Fabrication and replication of high efficiency blazed gratings with grayscale electron beam lithography and UV nanoimprint lithography

Abstract

In a waveguide-type display for augmented reality, the image is injected in the waveguide and extracted in front of the eye appearing superimposed on the real world scene. An elegant and compact way of coupling these images in and out is by using blazed gratings, which can achieve high diffraction efficiencies, thereby reducing stray light and decreasing the required power levels. This study investigates the fabrication of blazed gratings with grayscale electron beam lithography and the subsequent replication of the realized 3D grating structures in a polymer material with ultraviolet nanoimprint lithography. As such, diffractive elements are realized on a waveguide sheet, with very good control over the dimensions and the profile of the printed features. Blazed gratings are designed for green light (λ = 543 nm) and a diffraction angle of 43 • . Making use of a PMMA resist and by carefully optimizing the electron-beam parameters, electron dose distributions and development step, blazed gratings with a pitch of 508 nm and a fill factor of 0.66 are achieved. Finally, a master is realized with two blazed gratings, 3 cm apart, which are replicated using ultraviolet nanoimprint lithography onto a waveguide sheet. The in-and outcoupling of an image through these two blazed gratings is shown, appearing sharp and non-distorted in the environment, and a throughput efficiency of 17.4% is confirmed.

Nanoimprinting of Biomimetic Nanostructures

“…While for conventional optical lithography typically a pattern transfer is necessary, in nanoimprinting a functional material can be patterned directly, thus reducing the number of process steps significantly (e.g., [27][28][29]). Such functional materials can serve optical properties (such as for diffractive optical elements) [30][31][32][33][34] or can directly act as microfluidic channels [35][36][37][38][39] or substrates for further processing [40,41], where the nanoimprinted material remains a functional component of the final device. Also, organic semiconductors have directly been imprinted [42], sol-gel materials [7,43], even silicon [44] or metals and ceramics [45].…”

Non-destructive multi-parameter investigation of nanoimprinted structures

“…Nanoimprint Lithography is utilized to replicate structures with high precision and in a short time using a polymer-based working stamp [1][2][3][4]. This makes NIL a frequently discussed method for the cost-effective production of optical elements such as waveguides and diffractive structures.…”

Manufacturing of phase gratings using nanoimprint lithography

“…The phase gratings could have future applications in the field of virtual or augmented reality. 4 In general, NIL is a nanostructuring process that has been known for about 30 years and has opened up a broader field of application. 5 While the NIL process proves to be advantageous, there is room for improvement in the quality of replication.…”