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Comment by dgfl | Hacker News Reader

This is an optical transistor, meaning that a current is controlled with an optical pulse. That means that you can't pipe these things into each other, unless you can build an equivalently fast and efficient light->charge transducer (i.e. a photodetector). Moreover, this physically can't be scaled below approximately the wavelength of the laser (meaning at least 10x larger than CMOS transistors).

It might turn out to be great for the applications that they point out in the paper itself, not so much for logic. I would say bitcoin mining discussions are a bit premature, and potentially not relevant.

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> That means that you can't pipe these things into each other, unless you can build an equivalently fast and efficient light->charge transducer (i.e. a photodetector).

These exist:

https://ultrafast.mit.edu/

>(meaning at least 10x larger than CMOS transistors)

at petahertz (10^15) speeds, you could sacrifice a lot of space for larger components, and still come out on top vs gigahertz speeds (10^9) by doing more work but a hell of a lot faster, no?

if you can build a chip that's a million times faster, you can sacrifice 3/4 of that speed to doing more work with fewer components and still be 250,000x faster.

No, because propagation delay is the same.

Yep! That's a key thing to keep in mind here. As chips get bigger (especially at higher frequencies), propagation delay becomes an important blocker

it would be really interesting to see how this played out. the entire way you build circuits changes. e.g. current adder designs use extra transistors to save carry propagation latency, but for optical, that might make the latency worse...

Propagation delay is not the same, electrical signals travel much slower in semiconductors than light in a vacuum. If you could make an entirely optical chip, size would matter a whole lot less because light will travel much faster through whatever that material will be.

Propagation delay for light in a semiconductor tends to be roughly equal to propagation delay for electrical signals in a semiconductor. It's not exactly equal because the dielectric constant is a function of frequency.

This is assuming you use a waveguide and travelling waves to send the electrical signals. If you charge up the whole line then, sure, that's slower.

Make wave pipelining cool again?

> This is an optical transistor, meaning that a current is controlled with an optical pulse.

So more like an optical triode (the transistor apnplifies).

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