JPH09159862A - Optical fiber connector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the connector which can connect an optical fiber with high NA to an optical fiber with low NA and the same or a smaller internal diameter with low loss. SOLUTION: Signal light of the highest-order mode from a 1st optical fiber 3 is made temporarily high-order by a 1st internal reflecting surface 21a and then made lower-order than originally by a 2nd internal reflecting surface 22a, so that it is matched with the transmission mode of a 2nd optical fiber 4. At this time, signal light having a travel angle larger than the maximum travel angle of the 2nd optical fiber 4 about signal light made incident on the 1st tapered internal reflecting surface 21a from the 1st optical fiber 3 is reflected >=1 time by the 1st internal reflecting surface 21a. Then when the light is made incident on the 2nd tapered internal reflecting surface 22a from a repeating part 23, the light having the smallest travel angle as to the signal light having its mode converted by the 1st internal reflecting surface 21a is reflected >=1 time by the 2nd internal reflecting surface 22a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber connector required when connecting different kinds of optical fibers in a system such as an optical communication network using a plastic optical fiber as a transmission medium.

[0002]

2. Description of the Related Art Conventionally, as a method of joining different kinds of optical fibers, a method of interposing a taper portion between both optical fibers has been disclosed (JP-A-53-116850). In this method, the first optical fiber end having a small numerical aperture and a large core diameter is connected to the second optical fiber end having a large numerical aperture and a small core diameter.
When connecting to the end of the optical fiber, a tapered portion whose diameter increases from the second optical fiber to the first optical fiber is arranged between the end faces of both optical fibers.

[0003]

However, as the use of optical fibers has advanced, many kinds of optical fibers have come into circulation. Therefore, in the above method, different kinds of optical fibers can be spliced well. There were cases where it was not possible. For example, in the case of joining a pair of optical fibers having the same core diameter but different numerical apertures, if the above method is forcibly applied, one of the optical fiber ends and the taper end that abuts on the other end This is because there is a difference in core diameter or aperture between them, and loss due to light leakage occurs in this portion.

Therefore, an object of the present invention is to provide an optical fiber connector capable of connecting various optical fibers with low loss.

[0005]

In order to solve the above-mentioned problems, the optical fiber connector of claim 1 is an optical fiber connector for connecting a pair of optical fibers having different numerical apertures, and one end of the optical fiber connector. And a tapered first internal reflection surface having a predetermined first taper angle that spreads toward one end side, and guides light incident from one end of the optical fiber connector to the other end side of the optical fiber connector. The first waveguide portion and the other end side of the optical fiber connector are provided and have a second taper angle larger than the first taper angle that spreads toward the other end side and are arranged coaxially with the first internal reflection surface. And a second waveguide portion that guides the light from the first waveguide portion side to the outside of the other end of the optical fiber connector.

The optical fiber connector according to claim 2 is
The relay unit is further provided which is disposed between the first and second waveguide units and guides the light from the first waveguide unit to the second waveguide unit.
It has a cylindrical third internal reflection surface, and the end on the small diameter side of the first internal reflection surface is connected to one end of the third internal reflection surface with the same diameter.
The end portion on the small diameter side of the internal reflection surface is connected to the other end of the third internal reflection surface with the same diameter.

The optical fiber connector according to claim 3 is
It is characterized in that the first and second waveguide portions are large-diameter portions formed at both ends of the rod-shaped optical fiber.

The optical fiber connector according to claim 4 is
It is characterized in that the first and second waveguide portions are large-diameter portions formed at both ends of a sheath-shaped metal ferrule whose inner surface is processed into a mirror surface.

[0009]

According to the optical fiber connector of the present invention, the first waveguide portion provided at one end of the optical fiber connector has a tapered shape having a predetermined first taper angle which spreads toward one end of the optical fiber connector. The second waveguide portion provided on the other end side of the optical fiber connector has the second internal taper angle and has a second taper angle larger than the first taper angle spreading toward the other end side of the optical fiber connector. Since the second inner reflecting surface having a tapered shape is provided coaxially with the first inner reflecting surface, the first taper angle for the first inner reflecting surface and the second taper angle for the second inner reflecting surface are appropriately adjusted. By doing so, it becomes possible to convert the transmission mode when connecting a pair of optical fibers having different numerical apertures, and it is possible to suppress the connection loss due to the difference in the transmission mode between the pair of optical fibers. Specifically, for example, an optical fiber with a high NA is connected to the first waveguide portion,
Considering the case where an optical fiber having a low NA is connected to the waveguide, by setting the second taper angle larger than the first taper angle by a predetermined value or more, the light of the higher mode from the optical fiber side having a higher numerical aperture can be obtained. Can be converted into low-order mode light suitable for an optical fiber having a low numerical aperture, and a connection loss due to a difference in transmission mode of light transmitted through the pair of optical fibers can be suppressed. At this time, by appropriately adjusting the length of the first waveguide portion and the length of the second waveguide portion, the opening on the large diameter side of the first internal reflection surface is changed to the opening on the large diameter side of the second internal reflection surface. Can be greater than or equal to. Therefore, even when the higher-order mode light from the optical fiber side with a large core diameter and a high numerical aperture is coupled to an optical fiber with the same or small core diameter and a small numerical aperture, a pair of optical fibers with the openings at both ends of the optical fiber connector are used. The core diameter of the fiber can be matched, and the loss at the connection surface can be minimized.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical fiber connector according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining the structure of the optical fiber connector of the first embodiment. The optical fiber connector 2 is a plastic optical fiber having a core 2a and a clad 2b cut out in a rod shape, and has a first waveguide portion 21 on one end side joined to a first optical fiber 3 having a high NA.
And a second waveguide portion 22 on the other end side that is joined to the second optical fiber 4 having a low NA, and a relay portion 23 that is arranged between the waveguide portions 21 and 22 and connects them.

The first waveguide portion 21 has one end side, that is, a high NA.
Taper core diverging toward the first optical fiber 3 of
The second waveguide 22 also has the first internal reflection surface 21a which is the cladding interface, and the second waveguide 22 also has the second optical fiber 4 of the other end side, that is, the low NA.
It has a second inner reflection surface 22a that is a tapered core / cladding interface that widens toward the.

On the large diameter side of the first internal reflection surface 21a, the diameter of the opening matches the core diameter of the first optical fiber 3, and when connecting to the first optical fiber 3, the first optical fiber 3 The core 3a is positioned. In addition, the first internal reflection surface 2
1a has a diameter of the opening on the smaller diameter side that matches the diameter of the cylindrical third internal reflection surface 23a of the relay portion 23, and is continuously connected to the third internal reflection surface 23a.

The diameter of the opening of the second internal reflection surface 22a is the same as the core diameter of the second optical fiber 4 on the large diameter side. The core 4a is positioned. Also, the second internal reflection surface 2
The diameter of the opening of 2a on the small diameter side matches the diameter of the cylindrical third internal reflection surface 23a of the relay portion 23, and is continuously connected to this third internal reflection surface 23a.

The conditions for reducing the connection loss in the optical fiber connector 2 of FIG. 1 will be described below.

As a condition for reducing the loss in the optical fiber connector 2, the signal light of the highest order mode from the first optical fiber 3 is once made higher in order by the first inner reflecting surface 21a and then the second inner reflecting surface. It is necessary to lower the order by 22a or more to match the transmission mode of the second optical fiber 4. At this time, the signal light having a larger traveling angle than the maximum traveling angle of the second optical fiber 4 among the signal light incident on the tapered first internal reflection surface 21a from the first optical fiber 3 is reflected by the first internal reflection. It is assumed that the light is reflected at least once on the surface 21a, and then the tapered second internal reflection surface 2 from the relay portion 23.
When incident on 2a, it is assumed that the signal light having the smallest advancing angle among the signal light whose mode has been converted by the first internal reflection surface 21a is reflected by the second internal reflection surface 22a one or more times.

Specific conditions will be described below with reference to FIG. The values A, B, C, r, and x are respectively the length in the optical axis direction of the relay portion 23, the length in the optical axis direction of the second internal reflection surface 22a, and the optical axis direction of the first internal reflection surface 21a. length,
It corresponds to the core diameter of the first optical fiber 3 and the core diameter of the relay section 23. Here, the taper angle of the first internal reflection surface 21a is θ
If the maximum traveling angle of the signal light of the highest mode incident on the first internal reflection surface 21a is α1, and the maximum traveling angle of the signal light incident on the second internal reflection surface 22a is α2, then θ1 = {Α2-α1} / 2 (1) holds. In this case, ideally the maximum advancing angle α
The signal light of 1 should not be reflected by the first internal reflection surface 21a more than once, and tan α1 <{(r- (r-x) / 2)} / C = r / C-tan θ1 (2) It is desired that θ1 and C satisfy the condition. However, from the viewpoint of not increasing the loss as compared with the case of direct connection, a traveling angle larger than the maximum traveling angle α3 of the second optical fiber 4 which is the final destination of the signal light from the first optical fiber 3 is set. It is necessary that the signal light that it has is reflected at least once by the second internal reflection surface 22a. Therefore, equation (2) becomes
Practically, it can be replaced with tan α3 ≧ {(r- (r-x) / 2)} / C = r / C-tan θ2 (3).

On the other hand, the taper angle of the second internal reflection surface 22a is set to θ.
2, and the core diameter of this second optical fiber 4 is r,
Ideally, light having a traveling angle of α3 or more should be reflected at least once among lights incident on the second internal reflection surface 22a, and light having a traveling angle of α2 should be less than or equal to the traveling angle α3. . Therefore, tan α3 ≧ {(r- (r-x) / 2)} / B = r / B-tan θ2 ... (4), θ2 ≧ {α2-α3} / 2 ... (5) Just fill. However, the signal light having the smallest traveling angle (traveling angle α2 ′) of the signal light converted to the higher order side by the first inner reflecting surface 21a is the second inner reflecting surface 22a.
Since the loss can be reduced as compared with the case of direct connection, the equation (4) is practically expressed as tan α2 ′ ≧ {(r- (r-x) / 2)} / B = r / It can be rewritten as B-tan θ2 (6).

Although unidirectional coupling has been considered above, bidirectional coupling must be considered in applications such as bidirectional optical communication. Also in this case, in order to reduce the loss in the optical fiber connector 2, it is necessary to determine the condition by the reverse logic of the above, but as a result, the above equations (3), (5), (6), etc. In the above, the symbols may be replaced appropriately.

Specific examples of the first embodiment will be described below. The first and second optical fibers 3 and 4 to be connected to each other were both plastic optical fibers having a core diameter of 1.0 mm. However, the first optical fiber 3 is a conventional type with an NA of 0.5, and the second optical fiber 4 is a low NA type with a wide transmission band and an NA of 0.3. Therefore, the maximum traveling angle α1 of the signal light transmitted through the first optical fiber 3 is 20 °, and the second optical fiber 4
The maximum advancing angle α3 of the signal light for transmitting is 11.6 °.

The maximum traveling angle α of the signal light in the repeater 23
It is necessary to change 2 according to other setting conditions, but here it is set to 29.6 °. That is, the plastic optical fiber forming the relay section 23 has an NA of 0.7. At this time, the taper angle θ of the first internal reflection surface 21a
1 is set to 4.8 ° from the equation (1). As described above, since the taper angle θ1 is 4.8 °, the geometrical relation shown in FIG. 1 is used, and as a critical condition, the relation of (r−x) /2C=tan4.8° is approximately calculated. Further, the relationship of (r + x) /2C=tan11.6° is obtained from the relationship of the expression (3). Solving these equations with r = 1.0 mm, the core diameter x = 0.38 mm of the relay portion 23
The length C of the internal reflection surface 21a in the optical axis direction is C = 3.36 mm.

The traveling angle α 2 incident on the second internal reflection surface 22a
Light is reflected here to have a traveling angle α3. Therefore, the taper angle θ2 of the second internal reflection surface 22a is 9.0 ° according to the equation (5). Also, α2 '= 2 × θ1 +
It is 11.6 °, and the relation (r + x) /2B=tan21.2° is obtained as the critical condition from the equation (6). r = 1.0 mm, x = 0.38 mm
By solving this equation, the length B of the second internal reflection surface 22a in the optical axis direction B = 1.77 mm is obtained. That is, the length of the second internal reflection surface 22a in the optical axis direction needs to be 1.77 mm or more.

However, since the diameter of the exit side opening (larger diameter side) of the second internal reflection surface 22a and the core diameter of the second optical fiber 4 must match, tan θ2 = (r−x) / 2C = tan9 It becomes 0.0 °, and it is necessary to set B = 2.0 mm in practice.

In the above description, the length A of the relay portion 23 in the optical axis direction is not particularly limited, and the length of the mount of the optical fiber connector 2 and the first and second optical fibers 3, 4 is not limited. It can be set appropriately in consideration of circumstances. This is because this length A does not directly affect the mode conversion. However, since scattering loss occurs at each reflection on the third internal reflection surface 23a of the relay portion 23, it is preferable to make the length A as short as possible. In the actual embodiment, A =
0.7 mm.

The production of the optical fiber connector 2 shown in FIG. 1 will be briefly described below. A sheath-shaped metal ferrule 5 was used for manufacturing the optical fiber connector 2. A plastic optical fiber of PMMA core having a small diameter and NA = 0.7 was inserted into the metal ferrule 5 and heated from the outside to cause heat shrinkage at both end portions of the metal ferrule 5. After that, the both end portions were cut and the end faces were polished to obtain the optical fiber connector 2 as illustrated.

The evaluation of the optical fiber connector 2 of FIG. 1 will be briefly described below. The end faces of the first and second optical fibers 3 and 4 were respectively brought into contact with both ends of the optical fiber connector 2, and a very small amount of index matching oil was injected into the contact faces. Wavelength 660 nm from the side of the first optical fiber with a large NA
When the stabilized test light of
An output of 29 μW with respect to W was obtained. Insertion loss is 1.1
7 dB.

On the other hand, the end faces of the first and second optical fibers 3 and 4 are directly brought into contact with each other without using the optical fiber connector 2 shown in FIG. did. When the same test light was made incident from the side of the first optical fiber with a large NA, the output was 2 for the input of 38 μW.
1 μW was obtained. The insertion loss was 2.57 dB.

FIG. 2 is a view for explaining the structure of the optical fiber connector of the second embodiment. The optical fiber connector 20 of the second embodiment is a modified example of the optical fiber connector 2 of the first embodiment, and the same portions or the same functional portions will be denoted by the same reference numerals and redundant description will be omitted.

Optical fiber connector 20 of the second embodiment
Is formed by processing the metal ferrule 20 itself instead of tapering the plastic optical fiber. That is, the optical fiber connector 20 has a high NA.
Of the metal ferrule 20 to be joined to the first optical fiber 3 of the first waveguide section 21 and a hollow of the other end of the metal ferrule 20 to be joined to the second optical fiber 4 of low NA. Second waveguide portion 22 composed of two parts and both waveguide portions 2
1 and 22 and a relay portion 23 which is a hollow portion that connects them.

The first waveguide portion 21 has a tapered first internal reflection surface 21a which spreads toward the first optical fiber 3 having a high NA, and the second waveguide portion 22 also has a low NA second light. It has a tapered second internal reflection surface 22a that spreads toward the fiber 4. Then, the relay portion 23 includes the first and second internal reflection surfaces 21.
a, 22a third inner reflection surface 2 connected to the opening on the smaller diameter side
3a.

The dimensions of the first and second internal reflection surfaces 21a and 22a are slightly different from those of the optical fiber connector 2 of the first embodiment. Since the optical fiber connector 20 is hollow, the traveling angle of the signal light emitted from the end face of the first optical fiber 3 and incident on the first waveguide 21 is the traveling angle in the first optical fiber 3. It will be larger than. However, the dimensions of the first and second internal reflection surfaces 21a and 22a are determined by the apparent NA of the first and third optical fibers 3 and 4.
However, it can be determined in the same manner as in the case of the first embodiment only by treating it as having increased by the amount of refraction at the end faces of the first and third optical fibers 3 and 4.

Specific examples of the optical fiber connector 2 according to the second embodiment will be described below. First and second
The optical fibers 3 and 4 are both plastic optical fibers having a core diameter of 1.0 mm, as in the specific example of the first embodiment. The first optical fiber 3 is a conventional type having an NA of 0.5, and the second optical fiber 4 is N
A is a low NA type with 0.3. Therefore,
Maximum traveling angle α1 of signal light transmitted through the first optical fiber 3
Is 20.0 °, but the maximum traveling angle α1 of the signal light incident on the first internal reflection surface 21a is 30.0 °. The maximum traveling angle α3 of the signal light transmitted through the second optical fiber 4 is 11.6 °, but the maximum traveling angle α2 of the signal light incident on the second internal reflection surface 22a is 17.4 °. .

The maximum traveling angle α of the signal light in the relay section 23
Although it is necessary to change the value 2 according to other setting conditions, here, it is set to 44.0 °. At this time, the taper angle θ1 of the first internal reflection surface 21a is 7.0 ° by applying the equation (1) in the same manner. In this way, since the taper angle θ1 is 7.0 °, the relation of (r−x) / 2C = tan 7.0 ° is roughly obtained, and from the relation of the equation (3), the critical condition is The relationship of (r + x) /2C=tan17.4° is obtained. Solving these equations with r = 1.0 mm, the core diameter x = 0.44 mm of the relay portion 23
The length C of the inner reflection surface 21a in the optical axis direction is 2.29 mm.

The traveling angle α2 incident on the second internal reflection surface 22a
Light is reflected here to have a traveling angle α3. Therefore, the taper angle θ2 of the second internal reflection surface 22a is 13.3 ° from the equation (5). Also, α2 '= 2 × θ1
It is + 17.4 °, and the relation (r + x) /2B=tan31.4° is obtained from the formula (6) as a critical condition. r = 1.0 mm, x = 0.44 mm
By solving this equation, the length B of the second internal reflection surface 22a in the optical axis direction B = 1.17 mm is obtained. That is, the length of the second internal reflection surface 22a in the optical axis direction needs to be 1.17 mm or more.

However, since the diameter of the emission side opening (large diameter side) of the second internal reflection surface 22a and the core diameter of the second optical fiber 4 must match, tan θ2 = (r−x) / 2C = tan13 It becomes 0.3 °, and it is necessary to set B = 1.2 mm.

The production of the optical fiber connector 20 shown in FIG. 2 will be briefly described below. Optical fiber connector 20
Cut a sheath-shaped metal ferrule based on the above calculation results. The inner surface of the cut was chrome-plated after mirror-polishing. Further, the plated inner surface was polished using chromium oxide. As a result, an ideal optical reflection surface could be obtained.

The evaluation of the optical fiber connector 20 shown in FIG. 2 will be briefly described below. The end faces of the first and second optical fibers 3 and 4 were connected to both ends of the optical fiber connector 20, respectively. At this time, since the two optical fibers 3 and 4 face each other with the air in the optical fiber connector 20 sandwiched therebetween, no matching oil or the like is required and the stability is high. When stabilized test light with a wavelength of 660 nm was made incident from the side of the first optical fiber 3 having a large NA, an output of 30 μW was obtained for an input of 38 μW. The insertion loss was 1.03 dB.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a vertical cross-sectional structure of an optical fiber connector according to a first embodiment.

FIG. 2 is a diagram illustrating a vertical cross-sectional structure of an optical fiber connector according to a second embodiment.

[Explanation of symbols]

 2, 20 optical fiber connector 3 high NA optical fiber 4 low NA optical fiber 21 first waveguide 22 second waveguide 23 relay 21a first internal reflection surface 22b second internal reflection surface 23c third internal reflection surface

Claims (4)

[Claims] 1. An optical fiber connector for connecting a pair of optical fibers having different numerical apertures, wherein the optical fiber connector is provided at one end side of the optical fiber connector and spreads toward the one end side. A first waveguide portion having a tapered first internal reflection surface having a first guiding portion for guiding light incident from one end of the optical fiber connector to the other end side of the optical fiber connector; A tapered second inner reflection surface that is provided and has a second taper angle larger than the first taper angle that spreads toward the other end side and that is arranged coaxially with the first inner reflection surface; An optical fiber connector comprising: a second waveguide portion that guides light from the first waveguide portion side to the outside of the other end of the optical fiber connector. 2. A relay unit, which is disposed between the first and second waveguide units and guides light from the first waveguide unit to the second waveguide unit, wherein the relay unit is a cylinder. Has a third inner reflecting surface, and the end on the smaller diameter side of the first inner reflecting surface is connected with the same diameter as one end of the third inner reflecting surface, and is on the smaller diameter side of the second inner reflecting surface. The optical fiber connector according to claim 1, wherein the end portion is connected to the other end of the third internal reflection surface with the same diameter. 3. The optical fiber connector according to claim 2, wherein the first and second waveguide portions are large-diameter portions formed at both ends of a rod-shaped optical fiber. 4. The large-diameter portion formed on each end of a sheath-shaped metal ferrule whose inner surface is mirror-finished, wherein the first and second waveguide portions are large diameter portions. Fiber optic connector.