^ no, they exist (all the CO2 surgical units uses them for guide the laser to the handheld part) ..... the only problem can be the cost ..... instead "common" solid core, they use sub-micrometric alternate layers of silica and special polymers, that made them useable from 750nm to 10600nm, and have a hollow core for permit the flow of the cooling gas, and the cost of these fibers is prohibitive for any non-specialized application.
Edit: found some catalogs from OmniGuide ..... 1000$ for a pair of meters of fiber, WTH :wtf:
Also, a precisation, cause i've seen that my words are expressed in not-so-clear way ..... the fiber uses the multilayer tube for product a MIRROR TUBE, are not the layers that conduct the beam as in the normal fibers ..... the whole fiber is a tube, with an internal reflection index near the 100% efficency (99,98%, i think is the best reached actually), so the light "bounce inside" it from one side to the other, and the hollow inside is also used for cool it with a cooling gas flow (for the heat generated from the fraction of the light that is not reflected perfectly) ..... and the whole fiber is like a pair of millimeters of diameter, and very flexible.