Laser Driving



Quantum cascade lasers exhibit I-Vcurves that have diode similar to those characteristics of short wavelength devices (l = 5 µm) to almost ohmic behaviour for l = 11 µm.  The differential resistance at the threshold is a few ohms. Longwavelength devices exhibit a maximum current above which, if driven harder, the voltage increases abruptly while the optical powerdrops to zero. This process which occurs only in unipolar lasers, is usually non-destructive and reversible if the device is not driven too hard above its maximum current.



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Room temperature I-V curves of a typical unipolar laser (measured in CW mode).
The device has a maximum operation current of 0.42 A. Using a higher current 
in the laser would result in no additional power (seen as aflattening of the power 
curve at high current) and eventually the apparition of Negative Differential 
Resistance (NDR).

Electrical model



Simply stated, the device can be modeled for electronic purpose by a combination of two resistorsand two capacitors. As shown by the I-V curves above, R1 increases from 10 to 20 Ohms at low biases and to 1-3 Ohms at the operating point.  C1 is a 100 pF capacitor (essentially bias independent) between the cathode and the anode coming from the bonding pads. C2 depends on how the laser is mounted in the Laboratory Laser Housing,C1<100 pF.