Enhanced nonreciprocal light propagation based on epsilon-near-zero medium in the visible regime

Abstract

We have experimentally demonstrated the nonreciprocal light propagation based on the axially asymmetric nonlinear absorption in the epsilon-near-zero (ENZ) media titanium nitride (TiN) nanosheets and C60 arranged in tandem in the visible regime. TiN nanosheets have been prepared and characterized to show broadband and ultrafast nonlinear optical response with the maximum nonlinear absorption coefficient about −5.05×10−8 m/W at its ENZ wavelength, which is about ten times larger than that at 400 nm. With the enhanced nonlinear absorption of TiN nanosheets, a passive photonic diode fabricated with TiN-C60 in a tandem structure shows enhanced nonreciprocal transmission of femtosecond laser pulses with a nonreciprocity factor of 9.5 dB at the ENZ wavelength. The results show the potential applications of TiN nanosheets in ultracompact, polarization-independent, and physiochemically stable nonreciprocal light propagation and may pave way for the application of broadband ENZ-based all-optical devices.