Deck 3: Fiber Optics: Dispersion, Absorption, and Losses

Question 1

One of the given statements is true for intermodal dispersion. Choose the right one.

A)low in single mode and considerable in multimode fiber
B)low in both single mode and multimode fiber
C)high in both single mode and multimode fiber
D)high in single mode and low in multimode fiber

Answer 1

low in single mode and considerable in multimode fiber

Question 2

Meridional rays in graded index fibers follow

A)straight path along the axis
B)curved path along the axis
C)path where rays changes angles at core-cladding interface
D)helical path

Answer 2

curved path along the axis

Question 3

Skew rays follow a

A)hyperbolic path along the axis
B)parabolic path along the axis
C)helical path
D)path where rays changes angles at core-cladding interface

Answer 3

helical path

Question 4

 Which of the following statements best explain the concept of material absorption?

A)a loss mechanism related to the material composition and fabrication of fiber.
B)a transmission loss for optical fibers.
C)results in attenuation of transmitted light.
D)causes of transfer of optical power

Question 5

How many mechanisms are there which causes absorption?

A)one
B)three
C)two
D)four

Question 6

Absorption losses due to atomic defects mainly include-

A)radiation
B)missing molecules, oxygen defects in glass
C)impurities in fiber material
D)interaction with other components of core

Question 7

The effects of intrinsic absorption can be minimized by-

A)ionization
B)radiation
C)suitable choice of core and cladding components
D)melting

Question 8

Which of the following is not a metallic impurity found in glass in extrinsic absorption?

A)fe2+
B)fe3+
C)cu
D)si

Question 9

Optical fibers suffer radiation losses at bends or curves on their paths. State true or false

Question 10

In the given equation, state what ?r suggests;

A)radius of curvature
B)refractive index difference
C)radiation attenuation coefficients
D)constant of proportionality

Question 11

A multimode fiber has refractive indices n1= 1.15, n2=1.11 and an operating wavelength of 0.7?m. Find the radius of curvature?

A)8.60?m
B)9.30?m
C)9.1?m
D)10.2?m

Question 12

A single mode fiber has refractive indices n1=1.50, n2= 2.23, core diameter of 8?m, wavelength=1.5?m cutoff wavelength= 1.214?m. Find the radius of curvature?

A)12 mm
B)20 mm
C)34 mm
D)36 mm

Question 13

How the potential macro bending losses can be reduced in case of multimode fiber?

A)by designing fibers with large relative refractive index differences
B)by maintaining direction of propagation
C)by reducing the bend
D)by operating at larger wavelengths

Question 14

Sharp bends or micro bends causes significant losses in fiber. State true or false

Question 15

A multimode step index fiber has source of RMS spectral width of 60nm and dispersion parameter for fiber is 150psnm^?1km^?1. Estimate rms pulse broadening due to material dispersion.

A)12.5ns km^?1
B)9.6ns km^?1
C)9.0ns km^?1
D)10.2ns km^?1

Question 16

. A multimode fiber has RMS pulse broadening per km of 12ns/km and 28ns/km due to material dispersion and intermodal dispersion resp. Find the total RMS pulse broadening.

A)30.46ns/km
B)31.23ns/km
C)28.12ns/km
D)26.10ns/km

Question 17

?g= d? / C*dk. What is ? in the given equation?

A)attenuation constant
B)propagation constant
C)boltzmann's constant
D)free-space

Question 18

A single mode fiber has a zero dispersion wavelength of 1.21?m and a dispersion slope of 0.08 psnm^?2km^?1. What is the total first order dispersion at wavelength 1.26?m.

A)-2.8psnm^?1 km^?1
B)-3.76psnm^?1 km^?1
C)-1.2psnm^?1 km^?1
D)2.4psnm^?1 km^?1

Question 19

The dispersion due to material, waveguide and profile are -2.8nm^?1km^?1, 20.1nm^?1km^?1 and 23.2nm^?1km^?1respectively. Find the total first order dispersion?

A)36.2psnm^?1 km^?1
B)38.12psnm^?1 km^?1
C)40.5psnm^?1 km^?1
D)20.9psnm^?1 km^?1

Question 20

Dispersion-shifted single mode fibers are created by

A)increasing fiber core diameter and decreasing fractional index difference
B)decreasing fiber core diameter and decreasing fractional index difference
C)decreasing fiber core diameter and increasing fractional index difference
D)increasing fiber core diameter and increasing fractional index difference

Question 21

An alternative modification of the dispersion characteristics of single mode fibers involves achievement of low dispersion gap over the low-loss wavelength region between -

A)0.2 and 0.9?m
B)0.1 and 0.2?m
C)1.3 and 1.6?m
D)2 and 3?m

Question 22

The fibers which relax the spectral requirements for optical sources and allow flexible wavelength division multiplying are known as-

A)dispersion-flattened single mode fiber
B)dispersion-enhanced single mode fiber
C)dispersion-compressed single mode fiber
D)dispersion-standardized single mode fiber

Question 23

For suitable power confinement of fundamental mode, the normalized frequency v should be maintained in the range 1.5 to 2.4?m and the fractional index difference must be linearly increased as a square function while the core diameter is linearly reduced to keep v constant. This confinement is achieved by-

A)increasing level of silica doping in fiber core
B)increasing level of germanium doping in fiber core
C)decreasing level of silica germanium in fiber core
D)decreasing level of silica doping in fiber core

Question 24

Any amount of stress occurring at the core-cladding interface would be reduced by grading the material composition.