Intersubband electro-optical modulators based on intervalley transfer in asymmetric double quantum wells

An electro-optical modulator, comprising:

• a first semiconductor barrier layer and a second semiconductor barrier layer;
• a first quantum well layer having a conduction band minimum at a point in the Brillouin zone that is optically active at normal incidence for intersubband transitions, disposed between said first and second semiconductor layers;
• a second quantum well layer having a conduction band minimum at a point in the Brillouin zone that is optically inactive at normal incidence for intersubband transitions, disposed between said first and second semiconductor layers;
• a spacer layer disposed between said first and second quantum well layers, wherein said spacer layer has a conduction band minimum for establishing quantum confinement in said first quantum well layer at said L or X point and in said second quantum well layer at said .GAMMA. point, and is adapted for tunnelling between said first and second quantum well layers, and
• means for applying a controllable electric field in a direction normal to said first and second quantum well layers.

A method for modulating light of a selected wavelength, comprising the steps:

• (a) interposing an electro-optical modulator in the path of said light, wherein said modulator comprises
• a first semiconductor barrier layer and a second semiconductor barrier layer;
• a first quantum well layer having a conduction band minimum at the L point or the X point, disposed between said first and second semiconductor layers;
• a second quantum well layer having a conduction band minimum at the .GAMMA. point, disposed between said first and second semiconductor layers;
• and
• a spacer layer disposed between said first and second quantum well layers, wherein said spacer layer has a conduction band minimum for establishing quantum confinement in said first quantum well layer at said L or X point and in said second quantum well layer at said .GAMMA. point, and is adapted for tunnelling between said first and second quantum well layers;
• and
• (b) applying a selected electric field in a direction normal to said first and second quantum well layers to thereby control modulation of said light .