Research On Broadband Terahertz Waveguide Splitter Based On F-STIRAP

Terahertz(THz)technology has the ability to carry large amounts of information over a wide frequency band,and has shown great potential in developing the next generation of ultra-high communication.Surface plasmon polaritons(SPPs)have attracted much attention due to the unique subwavelength characteristics and strong electromagnetic field binding ability.SPPs wavelength can be reduced below the diffraction limit.Therefore,using SPPs is a basic method for designing compact,miniaturized,and integrated terahertz functional devices.In this paper,a broadband and robust THz SPPs50%-50% waveguide beam splitter is designed using quantum control technology.The THz information is transmitted and processed through THz SPPs.Firstly,a brief overview of the principle for STIRAP is illustrated.The principle is to design two partially overlapping Gaussian shaped anti-intuitive laser pulses,achieving transfer of quantum states from the initial state to the target state with almost no energy loss in the intermediate process.The laser pulse duration of f-STIRAP is half that of STIRAP,only transferring the general population to the target state,while the other half of the population stays in the initial state and energy outputs in a ratio of 50%-50%.Based on this,as long as a pulse sequence similar to f-STIRAP is designed,the average splitting output of energy can be achieved.The design of 50%-50% waveguide beam splitter can be achieved by designing coupling strength curves between adjacent waveguides that satisfies the pulse sequence in f-STIRAP.Secondly,the method and steps of designing a 50%-50% waveguide beam splitter for THz SPPs couplers using f-STIRAP are described in detail.The coupling problem of two parallel SPPs waveguides at different gap distances is studied,and the curve relationship between the coupling strength and the waveguide distance at different terahertz frequencies is obtained;By adjusting the geometric parameters of the waveguide,the coupling strength curve of an anti-intuitive pulse sequence similar to fSTIRAP is obtained;According to the two curve relationships obtained above,the structure of the 50%-50% waveguide beam splitter to be designed in this paper is uniquely determined.Verify the transmission characteristics of the THz SPPs 50%-50% waveguide beam splitter through full wave simulation.Modeling and calculation in simulation software CST and Matlab show that the 50%-50% waveguide beam splitter designed using f-STIRAP in this paper supports transmission of THz SPPs on the structure surface,and can achieve 50%-50% energy beam splitting in 0.4THz-0.7 THz.Finally,two kinds of structures with different geometric shapes are selected,and it is deduced that when there is almost no coupling between the structures,the transmission spectrum formulas calculated by the Huygens superposition principle and the coupled mode theory are almost equal.Theoretically,it is proved that the Huygens principle is only applicable to non-coupling cases.In addition,a two-dimensional random metamaterial array is presented to verify the above inference,and the correctness of the inference is verified by full wave simulation and experimental results.It is further proved that in the absence of coupling,regardless of how the probability of the occurrence of the unit structure changes,the Huygens principle and the transmission spectrum formula obtained from simulation calculations are almost consistent;When the probability of the occurrence of a unit structure is constant,the position of the structure has no effect on the final spectra.