Calculation And Research Of Circularly Polarized Optical Antenna

ABSTRACTN:Nano optical antenna is a new subject which is just emerging in recent years. Its working frequency is in the optical frequency band, the main difference with traditional antennas (which are working in radio frequency band) is that nano optical antenna using noble metal materials, the real part of the permittivity is negative, which leads to the phenomenon of surface plasmon resonance, and has emerged a number of unique features which are different from the traditional antennas of using perfect conductor metal material. It has important application value in the field of quantum information technology, life science research, biological sensing and so on. Since traditional antenna has been developed for over a century, it has established a mature system of design and testing. Therefore, in the study of optical antenna, leaning the concept and design method of the traditional antenna for reference is very necessary, but we can’t directly apply the results of traditional antennas without thinking. This paper by reviewing several common linearly polarization antennas, points out the similarities and differences between the nano optical antenna and the traditional antenna. The influence of structure, size and other factors on the performance of antenna is discussed, several circular polarized optical antennas with different structures are calculated, and six-arm spiral of circular polarized optical antenna has been optimized and analyzed. On this basis, a kind of nano refractive index sensor with unidirectional radiation characteristics is designed. The specific content as follows:This paper first reviews the double nanorods dipole, bow-shaped, double-cone three common linearly polarized nano antennas. And the influence of different structures and sizes on the performance of antenna is analyzed. The similarities and differences between the nano antenna and the traditional antenna (using perfect conductor material) are discussed, These discussions and analysis provide theoretical clues for the design of the nano antenna.Then this paper calculates two broadband circularly polarized helical antenna: planar equiangular helical antennas and planar equidistant helical antenna. On this basis, I design and optimize the circular polarization six-arm spiral optical antenna with back cavity structure. The results show that the antenna can achieve linear polarization to circular polarization switching between near-field and far-field, the axial ratio is close to 1, has a unidirectional radiation characteristics and the near-field field enhancement can be up to about 30 times.Finally, a refractive index sensor is designed in this paper, it is composed of a cylindrical metal-dielectric-metal sandwich structure of the probe and a six arm spiral antenna with back cavity structure. The probe is placed in the central hole of the helical antenna, material to be tested is filled in the probe sandwich. By measuring the far field of the sensor, the refractive index of the probe core layer can be known. The results show that the signal of the probe can be increased by a thousand times by using the spiral antenna. Excitation optical path and the measuring optical path reciprocal, polarization directions perpendicular to each other, which can effectively restrain the interference caused by the excitation light source. At the same time, the real-time measurement of the refractive index to thousands of cubic nanometer material can be realized, it can be used in the field of biological, chemical trace detection.