RUI:GOALI: Maskless microfabrication using polarization-driven photomechanics

Nontechnical Description:

Optical microstructures on a film surface cannot be seen with the human eye, yet they can efficiently redirect light, giving the surface a vividly colored appearance. Such structures occur naturally, and for example give butterfly wings their brilliant color. In the lab, synthetic fabrication of optical microstructures has had deep technological impact in fields such as information storage and display, and is based on exposing a photosensitive film to laser light or an electron beam.

While this technique is well-established, it is not suited for rapid prototyping. Another limitation is that the fabricated structures are immobile on the film surface once the film processing is complete. However, an emerging material class of organic molecule coupled with a flexible polymer have been found to be sensitive to the direction of illumination and not its brightness.

This sensitivity to light polarization can be exploited to make dynamic surface microstructures, enabling not only permanent optical microstructures, but also structures which can be reconfigured in response to light. This mechanical response to light can be coupled with new technologies in programmable light modulators to create a new platform for the on-demand fabrication of both static and dynamic optical microstructures.

Such a system will make rapid prototyping of light-diffracting surfaces accessible to a wide range of optical manufacturers, while also enabling new techniques in color engineering that rely on the use of microscale surfaces. Technical Description:

Surface microstructures enable photonics applications in miniaturized planar optics and are likewise used in bioengineering and materials science applications where surfaces with tunable anisotropy are required. They are typically fabricated using laser light to expose a photosensitive film through a photomask. The proposed research exploits a new fabrication process that combines the photomechanical response of azopolymer films with programmable spatial light modulators to enable one-step, maskless, and reversible writing of surface microstructures.

The proposed research will advance this methodology towards the one-step laser printing of planar diffractive optics and the printing of light-reconfigurable microarchitectures using pre-patterned template films. To accomplish these, the proof-of-concept system developed by the principal investigator will be significantly advanced towards not only optimal spatial resolution but also enabled with a new intensity-masking spatial light modulator component that will facilitate the programmable spatial addressing of optical intensity and polarization at the film surface.

These new capabilities will transform the proof-of-concept system developed previously towards one capable of printing planar diffractive optics, which in many applications can replace bulky refractive optics, an essential step towards novel optical integrated circuits. Such flat optics are in high demand and the principal investigator will collaborate with a local photonics company on designs most appropriate for emerging applications.

This next-generation laser printing system will also enable a new form of hybrid lithography in which high-spatial resolution nanostructures fabricated with specialized techniques such as electron beam lithography are first replicated in equivalent azopolymer film structures and subsequently optically reconfigured towards the final design structure. This concept of using prepatterned template films will open up new optically-driven microarchitectures, not previously accessible using conventional lithography or laser-based lithography working independently

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.