| In the base station,the downlink transmission process of the signal is: first the optical signal is converted into an electrical signal,and then the electrical signal is converted into a wireless signal.The involvement of electrical signals not only complicates the signal transmission,requiring complex and high-cost signal processing equipment,but also makes it difficult to achieve high-speed transmission due to the limitations of the electronic devices themselves.In order to reduce the cost of base station construction,this paper proposes a graphene microwave modulated antenna scheme based on micro and nano structure enhancement,which does not need to convert the optical signal into electrical signal,but directly modulates the microwave signal with the optical signal.Without the involvement of intermediate electrical signals,the signal processing circuit becomes simple,and the ultrahigh carrier migration rate and extremely fast relaxation time of graphene can realize highspeed signal transmission.Graphene has attracted much attention as an emerging two-dimensional material,and its unique optoelectronic properties make it a favorite for modulation devices and a key material for achieving direct modulation of microwave signals by optical signals in this paper.However,the lower optical response of graphene limits the modulation capability of graphene antennas.Therefore,the local field enhancement effect of the metal micro-nano structure is used to enhance its interaction with light in order to improve the modulation capability of graphene antennas.And,the theory of light modulated microwave and the enhancement effect of micro-nano structure are verified by combining simulation and experiment,also the light modulated microwave device is obtained.The scheme provides a new idea for the research of microwave modulation devices.The main research and conclusions of this paper are as follows.(1)Through the existing research,the principle of graphene antenna to realize light modulated microwave and the enhancement principle of metal micro-nano structure on the optical response of graphene are analyzed and theoretical models are established.It is concluded that: graphene can modulate the Fermi energy level of graphene by means of optical doping,which in turn affects its electrical conductivity,and the change of electrical conductivity affects the radiation performance of the antenna of graphene;the local field is enhanced by metal micro-nano structures to improve the optical absorption coefficient of graphene,thus improving the modulation depth of the graphene antenna.(2)Based on the theoretical model,several graphene antenna structures were designed and simulated with electromagnetic simulation software.The radiation performance of graphene antennas was studied by changing the Fermi energy level of graphene.Then the enhanced capability of the metallic micro-nano structure was designed and simulated by the software.And the effect of the shape and size of the designed metal micro-nano structure on the light absorption rate of graphene was investigated.Then the processing and preparation of the designed graphene antennas and micro-nano structures are completed by using photolithography,wet etching and free diffusion,and finally the processed devices are tested and the results are analyzed.(3)In this paper,the modulation of optical signals at two wavelengths is investigated:under the light source of 532 nm from 0 to 36.4 m W,the dumbbell-type graphene antenna has a maximum modulation depth of about 1.8 d B after the introduction of the metal micronano structure,which is 1.6 d B more than that without the enhancement of the metal micronano structure;under the light source of 1550 nm from 0.to 29.4 m W,the class elliptical graphene antenna has a modulation depth of about 1 d B,which is 0.6 d B more than that without the metal micro-nano structure enhancement.From the above test results,firstly,the graphene antenna can realize the direct conversion from optical signal to microwave signal without the electrical signal as an intermediate process;secondly,the metal micro-nano structure can enhance the modulation depth of the graphene antenna. |
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