Halogen-doped silica preforms for optical fibers

#This description relates to optical fiber preforms doped with halogens and methods of making such preforms. More particularly, this description relates to preforms for optical fibers made from silica that include high concentrations of halogen doping and low internal gas void volume.

#Optical fiber performance depends on the ability to control refractive index profiles in low loss fiber media. Most typically, silica glass is used as the base medium for optical fibers used to transmit light over lengths ranging from several meters to hundreds of kilometers. Silica is a preferred base medium because it exhibits low attenuation in the 1300 nm to 1600 nm wavelength range commonly used to transmit optical signals. Attenuation loss in silica-based optical fibers is as low as 0.18 dB/km at 1550 nm for single-mode optical fiber. Optical loss is determined by the Rayleigh scattering of the silica-based medium, the concentration of impurities, and wavelength dependent factors such as UV and IR absorption tails.

#Optical fibers include a central glass core surrounded by a glass cladding. The base glass medium for the core and cladding is typically silica. To achieve waveguiding, the core is configured to have a higher refractive index than the cladding. The refractive index of silica can be modified by doping. Various dopants are known that either increase (“updopants”) or decrease (“downdopants”) the refractive index of silica relative to undoped silica. In most single-mode silica fibers, germanium dioxide (GeO2) is used to dope the core region. GeO2 doping levels are typically adjusted to provide an increase in the relative refractive index of 0.35%. Although GeO2 is a relatively expensive dopant, it comprises only about 8% by weight (wt %) of the core region of the fiber and only about 0.5 wt % of the total glass fiber (core+cladding). Germanium doping is also relatively easy to accomplish during laydown of silica soot and complex refractive index profiles can be made simply by varying the ratio of silicon and germanium precursors supplied to the deposition system during the laydown process (typically an OVD (outside vapor deposition) silica soot deposition process). SiCl4 and GeCl4 are common precursors for forming Ge-doped silica glass in the preform laydown process. A drawback of using GeO2 as an updopant for silica cores is that the presence of Ge increases the Rayleigh scattering of the fiber relative to pure silica fibers. As a result, there is interest in identifying alternate dopants that enable the refractive index profile control of silica needed in optical fibers to achieve fibers with low Rayleigh scattering and efficient waveguiding at reasonable cost.

#While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the written description, it is believed that the specification will be better understood from the following written description when taken in conjunction with the accompanying drawings, wherein:

#FIG. 1 is a schematic depiction of soot preform deposition via an OVD process.

#FIG. 2 depicts an apparatus for doping and consolidating a soot preform.

#The embodiments set forth in the drawings are illustrative in nature and not intended to be limiting of the scope of the detailed description or claims. Whenever possible, the same reference numeral will be used throughout the drawings to refer to the same or like feature.

#The present disclosure is provided as an enabling teaching and can be understood more readily by reference to the following description, drawings, examples, and claims. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made to the various aspects of the embodiments described herein, while still obtaining the beneficial results. It will also be apparent that some of the desired benefits of the present embodiments can be obtained by selecting some of the features without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations are possible and can even be desirable in certain circumstances and are a part of the present disclosure. Therefore, it is to be understood that this disclosure is not limited to the specific compositions, articles, devices, and methods disclosed unless otherwise specified. It is also to be understood that the terminology used herein is for the purposes of describing particular aspects only and is not intended to be limiting.

#In this specification and in the claims which follow, reference will be made to terms which shall be defined to have the following meanings: