Femto-Joule All-Optical Switching Using Epsilon-Near-Zero High-Mobility Conductive Oxide

Recently discovered extraordinary optical nonlinearities in epsilon-near-zero (ENZ) materials open a new realm of ultra-energy-efficient, all-optical switching devices for future optical communication and computation. In this paper, we propose a sub-micron, sub-pico-second, femto-joule level all-optical switch (AOS) using hybrid plasmonic-silicon waveguides driven by high mobility transparent conductive oxides (HMTCOs) such as cadmium oxide. Our analysis indicates that the ENZ-induced nonlinear optical effect is greatly enhanced by the high free carrier mobility in the telecom wavelength region. We propose an electrically tunable AOS device which is precisely biased at the ENZ condition, or the high-loss “OFF” state. Then the AOS device can be switched to the “ON” state with an unprecedented modulation strength of 15.9 dB/μm and a rapid switching time of 230 fs at the cost of an ultralow switching energy of 13.5 fJ. By defining a comprehensive metric using the product of device size, switching energy and switching time, the proposed ENZ-enabled device shows superior performance than any existing on-chip AOS device. We envision that such HMTCO-driven AOS device can be integrated with silicon photonic integrated circuits to realize on-chip optical signal processing and computation with ultra-low energy and ultra-high bandwidth.