A GRIN Microlens Array With Hexagonal Aperture Simulated Compound Eyes Buried In A Convex Substrate

Compound eyes have some excellent features such as small size, light weight, big field angle of view and high time resolution. At the same time, microlens arrays play important roles in the development of modern optical systems advancing to micromation, lightweight, arraying, integrating and intelligentizing. To combine the novel microlens arrays and the simulation of compound eyes is one of the hot topics about microlens arrays and bionics. At the present time, phasic results have been obtained on microlens arrays simulated compound eyes, but it is limited in arrangement, material, thermal stability, corrosion resistance, anti-aging, responding to external stress or simulating whole optical functions of compound eyes.In this dissertation, based on analysis of optical structure of compound eyes, a model was founded. A method of fabricating a novel microlens array simulated compound eyes by photolithography and ion-exchange techniques is presented and designed. This kind of microlens with hexagonal aperture, high fill factor and gradient refractive index distributed in 3D is buried in a convex glass substrate, and each element of the microlens is a“compound lens”formed in a same process and in same time, which would breake the limitations of current ones in some aspects.The dissertation is focused on the diffusion theoretics of symmetrical apertured ion-exchange of Tl+-Na+, analysing the formation of hexagonal borders while the neighboring diffusion regions meet by theory of diffusion kinetics, analysis of optical and imaging characteristics of the microlens with hexagonal aperture and gradient refractive index in 3D and the bulge like a convex lens, and discussing the optical characteristics of the microlens array with hexagonal aperture buried in a convex substrate by method of matrix optics. Then a microlens array with hexagonal aperture and buried in a convex substrate was fabricated by photolithography and ion-exchange techniques including such key steps as design of a photomask, fabrication of the substrate, photolithography, etching apertures and ion-exchange. Firstly, the defusion characteristics of the glass used in the following fabrications was tested. Then, based on the testing results, the author studied the defusion characteristics of two samples with hexagonal and circular aperture, separately (The circle is just an incircle of the hexagon). Followed, a microlens array with hexagonal aperture and 2052 available microlenses was fabricated in a convex substrate with curvature radius of 250mm and diameter of 25mm. Finally, the appearance and cutting section of the microlens array, deformation in photolithography, multiple imaging, focal length, F number, spherical aberration, focused spot and distribution of refractive index is observed, measured and analyzed, then the following results are obtained.(1) A microlens array with hexagonal aperture and buried in a convex substrate simulated the dioptric apparatus of a compound eye can be fabricated by photolithography and ion-exchange.(2) A microlens array with high fill factor and hexagonal borders between any two neighboring microlenses can be made by photolithography and ion-exchange techniques if the designed apertures are arranged in hexagon symmetrically.(3) There are different laws in average deffusion rate, deffusion coefficient for different apertured shapes and in different directions.(4) A plane photomask can be suitable for a convex substrate when the photolithography and ion-exchange techniques are employed if the radius of curvature is big enough (20 times of the diameter of the substrate) to the size of the substrate. At the same time, the pattern deformations can be ignored too.(5) The microlens array fabricated by photolithography and ion-exchange techniques is every good in quality of multiple imaging, optical symmetry and uniformity. From center of the microlens array to the edge, the focal length and F number decrease a little gradually, but the NA increases. The spherical aberration of the microlens array is conspicuous and it can focus a laser beam into a spot of 4.92μm.Furthermore, some comcepts such as time resolution and deformation rate, a simple and convenient method of testing spherical aberration of microlens array are presented and discussed in the dissertation.