Monday, January 29, 2018

Photonics West

A significant piece of my research program is optics-related, and thanks to an invited talk, I'm spending a couple of days at the SPIE Photonics West meeting in San Francisco, a mix of topics from the very applied (that is, details of device engineering and manufacturing) to the fundamental.   It's fun seeing talks on subjects outside of my wheelhouse.

A couple of items of interest from talks so far today:

  • Andrew Rickman gave a talk about integrated Si photonics, touching on his ideas on why, while it's grown, it hasn't taken off in the same crazy exponential way as Moore's Law(s) in the microelectronics world.  On the economic side, he made a completely unsurprising argument:  For that kind of enormous growth, one needs high volume manufacturing with very high yield, and a market that is larger than just optical telecommunications.  One challenge of Si-based photonics is that Si is an indirect band gap material, so that for many photonic purposes (including many laser sources and detectors) it needs to be integrated with III-V semiconductors like InP.  Similarly, getting optical signals on and off of chips usually requires integration with macroscopically large optical fibers.   His big pitch, presumably the basis for his recent founding of Rockley Photonics, is that you're better off making larger Si waveguides (say micron-scale, rather than the 220 nm scale, a standard size set by certain mode choices) - this allegedly gives you much more manufacturing dimensional fault tolerance, easier integration with both III-V and fiber, good integration with electroabsorption modulators, etc. One big market he's really interested in is cloud computing, where apparently people are now planning for the transition form 100 Gbs to 400 Gbs (!) for communication within racks and even on boards.  That is some serious throughput.
  • Min Gu at Royal Melbourne Institute of Technology spoke about work his group has been doing trying to take advantage of the superresolution approach of STED microscopy, but for patterning.   In STED, a diffraction limited laser spot first illuminates a target area (with the idea of exciting fluorescence), and then a spot from a second laser source, in a mode that looks donut-shaped, also hits that location, depleting the fluorescence everywhere except at the location of the "donut hole".  The result is an optical imaging method with resolution at the tens of nm level.  Gu's group has done work combining the STED approach with photopolymerization to do optical 3d printing of tiny structures.  They've been doing a lot with this, including making gyroid-based photonic crystals that can act as helicity-resolved beamsplitters for circularly polarized light.  It turns out that you can make special gyroid structures so that they have broken symmetries so that these photonic crystals support topologically protected (!) modes analogous to Weyl fermions.
  • Venky Narayanamurti gave a talk about how to think about research and its long-standing demarcation into "basic" and "applied".  This drew heavily from his recent book (which is now on my reading list).   The bottom line:  In hindsight, Vannevar Bush didn't necessarily do a good thing by intellectually partitioning science and engineering into "basic" vs. "applied".  Narayanamurti would prefer to think in terms of invention and discovery, defined such that "Invention is the accumulation and creation of knowledge that results in a new tool, device, or process that accomplishes a particular specific purpose; discovery is the creation of new knowledge and facts about the world."  Neither of these are scheduled activities like development.  Research is "an unscheduled quest for new knowledge and the creation of new inventions, whose outcome cannot be predicted in advance, and in which both science and engineering are essential ingredients."  He sounded a very strong call that the US needs to change the way it is thinking about funding of research, and held up China as an example of a country that is investing enormous resources in scientific and engineering research.

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