ELI5: How is sugar free fruit juice made?

r/

I’ve been searching for like ten minutes trying to find an answer to this question, but I keep getting bupkis. I’m referring to juices like Ocean Spray’s diet cranberry juice and such. I want to make my own juice so I can have homemade soda, but being diabetic means a lot of juices spike my sugar. So I’d really appreciate knowing how stuff that’s sugar free is made, whether I can make it myself or not.