Dispersion, expressed in terms of the symbol At, is defined as pulse spreading in an optical...

 

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Dispersion, expressed in terms of the symbol At, is defined as pulse spreading in an optical fiber. As a pulse of light propagates through a fiber, elements such as numerical aperture, core diameter, refractive index profile, wavelength, and laser linewidth cause the pulse to broaden. Dispersion is generally divided into two categories: modal (or multimode) dispersion and chromatic dispersion. a) Define modal dispersion and chromatic dispersion. b) When considering the total dispersion from different causes, how can we approximate the total dispersion (denoted by Atrot)? c) A 2-km-length multimode fiber has a modal dispersion of 1 ns/km and a chromatic dispersion of 100 ps/km nm. This fiber is used with an LED of linewidth 40 nm. i. What is the total dispersion? ii. If the approximate bandwidth (BW) of a fiber can be related to the total dispersion by the following relationship: BW = 0.35/Attot, calculate the bandwidth of the fiber. (10 marks) (10 marks) (12 marks) (4 marks) iii. Find the transmission capacity of the fiber is expressed in terms of bandwidthxdistance. (6 marks) d) In building a network it is often useful to add together the signals from two or more fibers, or to send the signal from a single fiber out onto a number of fibers. How can this be done optically, without the need for intermediate electronics? Draw a simple sketch for this device. Dispersion, expressed in terms of the symbol At, is defined as pulse spreading in an optical fiber. As a pulse of light propagates through a fiber, elements such as numerical aperture, core diameter, refractive index profile, wavelength, and laser linewidth cause the pulse to broaden. Dispersion is generally divided into two categories: modal (or multimode) dispersion and chromatic dispersion. a) Define modal dispersion and chromatic dispersion. b) When considering the total dispersion from different causes, how can we approximate the total dispersion (denoted by Atrot)? c) A 2-km-length multimode fiber has a modal dispersion of 1 ns/km and a chromatic dispersion of 100 ps/km nm. This fiber is used with an LED of linewidth 40 nm. i. What is the total dispersion? ii. If the approximate bandwidth (BW) of a fiber can be related to the total dispersion by the following relationship: BW = 0.35/Attot, calculate the bandwidth of the fiber. (10 marks) (10 marks) (12 marks) (4 marks) iii. Find the transmission capacity of the fiber is expressed in terms of bandwidthxdistance. (6 marks) d) In building a network it is often useful to add together the signals from two or more fibers, or to send the signal from a single fiber out onto a number of fibers. How can this be done optically, without the need for intermediate electronics? Draw a simple sketch for this device.