Study Of Mode Controling Based On Metasurface Optical Waveguide Devices

Optical metasurface devices are one of the popular research fields of micro-nano optics,and they have great application value and potential in the fields of sensing,imaging,holographic projection,photoelectric detection,and optical integration.Highspeed and large-capacity optical integrated communication network is the development trend of the next generation Internet.In order to improve the capacity of optical storage,optical transmission and optical processing in the network,the use of metasurface structure to improve the integration of optical waveguide devices has become a research focus.The size of the traditional optical waveguide device has a limit bandwidth?about 70 nm?.The optical waveguide material uses SiO₂ and LiNbO₃,but these two materials can only have good transmission performance for part of the light?the wavelength range is near infrared?,which limits the further development of the integration of optical waveguide devices.In order to realize a highly integrated,high-performance and largebandwidth optical communication network,new materials and new technologies need to be considered.Optical waveguide devices are the main basic components for the realization of integrated optical communication networks.It is still a problem how to realize high-efficiency optical waveguide devices within a specific operating wavelength range,especially for polarization and mode control devices,multi-mode interferometers,optical power splitters,mode converters,all-optical logic gate devices In addition,the preparation of optical waveguide devices used for optical communications and information processing often requires sophisticated manufacturing technology and time cost.It is also one of the research priorities that looking for new manufacturing solutions to reduce the difficulty of manufacturing optical waveguide devices,while ensuring device performance.The metasurfaces can effectively reduce the size of the photonic device,but at the same time introduce significant polarization correlation for efficient polarization control,which can expand the scope of application of the metasurface optical waveguide device.Through the introduction of optical metasurfaces,the integration of devices in the optical path is improved,which provides an important way for the realization of optical devices required for integrated optical communication networks and the exploration of new functions of optical waveguide devices.In the optical waveguide device,by combining the characteristics of the metasurfaces,the devices can be miniaturized,low loss,high efficiency,wide frequency band and adjustable characteristics.The metasurfaces enable flexible control of modes in optical waveguides at the propagation distance of sub-wavelength dimensions.With the advancement of the micro-nano fabrication process,the structure quality of the prepared optical waveguide device is getting higher and higher,and the functions that can be realized by the optical waveguide device based on the metasurface are gradually increasing.This thesis focuses on the mode control characteristics of metasurface optical waveguides and their applications.The main contents include:1)An optical waveguide device that realizes multimode interference based on a metal metasurface structure on a dielectric-loaded waveguide.We proposed the use of quasi-rhombus shaped silver nano-antennas to form a metasurface structure.The metasurface structure regulates the interference between multiple modes to achieve a high-performance multi-mode interference coupler that can work in the visible light band.The length is only 2.75 ?m.The metasurface multimode interference coupler makes the transmission waveguide combined with the multimode interferometer,reduces the connection points,and improves the integration of the device.The relationship between the characteristics of the self-focusing point and changing the structural parameters of the quasi-rhombus metasurfaces are studied.By changing the structural parameters of the quasi-rhombus metasurfaces,the mode propagation direction can be adjusted.Therefore,we have designed and implemented a beam coupler that can replace a tapered coupler and a Y-shaped power splitter with adjustable polarization-insensitive power ratio.For the beam coupler,after optimizing the structural parameters of the metasurface,the metasurface enables approximately 90% of the TE-polarized modes in a 1 ?m wide dielectric-loaded waveguide to be coupled into a 500 nm narrow waveguide.For the Y-shaped power splitter,the metasurface achieves a power ratio of 1: 3 for the upper and lower branches.2)An optical waveguide device that realizes mode conversion on a silicon waveguide through a dielectric metasurface.We propose to use a complementary structure of the nano-antennas array?completely etched nano-holes array?in a silicon waveguide with abrupt width change to achieve the metasurfaces.The metasurfaces structure controls the mode conversion coefficient to achieve a miniaturization,low loss and low crosstalk.The total length of the mode converter is about 2.42 ?m.The influence of the structural parameters of the metasurface on each order mode propagating in the waveguide is studied,so that each order mode has constructive interference or destructive interference,and the output mode is converted into the required mode.For the TE00 mode converted to TE10 mode,the mode transmission rate exceeds 90% and the mode purity exceeds 95% under the operating bandwidth of 300 nm.The experimental preparation and test process of the mode converter are studied.This mode converter can achieve CMOS process compatibility,and the preparation process only needs one-step etching,which greatly simplifies the process flow of device preparation.This mode converter only uses silicon material,which can reduce material and manufacturing costs.In the test,the TE00 mode to TE10 mode converter achieved a transmission efficiency of 83.1%?0.8 d B?and a low crosstalk of-14.2 d B at a wavelength of 1.55 ?m.Finally,the proposed high-efficiency and compact mode converter can be applied to input / output waveguides with different relative positions,different modes?including TM mode?,and silicon waveguides with different thicknesses.3)An optical waveguide device that uses a metasurface structure to realize optical information processing on a Y-shaped waveguide.We propose an all-optical logic gate device that can work in the visible light range and is wavelength-insensitive based on the Y-shaped dielectric loading waveguide,which controls the interference of the waveguide mode through the metasurface structure.The metasurface structure makes the TM mode multi-mode interference,thereby improving the transmission rate of the TM mode in the medium-loaded waveguide.By adjusting the phase of the input light field,each logic state is realized,thereby forming an all-optical logic gate device.The all-optical logic gate device can realize three logic functions of AND logic gate,OR logic gate and XOR logic gate in the same structure,and then based on the Y-shaped waveguide,cascade a control waveguide to realize three other Inverted logic gate function?NAND logic gate,NOR logic gate and XNOR logic gate?.The all-optical logic gate device simplifies the structure and control complexity while realizing the logic function,realizes the reconfigurability of the device,and thus can provide a variety of logic functions.By appropriately adjusting the phase of the input mode through the metasurface structure,constructive interference and destructive interference occur between the modes.The light field distribution and extinction ratio of the designed logic gate structure under different input states are analyzed.The extinction ratios of the three logic gates?AND,OR and XOR?are higher than 24 d B,and the high extinction ratios of NAND,NOR and XNOR logic gates are about 33.39,27.69 and 33.11 d B,respectively.