Glass material and optical fiber

Abstract

This glass material comprising silica glass contains at least one element selected from the Group 13 element group constituted by boron, aluminum, gallium, and indium.

Description

Glass materials and optical fibers

[0001] This disclosure relates to a glass material and an optical fiber. This application claims priority to Japanese Application No. 2022-104474, filed on June 29, 2022, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Document 1 discloses an optical fiber having a core doped with germanium, which can increase the refractive index of the core.

[0003] Japanese Patent Application Laid-Open No. 2013-218247

[0004] A glass material according to one aspect of the present disclosure is a glass material including silica-based glass, and includes at least one element selected from the group 13 elements consisting of boron, aluminum, gallium, and indium.

[0005] Fig. 1 is a cross-sectional view showing an optical fiber according to an embodiment, Fig. 2 is a graph showing the relationship between the concentration ratio of aluminum and sodium and the transmission loss, and Fig. 3 is a graph showing the relationship between the concentration ratio of aluminum and calcium and the transmission loss.

[0006] [Problems to be Solved by the Present Disclosure] Increasing the concentration of an added element (dopant) can cause the following problems: Namely, Rayleigh scattering due to compositional fluctuations increases. Also, the probability of impurities contained in the dopant being mixed in increases, which can lead to absorption in the ultraviolet and visible light regions due to the impurities. Furthermore, the probability that the added element will distort the network structure of silica glass increases, which can lead to glass defects and result in increased absorption in the ultraviolet wavelength region. In this field, there is a demand for glass materials and optical fibers that have high transmittance over a wide wavelength region.

[0007] An object of the present disclosure is to provide a glass material and an optical fiber that have high transmittance over a wide wavelength range.

[0008] Effect of the Present Disclosure The present disclosure can provide a glass material and an optical fiber that have high transmittance over a wide wavelength range.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) A glass material according to one aspect of the present disclosure is a glass material containing silica-based glass, and includes at least one element from the Group 13 element group consisting of boron, aluminum, gallium, and indium. Since elements from the Group 13 element group exhibit a large change in refractive index relative to the amount added, this glass material can suppress the concentration of dopants used to change the refractive index. As a result, high transmittance is achieved over a wide wavelength range.

[0010] (2) The glass material of (1) above may contain at least one element from an alkali element group consisting of an alkali metal element and an alkaline earth metal element, and where x is the concentration of the alkali metal element and y is the concentration of the alkaline earth metal element, x + 2y may be 0.1 to 10 times the concentration of the element from the Group 13 element group. In this case, the element from the alkali element group aligns the valence of the element from the Group 13 element group with the valence of silicon, thereby suppressing distortion of the glass structure caused by the Group 13 element. As a result, the occurrence of defects is suppressed and the uniformity of the glass structure is promoted. Therefore, higher transmittance is achieved over a wide wavelength range.

[0011] (3) The glass material of (1) above may contain at least one element from an alkali element group consisting of an alkali metal element and an alkaline earth metal element, and where x is the concentration of the alkali metal element and y is the concentration of the alkaline earth metal element, x + 2y may be 0.2 to 5 times the concentration of the element from the Group 13 element group. In this case, even higher transmittance is achieved over a wide wavelength range.

[0012] (4) The glass material of (1) above may contain at least one element from an alkali element group consisting of an alkali metal element and an alkaline earth metal element, and where x is the concentration of the alkali metal element and y is the concentration of the alkaline earth metal element, x + 2y may be 0.8 to 1.2 times the concentration of the element from the Group 13 element group. In this case, particularly high transmittance is achieved over a wide wavelength range.

[0013] (5) In any of the glass materials (1) to (4) above, the relative refractive index difference based on the refractive index of pure silica glass may be 0.0% or more. When this glass material is used to form a core, excessive doping of a downdopant in the cladding can be suppressed.

[0014] (6) Any of the glass materials (1) to (5) above may contain silica glass in a mass ratio of 50% or more, which prevents adverse effects on optical properties.

[0015] (7) Any of the glass materials described in (1) to (6) above may contain at least two elements from the group 13 element group. In this case, the inclusion of a large amount of a specific element from the group 13 element group is suppressed. Therefore, phase separation of the substance into two components due to an increase in concentration can be suppressed.

[0016] (8) An optical fiber according to one aspect of the present disclosure includes a core containing silica-based glass and at least one element selected from a group of elements consisting of boron, aluminum, gallium, and indium, and a cladding containing silica-based glass and surrounding the core. Since elements from the Group 13 element group exhibit a large change in refractive index relative to the amount of doping, this optical fiber can suppress the concentration of dopants used to change the refractive index. This allows for high transmittance over a wide wavelength range, thereby reducing loss in the transmission wavelength band.

[0017] [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. Note that the present invention 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 redundant explanations will be omitted.

[0018] (Glass Material) The glass material according to this embodiment is, for example, an optical glass material. More specifically, the glass material is, for example, a glass material for optical fibers, and is used to form the core of an optical fiber. The glass material is made of silica-based glass containing silica glass as a main component. The glass material further contains other elements in addition to silicon (Si) and oxygen (O), which constitute silica glass.

[0019] The glass material contains at least one element from a group 13 element group consisting of boron (B), aluminum (Al), gallium (Ga), and indium (In). The concentration of the element from the group 13 element group, i.e., the group 13 element, may be 10 ppm or more, 50 ppm or more, or 1000 ppm or more.

[0020] The glass material may contain at least two elements from the group 13 element group, or may contain three or more elements. When the glass material contains multiple group 13 elements, the concentration of each group 13 element required to achieve a desired refractive index can be reduced. Therefore, it is possible to suppress the phase separation into two components of a compound of the group 13 element and an element present in the glass as the concentration increases.

[0021] When such a phase separation state occurs, light absorption and scattering occur at the phase interface, resulting in changes in optical properties. These phase states change significantly depending on the cooling rate in the glass manufacturing process or even on slight temperature variations of, for example, around 10°C. This significantly deteriorates the controllability of optical properties. Therefore, it is extremely important to suppress phase separation in the first place. In optical fiber glass materials, if other substance phases are generated during the fiberization process, the hardness within the glass becomes non-uniform, making it impossible to achieve the desired fiber diameter and refractive index profile. Therefore, it is important to suppress the concentration of each Group 13 element in order to prevent a decrease in the yield of optical fibers.

[0022] In optical fiber glass materials, if other substance phases are generated during the fiberization process, the hardness within the glass becomes non-uniform, making it impossible to achieve the desired fiber diameter and refractive index profile. Therefore, in order to prevent a decrease in the yield of optical fiber, it is important to suppress the concentrations of each Group 13 element.

[0023] If phase separation of the additive substances occurs due to the addition of multiple elements, it will have an adverse effect on the optical properties as described above. Therefore, the proportion of silica glass, which is the main component, may be 50% or more, 90% or more, 95% or more, 98% or more, or 99% or more by mass ratio. Here, mass ratio means mass fraction.

[0024] Pure silica glass (SiO ２ ), i.e., the relative refractive index difference Δ of the glass material based on the refractive index of silica glass may be 0.0% or more, 0.2% or more, or 0.3% or more. When such a glass material is used to form the core, it is possible to prevent excessive doping of a downdopant such as fluorine (F) in the cladding. Therefore, it is possible to prevent an increase in transmission loss due to an increase in the doping concentration.

[0025] All Group 13 elements are upper dopants and are added according to the refractive index of the target glass material. When a single element is added, i.e., when only one type of Group 13 element is added, in the case of aluminum, the mass ratio may be 10 ppm or more, 1,000 ppm or more, or 10,000 ppm or more. In the case of boron, the mass ratio may be 10 ppm or more, 300 ppm or more, or 3,000 ppm or more. In the case of gallium and indium, the mass ratio may be 10 ppm or more, 50 ppm or more, or 100 ppm or more. Since Group 13 elements exhibit a large change in refractive index relative to the amount added, the concentration of the dopant for refractive index change can be suppressed. Therefore, problems associated with increasing the dopant concentration are suppressed. That is, Rayleigh scattering due to composition fluctuations is suppressed. Furthermore, the probability of impurities being mixed into the dopant is reduced, thereby suppressing absorption in the ultraviolet and visible light regions due to impurities. Furthermore, the probability that the added element distorts the network structure of the silica glass is reduced, and glass defects are suppressed, resulting in suppression of absorption in the ultraviolet wavelength region. Here, the mass ratio means mass fraction.

[0026] The glass material may contain at least one element selected from an alkali element group consisting of alkali metal elements and alkaline earth metal elements. Examples of alkali metal elements include lithium (Li), sodium (Na), potassium (K), and rubidium (Rb). Examples of alkaline earth metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).

[0027] The alkali element group element has the effect of matching the valence of the Group 13 element added to the glass material to the valence of silicon. By performing such valence matching, distortion of the glass structure caused by the Group 13 element is suppressed. As a result, effects such as suppression of the occurrence of defects and promotion of uniformity of the glass structure can be expected. Therefore, a wide wavelength range is expected for the glass material in optical glass applications, and reduction of transmission loss is expected in optical fiber applications.

[0028] When the total amount (molar concentration) of alkali metal elements added is x and the total amount (molar concentration) of alkaline earth metal elements added is y, x + 2y may be 0.1 times or more and 10 times or more, 0.2 times or more and 5 times or less, or 0.8 times or more and 1.2 times or more of the concentration of the elements of the group 13 element group. The concentration of the elements of the alkali element group may be 10 ppm or more, 50 ppm or more, or 1000 ppm or more. The trivalent of the group 13 element and the monovalent of the alkali metal element can compensate for the tetravalent of silicon. Therefore, the amount of alkali metal element ions added may be greater than the amount of alkaline earth metal element ions added.

[0029] The glass material may contain a halogen element, such as fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0030] The synthesis of glass materials is achieved by heating and diffusing the solid or gas of the element to be doped. To achieve the above-mentioned valence matching, the diffusion states of the alkali element group element and the Group 13 element may be equivalent. The diffusion rate varies depending on the element, and the diffusion coefficient of the alkali element group element is greater than the diffusion coefficient of the Group 13 element. Therefore, the diffusion doping of the element is carried out after calculating the diffusion rate x time so that the diffusion rate is approximately equivalent at the temperature at which the element is diffused.

[0031] (Optical fiber) Fig. 1 is a cross-sectional view showing an optical fiber according to an embodiment. The optical fiber 1 according to an embodiment includes a core 10 extending along a central axis 1a and a cladding 20 surrounding the core 10. The optical fiber 1 is formed using a glass material according to an embodiment. More specifically, the core 10 is formed using the glass material according to an embodiment. The cladding 20 is made of silica-based glass containing silica glass as a main component.

[0032] Table 1 shows the relationship between the concentration ratio and the transmission loss.

[0033] Fig. 2 is a graph showing the relationship between the concentration ratio of aluminum and sodium and transmission loss. As shown in Table 1 and Fig. 2, the transmission loss is lowest when the concentration ratio of aluminum and sodium [Al] / [Na] is 1. As the concentration ratio [Al] / [Na] becomes lower than 1, the transmission loss increases. As the concentration ratio [Al] / [Na] becomes higher than 1, the transmission loss increases.

[0034] Fig. 3 is a graph showing the relationship between the concentration ratio of aluminum and calcium and the transmission loss. As shown in Table 1 and Fig. 2, the transmission loss is lowest when the concentration ratio of aluminum and calcium [Al] / [Ca] is 2. As the concentration ratio [Al] / [Ca] becomes lower than 2, the transmission loss increases. As the concentration ratio [Al] / [Ca] becomes higher than 2, the transmission loss increases.

[0035] The concentration of each of the above elements can be determined by measurements using an electron probe microanalyzer. The concentration is evaluated by analyzing the measurement results of the spectral intensity of the characteristic X-rays of each element. The concentration is determined from a calibration curve of spectral intensity and concentration created using multiple standard samples with different concentrations. The measurement conditions are, for example, an acceleration voltage of 20 kV, a probe beam diameter of 1 μm or less, and a measurement interval of 100 nm.

[0036] Although the embodiments have been described above, the present disclosure is not necessarily limited to the above-described embodiments and modifications, and various modifications are possible without departing from the spirit of the present disclosure.

[0037] REFERENCE SIGNS LIST 1...optical fiber 1a...central axis 10...core 20...cladding

Claims

1. A glass material including a silica-based glass, At least one element selected from the group 13 elements consisting of boron, aluminum, gallium, and indium; Glass material.

2. Contains at least one element selected from the alkali element group consisting of alkali metal elements and alkaline earth metal elements, When the concentration of the alkali metal element is x and the concentration of the alkaline earth metal element is y, x+2y is 0.1 to 10 times the concentration of the element of the Group 13 element group. The glass material according to claim 1 .

3. Contains at least one element selected from the alkali element group consisting of alkali metal elements and alkaline earth metal elements, When the concentration of the alkali metal element is x and the concentration of the alkaline earth metal element is y, x+2y is 0.2 to 5 times the concentration of the element of the Group 13 element group. The glass material according to claim 1 .

4. Contains at least one element selected from the alkali element group consisting of alkali metal elements and alkaline earth metal elements, When the concentration of the alkali metal element is x and the concentration of the alkaline earth metal element is y, x+2y is 0.8 to 1.2 times the concentration of the element of the Group 13 element group. The glass material according to claim 1 .

5. The relative refractive index difference based on the refractive index of pure silica glass is 0.0% or more. The glass material according to any one of claims 1 to 4.

6. Contains 50% or more silica glass by mass ratio; The glass material according to any one of claims 1 to 4.

7. At least two elements from the Group 13 element group are included, The glass material according to any one of claims 1 to 4.

8. a core including a silica-based glass and including at least one element selected from the group of elements consisting of boron, aluminum, gallium, and indium; a cladding including a silica-based glass and surrounding the core; Optical fiber.