Theoretical Study On Terahertz Sensing Characteristics Of Subwavelength Metal Coupled Cavity Gratings

Subwavelength structure devices have attracted more and more researchers' extensive attentions.Because when the size of devices is in subwavelength order,there will be many new features and phenomena that conventional devices do not have.Because of its unique characteristics,terahertz(THz)spectrum provides an efficient and fast spectral analysis method for most devices,which is suitable for many sensing fields,such as biochemical identification,production control and environmental monitoring.Based on the characteristics of subwavelength structure and THz spectrum,a novel subwavelength sensor can be designed.However,most of the subwavelength sensors still cannot meet people's needs,and need to further improve the subwavelength sensors.In this thesis,we used COMSOL multiphysical field,to simulate the reflection characteristics of subwavelength metal slit grating structure.According to the calculated results,the resonance spectra and local electric field diagrams are drawn,and the sensing characteristics are analyzed.However,its low sensitivity and low spectral resolution cannot well meet the needs of people.In order to improve the sensing performance of metal slit grating,an improved scheme is proposed.The core design criterion of the sensors is to maximize the interaction between light and the analyte,so as to realize high sensitivity and high resolution sensing.Based on the sensitivity of metal surface plasmon to the environment,combined with the enhancement mechanism of guide mode resonance and the strong localication of cavity mode resonance,subwavelength metal coupled cavity grating is proposed.The coherent coupling of the resonant cavity resonance and guided mode resonance results in high quality electromagnetism like induced transparent mode,which leads to cavity induced abnormal THz reflection.The influences of five dimensional parameters of subwavelength metal coupled cavity grating on its THz resonance spectral response are systematically studied and a conclusion is drawn.Subwavelength metal coupled cavity gratings perform electromagnetism-like induced transparent mode with high quality factor and strong localized fields,which have obvious advantages for the high sensitivity and high precision sensor detection of biochemical samples.A THz sensor design based on subwavelength metal coupled cavity grating with high sensitivity and excellent sensing value is proposed in this thesis.The comprehensive sensing performance of the structure in refractive index sensing is analyzed and the relevant sensing parameters are calculated.Metal subwavelength grating coupled by cascaded resonant cavity is designed by using subwavelength rectangular cavity structural element,which enhances the interaction ability between the electromagnetic field and the analyte,greatly improves the sensing ability of THz wave to analyte,and improves the sensing sensitivity and spectral resolution of subwavelength metal grating.Full wave electromagnetic simulations show the sensitivity of metal coupled cavity grating can reach 6?22 THz per refractive index unit in THz frequency band and the figure of merit is as high as 55?103.Compared with the previous THz sensor designs,the subwavelength metal coupled cavity grating sensor design has greatly improved the sensitivity and the sensing value of the sensor.Moreover,the design of subwavelength metal coupled cavity grating sensor has a wider effective working angle and the proposed structure has effective THz sensing ability with a wide operation angle of50°,which can adapt to the sensing operation for large aperture angle THz beam.Our proposed scheme with subwavelength metal coupled cavity grating sensor effectively combines the coherent coupling of the cavity resonance and the guided mode resonance.The integrated structure can confine the detecting field in a microscale cavity infiltrated with analyte sample,with intensive interactions between the detecting field and analyte.The detection sensitivity and accuracy of sensor are greatly improved,and it has an important application prospect in THz sensor technology for the sensing detection field.