Polarization sensitive optically addressed light modulators based on excitonic optical nonlinearities in optically anisotropic materials

We present optically addressed light modulators in which femtosecond pulses are used to manipulate the amplitude and polarization state of the modulated light through bleaching of the optical anisotropy inherent in these devices due to either a processing-related lowering of symmetry or growth on a low er symmetry surface. An optically addressed anisotropically strained GaAs/AlGaAs multiple quantum well modulator employing an ultrafast dynamic polarization rotation of similar to 17 degrees associated with the bleaching of the anisotropic excitonic absorption to achieve a femtosecond rise time and a contrast ratio of 160:1 is demonstrated. The underlying polarization dependent excitonic optical nonlinearities governing the performance of this device are measured and found to be in qualitative agreement with theoretical calculations performed using the generalized anisotropic multiband semiconductor Bloch equations. In addition, the extension of this device concept to other semiconductors is presented within the context of an optically addressed ultraviolet light modulator which exploits the bleaching of the optical anisotropy inherent in a ZnO film epitaxially grown on R-plane sapphire to achieve high contrast. The resultant modulation is characterized by a contrast ratio of 70:1, corresponding to a dynamic polarization rotation of 12 degrees.