Laser ablation of micro-photonic structures for efficient light collection and distribution

In this work we report the fabrication of polymer micro-photonic gratings for use in liquidcrystal based actively tunable electro-optic components. The gratings are produced by moving the sample surface sideways across a perpendicularly impinging KrF excimer laser beam (lambda = 248 nm), which is shaped by specially designed triangular and trapezoidal masks. To obtain correctly dimensioned and smooth grating surfaces, different materials (SU-8, polycarbonate, Epoclad and Epocore) are subjected to the laser ablation with optimized laser processing parameters. The resulting grating structures on Epocore exhibit the best surface roughness and dimensional fidelity. Optionally, spacers for maintaining the cell gap of the superimposed liquid crystal layer can also be fabricated in the same process. Two different methods were demonstrated: overlapping ablation and double mask ablation. Micro-grating structures were produced that deflect a monochromatic (543 nm) laser beam to the theoretically predicted 11th order with an angle of 7 degrees