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Meta has a new post talking a bit more about the silicon carbide waveguides used in the Orion AR glasses. Funny they mentioned lithium niobate, I wonder how much they suffered (or put to good use) from the birefringence, the pyroelectric effect, the goddamn lithium that diffuses everywhere...
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Crystal Clear: Our Silicon Carbide Waveguides & the Path to Orion’s Large FoV

Mandatory mention of this paper from Jacob Khurgin since we are talking about going after higher refractive index

And this work to show the power of pyroelectric effect

I'd never wish to reduce my sensory spectrum but oh wouldn't it be nice if we can't see below ~530 nm, and Gallium Phosphide (GaP) would be transparent with a refractive index of ~3.3! Optical constants of GaP

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Lithium Niobate. Does exactly what you want and all the things you don’t.

lol so accurate, plus often not exactly what you want 😂

What’s special about lithium niabate ?

Maybe I should make a thread about it, but it's the go to material for EO modulators for decades, converting electrical signals from computers to optical signals in fibers so they could network in long range and high speed. About a bit more than 10 years ago people figured out how to make thin film of it on wafers, and since then it's been getting hotter and hotter for photonic circuits. In their case it is because of its higher refractive index ~2.3 compared to glass ~1.5, and you could make waveguides with more states of light in it and larger FOV. But SiC is even higher ~2.6 so that's what they end up using.

Also, when I hear lithium niobate, doesn’t this mean much of this is custom made?

“It was a huge investment, and we established the whole pipeline there. The tooling was custom-made for us by our partners, and the process was developed in-house in Meta, though our systems are research-grade because there were no manufacturing-grade systems out there. We worked with a manufacturing partner to develop manufacturing-grade slant etch tooling and processes. And now that we’ve shown what’s possible with silicon carbide, we want others in the industry to start making tools of their own.”
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