Two-dimentional Surface Plasmonic Grating Optical Absorber With Gradually Varying Structure

When the metal and the dielectric interface is irradiated under electro-magnetic waves in optical frequencies, free electrons which distribute on the surface of the metal will oscillate collectively, and they will form surface plasma (Plasmas). Due to the resonance, a majority of photon energy transforms into free electron oscillation energy, thus forming the strong absorption of light. With the help of surface plasmon, it is expected to produce a surface plasmon absorber of light on subwavelength scale, which can be used in solar cells, photonic circuit, sensor, filter, THz imaging and thermal radiation detection, etc.How to improve the light absorption efficiency of the surface plasmon absorber is the main research topic in this paper. The specific content is organized as follows:(l)Firstly, this paper introduces the concept of the optical absorber, surface plasma optical absorber and surface plasmon grating optical absorber, summarizes the research progress of the irregular combination morphology surface plasma light absorber, and make a detailed overview of the research status of surface plasma grating light absorber. Moreover, it introduces the model of the surface plasmonic grating absorber with gradually varying structure, the set of dielectric constant and geometric parameters of the absorber, two-dimensional finite difference time domain method and the calculation method of reflectivity.(2) Secondly, in this paper, we make a detailed simulation under different groove depth, groove width and wall width, groove width and the wall width change according to the linear rule, and different width the of incident beam, to research the change of the absorption characteristics of the surface plasmonic grating absorber with gradually varying structure. The calculation results show that:Within the range of the wavelength of 400 nm to 800 nm, groove depth has great influence to the absorption characteristics. But when the depth of the groove larger than 2950 nm, the reflection spectrum saturation phenomenon appeared. The reflection curve can be fine-tuned to flatten the wavelength range of the calculated by making the groove width linear increase and making the wall wide linear decreases from the center to both sides appropriately at the same time. For different space half width of the incident light, the shape of the reflection spectrum is different. When the width of the incident light is narrow, it will strengthen the absorption of short wavelength light. When the width of the incident light is wide, it will enhance the absorption of long wavelength light.(3) Finally, we put the improvement and innovation forward in the paper: some improvement of new structure models of the two-dimentional surface plasmonic grating optical absorber, new idea of optimization computing methods.We also make some prospects of the surface plasmonic, and point out the drawbacks in our work.