Page 187 - Photonics Essentials an introduction with experiments

Direct Modulation of Laser Diodes

Direct Modulation of Laser Diodes 181

Figure 8.2. There are interactions between the drive current and the carrier concentra-
tion, and between the photon density and the carrier concentration. These interactions
act to increase or decrease the population of carriers and the population of photons. The
photon and carrier concentrations interact to produce stimulated emission.

An increase in the carrier concentration leads to an increased rate of
photon emission. An increase in the photon emission increases the
rate of stimulated emission, which decreases the carrier concentra-
tion.
The equations for dN/dt and dN /dt are coupled:

dN J (N – n )
D
= – B(NP – n i ) – (8.1)
2
dt qd
For this discussion, let us rewrite this simply as
dN J
= – recombination rate
dt qd

N
Recombination rate = B 21 N fK th + (8.2)
r

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.