Active Terahertz Silicon-based Metasurface Devices Integrated With Liquid Crystals

The recently developed fifth-generation(5G)wireless network has been industrialized across the world.It is necessary to accelerate the fundamental researches on the next-generation(6G)communications.As the demanded channel capacity in 6G systems goes far beyond today's,the terahertz(THz)band with higher carrier frequencies than the RF band is very promising.In the THz wave modulation device,the metasurface with resonance characteristics can accurately control the THz wavefront at the sub-wavelength level while keeping the device thin and light,and introduce an abrupt phase,which avoids the bulky problem of traditional THz modulation devices.In addition,the tunability of the device will greatly expand the functionality of the device,so how to realize an active dielectric metasurface is also a hot topic of research.In this article,we attempt to integrate liquid crystal to achieve the active metasurface,because liquid crystal has excellent electro-optic response and broadband birefringence from visible spectrum to microwave.First for the modulation of THz wave intensity,we propose a new type of dielectric metasurface tunable absorber.A mutation of intensity absorption can be realized by setting the radius of the resonance unit at the boundary condition when the director of the liquid crystal as the environmental medium is changed.As for the THz wavefront manipulation,a photopatterned liquid crystal grating is integrated on a polarization-dependent silicon-based metasurface to achieve dynamic modulation of the THz wavefront,which can actively change the focal position of the metasurface.High-purity silicon,with high transmittance in THz band and mature process technology,has become the first choice for preparing THz dielectric metamaterials,which also avoids the expensive and timeconsuming difficulties of preparing optical metamaterials.Besides,the process is introduced in detail from design and simulation to experimental preparation and testing.Our design may supply a promising strategy to realize multifunctional and tunable THz metasurface device and may promote the development of active tuning metasurface in THz regime.