I have a MD recorder with (a line and) an optical output. I'd like to get a digital signal into the computer.
I'm just assuming that the optical signal uses the same 'digits' as a computer, via a light medium. So obviously the light must be converted to electric somehow, before the computer can use it.
How? Please.

It may sound silly, but it's something I've never come across.
Logic (MY logic) tells me that there should be a translation device that plugs into a USB or another port. So, is there? If so, are they ruinously expensive?
Or should I just carry on redigitising via the line-out ports?
Donations gratefully received.