* "USB4 20 Gbit/s Transport" (= USB4 20Gbps = USB4 Gen 2x2) is required for host to support
* "USB4 40 Gbit/s Transport" (= USB4 40Gbps = USB4 Gen 3x2) is not
Also USB4 apparently only requires support for tunneling "SuperSpeed USB 10Gbps" (USB 3.2 Gen 2×1), "SuperSpeed USB 20Gbps" (USB 3.2 Gen 2x2) is optional.
You can actually get optical usb3 and thunderbolt (all generations) cables. Thunderbolt was originally called light peak and shown off by Intel and Apple in demos as optical, and Sony had a line of laptops with optical light peak connectors to connect
to external GPUs. But ultimately the default became non-optical because it can carry power too.
According to the wiki table (https://en.wikipedia.org/wiki/USB4#Support_of_data_transfer_...), it's "optional":
* "USB4 20 Gbit/s Transport" (= USB4 20Gbps = USB4 Gen 2x2) is required for host to support
* "USB4 40 Gbit/s Transport" (= USB4 40Gbps = USB4 Gen 3x2) is not
Also USB4 apparently only requires support for tunneling "SuperSpeed USB 10Gbps" (USB 3.2 Gen 2×1), "SuperSpeed USB 20Gbps" (USB 3.2 Gen 2x2) is optional.
It would have a longer max length if the data lanes were optical.
You can actually get optical usb3 and thunderbolt (all generations) cables. Thunderbolt was originally called light peak and shown off by Intel and Apple in demos as optical, and Sony had a line of laptops with optical light peak connectors to connect to external GPUs. But ultimately the default became non-optical because it can carry power too.
> But ultimately the default became non-optical because it can carry power too.
There's no problem in making a cable with two fibre leads for data and two (at higher lengths thicker to reduce issues with voltage drop) power lines.
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