Quantum interference, stark, and carrier density infrared electrooptical modulation based on intersubband transitions in asymmetrical quantum wells

A new approach toward studying electrooptic modulation utilizing intersubband transitions in quantum wells is presented. Using first-order perturbation theory for analyzing the effect of a dc electric field on the linear susceptibility, an understanding of the mechanisms which give rise to intersubband electrooptic susceptibility is presented. This includes modulation due to the dc Stark effect, modulation due to coherent interference of the envelope states, and modulation of the carrier densities in populated subbands. We study several structures that maximize the electrooptic susceptibility of a particular origin and discuss the suitability of the various schemes for practical realizations. Finally, we derive a figure of merit for each type of modulator, taking into account the linear intersubband absorption, and show that highly efficient near-infrared modulators that operate at a wavelength of 1.5 μm can be realized.