KR19990044289A - Optical Fiber with Tantalum Doped Clad - Google Patents

Abstract

The enhanced optical waveguide fiber 1 comprises a region of the central core 10 surrounded by an inner clad region 12. The second annular region 14 is doped with tantalum. Core 10 is doped with germanium. The first annular region 20 is located between two adjacent regions with a relatively high refractive index. The refractive indices of the adjacent regions 10, 20 are greater than the central region 20.

Description

Optical Fiber with Tantalum Doped Clad

U.S. Patent 4,715,679 discloses an optical fiber with little or no dispersion over a wide range of wavelengths. The optical fiber has a central core wrapped by an inner clad which is in turn wrapped by an outer clad. The core and clad have one or more regions with reduced refractive index compared to adjacent regions. The core has a maximum refractive index that reduces the distance from the center. The first annular region of the inner clad with the reduced refractive index is adjacent to the core. A second annular region having a refractive index greater than the reduced first annular region is adjacent to the reduced region. The reduced refractive index alters the optical energy propagation properties of the fiber, providing a desirable relationship between waveguide dispersion and wavelength. Thus, the dispersion is adjusted to reduce the refractive index of the inner clad region adjacent to the central core. Reduction of the refractive index occurs by adding a suitable reducing dopant such as fluorine or boron.

However, reduced regions of fluorine and boron dopants have undesirable limits. The reduced area of fluorine typically has 0.3% but exhibits a maximum refractive index reduction of about 0.5% (delta). Fluorine is corrosive and fluorine has a manufacturing problem because conventional sources of dry fluorine for conventional outside vapor deposition (OVD) are not currently used. Boron greatly affects the propagation of light having a wavelength of about 1200 nm or more. The boron is generally not available for single mode optical fibers that transmit light at about 1500 nm.

As another method, instead of lowering the refractive index of the region, a method of increasing the refractive index of the clad with germanium has been proposed. However, germanium is not suitable for increasing the refractive index of the clad. Germanium reacts with chlorine during drying and solidification to produce germanium monoxide. The monoxide is relatively volatile and is transported out of the clad during the drying and solidification steps of chlorine. Thus, it is difficult to maintain germanium in the clad to increase the refractive index of the clad with respect to adjacent regions of reduced refractive index, such as fused silica.

Thus, an unmet need for optical fiber structures that is compatible with fused silica glass, increases the refractive index of clad regions with dopants that do not move from their initial positions, and does not absorb light at wavelengths transmitted through the optical fiber. Is present.

summary

The inventors have found an unexpectedly desirable result by doping the clad with tantalum to increase the refractive index of the clad above the adjacent reduction region of the core. The present invention can be obtained by an optical fiber using a dopant that changes the chromatic dispersion to increase only the refractive index. Optical fibers made in accordance with the present invention eliminate the unwanted side effects of such dopants because they do not require dopants that lower the refractive index, such as boron and fluorine.

Tantalum has several technical advantages. First, tantalum does not move from its initial position. Tantalum is less volatile and does not move even when applied at high temperatures while the fiber dries and solidifies. Since it does not move, the doping profile of the tantalum doped region is sharply limited. The second advantage of tantalum is that tantalum has low light attenuation at the wavelength selected for transmission. This wavelength is about 1300 nm to 1550 nm. At this wavelength tantalum has a relatively low light attenuation. In addition, Rayleigh scattering by tantalum is relatively low at this wavelength. The third advantage is that glass doped with tantalum exhibits lower thermal expansion than glass doped with germanium. The fourth advantage is that it has a greater effect on the refractive index by weight than with germanium. Thus, less tantalum is needed to produce the same refraction produced by germanium. Also, the attenuation is also related to the quality, so the attenuation of the optical fiber using tantalum is less because less tantalum is used. The fifth advantage is that tantalum is chemically stable. Tantalum is insoluble in water and most acids and bases and is only slowly affected by strong hydrofluoric acid. The present invention can be applied to all fibers including single mode fibers as well as multimode fibers, dispersion transfer fibers, fibers with large efficiency areas, and ultra long distance fibers with adjusted linear dispersion.

In the optical fiber manufacturing method, the materials for the core and clad (inner and outer) regions of the optical fiber are made of glass having minimal light attenuation properties. Although glass of optical properties is used, fused silica is a particularly suitable glass. Glass for core and cladding glass should have similar physical properties for structural and other practical considerations. Since the core glass must have a higher refractive index than the clad glass, the core glass is made in the same form as the glass used for the clad, and is doped with a small amount of material in order to increase the refractive index of the core slightly. Thus, the core is doped with germania. The first annular reduced area may be formed entirely in the initial portion of the inner clad, in the adjacent portion of the core and inner clad, or in the outer annulus of the core. In a preferred embodiment, the central region of the core is doped with germanium. The outer annulus of the core remains undoped. The cladding region adjacent the undoped core annulus and surrounding the core is doped with tantalum to increase the refractive index. The tantalum doped cladding region extends out of the fiber from the undoped core annulus.

1 is a cross-sectional view of an optical fiber manufactured according to the present invention,

2 is a doping profile of one optical fiber of the present invention,

3 and 4 are doping profiles of other optical fibers made according to the invention,

5 is a graph showing dispersion results of silica overclad fibers doped with tantalum,

FIG. 6 is a graph showing refractive index versus wavelength for tantalum and fused silica.

details

1 is a cross sectional view of a single mode optical fiber 1 made according to the invention. The optical fiber has a center core 10 defined by the outer surface 11. The inner clad region 12 has an inner surface formed on the outer surface 11 of the core 10. The inner clad region 12 has an outer surface 13. The inner clad region 12 is surrounded by an outer clad 14 having an outer surface 15.

The material of the core 10 is fused silica doped with germanium. The inner clad region 12 has at least one annular region 20 of substantially pure fused silica. The dotted line 21 represents the boundary between the regions 20 and 22. Tantalum doping unfolds from dashed line 21 to outer surface 15. Although the present invention illustrates an inner cladding having an undoped region 20 and a tantalum doped region 22, the present invention also shows that the entire inner clad 12 is not doped and the outer clad 14 is tantalum. It also includes fibers doped with.

2 shows a typical doping profile for an optical fiber made in accordance with the present invention. The core region 10 is doped with a combination of germanium and tantalum or germanium to provide a gradient refractive index from maximum to zero at the center on the outer surface 11 of the core 10. The first annular region 20 of substantially pure fused silica is adjacent to the core 10. The second annular region 22 is doped with tantalum. The tantalum doped region 22 has a refractive index that is less than the maximum of the core 10 but greater than the region 20. In this way, there is a large change in refractive index between the regions 20 and 22. Thus, region 20 forms a reduced annular region located between two adjacent regions 10, 22, each of which has a refractive index greater than reduced region 20. The boundary 21 between the undoped region and the tantalum doped region may coincide with the outer surface 13 of the inner clad 12.

In the optical fiber 1, the core has a maximum refractive index I ₀ Has Refractive index I ₁ A first annular region 20 having a is positioned adjacent to the core. The second annular region 22 surrounds the first annular region 20 and has a refractive index I ₂ Has Reduced refractive index I ₁ The first annular region 20 having a totally formed along the outer annulus of the core 10 is adjacent to the annular regions of the core and the inner clad or entirely within the inner clad. therefore, I ₀ > I ₂ > I ₁ to be.

A feature of the present invention is the cladding region, which extends from the outer edge of the outermost annular A to the outer edge of the optical fiber B. This clad region is tantalum which increases the refractive index of the clad above at least one inner annulus, which is typically pure silica and SiO ₂ It includes. The clad also contains other dopants, such as titanium, for increased stress. Other useful profiles are shown in FIGS. 3 and 4.

The fiber of FIG. 3 has a stepped refractive index region 30 made by doping the annular portion of the fiber with germanium. Tantalum doped region 32 extends from stepped refractive index region 30 to the outer surface of the fiber. The fiber of FIG. 4 has two stepped refractive index regions 30, 31, each formed by doping the annular portion of the fiber with germanium. Region 30 is more heavily doped than in region 31. The region 32 doped with tantalum has a refractive index less than that of the region 30 but greater than that of the region 31. It extends to the outside of the fiber.

5 shows the dispersion results of silica overclad fibers doped with tantalum. These results indicate that the dispersion of tantalum doped silica material is very similar to the dispersion of silica doped with germanium.

This prediction was confirmed by subsequent experiments. Experimental results on silica doped with 7.26 wt% tantalum were compared with silica and fused silica doped with 5.9 wt% GeO ₂ and 9.26 wt% GeO ₂ . The data shown in FIG. 6 shows that the tantalum doped silica is nearly similar to the expected refraction of silica doped with 7.5% by weight germanium.

The invention also relates to an optical waveguide having a core having one of constant or varying refractive indices. Modifications, changes and variations to the profiles of the core 10 and the clads 5, 12 and 14 may be made in accordance with the contents of US Pat. No. 4,715,679, which is hereby incorporated by reference. For example, core 10 has a stepped refractive index profile, an α-refractive index profile, a profile that changes at a constant rate, or a profile that changes at one or more speeds. In addition, the reduced area may be formed in the core by terminating germanium doping before the core is complete. The balance of the core is undoped silica.

The present invention is used in a suitable optical fiber which is desirable for raising the refractive index of the clad. Thus, the present invention is applicable not only to single mode fibers but also to multimode fibers, dispersed transfer fibers, fibers with large efficiency areas, and high performance, ultra long distance fibers with adjusted linear dispersion. In the present invention, the dispersion of any fiber can be modified. The present invention eliminates the unwanted effects of low refractive index dopants, such as boron and fluorine, since the optical fibers made in accordance with the present invention do not require such dopants.

As described above, there are various technical advantages by using tantalum. Tantalum has low volatility so that it does not move even when applied at high temperatures while the fiber dries and solidifies. The doping profile of the tantalum doped region is relatively sharp. Tantalum has low Rayleigh scattering and low light attenuation at the wavelength selected for transmission. This wavelength is about 1300 nm to 1550 nm. Glass doped with tantalum has a lower thermal expansion than glass doped with germanium. Tantalum has a greater weight-to-light effect than germanium, so less tantalum is needed to produce the same refraction produced by germanium. Also, because the attenuation is proportional to quality, the attenuation of the optical fiber using tantalum is less because less tantalum is used. Tantalum is chemically stable. Insoluble in water, insoluble in most acids and bases, only slowly affected by strong hydrofluoric acid.

The fibers 1 of the present invention with reduced refractive index regions are made by conventional fiber making processes.

According to the invention, a process for the application of the residue of the second coating of soot which eventually forms the clad 14 is TaCl ₅ It is altered from conventional techniques by the addition of suitable concentrations of precursors of tantalum such as. Those skilled in the art will also recognize that other materials increase the refractive index. Such other materials include zirconium, lanthanum, yttrium, cerium, and germanium. In addition, florid, zirconium, tetrachloride and hexaflorin, hexafluoroacetylacetonate, and analog compounds of lanthanum, yttrium, and cerium are compatible with the OVD process. Any one of these may be produced as a dopant with increased refractive index in the region 14 at an appropriate concentration. In a preferred embodiment, SiO ₂ In the composition of the soot precursor Ta ₂ O ₅ The concentration of the precursor is in the range of up to about 10% by weight, preferably in the range of about 3-5% by weight. Although the above description illustrates the process of the present invention, the process is generally conventional except for adding tantalum to the inner clad region 12. Therefore, any modification can be applied to conventional process steps known to those skilled in the art. For example, one of various laydown processes may be used, including external vapor deposition as well as internal vapor deposition, vapor axial deposition, modified chemical vapor deposition, or plasma external internal deposition.

Conventional fiber optic waveguide techniques are readily applied by those skilled in the art in the embodiments of the present invention, all of which are incorporated by reference to the following non-limiting examples.

US Pat. No. 5,043,002 to Dobbins for raw materials useful as soot precursors; And Blackwell, U.S. Patent No. 5,152,819.

US Pat. No. 5,078,092 to Antos for processes for evaporating or spraying soot precursors; United States Patent No. 5,356,451 to Cain; U.S. Patent No. 4,230,744 to Blankenship; United States Patent No. 4,314,837 to Blankenship; And US Pat. No. 4,173,305 to Blankenship.

US Pat. No. 5,116,400 to Abbott for burning soot precursors and laydowns of cores and claddings; Abbott, US Pat. No. 5,211,732; Berkey, US Pat. No. 4,486,212; US Patent No. 4,568,370 to Powers; US Patent No. 4,639,079 to Powers; Berkey, US Pat. No. 4,684,384; US Patent No. 4,714,488 to Powers; US Patent No. 4,726,827 to Powers; US Patent No. 4,230,472 to Schultz; And US Pat. No. 4,233,045 to Sarkar.

Lane, US Pat. No. 4,906,267 for stages of core preform solidification, core rod drawing, and overclad preform solidification; U.S. Patent No. 4,906,268 to Lane; Lane, U.S. Patent No. 4,950,319; United States Patent No. 4,251,251 to Blankenship; US Patent No. 4,263,031 to Schultz; Bailey, US Pat. No. 4,286,978; US Patent No. 4,125,388 to Powers; US Patent No. 4,165,223 to Powers; And US Pat. No. 5,396,323 to Abbott.

Harvey, US Pat. No. 5,284,499 for drawing fibers from solidified overclad preforms; United States Patent No. 5,314,517 to Koening; United States Patent No. 5,366,527 to Amos; Brown, U.S. Patent 4,500,043; United States Patent No. 4,514,205 to Darcangelo; US Pat. No. 4,531,959 to Kar; Lane, US Pat. No. 4,741,748; Deneka, U.S. Patent No. 4,792,347; United States Patent No. 4,246,299 to Ohls; US Patent No. 4,264,649 to Claypoole; And Brundage, US Pat. No. 5,410,567.

Claims (16)

Maximum refractive index, I ₀ A central region having; I ₀ Less refractive index I ₁ A first annular region having a first region adjacent to the central region; The refractive index of the second annular region is greater than or equal to the refractive index I of the first annular region. I ₂ A refractive index comprising tantalum to increase the refractive index of the region with a refractive index enhancement dopant sufficient to increase I ₂ And a core and an inner clad consisting of a second annular region surrounding the first annular region. The method of claim 1, wherein the central region comprises a core, and the second annular region is I ₂ Less refractive index I ₁ And at least one multiple sub-region having an optical fiber waveguide. The method of claim 1, wherein the relationship between the refractive indices of the regions I ₀ > I ₂ > I ₁ Optical fiber waveguide, characterized in that the. The optical fiber waveguide of claim 1 wherein the dopant for the second annular region comprises tantalum. 2. The optical fiber according to claim 1, wherein the optical fiber is selected from the group consisting of single mode fiber, multi mode fiber, dispersed moving fiber, fiber with large efficiency area, and high performance, ultra long distance fiber with adjusted color dispersion. Optical fiber waveguide. Maximum refractive index, I ₀ A core having; I ₀ Less refractive index I ₁ An inner clad layer having a core having a first annular region surrounding the core; And I ₀ Refractive index of less but first annular region I ₁ Rather than the refractive index of the second annular region I ₂ Refractive index doped with a sufficient amount of tantalum to increase I ₂ And a second annular region surrounding the first annular region. 7. The optical fiber of claim 6 wherein the first annular region comprises fused silica and the second annular region comprises tantalum doped with fused silica. The optical fiber of claim 6 wherein the core comprises fused silica doped with germanium. 7. The optical fiber according to claim 6, wherein the optical fiber is one selected from the group consisting of single mode fiber, multi mode fiber, dispersed moving fiber, fiber having a large efficiency area, and high performance, ultra long distance fiber with adjusted linear dispersion. Optical fiber. A first region and a second annular region surrounding the core region and the core region, respectively, wherein the refractive index of the first annular region is reduced with respect to the adjacent core and the second annular region, and the second annular region is An optical fiber comprising tantalum. 12. The optical fiber of claim 11, wherein the core region comprises fused silica and tantalum. 12. The optical fiber of claim 11, wherein the core region comprises fused silica, germanium, and tantalum. The optical fiber of claim 10 wherein the second annular region comprises fused silica and tantalum. 11. The optical fiber of claim 10 wherein the amount of tantalum in the second annular region is up to about 10 weight percent. 15. The optical fiber of claim 14, wherein the amount of tantalum in the second annular region ranges from about 3 weight percent to about 5 weight percent. 11. The optical fiber according to claim 10, wherein the optical fiber is one selected from the group consisting of single mode fiber, multi mode fiber, dispersed moving fiber, fiber with large efficiency area, and high performance, ultra long distance fiber with adjusted linear dispersion. Optical fiber.