Two-Channel Omnidirectional Panoramic Svstem Based On Even Aspheric Surface

The use of a panoramic optical module has increased rapidly and significantly throughout the world.Normally,the design refers to the one-time to detection imaging in 360° of field of view(FOV),and without any moving parts.An alternative approach is to use a wide-angle imaging system such as;fish-eye lenses with a 280° of FOV or a Panoramic Annular Lens(PAL).In both cases,a wide field of view can be captured within a single image.However,the first problem with these kind of lens systems includes blurry image and low resolution.This is because the refractive is a main challenge for field compression methods.Moreover,the major limitation of the PAL structure is a large diameter of the PAL block in the wide FOV,which can create a blind area in the central of optical axis and extremely effects the pixel efficiency of sensor.In order to solve above problems,we need to design a Single View Point(SVP)Catadioptric system based on aspherical surface which can combine with two-channels of beam rays in optical path and the images of them can form on the same detector.This study starts with the Single-View Point and describes the Even-order aspheric surface and its aberration coefficients theory.We introduce a mathematical model of geometry by ray tracing to achieve a novel central SVP Catadioptric panoramic design based on aspherical surface.The optical system includes two major optical components;Panoramic Front Unit(PFU)that can create a compression image,and the decompression image aspheric Relay Lenses(RL)group.Here,the optical system modeled and optimized by using Zemax-OpticStudio.Using Even aspherical elements can be provided a higher performing,more degrees of freedom,compact structure,and uses to control aberration.Firstly,the SVP Catadioptric system have a clear advantage over fish-eye lens and PAL system,since they tend to have greater resolution in the periphery of the field of view.One effective method to increase the field of view(FOV)and image resolution is to use a pair of aspheric hyperbolic mirrors in optical system.Here,this kind of design is named Omnidirectional Catadioptric system(OCS).Frequently,a folding system with a fix single view point able to create a panoramic perspective images on the detector.Under fix SVP point constraint every pixel in the sensed images measures the irradiance of the light passing through the viewpoint in one particular direction and needs that every beam light passing the effective pin-hole point of the Catadioptric system in 3-D coordinate.The mathematical model of geometry as a SVP system based on aspherical able to improve field of view which can help to solve blind area problem and resolution.Hence,just two reflectors with conical shape;parabolic and hyperbolic can be used for the design configuration as a central SVP point Catadioptric system.Secondly,the aim of this study is design a new dual-field of view Catadioptic panoramic system based on Even aspherical elements to eliminate some main problem of PAL system,such as;field of view,blind area and optical resolution.In optical system the panoramic front unit(PFU)have two hyperbolic aspheric mirrors that associated with a forward imaging concave lens element,an aperture,the relay lens(RL)group and an image sensor.Two axially symmetric hyperbolic reflectors capable to provide a compressed image of a panoramic annular side view.The primary mirror with a spherical radius of 23.14mm and a conic constant of-4.09,and secondary mirror with a spherical radius of 219.2mm and a conic constant of-1.2,which both mirrors inside of a solid aspheric optical substrate,and it is very useful to align the axis of two mirrors with axis of optical system.Besides,the aperture is placed along the optical axis and can filter out light rays other than those reflected directly from the both convex reflectors.Moreover,the function of RL is decompression images of the two independent optical paths and then project onto an image sensor without any interfere,therefore,there is no blind point image on the detector and also lead to a more compact structure.Thirdly,in this design,the result shows that the front field of view expands about 80°(±40°)and panoramic annular view covers about 198°(40°-139°).Since aspheric surfaces directly modify wave-fronts of optical path difference(OPD),according to their own shape,it is necessary to realize how these shapes arise and how they are related to the classical aberrations such as:Petzval Chromatic and distortion aberrations.The Seidel Petzval aberration coefficient is dependent on the local surface curvature and difference in refractive index.Actually,the negative Petzval value comes from the surfaces in the PFU and RL arrangement,which Petzval values can easily be balanced by the negative and positive Petzval values of the surfaces.The RL include two negative lens elements that having a negative optical power with the Abbe number approximately 55.8 that expand bundles of rays,and a positive lens element with the Abbe number approximately 35.0 having a positive optical power to correct chromatic aberrations.The linear distortion(f-? distortion)can be control the image height.The fis the image focal length and ? represents the object FOV of the optical system.Here,the f-? distortion data is used to control the image focal length of the two-channel configurations of optical path,which indicates the image height that will increase observably when the FOV increases,and also represents the image height with the f-? distortion,which is suitable for the wide FOV of optical system.Besides,the RL group can be helped to expand the field of view,with the increase of the field of view and resolution,the RL surface structure will become more and more complicated,that means aspheric surfaces need to add a high order aspheric coefficients.In Zemax-OpticStudio,the analysis method of optical design is determined based on aspherical elements,and the performance of the optical system is modeled,evaluated and optimized.The using the Merit Function Editor function,Monte Carlo(MC)and Root Mean Square(RMS,Spot radius)for optimization were more effective,and qualified some of variable parameters along design processing.The MC tolerance analysis also can prepare a standard function of theoretical design by adding disturbance,that can be determine these errors in order to eliminate manufacturing problem and feedback to design modeled for final optimization.In this design,there are 13 radii,72 polynomial coefficients,10 conic constants,6 glass thicknesses,5 air spaces and 6 lens materials,this makes a total of 112 parameters that can vary coefficients during optimization.Although the Even aspheric uses for its simplicity and aberration control,however,the all of aberration cannot be controlled by surface shape variables.Here,the diameter of the PFU unit is controlled within 58 mm,and the total length of the system is less than 56 mm.The optical image magnification and the Focal ratio(F/#)are matched between front and annular side field of view(FOV),and the effective focal lengths of the two-channel panoramic system are kept the same about 0.8mm.The preferred design sensor according to its datasheet is optimized for the OV5680 as a 1/3" CMOS detector with a pixel size of 1.75 ?m format and image area is 4.8×3.63 mm,which can capture the rays in both bands with a high sensitivity.It can be observed that the MTF value of the wide angle view is about 0.22 at 2851p/mm.The f-? distortion is controlled within 7%,and the relative illumination(RI)is more than 0.71 within the whole image area.In conclusion,we introduce a mathematical model of geometry to achieve design a new S VP folding Catadioptric panoramic system with dual-channel and 360°×278° of FOV based on aspherical surface in the visible light band to solve some main problems of PAL system.The using aspherical surfaces in order to design PFU unit and RL group provides a higher performance to control aberrations and lead to a more compact structure.This method can be adopted by any surveillance system for inspection application,medical instruments,and autonomous robot navigation or by other practical implementation application.