Ultrafast Electro‐Absorption Switching in Colloidal CdSe/CdS Core/Shell Quantum Dots Driven by Intense THz Pulses

Next-generation high-speed optical networks demand the development of ultrafast optical interconnects capable of Tbit/s data rates. By utilizing colloidal CdSe/CdS core/shell quantum dots, gated by intense THz pulses, a proof of concept of an all-optical femtosecond electro-absorption switch is presented in this work. Without any additional enhancement of the THz electric field, an extinction contrast of more than 6 dB and transmission changes in the visible of more than 15% are achieved, with the latter setting a new record for solution-processed electro-absorption materials at room temperature. The absence of physical artifacts, originating from electrodes and field enhancing structures, allows to employ a simple and intuitive numerical model, which rationalizes the large field-induced electro-absorption response. Supported by theoretical calculations, the importance of the energy band alignment of heterostructure quantum dots are discussed for the first time and suggest that further improvement of the modulation depth and contrast may be achieved with Type-II quantum dots.