Voltage Modulation

 
Another efficient way to modulate an incoming optical signal is to use a saturable absorber based electro-optical modulator. Here, the imposed modulation of the reverse voltage induces a change in the band-gap frequency of the semiconductor material therefore modifying the amount of saturable absorption at the wavelength of the injected field. Freetwm can be used to study the optical response to an arbitrary modulation of the active medium band-gap.
 
figure ExampleJ_1.png
One can observe on the left the optical response of an absorber submitted to an 5 GHz sinusoidal modulation of its band-gap frequency. The incoming signal is 2 ns quasi-square pulse. Notice how such a few nanometers harmonic modulation of the band-gap give rise to a strongly non linear response with 100% modulation depth.