EE409_Exam_May2007_solutions

EE409_Exam_May2007_solutions - Question 1(a Main points The...

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EE409 Solutions 2007 Page 1 of 5 Question 1 (a) Main points : The terms on the right hand side of the equation for the photon density deal with the generation of photons by spontaneous and stimulated emission, and the loss of photons by recombination and emission from the laser facets. The terms on the right hand side of the equation for the carrier density deal with the loss of carriers by spontaneous and stimulated emission, and the gain of carrier by application of current to the laser device. [14 marks] Main points of the modulation response are that it is flat at low frequencies and then peaks around the relaxation oscillation frequency before rolling off. [6 marks] (b) The loss profile of silica optical fibre which is used for optical communication systems is dominated by rayleigh at wavelengths < 1 µ m, and by infra-red absorption at wavelengths > 1.6 µ m. It also has a large absorption peak at wavelengths around 1.4 µ m due to impurities, thus the two transmission windows which are normally used for optical communication systems are those around 1.3 and 1.5 µ m. To overcome the loss in optical fibre it is necessary to use either in- line regenerators consisting of a photodetector, an electrical amplifier and a laser, or an optical amplifier. The dispersion profile of standard fibre is normally zero around 1300 nm, but by using dispersion shifted fibre it is possible to put the dispersion at around 1550 nm. This optimises both fibre loss and dispersion at the same wavelength, which clearly becomes the optimum wavelength for data transmission.
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This note was uploaded on 03/23/2011 for the course EEE 174 taught by Professor Kasab during the Spring '11 term at ASU.

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EE409_Exam_May2007_solutions - Question 1(a Main points The...

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