| In recent years,with the development and progress of quantum optics,micro and nano-optics,and semiconductor processing technologies,as well as the gradual slowdown of traditional microelectronics processing processes,photonics has become a trend as a new generation of information carriers.Therefore,along with the rapid development of photonic integrated systems,photons have played an important role in fiber optic communication,optical computing,and photoelectric detection.At the same time,the continuous development of integration technology has also prompted the corresponding iteration and upgrade of optical components integrated.Beam splitters are widely used in various optical systems as the basic functional components in optics.Due to its dependence on the crystal birefringence effect and the optical path accumulation effect,the conventional cube beam splitter is hard to integrate into compact optical systems.Furthermore,as more compact alternatives,some flat-type beam splitters have been recently demonstrated.Although these beam splitters have significantly smaller sizes than cube beam splitters,they are still unsuitable for integration because of their sensitivity to the incident angle,fixed emergence angle,and other problems.The artificial subwavelength two-dimensional planar structure of the metasurface can freely regulate the wavefront of the optical field by introducing certain phase gradient changes on its surface,which can realize many amazing functions such as optical stealth,multispectral imaging,optical diffraction neural network,etc.With the advantages of small size,lightweight,low power consumption,and easy integration,the metasurface also shows an excellent potential application in photonic integrated systems.Therefore,in order to solve many problems of traditional beam splitters in photonic integrated systems,this thesis focuses on the design concept of an incomplete transmission fully dielectric metasurface,and constructs and numerically simulates a short-wave infrared transflective metasurface beam splitter as well as a short-wave infrared bifocal beam splitter,which is expected to be widely used in optical fields involving on-chip integrated optical systems such as photonic computing,fiber optic communication,and nano-lasers,and the incomplete transmissive metasurface design concept adopted in this thesis is also expected to provide a design idea for transflective metasurface functional devices different from existing transmissive or reflective metasurfaces.The main research contents of this article are as follows:1.Based on the incomplete transmission and double-end response phenomena exhibited by multiple metasurfaces arranged with silicon nanocylinders of different radii,a double-end phase modulation design study was carried out,and a metasurface all-dielectric beam splitter operating in the short-wave infrared was designed using transmission phase.By numerical simulation of the electromagnetic field and using TM light and TE light for incidence respectively,the beam splitter achieves a beam splitting function at 1550 nm with a splitting ratio(transmittance: reflectance)of 59% :41%,an outgoing angle of about 9°,and a theoretical total splitting efficiency of93.3%.The study also presents a numerical simulation analysis of the incident angle bandwidth and stability,and finally,the metasurface beam splitter achieves an operating incident angle tolerance with a large angular bandwidth of about 32° and a double-ended isophase stable deflection separation that is insensitive to incident angle variations.Compared to conventional cube and flat-type beam splitters,this design has the advantages of small size,easy integration,and high stability,the beam splitting effect is also not easily affected by processing accuracy.This transflective metasurface beam splitter can obtain a feedback signal while splitting the beam to correct the operating parameters of the optical system,which is hopeful to be used in the design of feedback links for optical detection,interferometer,and other integrated optical systems.2.Based on the above metasurface design concept of incomplete transmission double-ended response,this paper further validates the applicability of this structural design method by constructing a metasurface bifocal beam splitter composed of rectangular nanopillar arrangement and employing the Pancharatnam-Berry(PB)phase for the incident circularly polarized light.The Pancharatnam-Berry(PB)phase is used to modulate the incident circularly polarized light with the wavefront phase.By simulating the incident circularly polarized light and recording the electromagnetic field propagation of this beam splitter,the final numerical simulation achieves the double-ended deflected focusing beam splitting function at 1.55 um wavelength,and the focusing efficiency of both ends is more than 50%,the equivalent numerical aperture of both ends is over 0.85 and the splitting ratio is 59% : 41%.The simulation results of the metasurface double-ended optical axis on the same side and equal focal length focus further confirmed the phenomenon of double-ended synchronous phase modulation response under an incomplete transmission structure.Subsequently,by changing the polarization state of the incident light,the left-rotating circularly polarized light is changed to right-rotating circularly polarized light for control incidence,and the different outgoing light field distributions show its characteristic of polarization recognition of left-rotating circularly polarized light.Since this metasurface bifocal beam splitter integrates the focusing function on the basis of beam splitting,it can greatly reduce the overall assembly volume of optical components included in the beam splitting—focusing link in optical systems and is expected to further enhance the lightweight and integration of multi-focal optical systems such as laser optical tweezers. |
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