Biomimetic soft lithography on curved nanostructured surfaces

In this paper a nano-molding process using a nature-created master is demonstrated. The eye of night moth Agotis exclamationis having 100 nm-scale structures on a curved surface is used as biomimetic master mold from which nanostructures are replicated onto a flat substrate. Suitable conditions of this simple and cost-efficient process allows for minimal texture damage. The fabrication consists of two steps: first, a negative PDMS mold of the curved eye surface is made, and second, the flexible mold is replicated into a hybrid UV sensitive polymer, on a flat substrate. An accurate copy of the master surface with dense arrays of 200 nm high and 100–120 nm wide posts are generated, thus preserving the integrity of the nanostructures. The known anti-reflecting optical properties of the moth eye were reproduced with a reflectivity reduced by a factor of 2

Fabrication of polymeric micro structures by controlled drop on demand inkjet printing

Well controlled spherical microstructures could enable several novel MEMS devices. However, micro machining of spherical shapes has proven to be difficult with conventional planar microfabrication processes [1]. This paper presents a method allowing to fabricate controlled micro spherical structures. Drops of approximately 30 picoliters of polymeric solution were accurately inkjet printed on rounded platforms. The deposited volume is confined by rim of these platforms, thus allowing a fine control of the spherical cap edge angle as well as the volume and the radius of curvature. The process proposed allowed to fabricate large arrays of micro spherical shapes, with a controlled edge angle between 25° and 110°. Several arrays of 30 by 30 micro hemispheres with an edge angle of 90° have been successfully fabricated with a yield above 98%

Fabrication of epoxy spherical microstructures by controlled drop-on-demand inkjet printing

Well-controlled spherical microstructures open new possibilities for several MEMS devices, such as hemispherical microfluidic channels or micro-optical elements. However, machining of micro-spherical shapes has proven to be difficult with conventional planar micro-fabrication processes. This paper presents a fabrication method allowing the fabrication of controlled micro-spherical cap structures with defined edge angles. Drops of 30 pL of an epoxy solution were accurately inkjet printed on circular platforms. The deposited volume is confined by the rim of the platforms. This allows a fine tuning of the spherical cap edge angle as well as its height and radius of curvature. The presented method allowed fabricating large arrays of well-controlled micro-spherical shapes of different diameters, ranging from 50 to 930 μm, with a maximum controlled edge angle tuning of 85°. Theoretical investigations of the underlying phenomena are also presented. Good agreement between experimental results and theoretical expectations has been observed, with standard deviations below 3%. Using the proposed method, several 2D arrays up to 900 micro hemispheres with an edge angle of 90° ± 2° have been fabricated with a yield above 98%

Fluorophore-doped xerogel antiresonant reflecting optical waveguides

Rhodamine B and Alexa Fluor 430 fluorophores have been used as doping agents for xerogel waveguides defined over an antiresonant (ARROW) filter. This configuration has a significant level of integration, since it merges the waveguide, the light emitter and the filter in a single photonic element. Different technologies have been combined for their implementation, namely soft lithography, standard silicon-based technology and silicon bulk micromachining. The spectral response of 15-mm long waveguides without fluorophore is first analyzed as a function of the waveguide width. Here, it has been observed how the xerogel used has a high transparency in the visible spectra, having only significant absorption at the wavelength where the ARROW filter is in resonance. In a second step, identical waveguides but doped with two different concentrations of Rhodamine B and Alexa Fluor 430 are studied. In addition to the effect of the filter, fluorophore-doped xerogel waveguides show losses close to 2 dB (equivalent to 2 dB of light emission). In addition, it has been observed how an increase of the fluorophore concentration within the xerogel matrix does not provide with a emission increase, but saturation or even a decrease of this magnitude due to self-absorption. Finally, the total losses of the proposed waveguides are analyzed as a function of their width, obtaining losses close to 5 dB for waveguide widths higher than 50 µm

Microlenses with defined contour shapes

Ink-jet printing of optical ink over SU-8 pillars is here proposed as a technology for obtaining microlenses with shape control. To demonstrate the flexibility of this method, microlenses with five different contour shapes (ranging from circular and elliptical to toric or more advanced geometries) have been fabricated. Furthermore, the optical properties of the different fabricated lenses have been experimentally investigated. Focal distance, numerical aperture (NA) and full-width at half maximum (FWHM) of the microlenses have been determined. Arrays of microlenses showed an identical behavior with a standard deviation in the total intensity of only 7%. Additionally, the focal plane of the fabricated symmetric microlenses and the Sturm interval of the non-symmetric ones have been obtained. The experimental results demonstrate the validity and flexibility of the proposed technology