Large area optical devices with glass-pressed/metal-embedded sub-wavelength grating

Abstract

INTRODUCTION Optical devices with micro-features of about half the size of optical wavelengths have recently been gathering much attention [1]. Advancements in micro-fabrication have realized developing such optical devices with a variety of functionalities. For example, embedding metal in gratings (cyclic grooves) of sizes about half the optical wavelengths, produced on the surface of transparent material like glass or plastic, makes optical devices like color filters, polarizing filters, or photonic crystals [2]. The superior optical performance of glass gives it a lead as transparent substrate material. Common forming methods of glass are pressing for mass production in case of smooth shapes like lenses. On the other hand, however, producing cyclic grooves on the surface in the sub-micron order requires lithography that repeats masking and etching or ion-beam etching. These processes consume large cost and time, thus are not suited for mass production. Press forming micro-structures can only reproduce forms to small areas and have not succeeded in forming larger areas in the millimeters to centimeters scale. The study we report in this paper developed the entire sequence of processes starting with glass material with superior optical characteristics, pressing gratings with sizes of about half wavelengths of optical light on a large area, and embedding metal to the grooves. These processes produced guide light plates with cyclic micro-structures and ones with metal embedded in the grooves. We measured the optical performance of these plates to evaluate the effect of tolerances in our processes.