Patent Application
20130094808
1. Field of the Invention
The present invention relates to producing a fiber Bragg grating optical fiber with a coating.
2. Description of the Related Art
Optical fibers with fiber Bragg grating (FBG) are used as sensors due to their characteristic of reflecting certain wavelengths of light, which can be controlled based on the particular grating pattern, and transmitting all other wavelengths. FBG sensors can be particularly useful in situations that preclude physical access to a monitored system. For example, an FBG sensor may be used to sense inflation pressure of a packer used to isolate zones downhole.
A FBG is typically configured in a germanium-doped silica fiber. Such fibers tend to be susceptible to hydrogen diffusion, which can change the refractive index of the grating. This susceptibility can increase with fiber length. Prior art systems have described a coating applied to the fibers to hermetically seal the fiber. The prior view in the art is that the coating had to be applied after the grating process.
According to one aspect of the invention, a method of producing a coated fiber Bragg grating (FBG) optical fiber includes drawing fiber from a high temperature furnace; coating the fiber; and writing a Bragg grating on the coated fiber to produce the coated FBG optical fiber.
According to another aspect of the invention, a coated fiber Bragg grating (FBG) optical fiber is produced by a process including drawing fiber from a high temperature furnace; coating the fiber; and writing a Bragg grating on the coated fiber to produce the coated FBG optical fiber.
According to yet another aspect of the invention, a system to produce a coated fiber Bragg grating (FBG) optical fiber includes a high temperature furnace from which an optical fiber is drawn; a coating applicator to coat the optical fiber; and a grating writing station to write a Bragg grating on the coated fiber and produce the coated FBG optical fiber.
According to yet another aspect of the invention, a hermetic carbon-coated fiber including fiber Bragg gratings (FBGs) includes a silica-based fiber; a carbon coating applied to the silica-based fiber; a Germanium dopant disposed in the coated silica-based fiber; a plurality of FBGs written in the doped silica-based fiber.
According to yet another aspect of the invention, a hermetic carbon-coated fiber including fiber Bragg gratings (FBGs) for downhole applications includes a silica-based fiber; a Germanium dopant disposed in the silica-based fiber; a plurality of FBGs written in the doped silica-based fiber, the FBGs being written at a higher density than for above-hole applications; and a carbon coating applied to the silica-based fiber with FBGs to hermetically seal the silica-based fiber with FBGs.
Referring now to the drawings wherein like elements are numbered alike in the several Figures:
The fiber drawn from the high temperature furnace at block S101 may be silica-based optical fiber, for example. The coating may be a carbon coating. The coating may also be a ceramic or metal material or diamond-like carbon (DLC) coating or any other suitable material capable of forming a hermetic barrier. The coating in some embodiments will reduce the diffusion of hydrogen or, alternatively, the coating in other embodiments will hermetically seal the fiber. The process of writing the Bragg gratings includes doping the optical fiber. For example, silica-based optical fiber may be doped with Germanium in order to write the FBG. For downhole applications, the density of the FBGs must typically be higher than for above-ground applications. The FBG optical fiber may be produced from the coated fiber at block S260 by exposing the fiber to a UV light that is passed through a phase mask.
The cooling and writing steps, S250 and S260, respectively, of the process 200 may be similar to but need not necessarily be the same as the cooling and writing steps, S120 and S110, respectively, of the prior art process 100 but they come at different places in the process. For example, at S120, the FBG optical fiber may be cooled to a certain temperature range in order to proceed to the reheating and coating step at S130. This temperature range may differ from the temperature range for the cooling of the coated fiber at S250. Also, the step of writing the Bragg grating on the fiber drawn from the furnace (at S101) to produce the FBG optical fiber at S110 may differ from the step of the writing the Bragg grating on the already-coated fiber at S260.
Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first” and “second” are used to distinguish elements and are not used to denote a particular order.
It will be recognized that the various components and technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations therefore, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
