Ultra-thin multifocal integral LED-projector based on aspherical microlens arrays.

Multifocal imaging has been a challenging and rewarding research focus in the field of imaging optics. In this paper, an ultra-thin multifocal integral LED-projector based on aspherical microlens array (MLA) is presented. A two-layer aspherical sub-lens with NA = 0.3 is proposed as a sub-channel projector and the optimization design ensures high optical integration precision and improves optical efficiency. To avoid the tailoring loss of the projected images between multi-plane projections, the central-projection constraints between size and projection distance for the multifocal projection are defined. The depth of focus (DOF) analysis for MLA and sub-lens is also introduced to proof the sufficiency of realizing multifocal projection. Combined with the radial basis function image warping method, multifocal sub-image arrays were acquired, and three types of multifocal integral projection were realized, breaking through the traditional limitations of the single-focal DOF. A prototype with thickness of less than 4 mm is developed. Substantial simulations and experiments are conducted to verify the effectiveness of the method and the design.