101. Any amount of stress occurring at the core-cladding interface would be reduced by ______
Increasing Bandwidth
Increasing core Radius
Increasing Cladding Radius
Grading material composition
Answer.4. Grading material composition
Explanation:-
A problem that arises with the simple step-index approach to dispersion shifting displayed is that the fibers produced exhibit relatively high dopant-dependent losses at operation wavelengths around 1.55 µm.
This excess optical loss, which may be of the order of 2 dB km−1, could be caused by stress-induced defects which occur in the region of the core-cladding interface.
Alternatively, it may result from refractive index inhomogeneities associated with waveguide variations at the core-cladding interface.
A logical assumption is that any stress occurring across the core-cladding interface might be reduced by grading the material composition and therefore an investigation of graded-index single-mode fiber designs was undertaken.
102. In the equation of transit time or a group delay, the β in the given equation represent
Attenuation constant
Propagation constant
Boltzmann’s constant
Free-space
Answer.2. Propagation constant
Explanation:-
The transit time or group delay Γg for light pulse propagation along a unit length of fiber is the inverse of the group velocity Vg Hence:
‘The rate of change of phase of the fundamental mode propagating along a straight fiber is determined by the phase propagation constant β.
103. Most of the power in an optical fiber is transmitted in the fiber _________
Cladding
Core
Jacket
Any of the above
Answer.3.
Explanation:-
Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of infrared light through an optical fiber.
Usually in an optical fiber which is consist of a core inside and cladding outside. the function of the core is for light propagation, In order to avoid leakage of light during propagation, the cladding act as a protector usually has a lower refractive index than the core. It enables light confined well inside the core.
Most of the power in optical fiber is transmitted in the fiber core.
Most modes in multimode step-index fibers propagate far from the cutoff.
Modes that are cut off cease to be bound to the core of the fiber. Modes that are farther away from the cutoff wavelength concentrate most of their light energy into the fiber core. Modes that propagate close to cutoff have a greater percentage of their light energy propagate in the cladding.
Since most modes propagate far from the cutoff, the majority of light propagates in the fiber core.
104. For suitable power confinement of fundamental mode, the normalized frequency v should be maintained in the range 1.5 to 2.4μm 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?
Increasing level of silica doping in the fiber core
Increasing level of germanium doping in the fiber core
Decreasing level of silica germanium in the fiber core
Decreasing level of silica doping in the fiber core
Answer.2. Increasing level of germanium doping in the fiber core
Explanation:-
For suitable power confinement of the fundamental mode, the normalized frequency V should be maintained in the range 1.5 10 2.4 μm and the fractional index difference must be increased as a square function while the core diameter is linearity reduced to keep V constant.
This is normally achieved by substantially increasing the level of germanium doping in the fiber core.
It may be observed that higher concentrations of the dopant cause a shift to a longer wavelength which, when coupled with a reduction in the mode field diameter (MF, giving a larger value (negative of waveguide dispersion), leads to the shifted fiber characteristic.
105. A single-mode fiber has a zero-dispersion wavelength of 1.21μm and a dispersion slope of 0.08 psnm-2km-1. What is the total first-order dispersion at wavelength 1.26μm?
-2.8psnm-1 km-1
-3.76psnm-1 km-1
-1.2psnm-1 km-1
2.4psnm-1 km-1
Answer.2. -3.76psnm-1km-1
Explanation:-
The total first order dispersion for fiber at two wavelength is obtained by
106.The fibers which relax the spectral requirements for optical sources and allow flexible wavelength division multiplying are known as __________
Dispersion-flattened single-mode fiber
Dispersion-enhanced single-mode fiber
Dispersion-compressed single-mode fiber
Dispersion-standardized single mode fiber
Answer.1. Dispersion-flattened single-mode fiber
Explanation:-
A type of Glass optical Fiber providing low pulse Dispersion over a broad portion of the Light spectrum. This means it can operate at 1300-nm and 1550-nm wavelengths simultaneously.
The dispersion characteristics of single-mode fibers may be modified by the achievement of a low dispersion window over a low loss wavelength region between 1300 nm and 1600 nm. Such fibers are called Dispersion Flattened (DF) single-mode fibers.These types of fibers relax the spectral requirements for optical sources and allow flexible WDM.
To obtain DF fibers multilayer index profiles are fabricated with increased waveguide dispersion which provides overall dispersion over the entire wavelength range 1300 to 1600 nm. Basically, these fibers exhibit two wavelengths of zero total chromatic dispersion.
The dispersion-flattened single-mode fibers (DFFS) are obtained by fabricating multilayer index profiles with increased waveguide dispersion. This is tailored to provide overall dispersion say 2psnm-1km-1 over the wavelength range 1.3 to 1.6μm.
107. 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?
36.2 psnm-1 km-1
38.12 psnm-1 km-1
40.5 psnm-1 km-1
20.9 psnm-1 km-1
Answer.3.
Explanation:-
The total first-order dispersion DT a practical single-mode fiber may be written as:
108. An alternative modification of the dispersion characteristics of single-mode fibers involves the achievement of a low dispersion gap over the low-loss wavelength region between __________
0.2 and 0.9μm
0.1 and 0.2μm
1.3 and 1.6μm
2 and 3μm
Answer.3. 1.3 and 1.6μm
Explanation:-
An alternative modification of the dispersion characteristics of single-mode fibers involves the achievement of a low-dispersion window over the low-loss wavelength region between 1.3 and 1.6 μm.
Such fibers, which relax the spectral requirements for optical sources and allow flexible wavelength division multiplexing are known as dispersion-flattened single-mode fibers (DFFs).
109. Dispersion-shifted single-mode fibers are created by __________
Increasing fiber core diameter and decreasing fractional index difference
Decreasing fiber core diameter and decreasing fractional index difference
Decreasing fiber core diameter and increasing fractional index difference
Increasing fiber core diameter and increasing fractional index difference
Answer.3. Decreasing fiber core diameter and increasing fractional index difference
Explanation:-
Dispersion Shifted Fiber is a type of single-mode optical fiber with a core-clad index profile tailored to shift the zero-dispersion wavelength from the natural 1300 nm in silica-glass fibers to the minimum-loss window at 1550 nm.
Dispersion-shifted single-mode fibers are created by decreasing fiber core diameter and increasing fractional index difference. It is possible to modify the dispersion characteristics of single-mode fibers by tailoring some fiber parameters. These fiber parameters include the core diameter and relative index difference.
100. Dispersion-shifted fiber (DSF) was developed for use with ____
1000-nm Laser
1550-nm Laser
1000-nm LED
1550-nm LED
Answer.2. 1550-nm Laser
Explanation:-
Dispersion-shifted fiber (DSF) was developed for use with 1550-nm lasers.
In this fiber type, the zero-dispersion point is shifted to 1550 nm where the fiber attenuation is about half that at 1310 nm. Therefore this fiber allows a high-speed data stream of a single-wavelength channel at or near 1550 nm to maintain its fidelity over long distances.
111. Geometrical, mechanical, and transmission characteristics of a single-mode optical fiber, which has a zero-dispersion wavelength around _____
100 nm
500 nm
1300 nm
200 nm
Answer.2. 1550-nm Laser
Explanation:-
The cutoff-wavelength-shifted fiber is designed for long-distance high-power signal transmission. It describes the geometrical, mechanical, and transmission characteristics of a single-mode optical fiber, which has a zero-dispersion wavelength around 1300 nm wavelength. The fiber has a very low loss in the 1550-nm band, which is achieved by using a pure silica core. Since it has a high cutoff wavelength of 1500 nm, this fiber is restricted to operation in 1500 to 1600-nm region. It typically is used only in long-distance undersea applications.
