Patent Application
20140299059
1. Field of the Disclosure
The present invention relates to a vapor delivery system for chemical deposition. More specifically, the invention relates to a vapor delivery system for manufacturing optical fiber preforms.
2. Description of Related
Optical fibers are made from optical fiber preforms. There are many known methods to manufacture the optical fiber preforms. One of them is Plasma Chemical Vapor Deposition (PCVD) process. In PCVD, one or more chemical reactants are delivered to an inner surface of a substrate tube to make the preform. Any desired chemical reactants must be converted from liquid to vapor before they are delivered to the substrate tube. Current vapor delivery systems convert the chemical reactants to vapor, however it is difficult for the current system to simultaneously buffer and respond quickly to a change in the flow of chemical reactants. Therefore, there is a need for a vapor delivery system that is capable of simultaneous buffering and fast response.
The present disclosure provides vapor delivery systems for simultaneous buffering and fast response to a change in the vapor flow. Briefly described, for some embodiments, the vapor delivery system comprises two volumes to deliver the vaporized chemical reactants to downstream. The vaporized chemical reactants pass through a large first volume and then a small second volume before they are delivered to the downstream. By having a dual-volume system, the vapor delivery systems can simultaneously buffer and respond quickly to a change in the vapor flow.
Other systems, devices, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.
Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
One way of manufacturing an optical fiber preform is known in the art as the Plasma Chemical Vapor Deposition (PCVD) process. According to this process, one or more doped or undoped glass layers are deposited onto the interior of a substrate tube using low-pressure plasma in the glass substrate tube. After the glass layers have been deposited onto the interior of the glass substrate tube, the glass substrate tube is subsequently contracted by heat and the process creates a solid rod. In one embodiment, the solid rod may be externally provided with an additional amount of glass (i.e., by means of an external vapor deposition process), or by using one or more preformed glass tubes, thereby obtaining a composite preform. From this preform, one end is heated and drawn down in diameter to produce optical fibers.
As shown in
After the glass layers have been deposited onto the interior of the glass substrate tube 12 (sometimes called as soot preform), the glass substrate tube 12 is heated so that the glass substrate tube 12 subsequently contracted into a solid rod. The solid rod may be further processed to obtain an optical fiber preform. From this preform, one end is heated and drawn down in diameter to produce optical fibers.
In order to have desired optical and mechanical properties of an optical fiber, or to effect a change in the index of refraction of a vapor deposited soot preform for the optical fiber, the chemical composition of the vapors which are reacted to form the deposited soot may be varied. In the soot deposition process, the vapor mixture is oxidized/hydrolyzed at a burner to form a glass soot which is subsequently fused to form a high quality glass. Typically, SiCl4 is the primary vapor constituent. One or more additional vapors can be supplied to the oxidation/flame hydrolysis burner, the one or more vapors comprising chemical precursors of dopants whose presence affects the properties of the glass being formed.
Any desired chemical precursors must be converted from liquid to vapor. Current vapor delivery systems only used a one-volume system to ultimately convert the liquid to vapor. The one-volume acts as a buffer; however, simultaneous buffering and fast response would be difficult with the current one-volume system.
The various embodiments disclosed herein overcome this difficulty by using a two-volume system for a vapor delivery system. The first volume is a large volume mainly functions as a buffer. The second volume is a small volume that quickly responds to a change in vapor flow. Optionally, a fixed flow restrictor is connected to the second volume and the fixed flow restrictor buffers downstream fluctuations.
Anything other than one-volume systems had not been approached due to cost and requirements for fast response and high accuracy were not required for previous applications. However, because optical fibers with more uniform and precise refractive index are in demand, there is a need to create a system that can achieve both buffering and fast response simultaneously. Furthermore, current systems have not used a choked flow element such as fixed flow restrictor after the volume system because little attention was made to downstream fluctuations.
Having generally described a vapor delivery system that satisfies both buffer and fast response conditions, reference is now made in detail to the description of the embodiments as illustrated in the drawings. While several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents. Furthermore, to the extent that some of the foundational information is described in detail in this application, one having ordinary skill in the art is presumed to have knowledge of that foundational information.
With this in mind, attention is turned to
The vaporized chemical reactants delivered to the first volume Tare further delivered to the second volume 2 through one or more tubes 6 having a second gas control valve 61. The second volume 2 is a relatively small volume compared to the first volume 1 and the second volume 2 quickly responds to a change in vapor flow. A second pressure sensor 21 is connected to the second volume 2 to measure real-time pressure inside of the second volume 2 for any given time. After passing through the second volume 2, the vaporized chemical reactants are delivered downstream.
When pressure change in the first volume 1 is measured in the first pressure sensor 11, the first control valve 51 responds to the change and adjusts the flow to reduce disturbance. Similarly when pressure change in the second volume 2 is measured in the second pressure sensor 21, the second control valve 61 responds to the change and quickly adjusts the flow.
Optionally, a fixed flow restrictor 7 is connected to the second volume 2 and the vaporized chemical reactants are delivered to downstream through the fixed flow restrictor 7. The fixed flow restrictor buffers downstream fluctuations.
The appropriate size of the first volume 1 depends on the application. However, the first volume 1 must be larger than the second volume 2. A number of parameters that affects the size of the first volume 1 are, for example, the output flow rate (Qout), accuracy required to minimize Qout glitches when the vapor enters the first volume 1, type of control valve used for the first control valve 51, and type of liquid being used.
The second volume 2 is sufficiently small to allow quick response time. Preferably, the size of the second volume 2 is approximately 30% or less of the size of the first volume 1. For example, if the first volume 1 is 100cc in volume then the second volume should be less than 30cc in volume. More preferably, the size of the second volume 2 is approximately 5% or less of the size of the first volume 1. For example, if the first volume 1 is 160 cm3 in volume then the second volume 2 should be less than 7 cm3 in volume.
Performance of an actual vapor delivery system may differ depending on the configuration of the vapor delivery system. For example, response time improves if the second volume is small and/or fast response pressure sensors are used to measure real-time pressure inside the first and second volumes. Overall performance increases if fast acting control valves are used and/or accurate pressure sensors are used.
As shown from the various embodiments and results disclosed in
Although exemplary embodiments have been shown and described, it will be clear to those of ordinary skill in the art that a number of changes, modifications, or alterations to the disclosure as described may be made. The delivery system is applicable to any process where a vapor delivery system is required. Although specific attention was made to optical fiber preform manufacturing process, the vapor delivery system could be used in other manufacturing processes such as semiconductor manufacturing process or solar panel manufacturing process. In some processes, there may be no soot, no substrate tubes or no oxidation/flame. The system is uniquely suited for low pressure deposition processes where it is easy to maintain the choked flow regime.
In optical fiber preform manufacturing process, it should be appreciated that, although specific attention is made for PCVD process, the disclosed vapor delivery systems can be adjusted to achieve similar results in other methods to manufacture the optical fiber preforms such as Chemical Vapor Disposition (CVD), Modified Chemical Vapor Disposition (MCVD), Outside vapor deposition (OVD), Vapor phase axial deposition (VAD) and plasma-enhanced chemical vapor deposition (PECVD). Although the vapor delivery system is uniquely suited for low pressure deposition processes, it may be used for MCVD/VAD processes as well where the downstream pressure is higher.
Any process descriptions or blocks in flow charts should be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included within the scope of the preferred embodiment of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present disclosure.
The present application claims the priority benefit of United States Provisional Patent Application Serial No. 61/808,033, entitled “VAPOR DELIVERY SYSTEM,” filed on Apr. 3, 2013, which is owned by the assignee of the present application, and which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61808033 | Apr 2013 | US |
