Transcription of 08 modulators 2015 - UCY
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08 modulators 2015 - UCY
1 Electrical-to-optical conversion: modulators HMY 645 Lecture 08 Spring Semester 2015 Stavros IezekielDepartment of Electrical and Computer EngineeringUniversity of Cyprus2PL(mW)IL(mA)[])(cos1tiItmIIBmBL+= += BI())(cos100tpPtmPPmL+=+= 0P)()(tIstPLLL=Consider the static optical power-versus-current characteristic of a laser diode; if we bias at point IBand then superimpose modulation, then the optical power will track changes in this. We show it here for sinusoidal modulation:Direct modulationLILP3 Although the method of direct modulation is a useful one, it suffers a number of problems:1. As well as the intensity of the light, the wavelength is modulated. (This phenomenon is called chirp.) Along with fibre dispersion, this leads to a chirp-induced dispersion limit on transmission The maximum bandwidth we can modulate up to is only a few tens of GHz at the very The maximum quantum efficiency ( ) in theory is 100%, and this places an upper limit on the slope efficiency (and therefore the gain ).
MACH-ZEHNDER MODULATORS 13 Lucent 14 Light from a laser can be described by its electric field. To keep things simple we consider a purely monochromatic laser (i.e. a …
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