CAPILLARY AND MANUFACTURING METHOD THEREFOR

Abstract

A capillary includes a capillary main body made of glass and formed in an elongated shape. The capillary main body includes an accommodating portion configured to accommodate a part of an optical fiber. The accommodating portion includes an opening portion, which is formed in a first end surface of the capillary main body and is configured to allow insertion of the optical fiber. The capillary main body includes a compressive stress layer, which is formed on an opening portion and is observable by a two-dimensional birefringence measurement method, a tensile stress layer, which is formed at a position away from the compressive stress layer toward a second end surface of the capillary main body and is observable by the two-dimensional birefringence measurement method and a stress-neutral layer, which is formed between the compressive stress layer and the tensile stress layer and is observable by the two-dimensional birefringence measurement method.

Claims

1. A capillary for holding an optical fiber, the capillary comprising a capillary main body being made of glass and formed in an elongated shape, wherein the capillary main body comprises: an accommodating portion configured to accommodate a part of an optical fiber, a first end surface formed at one end portion of the capillary main body in a longitudinal direction; and a second end surface formed at another end portion of the capillary main body in the longitudinal direction, wherein the accommodating portion comprises an opening portion, which is formed in the first end surface and is configured to allow insertion of the optical fiber, and wherein the capillary main body comprises: a compressive stress layer, which is formed on the opening portion and is observable by a two-dimensional birefringence measurement method; a tensile stress layer, which is formed at a position away from the compressive stress layer toward the second end surface and is observable by the two-dimensional birefringence measurement method; and a stress-neutral layer, which is formed between the compressive stress layer and the tensile stress layer and is observable by the two-dimensional birefringence measurement method.

2. A capillary for holding an optical fiber, the capillary comprising a capillary main body being made of glass and formed in an elongated shape, wherein the capillary main body comprises: an accommodating portion configured to accommodate a part of an optical fiber, a first end surface formed at one end portion of the capillary main body in a longitudinal direction; and a second end surface formed at another end portion of the capillary main body in the longitudinal direction, wherein the accommodating portion comprises an opening portion, which is formed in the first end surface and is configured to allow insertion of the optical fiber, and wherein the capillary main body comprises: a compressive stress layer, which is formed on the opening portion and is observable by a two-dimensional birefringence measurement method; and a tensile stress layer, which is formed at a position away from the compressive stress layer toward the second end surface and is observable by the two-dimensional birefringence measurement method, and wherein a length of the compressive stress layer in the longitudinal direction of the capillary main body is longer than a length of the tensile stress layer in the longitudinal direction of the capillary main body.

3. A capillary for holding an optical fiber, the capillary comprising a capillary main body being made of glass and formed in an elongated shape, wherein the capillary main body comprises: an accommodating portion configured to accommodate a part of an optical fiber, a first end surface formed at one end portion of the capillary main body in a longitudinal direction; and a second end surface formed at another end portion of the capillary main body in the longitudinal direction, wherein the accommodating portion comprises an opening portion, which is formed in the first end surface and is configured to allow insertion of the optical fiber, and wherein the capillary main body comprises: a compressive stress layer, which is formed on the opening portion and is observable by a two-dimensional birefringence measurement method; and a tensile stress layer, which is formed at a position away from the compressive stress layer toward the second end surface and is observable by the two-dimensional birefringence measurement method, and wherein the tensile stress layer extends in the longitudinal direction from a position 0.1 mm or more away from the first end surface.

4. The capillary according to claim 1, wherein a maximum value of a tensile stress in the tensile stress layer, which is measured by the two-dimensional birefringence measurement method, is 20 MPa or smaller.

5. The capillary according to claim 1, wherein a length of the stress-neutral layer in the longitudinal direction of the capillary main body is 0.01 mm or longer.

6. The capillary according to claim 1, wherein the opening portion has an inner wall surface formed in a tapered shape.

7. The capillary according to claim 1, wherein the opening portion is filled with an adhesive.

8. A method of manufacturing a capillary for holding an optical fiber, the capillary comprising a capillary main body being made of glass and formed in an elongated shape, the capillary main body comprising: an accommodating portion configured to accommodate a part of an optical fiber, a first end surface formed at one end portion of the capillary main body in a longitudinal direction; and a second end surface formed at another end portion of the capillary main body in the longitudinal direction, the accommodating portion comprising an opening portion, which is formed in the first end surface and is configured to allow insertion of the optical fiber, the method comprising: a preparation step of preparing the capillary main body; and a heating step of heating the first end surface and the opening portion of the capillary main body, wherein, in the heating step, the first end surface and the opening portion are irradiated with a laser beam having a beam diameter larger than the first end surface, and wherein, in the heating step, the first end surface and the opening portion are heated to form a compressive stress layer observable by a two-dimensional birefringence measurement method on the opening portion, a tensile stress layer observable by the two-dimensional birefringence measurement method at a position away from the compressive stress layer toward the second end surface, and a stress-neutral layer observable by the two-dimensional birefringence measurement method between the compressive stress layer and the tensile stress layer.

9. A method of manufacturing a capillary for holding an optical fiber, the capillary comprising a capillary main body being made of glass and formed in an elongated shape, the capillary main body comprising: an accommodating portion configured to accommodate a part of an optical fiber, a first end surface formed at one end portion of the capillary main body in a longitudinal direction; and a second end surface formed at another end portion of the capillary main body in the longitudinal direction, the accommodating portion comprising an opening portion, which is formed in the first end surface and is configured to allow insertion of the optical fiber, the method comprising: a preparation step of preparing the capillary main body; and a heating step of heating the first end surface and the opening portion of the capillary main body, wherein, in the heating step, the first end surface and the opening portion are irradiated with a laser beam having a beam diameter larger than the first end surface, wherein, in the heating step, the first end surface and the opening portion are heated to form a compressive stress layer observable by a two-dimensional birefringence measurement method on the opening portion and a tensile stress layer observable by the two-dimensional birefringence measurement method at a position away from the compressive stress layer toward the second end surface, and wherein a length of the compressive stress layer in the longitudinal direction of the capillary main body is longer than a length of the tensile stress layer in the longitudinal direction of the capillary main body.

10. A method of manufacturing a capillary for holding an optical fiber, the capillary comprising a capillary main body being made of glass and formed in an elongated shape, the capillary main body comprising: an accommodating portion configured to accommodate a part of an optical fiber, a first end surface formed at one end portion of the capillary main body in a longitudinal direction; and a second end surface formed at another end portion of the capillary main body in the longitudinal direction, the accommodating portion comprising an opening portion, which is formed in the first end surface and is configured to allow insertion of the optical fiber, the method comprising: a preparation step of preparing the capillary main body; and a heating step of heating the first end surface and the opening portion of the capillary main body, wherein, in the heating step, the first end surface and the opening portion are irradiated with a laser beam having a beam diameter larger than the first end surface, and wherein, in the heating step, the first end surface and the opening portion are heated to form a compressive stress layer observable by a two-dimensional birefringence measurement method on the opening portion, a tensile stress layer observable by the two-dimensional birefringence measurement method at a position away from the compressive stress layer toward the second end surface, and wherein the tensile stress layer extends in the longitudinal direction from a position 0.1 mm or more away from the first end surface.

11. The method of manufacturing a capillary according to claim 8, comprising a cooling step of cooling the first end surface and the opening portion at a cooling rate of 100 C./second or lower.

12. The method of manufacturing a capillary according to claim 8, wherein the laser beam is a CO.sub.2 laser beam.

13. The capillary according to claim 2, wherein a maximum value of a tensile stress in the tensile stress layer, which is measured by the two-dimensional birefringence measurement method, is 20 MPa or smaller.

14. The capillary according to claim 2, wherein the opening portion has an inner wall surface formed in a tapered shape.

15. The capillary according to claim 2, wherein the opening portion is filled with an adhesive.

16. The capillary according to claim 3, wherein a maximum value of a tensile stress in the tensile stress layer, which is measured by the two-dimensional birefringence measurement method, is 20 MPa or smaller.

17. The capillary according to claim 3, wherein the opening portion has an inner wall surface formed in a tapered shape.

18. The capillary according to claim 3, wherein the opening portion is filled with an adhesive.

19. The method of manufacturing a capillary according to claim 9, comprising a cooling step of cooling the first end surface and the opening portion at a cooling rate of 100 C./second or lower.

20. The method of manufacturing a capillary according to claim 9, wherein the laser beam is a CO.sub.2 laser beam.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is a sectional view of an optical device.

[0032] FIG. 2 is a sectional view of a first capillary.

[0033] FIG. 3 is a sectional view of a second capillary.

[0034] FIG. 4 is a sectional view for illustrating a capillary main body.

[0035] FIG. 5 is a sectional view of an end portion of the capillary main body.

[0036] FIG. 6 is a side view for illustrating a device for measuring a stress in the capillary main body.

[0037] FIG. 7 is a flowchart for illustrating a method of manufacturing a capillary.

[0038] FIG. 8 is a flowchart for illustrating a preparation step of the method of manufacturing a capillary.

[0039] FIG. 9 is a sectional view for illustrating a processing step of the method of manufacturing a capillary.

[0040] FIG. 10 is a sectional view for illustrating the processing step of the method of manufacturing a capillary.

[0041] FIG. 11 is a side view for illustrating a heating step of the method of manufacturing a capillary.

[0042] FIG. 12 is a plan view as viewed in the direction indicated by the arrows of the line XII-XII of FIG. 11.

[0043] FIG. 13 is a plan view for illustrating a heating method for a capillary main body according to Comparative Example.

[0044] FIG. 14 is a stress state image of a capillary main body according to Example 1.

[0045] FIG. 15 is a stress state image of a capillary main body according to Example 2.

[0046] FIG. 16 is a stress state image of a capillary main body according to Example 3.

[0047] FIG. 17 is a stress state image of the capillary main body according to Comparative Example.

DESCRIPTION OF EMBODIMENTS

[0048] Embodiments of the present invention are described below with reference to the drawings. FIG. 1 to FIG. 12 are illustrations of an embodiment of a capillary and a method of manufacturing the same according to the present invention.

[0049] In FIG. 1, an optical device comprising capillaries according to the present invention is illustrated. In this embodiment, an optical multiplexer/demultiplexer is described as an example of the optical device. An optical device 1 mainly comprises a plurality of optical fibers 2a to 2c, a first capillary 3a, a second capillary 3b, lenses 4a and 4b, an optical filter 5, and an accommodating member 6. The first capillary 3a and the second capillary 3b are configured to hold the optical fibers 2a to 2c.

[0050] The optical fibers 2a to 2c comprise a first optical fiber 2a, a second optical fiber 2b, and a third optical fiber 2c. The first optical fiber 2a and the second optical fiber 2b are held by the first capillary 3a. The third optical fiber 2c is held by the second capillary 3b. Each of the optical fibers 2a to 2c comprises a clad 7 and a coating portion 8 that coats the clad 7. At a distal end portion of each of the optical fibers 2a to 2c, the clad 7 is exposed from the coating portion 8.

[0051] As illustrated in FIG. 1 to FIG. 3, each of the first capillary 3a and the second capillary 3b comprises a capillary main body 9. The capillary main body 9 is made of glass and formed in an elongated shape. Specifically, it is preferred that the capillary main body 9 be made of borosilicate glass. However, a material of the capillary main body 9 is not limited to borosilicate glass and may be various other kinds of glass such as quartz glass, soda-lime glass, and crystallized glass. A thermal expansion coefficient of the capillary main body 9 is set to preferably 310.sup.7/ C. or larger, more preferably 010.sup.7/ C. or larger, preferably 10010.sup.7/ C. or smaller, more preferably 8010.sup.7/ C. or smaller at a temperature failing within a range of, for example, from 30 C. to 380 C.

[0052] The capillary main body 9 is formed of a capillary tube having a cylindrical shape. However, a shape of the capillary main body 9 is not limited to that described in this embodiment. It is preferred that a length dimension L1 (see FIG. 2) of the capillary main body 9 be from 3 mm to 15 mm. It is preferred that an outer diameter of the capillary main body 9 be from 0.5 mm to 3 mm.

[0053] As illustrated in FIG. 1 and FIG. 2, the capillary main body 9 of the first capillary 3a comprises an accommodating portion (hereinafter referred to as first accommodating portion) 10, a first end surface 9a, and a second end surface 9b. The accommodating portion 10 accommodates a part of the first optical fiber 2a and a part of the second optical fiber 2b. The first end surface 9a is formed at one end portion of the capillary main body 9 in a longitudinal direction. The second end surface 9b is formed at another end portion of the capillary main body 9 in the longitudinal direction.

[0054] The first accommodating portion 10 comprises an opening portion (in a tapered shape) 11 and a through hole 12. The clads 7 of the first optical fiber 2a and the second optical fiber 2b can be inserted into the opening portion 11. The clad 7 of the first optical fiber 2a and the clad 7 of the second optical fiber 2b can be accommodated in the through hole 12.

[0055] In this embodiment, the clad 7 of the first optical fiber 2a and the clad 7 of the second optical fiber 2b are inserted into one through hole 12 of the first accommodating portion 10. The through hole 12 can be formed in various shapes such as a circular or rectangular sectional shape. When an outer diameter of the clad 7 of the first optical fiber 2a and an outer diameter of the clad 7 of the second optical fiber 2b are different from each other, the through hole 12 may have concavely curved surfaces with different radii of curvature so as to hold outer surfaces of the clads 7. It is preferred that a hole diameter of the through hole 12 be from 0.05 mm to 1.0 mm.

[0056] A configuration of the through hole is not limited to that described above. For example, the first accommodating portion 10 may have a plurality of (may be three or more) through holes so that clads of a plurality of (may be three or more) optical fibers are individually inserted into the through holes, respectively.

[0057] The opening portion 11 serves as a guide portion configured to allow easy insertion of the clad 7 of the first optical fiber 2a and the clad 7 of the second optical fiber 2b into the through hole 12. The opening portion 11 is formed on the first end surface 9a side of the capillary main body 9. When the capillary main body 9 has a plurality of through holes 12, it is preferred that the opening portion 11 be formed so as to communicate with all the through holes 12.

[0058] The opening portion 11 has an inner wall surface 11a formed in a tapered shape. The inner wall surface 11a is a surface gradually radially expanding from the second end surface 9b side toward the first end surface 9a of the capillary main body 9.

[0059] It is preferred that a length dimension L2 (see FIG. 2) of the opening portion 11 in the longitudinal direction of the capillary main body 9 be from 0.5 mm to 7 mm. It is preferred that a maximum opening diameter of the opening portion 11 be from 0.5 mm to 1.5 mm. It is preferred that a minimum opening diameter of the opening portion 11 be from 0.3 mm to 1.3 mm.

[0060] An adhesive 13 fills the opening portion 11 so as to fix a part of the first optical fiber 2a and a part of the second optical fiber 2b, which are accommodated in the first accommodating portion 10. Specifically, a space defined by the inner wall surface 11a of the opening portion 11 functions as a filled portion to be filled with the adhesive 13. The adhesive 13 filling the opening portion 11 is present between the first optical fiber 2a and the second optical fiber 2b and the inner wall surface 11a to thereby fix each of the optical fibers 2a and 2b to the first capillary 3a. Although not shown, the adhesive 13 also fills the through hole 12 (between an inner surface of the through hole 12 and outer surfaces of the clads 7).

[0061] As the adhesive 13, for example, an epoxy-based adhesive is used. However, the adhesive 13 is not limited to the epoxy-based adhesive. For example, a silicone-based or acrylic adhesive or a photocurable adhesive (for example, a UV-curable adhesive) may be used. A thermal expansion coefficient of the adhesive 13 is set to fall within a range of from 1010.sup.6/ C. to 10010.sup.6/ C.

[0062] The first end surface 9a of the capillary main body 9 is a surface formed so as to be orthogonal to the longitudinal direction of the capillary main body 9. The second end surface 9b of the capillary main body 9 is a surface inclined with respect to a direction orthogonal to the longitudinal direction of the capillary main body 9. It is preferred that an inclination angle (see FIG. 2) of the second end surface 9b be from 3 to 10.

[0063] Distal end portions of the clads 7 of the first optical fiber 2a and the second optical fiber 2b, which are inserted into the through hole 12, have inclined surfaces so as to be flush with the second end surface 9b.

[0064] As illustrated in FIG. 1 and FIG. 3, the capillary main body 9 of the second capillary 3b comprises an accommodating portion (hereinafter referred to as second accommodating portion) 14 configured to accommodate a part of the third optical fiber 2c. The second accommodating portion 14 comprises an opening portion 11 and a through hole 12. The third optical fiber 2c can be inserted into the opening portion 11. The clad 7 of the third optical fiber 2c is inserted into the through hole 12. Other configurations of the second capillary 3b are the same as those of the first capillary 3a. Constituent elements of the second capillary 3b, which are common to the first capillary 3a, are denoted by the same reference symbols.

[0065] In FIG. 4 and FIG. 5, the capillary main body 9 before the optical fibers 2a to 2c are mounted thereinto is illustrated. The capillary main body 9 comprises a compressive stress layer CSL, a tensile stress layer TSL, and a stress-neutral layer NSL. The compressive stress layer CSL is formed so as to include the first end surface 9a and the opening portion 11. The tensile stress layer TSL is formed at a position away from the compressive stress layer CSL toward the second end surface 9b. The stress-neutral layer NSL is formed between the compressive stress layer CSL and the tensile stress layer TSL.

[0066] Observation of a direction of a stress and measurement of a value of the stress in each of the compressive stress layer CSL, the tensile stress layer TSL, and the stress-neutral layer NSL are executed by a two-dimensional birefringence measurement method. In FIG. 6, a measurement device that enables the execution of the two-dimensional birefringence measurement method is illustrated. As a measurement device MD, a commercially available device (for example, a two-dimensional birefringence evaluation system WPA-100 model manufactured by Photonic Lattice, Inc.) can be used.

[0067] The measurement device MD comprises a stage S, a light source LS, a polarizing member P, and a measurement unit H. The capillary main body 9 being a target to be measured is placed on the stage S. The light source LS is provided below the stage S. The polarizing member P is provided between the light source LS and the stage S. The measurement unit H is provided above the stage S. Besides, the measurement device MD comprises an arithmetic device and a display device. The arithmetic device is configured to perform an arithmetic process on data measured by the measurement unit H. The display device is configured to display the result of measurement.

[0068] The stage S has an opening portion Sa. Light emitted from the light source LS is allowed to pass upward through the opening portion Sa. The capillary main body 9 is placed on the stage S so as to overlap the opening portion Sa of the stage S. The capillary main body 9 is placed on the stage S so that a side surface of the capillary main body 9 is brought into contact with the stage S, specifically, a center axis O of the capillary main body 9 becomes parallel to a placement surface of the stage S.

[0069] The measurement unit H is formed of, for example, a polarization imaging camera. The measurement unit H comprises, for example, an objective lens, a polarization array, and a CCD device. The polarization array is configured to pick up an image formed through the objective lens.

[0070] After being transmitted through the polarizing member P, the light emitted from the light source LS is radiated onto the capillary main body 9. After that, the light is transmitted through the capillary main body 9 and reaches the measurement unit H. In this case, after being transmitted through a lower part 9c of the capillary main body 9 and passing through the opening portion 11 being a hollow portion, the light is transmitted through an upper part 9d of the capillary main body 9.

[0071] The arithmetic device performs a predetermined arithmetic process on data about polarized light measured by the measurement unit H to thereby calculate a retardation of the polarized light. Further, the arithmetic device calculates a stress value of the capillary main body 9 based on the retardation. A relationship between the retardation and the stress is expressed by the following Expression (1).

=Fd(1)

where represents a retardation (nm), represents an optical elastic constant (10.sup.2/Pa), F represents a stress (10.sup.5 Pa), and d represents a wall thickness (cm) of the capillary main body 9.

[0072] It is desirable that the measurement of a stress by the measurement device MD described above be performed only on the lower part 9c or the upper part 9d of the capillary main body 9. With the structure of the measurement device MD and the shape of the capillary main body 9 described above, however, it is difficult to perform such a measurement. Thus, the polarized light, which has been transmitted through the lower part 9c and the upper part 9d of the capillary main body 9 placed on the stage S, is measured from above the capillary main body 9 by the measurement unit H. Specifically, the measurement unit H is located above the capillary main body 9 and measures an area in which the lower part 9c and the upper part 9d overlap each other. Thus, in this embodiment, the retardation is calculated by using a sum of a wall thickness of the lower part 9c and a wall thickness of the upper part 9d, specifically, a value (2d) two times larger than the wall thickness d of the capillary main body 9, as the wall thickness d of the capillary main body in Expression (1) given above. In other words, the wall thickness d of the capillary main body 9 can be calculated from a difference between an outer diameter and an inner diameter of the capillary main body 9. In a strict sense, when the inner wall surface 11a of the opening portion 11 is formed in a tapered shape, the wall thickness d of the capillary main body 9 changes each time in accordance with a measured portion. However, it is complicated to set a value of the wall thickness d again in accordance with the measured portion. Thus, for convenience, in the present invention, the value of the wall thickness is fixed with a value of the outer diameter and a value of the inner diameter of the capillary main body 9 on the first end surface 9a to calculate the retardation .

[0073] The arithmetic processing device enables display of an image for showing a distribution state of a stress in the capillary main body 9 (hereinafter referred to as stress state image) on the display device. Lengths L3 to L5 of the stress layers CSL, TSL, and NSL in the longitudinal direction of the capillary main body 9 can be measured based on the stress state image displayed on the display device, respectively.

[0074] The compressive stress layer CSL is formed so as to include the first end surface 9a of the capillary main body 9 and a surface layer portion thereof. Further, the compressive stress layer CSL is formed in an edge portion (boundary portion between the inner wall surface 11a and the first end surface 9a) of the opening portion 11 and a part of the inner wall surface 11a of the opening portion 11 in the vicinity of the first end surface 9a. The compressive stress layer CSL may be located at such a position that its end portion (end portion on the first end surface 9a side) is away from the first end surface 9a. In this case, it is preferred that a distance between the first end surface 9a and the end portion of the compressive stress layer CSL be set to from 0 mm to 0.5 mm, more preferably from 0 mm to 0.1 mm.

[0075] The length (width) dimension L3 (see FIG. 5) of the compressive stress layer CSL in the longitudinal direction of the capillary main body 9 is preferably from 0.01 mm to 2 mm, more preferably from 0.1 mm to 1.5 mm, further preferably from 0.4 mm to 1.2 mm. It is preferred that a maximum value of a compressive stress in the compressive stress layer CSL be larger than 5 MPa and equal to or smaller than 15 MPa.

[0076] The tensile stress layer TSL is formed in a region (inside the capillary main body 9) between the inner wall surface 11a of the opening portion 11 and an outer surface of the capillary main body 9, which is away from the compressive stress layer CSL toward the second end surface 9b.

[0077] The length (width) dimension L4 (see FIG. 5) of the tensile stress layer TSL in the longitudinal direction of the capillary main body 9 is preferably from 0.1 mm to 1 mm, more preferably from 0.1 mm to 0.7 mm, further preferably from 0.2 mm to 0.5 mm. It is preferred that the maximum value of the tensile stress layer TSL be larger than 5 MPa and equal to or smaller than 20 MPa.

[0078] The stress-neutral layer NSL is a layer between the compressive stress layer CSL and the tensile stress layer TSL, which has a compressive stress or a tensile stress of 5 MPa or less.

[0079] A length (width) dimension L5 (see FIG. 5) of the stress-neutral layer NSL in the longitudinal direction of the capillary main body 9, specifically, a distance between the compressive stress layer CSL and the tensile stress layer TSL is preferably from 0.01 mm to 1 mm, more preferably from 0.05 mm to 0.5 mm, further preferably from 0.05 mm to 0.1 mm.

[0080] Before the optical fibers 2a to 2c are fixed, the second end surface 9b of the capillary main body 9 is formed as a flat surface being orthogonal to the longitudinal direction of the capillary main body 9 as indicated by a solid line in FIG. 4. After the clads 7 of the optical fibers 2a to 2c are inserted into the through hole 12, and the optical fibers 2a to 2c are fixed inside the through hole 12 with the adhesive 13, the second end surface 9b is polished. Thus, the second end surface 9b is formed as a surface inclined with respect to the direction orthogonal to the longitudinal direction of the capillary main body 9 as indicated by a two-dot-dash line in FIG. 4.

[0081] The lenses 4a and 4b comprise a first lens 4a and a second lens 4b. The first lens 4a is arranged between the first capillary 3a and the optical filter 5. The second lens 4b is arranged between the second capillary 3b and the optical filter 5. Each of the lenses 4a and 4b is formed of, for example, a columnar lens (so-called C lens) with a uniform refractive index, which has a partially spherical lens surface at one end portion, or a graded-index columnar lens (so-called GRIN lens). However, the lenses are not limited to those described above. Various types of lenses including, for example, a uniform refractive index lens having two partially spherical lens surfaces with the same curvature center at both ends (so-called drum lens) may be used.

[0082] As illustrated in FIG. 1, the first lens 4a is held in a first support member 15a arranged inside the accommodating member 6. The first support member 15a is formed of a cylindrical member made of glass. A part of the first lens 4a is inserted into one end portion of the first support member 15a. A part of the capillary main body 9 of the first capillary 3a is inserted into another end portion of the first support member 15a. The second lens 4b is held in a second support member 15b arranged inside the accommodating member 6. The second support member 15b is formed of a cylindrical member made of glass. A part of the second lens 4b is inserted into one end portion of the second support member 15b. A part of the capillary main body 9 of the second capillary 3b is inserted into another end portion of the second support member 15b. The support members 15a and 15b are fixed inside the accommodating member 6 with an adhesive (not shown).

[0083] The optical filter 5 is formed of, for example, a WDM filter. The optical filter 5 is not limited to the WDM filter and may be other optical elements. The optical filter 5 is arranged between the first lens 4a and the second lens 4b inside the accommodating member 6. The optical filter 5 is fixed to one end portion of the first lens 4a with an adhesive (not shown).

[0084] The accommodating member 6 is formed in a cylindrical shape. However, a shape of the accommodating member 6 is not limited to the cylindrical shape. The accommodating member 6 accommodates the first lens 4a, the second lens 4b, the optical filter 5, the first support member 15a, the second support member 15b, the first capillary 3a, and the second capillary 3b.

[0085] The optical device 1 having the above-mentioned configuration has two modes of use. A first mode of use is a demultiplexing mode in which, when, for example, multiple light beams having two wavelengths are emitted from the first optical fiber 2a, a light beam having one wavelength is reflected by one end surface of the optical filter 5 and is incident on the second optical fiber 2b and a light beam having another wavelength is transmitted through the optical filter 5 and is incident on the third optical fiber 2c. A second mode of use is a multiplexing mode in which, when single light beams having different wavelengths are emitted from the first optical fiber 2a and the third optical fiber 2c, respectively, those two kinds of single light beams are both incident on the second optical fiber 2b.

[0086] Now, a method of manufacturing the capillary main body 9 having the configuration described above is described. As illustrated in FIG. 7, this method comprises a preparation step S1, a heating step S2, and a cooling step S3.

[0087] The preparation step S1 is a step of preparing the capillary main body 9. As illustrated in FIG. 8, the preparation step S1 comprises a forming step S11, a cutting step S12, a polishing step S13, and a processing step S14.

[0088] In the forming step S11, a glass tube (capillary tube) is formed by, for example, a redraw method. With the redraw method, a glass preform is heated so that a part thereof is stretched to thereby form a glass tube having a desired diameter. In the cutting step S12, the glass tube formed through the forming step S11 is cut to have a predetermined length. After that, a plurality of glass tubes obtained by cutting are bundled together, and the bundle of the glass tubes is cut shorter.

[0089] In the polishing step S13, each of the end surfaces of the glass tube in the longitudinal direction, which are formed in the cutting step S12, is polished with a polisher such as a grindstone. Thus, for example, a crack formed in an end surface of the glass tube in the cutting step S12 can be eliminated. When a crack in the end surface of the glass tube is small, the polishing step S13 can be omitted.

[0090] In the processing step S14, a plurality of glass tubes G are held with a holding member 16 such as a banding band as illustrated in FIG. 9 to thereby form a bundle of the glass tubes G. After that, as illustrated in FIG. 10, the bundle of the glass tubes G is immersed into an etching solution ES containing, for example, hydrofluoric acid, which is stored in an etching tank ET. As a result, end surfaces and inner surfaces of the glass tubes G are subjected to an etching treatment. Further, the opening portion 11 having a tapered shape is formed in one end portion of each of the glass tubes G by the etching treatment. A length of the holding member 16 may be the same as a length of each of the glass tubes G. The holding member 16 holds the glass tubes G so that end portions of the holding member 16 are aligned with end portions of each of the glass tubes G to thereby prevent a side surface of each of the glass tubes G from being subjected to the etching treatment that is unnecessary therefor.

[0091] Through the process described above, the capillary main body 9 having the first end surface 9a with the opening portion 11 is prepared.

[0092] In the processing step S14, a method of forming the opening portion 11 (inner wall surface 11a) in one end portion of the glass tube G is not limited to the above-mentioned etching and may also be machining (for example, grinding with a drill or the like).

[0093] Next, in the heating step S2, the first end surface 9a and the opening portion 11 of the capillary main body 9 are irradiated with a laser beam L to thereby heat the first end surface 9a and the opening portion 11.

[0094] Specifically, as illustrated in FIG. 11, the capillary main bodies 9 are supported on a support device 17 so that the first end surfaces 9a of the capillary main bodies 9 face upward. After that, the laser beam L is radiated (spot irradiation) from a laser irradiation device 18, which is stopped above the support device 17, toward the first end surface 9a of the capillary main body 9. It is preferred that the laser beam L radiated onto the capillary main body 9 be a CO.sub.2 laser beam. However, a kind of the laser beam L is not limited to that described in this embodiment.

[0095] In the heating step S2, it is preferred that an output of the laser irradiation device 18 be set to 3 W to 50 W. It is preferred that irradiation time of the laser beam L be set to 1 second to 10 seconds. As illustrated in FIG. 12, it is preferred that the laser beam L having a beam diameter BD larger than a diameter of the first end surface 9a be radiated onto the first end surface 9a and the opening portion 11 in the heating step S2. It is preferred that the beam diameter BD be 1.1 times to 2.5 times larger than the diameter of the first end surface 9a.

[0096] The above-mentioned irradiation with the laser beam L softens the entire first end surface 9a to eliminate microcracks, which have remained in the first end surface 9a and the opening portion 11. Further, the irradiation with the laser beam L softens a peripheral edge portion of the first end surface 9a (boundary portion between the first end surface 9a and an outer peripheral surface), the edge portion of the opening portion 11, and a part of the inner wall surface 11a. Those softened portions are subjected to chamfering.

[0097] After completion of the spot irradiation with the laser beam L to the first end surface 9a of the capillary main body 9, the laser irradiation device 18 stops the irradiation with the laser beam L. After that, the laser irradiation device 18 and the support device 17 are moved relative to each other so that the next capillary main body 9 is arranged below the laser irradiation device 18 as indicated by two-dot-dash lines in FIG. 11. After that, the spot irradiation with the laser beam L is performed on the first end surface 9a of the next capillary main body 9 while the laser irradiation device 18 is in a stopped state. Thus, the laser irradiation device 18 repeatedly carries out the heating step S2 for each of the plurality of capillary main bodies 9 supported on the support device 17 while being in an immobile and stopped state.

[0098] This method enables the formation of the compressive stress layer CSL, the tensile stress layer TSL, and the stress-neutral layer NSL in the capillary main body 9 through the heating step S2 and the cooling step S3 described later.

[0099] It is preferred that the capillary maim body 9 be annealed in the cooling step S3 so as to form the compressive stress layer CSL, the tensile stress layer TSL, and the stress-neutral layer NSL in the capillary main body 9. A cooling rate for the annealing of the capillary main body 9 is preferably from 10 C./second to 100 C./second, more preferably from 20 C./second to 80 C./second, further preferably from 30 C./second to 70 C./second. When an upper limit of the cooling rate falls within the above-mentioned range, the stress-neutral layer NSL can be formed between the compressive stress layer CSL and the tensile stress layer TSL. Further, a maximum value of the tensile stress in the tensile stress layer TSL can be set to 20 MPa or smaller. Further, a length of the stress-neutral layer NSL can be set to 0.01 mm or larger. Further, when a lower limit of the cooling rate falls within the above-mentioned range, a reduction in production efficiency can be prevented. When a method of irradiating with the laser beam L is spot irradiation, the cooling rate can be controlled to fall within the above-mentioned range. Here, the cooling rate refers to a cooling rate within a temperature range from a temperature at which the entire surface of the first end surface 9a is softened through heating to a temperature at which the entire surface of the first end surface 9a reaches its strain point as a result of cooling. It is preferred that the cooling step S3 be carried out in a temperature-controlled space. The cooling step S3 can also be carried out by gradually reducing an output of the laser beam L.

[0100] With the above-mentioned capillary main body 9 and the method of manufacturing the capillary main body according to this embodiment, the compressive stress layer CSL is formed in the capillary main body 9 through the heating step S2 and the cooling step S3. As a result, the first end surface 9a and the opening portion 11 of the capillary main body 9 can be reinforced with the compressive stress layer CSL. As a result, occurrence of chipping or cracking in the end portion (the first end surface 9a and the opening portion 11) of the capillary main body 9 can be prevented.

[0101] In addition to the effects described above, the inventors of the present invention have found the following effects of the present invention as a result of intensive studies.

[0102] The adhesive 13 filling the opening portion 11 tends to expand and shrink due to a temperature change under an environment where the optical device 1 is used. In this case, the inner wall surface 11a of the opening portion 11 expands in such a way as to follow the expansion of the adhesive 13. As a result, cracking, which originates from a microcrack in the opening portion 11, may occur in the opening portion 11. In particular, when the value (maximum value) of the tensile stress in the tensile stress layer TSL is large, this phenomenon is noticeable.

[0103] In order to prevent the above-mentioned occurrence of cracking in the capillary main body 9, the tensile stress layer TSL is formed at a position away from the compressive stress layer CSL, specifically, the stress-neutral layer NSL is formed between the compressive stress layer CSL and the tensile stress layer TSL. As a result, the value (maximum value) of the tensile stress in the tensile stress layer TSL is successfully reduced as much as possible. Thus, even when the tensile stress layer TSL is formed in such a manner as to extend into the opening portion 11, the occurrence of cracking in the end portion of the capillary main body 9, which is caused by the expansion and shrinkage of the adhesive 13, can be prevented.

Examples

[0104] The inventors of the present invention conducted verification tests so as to confirm the effects of the present invention. Now, examples of the present invention are described. However, the present invention is not limited to the examples.

[0105] First, a capillary main body made of glass was manufactured through the steps of FIG. 8. The capillary main body had a tapered shape, a length of 8 mm, an outer diameter of 1.8 mm, and a through hole with a rectangular shape having hole dimensions of 0.51 mm0.51 mm. The used glass was borosilicate glass containing SiO.sub.2 at 70%, B.sub.2O.sub.3 at 15%, Al.sub.2O.sub.3 at 5%, CaO at 1%, BaO at 1%, Na.sub.2O at 7%, and K.sub.2O at 1% in percent by mass.

[0106] Capillary main bodies of Examples 1 to 3 were obtained through the steps of FIG. 7. The manufacturing method according to the embodiment described above used spot irradiation as a method of irradiating with a laser beam. Meanwhile, a capillary main body of Comparative Example was obtained also through the steps of FIG. 7 but by using scanning irradiation as the method of irradiating with a laser beam (see FIG. 13). As illustrated in FIG. 13, the scanning irradiation used a linear laser beam L having a length L6 larger than the diameter of the first end surface 9a of the capillary main body 9. In this case, as indicated by arrows A1 and A2 in FIG. 13, the laser beam L was linearly moved without being stopped so as to pass on the end portion of the capillary main body 9.

[0107] After that, sixteen optical fibers were inserted from the opening portion toward the through hole. Then, the opening portion was filled with an adhesive to thereby manufacture a capillary for holding optical fibers.

[0108] A temperature cycling test (twenty-four cycles of temperature changes within a range of from 40 C. to 85 C.) was performed on one thousand samples obtained in each of Examples 1 to 3 and Comparative Example. After that, the presence or absence of cracking in the end portion (the first end surface and the opening portion) was checked with use of an optical microscope.

[0109] The results of tests for Examples 1 to 3 and Comparative Example are shown in FIG. 1 and illustrated in FIG. 14 to FIG. 17. FIG. 14 is a stress state image for Example 1, FIG. 15 is a stress state image for Example 2, FIG. 16 is a stress state image for Example 3, and FIG. 17 is a stress state image for Comparative Example. A stress in each of the samples was observed and measured with use of a measurement device that enables the execution of the two-dimensional birefringence measurement method (WPA-100 model manufactured by Photonic Lattice Inc.).

TABLE-US-00001 TABLE 1 Example Example Example Comparative 1 2 3 Example Laser irradiation Spot Spot Spot Scanning method Laser output (w) 18 18 18 10 Laser irradiation 3 4.5 7 time (second) Laser scanning speed 500 (mm/minute) Cooling rate for 20 30 40 15 capillary ( C./second) Presence or absence Present Present Present Absent of stress-neutral layer Length (width in 0.45 0.77 1.15 0.05 longitudinal direction) of compressive stress layer (CSL) (mm) Length (width in 0.07 0.10 0.10 longitudinal direction) of stress- neutral layer (NSL) (mm) Length (width in 0.31 0.36 0.41 0.59 longitudinal direction) of tensile stress layer (TSL) (mm) Distance of tensile 0.52 0.87 1.25 0.05 stress layer from first end surface (mm) Maximum value of 14.5 15.2 15.7 30.4 tensile stress in tensile stress layer (MPa) Rate of occurrence of 0.2 0.9 1.0 21.7 cracking in end portion of capillary main body (%)

[0110] As shown in Table 1 and illustrated in FIG. 14 to FIG. 16, each of the samples of Examples 1 to 3 had the stress-neutral layer having a length of 0.01 mm or more, which was formed between the compressive stress layer and the tensile stress layer. The length of the compressive stress layer was longer than the length of the tensile stress layer. The tensile stress layer was located at a position 0.1 mm or more away from the first end surface. Further, the maximum value of the tensile stress in the tensile stress layer was 20 MPa or less. Thus, the occurrence of damage to the end portion of the capillary main body was remarkably low.

[0111] Meanwhile, as shown in Table 1 and illustrated in FIG. 17, the samples of Comparative Example did not have the stress-neutral layer between the compressive stress layer and the tensile stress layer. The maximum value of the tensile stress in the tensile stress layer exceeded 20 MPa. Further, the distance of the tensile stress layer from the first end surface was as short as 0.05 mm. Thus, the occurrence of damage to the end portion of the capillary main body was remarkably high.

[0112] The present invention is not limited to the configurations of the above-mentioned embodiments. In addition, the action and effect of the present invention are not limited to those described above. The present invention may be modified in various forms within the range not departing from the spirit of the present invention.

[0113] In the embodiment described above, there has been described an example in which the capillary main bodies 9 were heated one by one in the heating step S2. However, the present invention is not limited to the configuration described above. In the heating step S2, a plurality of capillary main bodies 9 may be bundled so that their first end surfaces 9a are aligned with each other, and the first end surfaces 9a and the opening portions 11 of the plurality of capillary main bodies 9 may be heated with the laser beam L.

[0114] In the embodiment, the capillary main body 9 comprising the stress-neutral layer NSL has been described. However, the present invention is not limited to the embodiment described above. The end portion (boundary portion between the tensile stress layer and the compressive stress layer CSL) of the tensile stress layer TSL may be set away from the first end surface 9a by setting the length dimension L3 of the compressive stress layer CSL longer than the length dimension L4 of the tensile stress layer TSL instead of providing the stress-neutral layer NSL. In this embodiment, the length dimension L3 of the compressive stress layer CSL is preferably 1.1 times to 4 times larger than the length dimension L4 of the tensile stress layer TSL, more preferably 1.2 times to 3 times larger, further preferably 2 times to 3 times larger. Further, the length dimension L3 of the compressive stress layer CSL may be set larger than the length dimension L4 of the tensile stress layer TSL in addition to the formation of the stress-neutral layer NSL.

[0115] In the embodiment, the capillary main body 9 comprising the stress-neutral layer NSL and the length dimension L3 of the compressive stress layer CSL were set longer than the length dimension L4 of the tensile stress layer TSL have been described. However, the present invention is not limited to the embodiments described above. The end portion (end portion on the first end surface 9a side) of the tensile stress layer TSL, which corresponds to the compressive stress layer CSL, may be set 0.1 mm or more away from the first end surface 9a in the capillary main body 9 regardless of the length dimension L3 of the compressive stress layer CSL. In this embodiment, the end portion of the tensile stress layer TSL is preferably 0.1 mm or more away from the first end surface 9a, more preferably 0.5 mm or more away, further preferably 1 mm or more away. Meanwhile, a distance between the first end surface 9a and the end portion of the tensile stress layer TSL is preferably 3 mm or shorter, more preferably 2 mm or shorter.

REFERENCE SIGNS LIST

[0116] 2a first optical fiber [0117] 2b second optical fiber [0118] 2c third optical fiber [0119] 3a first capillary [0120] 3b second capillary [0121] 9 capillary main body [0122] 9a first end surface of capillary main body [0123] 9b second end surface of capillary main body [0124] 10 first accommodating portion of capillary main body [0125] 11 opening portion of capillary main body [0126] 11a inner wall surface of opening portion [0127] 12 through hole [0128] 13 adhesive [0129] 14 second accommodating portion of capillary main body [0130] BD beam diameter of laser beam [0131] CSL compressive stress layer [0132] L laser beam [0133] NSL stress-neutral layer [0134] S1 preparation step [0135] S2 heating step [0136] S3 cooling step [0137] TSL tensile stress layer [0138] A1 direction in which laser beam travels [0139] A2 direction in which laser beam travels