Micromilling with nanoscale roughness for silica photonics

Carpenter, L.G., Cooper, P.A., Holmes, C., Gawith, C.B.E., Gates, J.C. and Smith, P.G.R. (2015) Micromilling with nanoscale roughness for silica photonics. SPIE Photonics West '15, , San Francisco, United States. 07 - 12 Feb 2015.

Abstract

We present Flame Hydrolysis Deposition (FHD) silica micromilled with nanoscale surface roughness, sub-micron form control and micron scale depths of cut for photonic applications. Using our in-house developed high-precision micromill and industrially standard micromill tools, we have machined slots 1.5 mm long and 17 µm deep, enabling access and interaction with the evanescent field of nearby UV-written waveguides. Potential applications vary from: biological sensing, plasmonic devices, refractometers and chemical sensing. The micromilling approach offers advantages over conventional cleanroom and laser-based machining of optical materials in both form control and achievable surface roughness. To assess optimum cutting conditions a wide parameter test was conducted, where the rotational and translational speeds were varied and feed speeds optimized to allow cutting in the high-quality low-chipping ductile regime. Whilst milling in the ductile regime our smoothest form slots had a surface roughness of 3.0 nm (Sa) at a 17.0µm depth of cut. This represents a forty times increase in cut depth and an eight times improvement in surface roughness over previously reported silica slot micromilling. We will present our latest machining results with studies into sequential slot milling and report on the subsequent slot form, surface roughness, and mill wear from prolonged sequential machining. We will also show results of integrating milled slots with optical waveguides and Bragg gratings to create refractometer devices.

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Contributors

Author: C. Holmes

Author: C.B.E. Gawith

Author: J.C. Gates

Author: P.G.R. Smith

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