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Comment by bicubic | Hacker News Reader

Would these problems persist if we switched to optical signaling instead of rf? Can we expect an optical PCIe equivalent one day?

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The nature of problems is different, but fundamentally the two questions of "how to distinguish between 1 and 0 in the presence of noise" and "can the reciever and transmitter change state fast enough" apply.

Optical PCIe would be hugely handicapped by lack of a standard optical PCB construction method. You'd have to print waveguides onto the PCB. And then it stops working if you get dust in the socket.

Eventually yes, we can expect to see optical in desktops. Fiber connections are "better" but also much more expensive. The price should eventually come down as volumes increase. The main delaying factor is that copper is still good enough.

Multimedia is the driving force behind increased data usage, and I think we'll continue to need more throughput until we no longer get any benefits from higher resolutions (aka when we have substantially more pixels than rods and cones in our eyes). At the moment a phone with a 4K display saturates your eyes at any distance greater than 2 feet from your face. I think a 16x PCIe 4.0 link will likely provide more than enough bandwidth to generate fully immersive VR experiences, so the question then becomes... why and when will we need optical PCIe 5.0 to quadruple the datarate of PCIe 4.0...

No mostly because the wavelength of light is large, and therefore has poor information density compared to electrons.

I doubt this be true as HF is also modulated onto wire ... it's not the electron per se which wander but modulated HF. Sure, the carrying device is the electron buts it's not like a stream of water

Basically in the optical regime it won't be possible to propagate the E field in a conduit smaller than the wavelength. This is because a small conduit doesn't have the right boundary conditions to support fields (like trying to fit waves into a didgeridoo). So you're always going to have these massive, massive 1um structures compare to state-of-the-art nm scale semiconductors.

There are advantages of optics including that light moves faster than electrons (important for HPC where the figure of merit is latency in us between nodes, etc) and typically has higher fidelity. But the size of these structures is orders of magnitude larger than conventional semiconductors.

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