Optical Characteristics Of Square-aperture Planar Microlens Array And Experimental Study Of Electric Field Assisted Preparation Technology

With the development of science and technology, planar microlens arrays are important elements in microoptics for the advantages of dense array, optical uniformity and high integration density. On the basis of microelectronics technology, optical micro processing technology is developed rapidly. Photolithography and thermal ion-exchanging technology become one of the important preparation methods because of simple process, stable process parameters and easily controlling.To improve filling factor of planar microlens arrays, square-aperture planar microlens arrays with good performance have been fabricated with photolithography and thermal ion-exchanging technology. Their fill factors have been improved up to100%. In this paper, optical and imaging characteristics of unit lens and region among the four adjacent lens units (be called corner area) of square-aperture planar microlens arrays are analyzed theoretically and experimentally. Imaging characteristics in corner area are reverse to those in focusing element lens, which are showed by ray tracing and MATLAB simulation. Results with image testing system show that a reversed real image of object A is formed after the ray passes through unit lens, while an erect virtual image is obtained because of divergent light out from corner area, which is caused by different refractive index distribution in these two areas. Therefore, square-aperture planar microlens arrays can achieve the function of focusing and defocusing. Moreover, with enough ion-exchanging time, the uniform refractive index region in the corner area is so little that a new-type gradient refractive distribution is formed which increases gradually out from the center, and this work is an important reference theoretically and experimentally for putting forward to a new-type distribution model in the further work.In addition, it is known that electric field assisted ion exchanging technology is used to fabricate optical waveguide. Learning from the experience, the method of electric field assisted ion-exchanging technology is used to optimize the performance of planar microlens arrays and reduce the fabrication time as far as possible. The glass substrate, in which alkali metal content is high and the refractive index is large, is selected to make planar microlens array. Various technical attempts mainly include four aspects as follows. The first is the construction of production platform; the second is the choice of ion source and its concentration; the third is the selection of a platinum electrode; and the last is the size of the voltage and time control of the applied voltage. Results show that preparation time is shortened obviously. By microoptical testing, it is found that under the action of electric field the original microlens are impelled strongly into the base plate. The depth of the ion exchange is significantly increased. Besides, refractive index distribution of microlens is further improved.