The specifications of this optical usb cable specify operating conditions of more than 0 °C. What is the physical reason behind this?
What is the physical reason behind this?
Probably, there's no specific physical reason for exactly this range.
It simply costs significant money to test electronics, and 0 °C – 45 °C is a common range for consumer electronics certifications. If you're an industrial customer of Corning, I'm sure they'll be willing to offer devices certified for a larger temperature range, of course, for a price.
But think about it: What USB equipment exactly do you have that is specified to work below 0 °C? I've yet to encounter one consumer device that has that certification. Hence, it's very unlikely a user of the cables would ever be able to complain about the temperature range – simply because the printer/hard drive/SSD/camera that he'll be using with it isn't certified for freezing temperatures, either.
If there are physical reasons, they'd be:
- electrolytic capacitors not being happy about freezing
- voltage converters used to power the internal electronics changing reference voltages, leading to malfunction
- laser diodes might not work great with reduced carrier mobility
- mechanical properties of the rubber/silicone tubing, plastic case making it e.g. more brittle
- increased chance of condensation/thaw on the device
The optical properties of the fiber optics almost certainly have nothing to do with it.
The short answer is that they didn't test them at lower temperatures.
The longer answer as to why many things aren't qualified to work at low temperatures is icing. If the thing isn't sealed (and I don't see an IP67 rating) then water from the atmosphere may freeze onto it at low temperature, shorting out the PCB in places.
There are also issues with temperature compensation - lots of oscillators, semiconductors and resistors change behaviour with temperature.