Application Of Nano-antennas In Biological Detection And Beam Steering

As a typical optical sensor,optical antennas are conducive to the radiation characteristics of light in the optical band.Until now,the research of optical antennas have been paid more and more attention,mainly focused on the super-diffraction limit imaging,the new near-field optical probe,the solar energy conversion efficiency,nano-scale optical information propagation control,nano-lithography and so on.Biosensor is a device which is sensitive to the biological materials and can convert it into an electrical signal,consisting of two parts: a molecular recognition section and a conversion section,essentially.The biological materials contains tissue,microorganisms,enzymes,antibodies,etc.The molecular recognition part of the sensor detects the interaction between the target and the immobilized biological material,and then converts the signal of physical chemistry,optics,piezoelectricity,heat,sound and magnetism into electrical signal and output at last.One of the evolving technologies currently in biosensor research is the use of optical antennas for unlabeled and real-time molecular recognition.Because of its advantages of mark-free,minimized interference and real-time monitoring,nano-antennas biological detection technology based on surface plasmon resonance is more and more concerned by researchers.In this paper,The nano-antennas proposed adopts the classical metal / medium / metal sandwich structure,and then make the gratings with width gradient by dry or wet etching process.When a specific wavelength of light is incident normally to the surface of the structure,a strong surface plasmon resonance can be generated at the interface between the metal and the medium,the transmission spectrum also produces a significant resonance peak.As the biological samples with different refractive index are placed on the structural surface,the position of the transmission spectrum will change accordingly,namely the detection function for biological samples with different refractive index can be realized.More importantly,this paper take the topological insulator materials Bi₂Se₃ as the intermediate dielectric layer in sandwich structure,it can change the state of Bi₂Se₃ by chemical method from the amorphous state into crystal state,with the refractive index of the material has a great change,which can also achieve beam steering function.We also introduce three commonly methods for numerical calculation in electromagnetic fields in this paper.Finally,FDTD Solutions based on finite difference time domain method is used to simulate the optical properties of nano-antennas.We study the change of the transmission spectrum of nano-antennas when placing a layer of material with a certain refractive index on the top of the structure which prove that the nano-antennas we propose has the good biological detection function.Then,it was researched that the optical properties such as far field radiation pattern and electromagnetic field strength distribution and so on when we change the state of Bi₂Se₃ by chemical method,the results show that it also has good function for beam steering.