Kinoform microlenses for focusing into microfluidic channels

Optical detection in microflow cytometry requires a tightly focused light beam within a microfluidic channel for effective microparticle analysis. Integrated planar lenses have demonstrated this function, but their design is usually derived from the conventional spherical lens. Compact, efficient, integrated planar kinoform microlenses are proposed for use in microflow cytometry. A detailed design procedure is given and several designs are simulated. A paraxial kinoform lens integrated with a microfluidic channel was then fabricated in a silicate glass material system and characterized for focal position and spotsize, in comparison with light emerging directly from a channel waveguide. Focal spotsizes of 5.6 μm for kinoform lenses have been measured at foci as far as 56 μm into the microfluidic channel.