Transparent colored signage and display enabled bynanoimprinted multi-layer gratings
Zeyang Liu1,2, and L. Jay Guo*1
1Department of Electrical Engineering and Computer Science
University of Michigan, Ann Arbor, MI 48109, USA
2
Key Laboratory of Opto-electronics Information Technology
Tianjin University, Tianjin 300072, China
E-mail: guo@umich.edu

With the popularity of transparent display, a promising approach of waveguide display [1] isdeveloping rapidly, and has demonstrated various functionalities, such as augmented reality
display [2] and glass-free 3D display [3]. The widely used gratings as optical elements can offer
periodic refractive index modulations and provide momentum matching to split the incident lightinto multiple diffraction order beams. Because of this feature, gratings have been used
extensively as the out-coupler of waveguide to extract light by diffraction, which interrupts thetotal internal reflection (TIR) of the propagating light. Here, we present a type of statictransparent signage using flat glass and embedded multi-layer gratings, by which multiple
patterns and colors with a wide field of view can be displayed.
The device is made on a piece of edge-polished glass, which can guide input light from the edges
by TIR. Multi-layer gratings are used to extract light that propagates inside the glass in different
directions. Grating of each layer is shaped into the specific pattern to be displayed. Each grating
is designed to have a proper period and orientation in order to independently out-couple lightincident from the corresponding edge. Three types of samples with a single-layer grating, twolayer gratings, and three-layer gratings on rectangular or hexagonal shaped glass aredemonstrated. The embedded multi-layer gratings are made of titanium oxide (TiO2) coated on
imprinted and UV-cured polyurethane acrylate (PUA) resin. The multi-layer gratings arefabricated by repeating the nanoimprint three times using the corresponding grating molds,
followed by electron beam evaporation of TiO2 after each imprinting process. This type oftransparent display offers the advantages of low cost, easy fabrication and wide field of view,
and it is suitable for signage and decorative applications.

References:[1] Eisen, L.; Meyklyar, M.; Golub, M.; Friesem, A. A.; Gurwich, I.; Weiss, V.; “Planarconfiguration for image projection,” Appl. Opt. 2006 45, (17), 4005–4011[2] Liu, Z.; Pang, Y.; Pan, C.; Huang, Z.; “Design of a uniform-illumination binocular
waveguide display with diffraction gratings and freeform optics,” Opt. Express 2017 25, (24)30720-30731.
[3] Fattal, D.; Peng, Z.; Tran, T.; Vo, S.; Fiorentino, M.; Brug, J.; Beausoleil, R. G.; “A multidirectional backlight for a wide-angle, glasses-free three-dimensional display,” Nature 2013 495,(7441), 348–351.

Figure 1. (a) Rectangular flat glass with a single-layer grating. (b)-(d) The monochrome pattern can havedifferent colors by changing the wavelength of the input light.

Figure 2. The first rectangular flat glass (a) has two-layer gratings with two complementary patterns.
When blue light and red light are input from the two adjacent edges simultaneously, a two-color pattern (b)is lit up. The two-layer gratings on the second rectangular flat glass (c) have two separate letter patterns“U” (d) and “M” (e), which can be selectively displayed by switching light sources at different edges ofthe glass.

Figure 3. (a) Hexagonal flat glass with three-layer gratings. (b)-(d) Different letter patterns with different
colors can be displayed when red, green, and blue light is input from the corresponding edges,respectively.