Properties of polycrystalline germanium-dioxide for the materials of hollow-core fiber

In this paper, we reported, for the first time to our knowledge, that polycrystalline germanium-dioxide has a n < 1 and the extinction coefficient becomes smaller than other materials given at 10.6 micrometers , n is 0.27 and K is 0.51, we also exactly measured the infrared reflective spectra of polycrystalline germanium-dioxide from the input angle 20 degree to 70 for wavelengths between 2 and 25 micrometers . Our measuring results are compared with an exact calculation, and the agreement is found to be excellent. On the other hand, in order to study on the properties of polycrystalline germanium-dioxide for the materials of hollow-core fiber in detail, we fabricated a hollow-core fiber by use of this material. After then, we measured the straight optical fiber losses, the transmission properties of the bending fiber and the spot size of the fiber's output beam, we found that the high order mode degenerate quickly with the increase of the length and the nonuniform in the structure of fiber causes the loss of all kinds of modes. We further found that the different focal length of coupling Len causes different bending loss and the diameter of the output beam depends strongly on the existence of transmission mode in the fiber, meantime, the transmission rate of fiber depends strongly on the divergence angle (theta) .