Hi Mohammad,
They are absolutely different from one another. Logical zero is not always an absolute zero, it has some amount. So the ratio of the power of logical one to logical zero is a great amount, but no infinite. It’s a factor in optical sources with two logical levels of power. Free spectral range, whose wikipedia definition is mentioned above and I won’t go through it again, is a parameter in interferometers. These two are quite distinct. If you know a case which might confuse these two, please state.
Regards