Bundle fiber and method for bonding bundle fiber

Abstract

[Problem] To provide: a bundle fiber in which an end part is bonded with glass and melting of the glass is prevented even when light in a wavelength region of 350-500 (nm) enters therethrough; and a method for bonding the bundle fiber. [Solution] A bundle fiber is composed of a plurality of optical fibers, glass containing at least phosphoric acid and no lead and having at least 95 (%) light transmittance of light in a wavelength region of 350-500 (nm) is melted by heating, portions between the respective optical fibers at an end part of the bundle fiber is filled with the molten glass, and the end part of the bundle fiber is bonded with the glass. Further, the bundle fiber is optically coupled with a light source in a wavelength region of 350-500 (nm), thereby preventing heat generation of glass, with which the end part of the bundle fiber has been bonded, when the light enters into the optical fiber.

Description

Bundle fiber and method for securing bundle fiber

[0001] This invention relates to bundled fibers and a method for fixing bundled fibers.

[0002] With the increasing power output of laser processing machines, there is a demand for higher density of multiple optical fibers. One method for achieving this density is the use of bundled fibers, which are made by bundling multiple optical fibers together and inserting them into ferrules or sleeves. Light with a wavelength of 500 nm or less is used as the incident light on these bundled fibers. Even metallic materials such as copper and gold, which have high reflectivity in visible light, will experience absorption at light wavelengths of 500 nm or less.

[0003] The ends of bundled fibers are fixed with an organic resin adhesive, such as epoxy resin (see Patent Document 1). However, when light with a wavelength of 350 nm to 500 nm is incident on each optical fiber of the bundled fiber, the temperature of the ends of the bundled fibers rises, and the organic resin adhesive deteriorates and burns due to the heat, which presents a problem.

[0004] Therefore, a method for forming bundle fiber terminals using glass (especially low-melting-point glass) instead of the aforementioned organic resin adhesive has been invented (see Patent Document 2). In Patent Document 2, the terminal portion (end) of the bundle fiber is fused by immersion in molten glass (low-melting-point glass), and lead-borate glass is mentioned as the type of glass.

[0005] JP-A-55-111908 JP-A-01-114804

[0006] However, the applicant's investigation revealed that when light with a wavelength of 405 nm, which falls within the wavelength range of 350 nm to 500 nm, is incident on the bundle fiber of Patent Document 2, the glass bonding the ends of the bundle fiber generates heat and melts. It was also found that this melting results in problems such as the movement of each optical fiber at the end of the bundle fiber, or the deposition of lead (Pb) in the glass.

[0007] The present invention has been made in view of the above problems, and aims to provide a bundled fiber in which the ends are fixed with glass, and in which melting of the glass is prevented even when light in the wavelength range of 350 nm to 500 nm is incident, and a method for fixing the bundled fiber.

[0008] The aforementioned problems are solved by the present invention as follows. Specifically, the bundle fiber of the present invention is composed of multiple optical fibers, glass is filled between each optical fiber at the end of the bundle fiber, the end of the bundle fiber is fixed with glass, the bundle fiber is optically coupled to a light source in the wavelength range of 350 nm to 500 nm, the glass contains at least phosphoric acid but does not contain lead, the light transmittance of light in the wavelength range of 350 nm to 500 nm is 95% or more, and the heat generation of the glass when light in the wavelength range of 350 nm to 500 nm is incident on the optical fiber is prevented.

[0009] Furthermore, the present invention's method for fixing bundled fibers is characterized by forming a bundled fiber with multiple optical fibers, melting a glass that contains at least phosphoric acid but does not contain lead, and has an optical transmittance of 95% or more for light in the wavelength range of 350 nm to 500 nm by heating, filling the spaces between each optical fiber at the end of the bundled fiber with the glass, and fixing the end of the bundled fiber with the glass.

[0010] According to the bundle fiber or bundle fiber fixing method of the present invention, when light with a wavelength range of 350 nm to 500 nm is incident on the optical fiber, heating and melting of the glass can be prevented. Therefore, movement of each optical fiber at the end of the bundle fiber, or lead deposition in the glass, can be prevented.

[0011] This is an explanatory diagram showing the fixing state of a bundle fiber end composed of seven optical fibers according to the first embodiment of the present invention. This is an explanatory diagram showing the fixing state of a bundle fiber end composed of twelve optical fibers according to the second embodiment of the present invention. This is a side view showing the structure of the bundle fiber in Figure 1. This is an image showing the fixing state of a bundle fiber end according to an embodiment of the present invention.

[0012] The first feature of this embodiment is that glass is filled between each optical fiber at the end of a bundle fiber composed of multiple optical fibers, fixing the bundle fiber end with glass, the bundle fiber is optically coupled to a light source in the wavelength range of 350 nm to 500 nm, the glass contains at least phosphoric acid but does not contain lead, has an optical transmittance of 95% or more for light in the wavelength range of 350 nm to 500 nm, and prevents the glass from heating up when light in the wavelength range of 350 nm to 500 nm is incident on the optical fiber.

[0013] The second feature is that the bundle fiber is constructed using multiple optical fibers, and the method of fixing the bundle fiber involves heating and melting glass that contains at least phosphoric acid but does not contain lead, and has an optical transmittance of 95% or more for light in the wavelength range of 350 nm to 500 nm, filling the spaces between each optical fiber at the end of the bundle fiber with the glass.

[0014] These bundled fibers or methods for fixing bundled fibers allow the light transmittance of the glass to be set to 95% or higher for light in the wavelength range of 350 nm to 500 nm, which has a high energy density. This prevents the glass from overheating and melting when light in the wavelength range of 350 nm to 500 nm is incident on the optical fiber. As a result, movement of each optical fiber at the end of the bundled fiber, or lead deposition in the glass, is prevented.

[0015] A third characteristic is that the difference in thermal expansion coefficients between the optical fiber and glass is 7.8 × 10⁻⁶. -6 This refers to a method for fixing bundled fibers at a temperature of ( / °C) or lower.

[0016] This method of securing bundled fibers prevents cracks from forming in the glass when it is secured between each optical fiber.

[0017] Hereinafter, a bundle fiber according to an embodiment of the present invention will be described with reference to Figures 1 to 3. The bundle fiber 1 according to the present invention is composed of a plurality of optical fibers 2. The number of optical fibers 2 can be set to any number of two or more, with seven in the first embodiment shown in Figure 1 and twelve in the second embodiment shown in Figure 2, and each optical fiber 2 is bundled together to form one bundle fiber 1.

[0018] A portion of the bundled fiber 1 is bundled and held in place by a cylindrical holding component 4. Furthermore, molten glass 3 is filled between each optical fiber 2 for a fiber axial length of 1 mm from the end of each optical fiber 2, as shown by the hatching in Figures 1 to 3. The ends of the bundled fiber 1 are fixed in place by this glass 3.

[0019] The optical fiber 2 is composed of a core and a cladding having a refractive index lower than that of the core, surrounding the core. The mode is not limited. Each optical fiber 2 has its coating stripped off and its outer diameter is set to any dimension of 1 mm, i.e., 1000 μm or less. The optical fiber 2 is made of quartz glass, with a glass transition temperature of 1000 °C or higher, a softening point of approximately 1600 °C or higher, and a thermal expansion coefficient of 0.5 × 10⁻⁶ -6 It is ( / °C).

[0020] The glass 3 that secures the ends of the bundle fiber 1 contains at least phosphoric acid (H3PO4) but does not contain lead (Pb), and has a bending point of 400°C or higher and less than 1000°C. It may also contain phosphorus (P), zinc (Zn), potassium (K), aluminum (Al), and silica (SiO2) as needed. Furthermore, the thermal expansion coefficient of the glass 3 is 0.5 × 10⁻⁶. -6 ( / ℃) or higher 8.3 × 10 -6 It is below ( / °C). The heating temperature of glass 3 is within a temperature range that is above the bending point of glass 3 and below the glass transition temperature of optical fiber 2.

[0021] When such glass 3 is heated, it melts and fills the space between each fiber 2 from the end along the fiber axial length by 1 mm, fixing each fiber 2 with the glass 3, thus forming a bundle fiber 1.

[0022] A portion of each optical fiber 2, excluding the portion with an axial length of 1 mm from the end, is bundled and held by a retaining component 4 along the circumferential direction of each optical fiber 2. Examples of retaining components 4 include cylindrical parts such as ferrules, pipes, or sleeves. The retaining component 4 only needs to have a circular inner circumference. Furthermore, the entire component is formed into a cylindrical shape by integral molding or assembly. The material of the retaining component 4 can be arbitrarily selected, but in this embodiment, examples include zirconia, stainless steel (SUS: Steel Special Use Stainless), and glass.

[0023] The bundle fiber 1 formed in this manner is optically coupled to a light source (not shown). The wavelength range of the light incident on each optical fiber 2 from the light source is between 350 nm and 500 nm, within the wavelength range from ultraviolet A (UVA) to blue light.

[0024] The light energy E of the light incident from the light source into the bundle fiber 1 is expressed by the following equation 1.

[0025]

[0026] As shown in equation 1, the shorter the wavelength λ (m) of light, the stronger the light energy E becomes. The wavelength range from 350 nm to 500 nm is a relatively short wavelength range within the overall wavelength range of light, so the light energy E is strong in this range. In this embodiment and this embodiment, the overall wavelength range of light is considered to be from 315 nm to 830 nm, and the explanation continues below. Note that E: light energy (J), h: Planck constant (6.62607 × 10⁻¹⁰). -34 (Js)), ν: frequency (Hz), c: speed of light in a vacuum (2.99792458 × 10⁻¹⁸) 8 (m / s), λ: wavelength (m) of light (electromagnetic wave) in a vacuum.

[0027] Based on the applicant's investigation, it was found that lead precipitation occurred due to the melting of the glass. Therefore, the causal relationship between the presence of lead and the melting of the glass was first investigated. It was then confirmed that by first making the glass lead-free, lead precipitation in the glass was prevented when light in the wavelength range of 350 nm to 500 nm was incident from the light source into the optical fiber 2.

[0028] However, further investigations by the applicant revealed that simply removing lead from the glass's composition is insufficient. When light with a wavelength range of 350 nm to 500 nm is incident from the light source into the optical fiber 2 after the glass has been fixed, the glass generates heat, which causes it to melt.

[0029] As a result of further investigation into the causes of heat generation and melting of glass, the applicant found that, assuming the glass is lead-free, the inclusion of phosphoric acid can prevent heat generation and melting of the glass. Specifically, the applicant found that the light transmittance of the glass changes due to the inclusion of phosphoric acid.

[0030] Furthermore, it was found that by setting the threshold for light transmittance at which heating and melting of the glass are prevented when light in the wavelength range of 350 nm to 500 nm, where the light energy E is relatively high, is incident on the optical fiber 2, heating and melting of the glass can be prevented even when such light is incident. Therefore, in the present invention, the light transmittance of the glass 3 for light in the wavelength range of 350 nm to 500 nm is set to 95% or higher.

[0031] Next, the method for fixing the bundle fiber 1 will be explained. First, multiple and arbitrary numbers of optical fibers 2 are prepared as optical fibers constituting the bundle fiber 1. Meanwhile, as described above, glass 3 is also prepared, which contains at least phosphoric acid but does not contain lead, has a bending point of 400°C or higher and less than 1000°C, and has an optical transmittance of 95% or higher for light in the wavelength range of 350 nm or higher and 500 nm or lower.

[0032] The immersion of the glass 3 between each pair of optical fibers 2 can be achieved by placing the glass 3 before melting in advance at the ends of the optical fibers 2 and melting and immersing it by heating, or by preparing the glass 3 melted by heating in a melt tank and immersing the ends of each optical fiber 2 with a fiber axial length of 1 (mm).

[0033] By any of the above methods, the melted glass 3 is filled between each pair of optical fibers 2 at the end of the bundle fiber 1. After filling, the bundle fiber 1 is cooled to fix the end of the bundle fiber 1 with the glass 3.

[0034] For the heating and melting of the glass 3, any heating method such as heating by laser irradiation, heating by a heater, heating by discharge, or heating by a lamp can be selected.

[0035] The bundle fiber 1 with the fixed end by the above process is optically coupled to a light source in a wavelength range of 350 (nm) or more and 500 (nm) or less.

[0036] According to the bundle fiber 1 with the above structure or the fixing method of the bundle fiber 1, since the light transmittance of the glass 3 for light in the wavelength range of 350 (nm) or more and 500 (nm) or less with a high energy density is 95 (%) or more, it is possible to prevent the heat generation and melting of the glass 3 when light in the wavelength range of 350 (nm) or more and 500 (nm) or less enters the optical fiber 2. As a result, the movement of each optical fiber 2 at the end of the bundle fiber 1 or the precipitation of lead in the glass 3 is prevented.

[0037] The content of phosphoric acid for obtaining the above effect is 40 to 45 (mol%).

[0038] Further, the difference in the coefficient of thermal expansion between the optical fiber 2 and the glass 3 is preferably set to 7.8×10 -6 ( / °C) or less. The reason is that when the glass 3 is fixed between each pair of optical fibers 2, crack generation in the glass 3 is prevented. When the difference in the coefficient of thermal expansion exceeds 7.8×10 -6 ( / °C), it has been confirmed by the applicant's study that cracks occur in the glass 3 having a composition containing phosphoric acid and not containing lead during fixing.

[0039] Examples according to the present invention will be described below, but the present invention is not limited only to the following examples. Descriptions overlapping with the above embodiments will be omitted or simplified.

[0040] As shown in FIG. 4, a bundle fiber according to this example was constituted by seven optical fibers. Each optical fiber was bundled and held by an integrally formed cylindrical zirconia ferrule as a holding component. The inner diameter of the ferrule is 377 (μm).

[0041] Furthermore, from the end of each optical fiber, glass melted as shown in FIG. 4 was filled between the optical fibers having a fiber axial direction length of 1 (mm), and the end of the bundle fiber was fixed with the glass.

[0042] Each optical fiber constituting the bundle fiber is a step index (SI: Step Index) type fiber, the coating is stripped, the core diameter is 105 (μm), the cladding diameter is 125 (μm), and the thermal expansion coefficient is 0.5×10 -6 ( / °C).

[0043] The glass contains phosphoric acid (H3PO4) and does not contain lead (Pb), and further contains phosphorus (P), zinc (Zn), potassium (K), aluminum (Al), and silica (SiO2). The content of phosphoric acid is 40 to 45 (mol%), the yield point is 450 to 505 (°C), the thermal expansion coefficient is 5.6×10 -6 to 8.3×10 -6 ( / °C), and the heating temperature is 500 to 800 (°C).

[0044] Such glass was disposed at the end of the optical fiber, heated by laser irradiation, immersed between the optical fibers, and the end of the bundle fiber was fixed with the glass.

[0045] The difference in thermal expansion coefficient between each optical fiber and the glass was set to 7.8×10 -6 ( / °C) or less.

[0046] After fixing each optical fiber with glass, a lightfastness test was performed on the optical fibers of the bundle fiber by continuously irradiating them with light of wavelength 405 nm and output power of 10 W from a light source for 2000 hours. The light transmittance of the glass for 405 nm light was 99%.

[0047] As a result, it was confirmed that no melting or deterioration occurred in the glass even after 2000 hours.

[0048] Furthermore, the difference in thermal expansion coefficients between the optical fiber and glass is 7.8 × 10⁻⁶ -6 By setting the temperature to ( / °C) or lower, it was confirmed that cracks in the glass were prevented when the glass bonded between each optical fiber.

[0049] 1. Bundle fiber 2. Optical fiber 3. Glass 4. Retaining component

Claims

1. A bundle fiber comprising multiple optical fibers, wherein glass is filled between each optical fiber at the end of the bundle fiber, and the bundle fiber end is fixed with glass; the bundle fiber is optically coupled to a light source in the wavelength range of 350 nm to 500 nm; the glass contains at least phosphoric acid but does not contain lead, and has an optical transmittance of 95% or more for light in the wavelength range of 350 nm to 500 nm; and the bundle fiber prevents heat generation of the glass when light in the wavelength range of 350 nm to 500 nm is incident on the optical fiber.

2. A method for fixing bundled fibers, comprising: forming a bundled fiber with multiple optical fibers; melting glass containing at least phosphoric acid but no lead, and having an optical transmittance of 95% or more for light in the wavelength range of 350 nm to 500 nm by heating; filling the spaces between each optical fiber at the end of the bundled fiber with the glass; and fixing the end of the bundled fiber with glass.

3. The difference in thermal expansion coefficients between the optical fiber and the glass is 7.8 × 10 -6 The method for fixing bundle fibers according to claim 2, wherein the temperature is less than or equal to ( / °C).

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