Research On Polarization Imaging Mechanism And Bionic Design Of Mantis Shrimp Eyes

Mantis shrimps have an amazing visual system.They have the spectral ability and own the ability to detect polarization which includes linear polarization and circular.Although it is still early days for the researches based on the structural features and polarized and spectral functions of mantis shrimp,the bionics techniques of mantis shrimp eyes have been applied to many areas,such as: cancer diagnosis and cure strategies,under-imaging,automatic drive,micro-polarizers and so on.Hence,the bioinspired techniques based on mantis shrimp eyes become a research hotspot.This paper study on the mantis shrimp eyes by dissecting the Oratosquilla compared with the eyes in the previous references.The mantis shrimp eye is apposition compound and divided to ventral,mid-band and dorsal ommatidia.A single ommatidium is composed of a cornea,crystalline cone,and rhabdomere over the retina.The rhabdomere in the ommatidium are the key for mantis shrimp to realize polarization and spectrum detection.The microvillus of rhabdomere in different ommatidia with different sizes,arrangement and opsin decide different functions of polarization and spectrum.Based on the structures of rhabdomere,the mechanisms of polarization and spectrum have been analyzed.The microvilli structure was simulated by finite difference time domain method(FDTD)and compared with the photoreceptors of the vertebrate.The results show that the tubal microvilli can enhance dichroic absorption.Meanwhile,the microvilli array can be equivalent to birefringence materials,and realize phase retardance.According to the features of mantis shrimp eyes,the mantis shrimp eyes were inspired in this paper.The microvilli with different sizes have different filtering functions of polarization and spectrum.Based on the characteristic,the bioinspired periodic holes photonic crystal model was established which can integrated polarization and spectrum filtering with a single material.The single layer hole was equivalent to the dielectric layer-grating layers-dielectric layer and the bionic model simulated by effective medium theory(EMT)and transfer matrix method(TMM).The simulation result shows that the bionic model can realize the polarization notch filter in the visible spectrum with different filling ratios and periods of holes.For further study,the shapes of the holes in the photonic crystal were analyzed.The thickness of the dielectric layer would influence on the transmittance of the passing band,and thicker of the dielectric layer,the transmittance of the passing band is lower.The boundary functions and slope of the holes which influence on the bandwidth of the rejection zone.Finally,the bionic model was analyzed with oblique incidence,and the results show that the bionic model was sensitive to the incident angle both the bandwidth and center wavelength of the rejection zone.The microvillus array can not only work as filters but also absorb the light and translate into an electrical signal.Hence,the microvillus array can be work as a filtering and detecting integrated element.The ability of mantis shrimp eyes is help for optical systems to integrate and minimize.For the contradiction between the absorptivity and extinction ratio of the integrated polarization detected system,the double wire grids with Al and Si structure was established to solve the contradiction.Silicon(Si)is semiconductor which can realize photovoltaic conversion,and the wire grid is easy to achieve polarization and spectrum characteristic.The bionic model with a single Si wire grid can realize polarization spectroscopy absorption.Firstly,the Si wire grid bionic model with period 364 nm,thickness 53 nm,and width 114 nm realize blue light(436 nm)polarization absorption,the absorptivity is more than 80% and extinction ratio is more than 15.Then,the bionic structure with the Si wire grid located on the center of the blazed grating substrate was studied.The bionic model with period 364 nm,width 114 nm,thickness 38 nm,and blazing angle 16°can realize yellow light(546 nm)polarization absorption,and the absorptivity at wavelength 546 nm is more than 86% and the extinction ratio is more than 145.Meanwhile,the bionic model with period 364 nm,width 180 nm,thickness 53 nm,and blazing angle 10°can realize red light(700 nm)polarization absorption,and the absorptivity at wavelength 700 nm is nearly 50% and the extinction ratio is more than 175.The results indicated that the bionic structure inspired by mantis shrimp microvilli array can integrate polarization filtering,spectrum filtering and light absorption.Besides,there is still high transmittance in absorption cur-off polarization direction.Compared with the integrated polarization detection,the bionic model can make the best of the incident light.There are two problems,resolution lost and position-matching error in division of the focal plane polarization imaging,because of the 2x2 micro-polarizers with 4 pixels for one imaging points.Inspired by the rhabdomere in row 5 and 6 of mantis shrimp eye mid-band,a bionic model was established to realize detecting two orthogonal in a single unit.According to the microvilli arrays in the rhabdomere,the bionic model with tubes arrays inspired microvillus.The simulation shows that if the material is not dichroic,there is nearly no polarization absorptivity.The material dichroism is the key to the structure: We analyzed the absorption distribution in the tube and established the bionic model by the orthogonal Si wire grid.The smaller Si filling ratio and thickness of the Si wire grid,the higher dichroic and extinction ratio will be got.The bionic orthogonal polarization detection model with period 50 nm,width 2 nm,thickness 5nm,distance 100 nm and the number of the orthogonal couples 600,the absorptivity in two directions are more than 60.Hence,the bionic orthogonal model can absorb two polarization directions respectively,and it is meant to reduce the loss of resolution and position-matching error.