High efficiency diffractive light incouplers for light guides are described. We show that it is possible to couple white
LED light into light guide with good white balance and high incoupling efficiency by using binary radial grating
structures. Furthermore, a double-sided perpendicularly oriented grating configuration at opposite sides of a thin light
guide is shown to provide significantly higher overall efficiency than one sided grating. This is a configuration that can
be used in many mobile backlighting applications. In addition, a double grooved binary grating is introduced which can
produce theoretically up to 100% incoupling efficiencies by using monochromatic light sources. This high efficiency is
comparable to the slanted gratings. Replication techniques and incoupling efficiency simulations for slanted gratings are
introduced by using a high refractive index material (n=1.71@525 nm).
Design and manufacturing of diffractive optical elements (DOEs) are presented. Mass replication methods for DOEs are explained including UV-replication, micro-injection moulding and reel-to-reel production. Novel applications of diffractive optics including spectroscopic surface relief gratings, antireflection surfaces, infrared light rejection gratings, light incoupling into thin waveguides, and additive diffractive colour mixing are presented.
A new negative low-contrast electron beam resist X AR-N 7700/18 is used in multilevel structuring with direct electron beam exposure. The developed multilevel resist profiles are transferred into SiO2 substrates with reactive ion etching (RIE) and the desired profile depths are achieved by a proper adjustment of the pressure during the etching process. The tolerance of profile depth errors is found to be less than 2.5%. Examples of multilevel pixel-structured gratings and diffractive lenses are given.
Subwavelength-period gratings exhibit a number of interesting polarization-selective properties. We investigate several such phenomena: an `inverse' wire-grid polarizer, which transmits TE light while stopping TM light, a guided-mode resonance filter with an order-of-magnitude difference in the width of the reflectance peak for the two orthogonal states of polarization, a metal-coated silicon grating that reflects only TM-polarized light while absorbing the TE-polarized field component, and a metallic polarizing beamsplitter.