Large-scale microlens arrays on flexible substrate with improved numerical aperture for curved integral imaging 3D display

Abstract

Curved integral imaging 3D display could provide enhanced 3D sense of immersion and wider viewing angle, and is gaining increasing interest among discerning users. In this work, large scale microlens arrays (MLAs) on flexible PMMA substrate were achieved based on screen printing method. Meanwhile, an inverted reflowing configuration as well as optimization of UV resin's viscosity and substrate's surface wettability were implemented to improved the numerical aperture (NA) of microlenses. The results showed that the NA values of MLAs could be increased effectively by adopting inverted reflowing manner with appropriate reflowing time. With decreasing the substrate's wettability, the NA values could be increased from 0.036 to 0.096, when the UV resin contact angles increased from 60.1° to 88.7°. For demonstration, the fabricated MLAs was combined to a curved 2D monitor to realize a 31-inch curved integral imaging 3D display system, exhibiting wider viewing angle than flat integral imaging 3D display system.

Figure 1

Morphology of MLAs with inverted reflowing manner. (a) 3D perspective images of a typical solidified microlens with inverted reflowing time of 1 h. (b) The profiles of MLAs with respect to reflowing time. (c) The evolution of NA and radius of MLAs with the reflowing time. The height profiles (red solid line) taken along the equatorial plane of a typical microlens and fitting of an ideal surface to the lens profiles (Red dash line) with inverted reflowing time of 1 min (d) and 1 h (e).

Figure 2

(a) The relationship between the NA value and the viscosity of UV resin, the inset presents the profiles of MLAs with respect to viscosity of UV resin. (b) Microscope image of a typical microlen fabricated using UV resin with viscosity of around 40,000 cps, showing the existence of bubbles on the lens surface. (c) Microscope image of MLAs fabricated using UV resin with viscosity of around 10,000 cps, showing linkages between adjacent microlens.

Figure 3

(a) The lens profile for MLAs fabricated on PMMA substrates with various contact angles of UV resin. (b) The NA of microlenses as a function of surface contact angle, the inset shows a typical optical micrograph of a drop of UV resin on PMMA substrate showing surface contact angle of 88.7°. (c) The photo of a 31-inch MLAs fabricated on PMMA substrate with TMCS treatment of 55 min and with inverted reflowing time of 1 h. The uniformity information in terms of the height (d) and diameter (e) information of 50 randomly selected micro-lenses from the MLAs shown in Fig. 4c. (f) A typical AFM image of the surface of micro-lens over a 5 μm × 5 μm area, showing excellent surface quality.

Figure 4

The focusing performances of the MLAs. (a) Schematic of experimental setup for examining the optical properties of the fabricated MLAs. (b) the 2D light intensity distribution with the sharpest focus spots. (c) The corresponding 3D light intensity distribution of a randomly selected focused spots.

Figure 5

(a) Scheme of reconstruction stage of integral imaging, a microlens covered 5 × 5 pixels. (b) Design scheme of microlens’s pitch for the curved integral imaging 3D display system. (c) An elemental image array captured using computer graphics techniques. (d) The photo of constructed 31-inch integral imaging 3D display system with a floating 3D reconstruction image viewed from the normal direction. (e) A photo of 3D reconstruction image viewed from the left 45° direction. (f) A photo of 3D reconstruction image viewed from the right 45° direction.

Figure 6

Schematic fabrication processes of MLAs. (a) The PMMA substrate was treated using TMCS vapor; (b) Schematic processes of screen printing; (c) The printed MLAs were laid flat with MLAs side down to reflow for various time followed by UV exposure. (d) Schematic of curved integral imaging 3D display system.