Using the principle of Surface Plasmons Polaritons, we propose a graphene broadband terahertz absorption structure that achieves the tunable absorption of electromagnetic waves. In our absorption structure, the method of patterning graphene is used to realize continuous broadband absorption from 0.5THz to 2.1THz. The absorption which is more than 50% reaches 1.1THZ, especially the structure designed here has three plasmonic resonance peaks which above 98% at 0.79THz, 1.18THz and 1.35THz, respectively. In addition, the symmetry in the pattern design consider that our absorption structure is not sensitive to the polarization and incident angle. Due to a series of excellent characteristics of the absorption structure, it may play an important role in the field of aircraft stealth, absorber, and light wave modulation.
A nanoslit array is introduced on the silicon waveguide, and the phase difference is controlled by the slit width to satisfy the function of the focusing lens. If keep the designed width and depth of the slit in accordance with the focusing effect unchanged, when the incident wavelength changes, the focal position must change accordingly, and the dispersion effect is significant. In order to achieve the achromatic effect, the refractive index of the surrounding medium is changed while changing the wavelength. Finally, the refractive index of the surrounding medium which can keep the focal length constant at the wavelength of 1550-1950nm is obtained, and the equation that the change of the refractive index and the wavelength of the medium makes the focal length constant is obtained. The achromatic effect can be effectively achieved, and applications range of achromatic metalens from imaging in optical communications to telescopes in the astronomical field.