This is the Review Notes in Fiber Optics as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Summary of Important Fiber Optics Review Notes
Christian Huygens founded the wave theory of light
Bockham and Kao proposed the use of a clad glass fiber as a dielectric waveguide
Theodore Maiman developed the first laser
Infrared – the band of light wavelengths that are too long to be seen by the human eye
Ultraviolet – the band of light wavelengths that are too short to be seen by the human eye
Blue color has the shortest wavelength of light
Laser generates a light beam at a specific visible frequency
Photoresist materials is sensitive to light
The core of an optical fiber has a higher refractive index than the cladding
Modes is the different angle of entry of light into an optical fiber when the diameter of the core is many times the wavelength of the light transmitted
The loss in signal power as light travels down a fiber is called attenuation
The bandwidth of optical fiber is 900 THz
If a mirror is used to reflect light, the reflected light angle is the same as the incident angle
Mode is a specific path the light takes in an optical fiber, corresponding to a certain angle and number of reflection
Spectral width is the width of the range of wavelengths emitted by the light source
Quantum theory states that light wave behaves as if it is consists of many tiny particles
Fiber optic cables operate at frequencies near 800 THz
When a beam of light enters one medium from another, frequency quantity will not change
Dispersion is used to describe the splitting of white light into its component colors
Luminance efficiency is minimum for a low wattage light bulb
An object farther from a converging lens than its focal point always has an inverted image
An object nearer to a converging lens than its focal point always has a virtual image
The real image formed by a spherical mirror is larger relative to its object
The wavelength of light has no role in polarization
Longitudinal waves do not exhibit polarization
Modal dispersion is caused by the difference in the propagation times of light rays that take different path down a fiber
The average insertion loss of fusion splice in fiber optics is 0.09 dB
The insertion loss of connector-type splices for a single mode fiber optics is 0.38 dB
The lifetime of LEDs is about 200,000 hours
The lifetime of ILDs is about 50,000 hours
Photodiodes used as fiber optic detectors are reversed bias
Step-index multimode type of fiber has the highest modal dispersion
Laser light is coherent and stimulated emission
Fiber optics – a dielectric waveguide for the propagation of electromagnetic energy at light frequencies
LED is a non-coherent light source for optical communications system
Semiconductor type of laser is the simplest to modulate directly by changing its excitation
Argon-ion laser emits light in the visible range, 400 to 700 nm
The proper measurement of average power emitted by a pulsed laser is pulsed energy times repetition rate
Atmospheric absorption does not harm laser efficiency
Doppler shift of moving atoms and molecules contributes to the broadening of laser emission bandwidth
The first laser emitted pulses of 694-nm red light
Molten is the stage of the sand becoming a silicon
LED is used as an optical transmitter in the Fiber Optical Communications
APD is used as an optical receiver in fiber optics communications
Then inner portion of the fiber cable is called core
Semiconductor laser is the simplest to modulate directly by changing its excitation
Consumer TV is not a common application of fiber-optic cable
Total internal reflection takes place if the light ray strikes the interface at a greater than angle to the critical angle
The operation of a fiber optic cable is based on the principle of reflection
Single-mode graded-index is not a common type of fiber-optic cable
Cable attenuation is usually expressed in terms of dB/km
The upper pulse rate and information-carrying capacity of a cable is limited by modal dispersion
The core of a fiber-optic cable is made of glass
The core of a fiber optic is surrounded by cladding
The speed of light in a plastic compared to the speed of light in air is slower
The main benefit of light-wave communications over microwaves or any other communications media is wider bandwidth
X-ray is not part of the optical spectrum
The wavelength of visible light extends from 400 to 750 nm
The speed of light is 300,000,000 m/s
Refraction is the bending of light waves
The ratio of the speed of light in air to the speed of light in another substance is called the index of refraction
A popular light wavelength in fiber-optic cable is 1.3 μm
Single-mode step-index type of fiber-optic cable is the most widely used
Single-mode step-index type fiber-optic cable is best for very high speed data
Single mode step-index type fiber-optic cable has the least modal dispersion
Reflection is not a factor in cable light loss
Laser is preferred for high-speed data in a fiber-optic system
Most fiber-optic light sources emit light in infrared spectrum
Both LEDs and ILDs operate correctly with forward bias
Single-frequency light is called monochromatic
Laser light is very bright because it is coherent
Photovoltaic diode is NOT a common light detector
Avalanche photodiode is the fastest light sensor
Photodiodes operate properly with reverse bias
An important requirement for successful transmission system using light: Powerful, reliable light source
Interference filter is used to block light from a laser and let other light through
Monochromatic and in-phase is a light that can be coherent
Coherence of laser light is important for holography
The ultrapure glass used to manufacture optical fibers is approximately 99.9999% pure
In fiber optics, PCS stands for Plastic-clad-silica
Longitudinal modes has no fixed limit, dependent on bandwidth and mode spacing
Infrared absorption is the result of photons of light that are absorbed by the atoms of the glass core molecules
In fiber optics, SCS stands for Silica-clad-silica
Helium laser was developed by A. Javen at Bell Laboratory in 1960
Spectral response of light detector determines the range of system length that can be achieved for a given wavelength
Dark current in light detectors is caused by thermally generated carriers in the diode
Ampere/watt is the unit of responsitivity
Dispersion is not a characteristic of light detectors
The typical wavelength of light emitted from epitaxially grown LEDs is 940 nm
SONET stands for Synchronous Optical Network
Bend loss is an attenuation increase caused by bends radiating from the side of the fiber
Infrared range of fiber optics is about 700 – 1200 nm
Higher losses is a disadvantage for plastic fiber optics
OTDR stands for Optical Time Domain Reflectometer
Under normal condition, a single fiber should not be used for a two-way communication mainly because of noise
A single mode optical fiber has a core diameter of 0.01 nm
A step-index multimode optical fiber has a core diameter of 0.02 nm
The graded-index multimode optical fiber has a core diameter of 0.05 nm
Stepped index operation is not a possible cause of optical fiber loss
Refractive index – the ratio of the speed of light in a vacuum and the speed of light in the material used
Splicing fiber means both fusion and butt
Optoisolator – an IC that represents a short distance one-way optical communications system
When light strikes a flat polished end of a fiber, it produces a loss of 4%
When light strikes a flat polished end of a fiber, the fiber loss produced can be reduced by antireflection coating
In fiber optics, higher-order mode refers to cladding boundary at high angle
Refraction is not a cause of light attenuation in fiber optics
Visible-light LEDs are not used for fiber optics because it has high losses
Optical cable testers are used for light power out of a fiber
A function of an optical isolator cancels reflected waves
An increase in light intensity produces fast optic switching due to amplification of optical signal
Light traveling in air optical fiber follows Snell’s law
Optical fibers for telecommunications are typically about 5 mils thick and consists of a glass core, a glass cladding of lower index of refraction, and a protective coating
Material dispersion is caused by the wavelength dependence of the index of refraction
The dominant loss mechanisms in silica fiber are absorption and Rayleigh scattering
The bandwidth of a fiber is limited by dispersion
Fiber bandwidth is generally specified as the product of the bandwidth and distance
The quantum efficiency of a detector is the fraction of incident photons that produce a photoelectron or electron-hole pair
In solid-state optical detectors, the excited charge is transported in the solid by holes and electrons
PMT is not a solid-state optical detector
Optical detectors are square-law devices because they respond to intensity rather than amplitude
The photocurrent is equal to the number of electrons emitted per second times the electron charge
PMT optical detector is used when high sensitivity and bandwidth are required
The average loss in fiber splice is about 0.15 dB
White color is not found in the visible light wave spectrum
The frequency limit of an optical fiber is about 40 GHz
The mechanical splice attenuation loss is 0.1 dB or less
Polymer jacket is applied to protect core and cladding of the fiber
The energy of the photon is directly proportional to the Planck’s constant
Refractive index of glass – 1.5
Refractive index of diamond – 2.0
The unit of light wavelength is Angstroms
The power loss of the fusion splice is about 0.01 dB or less
Optical power meter is used to test a fiber optics splice
Beam-splitting coupler – a coupler which consists of a series of lenses and a partly reflective surface
Diffuse reflection – Reflections in many directions
Lithium Niobate – commonly used electro-optic crystal for polarization modulation
Intensity modulation and polarization modulation are the most widely used in optical systems
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