Method for manufacturing optical coupling device

Abstract

A method for manufacturing an optical coupling device is provided, the method comprising: preparing two optical fibers (1, 2) arranged facing each other with their respective core axes positioned coaxially and with a photocurable resin (3) filled between the opposing end faces (1a, 2a); and forming a self-written optical waveguide connecting the cores of the two optical fibers (1, 2) by causing light to enter the photocurable resin (3) from one or both of the cores of the two optical fibers (1, 2) to cure the photocurable resin (3), wherein each of the end faces (1a, 2a) of the two optical fibers (1, 2) is an inclined surface inclined with respect to a direction orthogonal to the core axis direction, and wherein, where N_core denotes the refractive index of the cores of the two optical fibers (1, 2) with respect to the D-line, and N_resin denotes the refractive index of the photocurable resin (3), before curing, with respect to the D-line, N_resin satisfies formula 1. (Formula 1) N_core - 0.031 ≤ N_resin ≤ N_core + 0.031

Description

Method for manufacturing an optical coupling device Cross-reference of related applications

[0001] This application claims priority to Japanese Patent Application No. 2025-012935, filed on 29 January 2025, the entirety of which is incorporated herein by reference as particularly disclosed.

[0002] This invention relates to a method for manufacturing an optical coupling device.

[0003] In recent years, self-formed optical waveguides have attracted attention as a means of connecting two optical fibers (see, for example, Japanese Patent Publication No. 2007-178602 (the full description thereof is incorporated herein by reference as particularly disclosed)).

[0004] A self-forming optical waveguide can be formed by arranging two optical fibers opposite each other with their end faces facing each other, and curing a photocurable resin filled between the end faces with light incident from the core of the optical fibers. By forming a self-forming optical waveguide in this way, an optical coupling device can be fabricated in which two optical fibers are connected by the self-forming optical waveguide.

[0005] In optical coupling devices that connect optical fibers and self-forming optical waveguides, low insertion loss is desirable. This is because an optical coupling device with low insertion loss can suppress the loss of incident light within the optical coupling device.

[0006] In view of the foregoing, one aspect of the present invention aims to manufacture an optical coupling device with low insertion loss.

[0007] As a result of diligent research, the inventors have newly discovered that the following manufacturing method makes it possible to manufacture optical coupling devices with low insertion loss. Specifically, the inventors believe that with the following manufacturing method, the light emitted from the core of the optical fiber can travel straight through the photocurable resin without significantly bending in direction at the interface between the optical fiber and the photocurable resin, thereby suppressing the deviation between the optical axis direction of the formed self-formed optical waveguide and the core axis direction of the optical fiber. The inventors surmise that this contributes to the reduction of insertion loss.

[0008] One aspect of the present invention is as follows: [1] Prepare two optical fibers arranged opposite each other with their core axes coaxially located and a photocurable resin filled between their opposing end faces, and form a self-forming optical waveguide connecting the cores of the two optical fibers by injecting light into the photocurable resin from one or both of the cores of the two optical fibers and curing the photocurable resin, wherein the end faces of each of the two optical fibers are inclined surfaces tilted in a direction perpendicular to the core axis direction, and the refractive index of the cores of the two optical fibers with respect to the D line is N コア The refractive index of the above photocurable resin with respect to the D line before curing is set to N 樹脂 As N 樹脂 A method for manufacturing an optical coupling device that satisfies the following formula 1. (Formula 1) N コア -0.031 ≤ N 樹脂 ≤N コア +0.031 [2] The method for manufacturing an optical coupling apparatus according to [1], wherein the inclination angle of the inclined surface is in the range of 5.0° to 30.0°, with the direction perpendicular to the core axis direction being 0°. [3] The method for manufacturing an optical coupling apparatus according to [1] or [2], wherein the optical fiber is a glass fiber.

[0009] According to one aspect of the present invention, an optical coupling device with low insertion loss can be manufactured.

[0010] Figures 1(a) and 1(b) are schematic cross-sectional views showing a state in which photocurable resin 3 is filled between the end faces of two optical fibers. Figures 2(a), 2(b), and 2(c) are explanatory diagrams of the inclination angle of the end faces of optical fibers. A stereomicroscope image is shown of a state in which a self-formed optical waveguide is formed between two optical fibers in Example 1-1 (inclination angle: 8.0°, end face arrangement: approximately parallel). A stereomicroscope image is shown of a state in which a self-formed optical waveguide is formed between two optical fibers in Example 2-1 (inclination angle: 27.0°, end face arrangement: approximately parallel). A stereomicroscope image is shown of an example of a state in which a self-formed optical waveguide is formed between two optical fibers whose end faces (inclination angle: 27.0°) are arranged approximately non-parallel.

[0011] One aspect of the present invention relates to a method for manufacturing an optical coupling device, which includes preparing two optical fibers that are coaxially positioned with respect to each other's core axes and are disposed opposite to each other with a photocurable resin filled between their opposing end faces, and forming a self-forming optical waveguide that connects the cores of the two optical fibers by causing light to enter the photocurable resin from one or both of the cores of the two optical fibers to cure the photocurable resin. In the method for manufacturing the optical coupling device, each of the end faces of the two optical fibers is an inclined surface inclined with respect to a direction orthogonal to the core axis direction, and the refractive index of the cores of the two optical fibers with respect to the D line is N コア is defined as such, and the refractive index of the photocurable resin with respect to the D line before curing is N 樹脂 is defined as such, and N 樹脂 satisfies the following formula 1. Each refractive index can be measured by a known method. (Formula 1) N コア −0.031 ≤ N 樹脂 ≤ N コア +0.031

[0012] Hereinafter, the method for manufacturing the optical coupling device will be described in more detail.

[0013] FIGS. 1(a) and (b) are schematic cross-sectional views showing a state in which a photocurable resin 3 is filled between the end faces of two optical fibers. In FIGS. 1(a) and (b), the optical fiber 1 and the optical fiber 2 are disposed opposite to each other with their core axes coaxially positioned and with a photocurable resin filled between their opposing end faces. Specifically, the tip portions including the end face 1a of the optical fiber 1 and the end face 2a of the optical fiber 2 are inserted into a container 4 filled with the photocurable resin 3. As the container 4, it is preferable to use a container (so-called transparent container) having a light transmittance such that the photocurable resin 3 can be photocured when light irradiation is performed on the photocurable resin 3 filled inside the container 4 from the outside of the container 4.

[0014] Figures 2(a), (b), and (c) are explanatory diagrams of the inclination angle of the end faces of optical fibers. In the above method for manufacturing an optical coupling device, the end faces of the two opposing optical fibers are inclined surfaces tilted with respect to a direction perpendicular to the core axis direction of the optical fiber. If the inclination angle of such an inclined surface is θ, then θ takes an angle in the range of greater than 0° and less than 90°. On the other hand, when θ is 0°, the end face of the optical fiber is not an inclined surface, but a surface parallel to the direction perpendicular to the core axis direction of the optical fiber. In the above method for manufacturing an optical coupling device, since the end faces of the two opposing optical fibers are inclined surfaces, the inclination angle θ of each end face is greater than 0°. Having inclined surfaces on the end faces of the two opposing optical fibers in an optical coupling device can contribute to improving the reflection attenuation characteristics of the optical coupling device. The inclination angle θ of each end face of the two optical fibers is greater than 0°, and from the viewpoint of improving the reflection attenuation characteristics of the optical coupling device, it is preferable to be 5.0° or more, and more preferably in the order of 5.5° or more, 6.0° or more, 6.5° or more, 7.0° or more, 7.5° or more, and 8.0° or more. On the other hand, from the viewpoint of ease of end-face processing of optical fibers, the inclination angle θ of each of the two optical fibers is preferably 30.0° or less, and more preferably in the order of 29.5° or less, 29.0° or less, 28.0° or less, 27.5° or less, and 27.0° or less. End-face processing of optical fibers can be performed using known processing equipment such as a crebe cutter.

[0015] In one embodiment, the inclination angle θ of the end faces of two opposing optical fibers is the same, and in another embodiment, it is a different angle. In the present invention and this specification, it is permissible for the inclination angle to be "the same" to have a difference of an error that can normally occur in end face processing (for example, a difference of about 0.5° or less). Specific embodiments of the opposing arrangement include an arrangement where the inclination directions of the inclined surfaces are different (referred to as "approximately non-parallel") as shown in Figure 1(a), and an arrangement where the inclination directions of the inclined surfaces are the same (referred to as "approximately parallel") as shown in Figure 1(b). The arrangement of the two optical fibers in the manufacturing method of the optical coupling device described above may be approximately non-parallel or approximately parallel.

[0016] As the optical fiber mentioned above, an optical fiber commonly used as an optical fiber in an optical coupling device can be used. A specific example is a glass fiber. Although not shown in Figures 1 and 2, the optical fiber includes at least a central core and a cladding surrounding the core, and may further have one or more layers (e.g., a protective layer) on the outside of the cladding. In the present invention and this specification, "glass fiber" means an optical fiber in which at least the core is made of glass. The core of the glass fiber may be, for example, quartz glass.

[0017] In the above method for manufacturing the optical coupling device, the refractive index N of the photocurable resin filled between the end faces of the two optical fibers 樹脂 The refractive index N of the optical fiber core. コア Between these two points, the following equation 1 is satisfied. Here, in the present invention and this specification, "refractive index" means the refractive index for the D line, and the measurement temperature is 25.0°C. The wavelength of the D line is 589 nm.

[0018] (Formula 1) N コア -0.031 ≤ N 樹脂 ≤N コア +0.031

[0019] After diligent research, the inventors determined that N 樹脂 is N コアWe have newly discovered that by using a combination of a photocurable resin and an optical fiber such that the refractive index is within the range of ±0.031 (i.e., satisfying Equation 1), it is possible to manufacture an optical coupling device with low insertion loss. Specifically, the inventors believe that by satisfying Equation 1, the light emitted from the core of the optical fiber can travel straight through the photocurable resin without significantly bending in direction at the interface between the optical fiber and the photocurable resin, thereby suppressing the deviation between the optical axis direction of the formed self-formed optical waveguide and the core axis direction of the optical fiber. Claim 4 of Japanese Patent Application Publication No. 2007-178602 specifies that the refractive index of the optical waveguide portion formed by curing the photocurable resin and the refractive index of the core of the optical transmission means are approximately equal. However, since the refractive index of the photocurable resin changes before and after curing, the provision of claim 4 of Japanese Patent Application Publication No. 2007-178602 does not suggest anything about the above-mentioned Equation 1 (provision regarding the refractive index of the photocurable resin before curing).

[0020] From the viewpoint of further reducing insertion loss, Equation 1 is preferably Equation 1-1 below, more preferably Equation 1-2 below, and even more preferably Equation 1-3 below. (Equation 1-1)N コア -0.025 ≤ N 樹脂 ≤N コア +0.025 (Formula 1-2) N コア -0.020 ≤ N 樹脂 ≤N コア +0.020 (Formula 1-3) N コア -0.015 ≤ N 樹脂 ≤N コア +0.015

[0021] The photocurable resin comprises a core-forming resin and a cladding resin for the self-forming optical waveguide. The core-forming resin polymerizes and hardens when light of a predetermined wavelength band is incident on it, resulting in a refractive index of na. The cladding resin polymerizes and hardens when light of the same or different wavelength band as the light incident on the core-forming resin, and with an intensity equal to or greater than that of the light incident on the core-forming resin, is incident on it. Furthermore, it is preferable that the refractive index mb of the hardened cladding resin satisfies "mb < na".

[0022] As the core-forming resin and the cladding-forming resin, resins can be selected that undergo photopolymerization through different polymerization reactions. In the examples described later, the core-forming resin is an acrylic resin, and the cladding-forming resin is an epoxy resin. In the combination of an acrylic resin and an epoxy resin, the acrylic resin has a faster polymerization reaction rate than the epoxy resin, so only the acrylic resin is selectively polymerized by low-intensity light.

[0023] Furthermore, in the present invention and this specification, "photocurable resin" refers to a composition that can form a polymer (homopolymer or copolymer) by photocuring treatment. Such a composition may, for example, be a composition comprising one or more polymerizable compounds and a photopolymerization initiator. For example, an acrylic resin and an epoxy resin may be a solution obtained by adding a photopolymerization initiator to a mixture containing two or more polymerizable compounds. Hereinafter, polymerizable compounds will also be referred to as "monomers." A polymerizable compound is a compound having a polymerizable group, and is not limited to monomers; oligomers and prepolymers are also included in polymerizable compounds.

[0024] In the above method for manufacturing the optical coupling device, light is incident on the photocurable resin from one or both of the cores of two opposing optical fibers. By incidenting light on the photocurable resin in this way, a self-forming optical waveguide core can be created within the photocurable resin. That is, the two opposing optical fibers can be connected by the self-formed core. The wavelength λw1 of the light incident on the photocurable resin can be arbitrarily set according to the composition of the photocurable resin, for example, according to the type of photopolymerization initiator. As an example, λw1 can be in the range of 365 nm to 1675 nm. In the embodiment described later, λw1 was set to 405 nm. It is preferable that the light incident on the photocurable resin from the core of the optical fiber is light of an intensity that allows polymerization of only the core-forming resin (for example, laser light).

[0025] Next, the self-formation of the clad of the self-forming optical waveguide will be described. After the self-formation of the core, monomer interdiffusion is generated in the resin for forming the clad in the photocurable resin around the core. In the core region, the monomers are consumed in the polymerization reaction, while in the photocurable resin outside the core, the monomers have not undergone the polymerization reaction and are uncured and unconsumed. Therefore, a concentration gradient of the monomers occurs around the core, and the interdiffusion proceeds. In the examples described later, the monomer interdiffusion was promoted by leaving it for 120 seconds after the formation of the core. Specifically, after the self-formation of the core, light with a wavelength λw2 is incident on the core through the core of the optical fiber. Preferably, light with an intensity equal to or higher than the intensity of the light that polymerizes the resin for forming the core is incident on the core, and more preferably, light with an intensity exceeding the intensity of the light that polymerizes the resin for forming the core is incident on the core. The intensity of the light is set to an intensity that can polymerize the resin for forming the clad. The light incident on the core propagates through the core and generates leakage light into the uncured resin for forming the clad around the core. As a result, the resin for forming the clad around the core is polymerized and cured by the leakage light, and the clad is self-formed in a form that surrounds the surface of the core.

[0026] The wavelength λw2 can be arbitrarily set according to the photoinitiator. As an example, λw2 can be in the range of 365 nm to 1675 nm. λw2 may be the same wavelength as λw1 or a different wavelength. In the examples described later, λw2 was set to 405 nm.

[0027] It is preferable that the refractive index nb of the clad self-formed after curing is less than the refractive index na of the core. Thus, an optical waveguide (self-forming optical waveguide) is formed by the core and the clad.

[0028] After the self-forming optical waveguide is formed as described above, it is preferable to remove the uncured photocurable resin around the clad by a known cleaning method.

[0029] Thus, a self-forming optical waveguide can be formed between two oppositely arranged optical fibers.

[0030] In one embodiment, the above manufacturing method allows only one pair (i.e., two) of optical fibers to be connected by a self-forming optical waveguide. In another embodiment, multiple pairs (i.e., n pairs) of optical fibers can be connected by self-forming optical waveguides by arranging n optical fibers (where n is an integer of 2 or more) on one side and n optical fibers on the other side, and connecting the optical fibers on one side with the optical fibers on the other side simultaneously or in any order.

[0031] The optical coupling device manufactured by the above manufacturing method can be used, for example, as an optical coupling device that performs optical branching and / or merging using optical fibers. A specific example of such an optical coupling device is an APC (Angled Physical Contact) connector.

[0032] The present invention will be further described below based on examples. However, the present invention is not limited to the embodiments shown in the examples.

[0033] In the following examples and comparative examples, a glass fiber with a synthetic silica glass core was used as the optical fiber. The refractive index of synthetic silica glass with respect to the D line (measurement temperature: 25.0°C) is 1.458. Therefore, the refractive index N of the core of the glass fiber with respect to the D line is コア It is 1.458.

[0034] The refractive index of the photocurable resins shown below with respect to the D line 樹脂 This value was measured using an Abbe refractometer (measurement temperature: 25.0°C).

[0035] The following is shown: 樹脂 -N コア The values ​​shown are all rounded to the fourth decimal place.

[0036] [Examples 1-1 to 1-5, Comparative Example 1-1 (Inclination Angle: 8.0°)] As optical fibers, optical fibers having an end face (inclined surface) with an inclination angle of 8.0° were prepared by processing the end face with a cleave cut machine. In each of Examples 1-1 to 1-5 and Comparative Example 1-1, refractive index N 樹脂A photocurable resin with the values ​​shown in Table 1 was filled into the container, and the tip portions including the end faces (inclined surfaces) of two optical fibers (inclined angle 8.0°) were inserted into this container. The end faces (inclined surfaces) of the two optical fibers were arranged to be approximately parallel, as shown in Figure 1(b). By injecting laser light (wavelength: λw1) into the photocurable resin from both cores of the two optical fibers, the core-forming resin in the photocurable resin was polymerized and cured to form the core of a self-formed optical waveguide. As an example, Figure 3 shows a stereomicroscope image of the state in which a self-formed optical waveguide was formed between the two optical fibers in Example 1-1. Note that here, light was injected into the photocurable resin from both cores of the two optical fibers (bidirectional injection), but light may also be injected from the core of either one of the optical fibers (unidirectional injection).

[0037] Table 1 shows the insertion loss measured for each of Examples 1-1 to 1-5 and Comparative Example 1-1, after introducing light (wavelength 1550 nm) from an optical fiber into the core of the self-formed optical waveguide with the core thus formed. Specifically, the insertion loss of the formed core was measured by using the insertion loss of the optical fiber used in the Examples and Comparative Examples at a wavelength of 1550 nm as a reference. Light at a wavelength of 1550 nm was projected from one optical fiber, and the light that entered the other optical fiber after passing through the core of the self-formed optical waveguide was received by an optical power meter.

[0038]

[0039] The target level of insertion loss was set to 1.20 dB or less, which is a practically desirable level, and N was used in Examples 1 to 5 and Comparative Example 1. 樹脂 When the value of was set to X and the insertion loss value to Y, a curve approximation was performed using a known fitting method, and the N at 1.20 dB was obtained from the resulting approximation formula. 樹脂 The value was 1.4889. 1.4889 and N コア Since the difference with (1.458) is 0.031, we determined the above equation 1.

[0040] [Examples 2-1 to 2-5, Comparative Example 2-1 (Inclination Angle: 27.0°)] In Example 2-1, the core formation and insertion loss of the self-formed optical waveguide were measured using the method described for Example 1-1, except that the inclination angle of the end face of the optical fiber was set to 27.0°. Similarly, in Examples 2-2 and beyond, the core formation and insertion loss of the self-formed optical waveguide were measured using the method described for the corresponding numbered example or comparative example, except that the inclination angle of the end face of the optical fiber was set to 27.0°. The measured values ​​of the insertion loss are shown in Table 2. As an example, Figure 4 shows a stereomicroscope image of the state in which a self-formed optical waveguide is formed between two optical fibers in Example 2-1.

[0041]

[0042] The results shown in Tables 1 and 2 confirm that when Equation 1 is satisfied, an optical coupling device with low insertion loss can be manufactured.

[0043] In Examples 2-1 to 2-5, the arrangement of the end faces of the two optical fibers was made substantially non-parallel, as shown in Figure 1(a). Except for this difference, the formation of a self-forming optical waveguide and measurement of the insertion loss were carried out in the same manner as described above. The insertion loss values ​​were approximately the same as those shown in Table 2, and were 1.20 dB or less. Figure 5 shows a stereomicroscope image of an example of a self-forming optical waveguide formed between two optical fibers whose end faces are arranged substantially non-parallel.

[0044] In each of Examples 1-1 to 1-5, the core of a self-forming optical waveguide was formed by the method described above. Subsequently, the cladding resin in the photocurable resin was polymerized and cured by irradiating the photocurable resin with laser light (wavelength: λw2) from both cores of the two optical fibers, thereby forming the cladding of the self-forming optical waveguide. The return loss of the self-forming optical waveguide with the core and cladding thus formed was measured by connecting one of the optical fibers connected by the self-forming optical waveguide to a back-referral meter and terminating the other optical fiber with an optical terminator. The measurement results are shown in Table 3.

[0045]

[0046] Regarding the reflection loss characteristics of the optical coupling device, a larger reflection loss value is preferable. For example, an optical coupling device with a reflection loss of 45 dB or more, as determined by the above method, is useful in various applications.

[0047] This invention is useful in various technological fields where optical coupling devices are used.

Claims

1. The process includes preparing two optical fibers arranged opposite each other with their core axes coaxial and a photocurable resin filled between their opposing end faces, and forming a self-forming optical waveguide connecting the cores of the two optical fibers by injecting light into the photocurable resin from one or both of the cores of the two optical fibers to cure the photocurable resin, wherein the end faces of each of the two optical fibers are inclined surfaces tilted in a direction perpendicular to the core axis direction, and the refractive index of the cores of the two optical fibers with respect to the D line is N コア The refractive index of the photocurable resin with respect to the D line before curing is set to N 樹脂 As N 樹脂 A method for manufacturing an optical coupling device that satisfies the following formula 1. (Formula 1) N コア -0.031 ≤ N 樹脂 ≤N コア +0.031 2. The method for manufacturing an optical coupling apparatus according to claim 1, wherein the inclination angle of the inclined surface is in the range of 5.0° to 30.0°, with the direction perpendicular to the core axis direction being 0°.

3. The method for manufacturing an optical coupling apparatus according to claim 1 or 2, wherein the optical fiber is a glass fiber.

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