Abstract

Quantum dots (QD) offer new and promising possibilities for device applications in the optical communication 1.3 μm wavelength range. We are currently theoretically investigating the nonlinear optics of QD, in the continuous wave regime, of thin and thick quantum dot samples to have information on transmission properties, saturation parameter, self-lensing and nonlinear refractive index change. In particular we are exploiting whether self lensing can be used as indication for the nonlinear refractive index change. The long-term aim to use self-lensing in QD to have cavity solitons as predicted in [1]. The quantum dot material parameters used in the simulation are typical for the ones grown by Innolume and used e.g. in [2]. They are made of 10 layers of InAs quantum dots inside GaInAs quantum wells with size and composition of the dots such that the peak of the emission is around 1280 nm. The sheet density is of the order of 5 × 10¹⁰ cm². We follow a model developed by [1] that describes QD as a collection of inhomogeneously broadened two-level systems characterized by a homogeneous linewidth γ peaked around a frequency ω0 with coupling to a wetting layer. For a starting point we focus on a short sample so we do not need to consider diffraction and diffusion inside the medium. We calculated the response of these dots to a Gaussian beam of certain beam radius (15 μm), real and imaginary part of susceptibility as function of space. From that we obtain the transmission through these samples in absorption and gain regimes (Fig. 1). Fitting a suitable saturable absorption model we obtain absorption coefficient and saturation intensity as function of the detuning of the beam. The saturation is shown to follow a behavior in between the one for a dominantly homogeneously and inhomogeneously broadened medium.

© 2009 IEEE