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1. What does meant by Optical Fiber communication?
Optical Fiber Communication is the method of communication in which signal is transmitted in the form of light and optical fiber is used as a medium of transmitting those light signal from one place to another.
2. What is meant by BER?
In telecommunication transmission, the bit error rate (BER) is the percentage of bits that have errors relative to the total number of bits received in a transmission.
3. What is the full form of LASER?
Light amplification by stimulated emission of radiation.
4. What is electromagnetic spectrum ?
The electromagnetic (EM) spectrum is the range of all types of EM radiation.
5. What is meant by Bit Interval ?
The bit interval corresponding to one single bit.
6. what is the full form of EDFA and what is the use ?
Erbium-Doped Fiber Amplifier (EDFA) is an optical amplifier used in the C-band and L-band, where loss of telecom optical fibers becomes lowest in the entire optical telecommunication wavelength bands.
7. Various Bands used in communication :
O-band (Original band) _ Used for single mode fiber
E-band (Extend band)_ Extend into region for fibers with low water content
S-band (short band)
C-band (Conventional band)
L-band (Long band)
U-band (Ultra long band)
8. What are the advantages and Disadvantages of Optical Fiber Communication ?
Advantages:
Secure communication
Speed
Distance
High bandwidth
Electromagnetic compatibility
Small size and Weight
Low cost
Immunity to interference and cross talk
Low transmission loss
Disadvantages:
Sophisticated plants are required for manufacturing optical fibers.
The initial cost incurred is high.
Joining the optical fibers is a difficult job.
9. What is the use of Hybrid device ?
It converts electrical signals into optical signals.
10. What is the intrinsic and Extrinsic type semiconductor ?
The pure type of semiconductor is the intrinsic type whereas the extrinsic is, the semiconductor in which impurities can be added to make it conductive.
11. What is Direct band gap ?
The band gap is called "direct" if the crystal momentum of electrons and holes is the same in both the conduction band and the valence band.
12. What is indirect band gap ?
In an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum value in the conduction band energy.
13. What are the characteristics of light source for communication ?
High coupling efficiency
High reliability
Low weight & Low cost
Better linearity
Power requirement must be low
Intensity
Wavelength
14. What is optical sours ?
A device that converts an electrical signal into an optical signal in optical communication is called optical sours. Two main optical sources used in OFM is LED and LASER.
15. write difference between Satellite communication and Optical fiber communication.
16. Draw block diagram of optical fiber communication.
17. What is the frequency range of Optical fiber communication ?
10 terahertz (104 gigahertz) to 1 million terahertz (109 gigahertz).
18. What is Light Intensity ?
Light intensity refers to the strength or amount of light produced by a specific lamp source.
19. What is Spectral Width ?
The spectral width of an optical source is defined as the range of wavelengths.
20. What is Polarization ?
The polarization means how your Electric Field inside the light changes with time.
21. What is Light Rays ?
A light ray is a line that is perpendicular to the light's wavefronts .
22. What is wave ?
A wave is a disturbance that moves energy from one place to another. Wave is a function of time and space.
23. What is plane waveform ?
When your waves having same phase at a same time is called as a plane wave form.
24. What is the difference between Reflection and Refraction ?
When light enters from one medium to another medium is called Reflection and When light bounce from the same material is called Refraction.
25. What is Refractive index(n) ?
Refractive index is the ratio of Velocity of light in the air to the Velocity of light in the particular medium. [ n = c/v ]
n of Air : 1
n of Water : 1.33
n of Glass : 1.50
n of Diamond : 2.42
26. What is Snell's law ?
When light travels from one medium to other, it gets refracted. Snell's law is the Relation between the angle of incidence and the angle of refraction.
[ n1sin θ 1 = n2sin θ 2 ]
For total internal reflection θ 2 should be 90.
27. What is Angle of incidence ?
The angle between the normal and the ray of light is called the angle of incidence.
28. What is Critical Angle ?
Minimum required angle for total internal reflection is called Critical Angle ( θ c)..
Eq for Critical angle : sin θ c = n2/n1
condition for Critical angle : n2>n1.
29. What is External reflection and Internal reflection ?
When light reflected off an optically denser material the process is referred as External reflection.
When light reflected off in less optically denser material the process is referred as Internal reflection.
30. Which principle used in Optical Fiber ?
Total internal reflection.
31. What is Mode ?
Mode is the combination of bunch of Plane waves.
32. What is Ray Congruence ?
Family of plane waves of corresponding mode form set of rays called Ray Congruence.
33. What is the condition for the light to propagate inside the fiber ?
For the light to propagate inside the fiber though total internal reflections at core-cladding interface, the refractive index of the core(n1) must be greater than the refractive index of the cladding(n2). [ n1>n2 ]
34. Which are the types of Fiber ?
Single mode fiber: ( only one mode is propagated )
single mode step index fiber
Multimode fiber ( many mode is propagated )
Multimode step index fiber
Multi mode graded index fiber
Step index fiber (Refractive index of core is uniform and undergoes an abrupt change at cladding boundary )
Graded index fiber ( Refractive index of core varies as function of the radial distance from the center of the fiber )
35. What is Core and Cladding in optical fiber ?
The optical fiber consist of two concentric cylinders , the inside solid cylinder is called the core and the surrounding shell is called the cladding.
36. What is Wave guide ?
A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction.
37. Which are the applications of Optical fiber ?
Medical. Used as light guides, imaging tools
Defense/Government
Data storage
Telecommunication
Networking
Industrial
Broadcast
Cable Television
Lighting and Decorations
38. What is Radiative Recombination and Non radiative recombination ?
Radiative recombination occurs when an electron in the conduction band recombines with a hole in the valence band and the excess energy is emitted in the form of a photon while in Non radiative recombination energy is emitted in the form of thermal heat.
39. What is Coherent source of light and Non-coherent source of light ?
Coherent source of light are those sources which emit a light wave having the same frequency and same wavelength while in Non-coherent source of light are those sources which emit a light wave having the different Frequency and different wavelength.
40. What is Lambertian pattern?
Emission pattern is isotropic with 120degree half power beam width. this pattern is called as Lambertian pattern.
41. What is isotropic and anisotropic ?
isotropic: Properties of a material are identical in all directions. anisotropic: Properties of a material depend on the direction.
42. What is carrier confinement ?
it's a percentage of a recombination of hole and electron in PN junction.
43. What is optical confinement or light confinement ?
Optical confinement is a property of waveguide. it describes how large in space the light mode is.
44. What is Homo junction and Hetro junction ?
In a simplest definition, a homojunction is a junction between the same materials. while A heterojunction is a junction between different materials.
45. LED and the LASER is the example of Double Hetro junction.
46. which transmission windows are used in Optical fiber communication ?
First window - 800-900 nm ( GaAs based source, multi mode fiber )
Second window - 1250-1350 nm ( Single mode and multi mode fiber used in LAN )
Third window - 1500-1600 nm ( Long span terrestrial and undersea transmission)
47. What is internal quantum efficiency ?
The internal quantum efficiency is defined as the ratio of radiative recombination to the total recombination rate.
48. What is External quantum efficiency ?
The ratio of the number of photons emitted from the LED to the number of electrons passing through the device.
49. Derive the equation of Quantum efficiency and Power.
50. What is Numerical aperture?
The Numerical aperture is defined as the sine of the acceptance angle θin. It is used to describe the light gathering or light collecting ability of optical fiber.
51. What is Acceptance angle ?
Acceptance angle is defined as the maximum angle at which the external light ray can strike the air/glass core interface and still propagate down the optical fiber.
51. What is the condition for wave propagation in dielectric slab.
Condition required for wave propagation in dielectric slab is that all points on the same phase fronts of plane wave must be in phase.
52. What are the limitation of ray model ?
The ray model gives an impression that during total internal reflection the energy is confined to the core only. However, it is not so. In reality the optical energy spreads in cladding also .
The ray model does not speak of the discrete field patterns for propagation inside a fiber.
The ray model breaks down when the core size becomes comparable to the wavelength of light.
53. what is the difference between step index and graded index fiber ?
Step index fiber is a fiber in which the core is of a uniform refractive index and there is a sharp decrease in the index of refraction at the cladding. Graded index fiber is a type of fiber where the refractive index of the core is maximum at the center core and then it decreases towards core-cladding interface.
54. what is V number ?
V number is a normalized frequency which gives you information about modes.
55. What is cut-off frequency ?
Cut-off frequency is a minimum frequency at which the signal can propogate.
56. What is Dispersion ?
Dispersion is the spreading of light pulse as its travels down the length of an optical fiber.
57. What is the difference between intermodal and intramodal dispersion ?
Dispersion caused by multipath propagation of light is known as intermodal dispersion. while the dispersion occure within a single mode fiber is known as intramodal dispersion.
58. What is Propagation constant ?
Propagation constant determines how the amplitude and phase of that light with a given frequency varies along the propagation direction.
59. What is ISI?
Intersymbol Interference (ISI) is the spreading of a 'bit' into the adjacent 'bit' periods.
60. What is Group velocity ?
The group of waves travel with certain velocity is called group velocity.
61. What is phase velocity ?
The velocity with which the phase of a wave travels is called phase velocity.
62. What is population inversion ?
The process in which the number of excited atoms is made larger than that of the number of atoms present at ground state is called population inversion.
63. What is pumping ?
The process of supplying energy to the laser medium is called pumping.
64. What is Mode of propagation?
Mode of propagation is defined as the path followed by light rays inside the fiber.
65. Why mirrors are used in Fabry-perot laser ?
The mirrors are used to establish a strong optical feedback in the longitudinal direction.
66. What is lasing ?
The condition at which light amplification becomes possible in the laser diode is defined as lasing. ( gain must be greater then threshold gain).
67. what is Radiance?
Radiance is defined as the optical power radiated into a unit solid angle per unit emitting surface area.
68. What is coupling efficiency or launching efficiency?
coupling efficiency is defined as the portion of the total optical power emitted by the light source, that is actually coupled into a fiber.
69. Define optical transmission windows.
The optical transmission windows are defined as the wavelength regions that offer low optical attenuation.
70. Define material absorption losses.
Due to some defects in the fabrication process of fiber optic cable some of the transmitted light is dissipated in it as heat. It is called as material absorption loss.
71. Define scattering losses.
The loss of signal energy caused by the diffusion of a light beam is known as scattering loss.
72. Define linear scattering losses.
The losses in which optical power gets transferred linearly from one mode to another mode without changing frequency are known as linear scattering losses.
73. Define non-linear scattering losses.
The losses taking place when the optical power is transferred from one mode to another mode in either the forward or backward direction at different frequencies are known as non linear scattering losses.
74. Define macrobending losses or Large radius losses.
The power loses taking place in the optical cables when the radius of bend is larger than the diameter of optical fiber, are called as the macrobending losses.
75. Define microbending losses or cabling losses.
The losses occuring due to small bending or distortions are known as Microbending losses.
76. Define quantum efficiency.
The Quantum efficiency of an LED is defined as the ratio of number of photons emitted out to the number of electrons injected in.
77. Define response time.
The response time of an optical source indicates how quickly, an electrical input drive signal can vary the optical output level.
78. Define modes of a cavity?
The modes of a cavity are defined a pattern of electric and magnetic field lines which is set up by the optical radiation inside the resonance cavity of a laser diode.
79. Define forward biased diode.
When positive terminal of source is connected to the P-side and negative terminal to N-side the diode is said to be forward biased.
80. Define reverse bias diode.
When positive terminal of source is connected to the N-side and negative terminal to P-side the diode is said to be forward biased.
81. Define attenuation.
Attenuation is the power loss taking place inside the fiber optic cable.
82. Define fresnel losses.
In case of fiber optic cable, at the interface of core and cladding layer there is a change in refractive index. This causes the fresnel loses.
83. Define Rayleigh scattering losses.
The power loss resulting due to tiny impurities is called as Rayleigh scattering losses.
84. Define Fresnel reflection.
The reflection of light occuring at an interface between two media having different refractive indices is called as fresnel reflection.
85. What is index profile ?
The index profile of an optical fiber is a graphical representation of the magnitude of refractive index on the x axis and the radial distance from the core axis on the y axis.
86. What is sintering ?
The process of converting perform into solid mass of material in the OVPO method is called sintering.
87. What is Mie scattering ?
The scattering of such inhomogeneity whose size is greater than λ /10 is always in forward direction and is known as Mie scattering.
88. What is stimulated brillouin scattering(SBC) ?
when loss occures due to thermal molecular vibrations within the fiber it is the known as the stimulated brillouin scattering loss.
89. What is stock shift and antistoke shift ?
If the scattered photons loss their energy then it is called as stoke shift and if they gain the energy then it is called as antistoke shift.
90. What is avalanche region ?
The avalanche region is the gain region, which is created in the n+ -p region.
100. What is the difference between intermodal and intramodal dispersion?
Intermodal dispersion : Dispersion caused by the delay between different modes. Typically, it is the delay between the shortest path (zero mode) and the longest path (critical mode).
Intramodal dispersion: Dispersion that is independent of modes, related to the line width of the source and caused by variations in the refractive index as a function of wavelength.
111. What is the difference between step index and graded index fiber ?
Step index fiber is a fiber in which the core is of a uniform refractive index and there is a sharp decrease in the index of refraction at the cladding. Graded index fiber is a type of fiber where the refractive index of the core is maximum at the center core and then it decreases towards core-cladding interface.
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