Metasurface Enabled Three-Dimensional Point Spread Function And Its Application In Imaging

Three-dimensional(3D)imaging can capture the scene in the environment and the 3D structure of the objects,it can estimate the depth or distance(z)of each transverse position(x,y)in the object space to the camera and extract the 3D information of the object space by analyzing and processing the output information of3 D imaging.Based on the these characteristics,3D imaging has been widely used in object recognition,face recognition and monitoring,robot navigation,mapping of the earth's surface,forests and urban areas,as well as in the fields of medicine,clinical and 3D localization of intracellular molecules.However,traditional depth estimation methods based on vision and depth of defocus have strong limitations and low measurement accuracy.A more promising approach is to replace the standard point spread function with a three-dimensional point spread.Depth measurement based on three-dimensional point spread function is non-contact measurement,which has the advantages of high precision of depth estimation and simple measurement systems,has been applied in 3D tracking,super-resolution imaging of molecules or particles and other fields.In the previous works,three-dimensional point spread function is mainly realized by computer-generated hologram(CGH)or spatial light modulator(SLM),which has the disadvantages of large volume,complex system and difficult to be integrated.Metasurface is an artificial two-dimensional layered material with a thickness smaller than the wavelength.It can flexibly and effectively regulate the polarization,amplitude,phase,propagation mode and other characteristics of electromagnetic waves.In recent years,the metasurface composed of subwavelength antenna arrays arranged according to specific shape and size has been widely studied in the field of regulating light wave surface.In this paper,the three-dimensional point spread function is realized based on the metasurface,and the three-dimensional imaging of the micro-point object on the axis and the actual three-dimensional scene is carried out.In addition,the three-dimensional point spread function and the metalens are integrated on the same metasurface to realize the three-dimensional imaging of the single micro-point on the axis and the double micro-points off the axis.Compared with the traditional methods,it has the advantages of small component size and strong system integration.Thespecific research contents are as follows:(1)The high efficiency optimization algorithm of the double helix point spread function of the three-dimensional point spread function is studied.The double helix point spread function is optimized by using restriction and optimization functions.(2)The reconstruction algorithm of 3D information of objects is studied.By analyzing the image acquisition,depth map restoration and object reconstruction process of the object after passing through the 3D imaging optical system,the reconstruction algorithm of 3d information is obtained.(3)For the Huygens' all-dielectric metasurface,the phase distribution of the high-efficiency double helix point spread function was discretized to solve the complex problem of continuous phase distribution in its design and processing.The minimum discrete order without affecting the imaging effect was obtained through numerical analysis,which simplified the design and processing process.(4)High-transmission Huygens' all-dielectric metasurface samples with phase distributions of different discrete phases were designed.Their optical properties were processed and analyzed experimentally,the 3D imaging was performed on the object points on the axis and the actual 3D scene.The 3D information restoration algorithm was used to recover the 3D information of each object in the object points and scene.(5)For the plasmonic geometric metasurface,the light efficiency of the high-efficiency double-helix point spread function was further optimized due to the low transmission rate caused by the high absorption loss of the metal layer.In order to realize the integration of the imaging system,an integrated double-helix metalens is proposed,which integrates the double-helix phase mask with the convergent lens,so that the volume of the components is greatly reduced.(6)The plasmonic geometric metasurface encoded with the phase distribution of the double helix-metalens was designed.A double-layered metasurface with high transmission is composed of a multi-pole subatomic array with electric dipole,magnetic dipole,electric quadrupole moment and magnetic quadrupole moment.Using the processed samples,the imaging experiments of single micro-point on the axis and double micro-points off the axis were carried out,and the three-dimensional information of the points was recovered.