For a floating display system using a prism or bread type retro-reflector, non-retro-reflected light is the key causes of the deterioration in image resolution. In the present study, a micro aperture array (pinhole array) is used to enhance image resolution of aerial imaging display based on prism and bread retro-reflector. The effects of different micro aperture parameters on the divergence angle and stray light of the retro-reflector are experimentally studied, and the modulation of the point spread function of different retro-reflectors is also explored in detail. The experimental results show that by properly arranging the micro aperture array, the divergence angle of the retro-reflective light can be effectively reduced; Moreover, the full width at half maxima of the point spread function of the retro reflector has been effectively narrowed. Finally, after the modulation of micro aperture array, the imaging resolution can be increased by 119% compared to the original one. The proposed micro array is low cost, easy processing and flexible when it is applied to retro-reflector based aerial imaging system to provide high image quality.
Illumination design problem for light source with zero-étendue can be transformed into optimal mass transport problem based on ray mapping. In this paper, an improved numerical method for constructing freeform surface that best fits the normal field is proposed. First, the normal vectors at each point on freeform surface are constructed by two adjacent orthogonal tangent vectors. Then the nonlinear equations corresponding to the surface coordinates can be constructed according to the geometric relationship and Snell's law. Finally, a continuous and accurate freeform surface can be acquired by solving these nonlinear equations. Compared with the previous work, this method combines the coordinates of the initial boundary and the internal ones of the surface to construct a set of nonlinear equations, which effectively eliminates the bad points generated in the equation solving process caused by the arbitrariness of the initial boundary, and improves the integrability and accuracy. The simulation results show that for point light source illumination, freeform surface constructed by traditional methods have large distortion and relative standard deviation (RSD) values in the target area, while using this method can effectively reduce the distortion and RSD. Furthermore, the proposed method can provide lower normal deviation than the traditional methods, especially for the point-source lighting condition. In addition, the simulation found that when the illuminated area increases the normal deviation of both methods decrease, the RSD of the traditional method decrease, while the RSD of proposed method will increase slowly
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