While the usable bandwidth for AM modulated carrier is obviously smaller than for visible light, it does not matter in any meaningful way, because it is still significantly larger than anything that could be processed by today's electronics.

There are different protocols specified for IR transmissions:

- IrDA - master-to-multiple-slaves, directly amplitude modulated IR with RZ coded 8N1 asynchronous serial port frames frames (which is directly supported by reasonably modern UARTs) with HDLC-like protocol suite on top. This supports standard serial port speeds up to 115k2 and has extensions with different modulation schemes that go up to 512Mbps, with 4Mbps variant being generally supported by most PC hardware. It serves mostly same purpose as bluetooth, protocol stack is largely similar and for long time it was in practice significantly faster than bluetooth.

- Above mentioned 802.11 IR Physical layer - IIRC something like 1 or 10 Mbps, protocols same as for 802.11, there probably were no commercially successful implementations.

- Various standard, "standard" and completely proprietary protocols for remote controls. Hundreds to thousands bps, typically using few tens of kHz carrier wave that gets modulated on to the IR.

That's more protocol than anything. The IR used day-to-day was designed for consumer products in the 70s and 80s, so by necessity was a very simple protocol. There's no physical limitation for higher bandwidth IR.

As I understand

https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampli...

IR has a frequency of between 430THz and 300GHz, so Max bandwidth would be between 215Tsymbols and 150Gsymbols (I used symbols instead of bits because I forgot the right term...)

So there is an information-theory limit, as I understand it. If I was ever wrong, this is the right crowd to find the person who will correct me!

IR comma doesn't the frequwncy of the light as a carrier, it uses pulsed IR (on=1 off=0 usually in the KHz range) the limitation is usually the rise time of the LEDs

Yeah, but I wondered what the absolute upper limit would be. Good point about the rise time of the LEDs though.

Symbols/second = baud (https://en.m.wikipedia.org/wiki/Baud)

And, ignoring other physical or 'current technology' limits, you can put as many bits in each symbol as you like.

Thank you! Can't believe I couldn't remember that word, although I never really understood why you can put as many bits in each symbol as you like - it seems like that would just mean stuff an infinite number of bits into each one? (Obviously silly, but then why is it defined that way?) - Great, now I have to read about that this morning. :)

Yeah, there is the Shannon Limit which gives the theoretical max, I was more trying to get at there not being a reason why we'd be stuck at remote control/irda speeds.