Dynamic Coherence Control Of Bessel Beams Through Different Polarizations In Metamaterials

The acquisition of information has been a necessary means for human survival since ancient times.In the primitive feudal society,people exchanged information through the beacon and the swan geese.Although the brilliance of human civilization recorded by these methods represented the wisdom of the ancient people,these primitive communication methods were slow in transmission and inaccurate.,Easy to lose,and cannot be flexibly manipulated.With the continuous progress of human civilization and the continuous in-depth exchanges between countries in the world,globalization has become an inevitable trend,and how to quickly and accurately become an urgent matter.As we all know,photons are the fastest propagating particles in the world,so photons are also the particles that transmit information the fastest.When photons propagate in free space,diffraction occurs,so the transmission distance is limited.In order to make the transmission distance of photons larger,people use light beams to transmit photons in space.Among them,the Bessel beam is a beam commonly studied by people.At present,people have designed many optical devices to generate and control Bessel beams.In order to manipulate photons flexibly,many new materials and new structures have been invented.In the past ten years or so,the micro-nano photonics subject based on metamaterials and metasurfaces as carriers has recently attracted the attention of academia and even the business community.Many achievements have been made in optical imaging,quantum information processing,optical information transmission,optical sensing and detection,etc.Practical application.Among them,metasurfaces are also used to generate and control various beams.In addition,metasurfaces with dynamic control functions have important applications in rapid information processing,and various methods are used to achieve dynamic control of metasurfaces.In addition,the polarization of photons has always been an important degree of freedom for photons.By adjusting the polarization of photons,people can not only transmit more information,but also quickly adjust the state of photons.Using the regulation of the circular polarization of photons,people realize various light field regulation applications by simulating the photon spin Hall effect.Although people have used circular polarization to generate Bessel beams,no one currently uses polarization to dynamically control Bessel beams.This thesis takes this as an entry point,from the perspective of dynamically controlling the Bessel beam of the micro-nano structure,expounds its research background,theoretical basis deduction simulation calculation,sample design is the experimental test,the specific content includes:1.Start with one-dimensional metal nanochains,consider the spin-light excitation of the metasurface to generate plasmons,calculate the specific form of a component of the electric field under paraxial approximation conditions,and push it to the complete electric field.Immediately introduced another specific form of spin-light excitation of the metasurface to generate plasmons.The results obtained are generalized to produce a two-dimensional metal nano-surface,and the specific form of a paraxial approximate beam is obtained.2.Consider the specific form of the co-polarization term in which the spin-light excites the metasurface to generate plasmon radiation.Analogy to the cross-polarization term discussed earlier,but at this time it should be noted that the term that carries the geometric phase is located on the cross-polarization term.Through derivation and calculation,we obtain the specific form of the co-polarized radiation field of plasmon generated by the spin-light excitation of the metastructure under the paraxial approximation condition.Interfere the previously calculated cross-polarized radiation field and co-polarized radiation field to form a Bessel beam.3.Using the “metal/medium/metal” metasurface,taking into account the paraxial approximation conditions and the geometric size of the metal nanopores,design samples with integrated performance within a limited size range to verify our theory.By controlling the polarization state of the incident light,we can dynamically control the intensity of the Bessel beam,and use two methods(wavelength control and spin light selection)to control the transmission distance of the outgoing beam.The proposed structure can work in a wide range of wavelengths without dispersive phase discontinuity.In conclusion,based on rotation transformation in this paper,a rotationally symmetric metasurface consists of one-dimensional nanoholes is designed.The Bessel beam can be produced through the spin Hall effect of left-handed circularly polarized(LCP)and right-handed circularly polarized(RCP)light simultaneously.Through the excitation of linearly polarized light,we can dynamically control the intensity and polarization of Bessel beam by controlling the coherent interference between two circularly polarized light excitation beams.At the same time,this method has the advantage of broadband modulation range.