Femtosecond-laser-based prototyping of light pipe circuits
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abstract
2019 SPIE. Glass light pipes are fabricated using femtosecond laser irradiation followed by etching and thermal processing for minimizing sidewall scattering loss due to surface roughness. Turning mirrors and combiners, or splitters, are demonstrated. A critical step is assembly of the light pipe for coupling to a source or detector, which requires alignment and attachment, typically to a substrate. A combination of such structures has been realized to aid in assembly and optical transmission efficiency. Coupling from a distributed source through a lens array and into a light pipe array has been pursued for a waveguiding solar concentrators. The opposite propagation direction enables LED coupling and light distribution. Light pipes are fabricated with large cross-sectional areas, up to several square millimeters, compared to optical fibers. For glass-to-air cladding, the numerical aperture is substantially larger than for most optical fibers, thus enabling low loss transmission for high etendue sources. Instead of coating with a lower index material, as with optical fibers, a holding structure is desired to maximize the angular range for total internal reflection. We discuss the issues related to surface scattering and losses due to the cladding and light pipe mechanical support for LED lighting and solar applications.
