Glass material and optical fiber

Abstract

Provided is a glass material, wherein the full width at half maximum of a first diffraction peak in an X-ray scattering spectrum is 5.9 nm-1 or less. In this glass material, the network structure of glass is less disordered regardless of the number of ring members in the main ring structure.

Description

Glass materials and optical fibers

[0001] This application claims priority to Japanese Patent Application No. 2024-081832, filed May 20, 2024, and incorporates by reference the entire contents of said Japanese application.

[0002] Reducing Rayleigh scattering is extremely important for reducing transmission loss in optical fibers. Rayleigh scattering occurs due to disturbances in the network structure of the glass. Disturbances in the network structure of the glass depend on the fictive temperature, which indicates the temperature at which the glass freezes. Raman scattering has traditionally been used as an index for evaluating fictive temperature.

[0003] Patent Document 1 describes a ratio I between the intensity of Raman scattered light ω3 due to Si—O stretching vibration and the intensity of Raman scattered light D2 due to the three-membered ring structure of silica. Ｄ２ / I ω３ It is stated that the smaller the value, the lower the fictive temperature.

[0004] US Patent Application Publication No. 2017 / 305781

[0005] In the glass material according to one embodiment of the present disclosure, the full width at half maximum of the first diffraction peak in the X-ray scattering spectrum is 5.9 nm －１ The following is the result.

[0006] FIG. 1 is a cross-sectional view showing an optical fiber according to an embodiment. FIG. 2 is a diagram showing an example of a typical Raman scattering spectrum. FIG. 3 is a diagram showing the transmission loss and the ratio I Ｄ２ / I ω３ FIG. 4 is a graph showing the relationship between the full width at half maximum of the first diffraction peak in the X-ray scattering spectrum of an optical fiber. FIG. 5 is a graph showing the relationship between the full width at half maximum of the first diffraction peak in the X-ray scattering spectrum of an optical fiber containing silica as the main component and the transmission loss. FIG. 6 is a graph showing the relationship between the full width at half maximum of the first diffraction peak in the X-ray scattering spectrum of an optical fiber containing germanium as the core and the transmission loss.

[0007] On the premise that the number of non-six-membered ring structures such as three-membered ring structures and other elements is small relative to the six-membered ring structures of silica, the fictive temperature can be appropriately expressed by the abundance ratio of three-membered ring structures as described in Patent Document 1. However, if the above premise is not met, the abundance ratio of three-membered ring structures does not necessarily correlate with the fictive temperature. In other words, an increase in fictive temperature does not necessarily mean a disturbance in the network structure of the glass, and therefore an increase in transmission loss.

[0008] For example, in glass to which elements other than silicon (Si) and oxygen (O) are added at high concentrations, the absolute number of basic Si-O network structures decreases. As a result, the fictive temperature, which is expressed by the abundance ratio of three-membered ring structures, increases. In this case, the transmission loss may decrease.

[0009] For example, in densified glass, ring structures with fewer ring members, such as three-membered ring structures and four-membered ring structures, develop. The fictive temperature, which is expressed by the ratio of three-membered ring structures, rises. However, it is known that transmission loss decreases because an ordered structure actually develops.

[0010] Therefore, it is difficult to control the reduction of Rayleigh scattering using the abundance ratio of non-six-membered ring structures as an index. It is desirable to evaluate the uniformity of the glass network structure regardless of the number of ring members in the main six-membered ring structure, and thereby achieve glass with a highly uniform network structure.

[0011] The present disclosure provides glasses and optical fibers that have a highly uniform network structure regardless of the number of ring members in the main ring structure.

[0012] According to the present disclosure, it is possible to provide glass and optical fiber having a highly uniform network structure, regardless of the number of ring members in the main ring structure.

[0013] The details of the embodiments of the present disclosure will be described. (1) In a glass material according to one aspect of the present disclosure, the full width at half maximum of the first diffraction peak in the X-ray scattering spectrum is 5.9 nm. －１ This glass material has a highly uniform network structure regardless of the number of ring members in the main ring structure.

[0014] (2) An optical fiber according to an aspect of the present disclosure is an optical fiber including a core and a cladding surrounding the core, wherein the distribution of the full width at half maximum of the first diffraction peak of the X-ray scattering spectrum in the core radial direction is weighted by the electric field distribution of guided light having a wavelength of 1550 nm calculated based on the refractive index profile in a region with a diameter of 20 μm, and the weighted value is 5.9 nm. －１ In this optical fiber, the network structure is highly uniform regardless of the number of ring members in the main ring structure, thereby reducing transmission loss.

[0015] (3) In the above (2), the difference between the maximum and minimum values ​​in the core is 0.6 nm －１ In this case, it is possible to reduce the scattering intensity caused by differences in uniformity of the glass in the radial direction.

[0016] (4) In an optical fiber according to an aspect of the present disclosure, the optical fiber includes a core containing germanium and a cladding surrounding the core, and the value obtained by weighting the full width at half maximum (FWHM) distribution of the first diffraction peak of the X-ray scattering spectrum in the core radial direction with the electric field distribution of guided light having a wavelength of 1550 nm calculated based on the refractive index profile in a region with a diameter of 20 μm is 7.0 nm or less. －１ In this optical fiber, the network structure is highly uniform regardless of the number of ring members in the main ring structure, thereby reducing transmission loss.

[0017] (5) In the above (4), the difference between the maximum and minimum values ​​in the core is 0.4 nm －１ In this case, it is possible to reduce the scattering intensity caused by differences in uniformity of the glass in the radial direction.

[0018] [Details of the embodiments of the present disclosure] Specific examples of the glass material and optical fiber of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0019] (Glass Material) The glass material according to the embodiment is used, for example, as a material for an optical fiber. The glass material contains, as a main component (matrix), for example, an oxide or a fluoride. The oxide is, for example, silica (SiO ２ , tetrahedral structure SiO ４ ), alumina (Al ２ O ３ The concentration of the main component may be 50% or more, 80% or more, or 90% or more in mass fraction.

[0020] The glass material may contain, as a minor component, alkali metal elements such as Li, Na, K, Rb, and Cs, alkaline earth metal elements such as Be, Mg, Ca, Sr, and Ba, Group 13 elements such as B, Al, Ga, and In, Group 14 elements such as Ge and Sn, Group 15 elements such as P and N, or Group 17 elements such as F, Cl, Br, and I. The glass material may contain a plurality of these elements simultaneously.

[0021] In general, adding a different element to glass from the main component has the effect of weakening the network bonds of the main component, which is, for example, an oxide. This makes structural relaxation more likely at high temperatures. If the concentration of the different element is too high, the effect of network destruction due to the addition becomes too strong, reducing the uniformity of the glass network. Therefore, the sum of the concentrations of the elements of the minor components may be 0.001% or more and 20% or less, 0.01% or more and 15% or less, or 0.1% or more and 10% or less, in mass fraction.

[0022] Of the above compositions, SiO ２ The glass based on this may be a densified glass. The glass density is 2.21 g / cm ３ or more, and 2.25 g / cm ３ or more, and 2.3 g / cm ３or more. In densified glass, the three-membered ring structure and four-membered ring structure of silica become numerous, resulting in a uniform glass structure. For example, densified glass can be obtained by applying high pressure. Densifying glass changes the refractive index of the glass. The refractive index of ordinary glass is, for example, 1.45 or more and 1.47 or less. Ordinary glass also includes glass to which various elements are added. The refractive index of densified glass is, for example, 1.47 or more and 1.56 or less.

[0023] The glass material has a full width at half maximum of the first sharp diffraction peak (FSDP) of the X-ray scattering spectrum of 5.9 nm. －１ The full width at half maximum of FSDP can express the uniformity of the glass structure regardless of the number of ring members in the main ring structure. FSDP will be explained later with reference to FIG. 6. When FSDP is 5.9 nm, －１ The following glass materials have little disorder in the glass network structure and are highly uniform. The full width at half maximum of FSDP is 5.7 nm. －１ It may be 5.3 nm or less, －１ The FSDP may be 5.7 nm or less. －１ The following glass materials have even less disorder in the glass network structure and even higher uniformity: FSDP is 5.3 nm －１ In the following glass materials, the glass network structure is even less disordered and even more uniform.

[0024] (Optical fiber) Fig. 1 is a cross-sectional view showing an optical fiber according to an embodiment. As shown in the figure, the optical fiber 1 according to an embodiment includes a core 10 and a cladding 20. The core 10 and the cladding 20 contain the glass material according to an embodiment. The composition of the core 10 and the composition of the cladding 20 may be the same as or different from each other.

[0025] The core 10 extends along the central axis 1a of the optical fiber 1. The number of cores 10 may be one, or two or more. That is, the optical fiber 1 may be a single-core optical fiber or a multi-core optical fiber. When the optical fiber 1 is a multi-core optical fiber, the compositions of the cores 10 may be the same as or different from each other. The diameter of the core 10 (hereinafter also referred to as "core diameter") is, for example, 4.5 μm or more and 15 μm or less.

[0026] The cladding 20 surrounds the core 10. While the cladding 20 in the illustrated example has a single-layer structure, it may have a multi-layer structure. The multi-layer cladding 20 may have, for example, an optical cladding and a physical cladding called a jacket. The diameter of the cladding 20 is, for example, 125 μm.

[0027] The refractive index of the core 10 is higher than the refractive index of the cladding 20. The relative refractive index difference Δ between the core 10 and the cladding 20 is, for example, not less than 0.25% and not more than 0.4%.

[0028] The optical fiber 1 is doped with deuterium (D ２ ) treatment may be performed, which reduces defect absorption loss and promotes structural relaxation due to the disappearance of defect structures.

[0029] The optical fiber 1 has a core 10 and a cladding 20, and has different materials and heat distributions depending on the position in a plane perpendicular to the central axis 1a. In this case, the full width at half maximum of the FSDP in the optical fiber 1 is not necessarily uniform in a plane perpendicular to the central axis 1a. Therefore, when calculating the full width at half maximum of the FSDP in the optical fiber 1, the distribution of the full width at half maximum of the FSDP in the core radial direction is weighted by the intensity distribution of the guided light. In the case of a multi-core optical fiber, weighting is performed for each core 10.

[0030] The weighting is performed, for example, in an area of ​​a predetermined diameter centered on the central axis of the core 10. The predetermined diameter is equal to or greater than the core diameter and equal to or less than the distance between the central axes of adjacent cores 10. When the central axis of the core 10 coincides with the central axis 1a of the optical fiber 1, the distribution of the full width at half maximum of the FSDP in the core radial direction coincides with the radial distribution of the full width at half maximum of the FSDP. Specifically, the full width at half maximum of the FSDP of the optical fiber 1 is a value obtained by weighting the distribution of the full width at half maximum of the FSDP in the core radial direction of the X-ray scattering spectrum with the electric field distribution of guided light with a wavelength of 1550 nm calculated based on the refractive index profile in an area of ​​20 μm diameter (i.e., an area included within a radius of 10 μm from the central axis of the core 10).

[0031] In optical fiber 1, the full width at half maximum of the FSDP is 5.9 nm. －１ This reduces the disorder of the glass network structure, resulting in a reduction in transmission loss. The full width at half maximum of FSDP is 5.7 nm. －１ In this case, the transmission loss can be further reduced. －１ In this case, the transmission loss can be further reduced. －１ It may be 4 nm or more. －１ It may be 5 nm or more. －１ It may be more than that.

[0032] A smaller difference between the maximum and minimum values ​​of the full width at half maximum of FSDP at the same site (hereinafter also referred to as "full width at half maximum difference") is effective in improving the uniformity of the glass. Here, the site refers to the core 10 and the clad 20. When the clad 20 has a multilayer structure, the site may be each layer of the clad 20, such as an optical clad or a physical clad.

[0033] A smaller difference in full width at half maximum of FSDP in the core 10 is effective in improving the uniformity of the glass. －１ It may be 0.4 nm or less, －１ It may be 0.2 nm or less, －１The smaller the difference in full width at half maximum of FSDP in the cladding 20, the more effective it is for improving the uniformity of the glass. The difference in full width at half maximum of FSDP in the cladding 20 may be 1.0 nm or less. －１ It may be 0.8 nm or less, －１ It may be 0.6 nm or less, －１ This can reduce the scattering intensity caused by differences in uniformity of the glass in the radial direction.

[0034] (Germanium-Doped Core) When the core 10 contains germanium (Ge), the full width at half maximum of the FSDP of the optical fiber 1 is 7.0 nm. －１ This reduces the disorder of the glass network structure, resulting in a reduction in transmission loss. The full width at half maximum of FSDP is 6.7 nm. －１ In this case, the transmission loss can be further reduced. －１ In this case, the transmission loss can be further reduced. －１ It may be 4 nm or more. －１ It may be 5 nm or more. －１ It may be more than that.

[0035] Even when the core 10 contains germanium, a smaller difference in the full width at half maximum of the FSDP at the same location is effective in improving the uniformity of the glass. A smaller difference in the full width at half maximum of the FSDP within the core 10 is effective in improving the uniformity of the glass. The difference in the full width at half maximum of the FSDP within the core 10 is 0.6 nm. －１ It may be 0.4 nm or less, －１ It may be 0.2 nm or less, －１ It may be the following:

[0036] A smaller difference in full width at half maximum of FSDP in the cladding 20 is also effective in improving the uniformity of the glass. －１ It may be 0.5 nm or less, －１ It may be 0.3 nm or less, －１This can reduce the scattering intensity caused by the difference in uniformity of the glass in the radial direction. The difference in full width at half maximum of FSDP over the entire optical fiber can be 0.8 nm or less. －１ It may be 0.6 nm or less, －１ It may be 0.4 nm or less, －１ It may be the following:

[0037] (Low-loss evaluation method) As a low-loss evaluation method, the method described in Patent Document 1 will be described. In this method, the ratio I Ｄ２ / I ω３ This method is limited to silica glass.

[0038] Fig. 2 shows an example of a typical Raman scattering spectrum. Generally, when a substance is irradiated with light, Raman scattered light with a wavelength different from the wavelength of the irradiated light is generated due to the interaction between the light and the substance (molecular vibration). The Raman scattered light is separated and the Raman scattered spectrum obtained allows the molecular-level structure of the substance to be analyzed. When silica glass is irradiated with laser light with a wavelength of 532 nm, a typical Raman scattered spectrum as shown in Fig. 2 is obtained. In the figure, Raman scattered light ω3 due to Si-O stretching vibration is observed in the wavenumber range of 750 cm －１ 875cm or more －１ The Raman scattering light D2 attributed to the silica three-membered ring structure is observed in the wavenumber range of 565 cm －１ More than 640cm －１ The Raman scattering light D1 attributed to the silica four-membered ring structure is observed in the wavenumber range of 475 cm －１ 525cm or more －１ The following is recognized:

[0039] Intensity I of Raman scattered light ω ω３ is in the wavenumber range 750 cm in the Raman scattering spectrum. －１ 875cm or more －１ The intensity of the Raman scattered light D2 is expressed as the average intensity of the region between the baseline and the Raman scattered spectrum. Ｄ２ is in the wavenumber range 565 cm in the Raman scattering spectrum. －１ More than 640cm －１The Raman scattering spectrum is shown as the average intensity in the region between the baseline drawn below.

[0040] Figure 3 shows the transmission loss and relative I Ｄ２ / I ω３ 1 is a graph showing the relationship between the transmission loss and the relative I. The figure shows data for optical fibers manufactured under conditions 1 and 2. The optical fiber manufactured under condition 1 has a conventional glass composition range mainly composed of a six-membered ring structure of silica. As mentioned above, in order to reduce Rayleigh scattering, it is not necessary to limit the main ring structure to a six-membered ring structure. The optical fiber manufactured under condition 2 has a new glass composition range that is homogenized mainly composed of three-membered and four-membered ring structures of silica, or ring structures mainly composed of other elements. In the optical fiber manufactured under condition 1, the transmission loss and relative I Ｄ２ / I ω３ On the other hand, in the optical fiber manufactured under condition 2, the correlation is not necessarily observed.

[0041] 4 shows the Raman spectrum of glass doped with 10% potassium (K) by mass fraction. As shown in the figure, the addition of a high concentration of elements disrupts the six-membered ring structure, resulting in a peak at a wavenumber of 1100 cm due to non-bridging oxygen. －１ The ratio of the six-membered ring structure of silica decreases, so the ratio I Ｄ２ / I ω３ However, the uniformity of the actual glass structure cannot be properly evaluated depending on the material.

[0042] Fig. 5 is a graph showing the Raman spectrum of glass produced under 4 GPa. In the case of such high-pressure glass (i.e., densified glass), the shape of the Raman spectrum changes due to the formation of smaller rings in the glass structure, as shown in the figure. Similarly, the proportion of six-membered ring structures in silica throughout the glass is reduced.

[0043] The present inventors have found that evaluation using the FSDP of the X-ray scattering spectrum is desirable to solve the above problems and ensure low transmission loss. Figure 6 shows the FSDP of the X-ray scattering spectrum of an optical fiber. The X-ray scattering spectrum is measured using X-rays in the incident energy band of 8.3 keV, for example. As the FSDP, －１ ) is q ≥ 1 Å －１ (i.e., 10 nm －１ ) is selected. For example, for pure silica, it is 1.6 Å. －１ Near (i.e., 16 nm －１ FSDP is obtained in the vicinity of

[0044] The full width at half maximum of the FSDP is calculated using the split pseudo-Voigt function, A, μ Ｌ , μ Ｈ , B, w, y ０ , y １ It can be obtained by performing fitting of x<x ｃ Then, the following function is obtained: x>x ｃ Then, in the following function, replace B with 1 / B, and μ Ｈ μ Ｌ Reference: H. Toraya, J. Appl. Crystallogr. 23, 485 (1990)

[0045] FSDP is an index resulting from the bond distance of the main component glass, and its full width at half maximum indicates the variation in the bond length of the main component glass. Therefore, the full width at half maximum of FSDP is a very suitable method for expressing the uniformity of the medium-range order of the glass structure, which is the cause of Rayleigh scattering. It is very suitable for evaluating the relationship between Rayleigh scattering and loss, regardless of the main ring structure and the type of main oxide.

[0046] 7 is a graph showing the relationship between the full width at half maximum of the FSDP of the X-ray scattering spectrum of an optical fiber mainly composed of silica and the transmission loss. Here, the full width at half maximum of the FSDP of the optical fiber is a value calculated by weighting it with the intensity distribution of the guided light, as described above. The state of the glass (i.e., the state of the optical fiber) at the time of the transmission loss measurement was determined to be 5.9 nm. －１ It can be confirmed that a transmission loss of 0.150 dB / km or less can be achieved when the wavelength is 5.7 nm or less. －１ It can be confirmed that a transmission loss of 0.145 dB / km or less can be achieved in the following cases: －１ It can be seen that a transmission loss of 0.141 dB / km or less can be achieved in the following cases.

[0047] (Germanium-doped core) A case where the core contains germanium will be described. Fig. 8 is a graph showing the relationship between the full width at half maximum of the FSDP of the X-ray scattering spectrum of an optical fiber whose core contains germanium and the transmission loss. Here, too, the full width at half maximum of the FSDP of the optical fiber is a value calculated by weighting it with the intensity distribution of the guided light, as described above. As the state of the glass (i.e., the state of the optical fiber) at the time of transmission loss measurement, the full width at half maximum of the FSDP was 7.0 nm. －１ It can be confirmed that a transmission loss of 0.185 dB / km or less can be achieved when the wavelength is 6.7 nm or less. －１ It can be confirmed that a transmission loss of 0.180 dB / km or less can be achieved in the following cases: －１ It can be seen that a transmission loss of 0.175 dB / km or less can be achieved in the following cases.

[0048] Although the embodiments have been described above, the present disclosure is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0049] REFERENCE SIGNS LIST 1...optical fiber 1a...central axis 10...core 20...cladding

Claims

1. The full width at half maximum of the first diffraction peak in the X-ray scattering spectrum is 5.9 nm. －１ The following is a glass material.

2. An optical fiber having a core and a cladding surrounding the core, wherein the distribution of the full width at half maximum of the first diffraction peak of the X-ray scattering spectrum in the core radial direction is weighted by the electric field distribution of guided light with a wavelength of 1550 nm calculated based on the refractive index profile in a region with a diameter of 20 μm, and the weighted value is 5.9 nm. －１ Below is the optical fiber.

3. The difference between the maximum and minimum values ​​of the above-mentioned values ​​in the core is 0.6 nm －１ The optical fiber of claim 2 , wherein:

4. An optical fiber having a core containing germanium and a cladding surrounding the core, wherein the distribution of the full width at half maximum of the first diffraction peak of the X-ray scattering spectrum in the core radial direction is weighted by the electric field distribution of guided light with a wavelength of 1550 nm calculated based on the refractive index profile in a region with a diameter of 20 μm, and the weighted value is 7.0 nm. －１ Below is the optical fiber.

5. The difference between the maximum and minimum values ​​of the value in the core is 0.4 nm －１ The optical fiber of claim 4 , wherein:

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