QUANTUM INTERFERENCE VERSUS STARK INTERSUBBAND ELECTROOPTICAL MODULATION IN ASYMMETRICAL QUANTUM-WELLS

Intersubband optical transitions in asymmetrical quantum well structur es can generate very large second order optical nonlinearities. In par ticular it is possible to develop phase and amplitude electro-optical modulators that operate in the mid-infrared spectral range. In this pa per we show that there are two alternative approaches how to develop e fficient intersubband electro-optical modulators. The first approach i s based on the linear Stark effect in quantum well structures for whic h the transition energy between the subbands is linearly shifted under the application of a de-electric held across the structure. The secon d approach is based on envelope states mixing (or quantum interference ) due to the application of a de-electric field. In both cases either the change of the transition energies or the exchange dipole matrix el ements (or both) lead to the generation of large electro-optical coeff icients in the structures. We have investigated the characteristics of these two types of modulators and found that the quantum interference modulator is more suitable for phase modulation. Finally, we have dem onstrated the operation of quantum interference modulator in asymmetri cal coupled quantum wells structure. (C) 1996 Academic Press Limited