![]() ![]() Generally, the thickness of such a layer is in the range of 100-10,000 A depending on the optical fiber application. To prevent hydrogen diffusion, and thus protect the fiber and extend its useful life, a buffer SiOxNy layer is typically applied. High optical losses due to hydrogen diffusion are found in known silica optical fibers. Adverse environmental conditions combined with stress serve to exacerbate this problem. The present invention is also useful for preventing hydrogen diffusion, or corrosion of the cladding due to environmental conditions, which can be especially severe in high temperature applications. However, this method cannot be used in commercial-scale manufacturing of large diameter and high quality silica preforms because of a lack of high power impulse microwave sources (both generators and amplifiers) that deliver microwaves in the 2450 MHz region with a 10 kW average power and 1 ms impulse duration. A method of PECVD is described wherein a surface plasma wave of either the symmetric E01 or the hybrid HE11 type is excited on the outside surface of a dielectric starting body, such as a silica tube. The closest analog to the present invention is disclosed in U.S. It is also impossible to increase productivity, as determined by deposition rate and silica rod diameter, by this method. This leads to deterioration of preform quality for large rods, and thus to a restriction on preform diameter. Microwave power losses on irradiation of large diameter silica rods and a hole in the reactor can be up to 20% of the incident microwave power. This limitation is due to the nonsymmetry of E020 mode excitation and arising nonsymmetrical wave of TE type. This method is limited in that it cannot produce a uniform deposition on a silica rod with a diameter greater than 25. The invention uses microwaves with a frequency of 2,450 MHz. 6,138,478 by Neuberger et al discloses a method and device for silica preform production by microwave plasma deposition of an SiO2-F cladding on a silica rod. Method in this category include plasma CVD (PCVD) and plasma enhanced CVD (PECVD). The second utilizes electromagnetic radiation to ionize precursor gas, thus forming a plasma from which the glass is deposited. The first is those methods that utilize thermal energy to create the precursor vapor, and includes modified chemical vapor deposition (MCVD), outside vapor deposition (OVD), and vapor axial deposition (VAD). The principle CVD methods can be grouped into two categories. The most common methods for the manufacture of fiber preforms involve chemical vapor deposition (CVD), which entail the use of vaporized raw materials that combine with oxygen and solidify into glass. The fiber cladding is often applied to the preform prior to drawing the fiber. These preforms are generally high purity glass or plastic. Optical fibers are currently manufactured through a drawing process, where fibers are drawn from a preform with a large diameter. The invention relates to methods of silica preform manufacturing, in particular for creation of optical fiber lightguides with reflective cladding deposited by microwave plasma enhanced chemical vapor deposition (PECVD). The benefits of the present invention over the prior art include increased absorption of delivered power, and the ability to uniformly deposit films such as flourine-doped silica on rods with diameters of up to 30-35 mm and thus produce optical fiber preforms with diameters greater than 40 mm. ![]() A microwave plasma is scanned along the length of the rod through a slit in the reactor to deposit a homogeneous film of a desired thickness. A microwave generator coupled with a resonator and an H10 waveguide delivers microwave energy to the reactor, producing simultaneously symmetrical excitations in the E010 mode and a plasma surface wave in E01 mode located at the surface of the rod. A furnace for regulating reactor temperature encases the reactor. The invention consists of a cylindrical reactor in which material such as flourine-doped silica glass is deposited on a cylindrical silica rod. A method is disclosed for the manufacture of optical fiber preforms using plasma enhanced chemical vapor deposition (PECVD).
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