| Surface plasmons are surface electromagnetic waves formed at the metal/ dielectric interface due to the interaction of free electrons and incident photons on the metal surface to form electromagnetic oscillation.The interaction between surface charge oscillation and light wave electromagnetic field makes surface plasmons have important applications in nonlinear optics,optical detection,super-resolution imaging,near-field optics and perfect absorbers.Metamaterial is an artificial composite structure based on surface plasmons.By adjusting the structure and material,its electromagnetic properties can be adjusted to make it have physical properties that natural materials do not have.In 2008,the metamaterial absorber was verified experimentally for the first time.Since then,various novel metamaterial absorber structures have emerged one after another,and gradually developed from single band response to multi-band or even broadband response.The asymmetry of light absorption,namely polarization,plays an important role in the construction of a series of optical devices.These devices are of great significance in thermal detection and imaging systems.However,most of these absorption devices need to be integrated with polarizers and it is difficult to achieve multi band or wide spectral response.The study of the surface plasmons of metamaterial structures can be used to manipulate the polarization properties of electromagnetic waves to realize polarization splitting.Polarization sensitive metamaterial absorber can obtain both intensity information and polarization information of incident radiation.Combining this polarization device with detection technology can realize polarization imaging detection.By measuring the polarization degree and polarization angle of target radiation,useful information can be distinguished in complex natural background.It has relevant applications in the fields of space exploration,remote sensing and biomedicine.The polarization device used for the generation and recognition of polarization state is the key of polarization detection imaging system.Due to the small volume and easy integration of polarization controlled metamaterial devices,it is expected to replace the traditional polarization devices and be applied to polarization detection and imaging systems.This paper briefly introduces the theory and application of optical polarization,summarizes the concept,development and application of polarization controlled metamaterial absorber.It also introduces the design,analysis and related basic theory of absorber in detail.Several different types of polarization sensitive metamaterial absorbers are proposed,and their properties are analyzed and discussed.The absorbers can adjust and control the polarized light in the infrared band,and achieve dual band or broadband polarization selective absorption response.The main research results of this paper are summarized as follows:1.The structure of metamaterials and the characteristics of surface plasmons are studied.The spectral principle of polarization sensitive metamaterial absorber is analyzed.The dual band and wide spectral response in infrared band are realized by using Fabry-Perot cavity mode,local plasmon resonance and propagation plasmon resonance mode.The application of polarization sensitive metamaterial absorber in polarization detection imaging system is explored.2.A polarization-selective dual-band infrared plasmonic absorber based on subwavelength gaps was proposed and numerically analyzed.The absorptivity of the absorber under different polarization angles was calculated,the electromagnetic field distribution was analyzed,and the influence of different geometric parameters on the absorption performance was discussed by numerical simulation.This absorber can almost completely absorb TM polarized radiation and almost completely reflect TE polarized radiation.It is very sensitive to the polarization angle of incident electromagnetic wave,but not to the oblique incidence angle.The extinction rate of the two resonance peaks can maintanin above 130 when the incident angle is close to 80°.The absorber can respond simultaneously to mid-and long-wave infrared atmospheric windows and achieve near-unity absorption at 3.3 ?m and 9.8 ?m for TM polarization light.Owing to its high absorptivity and fine polarization properties,the absorber combines the advantages of a light absorber and a polarizer.It can be applied to uncooled infrared polarization detectors,which not only simplify the design of optical system,but also avoid the polarization information reconstruction error caused by the misplacement between the polarizer and the pixel.3.The polarization-dependent absorber of metamaterials based on slit structure was prepared experimentally.The thin films were prepared by electron beam evaporation and magnetron sputtering system;The slit structure was prepared by electron beam lithography(EBL)and lift off technology.The structural parameters were characterized by profilometer,scanning electron microscope(SEM).The absorption properties of the absorber were measured by Fourier infrared spectrometer.4.A broadband polarization sensitive metamaterial absorber based on ladder network construction is proposed.This asymmetric ladder network construction can not only achieve broadband absorption,but also has good polarization sensitivity.Under normal incidence,the proposed absorber can possess 95.36% and 11.92% average absorptivity for 0° and 90° polarization light in 8.33 ?m-11.31 ?m,that is in the long wavelength infrared range.The relationship between the broadband absorption and the polarization angle is monotonically decreasing.The absorption performance of the metamaterial absorber can be adjusted by changing the polarization angle of the incident radiation.For oblique incidence,the absorber performs angle-insensitive.It can still maintain good broadband property when the incident angle increases to 60 °.The absorber not only has good bandwidth absorption performance,but also has simple structure and good polarization characteristics.5.Polarization sensitive broadband absorber based on composite metamaterial structure is proposed,which is different from the traditional three-layer metamaterial absorber.The bottom metallic film is replaced by a micro-nano structure.The grating structure can achieve polarization-sensitive response,while the cube structure can achieve broadband absorption response.When the grating structure is on the top layer and the cube structure is at the bottom,the absorber shows TM polarization-sensitive broadband absorption,and the absorptivity is more than 80% in the range of 8.37 ?m-12.12?m.When the grating structure is at the bottom layer and the cube structure is on the top,the absorber performs TE polarization-sensitive broadband response,and the absorptivity is more than 90% in the range of 8.5?m-11.61?m.Owing to its high polarization sensitivity,the absorption can be tuned by changing the polarization angle of the incident radiation.These two kinds of absorbers make full use of and design each layer structure of the absorber to achieve the target characteristics.Through simple design,they meet the diversified needs.They would have broad application prospects in the fields of thermal detection and imaging. |
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