JP3473230B2 - Optical fiber connector - 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 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 the same core diameter and different numerical apertures, An opening on the large diameter side of the first internal reflection surface is provided, which is provided on one end side of the optical fiber connector and has a tapered first internal reflection surface having a predetermined first taper angle that spreads toward the one end side. Has a diameter equal to the core diameter of the optical fiber on the high numerical aperture side, and guides light incident from one end of the high numerical aperture side optical fiber connector to the other end side of the optical fiber connector. One waveguide portion and a second taper angle that is provided on the other end side of the optical fiber connector and that spreads toward the other end side and that is larger than the first taper angle and is coaxial with the first internal reflection surface. Equipped with tapered second internal reflection surface The diameter of the opening of the second inner large diameter side of the reflecting surface coincides with the core diameter of the optical fiber of the small numerical aperture side, the optical fiber of the optical low numerical aperture side from the first waveguide portion a second waveguide for guiding the outer end of the connector, the first及
And the second waveguide portion, and is arranged between the first waveguide portion and
A relay section for guiding light to the second waveguide section,
The part has a cylindrical third internal reflection surface, and the first internal reflection surface
The end on the small diameter side of has the same diameter as one end of the third internal reflection surface.
The small-diameter-side end of the second internal reflection surface is connected to the first internal reflection surface.
It is connected to the other end of the internal reflection surface with the same diameter.
And θ1 = {α2-α1} / 2 tan α3 ≧ {(r- (r-x) / 2)} / C = r / C
−tan θ1 θ2 ≧ {α2−α3} / 2 tan α2 ′ ≧ {(r− (r−x) / 2)} / B = r /
B-tan θ2 However, the length of the second internal reflection surface in the optical axis direction is B, and the first internal reflection is
The length of the surface in the optical axis direction is C, and the core diameter of the pair of optical fibers is
r, the core diameter of the relay section is x, the first taper angle is θ1, and the second taper is
The super-angle is θ2, and the highest order mode incident on the first internal reflection surface
The maximum advancing angle of light should be α1 and should be incident on the second internal reflection surface.
Set the maximum traveling angle of light to α2, the optical fiber that is the output destination
The maximum advancing angle of light at is α3, and the high-order side is the first internal reflection surface
The traveling angle of the light with the smallest traveling angle among the light converted into
It is characterized by setting so that α2 'is satisfied .

[0006]

The optical fiber connector of claim 2 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 3 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 a door, etc. Shiimono. Therefore, even when the higher-order mode light from the optical fiber side with the same core diameter and a high numerical aperture is coupled to the optical fiber with the same core diameter and a low numerical aperture, a pair of light is used with the openings at both ends of the optical fiber connector. 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
It is desired that θ1 and C satisfy the condition of −tan θ1 ... (2). 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 first internal reflection surface 21a . Therefore, equation (2) becomes
Practically, tan α3 ≧ {(r- (r-x) / 2)} / C = r / C
-Tan θ1 can be replaced with (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 reference numerals 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 from the formula (6) as the critical condition. 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 reality.

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 =
It was 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
It was 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 = tan 31.4 ° 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 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 Fiber Optic Connector 3 High NA optical fiber 4 Low NA optical fiber 21 First Waveguide 22 Second Waveguide 23 Relay section 21a First internal reflection surface 22b Second internal reflection surface 23c Third internal reflection surface

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 6 / 14,6 / 26,6 / 38

Claims (3)

(57) [Claims] 1. An optical fiber connector for connecting a pair of optical fibers having the same core diameter and different numerical apertures, the optical fiber connector being provided on one end side of the optical fiber connector and expanding toward the one end side. Of the first inner reflection surface having a first taper angle, the diameter of the opening on the large diameter side of the first inner reflection surface is the same as the core diameter of the optical fiber on the high numerical aperture side, and the high opening A first waveguide portion that guides light incident from one end of the optical fiber connector on one side to the other end side of the optical fiber connector, and is provided on the other end side of the optical fiber connector and is directed toward the other end side. A tapered second inner reflection surface having a second taper angle larger than the widening first taper angle and arranged coaxially with the first inner reflection surface; Core diameter of the optical fiber whose opening diameter is on the low numerical aperture side Matching a second waveguide for guiding light from the first waveguide portion on the outside of the other end of the optical fiber connector of the small numerical aperture side, disposed between the first and the second waveguide section And the first guide
The light from the multiplexing part and a relay portion leading to the second waveguide, the relay unit includes a cylindrical third inner reflecting surface, said first
The end portion on the small diameter side of the internal reflection surface is one end of the third internal reflection surface.
Ends on the smaller diameter side of the second internal reflection surface that are connected with the same diameter
Is connected to the other end of the third internal reflection surface with the same diameter.
Ri, wherein, θ1 = {α2-α1} / 2 tanα3 ≧ {(r- (r-x) / 2)} / C = r / C
−tan θ1 θ2 ≧ {α2−α3} / 2 tan α2 ′ ≧ {(r− (r−x) / 2)} / B = r /
B-tan θ2 However, the length of the second internal reflection surface in the optical axis direction is B, and the first internal reflection is
The length of the surface in the optical axis direction is C, and the core diameter of the pair of optical fibers is
r, the core diameter of the relay section is x, the first taper angle is θ1, and the second taper is
The super-angle is θ2, and the highest order mode incident on the first internal reflection surface
The maximum advancing angle of light should be α1 and should be incident on the second internal reflection surface.
Set the maximum traveling angle of light to α2, the optical fiber that is the output destination
The maximum advancing angle of light at is α3, and the high-order side is the first internal reflection surface
The traveling angle of the light with the smallest traveling angle among the light converted into
An optical fiber connector that is set to satisfy α2 ' . 2. The first and second waveguides are rod-shaped.
It is a large diameter part formed at both ends of the optical fiber
The optical fiber connector according to claim 1, which is characterized in that. 3. The first and second waveguides have a mirror-finished inner surface.
Formed on both ends of a sheath-shaped metal ferrule processed to
The optical fiber according to claim 1, wherein the optical fiber is a large diameter portion.
Iva connector.