Research On Non-reciprocal Devices For Terahertz Wave

Surface plasmon polaritons(SPPs)sustained by the interface between a dielectric and plasmonic material exhibit the nonreciprocity of propagation under an applied static magnetic field,and such type of nonreciprocal SPPs is generally referred to as surface magnetoplasmons(SMPs).When the cyclotron frequency of electrons in the plasmonic material is comparable to the plasma frequency,the SMP asymptotic frequency differs distinctly in the forward and backward directions,and as a result,SMPs propagate in only one direction within the interval between the two different asymptotic frequencies.To ensure one-way SMPs immune to backscattering,bulk modes in the dielectric cladding must be suppressed,and this can be realized by introducing a band-gap material to terminate the dielectric.At terahertz frequencies,metal is an ideal band-gap material because it resembles a perfect electric conductor(PEC),therefore robust one-way SMPs can be realized in the layered system of plasmonic material,dielectric,and metal.Since one-way mode can completely suppress backscattering from discontinuities or bends,the one-way waveguide can be utilized to construct nonreciprocal optical devices with high transmission efficiency,thus the problem of device design is largely simplified.Terahertz Y-branch power splitters formed by one-way waveguide are investigated theoretically.For such splitters,there exists no backward reflection from the Y-junction region for incident waves because the input channel supports no backward-propagating mode,therefore the transmission efficiency is perfect in the lossless case.Moreover,by varying the applied external magnetic field,the power splitting ratio of the splitters can be tunable for a given operation frequency,and required(equal or unequal)splitting ratio can also be achieved over a wide frequency band.In addition,we have proposed an approach to completely trap EM radiation based on one-way SMPs.It has been shown that,in a system consisting of a magnetized semiconductor with cladding of a dielectric heterostructure,terahertz one-way SMPs can be completely trapped near the interface of the heterostructure,and a trapped hotspot on subwavelength scale has been generated there.Finally,we present an application example of one-way terahertz waveguide for realizing a THz transmission line and switch.