JP2009223258A - Self-forming optical waveguide manufacturing method, and optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cure photo-curing resin so as to not cause bias of stress, and to form a clad in a self-forming optical waveguide manufacturing method. <P>SOLUTION: Light from an optical fiber 11 is made incident into a core 17 self-formed by curing a first photo-curing resin 13, and the clad 20 is formed by curing a second photo-curing resin 18 around the core 17 by leaking light from the core 17. To increase light intensity of the leaking light, a condensing lens 19 with NA larger than the numerical aperture of the optical fiber 11 is used when making light from a blue semiconductor laser 14 incident in the optical fiber 11. Since the second photo-curing resin 18 is symmetrically cured around the core 17, the bias of stress around the core 17 is prevented. As a result, loss of the optical waveguide is reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a manufacturing method of a self-forming optical waveguide, and more particularly to a manufacturing method in which no stress bias occurs in a clad.

  In recent years, a self-forming optical waveguide technique for forming an optical waveguide using a photocurable resin has been developed. This is a technique for filling the inside of a housing with a photocurable resin and irradiating light through an optical fiber to cure the photocurable resin in a linear shape to form the core of the optical waveguide. As a method for forming a clad in the self-forming optical waveguide technique, for example, the method of Patent Document 1 is known.

  The cladding forming method disclosed in Patent Document 1 is as follows. First, a low-refractive-index first photocurable resin having a different curing wavelength and a high-refractive-index second photocurable resin are mixed and filled into a casing. Next, the first photo-curing resin is cured, and the second photo-curing resin is irradiated with light having a wavelength not to be cured through the optical fiber, so that the second photo-curing resin is taken in. A core is formed by curing one photo-curing resin into a shaft. Then, light irradiation is continued after the core is formed, and the first photo-curable resin is cured by light leakage due to light leaking from the core, thereby forming a clad around the core. Thereafter, ultraviolet light is irradiated from the direction perpendicular to the axial direction of the core to cure all uncured resin.

Other clad formation methods include removing the uncured photocurable resin after forming the core and replacing it with a photocurable resin for clad formation, and irradiating ultraviolet rays from the direction perpendicular to the axial direction of the core. A method of curing is known.
JP 2004-151160 A

  In general, photocurable resins, particularly acrylic photocurable resins, are accompanied by volume shrinkage during curing. For this reason, when the clad is formed by curing the photocurable resin, stress shrinkage occurs due to shrinkage of the clad or deformation of the casing due to volume shrinkage, and stress is biased around the core. As a result, optical loss increased and durability deteriorated.

  Further, in the method of Patent Document 1, the clad diameter cannot be increased because the clad is formed by hardening by light leakage due to bleeding.

  Therefore, an object of the present invention is to form a clad so that stress is not biased around the core in the method of manufacturing a self-forming optical waveguide.

  1st invention fills the inside of a housing | casing with 1st photocurable resin, and irradiates light through an optical fiber, the 1st photocurable resin is hardened to axial shape, and optical waveguide A second step of forming the core, a third step of removing the uncured first photocurable resin in the housing and filling it with the second photocurable resin, and allowing light to enter the core via the optical fiber, And a fourth step of forming a clad by curing the second photo-curing resin around the core by light leakage from the core, and a method for producing a self-forming optical waveguide.

  Light leakage from the core is light scattered by the core or light that is transmitted without being totally reflected at the interface between the core and the clad.

  A second invention is a method for producing a self-forming optical waveguide according to the first invention, wherein the second photocurable resin is more reactive than the first photocurable resin.

  According to a third invention, in the first invention or the second invention, the fourth step includes a step of condensing light by a condensing lens and causing the light to enter an optical fiber, and the aperture of the condensing lens The number is a method of manufacturing a self-forming optical waveguide characterized in that the number is larger than the numerical aperture of the optical fiber.

  According to a fourth invention, in the first to third inventions, the first photocurable resin and the second photocurable resin are cured by light having the same wavelength. It is a manufacturing method.

  In a fifth aspect based on the first aspect through the fourth aspect, the fourth step is to form a clad by curing the second photocurable resin so that the clad diameter is twice or more the core diameter. This is a method for manufacturing a self-forming optical waveguide.

  According to a sixth aspect of the invention, in the fifth aspect of the invention, in the fourth step, the second photocurable resin is cured to form a clad so that the clad diameter is 10 times or more the core diameter. This is a method of manufacturing a formed optical waveguide.

  A seventh invention is an optical waveguide composed of an axial core and a clad covering the core. The core and the clad are made of a cured product of a photocurable resin, and the clad diameter is twice or more the core diameter. The optical waveguide is characterized in that there is no stress bias in the clad.

  According to the first invention, the second photocurable resin is cured in contrast to the core. For this reason, stress unevenness around the core is eliminated, and stress concentration can be prevented from occurring. As a result, optical loss can be reduced and the durability of the optical waveguide is improved.

  Moreover, like 2nd invention, by making the reactivity of 2nd photocurable resin high, hardening of 2nd photocurable resin can fully be advanced also by light leakage with comparatively weak light intensity. .

  Further, according to the third invention, the light intensity of light leakage from the core can be increased, so that the second photocurable resin can be cured more easily.

  Further, as in the fourth invention, the core and the clad can be formed with light of the same wavelength, and the manufacturing process can be simplified.

  Further, if the clad is formed by curing the range of more than twice the core diameter as in the fifth invention, more preferably more than 10 times as in the sixth invention, there is no range of stress unevenness. It becomes wider and light loss can be further reduced.

  The optical waveguide according to the seventh aspect of the invention has little optical loss and high durability because there is no stress bias in the clad.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to these examples.

  FIG. 1 is a diagram illustrating the manufacturing process of the self-forming optical waveguide according to the first embodiment. Hereinafter, the manufacturing process of the self-formed optical waveguide will be described in detail with reference to FIG.

  First, a rectangular parallelepiped casing 10 made of methyl methacrylate resin (PMMA) and having an optical port and a hollow portion 10a is prepared. And the connector 12 of the optical cable using the optical fiber 11 is inserted in the optical port of the housing | casing 10, and it fixes so that the edge part of the optical fiber 11 may become the hollow part 10a side of the housing | casing 10 (FIG. 1A). The optical fiber 11 has a diameter of 200 μm and an NA (numerical aperture) of 0.37. Further, the housing 10 is provided with a through hole 10b penetrating from the optical port side to the hollow portion 10a side. Thereby, the light from the optical fiber 11 is directly irradiated to the hollow portion 10 a side without passing through the housing 10. The diameter of the through hole 10b is substantially the same as the ferrule diameter at the tip of the connector 12.

  Next, the hollow portion 10a is filled with the first photocurable resin 13 for core formation (FIG. 1B). The main component of the first photocurable resin 13 is an aromatic acrylate, and a photopolymerization initiator having an absorption edge near the purple wavelength is mixed. The first photocurable resin 13 is a resin whose refractive index increases by curing. In addition, since the 1st photocurable resin 13 has viscosity, the 1st photocurable resin 13 does not leak from the through-hole 10b.

  Next, after the beam diameter of the light from the blue semiconductor laser 14 is expanded by the beam expander 15, the light is condensed by the condenser lens 16 having an NA of 0.1 and is incident on the optical fiber 11. The emission wavelength of the blue semiconductor laser 14 is 408 nm. Then, the first photocurable resin 13 in the housing 10 is irradiated through the optical fiber 11. Since the refractive index of the first photocurable resin 13 is increased by curing, the first photocurable resin 13 is cured in an axial shape by this light irradiation, and the core 17 of the optical waveguide is formed (FIG. 1C). . The light irradiation intensity is 5 mW, and a core 17 having a length of about 1 cm and a diameter of about 0.2 mm is formed by irradiation for 10 seconds.

  Next, the uncured first photocurable resin 13 in the housing 10 was removed, and the hollow portion 10a was filled with a second photocurable resin 18 for forming a clad (FIG. 1D). The main component of the second photocurable resin 18 is an aliphatic acrylate, and a photopolymerization initiator whose absorption edge is near the blue wavelength is mixed. Further, as the second photocurable resin 18, a resin having a refractive index after curing lower than the refractive index after curing of the first photocurable resin is used. The reason why the first photocurable resin 13 for core formation is replaced with the second photocurable resin 18 for clad formation is to increase the refractive index difference between the core and the clad. Is required to make a multimode optical waveguide.

  Next, after the beam diameter of the light from the blue semiconductor laser 14 is expanded by the beam expander 15, the light is condensed by a condensing lens 19 (corresponding to the condensing lens of the present invention) having an NA of 0.55, and an optical fiber. 11 is incident. Then, light is incident on the core 17 through the optical fiber 11. Since the NA of the condensing lens 19 is larger than the NA of the optical fiber 11, the light transmitted to the outside of the core 17 without being totally reflected due to the NA mismatch increases. Further, in the manufacturing process in FIG. 1C, the core 17 is not sufficiently cured, and there is a density fluctuation in the core 17. Therefore, part of the light is scattered and emitted to the outside of the core 17. Due to light leakage from the core 17 due to NA mismatching and scattering, the second photocurable resin 18 around the core 17 is cured, and a clad 20 is formed so as to cover the core 17 (FIG. 1E). The incident intensity of light on the core 17 is 15 mW, and the clad 20 having a diameter of 3 mm (about 15 times the core diameter) is formed by irradiation for 5 minutes. Further, the core 17 is sufficiently cured by light irradiation inside the core 17. The refractive index difference between the core 17 and the clad 20 formed as described above is about 0.05.

  Here, since the second photocurable resin 18 is cured symmetrically over a range of 10 times or more the core diameter with the core 17 as the center, no distortion occurs and no stress is biased around the core 17.

  Thus, since the clad 20 is formed by curing the second photocurable resin 18 by light leakage from the core 17, the second photocurable resin 18 may be more reactive than the first photocurable resin. desirable. The difference in reactivity can be adjusted depending on the type of photopolymerization initiator to be mixed. Further, by adjusting the reactivity in this way, the clad can be efficiently formed even when the core 17 and the clad 20 are formed by curing with light of the same wavelength.

  The clad 20 is desirably formed so that the clad diameter is twice or more the core diameter. This is because the range without stress bias becomes wider. It is more desirable if the cladding diameter is 10 times or more the core diameter.

  Next, ultraviolet rays are irradiated by an ultraviolet irradiation lamp for 30 seconds to completely cure the gel-like or uncured second photocurable resin 18 (FIG. 1F).

  The above is the manufacturing process of the self-forming optical waveguide of Example 1.

  In order to investigate the state of stress in the cross section of the optical waveguide produced by the above manufacturing process, the measurement of isochromatic lines and the measurement of isoclinic lines were performed using a photoelastic microscope.

  FIG. 2 is an image showing the result of the color matching line measurement in a cross section perpendicular to the axial direction of the optical waveguide core. 2A is a sample of an optical waveguide manufactured by the manufacturing method of the conventional example, and FIG. 2B is a sample of the optical waveguide manufactured by the manufacturing method of the first embodiment. A rectangular dotted line in FIG. 2 indicates that the inside of the rectangle is the inside of the housing 10. Here, in the manufacturing method of the conventional example, the cladding is not formed by light leakage from the core of FIG. 1E in the manufacturing method of Example 1, but ultraviolet rays are irradiated for 3 minutes from a direction perpendicular to the optical axis by an ultraviolet irradiation lamp, The optical waveguide is manufactured by curing the second photocurable resin 18 to form a clad. As shown in FIG. 2A, a clear bright and dark striped pattern can be observed in the measurement of the equal color line of the optical waveguide by the conventional manufacturing method. These stripes are formed by connecting points having the same main stress difference. In other words, stress deviation occurs in the optical waveguide produced by the conventional manufacturing method. On the other hand, as shown in FIG. 2B, in the color matching line measurement of the optical waveguide by the manufacturing method of Example 1, it can be seen that no striped pattern can be observed, and no noticeable stress bias has occurred.

  FIG. 3 is an image showing the results of isoclinic measurement in a cross section perpendicular to the axial direction of the optical waveguide core. As in FIG. 2, a portion surrounded by a rectangular dotted line is the inside of the housing 10. FIG. 3A shows a sample of an optical waveguide manufactured by the manufacturing method of the conventional example, and FIG. 3B shows a sample manufactured by the manufacturing method of Example 1. As shown in FIG. 3A, in the isotropic line measurement of the optical waveguide by the manufacturing method of the conventional example, it can be observed that a plurality of black lines run around the core. This black line indicates the direction of the main stress, and it can be seen that stress is applied in various directions from the periphery of the core. On the other hand, as shown in FIG. 3B, in the measurement of the isoclinic line of the optical waveguide by the manufacturing method of Example 1, it is understood that no black line is observed and no noticeable stress is generated.

  Further, the optical characteristics of the optical waveguide manufactured by the manufacturing method of Example 1 and the optical waveguide manufactured by the conventional manufacturing method were compared. The evaluation of optical characteristics was performed by measuring the insertion loss of the optical waveguide, the measurement wavelength was 780 nm, and the incident NA was 0.2. As a result, the insertion loss of the optical waveguide manufactured by the manufacturing method of Example 1 was 0.5 dB, whereas the insertion loss of the optical waveguide manufactured by the conventional manufacturing method was 10.8 dB. The reason why the optical waveguide produced by the manufacturing method of the conventional example has a larger loss is considered to be that the bending of the optical waveguide or the axial deviation between the optical fiber and the optical waveguide is caused by the stress.

  As described above, in the manufacturing method of the self-forming optical waveguide of Example 1, since the clad is formed by symmetrically curing the second photocurable resin by light leakage from the core, stress bias due to curing shrinkage is suppressed. Is done. Therefore, the loss of the optical waveguide can be reduced and the durability can be improved.

  In the first embodiment, the core and the clad are formed by curing with light having the same wavelength. However, the core and the clad may be cured using light having different wavelengths.

  Further, in Example 1, the second photocurable resin for forming the clad is made of one kind of resin, but may be a mixture of two or more kinds of resins.

  Moreover, in Example 1, the light collecting from the core is increased by using a condensing lens having a NA larger than that of the optical fiber as the condensing lens used when curing the second photocurable resin for forming the clad. However, it is not always necessary to use a condensing lens whose NA is larger than that of the optical fiber.

  The present invention can be used for manufacturing an optical module.

The figure shown about the manufacturing process of the self-formation copper waveguide of Example 1. FIG. The figure shown about the manufacturing process of the self-formation copper waveguide of Example 1. FIG. The figure shown about the manufacturing process of the self-formation copper waveguide of Example 1. FIG. The figure shown about the manufacturing process of the self-formation copper waveguide of Example 1. FIG. The figure shown about the manufacturing process of the self-formation copper waveguide of Example 1. FIG. The figure shown about the manufacturing process of the self-formation copper waveguide of Example 1. FIG. The image which shows the result of the color matching line measurement of an optical waveguide. The image which shows the result of the color matching line measurement of an optical waveguide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Housing | casing 11: Optical fiber 13: 1st photocurable resin 14: Blue semiconductor laser 15: Beam expander 16, 19: Condensing lens 17: Core 18: 2nd photocurable resin 20: Cladding

Claims (7)

A first step of filling the housing with a first photocurable resin;
A second step of forming the core of the optical waveguide by curing the first photocurable resin in an axial shape by irradiating light through an optical fiber;
A third step of removing the uncured first photocurable resin in the housing and filling with a second photocurable resin;
A fourth step in which light is incident on the core through the optical fiber, and the second photocurable resin around the core is cured by light leakage from the core to form a cladding;
A method for producing a self-forming optical waveguide, comprising:   The method of manufacturing a self-forming optical waveguide according to claim 1, wherein the second photocurable resin is more reactive than the first photocurable resin. The fourth step includes a step of condensing light by a condensing lens and causing the light to enter the optical fiber,
The method of manufacturing a self-forming optical waveguide according to claim 1, wherein the numerical aperture of the condensing lens is larger than the numerical aperture of the optical fiber.   4. The self-forming optical waveguide according to claim 1, wherein the first photocurable resin and the second photocurable resin are cured by light having the same wavelength. 5. Manufacturing method. 5. The method according to claim 1, wherein in the fourth step, the clad is formed by curing the second photocurable resin so that the clad diameter is twice or more the core diameter. The manufacturing method of the self-forming optical waveguide as described in the item.
  6. The self-forming optical waveguide according to claim 5, wherein in the fourth step, the clad is formed by curing the second photocurable resin so that the clad diameter is 10 times or more of the core diameter. Production method. In an optical waveguide composed of an axial core and a clad covering the core,
The core and the clad are made of a cured product of a photocurable resin,
The cladding diameter is more than twice the core diameter,
An optical waveguide characterized in that the clad has no stress bias.