Research On The Optics Design Method Of Freeform Illumination

Compared with the conventional surface illumination system,freeform surface illumination is an elegant way of lighting,due to its high degrees of design freedom.The layout of freeform illumination system is more flexible which usually makes more compact lighting structures.With the continuous development of freeform surface technology,freeform surface lighting is expected to gradually replace the traditional lighting system,and promote more energy-saving,compact,efficient and low-cost lighting applications.Current freeform illumination optical designs are mostly focused on producing prescribed irradiance distributions on planar targets with ideal light sources.However,with the increasing demands of illumination applications,such as 3D targets lighting,ultracompact illumination systems,etc,optical designers are required to take the size and shape of light source,as well as the spatial location and the surface information of the illumination target into consideration in illumination optics design.The related researches are still in their infancy.To address these problems,we conduct a detailed study on illumination optics design based on freeform surface,aiming to develop a set of efficient,reliable and general illumination optical design solutions.The specific research contents are listed as follows:(1)For the zero-étendue sources,we successfully study the separating variables ray mapping method,optimal mass transport ray mapping method,symplectic flow ray mapping method and least square ray mapping method.The first method is a simple energy grids division,which is easy to be understand and implemented.For the second method,we use the optimal mass transport theory to divide the source energy distribution and the lighting target energy distribution into grids respectively.This ray mapping method can deal with some complex lighting problems.The third and fourth methods are proposed to improve the integrability condition of the ray mapping.The purpose is to make the actual deflection directions of the light rays leaving the freeform surface close to the predefined ones,thus improving the light control ability of the freeform surface.(2)For 3D target illumination problem,we propose a general freeform surface optics design method.The complicated 3D target lighting design problem is simplified to the conventional 2D target lighting design problem via an elaborate energy transport.Specifically,we introduce a virtual plane which is perpendicular to the optical axis,the irradiance distribution on the 3D target is transformed to the virtual plane,and the irradiance distribution on the 3D surface can be realized automatically by designing freeform surface optical element to achieve the transformed irradiance distribution on the virtual plane.The design framework can deal with far-field and near-field lighting problems.Any design methods for zero-étendue sources may be applicable for freeform surface design as long as the irradiance distribution is transformed by the proposed method.The design results have verified the effectiveness of the proposed method.(3)To avoid the tedious Monte-Carlo ray tracing,two methods of irradiance calculation have been studied.The first method is implemented based on the projected solid angle calculatation,which calculates the projected solid angle of the light cone formed by the light ray from the boundary of the extended light source to the testing point on the target plane,and then obtain the irradiance value via the radiation theory.The second method is implemented by backward ray tracing.The ray tracing is started from the testing point on the target plane to the source domain,and find the useful part of freeform surface which contributes to the illuminance at the testing point,then calculate the illuminance at the testing point.The simulation results show that these two irradiance calculation methods are more efficient than the Monte-Carlo ray tracing method.(4)For extended light source illumination optics design,three optimization methods have been studied,including particle swarm optimization(PSO)method,feedback optimization method and local curvature control optimization method.The PSO method is used to design ultra-compact aspheric lenses for rotational illumination configurations,and its effectiveness is verified by simulation and experimental tests.For the feedback optimization method,the feedback mechanism with the memory function is introduced to achieve rapid convergence.In the local curvature control optimization method,the local curvature of the freeform surface is adjusted to change the illuminance value of the corresponding testing point on the target plane.So,the optimization is more targeted and improves the whole design efficiency.