The answer depends on what you mean by "optical telescope." Optical telescopes use visible light, but there are many other types of telescopes that use different wavelengths of light.

Here's a breakdown:

* If you mean a telescope that uses visible light: Then the most similar type of telescope is a radio telescope. Both use reflective surfaces to gather and focus radiation, but radio telescopes collect much longer wavelengths than optical telescopes.

* If you mean a telescope that uses electromagnetic radiation: Then the most similar type of telescope is a radio telescope. This is because both use antennas to gather and focus radiation.

* If you mean a telescope that uses lenses or mirrors: Then the most similar type of telescope is a radio telescope. This is because both use reflective surfaces to gather and focus radiation.

* If you mean a telescope that is based on the principles of reflection and refraction: Then the most similar type of telescope is a radio telescope. This is because both use reflective surfaces to gather and focus radiation, and some radio telescopes also use lenses to focus the radiation.

Ultimately, the most similar type of telescope depends on what specific features you consider most important.