Property Investigations Of Optical Antenna Based On Silver Nanowire

Antenna is a device that can convert energy between current or magnetic energy in the transmission line and free space radiation.As an essential component of wireless communication,antenna provides a method to manipulate electromagnetic wave in subwavelength scale,which enables it to be used in radio communications,multimedia communications,radar,navigation,electronic warfare,remote sensing,radio astronomy and other engineering systems.In recent years,with the development of nano-optics,optical antenna,the antenna working in the optical regime,is put forward to adapt to manipulate the light at the nanometer scale.Similar to the classic antenna,optical antenna is a functional device to convert the energy between free space radiation and local electromagnetic energy.At present,optical antenna are mainly realized based on surface plasmon of metallic nanostructures,with which the energy can be confined in subwavelength scales,and can be radiated,guided and received.Typically,they have strong interaction with environment or quantum dots due to the ultrostrong field at the metal surface,which enables it to be used in the nonlinear optics,such as the Raman enhancement,the molecular biology,the single molecule detection and the optical tweezers and so on.At present,the investigation about optical antennas is still in the primary stage due to the high accuracy requirement in the fabrication.In recent years,the development of micro-processing technology and equipment in recent years,etc.,promotes the realization and development of optical antennas.By referring to the design and principle of the classical antennas in the microwave regime,a variety of optical antennas,such as the dipole antennas,the Bow-tie antennas,the Yagi-Uda antennas,the slot antennas have been designed and implemented.In order to take a further development and application of optical antennas,the following points are important direction for the furture research:1,the integrations of optical antennas with waveguides,which are beneficial to the energy feeding by using transmission lines or waveguides,thus are of great significance for the integrated optics and nanometer sensing.2,the further investigations and realizations of directional optical antennas.3,the investigations of broadband optical antennas.4,the investigations about the interaction between optical antennas and quantum dots,which is an novel advantage compared with the classical antennas.5,the researches about the optical waveguides.Although optical waveguide is not directly related to the optical antenna,it is of indispensable significance for the optical antenna energy feeding,coupling,guiding applications.Therefore,in this paper,we innovatively proposes and investigate the V shaped optical traveling wave antenna,which is highly directivity,broadband and its direction can be adjusted.In addition,as a supplement,an slot optical antenna analog of electromagnetically induced transparency is and investigated.The main contents and innovations of this paper are as follows:(1)By using a modified wet chemical method,we synthesize high-quality silver nanowires with smooth surfaces,whose diameter follows a normal distribution whose average and square deviation are 252 nm and 46 nm,respectively.The properties of the guiding modes is investigated based on waveguide theory,and three modes,i.e.:TM00,HE11 and HE1-1 are found to be supported.The intensity of the modes launched by laser with different polarizating is investigated,and we reveal that when the polarizating is parallel to the axis of the silver nanowire,the TM00 and the HE1-1 modes are excited,while when the polarization direction is perpendicular to the silver nanowire axis,the HE1 mode is mainly excited.Such a phenomenon is verified in experiment.(2)The mode properties of the silver nanowire-substrate configuration is investigated,and we confirmed that there exist another two leaky modes besides the fundamental mode.In the previous reports,only the theoretical analysis indicates that these two modes exist,no experimental results have confirmed.The result contributes to the applications of Ag nanowire as multi-channel waveguides in nanoscale optics(3)Based on V-shaped silver nanowires,we successfully realize highly directional and direction tunable optical traveling wave antennas.By feeding it with an optical waveguide that carrying the surface plasmon polarizations,we find the radiation of is highly directional.The half power beam-width can be achieves as small as 20°,which is comparable with the best directional optical antenna,i.e.:Yagi-Uda antenna.Different radiation direction of the silver nanowires with different corners are investigated,which indicates the radiation direction can be adjusted by changing the bending angle of the V shaped nanowire.Besides,the radiation direction can be adjusted by change the feeding modes without changing the physical structure of the V-shaped traveling wave antenna.Therefore,our traveling wave antenna can be used as a highly directional,multi-channel,direction adjustable and broadband nano-optical antenna.Its natural facility to be integrated with transmission lines enables it has great potential applications in nano-optics.(4)A theoretical model is constructed based on the mode coupling theory to calculate the radiation pattern and the coupling precession of the guiding modes.The results obtained by it agree well with the experimental results.The model calculated the energy exchange in the corner,which is insightful for the mode coupling processes at the corner.The application scope of the model is not limited to V-shaped traveling wave antenna,it can be used to calculate the coupling precession and radiation of any waveguides in principle,which is helpful for the further design and research of traveling wave antenna.(5)An optical antenna analog of electromagnetically induced transparency is achieved based on the interference of resonant gap elements,which is of important application potential in self-modulated radiation suppression and optical switching.