Which is correct spelling fibre or fiber?

Answer 1

Both are correct English spellings.  Fiber is the generally accepted spelling in the USA and fibre is preferred in the UK & Commonwealth nations (and in "International English").

For something like "Fibre Channel" fibre is preferred often even in the US b/c it's something of standard name (though you do see "fiber channel" used a lot).

ISO prefers fibre
TIA prefers fiber

Unless you're with a group or org that strongly prefers one or the other