate light wavelength.
Which device is used at the receiving end to convert light signals back into electrical signals?
- Photodiode
- Transistor
- Capacitor
- Inductor
Explanation: A photodiode (or photodetector) detects incoming photons and converts them into an electrical current.
Which Indian-born physicist is widely regarded as the 'Father of Fibre Optics'?
- C.V. Raman
- Homi J. Bhabha
- Narinder Singh Kapany
- Satyendra Nath Bose
Explanation: Narinder Singh Kapany coined the term 'Fiber Optics' and demonstrated high-speed light transmission in glass fibres in the 1950s.
The technology that sends multiple data signals at different wavelengths through one fibre is called:
Explanation: Wavelength Division Multiplexing (WDM) significantly increases capacity by using different 'colors' of light to carry separate data streams.
The term 'Attenuation' in optical fibre communication refers to which of the following?
- Pulse width broadening
- Frequency shift
- Signal strength loss
- Data rate increase
Explanation: Attenuation is the reduction in intensity of the light signal as it travels through the fibre, measured in decibels per kilometer (dB/km).
Why are optical fibres preferred for undersea (submarine) communication cables?
- Total water resistance
- Cheap raw material
- High bandwidth capacity
- Zero maintenance needs
Explanation: Fibres can carry terabits of data per second across oceans, which is far beyond the capability of satellite or radio links.
The permanent joining of two optical fibres using heat is known as:
- Fusion splicing
- Adhesive fixing
- Mechanical coupling
- Thermal bonding
Explanation: Fusion splicing uses an electric arc to melt the ends of two fibres together, creating a continuous, low-loss path for light.
What is 'Birefringence' in optical fibres?
- Double refractive index
- Rapid pulse generation
- Total light absorption
- Core cladding fusion
Explanation: Birefringence occurs when a material has a refractive index that depends on the polarization and propagation direction of light.
Which material is commonly added to pure silica to increase its refractive index for the core?
- Lead phosphate
- Magnesium oxide
- Calcium carbonate
- Germanium dioxide
Explanation: Germanium is a common dopant used to raise the refractive index of the core relative to the cladding.
Why is 'Infrared' light used instead of 'Visible' light for telecommunications?
- Better visibility
- Lower cost
- Higher velocity
- Lower attenuation
Explanation: Silica glass has much lower signal loss at infrared wavelengths (like 1310nm and 1550nm) than at visible wavelengths.
Which light source is typically used for high-speed, long-distance optical communication?
- Incandescent bulb
- Neon tube
- Laser diode
- Fluorescent lamp
Explanation: Laser diodes provide coherent, monochromatic light that can be coupled efficiently into narrow single-mode fibres.
Which of the following is a major 'Safety' advantage of optical fibers in industrial plants?
- High melting point
- Visible signal path
- No spark risk
- Strong magnetic field
Explanation: Since fibers carry light instead of electricity, they do not produce sparks and are safe for use in explosive or flammable environments.
Which connector type is known for its small form factor and 'push-pull' locking mechanism?
- FC Connector
- ST Connector
- BNC Connector
- LC Connector
Explanation: The LC (Lucent Connector) is widely used in data centers due to its small size and easy-to-use latch.
Which optical fibre component is responsible for 'Total Internal Reflection' by providing a lower refractive index?
- Jacket
- Core
- Buffer
- Cladding
Explanation: The cladding must have a lower refractive index than the core for the light to stay trapped within the core via reflection.
Which 'last-mile' technology brings optical fibre directly into a subscriber's residence?
- FTTH
- Bluetooth
- Dial-up
- Wi-Fi
Explanation: Fiber to the Home (FTTH) replaces traditional copper with optical fibre all the way to the end-user's premises.
Which of these is the most significant disadvantage of 'Multimode' fibre?
- Fragile material
- Large physical size
- High power needs
- Limited distance
Explanation: Due to high modal dispersion, multimode fibre is restricted to much shorter distances than single-mode fibre.
The 'Bit Error Rate' (BER) in optical systems is a measure of:
- Light wavelength
- Cable length
- Transmission accuracy
- Signal power
Explanation: BER is the number of bit errors per unit time, indicating the overall quality and reliability of the data link.
In 'Wavelength Division Multiplexing', what serves as the different data channels?
- Cable thicknesses
- Pulse timings
- Signal voltages
- Light colors
Explanation: WDM uses different wavelengths (essentially different colors of infrared light) to carry multiple signals simultaneously.
What is 'Fresnel Reflection' in the context of fibre optics?
- Signal phase delay
- Light absorption loss
- Reflection at interfaces
- Internal light scattering
Explanation: Fresnel reflection occurs at the junction of two materials with different refractive indices, such as a connector air gap.
Which component in an optical receiver converts the optical signal into current?
- Quartz crystal
- Step-up transformer
- Copper electrode
- PIN photodiode
Explanation: The PIN photodiode is the standard detector used to convert incoming photons into an electrical signal.
What is the function of the 'Cladding' layer in an optical fibre?
- Electrical power conduction
- Heat dissipation
- Structural weight increase
- Light signal reflection
Explanation: The cladding surrounds the core and has a lower refractive index, which causes light to reflect back into the core via TIR.
Which light-emitting source is best for short-distance, low-cost multimode fibre links?
- Neon tube
- LED
- Laser Diode
- Halogen lamp
Explanation: LEDs are cheaper and have a longer life, making them suitable for local area networks and short-distance data links.
Which type of dispersion is caused by the physical dimensions and structure of the fibre guide?
- Material dispersion
- Modal dispersion
- Waveguide dispersion
- Polarization dispersion
Explanation: Waveguide dispersion is a result of the light signal traveling in both the core and the cladding at different speeds.
What is the primary effect of 'Chromatic Dispersion' on an optical signal?
- Total power increase
- Signal phase shifting
- Pulse width broadening
- Frequency band compression
Explanation: Chromatic dispersion causes different wavelengths of light to travel at different speeds, leading to the spreading or 'smearing' of data pulses.
The 'V-number' (Normalized Frequency) of an optical fibre determines:
- Number of modes
- Max tensile strength
- Battery life span
- Signal noise ratio
Explanation: The V-number is a dimensionless parameter that indicates how many modes a fibre can support; if V < 2.405, the fibre is single-mode.
Which term describes the number of independent light paths in an optical fibre?
Explanation: Modes are the various paths that light waves can take as they travel through the core of the fibre.
What is 'Dark Fiber' leasing?
- Renting unused fiber
- Trading scrap glass
- Buying used hardware
- Selling broken cable
Explanation: Leasing dark fiber allows companies to build their own private networks using existing underground fiber infrastructure.
What does 'PMD' stand for in high-speed optical transmission?
- Phase Modulation Delay
- Pulse Mode Detection
- Power Measurement Device
- Polarization Mode Dispersion
Explanation: PMD is a form of dispersion where different polarizations of light travel at different speeds due to fibre imperfections.
Optical fibres are secure because they are difficult to:
Explanation: Unlike copper, optical fibres do not radiate signals, making it very difficult for hackers to intercept data without physically breaking the cable.
Which of these is a 'Passive' optical network component?
- Optical Splitter
- Signal Repeater
- Optical Amplifier
- Laser Source
Explanation: Passive components, like splitters and couplers, do not require electrical power to function.
What is the main drawback of 'Plastic Optical Fibre' (POF) compared to glass fibre?
- Extreme brittleness
- Heavy physical weight
- High manufacturing cost
- High signal attenuation
Explanation: POF has much higher loss than glass and is therefore restricted to short-distance applications like home networking or car systems.
In 5G networks, what role does optical fibre primarily play?
- Wireless signal generation
- High-speed backhaul
- Satellite orbit control
- Device battery charging
Explanation: Optical fibre provides the high-capacity 'backhaul' connection that links 5G small cells and base stations to the core network.
What is the primary material used to manufacture high-quality communication-grade optical fibres?
- Lead-based crystal
- Polished aluminum
- Pure fused silica
- Carbonized graphite
Explanation: Ultra-pure silica (glass) is used due to its exceptional transparency and low signal attenuation over long distances.
Which component of an optical fibre provides the primary mechanical protection and prevents moisture ingress?
- Buffer coating
- Optical coupler
- Cladding
- Core
Explanation: The buffer coating (or jacket) protects the delicate glass from physical damage, bending stress, and environmental factors.
What is the primary purpose of a 'Coupler' in an optical network?
- Cable cooling
- Light generation
- Signal splitting
- Signal amplification
Explanation: Optical couplers are used to redistribute or combine optical signals from multiple fibres.
What is the 'Acceptance Angle' of an optical fibre?
- Maximum entry angle
- Light exit speed
- Core vibration frequency
- Minimum bending radius
Explanation: The acceptance angle is the maximum angle at which light can enter the fibre and still be captured by total internal reflection.
Which organization manages the global standards for optical fibre specifications?
Explanation: The International Telecommunication Union (ITU-T) sets the G-series recommendations that define fibre types like G.652.
Which wavelength range is known as the 'Third Window' for minimal attenuation in silica fibres?
- 850 nm
- 1550 nm
- 633 nm
- 1310 nm
Explanation: The 1550 nm wavelength region offers the lowest possible attenuation (approx. 0.2 dB/km) in standard silica-based fibres.
In an optical fibre, how does the refractive index of the core compare to the cladding?
- Core is lower
- Core is zero
- Core is higher
- Both are identical
Explanation: For total internal reflection to occur, the light must travel from a medium with a higher refractive index (core) toward one with a lower index (cladding).
Which type of optical fibre is most suitable for long-distance, high-bandwidth telecommunications?
- Plastic optical fibre
- Step-index multimode
- Graded-index multimode
- Single-mode fibre
Explanation: Single-mode fibres have a very small core that allows only one path for light, eliminating modal dispersion and allowing longer transmission distances.
What is the typical diameter of the core in a 'Single-mode' optical fibre?
- 8-10 micrometers
- 50-60 micrometers
- 90-100 micrometers
- 1-2 micrometers
Explanation: Single-mode fibres have a very narrow core, usually around 9 microns, to ensure only one mode of light propagates.
Which mechanism is used to compensate for signal attenuation in transoceanic cables?
- Optical amplifiers
- Shorter cables
- Copper shielding
- Plastic jackets
Explanation: Repeater stations with optical amplifiers are placed at regular intervals to boost the signal without converting it to electricity.
Which phenomenon is the primary cause of signal loss due to microscopic impurities in the glass?
- Rayleigh scattering
- Chromatic aberration
- Total absorption
- Modal overlap
Explanation: Rayleigh scattering occurs when light interacts with density fluctuations or impurities in the glass core, reflecting light in all directions.
What occurs when light pulses spread out in time as they travel along a fibre, potentially overlapping?
- Refraction
- Polarization
- Dispersion
- Absorption
Explanation: Dispersion causes the broadening of light pulses, which limits the data-carrying capacity (bandwidth) of the fibre.
What provides the 'Backbone' for the global internet infrastructure?
- Satellite links
- Underground copper
- Submarine fibre cables
- Microwave towers
Explanation: Over 95% of international data traffic is carried via a massive network of undersea optical fibre cables.
Which specific device is used to measure the loss and identify breaks along a fibre cable?
- OTDR
- Laser Spectrum Analyzer
- Digital Signal Tester
- Optical Power Meter
Explanation: The Optical Time-Domain Reflectometer (OTDR) sends light pulses and analyzes the backscattered light to map losses and faults.
Which physical phenomenon is the fundamental principle behind light transmission in optical fibres?
- Optical wave refraction
- Total internal reflection
- Atmospheric light diffraction
- Diffuse light scattering
Explanation: Light propagates through the fibre core by reflecting repeatedly off the cladding interface, a process called Total Internal Reflection (TIR).
What happens to the light signal if the fibre is bent beyond its 'Critical Bending Radius'?
- Light leaks out
- Fibre becomes radioactive
- Signal speed increases
- Wavelength shifts blue
Explanation: Excessive bending causes light to strike the cladding at an angle smaller than the critical angle, causing it to escape the core (bending loss).
Which phenomenon limits the transmission distance due to light energy being converted into heat?
- Absorption
- Refraction
- Scattering
- Diffraction
Explanation: Absorption occurs when impurities in the glass or the glass itself convert light energy into thermal energy.
What is 'Dark Fibre' in the context of telecommunications infrastructure?
- Non-reflective glass fibres
- Unused optical capacity
- Underground backup cables
- Broken fibre cables
Explanation: Dark fibre refers to already-laid optical fibre cables that are not yet 'lit' or carrying data traffic.
What does 'Numerical Aperture' (NA) measure in an optical fibre?
- Maximum tensile load
- Signal processing speed
- Light gathering capacity
- Core physical thickness
Explanation: Numerical Aperture represents the range of angles over which the system can accept or emit light.
Which medical instrument utilizes optical fibres to view the internal organs of the human body?
- Sphygmomanometer
- Stethoscope
- Endoscope
- Electrocardiogram
Explanation: Endoscopy uses bundles of optical fibres to transmit light into the body and return images of internal structures to the physician.
What is the purpose of the 'EDFA' (Erbium-Doped Fibre Amplifier)?
- Cooling the cable
- Multiplexing wavelengths
- Filtering noise
- Optical signal amplification
Explanation: EDFAs amplify optical signals directly without converting them to electrical signals, which is essential for undersea and long-haul cables.
What is 'Microbending' in an optical fibre?
- Small surface deformities
- Core material melting
- End-to-end splicing
- Large cable loops
Explanation: Microbending refers to microscopic bends in the fibre axis caused by pressure or poor cabling, leading to light leakage.
What is the primary role of 'Kevlar' or 'Aramid yarn' in an optical fibre cable?
- Signal amplification
- Electrical insulation
- Light reflection
- Tensile strength
Explanation: Kevlar is used as a strength member to protect the fragile glass fibres from being stretched or broken during installation.
Which of these is a major advantage of optical fibres over traditional copper cables?
- Easier manual splicing
- Higher tensile strength
- Electromagnetic interference immunity
- Low installation cost
Explanation: Since fibres are made of glass (dielectric), they are not affected by electromagnetic interference (EMI) or radio frequency interference (RFI).
What is a 'Soliton' in fibre optic research?
- Satellite relay station
- Light-to-heat converter
- Defective fibre segment
- Pulse-maintaining wave
Explanation: Solitons are special light pulses that can travel vast distances without changing shape or dispersing.
In a 'Graded-index' multimode fibre, the refractive index of the core:
- Is always zero
- Is constant
- Decreases from center
- Increases from center
Explanation: The index decreases gradually toward the cladding, which helps reduce modal dispersion by equalizing the speeds of different light paths.
What is a 'Fiber Bragg Grating' (FBG) primarily used for?
- Data encryption
- Wavelength filtering
- Light source cooling
- Physical cable tying
Explanation: FBGs are used as optical filters to block or reflect specific wavelengths while letting others pass.