Chip-based Electronically Controlled Beam-scanning Nanoantenna Array

Optical beam scanners?OBSs?,capable of dynamically steering light beams,constitute a key building block for numerous technologies like sensing,imaging,image projections,displays,light detection and ranging?Li DAR?and autonomous driving.Traditionally,optical beam scanning can be achieved by mechanically rotating reflective mirrors or using liquid-crystal spatial light modulators.However,their low response speed and bulky structure have posed severe limitations on their practical applications.For agile and compact OBSs,it has emerged over the past decade that chip-based OBSs,which allow for a dense integration of thousands of optical antennas into an area of fingernail sizes and a beam scanning speed over GHz,could be a practical solution.Nanoantennas,with their unique abilities to concentrate light into deep-subwavelength scale and tailor the emission pattern of light,have received great attention in the past decade.For chip-based applications,integrated devices with different radiation characteristics have been demonstrated by taking full advantages of the flexible design freedoms provided by nanoantennas.These nanoantenna-based devices have enabled a lot of fascinating applications including reconfigurable on-chip interconnects,ultra-compact lab-on-a-chip microflow cytometers,wireless on-chip communications and networks.However,the majority of these researches,focuses on the manipulation of in-plane light emission.The potential of using nanoantenna array as the on-chip OBS has largely remained unexplored.In this thesis,the on-chip nanoantenna and nanoantenna array are studied to improve the performances of the on-chip OBS.Specifically,the studies in this thesis focus on the improvement of the device efficiency and the expansion of the field-of-view?FOV?,which are two crucial parameters for the on-chip OBS.The main contributions of this thesis are summarized as follows:1.A large-scale beam-scanning plasmonic nanoantenna array is designed.The nanoantenna array is fed by a low-loss plasmonic waveguide operating in a hybrid mode supported by a nanostrip and silver thin film.By proper engineering the dimensions of the waveguide,a low propagation loss can be achieved.With the aid of the low-loss nanostrip waveguide,small-beam-divergence wavelength-controlled beam scannings are successfully demonstrated with experimental verification.In addition,the impact of the delocalized surface plasmons is discussed.2.Novel on-chip nanoantenna and phase shifter are proposed to improve the efficiency of the silicon OBS,including a nanoantenna design with unidirectional light emission and an electro-optic phase shifter design with simultaneously low loss and low power consumption.The optical beam scanner formed by the proposed nanoantenna array,shows significant gain enhancement over the conventional waveguide grating antennas.3.In the development of the on-chip optical beam scanners,a wide Field-of-view?FOV?is always pursued.Three designs are proposed to expand the FOV of the on-chip OBS.?a?A silicon shared-aperture beam-switching nanoantenna array is designed,tripling the FOV of the conventional on-chip optical antennas within the same bandwidth.The proposed device leverages the design flexibilities provided by nanoantennas and the on-chip multiplexing technique to engineer the waveguide-antenna couplings of multiple shared-aperture nanoantenna subarrays independently.The design principles and operating mechanisms of the proposed device are introduced in detail.?b?A plasmonic impedance modulation nanoantenna is designed.A FOV over 90°is demonstrated with the presented plasmonic nanoantenna.?c?A wide-angle-scanning silicon phased array is designed.The proposed design achives a wide FOV with an inter-waveguide spacing over 0.71?₀,overcoming the trade-off between the device FOV and the suppression of the waveguide crosstalk.The presented device benefits from the superiority of the Luneburg lens and a flexible radiation pattern synthesis method based on the active element pattern.As a result,the presented device achieves an ideal 180°FOV with a low gain drop when scanning to large angles.