Research On Rare Earth Doped Tellurite Glass Optical Fiber

Optical fiber telecommunication was a novel technology which came into use in the 1980s. Optical fiber telecommunication has larger capacity, longer distance without repeaters, digital communication enable it become the basic way for international communications. Optical fiber telecommunication benefits a lot from the invention of EDFA either in SDH technology or in DWDM technology. Now the telecoms companies focus on the benefit per cost make them use more bandwidth of optical fiber, but only be limited by broadband EDFA. Though Raman amplifier can amplify any wavelength, but the cost is too expensive. So a lower-cost broadband EDFA technology is in need of low-cost, large capacity optical fiber telecommunication systems. There have S+C+L band amplifier based on rare earth doped tellurite glass in European. And in Japan, there have practicable S+C+L band amplifier based on rare earth doped tellurite glass. In China, the very beginning research has been done in this field.In this paper, first, we analyse the glass forming ability by theoretic method and experiment. Then we have the glass forming zone by experiment for our research's convenience. In this zone, we have detrail research on the Na₂O-TeO₂-WO₃ glasses and analyse the microstructure, raman spectra, thermal stability, crystallization of the tellurite glasses. The test result does not satisfy us so we try to make some modification for better properties. Second we do some research on Na₂S-TeO₂-WO₃ glasses and find out these system has quite well glass forming ability. The DSC test shows that the Tg of the glass is the highest of all tellerite glasses in our research, but maybe not so good in thermal stability.Third two kinds of tellurite glasses have been achieved, which are Na₂O-TeO₂-WO₃-Al₂O₃ galss and TeO₂-TiO₂-La₂O₃ glass. DSC test shows that the Tg and Tx-Tg value are quite well for our optical fiber preform manufacture. Then we test the density, transmittance properties of these tellurite glasses. The result shows that these glasses' density is 2～3 times of that of silica and UV cut-off wavelength is quite short. So these tellurite glasses may be good candidates for broadband optical window material.Different concentration rare earth ions doped different kinds of tellurite glasses have been done in our experiment. As we find out that these glasses are quite well in glass forming ability. The transmittance spectra and refractive index of these glasses have been acquired in our research. These data are useful for optical fiber waveguide design. There has a big peak in 976nm and an even bigger peak in 1531nm in the absorption spectra which means big pump absorption and big emission cross section of Er³⁺ in tellurite glass. From the FWHM calculation result we draw the conclusion that TeO₂-TiO₂-La₂O₃ glass is superior to Na₂O-TeO₂-WO₃-Al₂O₃ glass in the fluorescence spectra. The reason is because the former has more doped site than the latter. But Er³⁺ ions have bigger amplification bandwidth in Na₂O-TeO₂-WO₃-Al₂O₃ glass. There has no clusters phenomenon even the concentration of the rare earth is up to 10143ppm, which means that teUurite glass is one of the best candidate for rare earth ions.We use numerical method design the waveguide of the tellurite glass optical fiber and analyse the propagation mode and cut-off condition of the fiber. We get the optic properties of the fiber by the help of the software. The cut-off wavelength of the fiber is about 1270nm. The dispersion of the fiber is about -25ps/nm^*km at 1550nm. The MFD the fiber is about 7.12μm at 1550nm. These optic properties are suitable for EDFA application. Then we discuss the loss model of the tellurite glass and try to give a practicable way to reduce the loss of the fiber.To make a preform of the tellurite optic fiber, we use a mode to cast the glass and use machining method to get the preform. We test the melt glass viscosity and determine the drawing process parameters. A brief introduction of the drawing equipment and drawing process is given out. Finally we simulate the drawing process by use a same diameter rare earth doped silica preform to get the whole process parameters except the power.From our research we find out that more research should be done on the dopant site of the glass network. The whole glasses system may be Na₂O-TeO₂-WO₃-Al₂O₃ and TeO₂-TiO₂-La₂O₃. Also more research should be done on Er³⁺/Yb³⁺ co-doped tellurite to find out better gain property of the EDTFA. We hope to put forward our research to machining method, drawing process and reducing the loss of the tellurite glass fiber. A test total solution of rare earth doped tellurite fiber is in need of the research.