Every year, SPIE San Diego organizes 25 major optics and photonics forums, exhibitions, and education programs gathering around 35,000 scientists, engineers, and entrepreneurs to showcase and collaborate on the latest tech, focusing on optics and photonics. We caught up with optics engineering wiz, Ray Williamson on the design challenges in optical manufacturing.
Q&A with Ray Williamson at SPIE San Diego
For uninitiated designers, what is the most common design challenge or mistake when manufacturing of spherical optical components?
Ray Williamson: Unfamiliarity with optical manufacturing and metrology “gotchas.” The designer works in bit-space, in which nothing can be machined, instrumentally verified, physically aligned, or subjected to stresses. Of course they know that, but they may not know the particular issues with available manufacture and metrology technologies, or of material responses to processing or environments.
A few examples:
- Polishing creates local frictional heat. A material with high coefficient of thermal expansion and low thermal diffusivity, configured so that it is thin in the center, will bulge and buckle during polishing. Maybe not much, but enough to make it difficult to achieve the necessary surface form tolerance once it has settled.
- A window works in transmission, so specify transmitted wavefront, not flatness, because thin sections are flimsy. (You don’t need paper to «be» flat, only to be uniform in thickness.)
- Wedge or beam deviation in a concentric meniscus lens should be specified as such, not as decenter, which refers to the lateral displacement of the optical axis with respect to the lens’ physical center. (A small wedge in such a lens can push the optical axis completely outside the physical lens.)
- Think in terms of curvature rather than radius: A percentage radius tolerance on a small enough radius may be less than the resolution of an interferometer slide, while a percentage tolerance on a large enough radius may be less than the figure tolerance.
There are many more examples. In general, the aspiring designer would benefit by cultivating collegial relationships with experienced manufacturers and metrologists. And vice versa.
What materials are most challenging to work with and which configurations are frequently problematic in optical manufacturing?
Ray Williamson: Materials: beside the occasional toxic ones requiring special handling such as those containing Be, Cd, As, Th, Sr, etc. – all of which have characteristics too rare and desirable to entirely avoid – it comes down to materials that are very hard or very soft, thermally sensitive, or chemically sensitive, and crystals that cleave easily. Sapphire, AlON, BaF2, bare aluminum or copper (unless diamond turned), YLF, KCl and NaCl, and any glass with chemical sensitivities of grade 4 and 5.
Configurations: I’d count thin small-angle wedges, steep nearly concentric menisci, nearly hemispheric lenses, very thick (long) lenses, and specialty edge configurations such as oval and octagon. And anything too small to pick up and turn over without tweezers.
What is a proven method team can internalize to avoid repeated communication failures between engineers, sales, and opticians?
Ray Williamson: Ah, I love questions related to communication and company culture! Compartmentalization of job functions and departmental reporting inevitably attenuates communication, mutual understanding, and shared responsibility, yet job descriptions and a hierarchical structure are nearly inevitable in any concern with more than a dozen people. Culture must start at the top. Top management must affirm that part of everyone’s job function is to understand and take responsibility for their interlinked relationships with others, and that the only way to succeed is to talk with one another constructively. Strive to discuss interests and goals, not positions and blockages.
More About Ray Williamson
Mr. Williamson will be presenting on Optical Manufacturing Fundamentals (SC1169) on August 12, 2019 at SPIE San Diego. Williamson is an optical engineering consultant with a concentration in optical fabrication, metrology, and polarization optics. He has worked as process engineer, quality manager, and engineering manager, at Spectra-Physics, Coherent, Los Alamos, Laser Power, and VLOC.