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MOST FREQUENT QUESTIONS FROM OPTICS & FIBER
OPTICS WITH SOLVED ANSWERS
(1) Define total internal reflection
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refracted
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which among the following is the property of light?
a
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c
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Diffraction
Reflection
Total internal reflection
All the options
Answer: d) All the options
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(3)How can you observe Dispersion?
(1) Wood
(2) Wall
(3) Paper
(4) Prism
Answer: (4) Prism
Explanation: A prism is an optical device through which we can observe the dispersion of white light into its
constituent colors
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what are the types of images formed?
(1) Real
(2) Virtual
(3) Neither real nor virtual
(4) Both real and virtual
Answer: (4) Both real and virtual
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(6)
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b
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d
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Explanation: Light displays both wave and particle nature
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Photons have a mass of more than two grams
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TRUE
b
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(8)
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a
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NO
Answer: a) YES
(8)
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b
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d
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(9)
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b
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d
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(11) Refraction is used in which devices Cameras?
a
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Telescopes
c
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(11)
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A ray of light travelling
horizontally is reflected first from one mirror and then from the other
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A plane mirror reflects a pencil of light to form a real image
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(b) Convergent
(13) For the sustained interference of light, the necessary condition is that the two sources should
(a) Have constant phase difference
(b) Be narrow
(c) Be close to each other
(d) Of same amplitude
Ans
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(c) 49:1
(15) Intensity of light depends upon which factor?
(a) Velocity
(b) Wavelength
(c) Amplitude
(d) Frequency
Ans
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(b) Spherical
(17)
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Now ratio of their intensities will be
(a) 16/9
(b) 49 : 1
(c) 9/16
(d) None of these
Ans
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Ratio of (intensity) max(intensity) min is
(a) 1/100
(b) 1/10
(c) 10/1
(d) 3/2
Ans
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(20) What is multimode fiber?
Multimode fiber is optical fiber that allows light to travel down multiple paths, also referred to as modes
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5 microns
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(21)What is singlemode fiber?
Singlemode fiber is optical fiber that allows light to travel down a single path known as the fundamental
mode
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Singlemode fiber can be used to transmit AV signals
over extreme distances up to many miles or kilometers
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How is an AV signal transmitted down a fiber?
A fiber optic transmitter converts the AV signal into an optical signal, using a VCSEL or laser diode as a
light source
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A photo detector in a fiber optic
receiver at the far end of the fiber converts the optical AV signal back into an electrical AV signal
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what is a light-emitting diode?
A light-emitting diode — LED is a semiconductor device that emits light when an electrical current passes
through it
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In fiber optics, an LED is used as a
light source for low-speed signals such as, TOSLINK or 100BASE-SX Ethernet, due to its low cost
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(24) What is a laser diode?
A laser diode is a semiconductor device that emits a narrow beam of coherent light, such as the beam of
light from a laser pointer
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(25)
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A VCSEL is a special type of laser diode that has
lower manufacturing costs than other types of laser diodes
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(26) What is a photo detector?
A photodetector is a semiconductor device that converts an optical signal into an electrical signal
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(27) What wavelengths are used with multimode fiber?
Multimode fiber is capable of transmitting a wavelength at or around 850 nm, 1300 nm, or 1550 nm
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(28) What wavelengths are used with singlemode fiber?
The most common wavelengths are 1310 nm and 1550 nm
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In OS1 singlemode fiber, wavelengths around 1390 nm
should be avoided due to high attenuation caused by absorption
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(29) What is the cutoff wavelength for singlemode fiber?
The cutoff wavelength for singlemode fiber is the minimum wavelength that supports one mode of
propagation
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Below the cutoff
wavelength, singlemode fiber propagates more than one mode, similar to multimode fiber
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An optical transmitter uses a laser diode as the light source, varying the intensity of the
laser light in accordance with the electrical signal
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For digital signals, the light intensity is high or low,
which represents logical ones or zeros
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The optical receiver uses a photodetector to receive the optical signal and convert it into an
electrical signal
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what are the problems with the direct conversion of analog video signals into optical signals?
The direct conversion of an analog electrical signal to an optical signal and back has non-linear effects that
distort analog video signals
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Fiber also has attenuation that
causes optical power to dim over longer distances
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Amplifiers can compensate for low voltage, but also
increase signal noise, thereby reducing the signal-to-noise ratio
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(33)
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Converting the analog video signal to a digital signal for optical transmission
ensures the highest quality video
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How far can I transmit an AV signal on an optical fiber?
Optical AV signals can be transmitted for several kilometers or miles on singlemode fiber, and hundreds of
meters or thousands of feet on multimode fiber
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Typically, multimode fiber is used within buildings, between floors or on
the same floor, while singlemode fiber is designed for long haul transmission between buildings on a
campus or between facilities
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Long
distance transmission makes fiber optic products ideal for installation in stadiums, college campuses,
medical facilities, corporate campuses, performing arts centers, concert halls, and office buildings
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Fiber optics is the ideal technology for multi-gigabit digital video standards,
ensuring that an AV system is upgradable to future standards
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Comparatively, optical transmission is lower in cost than electrical
transmission for long distances
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To avoid these
emissions, secure areas in government buildings and at military installations are electrically isolated from
other parts of the facility to prevent any stray electrical emissions
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To intercept an optical signal traveling down a fiber, the connection must be interrupted, which
is easily detectable
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(38) What are the advantages of fiber optic AV systems in medical applications?
Medical systems need to isolate electrical equipment from the patient for safety, usually have space
constraints for cable runs, and must limit the effect of electrical interference on other sensitive medical
equipment
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Often, the displays are mounted on booms so that they can be adjusted for optimal viewing by the surgeon
and other medical staff
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Since fiber optic cables are made of glass, they isolate displays from medical imaging devices, are
small enough to fit inside of mounting booms, and emit no electrical signals that could affect other
equipment
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what are the advantages of fiber optic AV systems in hazardous environments?
There are often explosive or flammable vapors or gases in hazardous environments
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Since fiber optic cables carry light, they do not spark if broken
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(40) What are the advantages of fiber optic AV systems in electrically noisy environments?
Heavy equipment, such as industrial machinery, air conditioners, and motors emit strong electrical signals
that can interfere with AV signals carried in nearby copper wires
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(41) How can fiber optic technology future-proof an AV system?
The transition to digital video standards and higher resolutions has revealed the many limitations of copper
cabling
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Installing fiber optic cables in today's systems provides a path for future video signals
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(42) How does the size and weight of fiber cable compare to coaxial cable?
Optical fiber is much smaller and lighter than electrical cables, and has a capacity that is thousands of
times greater than coaxial cable
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7 mm (0
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5 inches)
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(43)When should singlemode fiber be used in an AV system?
Singlemode fiber is optimal for long haul transmissions of up to 30 km (18
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It is ideal for
transmitting signals between buildings on a university or corporate campus
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(44) When should multimode fiber be used in an AV system?
Multimode fiber is used to transmit signals for hundreds of meters or thousands of feet
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(45) What type of multimode fiber should be used for new installations?
OM4 or better multimode fiber is recommended for all new installations
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OM4 or better fiber optic cable provides a level of future proofing as video
resolution and data rates continue to rise
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If existing
fiber runs are being extended through fusing or connecting fibers together, the same fiber core size is
normally used
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(47) Why is singlemode fiber less costly than multimode fiber?
Singlemode fiber has a step index core, while multimode fiber has a graded index core with very tight
performance requirements
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(48) Why not always use singlemode fiber?
Laser light sources and photo detectors used for singlemode applications are significantly more expensive
than those used for multimode
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(49) Can singlemode and multimode fiber be intermixed?
Developing a system that uses both singlemode and multimode fiber is possible if using a switching system
that supports both fiber types, such as the Extron FOX Matrix Series
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Directly connecting
singlemode and multimode fiber is not
(50)
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The LC connector is
very popular due to its high performance, small size, and ease of use
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The MTP/MPO is the preferred connector type for 40 Gbps and 100 Gbps data
transmission standards
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However, the LC
connector is preferred for modern installations due to its compact size, self-locking feature, and alignment
capability
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Alternatively, an adapter can be used with a patch cable to convert from one connector type to
another
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what is an optical loss budget?
An optical loss budget is the maximum amount of optical loss or attenuation allowable in a fiber optic link
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(53)
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This number is subtracted from the loss budget to
determine the loss margin
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(54) What types of fiber optic cables are available for AV applications?
Fiber optic cables are available in many different construction types depending on the application
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Outdoor cables
are available as aerial cables or direct burial
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(55) What is dark fiber and how is it used for AV systems?
Dark fiber is pre-installed fiber optic cable that was installed for future use but is not currently being used
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If available, dark fiber
can be used to install new AV equipment without the added cost of installing new fiber
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(56) What types of fiber optic products does Extron offer?
Extron offers fiber optic matrix switchers, switchers, distribution amplifiers, signal processors, extenders,
cables, and accessories
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75 miles)
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(58)
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(59) What is the advantage of LC-type connectors on Extron products?
The LC-type connector used on Extron products is very popular in fiber optics due to its high performance,
small size, reliable connectivity, and precise core alignment
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All Extron fiber optic cables are bend-insensitive to simplify
installation and reduce bend-induced losses
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(61) What is the advantage of Extron bend-insensitive fiber optic cabling?
Extron multimode and singlemode fiber optic cables are bend-insensitive to simplify installation and reduce
bend-induced losses
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5 mm fiber bend radius
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It has the information-carrying capacity to handle the highest
resolution video resolutions in use today, and is designed to handle even higher resolution video signals of
the future
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The Extron Fiber Optic Termination Kit includes all of the
tools and equipment needed to strip, prepare, cleave, and terminate a fiber optic cable using Extron
Quick LC Fiber Optic Connectors
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(64) What type of fiber optic test equipment does Extron offer?
Extron offers a Fiber Optic Test Set with all of the tools needed to measure optical power and loss in
multimode and singlemode fiber optic AV equipment and cabling
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The power meter, compatible with both multimode and singlemode fiber and
featuring an easy-to-read LCD display, is used for measuring insertion loss in dB and optical power in dBm
or watts
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The School of
Emerging Technologies provides in-depth instruction designed to allow system designers and integrators to
master additional AV technologies within a short time span
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The student-instructor ratio is kept low to ensure that each class member receives
individual attention
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(66) What skills are needed to install optical fiber for AV systems?
The skills needed to install fiber optic cabling are similar to the skills required for installing copper cabling
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Field
termination kits are available that make fiber termination as easy as terminating coaxial cable
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(67)
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It is extremely important not to bend the
fiber beyond the manufacturer's recommendation
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Many newer
cables are using a special fiber construction called bend-insensitive fiber, which has an extremely tight
bend radius
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(69) What considerations exist when joining fibers using a connector?
Special care must be taken when connecting and disconnecting optical cables to avoid damaging the fiber
or the connector on the device
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The fiber and connector should be cleaned prior to mating
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(70) When do I clean the fiber optic connectors?
Both the fiber and connector ends should be cleaned immediately before mating
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(71) Why do I need to clean fiber optic connectors?
Even in clean environments, a single dust particle could completely block an optical signal
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(72)
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The swabs are for cleaning inside of
the connector on an instrument
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(73) Can fiber optic light cause harm?
Although the light used for fiber optic transmission is in the infrared range and is not visible to the human
eye, it can still cause damage
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Avoid
looking into a fiber if it is unknown whether there is an active light source
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The most appropriate method depends on the optical loss budget, the application type, what
equipment is available, and the skills of the repair technician
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A connector splice is generally used when another component or device must be
installed in line with the fiber
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Index matching gel is used to hold the cores together
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This produces a very low-loss connection that is superior to a mechanical splice
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(77) How do you identify the type of dark fiber installed if it is poorly documented?
The color of the fiber jacket may identify the type of fiber
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Cable markings may also help identify the manufacturer and type of cable
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However, field testing to (78)
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If the fiber optic cable includes a metallic armor, it is marked as OFCP for Optical Fiber
Conductive Plenum
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If the fiber optic cable includes a metallic armor, it is marked as OFCR for
Optical Fiber Conductive Riser
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(ii) Here waves should be of the same frequency
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(iv) The amplitudes of both the waves should also be the same
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(ii) The light waves should be of same
wavelength
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(83) Interference fringes are not formed by two independent sources why?

Interference can never be obtained with two independent sources of light, such as two bulbs or two
candles, due to the fact that any two independent beams of light are always incoherent
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(85) How does diffraction put a limit on the resolution power of instruments?
When two point objects lay close by, their diffraction patterns may overlap
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Hence their resolution becomes difficult
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(86) What are the difference between interference and diffraction of light?
In interference
The contrast between maxima and minima is very good
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The width of the fringes is not equal in diffraction
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(87) Give some examples of interference of light in nature

Blue Morpho Butterfly
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Color Patches on Wet Roads
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Oil on the Surface of Water
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(88) What is mirage?
an optical illusion caused by atmospheric conditions, especially the appearance of a sheet of water in a
desert or on a hot road caused by the refraction of light from the sky by heated air
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Also known as retinal persistence, this optical effect was
described by English-Swiss physicist Peter Mark Roget in the nineteenth century
(90) What is the minimum deviation of a prism?
In minimum deviation, the refracted ray in the prism is parallel to its base
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Also, the angles of refractions are equal i
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r 1 = r2
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(91) What is the minimum angle of deviation of a prism?
Angle of minimum deviation is the minimum angle at which the angle of incidence will be equal to the angle
of emergence and the refracted ray will be parallel to the base of the prism
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(93) What is the difference magnification and power of lens?
Magnification is equal to the ratio of size of image and size of object
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Magnifying power - magnifying is equal to the ratio of the dimension of the image
and the object
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This
causes the dispersion of light
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Find the radius of curvature of the convex surface of a plane convex lens, whose focal length is
0
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5?
Ans
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15 m
(96) Show that the limiting value of the angle of prism is twice its critical angle? Hence define

critical angle?

Ans
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(97) The magnifying power of an astronomical telescope in the normal adjustment position is 100
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calculate the focal length of the
objective and the eye piece
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—-(1)

fo = 100 fe —-(2)
Substituting equation
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Parallel
rays of light are incident on the lens
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(1) When

the lens behaves as a convex lens
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The phenomenon of reflection of light when a ray of light traveling from a denser medium is sent back
to the same denser medium provided the angle of incidence is greater than the angle called critical angle is
called total internal reflection
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No silvering needed

2
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(100)
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By what
distance would the pin appear to be raised if it is viewed from the same point through a 15 cm thick
glass slab held parallel to the table? Refractive index of glass = 1
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Does the answer depend on the
location of the slab?
Ans
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e
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