Research On Infrared Polarization-dependent Electromagnetic Manipulation With Metasurfaces

The phase,amplitude and other electromagnetic parameters of polarized light can be controlled by employing the interaction between polarized light and matter.Such polarization-dependent electromagnetic manipulation has been widely used in communication,display,detection and other fields.Conventionally,various polarizing devices and other optoelectronic devices are used together to realize such manipulation.The related optical systems are often complex to design and difficult to integrate.With the development of micro-nano machining and its characterization technology,a variety of artificial electromagnetic devices with excellent performance have emerged.Metasurfaces are ultra-thin planar artificial electromagnetic devices and own the ability of flexible electromagnetic manipulation on the sub-wavelength scale.Compared with the conventional approach,the polarization-dependent electromagnetic manipulation based on the metasurfaces can expand the functions that can be achieved by such control,and also facilitate the miniaturization and integration of related optical systems.Using the phase-controlled metasurfaces,this dissertation studies the problems in the middle infrared polarization-dependent electromagnetic control,including single polarization response.The main research contents of this dissertation include:1.Aiming at the problem that the functionality of polarization-dependent electromagnetic manipulation in the mid-infrared band is limited,a polarization-multiplexed modulated optical vortex generating device is designed.A new optical vortex modulation method based on metasurfaces is proposed,which realizes the modulation of the optical vortex intensity distribution by introducing a tangential modulation factor into the spiral phase.The modulated optical vortex has an actinomorphic intensity distribution that is different from conventional optical vortices.To characterize this function,a single-layer transmissive all-dielectric metasurface was designed.The fabrication process is simple and the metasurface can simplify the experimental light path.Experimental tests show that the designed metasurface can generate a doughnut and an actinomorphic votex beams respectively under the incident of 10.6μm orthogonal linearly polarized light.The intensity pattern of the optical vortex can be dynamically adjusted by changing the polarization angle of the incident light.This work has potential in applications including optical micromanipulation.2.For metasurfaces made of traditional optical materials such as SiO₂ and Si for polarization-dependent electromagnetic manipulation,the designed function often fails if the optical property of the component materials are changed.To solve this problem,a mid-infrared broadband（9.7μm¹1.5μm）switchable beam splitting metasurface is designed by introducing phase change material GST.The dielectric constant of GST was measured and the factors affecting its phase transition behavior were studied.Then,a GST based reflective grating type unit cell was constructed.Combined with the geometric phase modulation method,we designed a metasurface consisting of the metaunits arranged in a checkerboard style.The simulation results show that when the circularly polarized or linearly polarized light is normally incident,the metasurface will achieve uniform beam splitting if GST is amorphous,and normal reflection if GST is crystalline,which realizes switchable beam splitting.This work can be used for reference in the design of new virtual shaping devices.3.Typically,most polarization-dependent metasurfaces only respond to a single type of polarization.To solve this problem,a metasurface for real-time imaging of multiple polarization components is designed.Combining the two methods of propagation phase and geometric phase modulation,two types of all-silicon unit cells are optimized and selected.Each type of units can achieve independent phase response to a set of orthogonal linearly（circularly）polarized light.When designing the metasurface,the off-axis focus phase distribution is used and the two types of unit cells are arranged in a interleave way.In experiment,active illumination with 10.6μm laser is used to achieve division of focal plane imaging for multiple polarization components.The metasurface can filter,divide and focus multi-polarization components simultaneously,which is beneficial to improve the integration of real-time polarization imaging systems.