Calculate the numerical aperture of an optical fibre whose core and cladding are made of materials of refractive index 1.6 and 1.5 respectively.Įxplanation: Numerical aperture = n 1 2 − n 2 2−−−−−−−−√ġ3. Which of the following is known as fibre optic back bone?Įxplanation: Each computer on the network is connected to the rest of the computers by the optical wiring scheme called bus topology, which is an application known as fibre optic back bone.ġ2. A fibre optic telephone transmission can handle more than thousands of voice channels.Įxplanation: Optical fibre has larger bandwidth hence it can handle a large number of channels for communication.ġ1.
Since many modes are propagating, they will have different wavelengths and will take different time to propagate through the fibre.ġ0. When more than one mode is propagating, how is it dispersed?Įxplanation: When more than one mode is propagating through a fibre, then inter modal dispersion will occur. This micro-bends in fibre appears due to non-uniform pressures created during the cabling of fibre.ĩ.
This causes Rayleigh scattering.Įxplanation: Micro-bends losses are caused due to non-uniformities inside the fibre. Since the glass used in the fabrication of fibres, the disordered structure of glass will make some vibrations in the refractive index inside the fibre. Which of the following loss occurs inside the fibre?Įxplanation: Scattering is a wavelength dependent loss. Thus, there is no dispersion in the pulses and hence the output is not a distorted output.ħ. At the outer edge it travels faster than near the centre But almost all the rays reach the exit end at the same time due to the helical path. In which of the following there is no distortion?Įxplanation: The light travels with different speeds in different paths because of the variation in their refractive indices. Therefore the signal pulses are broadened thereby results in a distorted output.Ħ. Hence high angle rays arrive later than low angle rays. Which of the following has more distortion?Įxplanation: When rays travel through longer distances there will be some difference in reflected angles. Here the refractive index varies radially from the axis of the fibre.
How does the refractive index vary in Graded Index fibre?Įxplanation: The refractive index of the core is maximum along the fibre axis and it gradually decreases. Since a single mode has less dispersion than multimode, the single mode step index fibre also has low intermodal dispersion compared to multimode step index fibre.Ĥ. A single mode fibre has low intermodal dispersion than multimode.Įxplanation: In both single and multimode fibres the refractive indices will be in step by step. This angle is called a wave guide acceptance angle.ģ. Therefore, light incident on the core within the maximum external incident angle can be coupled into the fibre to propagate. What is the other name for a maximum external incident angle?Įxplanation: Only this rays which pass within the acceptance angle will be totally reflected. The reason for confining the light beam inside the fibres is the total internal reflection.Ģ. What is the principle of fibre optical communication?Įxplanation: In optical fibres, the light entering the fibre does not encounter any new surfaces, but repeatedly they hit the same surface.
0 kommentar(er)
