Page 191 - Photonics Essentials an introduction with experiments

Direct Modulation of Laser Diodes

Direct Modulation of Laser Diodes 185

dN N – spont N A 21
= +B 21 N · f·K th – 2 (8.9)
dt

dN J N
= – B 21 N · f·K th – (8.10)
dt qd r
As we have already noted, these equations are coupled by the stimu-
lated optical emission term that appears in both equations. However,
this term appears with the opposite sign, and so an increase in the
photon density causes a decrease in the carrier density, which leads to
a decrease in the photon density, which leads to an increase in the
carrier density. The response of the system is not immediate. There is
a delay that is governed by the recombination time r between the
stimulus and the response. We can imagine the process in the dia-
gram shown in Fig 3. The resulting effect of bringing the laser above

Figure 8.3. Schematic diagram of the relaxation oscillation cycle in a semiconductor
laser.

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