Current Modulation

 

One of the most direct way to transfer information into the output of a laser is to modulate the amplitude of the optical wave by varying the strength of the laser current excitation. Freetwm allows for arbitrary form of bias modulation, i.e. it is not limited to sinusoidal or square waveforms. Depending on the parameters of the modulation one can observe either a weakly non linear response or the onset of the so-called Q-switch regime.  

 

The latter case is depicted in the figure on the right where the laser emits bursts that exhibit a strongly multimode envelope evolving on the modal separation time scale. Another salient feature of the dynamics are the relaxation oscillation of the optical power around the frequency of 7 GHz.

figure ExampleI_2.png
 
 
The bursts repetition rate of 1 GHz is controlled by the frequency of the bias current modulation and is easily identifiable in the power spectrum. Some simple routines based on Octave or Matlab fft routines allow to perform optical and power spectrum of the field and of its intensity, respectively.