Research And Design Based On Microlens Array And Diffuse Free-form Surface

Nowadays,light emitting diode(LED)has become the most potential lighting source of the new generation,which has the advantages of high efficiency,energy saving,safety and environmental protection.It is widely used in various industrial production and daily life lighting fields.Because the light intensity of LED light source is similar to the Lambert cosine distribution,direct lighting with LED will form a circular spot on the target surface,which is bright in the center and darkens gradually around.Its uniformity is poor and energy utilization is low,so it is difficult to meet the actual lighting needs.Therefore,freeform surface is usually used as the secondary optical element of LED light source,so that its light energy distribution can meet the actual lighting needs,so as to achieve the purpose of high radiation uniformity and high lighting efficiency.In this paper,an optical system design method based on TIR and free-form surface microlens array is proposed.The design method of irradiance optimization based on free-form surface microlens array is used to plan the irradiance of light reaching the target illumination surface,so as to improve the illumination efficiency under the condition of ensuring the irradiance uniformity.Firstly,microlens array has been widely used in LED lighting due to its special optical properties,but most of the current research lacks complete mathematical model analysis and optimization.Therefore,according to the requirements of lighting environment,a complete mathematical model of free-form surface microlens is established.The model consists of LED array connected by TIR lens and free-form surface microlens array.The energy of LED is redistributed through the designed freeform microlens array,so as to obtain a uniform illumination area on the target plane.Based on the characteristics of TIR and the refraction law,a set of differential equations of free-form surface contour is established.The contour coordinates of free-form surface microlens are obtained by solving the differential equations with MATLAB.Then the freeform surface microlens model is obtained by using Solid Works to rotate the profile.Finally,the proposed microlens array is simulated in the near-field and farfield,and the influence of microlens array characteristics on illumination performance is discussed.The results show that the uniformity and efficiency have been improved,which can reach more than 90%.Generally,the bottom of most microlenses is circular,so the gaps can not be avoided in any arrangement.The light collimated by TIR lens will pass through the gaps of the microlens array,which is easy to cause the problem of low uniformity.In order to solve this problem,a free-form microlens array optical system for rectangular illumination is designed.A free-form surface microlens model with a rectangular bottom shape can be obtained by stretching the obtained two-dimensional profile curve of the free-form surface microlens along the threedimensional direction.The optical system composed of the free-form surface microlens array can obtain a rectangular spot with excellent effect on the target illumination surface.During the experiment,the influence of the length of the bottom surface of the free-form surface microlens,the distance from the microlens to the target surface and the length of the target surface on the illumination effect is also studied,and an optical system with the best illumination effect is obtained.The experimental results show that the maximum uniformity is 96.50% and the lighting efficiency is 90.275%.By realizing the high filling of the microlens array arrangement,the LED light after collimated by TIR lens is evenly distributed on the target illumination surface,which improves the illumination efficiency of the system.The introduction of diffuse transmission can effectively improve the uniformity of the system.Based on the Lambert characteristic of LED and the collimating characteristic of TIR,a mathematical model of collimating lens is established.Then,a mathematical model of two-dimensional microlens profile is established.After two sets of mathematical models are established,the corresponding two-dimensional curves can be solved.Finally,the two groups of two-dimensional curves are rotated by Solid Works software to obtain the required symmetrical free-form surface.After the single freeform surface microlens model is obtained,the high fill free-form surface microlens array is obtained by overlapping synthesis in different degrees.The experimental results show that the designed free-form surface microlens array has good illumination effect in near and long distance illumination,and the uniformity of the target surface can reach more than 64.44%.When the overlap length D= 0.08 mm,the lighting effect is the best.