We found that the optical power increases with an increasing current across the diode, provided that the current was greater than some threshold current, as expected.  Experimentally, we found this threshold current to be in the range from 20mA to 20.5mA.  This coincides with the specifications for the diode laser which gives a threshold current of 20mA.  

When the current reached 50mA, a standard operating current according to the specifications, the power jumped down 30% before leveling off (see graph above).  An interesting feature was noticed in this region.  There is a hysterisis in this relation for currents of about 50mA.  As was noted earlier, going in the direction of increasing current would cause the power decreased dramatically once the current was past 50mA.  However, once in this regime, decreasing the current would result in no change of power until a current of approximately 48mA, at which the power would jump back up to a unique value.  The temperature of the diode for this portion of the experiment was held constant at 20 degrees Celsius.

    As the diode current is increased, the spectrum of the laser should collapse into a single infinite peak.  As can be seen by viewing the graphs in the thumbnails below, the width of the peak does not appear to always decrease as the current increases.

23mA.gif (7156 bytes)     34mA.gif (7361 bytes)     44mA.gif (7235 bytes)     48mA.gif (6631 bytes)

A plot of the width of the spectrums at half of the maximum height is shown below.

The data seems to fall into three regions.  The first region corresponds to currents from 21mA, where lasing first occurs to about 25mA.  Here the width of the peak decreases with current.  The third region (skipping the second momentarily) is from 40mA to 48mA, where again the width of the peak decreases with current.  However, the region from 25mA to 40mA is different.  As the current increases, the width increases as well.  Despite this odd behavior, the laser did get closer to a single mode as current increased (see thumbnails and graph below).

Click for full sized image

    However, the relationship of the peak wavelength with respect to current did not behave as expected.  We expected either an increase or a decrease.  What we found was a decrease followed by an increase.  The plot of this data is shown below.

    

    Our wavelength vs. temperature dependence was performed by measuring the peak of various spectra.  The individual spectrums are thumbnailed below.  As can be seen in the peak wavelength below the peak wavelength seems to asymptotically approach some wavelength as the temperature is increased.  The current was fixed at 47.8mA so that the output was single mode. 

(Individual spectra)

10C.gif (7213 bytes)   15C.gif (8024 bytes)   20C.gif (7394 bytes)   25C.gif (7405 bytes)   30C.gif (7758 bytes)

 

 

 

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