Diamond double-sided micro-lenses and reflection gratings

Abstract

Double-sided micro-lenses have been successfully fabricated on natural diamond substrates using photoresist reflow method followed by Inductively Coupled Plasma (ICP) etching. The micro-lenses were fabricated on both sides of the substrates which were aligned to each other. The optical properties of these lenses were characterised by a laser scanning transmission/reflection confocal microscope. It has been confirmed by the confocal microscopy technique that the laser beam was focused twice as it shone through the substrates. The focal length was calculated based on refraction formula at the spherical surface which has been derived from Fermat’s principle. The top focused point was found lying within the substrates while the bottom focused point lying outside of the substrates. Both focal lengths of the top and bottom micro-lenses agree well with the theoretical calculation based on the refraction formula. This demonstrates the functionality of the double-sided micro-lenses. In addition, highly smooth diffraction gratings (surface rms roughness of 1 nm) with near-vertical sidewalls (85 ± 5°) have also been successfully fabricated on the HPHT diamond substrate utilising SiO 2 as mask and Reactive Ion Etching (RIE) and ICP plasma etching. The optical functionality of the diamond reflection grating has been confirmed by the reflection measurement.