Advanced design, test and fabrication of silica based micro optics
Currie, Matthew Oren
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This thesis presents important advances in the laser processing of fused silica in order to create micro-optical structures using the techniques originally developed by the Lasers and Photonics Applications (LPA) group at Heriot-Watt University and subsequently by PowerPhotonic Ltd., the company created to commercialise the technology. This technology uses a CO2 laser operating in two separate modes at a wavelength of 10.6µm in order to first create a desired surface profile and subsequently to polish the surface, creating arbitrary freeform surface topologies with high quality optical surfaces. The first fabrication mode undertaken during processing, referred to as laser cutting, was investigated to determine whether the upper limit of achievable cut depth could be increased, which was approximately 60µm at the start of the EngD project. This resulted in the establishment of new methods that increase the sag of optics that can be manufactured using this laser machining process, with cut depths over 400µm. This in turn enabled the design and fabrication of fast-axis collimator arrays (FACAs), for which a patent was granted in 2014. During fabrication of these deep optics it was found that the silica dust produced during the laser cutting process can have a detrimental effect on final surface quality as it may be re-melted and fuse with the optical surface, changing the expected shape. Mechanisms that remove the dust as it is being produced were investigated and refined and subsequently used to create a system and methodology that is suitable for use in a production environment. This extraction system can now be used to create high quality optics even where volume removal, and thus dust generated, is large. The experience gained when designing, fabricating and testing a wide range of optical surfaces over the course of this EngD period enabled the design, development and implementation of a web-based rapid fabrication service for prototype freeform optics called LightForge. This original work now offers the unique ability in the micro-optics market for a customer to upload a fully defined optical design through a web portal and have it manufactured within 2 weeks. This revolutionary service has, and continues to, considerably expand the visibility and reach of PowerPhotonic within the micro-optics market. A patent has been applied to cover this process and is currently being examined.