Semiconductor quantum dots are an exciting new material for photonics and quantum information because their properties can be tailored to a wide extent. In a first approximation, they can be considered as artificial atoms, though it is quite clear that they are ‘atoms’ strongly interacting with their environment. This provides challenges as well as opportunities.
In nonlinear optics at high light intensity, the optical properties of materials – refractive index and absorption coefficient – are not longer constant but depend on the light intensity. The project was directed on exploring and characterizing the nonlinear optics characteristics of quantum dots as a novel photonic material with tailored properties under continuous (cw) laser driving. We choose to investigate room temperature ensembles of quantum dot because we consider these to be of potential relevance for future devices for all-optical switching applications and soliton-based photonics.
We demonstrated the saturation of absorption of quantum dots at room temperature under cw driving for InAs/GaAs QD close to the telecommunication wavelength range and for InAlAs/GaAlAs quantum dots in the 780 nm range. These results are in qualitative agreement with theoretical expectations.
Numerical simulations indicate that the nonlinear phase shifts induced by a saturation of the refractive index are strongly affected (and reduced) by the inhomogeneous broadening of the spectral characteristics of the quantum dots, but should be experimentally detectable by interferometric measurements and just sufficient to provide light localization and soliton formation, though absorptive losses are an issue. However, we did not find experimental evidence for this, which is possibly related to non-optimal sample quality.
Activities on the use of quantum dots for the generation of THz radiation are ongoing (click here for details).