JP3159022B2 - Optical fiber coupler and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler for branching and coupling an optical signal in an optical communication network or the like using a plastic optical fiber as a transmission medium, and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 7 is a diagram showing an example of the structure of a conventional equal distribution type optical fiber coupler. The optical fiber coupler 10 is formed by joining a pair of plastic optical fibers 11 and 12 by an ultrasonic welding method. In the optical fiber coupler 10, the light that has entered the input port IP1 is distributed and emitted from both output ports OP1 and OP2. At this time, the light emitted from both output ports OP1 and OP2 is set to have the same distribution ratio and small loss. Note that the input port IP2
Also exits from both output ports OP1 and OP2. At this time, the light emitted from these output ports OP1 and OP2 is also set to have a low loss at an equal distribution ratio.

[0003]

However, in the optical fiber coupler 10 as described above, since the incident light is evenly distributed, for example, the light incident on the input port IP1 is only transmitted from the output port OP1. It was not possible to give directionality to light coupling / branching such that light emitted and incident on the input port IP2 was emitted not only from the output port OP2 but also from the output port OP1.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber coupler having a directivity in branching and coupling of light and a method of manufacturing the same.

[0005]

According to a first aspect of the present invention, there is provided an optical fiber coupler comprising a plastic optical fiber portion for a trunk line and a plastic optical fiber portion for a branch line. An optical fiber coupler for coupling light transmitted to the main plastic optical fiber portion, wherein the main plastic optical fiber portion is sandwiched between a pair of small diameter regions having a small diameter and the pair of small diameter regions. A large-diameter region having a larger core diameter than the pair of small-diameter regions, and a pair of tapered regions in which the core diameter gradually changes between each of the pair of small-diameter regions and both ends of the large-diameter region. The plastic optical fiber portion has an arc region bent at a predetermined curvature, and
At least part of the convex side of the region, the plastic for the trunk line
The optical fiber portion is bonded to the large diameter region, and the core of the branch optical fiber portion is directly connected to the large diameter region core.

[0006]

[0007] The optical fiber coupler according to claim 2, wherein the branch line for plastic optical fiber section, a diameter reduction area core is reduced in diameter to a predetermined diameter, core diameter at both ends of the small diameter region Has a pair of tapered regions that gradually change,
The core of the plastic optical fiber portion for branch line is connected to the core of the large diameter region in the reduced diameter region.

According to a third aspect of the present invention, in the optical fiber coupler, the pair of tapered regions provided in the plastic optical fiber portion for the trunk line includes a portion of the light incident from one of the pair of small diameter regions to one of the pair of tapered regions. The light of the highest mode is reflected at an angle to be directly incident on the other of the pair of tapered regions.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an optical fiber coupler for coupling light transmitted to a branch optical fiber to a main plastic optical fiber. both If you form a large diameter region the core diameter is greater the predetermined area on the center side of the main line for a plastic optical fiber portions having a predetermined core diameter to a larger diameter, the larger diameter of both ends of the large diameter region Forming a pair of tapered regions in which the core diameter gradually changes between each of a pair of small diameter regions having a predetermined core diameter and both ends of the large diameter region, and a branch plastic optical fiber portion having a predetermined diameter . Of the arc region formed by bending to a curvature
At least a part of the convex side has a plastic optical fiber for the trunk line.
A step of directly connecting the core of the plastic optical fiber portion for branch line and the core of the large diameter region by joining the large diameter region of the rivet portion.

According to a fifth aspect of the present invention, there is provided a method of manufacturing an optical fiber coupler, wherein the plastic optical fiber portion for a branch line is joined to a large diameter region of the plastic optical fiber portion for a trunk line by an ultrasonic welding method. I do.

According to a sixth aspect of the present invention, there is provided a method of manufacturing an optical fiber coupler, wherein the large-diameter region of the plastic optical fiber portion for the trunk line comprises a tube having an inner diameter corresponding to the outer diameter of the large-diameter region. It is characterized in that it is formed by inserting a predetermined area on the center side of the portion and heating the predetermined area to cause the plastic optical fiber portion for trunk to contract in the fiber axis direction in the predetermined area.

According to a seventh aspect of the present invention, there is provided a method of manufacturing an optical fiber coupler, wherein when the large diameter region of the plastic optical fiber for trunk is contracted by heating, the small diameter region is separated from the small diameter region. It is characterized by applying a tensile load.

[0013]

In the optical fiber coupler according to the first aspect of the present invention, the plastic optical fiber portion for the trunk line is sandwiched between a pair of small diameter regions having a small diameter and the pair of small diameter regions. Since a large diameter region having a larger core diameter and a pair of tapered regions in which the core diameter gradually changes between each of the pair of small diameter regions and both ends of the large diameter region, a pair of small diameter regions is provided. The light incident on the large-diameter region from any one of the above is reflected by one of the pair of tapered regions, so that the traveling angle is reduced. At this time, the plastic optical fiber portion for the branch line is joined to the plastic optical fiber portion for the trunk line in the large diameter region, and the core of the plastic optical fiber portion for the branch line is directly connected to the core in the large diameter region. Therefore, the light from the plastic optical fiber for branch line is guided to the plastic optical fiber for trunk via the large diameter area. On the other hand, light from one of the pair of small diameter regions of the plastic optical fiber portion for the trunk line does not enter the entire region of the core / cladding interface in the large diameter region due to the decrease in the traveling angle, and the branch line Light leakage to the plastic optical fiber portion can be suppressed.

Further, the plastic optical fiber unit for supporting wire, has an arc region bent in a predetermined curvature, connected to the large diameter region of the trunk for a plastic optical fiber portion at least part of the convex side of the arc sections Therefore, the light from the plastic optical fiber for branch line is slightly higher-ordered in this circular arc region, and is easily incident on the plastic optical fiber for trunk line, and the light from the plastic optical fiber for branch line is coupled. Increases efficiency.

Further, in the optical fiber coupler according to the second aspect , the plastic optical fiber portion for the branch line has a reduced diameter region in which the core is reduced to a predetermined diameter, and core diameters at both ends of the reduced diameter region. Has a pair of tapered regions that gradually change, so that light from the plastic optical fiber portion for branch lines becomes higher-ordered in the tapered region before entering the narrow-diameter region. The coupling efficiency of light from the side increases.

According to a third aspect of the present invention, in the optical fiber coupler, the pair of tapered regions provided in the plastic optical fiber portion for the trunk line includes a portion of the light incident from one of the pair of small diameter regions to one of the pair of tapered regions. Since the light of the highest order mode is reflected at an angle at which the light is directly incident on the other of the pair of tapered regions, the light of the higher order mode from one of the pair of small diameter regions of the plastic optical fiber portion for branching is transmitted to the core / large diameter region. It is possible to prevent the light from entering the clad interface and prevent light leakage from the plastic optical fiber portion for the trunk line to the plastic optical fiber portion for the branch line.

According to a fourth aspect of the present invention, there is provided a method for manufacturing an optical fiber coupler, wherein a central area of a plastic optical fiber for trunk having a predetermined core diameter is increased in diameter to form a large diameter area having a large core diameter. It is that the both pair of tapered core diameter changes gradually between the two ends of each the large diameter region of the pair of small-diameter region of the predetermined core diameter that is not larger diameter at both ends of the large diameter region By forming the region and joining the plastic optical fiber portion for the branch line to the large diameter region of the plastic optical fiber portion for the trunk line, the core of the plastic optical fiber portion for the branch line and the core for the large diameter region are directly connected. In the obtained optical fiber coupler, light from the plastic optical fiber for branch line is guided to the large-diameter region with almost no loss, and is transmitted through the large-diameter region. It is guided to the main line for a plastic optical fiber portion. On the other hand, light from one of the pair of small diameter regions of the plastic optical fiber portion for the trunk line does not enter the entire region of the core / cladding interface in the large diameter region due to the decrease in the traveling angle, or Since the incident density is reduced, it is possible to suppress light leakage to the branch plastic optical fiber portion. Also, plastic optical fiber for branch line
Part has an arc region bent to a predetermined curvature, and this circle
At least part of the convex side of the arc area is plastic light
Because it is connected to the large diameter area of the fiber part,
The light from the plastic optical fiber section is
Slightly higher order for plastic optical fiber for trunk line
It is easy to enter and the plastic optical fiber for branch line side
The coupling efficiency of these lights increases.

In the method of manufacturing an optical fiber coupler according to a fifth aspect , the plastic optical fiber portion for a branch line comprises:
Since it is bonded to the large diameter region of the plastic optical fiber for trunk by the ultrasonic welding method, the optical fiber coupler can be easily made to have a low loss.

According to a sixth aspect of the present invention, there is provided a method of manufacturing an optical fiber coupler, wherein a large diameter region of a plastic optical fiber portion for a trunk line is formed into a tube having an inner shape corresponding to an outer diameter of the large diameter region. By inserting a predetermined region on the center side of the fiber portion and heating the predetermined region to shrink the plastic optical fiber portion for trunk in the fiber axis direction in this predetermined region, the large diameter region can be easily formed. Can be formed.

[0020] In the manufacturing method of the optical fiber coupler according to claim 7, in which heat shrinking the large diameter region of the trunk for a plastic optical fiber portion, in a direction away this thin area to each of the small-diameter region Since a tensile load is applied, a large-diameter region having a desired length can be easily formed.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(Optical Fiber Coupler of First Embodiment) Hereinafter, a first embodiment of an optical fiber coupler according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram for explaining the structure of the optical fiber coupler according to the first embodiment. The optical fiber coupler 2 includes a main optical fiber portion 21 made of a plastic optical fiber.
And a branch optical fiber portion 28 also made of plastic optical fiber.

The trunk optical fiber portion 21 includes a pair of small-diameter regions 22 and 23 at both ends and these small-diameter regions 22 and 23.
3 having a large-diameter region 24. A pair of tapered regions 2 where the core diameter gradually changes is provided between each of the pair of small-diameter regions 22 and 23 and both ends of the large-diameter region 24.
5 and 26 are formed.

The branch optical fiber portion 28 is joined to the large diameter region 24 of the trunk optical fiber portion 21 by ultrasonic welding while maintaining a predetermined curvature. As a result, the core 28a of the branch optical fiber portion 28 is directly connected to the core 24a of the large diameter region 24.

The optical fiber portion 21 for the trunk line and the optical fiber portion 28 for the branch line are general plastic optical fibers having a thermoplastic resin core, and are workable in forming the large-diameter region 24 and ultrasonic welding. Is good. Various types of optical fibers are used to form the trunk optical fiber portion 21 and the branch optical fiber portion 28, from a small NA “broadband optical fiber” to a relatively high NA general optical fiber. can do.

The two optical fiber portions 21 and 28 constituting the optical fiber coupler 2 are of the same type.
In other words, the plastic optical fibers having the same refractive index and composed of the cores 21a and 28a are joined to each other by the ultrasonic welding method, so that when the light is coupled from the branch optical fiber portion 28 to the trunk optical fiber portion 21, In addition, the loss at the branch connection can be minimized. The two optical fiber portions 21 and 28 may be made of different types of optical fibers. However, in this case, both optical fibers must have resin cores having similar softening points (temperatures).

The operation of such an optical fiber coupler will be described. The incoming light from the branch optical fiber portion 28 travels through the large diameter region 24 of the trunk optical fiber portion 21 at the same advancing angle. The light that has been converted to a higher-order propagation mode side by the tapered region 26 that has passed through the large-diameter region 24 passes through the cladding layer of the optical fiber portion 21 for the trunk line, and remains inside the optical fiber portion 21 for the trunk line as it is. And those that propagate. This propagating light becomes "coupled" light. In other words, the branch optical fiber portion 28
Of the light that enters from the side, the light that is not captured in the trunk optical fiber portion 21 is emitted to the outside as leak light as it is. Therefore, it is necessary to set the entering angle of light from the branch optical fiber portion 28 within a certain range.

The convex side of the arc formed by the branch optical fiber portion 28 is the large diameter region 2 of the trunk optical fiber portion 21.
4 is connected. Accordingly, the light from the branch optical fiber portion 28 is slightly higher-ordered in this circular arc region, and is easily incident on the trunk optical fiber portion 21. As a result, the coupling of light from the branch optical fiber portion 28 is performed. Increases efficiency.

On the other hand, on the side of the trunk optical fiber portion 21, the light incident from one of the small-diameter regions 22 to the large-diameter region 24 is reflected by the tapered region 25, so that the traveling angle is reduced. As a result, the light reflected by the tapered region 25 does not enter the entire region of the core / cladding interface of the large-diameter region 24, so that light leakage to the branch optical fiber portion 28 can be suppressed.

Hereinafter, the tapered region 23 will be described with reference to FIG.
Consider the specific conditions under which the light reflected at the core / cladding interface of the above does not completely enter the core / cladding interface of the large diameter region 24. In the following description, only the highest mode light in which light leakage easily occurs will be described.

The highest-order mode light from the small-diameter region 22 side is
The light enters the tapered region 25 side, and all of the light is
No. 6 directly into the core / cladding interface. Here, as shown, the diameter of the core 24a in the large diameter region 24 is D, the length is L, and the diameters of the cores 22a, 23a in the small diameter regions 22, 23 are both d. Further, the taper angles of the cores 25a and 26a of the tapered regions 25 and 26 are denoted by ψ1 and ψ2, respectively.
Assuming that TAL and θ are the advancing angles of the highest-order mode light transmitted through the small-diameter region 22, {D− (D−d) / 2} / (TBL + L) = tan (θ−2ψ1) (1) A relationship holds, where TBL and ψ1 satisfy the following relationship (D−d) / 2TBL = tan ψ1 (2). If the highest-order mode light from the small-diameter region 22 is reflected by the tapered region 25 and re-reflected by the tapered region 26 to return to the original traveling angle θ, T
BL = TAL and ψ1 = ψ2.

From the above equations (1) and (2), the following relationship is obtained: D + d = {(D−d) / tan {1 + 2L} × tan (θ−2ψ1) (3), where A = D−d + 2Ltanψ1, B = −
If (D + d) tanψ1, equation (3) can be rewritten as A × (tan θ−tan2ψ1) + B × (1 + tan θ × tan2ψ1) (4), and if tanθ = C, equation (4) becomes A × {C × (1-tan ² ψ1) -2tan {1} + B ×
{(1−tan ² ψ1) + 2Ctan {1} (4) When this is expanded and arranged with respect to tan ψ1, (−AC−B) tan ² ψ1-2 (A−BC) tan ψ1 + (AC + B) = 0 (5) Here, A, B, and C are returned to the original, and the equation (5) is obtained.
Is developed and arranged as follows: {(D + d) -2L tan θ} × tan ³ {1 + ψ− (3
D + d) tanθ-4L｝ × tan ² ψ1 + ｛-(3D-
d) + 2Ltan θ｝ × tanψ1 + (D−d) tan
θ = 0 (6) is obtained. Equation (6) is a cubic equation, and the values D, d, L,
coefficient {(D + d) -2Ltanθ} given by θ,
{-(3D + d) tan θ-4L}, ｛-(3D-d)
By preliminarily determining + 2Ltan θ｝ and (D−d) tan θ, it is possible to determine the value of tanψ1, that is, the value of ψ1. The taper angle ψ1 (= ψ2) obtained in this manner is such that after the highest-order mode light from the small-diameter region 22 is reflected by the tapered region 25, all of the light is re-reflected by the tapered region 26. This is an angle condition for entering the area 23 at the original traveling angle. In this case, the small-diameter region 22
Can be prevented from entering the core / cladding interface of the large-diameter region 24, and light leakage from the main optical fiber portion 21 to the branch optical fiber portion 28 can be prevented. However, unless the following condition {D− (D−d) / 2} / (TBL) ≦ tan θ (7) is satisfied, the highest-order mode light from the small-diameter region 22 is reflected by the tapered region 25. In some cases, the light may directly enter the large-diameter region 24 without causing light leakage from the trunk optical fiber portion 21 to the branch optical fiber portion 28.

Hereinafter, specific examples of the optical fiber coupler of the first embodiment will be described. First, a trunk optical fiber portion 21 and a branch optical fiber portion 28 are prepared. As the main optical fiber portion 21 and the branch optical fiber portion 28, an SI plastic optical fiber composed of a PMMA core having a refractive index of 1.495 was used. The outer diameter was 1.0 mm and the core diameter was 0.97 mm. The main optical fiber portion 21 is 1.5 m in length.
The tube was passed through a heat-resistant tube having an inner diameter of m and subjected to heating, shrinkage, partial cooling, pulling, and cooling steps. As a result, as shown in FIG. 2, a part of the diameter is increased to form a large-diameter region 24, and tapered regions 25 and 26 are formed at transition portions at both ends.

The dimensions of the large diameter region 24 and the tapered regions 25 and 26 to be formed in the trunk optical fiber portion 21 are as follows.
It is determined by appropriately determining the values of D and L and obtaining ψ1 from equation (6). When the SI type optical fiber used in the example is NA = 0.5, the core diameter is 1.0 mm, and other constants are appropriately set based on ultrasonic bonding conditions, θ = 20.
゜, d = 1.0 mm, D = 1.5 mm, L = 20 mm
Becomes Calculating based on equation (6), the taper angle ψ1
= 8.3 °, and the taper length TBL = 1.7 mm.

The allowable range of the outer diameter of the SI type optical fiber of the general specification is ± 3%, and there is no particular problem even if the core diameter is set to 1.0 mm in order to simplify the calculation.

Next, the prepared trunk optical fiber portion 21
And the branch optical fiber portion 28 are arranged in the longitudinal direction, and a part thereof is joined by ultrasonic welding under the following conditions. The specific method is almost the same as the conventional method. At this time, the joint length, which is the length directly connecting the core 21a of the trunk optical fiber portion 21 and the core 28a of the branch optical fiber portion 28, was set to 20 mm. The large-diameter region 24 of the main-line optical fiber portion 21 is held linearly on the fixed table side, and the branch-line optical fiber portion 28 is held at a predetermined curvature on the ultrasonic horn side, thereby deforming the optical fiber during ultrasonic welding. Suppress the degree. Here, the branch optical fiber portion 28 has a radius of 200 mm with the contact point with the trunk optical fiber portion 21 as a vertex.
Is held by the ultrasonic horn so as to draw an arc. The optical fiber contact surface of the ultrasonic bonding anvil (fixing jig) is processed smoothly so that scratches and the like are not transferred to the side surface of the optical fiber. The ultrasonic energy at the time of joining was set to 21 KHz and 100 W or less. The bonding time is 1
Set within 0 seconds. Furthermore, the joining form is 1 in compression ratio.
0%. Under these conditions, the two optical fiber portions 2
Parts 1 and 28 were partially ultrasonically bonded. The configuration of the completed optical fiber coupler 2 remains bent by an ultrasonic horn and a jig having a curvature, and the branch optical fiber portion 28 is formed in the large diameter region 2 of the main optical fiber portion 21.
4 was joined over about 20 mm.

The performance evaluation of the optical fiber coupler 2 obtained in the above embodiment will be described below. 66 as a light source
A stabilized light source generating 0 nm, 38 μW light was used.
The optical output from each channel of the optical fiber coupler 2 shown in FIG. 1 was as follows.

[0038]

[Table 1]

Further, when light of 38 μW was incident on both the channels 1CH and 2CH, an optical output of 42μW was obtained from the channel 3CH. That is, a part of the branch line was connected to the trunk without decay on the trunk.
From this result, without reducing the optical signal on the trunk side,
It can be confirmed that the optical signal from the branch line is injected into the main line. Therefore, in a LAN system or the like, the minimum receiving sensitivity does not need to be increased, and this is useful for improving the S / N ratio. Therefore, an effect of mainly reducing the load on the receiving device is expected.

Hereinafter, another specific example of the optical fiber coupler of the first embodiment will be described. This embodiment has almost no difference from the above embodiment. However, the conditions at the time of ultrasonic bonding of the main optical fiber portion 21 and the branch optical fiber portion 28 are different. That is,
The joining length between the core 21a of the large diameter region 24 provided in the trunk optical fiber portion 21 and the core 28a of the branch optical fiber portion 28 was reduced to 10 mm. Thus, by shortening the joint length, the joint area between the optical fibers is reduced, the leakage of light from the trunk optical fiber portion 21 to the branch optical fiber portion 28 is reduced, and an optical fiber coupler is provided. This can minimize the effect on the trunk optical fiber portion 21. In other words, the joining area is intentionally reduced during the ultrasonic joining of the optical fibers, and the probability that light having a small advancing angle enters the branch optical fiber portion 28 is reduced. On the other hand, since the light from the branch optical fiber portion 28 has the same advancing angle, a certain amount of light can be coupled to the main optical fiber portion 21 even if the joint area is small. .

The performance evaluation of the optical fiber coupler 2 obtained in the above embodiment will be described below. As the light source, the same light source as the above-mentioned stabilized light source was used. The optical output from each channel of the optical fiber coupler 2 shown in FIG. 1 was as follows.

[0042]

[Table 2]

Further, when 38 μW light was incident on both channels 1CH and 2CH, a light output of 42 μW was obtained from channel 3CH. That is, a part of the branch line was connected to the trunk without decay on the trunk.
From this result, without reducing the optical signal on the trunk side,
It can be confirmed that the optical signal from the branch line is injected into the main line.

In the above embodiment, the branch optical fiber portion 2
As a method of reducing the bonding area between the optical fiber 8 and the trunk optical fiber portion 21, a method of adjusting the bonding length between the two optical fibers is used. However, the compression ratio is reduced so that the two optical fibers are crushed and bonded. Can be made smaller. In this case, the light traveling in the optical fiber has a traveling angle of about 11 ° even if the NA of the optical fiber is about 0.3. The probability of entering the branch line during repeated reflections increases. On the other hand, in the method of shortening the joining length,
The number of reflections at the junction is limited, and the probability of entering the branch line is also reduced. Therefore, the method of adjusting the junction length is more useful for preventing light from leaking from the trunk line side.

(Optical Fiber Coupler of Second Embodiment) Hereinafter, an optical fiber coupler of a second embodiment will be described with reference to the drawings. Note that the optical fiber coupler of the second embodiment is a modification of the first embodiment, and the same portions are denoted by the same reference numerals and redundant description will be omitted.

FIG. 3 is a diagram for explaining the structure of the optical fiber coupler according to the second embodiment. The optical fiber coupler 2 '
As in the case of the first embodiment, the trunk optical fiber portion 2
1 and a branch optical fiber portion 28 ', but the structure of the branch optical fiber portion 28' is different from that of the first embodiment.

The branch optical fiber portion 28 'is formed by reducing the diameter of a predetermined region of the plastic optical fiber.
b, 28b and a small diameter region 28c sandwiched between these large diameter regions 28b, 28b. Then, between each of the pair of large-diameter regions 28b, 28b and both ends of the small-diameter region 28c, there is provided a pair of tapered regions 28 whose core diameter gradually changes.
d and 28d are formed.

Small-diameter region 2 of branch optical fiber portion 28 '
8c is bonded to the large-diameter region 24 of the main-line optical fiber portion 21 by an ultrasonic welding method while maintaining a predetermined curvature. As a result, the branch optical fiber portion 2
The 8 ′ core 28a is directly connected to the core 24a of the large diameter region 24.

Here, the light from the large-diameter region 28b of the branch optical fiber portion 28 'is converted into a higher-order mode in the tapered region 28d, and then enters the small-diameter region 28c. Diameter region 28b of optical fiber portion 21 for use
The coupling efficiency from the branch optical fiber portion 28 'to the main optical fiber portion 21 is improved. That is, when the two optical fibers are ultrasonically bonded to each other, the bonding area is reduced, and the probability that light having a small traveling angle from the main optical fiber portion 21 enters the branch optical fiber portion 28 'can be reduced. Further, since the light from the branch optical fiber portion 28 'is converted into a higher-order mode in the tapered region 28d, the light from the branch optical fiber portion 28' is converted into the trunk optical fiber even if the bonding area is small. It will be considerably coupled to the part 21.

Hereinafter, specific examples of the optical fiber coupler of the second embodiment will be described. First, the trunk optical fiber portion 21 and the branch optical fiber portion 28 'are prepared. As the main optical fiber portion 21 and the branch optical fiber portion 28 ', an SI type plastic optical fiber composed of a PMMA core was used. Both outer diameters are 1.0mm
And the core diameters were both 0.97 mm. The processing of the optical fiber portion 21 for the trunk line is the same as in the case of the specific example of the first embodiment, and the description is omitted here.

The branch optical fiber portion 28 'is partially heated and stretched. As a result, as shown in FIG. 3, a part of the diameter is reduced to form a small diameter region 28c,
Tapered regions 28d, 28d are formed at transition portions at both ends. The dimensions of the branch optical fiber portion 28 'are determined in consideration of the ultrasonic bonding conditions and the like, and the large-diameter region 28b
Core diameter d '= 0.97 mm, the core diameter D' of the small diameter region 28c = 0.7 mm, and the length L 'of the small diameter region 28c.
= 20 mm. The length of the tapered region 28d was 1.7 mm, and the taper angle was 5.3 °.
At the time of ultrasonic bonding between the small-diameter region 28c of the branch optical fiber portion 28 'and the large-diameter region 24 of the trunk optical fiber portion 21, the bonding length is made relatively small at 10 mm, and light leakage from the trunk line side is performed. Has been reduced.

The performance evaluation of the optical fiber coupler 2 'obtained in the above embodiment will be described below. As a light source, etc.
The same light source as the stabilized light source used in the performance evaluation of the specific example of the first embodiment was used. Optical fiber coupler 2 '
The light output from each channel shown in FIG. 3 was as follows.

[0053]

[Table 3]

When light of 38 μW was incident on both channels 1CH and 2CH, a light output of 42 μW was obtained from channel 3CH. That is, a part of the branch line was connected to the trunk without decay on the trunk.

(Manufacturing Method of Optical Fiber Coupler) The optical fiber couplers 2 and 2 ′ are prepared by preparing a main optical fiber portion 21 and shrinking it by heating to form a large diameter region 24 and the like.
The branch optical fiber portions 28 and 28 ′ curved at a predetermined curvature to the large-diameter region 24 are formed by ultrasonic welding.

First, the processing of the trunk optical fiber portion 21 will be described. Since plastic optical fibers are manufactured by a melt extrusion method, they have the property of shrinking in the fiber axial direction when heated. By utilizing this property, the diameter of the plastic optical fiber already formed to a predetermined diameter can be increased at a desired portion.
That is, the large-diameter region 24 can be formed at a desired position on the small-diameter trunk optical fiber portion 21. At this time, the trunk optical fiber portion 21 to be processed is passed through a heat-resistant tube having a smooth inner wall, and the heat-resistant tube is partially heated, so that the heating region is contracted in the fiber axis direction to thereby reduce the optical fiber portion for the trunk line. Although the diameter of the optical fiber 21 can be partially increased, the maximum diameter of the trunk optical fiber section 21 is limited by the heat-resistant tube.
A large-diameter region 24 having a columnar shape as shown in FIG. By such a processing method, it is possible to increase the core diameter of a part of the trunk optical fiber portion 21 without inserting another optical component that causes Fresnel loss or the like on the path of the trunk optical fiber portion 21. And a pair of tapered regions 25 at both ends of the large-diameter region 24 having a large core diameter.
Since 26 is formed, the large-diameter region 24 can be a low-order propagation mode section. Further, by using a heat-resistant tube whose inner surface shape is precisely maintained, the outer diameter of the large-diameter region 24 can be easily set to a desired value,
Light scattering due to excessive deformation can also be suppressed.

FIG. 4 is a diagram showing the overall structure of the processing apparatus. This processing apparatus includes a pair of support members 51 and 52 for supporting the optical fiber portion 21 for a trunk line,
Slide members 53 and 54 for supporting the slide members 1 and 52 and a linear guide 55 for guiding the slide members 53 and 54 are provided. The trunk optical fiber 2 held by the pair of support members 51 and 52 has a portion sandwiched between the support members 51 and 52 passed through a heat-resistant tube 60 made of a fluororesin. The heat-resistant tube 60 is supported by a member (not shown) while being aligned with the linear guide 55 and the like. An opening 70 a of the hot air supply device 70 is provided at a position facing the heat-resistant tube 60.
The warm air from the opening 70a heats the heat-resistant tube 60, and also heats the trunk optical fiber 21 in the heat-resistant tube 60. As a result, the trunk optical fiber portion 21 partially shrinks in the fiber axis direction, and the diameter increases at this portion. Although not shown, a cool air supply device can be provided at the position of the hot air supply device 70, and the partially contracted trunk optical fiber portion 21 is cooled to obtain a desired shape of the contracted portion. It can be. At this time, a pair of support members 51, 5 for supporting the trunk optical fiber portion 21 are provided.
By applying a predetermined tensile load for separating the two from each other, the length of the large-diameter region 24 to be formed and the length and the taper angle of the tapered regions 25 and 26 can be appropriately set. By changing the heat shrinkage temperature and the tensile load, the present invention can be applied to the case of processing a plastic optical fiber of another material.

Finally, the prepared trunk optical fiber portion 2
1 and the branch optical fiber portions 28 and 28 'are arranged in the longitudinal direction, and a part thereof is ultrasonically bonded under the following conditions. The specific contents are the same as those already described in the section of “Optical Fiber Coupler of First Embodiment”, and the description is omitted here.

Hereinafter, a specific embodiment of processing the optical fiber portion 21 for the trunk line will be described. The trunk optical fiber portion 21 is an SI-type plastic optical fiber composed of a PMMA core, having an outer diameter of 1.0 mm and a core diameter of 0.97.
mm and NA is 0.5 (the traveling angle of light in the optical fiber is 20 °). A large-diameter region 24 having an NA of 0.2 (the traveling angle of light in this portion is 7.7 ° in principle) is formed in a part of the trunk optical fiber portion 21 by utilizing thermal contraction. The deformation temperature of the trunk optical fiber portion 21 is about 150 ° C.

FIG. 5 is a view for explaining the dimensions and the like of the heat-resistant tube 60 through which the trunk optical fiber portion 21 passes. The heat-resistant tube 60 has an inner diameter φ = 1.5 mm and a length x
= 50 mm.

The optical fiber portion 21 for the main line is heated via the heat-resistant tube 60 in the range of the heating width xh = 30 mm. Next, after a lapse of about 2 minutes, the main optical fiber portion 21
Is confirmed to have sufficiently shrunk at the heated portion, and the main optical fiber portion 21 is cooled with cold air through the heat-resistant tube 60 in the range of the heating width xc = 20 mm. At this time, an appropriate load is applied to the slide members 53 and 54, and both ends of the main optical fiber portion 21 are pulled with a force of 200 g. Here, a portion of the trunk optical fiber portion 21 that is selectively cooled by cold air is a large-diameter region 24. Finally,
Cool while applying weight, and wait until the entire system falls below the deformation temperature. As a result, uniform tapered regions 25 and 26 are formed on both ends of the large-diameter region 24.

FIG. 6 is a diagram schematically illustrating the processing of the optical fiber portion 21 for the trunk line. FIG. 6A shows how the trunk optical fiber portion 21 is heated by the warm air via the heat-resistant tube 60. In FIG. 6B, the trunk optical fiber portion 21 that has been thermally contracted in the heated portion is partially cured by cold air to form a large-diameter region 24, and tapered regions 25 and 26 are formed in an uncooled portion. This is shown.

The optical fiber portion 21 for trunk line processed as described above has an outer diameter of 1.5 mm over 23 mm.
A tapered shape having a length of 2 mm was formed at the transition between the narrow diameter regions 22 and 23 having the original diameter (1 mm) at both end sides. The taper angles of the tapered regions 25 and 26 were 7.1 °. Since the core is also considered to have the same taper angle, light having a maximum traveling angle of 20 ° that propagates through the small diameter regions 22 and 23 having an NA of 0.5 is converted into light having a maximum traveling angle of 5.8 °. You. Note that this maximum advancing angle of 5.8 ° corresponds to 0.15 in terms of NA.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of an optical fiber coupler according to a first embodiment.

FIG. 2 is a diagram illustrating dimensions of the optical fiber coupler of FIG.

FIG. 3 is a diagram illustrating a structure of an optical fiber coupler according to a second embodiment.

FIG. 4 is a diagram illustrating an apparatus for performing a part of the method of manufacturing an optical fiber coupler.

FIG. 5 is a diagram illustrating an arrangement and a structure of an optical fiber which is a workpiece set in the apparatus of FIG. 4;

FIG. 6 is a diagram illustrating processing of an optical fiber in the apparatus of FIG.

FIG. 7 is a diagram illustrating a conventional optical fiber coupler.

[Explanation of symbols]

 Reference Signs List 2 optical fiber coupler 21 trunk optical fiber portion 21a core 22, 23 small diameter region 24 large diameter region 24a large diameter region core 25, 26 taper region 28 branch optical fiber portion 28a core 51, 52 support member 53, 54 slide Member 55 Linear guide 60 Heat-resistant tube 70 Hot air supply device

Claims (7)

(57) [Claims] An optical fiber coupler comprising a plastic optical fiber part for trunk and a plastic optical fiber part for branch, and an optical fiber coupler for coupling light transmitted to the plastic optical fiber part for branch to the plastic optical fiber part for trunk. The plastic optical fiber portion for the trunk line includes a pair of small diameter regions having a small diameter, a large diameter region sandwiched between the pair of small diameter regions, and having a core diameter larger than the pair of small diameter regions; A pair of tapered regions in which the core diameter gradually changes between each of the small-diameter regions and both ends of the large-diameter region, and the plastic optical fiber portion for branch lines has a predetermined curvature.
A curved arc region, and a small arc region on the convex side of the arc region.
At least part of the plastic optical fiber part for the trunk line
Wherein the core of the branch plastic optical fiber portion is directly connected to the core of the large diameter region. 2. A plastic optical fiber portion for said branch line.
Is a reduced diameter region in which the core is reduced to a predetermined diameter,
A pair of tapers with gradually changing core diameter at both ends of the reduced diameter area
And the branch wire plug in the narrowed area.
The core of the stick optical fiber part becomes the core of the large diameter region.
The optical fiber according to claim 1, wherein the optical fiber is connected.
Iva coupler. 3. The plastic optical fiber part for the trunk line.
The pair of tapered regions provided in the
Of light incident on one of the pair of tapered regions from one of the
The light of the highest mode is transmitted to the other of the pair of tapered regions.
Characterized by reflecting at an angle that is directly incident on
Item 2. The optical fiber coupler according to item 1. 4. The transmission to the plastic optical fiber for branch line.
Transmitted light to plastic optical fiber for trunk line
A method for manufacturing an optical fiber coupler for coupling, wherein said plastic optical fiber for trunk has a predetermined core diameter.
Larger core area by increasing the diameter of the predetermined area on the center side of the bar
While forming a large-diameter region, both ends of the large-diameter region
A pair of small-diameter regions of the predetermined core diameter that are not increased in diameter
Gradually core diameter between both ends of each the previous SL large diameter region of
Forming a pair of changing tapered regions, and forming the plastic optical fiber portion for branch line at a predetermined curvature.
At least part of the convex side of the arc region formed by bending
The large diameter area of the plastic optical fiber portion for the trunk line
By joining to the area, the plastic optical fiber
The core of the fiber portion is directly connected to the core of the large diameter region.
And an optical fiber cap.
La manufacturing method. 5. A plastic optical fiber portion for said branch line.
Is a plastic light for the trunk line by an ultrasonic welding method.
Characterized in that it is joined to the large diameter region of the fiber portion.
The method for manufacturing an optical fiber coupler according to claim 4. 6. A plastic optical fiber portion for the trunk line.
The large diameter region has an inner diameter corresponding to the outer diameter of the large diameter region.
Plastic optical fiber for trunk line in tube having
Insert the predetermined area on the center side of the part, and
By heating, the main line plus
The optical fiber can be shrunk in the fiber axis direction.
5. The light according to claim 4, wherein the light is formed by:
Fiber coupler manufacturing method. 7. The plastic optical fiber part for the trunk line.
When heat shrinking the large-diameter region, the small-diameter region
Tension load in the direction that separates the small diameter area
7. The optical fiber according to claim 6, wherein weight is given.
Manufacturing method of coupler.