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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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