Reviewer in Fiber Optics | ECE Board Exam

(Last Updated On: February 15, 2020)

Review Notes in Fiber Optics

This is the Reviewer 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

Complete List of Communications Engineering Review Notes

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