Editing Laser diode rate equations (section)

==Spectral Shift==

Dynamic wavelength shift in semiconductor lasers occurs as a result of the change
in refractive index in the active region during intensity modulation.  It is possible to
evaluate the shift in wavelength by determining the refractive index change of the active
region as a result of carrier injection.  A complete analysis of spectral shift during direct
modulation found that the refractive index of the active region varies proportionally to carrier density and hence the wavelength varies proportionally to injected current.

Experimentally, a good fit for the shift in wavelength is given by:

:<math>\delta\lambda=k\left(\sqrt{\frac{I_0}{I_{th}}}-1\right)</math>

where <math>I_0</math> is the injected current and <math>I_{th}</math> is the lasing threshold current.