Research On The Preparation Of Microlens Array Based On The Wetting Control Droplet Arrangement Technology

Microlens array is an important micro-optics component,which has important application value and broad prospect in the fields of stereoscopic display,optical information storage and optical communication.However,the processing problem of microlens array（MLA）has become an important factor restricting its rapid development and application.Therefore,the low-cost,high-efficiency and large-volume preparation technology of MLA attracts many researchers’interests.In this paper,the method of preparing MLA was proposed by using the wetting control droplet arrangement technology.This method had the advantages of that it can efficiently and quickly prepare MLA with high-throughput in a large area,and realize the precise regulation of the shape,size,position and curvature of the lens unit.Firstly,the preparation of microholes array patterned hydrophobic layer modified the substrate surface by using photolithology and coating method was proposed.The surface energies of hydrophilic and hydrophobic regions were measured by contact angle method.It was found that the surface energies inside and outside microholes were 71.45m N/m,and 13.19 m N/m,respectively.Polyvinyl alcohol（PVA）solution was coated onto the microhole array patterned hydrophobic layer modified substrate to form droplet array using scrap-coating method,taking advantage of the difference in wettability between inside and outside microholes.In one case,PVA solution moved from hydrophobic area into the hydrophilic area under the action of surface tension,In the other case,PVA solution in the hydrophilic area was trapped by the hydrophobic boundary.After the solvent in the PVA solution was completely evaporated by heating method,PVA MLA with the same curvature in a large area was obtained.During the evaporation of the solvent in the PVA droplet in the microhole,the change of contact angles was observed by in situ observation.It was founded that the contact radius of PVA solution in the microhole remained unchanged during the evaporation,the apparent contact angle decreased gradually,thus the curvature of the droplet was gradually increased.Secondly,the process parameters affecting the surface profile of PVA microlens were studied in depth.The curvature of PVA microlens could be adjusted by regulating the concentration of PVA solution.The curvature of PVA microlens decreased with increasing the concentration of PVA solution;While if the concentration of PVA solution was too high,the difficulty of scrap-coating method would be increased.By adjusting the volume of PVA solution,the curvature of PVA microlens was regulated.Because the existence of the line tension,the contact angle of PVA solution in the microhole became larger with increasing the volume of PVA solution.By designing the structure of the photomask,a microholes patterned hydrophobic with different apertures and different fill factors were prepared,and thus PVA MLAs with different apertures and different fill can be prepared.By adjusting the process parameters of the photolithology and coating method,the hydrophobic pattern layer was modified on the surface of the flexible polyester substrate to prepared a flexible PVA MLA.Thirdly,PVA has two characters 1.PVA was served as an arrangement layer to arrange liquid crystal（LC）molecules perpendicular to the substrate surface;2.The refractive index of PVA was～1.52,which was matched well with the refractive index of nematic LC（E7,n_o～1.52）.Thus,PVA MLA could be used to prepared LC MLA with tunable focal length.By building an experimental setup,the light intensity distribution and focusing property of LC MLA was evaluated,When the voltage was adjusted from 0 to0.6 V_rms,the focal length of the LC MLA was changed from-4.5 cm to infinity,which implied that the LC MLA was a divergent lens.