Is the fiber in an Optic Fiber Cable tubular or is it like a solid cylinder??

Question

Me and my friend had a bet on this!!

I said it is solid and he said it is like a tube!

Answer 1

It's solid...

Answer 2

An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber.

Thats from Wikipedia and in otherwords its solid