RU2314556C2 - Fiber-optic light-pipe with increased steadfastness to diffusion of molecules from the environment - Google Patents

Abstract

FIELD: the invention refers to the technology of creation of fiber-optic light-pipes.

SUBSTANCE: it may be used in the fields where conditions of the work demand protection of the light-pipe from diffusion of admixtures from without. Longitudinal cavities are created in a glass shell and these cavities are filled with gas not influencing on optical losses in the light-pipe. In quality of gas helium or heavy hydrogen is used. The diffusion of gas from the cavities of the light-pipe from without prevents diffusion of hydrogen from the environment inside the light-pipe to its light leading core of the light-pipe not to hinder propagation of light along the core. The core of the light-pipe may be single-mode or multi-mode, out of plain quartz glass or out of quartz glass alloyed with oxides of germanium, phosphorous, aluminum, boron. The cavities may be filled with gas not only from the end-face of the light-pipe but also from the outside through unsealed cavities in a definite place of the light-pipe.

EFFECT: possibility to work in atmosphere containing hydrogen at increased temperatures without additional optical losses connected with hydrogen.

10 cl, 5 dwg

Description

The invention relates to a technology for creating fiber optical fibers and can be used in areas where operating conditions require protection of the optical fiber from diffusion of impurities from the outside. For example, to increase reliability and increase the life time of devices based on fiber optical fibers that measure temperature, pressure, and other physical quantities.

It is known that fiber optic fibers operating in harsh environments, used for distributed temperature sensors in wells, sometimes unacceptably quickly lose their performance due to the large increase in optical loss (signal attenuation).

This effect is associated with the influence of hydrogen diffusing at high temperatures and pressure into the fiber and interacting with the material of the light guide core. There is a large number of studies devoted to the causes, mechanisms, and possible solutions to this problem, since any use of optical fibers after exposure to hydrogen becomes impossible.

The need to protect the fiber from the diffusion of hydrogen and, thus, to maintain its physical characteristics is a problem that needs to be addressed.

However, the solution to this problem by applying various "sealed" coatings gives only a temporary effect. They only slightly slow down the degradation of the fiber.

Known fiber based on a photonic crystal, selected as a prototype (Patent RU No. 2226705). The invention relates to fiber optic technology and can be used in optical amplifiers, lasers, spectral filters, gas sensors and telecommunication networks. The fiber contains a region with a uniform low refractive index, which is surrounded by a sheath, which is a periodic structure of regions with different refractive indices. The region with a low refractive index has the largest size, which is larger than the single shortest shell period. Light radiation is kept in the region with a lower refractive index due to the forbidden energy zone of the photonic crystal of the shell. The ratio of the regions of the shell with a low refractive index to the regions with a high refractive index by volume is at least 15%. A method of manufacturing a fiber includes forming a packet of rods that includes at least one truncated rod defining a cavity in the packets, and pulling the packet into a fiber having an elongated cavity. At the same time, an increase in transmitted power is provided. Thus, a distinctive feature of the above-described photonic crystal fiber is the presence of cavities in it located along the longitudinal axis, both in the light guide core and in the reflective glass shell. However, in a fiber based on a photonic crystal there is no mechanism of protection against hydrogen diffusion into the fiber, which leads to significant optical losses in it.

A subject of the invention is a fiber light guide that can operate in an atmosphere containing hydrogen at elevated temperatures without additional optical losses associated with hydrogen.

The solution to this problem is achieved by creating longitudinal cavities in the glass sheath of the fiber and filling the cavities with gas, which does not affect the optical loss in the fiber. In this case, the gas in the cavities is under a pressure exceeding the partial pressure of hydrogen in the environment.

Figure 1 shows a fiber waveguide 100, a light guide core 110, a reflective glass sheath 120 and cavity 130.

Figure 2 shows a fiber waveguide 200 with several rows of cavities, where a light guide core 210, a reflective glass sheath 220, a first row of cavities 230, a second row of cavities 240.

The invention describes a fiber light guide (optical fiber) with increased resistance to diffusion of molecules from the environment, which can operate in an atmosphere containing hydrogen at elevated temperatures, without having an increase in optical losses associated with hydrogen. This effect is achieved by creating longitudinal cavities in the glass sheath of the fiber and filling these cavities with gas, which does not affect the optical loss in the fiber. The diffusion of gas from the fiber to the outside prevents the diffusion of hydrogen from the environment into the fiber to its light guide core.

The core of the fiber can be single-mode or multi-mode, from undoped quartz glass or from quartz glass doped with oxides of germanium, phosphorus, aluminum, boron, etc.

In addition, the core of the fiber can be solid or microstructured (holey).

The protective coating may consist of a polymer coating, a sealed coating (for example: metal, carbon, ceramic) or a combination of sealed and polymer coatings.

In figure 3. an optical fiber 300 is shown with cavities and a protective coating, where 310 is a light guide core; 320 - reflective glass shell; 330 - cavity; 340 - a protective coating.

Helium or deuterium may be used as gas.

The cavities can be filled with gas not only through the end of the fiber, but also from the side through the opened cavities in a certain place in the fiber. In this case, the ends of the fiber can be welded with a conventional fiber and used for input-output signal, as shown in Fig.4.

The diameters of the fiber and the cavities can vary and be increased in order to obtain a better ratio between the gas diffusion outward velocity and the gas feed rate through the cavities over the entire length of the fiber in the case of a long fiber.

The physical essence of the proposed technical solution lies in the fact that the diffusion of gas from the cavities through the glass shell to the outside prevents the diffusion of hydrogen from the environment into the fiber to its light guide core. In this case, the cavities are located far enough from the light guide core of the light guide so as not to interfere with the propagation of light through the core. The diffusion of gas from the fiber to the outside prevents the diffusion of hydrogen from the environment into the fiber to its light guide core. Thus, hydrogen does not diffuse at high temperatures and pressure into the fiber and does not degrade the optical parameters of the light guide core. The experimental data presented in Fig. 5 confirm the advantages of the claimed technical solution when comparing the optical loss spectra in continuous fibers and in gradient fibers doped with germanium oxide after exposure to hydrogen at a pressure of 30 atm at a temperature of 300 ° C for 1 hour.

Thus, the proposed technical solution is new, it is not known from the modern level of technology, is industrially applicable in fiber optics and gives a positive effect in its application.

Claims (10)

1. An optical fiber with increased resistance to diffusion of molecules from the environment, containing a light guide core, a glass sheath, and a protective coating deposited on top of the sheath, characterized in that longitudinally parallel to the axis of the light guide cavity filled with helium are placed in the glass sheath along the entire length of the light guide or deuterium under pressure exceeding the partial pressure of hydrogen in the environment, the cavities are located at a distance from the light guide core of the fiber, which does not affect the propagation light on the core. 2. A fiber waveguide with increased resistance to diffusion of molecules from the environment according to claim 1, characterized in that the light guide core is made of undoped quartz glass. 3. A fiber waveguide with increased resistance to diffusion of molecules from the environment according to claim 1, characterized in that the light guide core is made of quartz glass doped with oxides of one material from the group of germanium, phosphorus, aluminum, boron. 4. A fiber light guide with increased resistance to diffusion of molecules from the environment according to claim 1, characterized in that the light guide core is solid or microstructured. 5. A fiber waveguide with increased resistance to diffusion of molecules from the environment according to claim 1, characterized in that the light guide core is single-mode or multi-mode. 6. An optical fiber with increased resistance to diffusion of molecules from the environment according to claim 1, characterized in that the protective coating consists of a polymer coating. 7. An optical fiber with increased resistance to diffusion of molecules from the environment according to claim 1, characterized in that the protective coating consists of a sealed coating. 8. A fiber waveguide with increased resistance to diffusion of molecules from the environment according to claim 7, characterized in that the sealed coating consists of one of the materials from the group: metal, carbon, ceramics. 9. A fiber waveguide with increased resistance to diffusion of molecules from the environment according to claim 1, characterized in that the protective coating consists of a combination of sealed and polymer coatings. 10. An optical fiber with increased resistance to diffusion of molecules from the environment, containing a light guide core, a glass sheath, and a protective coating applied over the sheath, characterized in that longitudinally parallel to the axis of the light guide cavity filled with helium are placed in the glass sheath along the entire length of the light guide or deuterium under a pressure exceeding the partial pressure of hydrogen in the environment, the cavities are located at a distance from the light guide core of the fiber, which does not affect the distribution ix light within the core, wherein the side light guide at a certain place in the cavities have opening through which the cavity can be filled with gas.

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