Study On Dynamic Light Field Modulation Technology Based On Tunable Periodic Artificial Microstructure

In order to realize the control of the light field,people use periodic artificial microstructures to design various photonic devices,such as spatial light modulators,photonic crystals,and gratings.In recent years,periodic artificial microstructures represented by metasurfaces and high contrast gratings have attracted widespread attention in the academic field because of their great application potentials in the field of integrated photonics.Based on periodic artificial microstructures,through unique structural designs,the amplitude,phase,polarization and frequency of incident electromagnetic waves can be modulated.This dissertation starts from the light field modulation based on tunable periodic artificial microstructures,taking terahertz and near-infrared bands as examples,and focuses on cutting-edge exploratory research on the modulation of electromagnetic wave polarization and phase,in order to advance the control of tunable periodic artificial microstructures.The design and application of integrated photonics devices provide key technical and theoretical support.The innovative results achieved in this dissertation are summarized as follows:（1）In order to achieve dynamical polarization modulation,a 2D-3D convertible terahertz metasurface based on an integrated pneumatic actuator is designed.By applying pressure to the integrated pneumatic actuator,the 2D metal spiral will be transformed into a3D conical metal spiral with a controllable shape.The manufacturing of the structure only requires a planar photolithography process,which has the advantages of high efficiency and low cost,and can solve the current problems of high fabrication cost and complex fabrication process of 3D chiral metamaterials.By controlling the pressure of the integrated pneumatic actuator,the symmetrical modulation ability of the metamaterial chirality can be obtained.Through parameter design,pure polarization rotation and pure polarization conversion can be realized at the specified frequencies.By using the equivalent parameter extraction method,the physical mechanism of chiral modulation caused by the deformation of the metal spiral structure is analyzed and discussed in detail.The structure can be applied to linear polarization rotators and polarization converters in the terahertz band.（2）In order to achieve birefringence-free dynamical polarization modulation,a 2D-3D switchable polarization-insensitive terahertz metasurface based on an integrated pneumatic actuator is designed.By adopting a four-fold rotationally symmetrical planar metal spiral structure,the polarization sensitivity of chiral metamaterials to linearly polarized light can be suppressed.By controlling the pressure in the integrated pneumatic actuator to adjust the deformation of the metal spiral metasurface,a broadband and polarization-insensitive symmetric chiral modulation function can be obtained.Meanwhile,using Jones matrix theory,the relationship between the rotational symmetry of the metasurface structure and the polarization sensitivity was analyzed in detail.This structure can be applied to the polarization-insensitive terahertz broadband polarization rotator.（3）In order to achieve dynamical phase modulation,a high contrast reflective grating with adjustable phase and high diffraction efficiency is designed.This structure is composed of two layers of high contrast gratings with different periods.With the aid of the near-field coupling effect,the two layers of gratings are strongly coupled to each other to produce-1^storder diffracted light with high diffraction efficiency in the near-infrared band.By independently moving any layer of grating,a phase-only modulation can be realized while maintaining high diffraction efficiency.With the help of the energy band theory of photonic crystals,the physical mechanism of double-layer high contrast gratings to achieve high diffraction efficiency is analyzed,and the design process of high-diffraction efficiency double-layer high contrast gratings is proposed based on this mechanism.At the same time,with the help of Fourier expansion,the physical mechanism of the phase shift caused by the lateral displacement of the double-layer high contrast grating is analyzed.These theoretical results provide a reference and basis for the design of phase-adjustable,high-diffraction-efficiency high contrast gratings in the future.（4）In order to explore dynamical phase modulation based on the bi-layered high contrast gratings,a two-dimensional optical phased array design based on a double-layer high-contrast grating phase tuner is proposed.The design scheme of two-dimensional optical phased array under the application of beam deflection and holographic imaging is proposed.By using a phase tuner based on a double-layer high-contrast grating,the pixel size of the optical phased array can be effectively reduced,the field of view of the device can be improved,the beam quality,as well as the response frequency can be improved.Starting from the light field modulation based on tunable periodic artificial microstructures,this dissertation systematically studies the physical mechanisms of chirality modulation,polarization sensitivity,phase modulation,and high diffraction efficiency in periodically tunable artificial microstructures.The polarization modulation of the structure and the design of the phase modulation device provide guidance.The polarization modulation periodic artificial microstructures introduced in this dissertation can be used for dynamic chiral modulation:such as polarization rotators,polarization converters,and elliptical polarizers,etc.,or for chiral sensing:such as chiral molecular recognition and high-sensitivity biological detection and so on.The phase modulation periodic artificial microstructures introduced in this dissertation can be used in the fields of light detection and ranging,free-space optical communications,optical switches,holographic displays,and three-dimensional brain imaging.