Design And Study Of Polarization Filter Based On Metamaterials

Artificial composite metal subwavelength structure can excite surface plasmon which makes it possess some special optical properties, such as super transmission, negative refraction and perfect absorption, etc. And this artificial metal structure is also called metamaterials. On the other hand, the photonic devices based on the surface plasmon have the ability to manipulate the surface plasma wave, which can realize information transmission and modulation in nanoscale. Surface plasma technology can be used to make the photonic devices size at the subwavelength magnitude so as to have the ability to break through the diffraction limit. It makes the device has some advantages, such as miniaturization, compact structure and high integration which supply opportunity of making photonic chips.From the above, we can see that the metamaterials photonic devices based on the surface plasmon are greatly promoted the development of integrated optics, subwavelength optical fields and so on. In this thesis, by utilizing the finite difference time domain method of electromagnetic calculation, we designed a series of periodic subwavelength metal microstructure, which can realize the perfect absorption. From these perfect absorption characteristics, several kinds of reflective polarizing filter have been designed. The main research work and achievements are as follows:1. The material tunable polarization filter based on asymmetric "cross" metal structure has been designed and analysised. The perfect absorption of this structure are realized in the Ex and Ey directions at the same time. Results show that the two polarization directions have different resonance absorption wavelength. Further analysis showed that:Metal strip length has a decisive influence on resonance wavelength. The resonance absorption wavelength of a polarization direction only depends on the length of the metal strip which parallel to it, and independent of the length of the vertical one. The asymmetrical cross structure has opened up a new way for the polarization tunable filter research work. We can fix a filter absorption wavelength of one polarization direction and adjust the filtering absorption wavelength of the other polarization, or adjust the filter absorption wavelength of two polarization directions at the same time.2. The double band tunable polarization filter based on metamaterials has been designed and analysised. Because the absorption wavelength is only depended on the length of the metal strip parallel to incident light polarization. So add a metal strip which parallel to the incident light polarization direction in the asymmetric cross metal structure can realize the two wavelengths perfect absorption, which means the double band polarization filter has been realized. Meanwhile, the other polarization direction maintains the single band polarization filter. All filter wavelengths can be adjust by changing the length of the corresponding metal strip.3. Square-wave broadband tunable polarization filter based on metamaterials has been designed and analysised. Square wave filter realized perfect filtering effect in a wider band range, thus has a particular application meaning. On the basis of the double wave band filter, by adding a new metal strip in the direction of the two metallic strip in order to offset the reflection peak in the absorption spectrum of double wave band filter. The zero position of the reflection spectrum of the new structure change into a rectangle, thus the function of the square wave filtering is realized and the scope of band filter is broadened.Highlights of the thesis are as following:Based on the perfect absorption properties of metamaterials, tunable polarization filter, double band polarization filter and square wave polarization filter are proposed and designed. These new type of polarization filter has the wavelength tunable, simple manufacturing process, characteristics, the size of the device can be as small as a few wavelengths, thus can be used in the future of the photon chip.