Study On Unidirectional Reflectance And Polarization Devices Based On Terahertz Grating Structures

The optical system with parity-time(PT)symmetry is a new type of optical structure.The real and imaginary parts of refractive index are required to satisfy even symmetry and odd symmetry respectively.By utilizing the adjustment of complex refractive index,the structure can be used to realize the unidirectional reflection of light.Most of the previous studies focused on the optical band and infrared band,but the design principle was applied to the terahertz band in this paper,and the unidirectional reflectors in the terahertz band were successfully designed.In addition,most of the studies have recently focused on the narrow THz band near 1 THz,and mainly focused on the polarization characteristics of transmitted light.In fact,polarization with wide spectrum can greatly expand the application of polarization.The study of reflected light is of great significance because of its can not being ignored in practical optical systems.Based on this,this paper is divided into two parts.In the first part,we analyzes the phenomenon of unidirectional invisibility and unidirectional reflection of two-layer non-PT symmetrical plate in infrared band.Thus,the unidirectional stealthy device of terahertz wave based on grating structure with flexible and adjustable effective refractive index is designed.In the second part,two kinds of two-dimensional sub-wavelength metal grating arrays with different structure periods have been designed theoretically.And the electromagnetic simulation software CST studio suite 2014 is used for stimulating the two-dimensional metal grating arrays in the 0.1-10 THz band.And the characteristics of reflection,transmission and polarization are numerically analyzed.Experimentally,we complete the fabrication of different periods structure of copper metal grating arrays with a thickness of 20 nm on a 500 um thick high-resistance silicon substrate using MEMS processes.The transmission and reflection characteristics of the grating array are measured by Fourier transform spectrometer.The results show that both of the transmitted light and the reflected light have good polarization performance in the wide spectrum range of the grating array structure.And the polarization region can be adjusted by adjusting the structure period.The study provides a reference for the further study and application of THz polarizer.