Electroabsorption and electrorefraction in InAs∕GaAs and InAs∕InP quantum dots

Abstract

Integrated optical cross connects and add-drop multiplexers require low loss polarization independent phase shifting elements. In a composite quantum well, a 0.46mm phase shifter provides a π∕4 phase shift by combining the quantum confined Stark effect (QCSE) and carrier depletion effect. All-optical switching due to state filling effect is also experimentally investigated recently. We investigate whether the discrete energy levels and the high peak absorption in quantum dots (QDs) provide an opportunity for increasing the electrorefraction. The electrorefraction in strained InAs∕GaAs and InAs∕InP quantum dots (QDs) is explored using a numerical model based on the 4×4 Luttinger-Kohn Hamiltonian. The excitonic states are calculated by matrix diagonalization with plane-wave basis states. We observe that the QCSE sharply increases with the height of the QD and is also optimized for small radius QDs. The QCSE in pyramidal QDs is considerably larger than in squares or cylinders. We finally present large electrorefraction in cone shaped pyramidal QDs. State filling effect in QDs further resulted to an electrorefraction higher than an order of magnitude compared to that by QCSE for an acceptable waveguide absorption loss.