The Study On The Performance Of Second Harmonics In Split Ring Resonator

The metal micronano structure can support the plasmon resonance,that is,the collective excitation oscillation generated by the interaction between the free electrons of the metal conduction band and the incident electromagnetic field.With the excitation of plasmon resonance,the local electric field and photon local density of the nano-scale space around the metal micro-nano structure will be greatly enhanced,resulting in a significant increase in the effective distance or time of light-substance interaction.In order to enhance the second harmonic,it is considered to construct a non-centrosymmetric metal micro/nano structure.Among them,the split ring resonator(SRR)and its inverse structure(CSRR)are the most efficient.The whole paper revolves around this structure,theoretically and experimentally,to explore the regulation of the second harmonic frontage by the open loop.The main contents include:1.The modulation of the second harmonic intensity and polarization by metamolecules.Meta-molecules provide more freedom of modulation due to the electromagnetic interaction of internal subunits.We used a three-dimensional metamolecule composed of two split-ring resonators to adjust the arrangement of the two split rings,changing the coupling strength.The optimized structure makes the far-field radiation efficiency of the second harmonics 4times higher than that of a single split ring.At the same time,it is found that the phase difference and amplitude ratio of the second harmonic of the far field in the two orthogonal directions change with the change of the arrangement of the split ring.Then by changing the internal structure,we realize the change of the second harmonic elliptical polarization state,which is of great significance for the realization of the nonlinear polarization conversion device.2.Continuous phase regulation of the second harmonic on the surface of the super material.At present,the continuous regulation of local phase in the nonlinear field is mostly achieved by the Berry Phase introduced by the rotating structural unit,but they can only be used for circularly polarized light.Therefore,we propose an array of the reverse structure of the open-loop resonator.By precisely adjusting its structural parameters,the second harmonic of the far-field radiation can be continuously phase-changed from 0 to ?,and then combined with the flip-oriented band.The sudden change of ? makes the phase gradient achieve 0-2? coverage,and we experimentally realizes the bending function of the second harmonic beam which is in good agreement with the theoretical prediction.This is a good development direction for nonlinear phase regulation in the future.3.Process exploration of dynamic regulation of nonlinear metamaterials.In the field of linearity,there have been many reports on the dynamic regulation of superstructure materials by changing the external physical environment.Most of the implemented nonlinear components are passive devices and can only work at fixed wavelengths.Therefore,we consider introducing the metasurface of the split ring into the capacitive environment to apply a varying voltage to the nonlinear structure.This changes the carrier density of gold,causing a change in the complex refractive index of the material,thereby realizing the dynamic regulation of the optical properties of the open ring structure.This has done some advancement for the nonlinear dynamic regulation.