Is the Nyquist theorem true for high-quality single-mode optical fiber or only for copper wire?

The Nyquist theorem is a property of mathematics and has nothing to do with

technology. It says that if you have a function whose Fourier spectrum does

not contain any sines or cosines above f, then by sampling the function at a frequency of 2f you capture all the information there is. Thus, the Nyquist

theorem is true for all media.