Mid-infrared phase modulation by intersubband transitions in quantum wells

A mid-infrared phase modulator using the Stark effect on intersubband transitions in step GaAs-GaAlAs n-doped quantum wells is demonstrated. Upon illumination the carriers are excited from a ground state E₁ to a global state E₂. Because of the strong asymmetry of the structure, the transition energy is linearly blue or red shifted depending on the direction of the applied electric field. Owing to the Kramers-Kronig relations, absorption and refractive index are correlated. The present study consists in experimentally demonstrating this correlation in relation to intersubband transitions. To do so, an interferometer and standard lock-in techniques were used to simultaneously measure amplitude and phase modulation around 10.6 μm