A Research On Flexible And Ultra-thin Terahertz Beam Steering Device

Terahertz(THz)waves are electromagnetic waves between microwave and infrared bands.Due to their special position in the electromagnetic spectrum,terahertz wave has important applications in high-frequency communication,astronomical remote sensing,fingerprint spectroscopy,security imaging and other fields.In the design and research of terahertz systems,terahertz functional devices have always been one of the emphasis of research.Among them,the terahertz beam steering device,as one of the terahertz functional devices,has the functions of deflecting and focusing the terahertz wave,and is often used in terahertz communication and imaging systems.Due to the short wavelength of terahertz wave(wavelength of 30-3000 ?m),the feature size of the terahertz beam steering device is also very small,which leads to the complexity of the processing technology.Meanwhile,the traditional metal beam steering device substrate uses hard materials,which cannot be bent.The thickness is large,and the reflection of terahertz waves is also high.Excessive reflection would affect the normal operation of the terahertz system.Therefore,the work of this paper focuses on the design of terahertz beam steering devices,which deflect terahertz waves,and take the advantages of ultra-thin,flexible and low reflection,and are fabricated by simpler and faster methods.The main research contents of this thesis are as follows:First,terahertz beam steering devices based on Fresnel zone plate(FZPs)were fabricated using graphene oxide(GO)and laser reduced graphene oxide(LRGO).LRGO was prepared on graphene oxide films by laser direct writing equipment.The terahertz time-domain spectroscopy system(THz-TDS)was used to test the response characteristics of the prepared LRGO to the terahertz beam.The results showed that the transmission of the prepared LRGO to terahertz wave is reduced to less than 60%,while the transmittance of the GO film can reach about 90%.Using this fabrication method,a specific pattern can be drawn on the GO film.First,according to the response characteristics of GO/LRGO to terahertz waves,the parameters of the designed pattern are optimized.The laser direct writing equipment is directly processed on the GO film,and the terahertz reflectivity of the fabricated device is reduced to 10%,which is only 1/5of other devices of the same type.The prepared 1D-FZPs according to this method can also realize the deflection of parallel beam.Then,laser-induced graphene(LIG)was prepared on polyimide film by laser direct writing equipment,and phase-shifting surface(PSS)terahertz beam steering devices were fabricated using LIG materials.PSS is a type of metasurface that adjusts the phase of the incident beam.The transmittance of the prepared LIG to terahertz waves is only about5%,but it has higher reflection,more than 60%.According to the electromagnetic simulation software CST,the phase response of each unit to the incident terahertz wave is scanned and simulated,and the corresponding LIG-PSS is made.The phase response of each unit to the incident terahertz wave is scanned and simulated.The two units with a phase difference of 180° are scanned and obtained,and then the device processing pattern is obtained after calculation and rearrangement.A phase-shifted planar terahertz beam steering device was fabricated on a polyimide film substrate using a laser direct writing device.Finally,a terahertz communication imaging verification system based on a 340 GHz terahertz continuous source is built,and the two designed terahertz beam steering devices are tested with this system.The test results show that the designed laser-reduced graphene oxide-based terahertz beam steering device can achieve beam deflection performance of5.7° and 10.2° for incident terahertz waves.The laser-induced graphene-based terahertz beam steering device realizes the beam splitting effect on the incident beam.The incident wave is divided into direct transmission wave and refracted wave.The final test results show that the difference angle between the direct transmission wave and the refracted wave is 33.6 °.Both devices are made of flexible ultra-thin substrate and quickly prepared by laser direct writing,which realize the functions of terahertz wave deflection and beam splitting respectively.