The Optical Field Regulation Mechanism And Broadband Focusing Characteristics Research Of Gallium Nitride Metalens

This paper is supported by National Key R&D Program of China(NO.2017YFB043002)and the National Natural Science Foundation of China(NO.61574097),research on the regulation of light output characteristics of GaN-based luminescent devices based on micro-nano structure surface.Traditional optical elements are large in size and single in function,whose spherical aberration and chromatic aberration are obvious.In order to reduce the volume of optical devices and realize device planarization,researches on metasurface that can be applied to micro imaging systems have emerged.The metasurface can modulate and control the phase,amplitude,polarization state and other parameters of the electromagnetic wave in a two-dimensional plane through the subwavelength geometric structures.The metasurface can realize the functions of abnormal refraction,abnormal reflection,focused imaging,polarization state selection,perfect absorption,holographic imaging,vortex beam generation by breaking through the limitation of the traditional electromagnetic law.Metalens,the focusing metasurface device,can realize achromatic focusing imaging in a wide wavelength range.The approximate plane structure of metalens makes spherical aberration smaller and has higher integration.The main works are given as follows:Metalens devices composed of gallium nitride(GaN)nano-cuboid array on GaN substrate are proposed.The 2? phase modulation of incident light is achieved by changing the width or height of cuboid to realize the optical field regulation.Considering the subsequent process of making the metalens,we optimize the method of the height modulating phase and propose the method of the etching depth modulating phase.In this paper,the finite difference time domain(FDTD)algorithm and FDTD solutions software are used to simulate and research the transmission electromagnetic properties of the metalens.The mechanism of optical field regulation of metalens is researched,and the Mie theory involved in the metalens based on transmission phase is analyzed.The optical field regulation characteristics of width modulating phase metalens,height modulating phase metalens and etching depth modulating phase metalens are researched.The wide band focusing of the three metalens structures is simulated under the condition of linear polarized light incident with the wavelength of 400 nm-700 nm.The focusing characteristics and results of the three metaiens structures are compared and analyzed.The effects of the incident wavelength when selecting geometric parameters,incident angle and geometric structure on the focusing characteristics are discussed and analyzed.The 40-nm achromatic focusing superlens is proposed.Metalens devices based on GaN materials proposed in this paper can achieve continuous focusing in a wide band range.It is significant to improve the utilization rate of light source for integration into GaN-based LED.GaN metalens also has a broad potential application in other fields like integrated photonic devices and micro-imaging.