Encoding of URL: force lowercase

I have a page with a link field, that works for link. But it also encodes special characters, using Uppercase.

eg: http%3A%2F%2F
for http://

These Uppercases for F and A cause trouble in some rare cases. Any way to force those to lowercase, so the result is http%3a%2f%2f

Twig has a lower filter.