JPH1158203A - End surface polishing method of optical fiber connector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold a favorable physical contact without deviation of mutual optical axis point of an optical fiber on the optical fiber connection surface of a slant projection spherical surface ferrule with a truncated conical shape. SOLUTION: In this polishing method, an angle made by the straight line for connecting the curvature center RC of a slant projection spherical surface ferrule 2 with an optical fiber optical axis point P1 and an optical fiber axis S is used as θ deg.. In this case, the truncated conical shape ferrule 2' on whose axis an optical fiber 1 is inserted and fixed is pressed perpendicularly to a polishing plate 20A and polished smoothly and next, the axis S of the ferrule 2' is held by a slant angle θ deg. for the vertical axis V of the polishing plate 20B and the tip of the ferrule 2' is polished from the orthogonally crossing surface with the axis S of the ferrule 2' to a slant plane F1 slanted by θ deg. and next the axis S of the ferrule s' is held to a slant angle (θ+α) deg. for the vertical axis V of an elastic polishing plate 20C and polished to a slant projection spherical surface Q1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing an end face of an optical fiber ferrule, and more particularly, to a CAT.
It relates to a method for polishing an end face of an optical fiber connector that requires good connection characteristics, such as an optical fiber connector or an optical fiber connector having an isolator function used for analog image optical communication such as V, ultra-high speed optical communication, optical amplifier and the like. is there.

[0002]

2. Description of the Related Art When connecting optical fibers to each other, as shown in FIG. 3, a central axis is used to reduce connection loss and reflected return light due to a shift of an axis center between optical fibers and a gap at a connection surface. The end faces of the two optical fiber ferrules A and B into which the optical fibers LA and LB are inserted and fixed have a curvature radius R having curvature center points RA and RB at positions deviated from the optical fiber center axes SA and SB of the ferrules A and B. Polished into oblique convex spherical surfaces QA and QB, these two ferrules A and B
Of the slanted convex spherical surfaces QA and QB of the ferrules are set at a predetermined angle θ ° between a straight line connecting the center points RA and RB of curvature of each ferrule and the optical axis points PA and PB and the central axes SA and SB of the optical fibers. For example, Japanese Patent Application Laid-Open No. 61-87111 and Japanese Patent Application Laid-Open No. 1-1218
No. 05 is proposed. By butt-connecting the ferrules whose connection end surfaces are polished to oblique convex spherical surfaces QA and QB in this manner, the optical fibers LA and LB form physical contacts in close contact with each other, and loss and reflection return light on the connection surface are reduced. .

The tip shape of a ferrule used for forming such an oblique convex spherical surface includes a stepped cylindrical shape as shown in FIG. 4A and a ferrule tip as shown in FIG. There is a truncated conical shape with a chamfered peripheral edge. In the figure, A and A 'indicate ferrules, and L indicates an optical fiber.

As a method for polishing an end face of an optical fiber connector for forming such an oblique convex spherical surface, a conventional method is shown in FIG.
A polishing step as shown in FIGS. FIG. 5 illustrates the case where the tip shape of the ferrule is a frusto-conical shape, but the same polishing step is also performed when the ferrule is a stepped cylindrical shape. In the polishing step, first, as shown in FIG. 5A, a frusto-conical tip of a ferrule 12 'in which an optical fiber 11 is inserted into a central axis S and fixed with an adhesive H is attached to a polishing sheet on a surface plate. Press vertically onto the abraded polishing plate 20A and rotate it around a vertical rotation axis to obtain a ferrule 12 ′.
The adhesive H adhering to the tip of the substrate is polished smoothly. Next, as shown in FIG. 5B, the center axis S of the ferrule 12 ′ is held at an angle θ ° from the vertical axis V of the polishing plate 20B, and the tip of the ferrule 12 ′ is polished with a polishing grindstone. The ferrule 12 ′ is pressed against the plate 20 B and rotated around a vertical rotation axis, and the tip of the ferrule 12 ′ is polished to an oblique plane F 10 inclined by θ ° from a plane perpendicular to the central axis S of the ferrule 12 ′.
At the time of this polishing, the formed oblique plane F10 becomes the oblique plane F
A shift occurs between the center point FC ′ of the optical fiber 11 and the optical axis point P ′ of the optical fiber 11. Next, as shown in FIG. 5 (c), the center axis S of the ferrule 12 'is held at the same angle θ ° with respect to the vertical axis V of the elastic polishing plate 20C as in the oblique plane polishing step of FIG. 5 (b). And the oblique plane F10 of the ferrule 12 '
Is an elastic body polishing plate 20C in which a polishing sheet is pasted on a rubber plate.
And rotated about a vertical rotation axis by using an elastic recess formed in the elastic polishing plate 20C, thereby obtaining an oblique plane F1.
0 is θ ° from a plane perpendicular to the central axis S of the ferrule 12 ′.
Polishing to the inclined oblique convex spherical surface Q10. In the formed oblique convex spherical surface Q10, there is a shift Δ1 between the center point QC ′ of the oblique convex spherical surface Q10 and the optical axis point P10 of the optical fiber 11. In the figure, RC ′ is the center point of curvature of the oblique convex spherical surface Q10, R
Denotes the radius of curvature, and α denotes the angle corresponding to △ l.

In the case of the oblique convex spherical ferrule 12 formed as described above, the optical axis S of the oblique convex spherical ferrule 12 is inclined by θ ° from the vertical axis V and joined to a plane X orthogonal to the vertical axis V. As shown in FIG. 6, the oblique convex spherical surface Q10 of the ferrule 12 has its machining center point QC 'as a contact point with the plane X, and the contact point between the oblique convex spherical surface Q10 with the plane X and the optical axis point P10 of the optical fiber 11. Is equal to the shift Δl between the center point QC ′ of the oblique convex spherical surface Q10 and the optical axis point P10 of the optical fiber 11. Therefore,
There is a gap between the optical axis point P10 of the optical fiber 11 and the plane X.

[0006]

As described above, the tip shape of the ferrule is classified into a stepped cylindrical shape and a frusto-conical shape. However, when the stepped cylindrical ferrule is subjected to the processing of the oblique convex spherical surface, the occurrence of the shift Δl between the center point of the oblique convex spherical surface and the optical axis point of the optical fiber as described above is relatively small. There was a major drawback in that chipping occurred at the peripheral edge of the ferrule. This is due to the fact that the ferrule is formed from hard and brittle zirconia (ZrO ₂ ). Therefore, there is a difficulty in using a stepped cylindrical ferrule for oblique convex spherical surface polishing from the viewpoint of quality.

On the other hand, the frusto-conical ferrule does not have a problem that the peripheral edge of the ferrule is chipped during polishing, but as shown in FIG. 5C, the center of the formed oblique convex spherical surface Q10 is formed. There is another problem that the point QC ′ is shifted from the optical axis point P10 of the optical fiber 11 by Δ1. When the deviation Δl is present, as shown in FIG. 6, when the tip of the oblique convex spherical ferrule 12 is brought into contact with a plane X inclined by θ ° from a plane orthogonal to the optical axis S of the oblique convex spherical ferrule 12. The center point QC ′ of the oblique convex spherical surface Q10 is in contact with the plane X, and the optical axis point P10 is in a state where a gap is formed from the plane X. In a state where such a gap is generated, when the obliquely convex spherical ferrules 12 are butt-connected to each other, a gap or gap is generated between the optical axis points P10 of the optical fiber 11, and an air layer is formed on the connection surface of the optical fiber. , The physical contact at the optical fiber connection surface is broken, Fresnel reflection loss and gap loss are caused, and the connection loss is increased. The deviation Δl is the amount of curvature eccentricity with respect to the curvature radius R of the oblique convex spherical surface, and varies depending on the value of the curvature radius R. In order not to break the physical contact at the optical fiber joint surface when the oblique convex spherical ferrules 12 are butt-connected to each other, the structure of the oblique convex spherical ferrule is as follows.
For example, the curvature radius is set to 5 to 12 mm, and the curvature eccentricity Δl is set to 5
It is necessary to suppress it to 0 μm or less.

Accordingly, an object of the present invention is to eliminate the deviation of the optical axis of the optical fiber at the connection surface when the optical fibers are butt-connected in forming a frusto-conical obliquely convex spherical ferrule, thereby providing a good physical contact. It is an object of the present invention to provide a method for polishing an end face of an optical fiber connector which can maintain a low connection loss and a small amount of reflected return light.

[0009]

SUMMARY OF THE INVENTION According to the present invention, an end face of a truncated conical ferrule having an optical fiber inserted and fixed to a central axis has a radius of curvature having a center of curvature at a position deviated from the optical fiber central axis of the ferrule. An oblique convex spherical ferrule is formed by forming an oblique convex spherical ferrule of R, and two of the oblique convex spherical ferrules are connected to a straight line connecting the curvature center point of the oblique convex spherical surface of the two ferrules and the optical fiber optical axis point to the optical fiber center. A method of polishing an end face of an optical fiber connector which is used by butt-connecting an inclined angle with respect to an axis to a predetermined angle θ ° and using the same, wherein the frusto-conical ferrule is held at a required polishing angle and pressed against an elastic polishing plate. In the elastic polishing step of polishing the front end surface of the ferrule into an oblique convex spherical surface by relatively rotating the elastic polishing plate around the vertical rotation axis of the elastic polishing plate, The polishing angle between the optical fiber center axis of the rule and the vertical axis of the elastic polishing plate is (θ + α) °
And a method of polishing an end face of an optical fiber connector characterized by polishing a ferrule while holding the ferrule.

In the present invention, it is preferable that the angle α ° is an angle determined by the following equation (1). α ≒ tan ⁻¹ (△ l / R) ─── (1) Here, △ l represents curvature eccentricity, and R represents the radius of curvature.

In the present invention, the radius of curvature R is 5
It is desirably in the range of 12 mm to 12 mm.

[0012]

The occurrence of the curvature eccentricity Δl is caused by the fact that the peripheral edge of the ferrule 12 ′ is tapered. That is, in the above-described oblique plane polishing shown in FIG. 5B, a shift occurs between the center point FC ′ of the oblique plane F10 and the optical axis point P ′, and further, the oblique convex spherical elastic polishing shown in FIG. The elastic polishing is performed at the center point F of the oblique plane F10.
As a result of centering on C ', the center point of the ferrule 12', that is, the optical axis point P10 of the optical fiber 11, is formed shifted from the center point QC 'of the formed oblique convex spherical surface Q10 by the curvature eccentricity? 1. Will be. It is difficult to avoid the curvature eccentricity Δl as long as the peripheral edge of the ferrule 12 ′ is tapered.

The curvature eccentricity Δl is uniquely determined by the value of the radius of curvature R of the obliquely convex spherical surface if the taper angle of the frustoconical ferrule is determined, and the curvature eccentricity corresponding to the radius of curvature R Δl can be obtained. Therefore, if the curvature eccentricity △ l corresponding to the curvature radius R of the oblique convex spherical surface ferrule 12 is obtained in advance, a straight line and a light passing through the center point QC ′ of the oblique convex spherical surface Q10 can be obtained as is known from FIG. The intersection angle with the fiber center axis S, in other words, the curvature eccentric angle α ° corresponding to the curvature eccentricity △ l can be obtained from the equation (1). α ≒ tan ^-1 (△ l / R) ───── (1) △: curvature eccentricity, R: curvature radius

Therefore, in the polishing method of the present invention, the processing polishing angle between the optical fiber center axis of the ferrule and the vertical axis of the polishing plate surface in the oblique convex spherical elastic polishing is determined in advance by the butt connection of the oblique convex spherical ferrule. Tilt angle θ
Polishing with an oblique convex sphere is performed while maintaining the eccentricity angle α ° larger than °. Even in the case of the polishing method of the present invention, the curvature eccentricity Δl still occurs between the center point of the oblique convex spherical surface and the optical axis point. However, in the case of the oblique convex spherical ferrule 2 by the polishing method of the present invention, the optical fiber center axis S is formed at an angle of (θ + α) ° with respect to the vertical axis V.
For this reason, as shown in FIG.
When the optical axis S is inclined by θ ° from the vertical axis V of the ferrule 2 and joined to a plane X orthogonal to the vertical axis V of the ferrule 2, the oblique convex spherical surface Q1 and the plane X correspond to the curvature eccentricity △ l. Is corrected by the angle α °, the optical axis point P of the oblique convex spherical surface Q1 is joined to the plane X, and the gap G between the X plane contact point of the oblique convex spherical surface Q1 and the optical axis point P is eliminated. Will be done. Therefore, the oblique convex spherical ferrules 2 of the present invention are set at an angle of θ ° between the straight line connecting the curvature center point R1 of the oblique convex spherical surface Q1 and the optical fiber optical axis point P1 and the optical fiber central axis S. In the case of the butt connection, the optical fiber optical axis points P1 form a good physical contact with each other, and the connection loss can be eliminated.

The taper angle of the frusto-conical ferrule is usually set to about 30 °. When the taper angle is smaller than 30 °, the frequency of occurrence of chipping of the peripheral edge of the ferrule at the time of polishing increases, and the taper angle becomes smaller than 30 °.
This is because there is not much effect in preventing the peripheral edge of the ferrule from being chipped at the time of polishing even if it is larger than 0 °.

For example, the inclination angle of the optical axis of the ferrule is set to 8
When polishing a 30-degree frusto-conical ferrule with a chamfer angle of 30 ° into an oblique convex spherical surface with a radius of curvature of 7 mm, use the processing and polishing angle between the optical fiber optical axis of the ferrule and the vertical axis of the elastic polishing plate in elastic polishing. When the polishing is maintained at 8 ° which is the same as the inclination angle, a curvature eccentricity Δl of 70 μm is finally generated. Therefore, when the curvature eccentric angle α ° corresponding to the curvature eccentricity Δl of 70 μm is obtained from the above equation (1), α = tan ⁻¹ (0.07 / 7) = tan ⁻¹ (0.01), that is, α = 0.57 ° ≒ 0.6 °. Accordingly, the working polishing angle formed by the center axis of the ferrule and the vertical axis of the polishing plate at the time of polishing the oblique convex spherical surface is set to 0.6 ° in advance from 8 ° to 8.6 °.
If set to a large value and polished, an oblique convex spherical ferrule that can maintain physical contact between optical fiber optical axis points when the oblique convex spherical ferrules are butt-connected at an inclination angle of 8 ° is formed. Can be.

In the method for polishing an end face of an optical fiber connector according to the present invention, the radius of curvature R is desirably 5 to 12 mm. This is because the range in which the physical contact does not collapse when the optical fiber ferrules having obliquely convex spheres are connected is 5 to 12 mm.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for polishing an end face of an optical fiber connector according to the present invention will be described below in detail with reference to an embodiment shown in the drawings.
It should be noted that the present invention is not limited by this.
FIG. 1 shows steps of an optical fiber end face polishing method according to the present invention. First, as shown in FIG. 1 (a), as in the conventional process, the conical tip of a frusto-conical ferrule 2 'in which the optical fiber 1 is inserted into the central axis S and fixed with an adhesive H is placed on a surface plate. Pressing vertically to the polishing plate 20A with the polishing sheet attached,
By rotating the polishing plate 20A about the vertical rotation axis of the polishing plate 20A, the adhesive H attached to the tip of the ferrule 2 'is polished smoothly.
Next, as shown in FIG. 1B, similarly to the conventional process, the center axis S of the ferrule 2 ′ is held at an angle θ ° from the vertical axis V of the polishing plate 20B, and the tip of the ferrule 2 ′ is polished. The tip of the ferrule 2 ′ is polished into an oblique plane F1 inclined by θ ° from a plane orthogonal to the central axis S of the ferrule 2 ′ by pressing against the polishing plate 20 </ b> B on which the grindstone is placed and rotating about a vertical rotation axis. In this case, the formed oblique plane F1 is located between the center point FC of the oblique plane F1 and the optical axis point P ′ of the optical fiber 1.
And there is a gap between them. Next, as shown in FIG. 1 (c), the center axis S of the ferrule 2 'is maintained at a processing polishing angle of (θ + α) ° with respect to the vertical axis V of the elastic polishing plate 20C,
The oblique plane F1 of the ferrule 2 'is pressed against an elastic polishing plate 20C in which a polishing sheet in which diamond powder is applied on an elastic plate made of rubber or the like is applied to the elastic polishing plate 20C. By rotating the ferrule 2 'around the vertical rotation axis, the tip of the ferrule 2'
Oblique convex spherical surface Q1 inclined at (θ + α) ° from a plane perpendicular to
Polish. In this case, the center point QC of the formed oblique convex spherical surface Q1 is shifted from the optical axis point P1 of the optical fiber 1 by Δ1.

FIG. 2 shows an obliquely convex spherical ferrule 2 formed as described above, wherein the optical axis S is the vertical axis V of the ferrule 2.
FIG. 9 is a diagram showing a state in which the ferrule is joined to a plane X orthogonal to a vertical axis V of the ferrule 2 while being inclined by θ ° from FIG. FIG.
As shown in FIG. 2, the oblique convex spherical surface Q1 of the ferrule 2 is in a state where the optical fiber optical axis point P1 is in contact with the plane X. This is because the polishing angle is increased by the curvature eccentric angle α ° corresponding to the curvature eccentricity Δl between the center point QC of the oblique convex spherical surface Q1 and the optical axis point P1 of the optical fiber 1 in advance, and the angle of the oblique convex spherical surface Q1 is increased.
Is formed, when the tip of the oblique convex spherical surface Q1 is joined to the plane X, the optical axis point P1 of the convex spherical surface Q1 is brought into contact with the plane X by being corrected by an angle α ° corresponding to the curvature eccentricity △ l. Join. Therefore, the oblique convex spherical ferrules 2 of the present invention are set at an angle of θ ° between the straight line connecting the curvature center point R1 of the oblique convex spherical surface Q1 and the optical fiber optical axis point P1 and the optical fiber central axis S. When butt-connected, the optical fiber optical axis points P1 form good physical contacts with each other.

Next, an example of manufacturing an oblique convex spherical ferrule in the case where a frusto-conical ferrule having a chamfer angle of 30 ° is polished into an oblique convex spherical surface having a radius of curvature of 7 mm and used at an optical axis inclination angle of 8 ° will be described. For a ferrule having a 7 mm radius of curvature of the oblique convex spherical surface, the previously determined curvature eccentricity Δl was 0.07 mm. From the above equation (1), the curvature eccentricity of 0.07 mmｍｍ
When the curvature eccentric angle α ° corresponding to ¹ is obtained, α = tan ⁻¹ (0.07 / 7) = tan ⁻¹ (0.01) ≒ 0.6 °. Therefore, the processing angle between the central axis S of the ferrule 2 and the vertical axis V of the elastic polishing plate 20C in the oblique convex spherical elastic polishing step of FIG. 1C is maintained at (8 + 0.6) °, and the oblique convex spherical surface is formed. Ferrule 2 was polished and manufactured.

As a comparative example, the chamfer angle is 30 °,
Fig. 5 (c) shows a frustoconical ferrule with a radius of curvature of 7mm.
The oblique convex spherical ferrule 12 polished while maintaining the processing angle between the center axis S of the ferrule 12 and the vertical axis V of the elastic polishing plate 20C in the oblique convex spherical elastic polishing step at 8 ° was prepared.

With respect to the oblique convex spherical ferrule 2 of the above-described manufacturing example and the oblique convex spherical ferrule 12 of the comparative example, the optical axis S of the oblique convex spherical ferrule is inclined by 8 ° from the ferrule vertical axis V to be orthogonal to the ferrule vertical axis V. Table 1 shows the results of measuring the gap G between the optical axis point and the contact point between the plane X and the oblique convex spherical surface at this time. In each of the production example and the comparative example, ten samples were prepared. The measured value is an average value of 10 samples.

As is clear from Table 1 below, when the oblique convex spherical ferrule manufactured by the polishing method of the present invention is inclined to the plane X by inclining the optical axis at a predetermined inclination angle of 8 ° from the vertical axis of the ferrule, it is oblique. It can be seen that the gap G between the X-plane contact point of the convex spherical surface and the optical axis point is very small. Therefore, when the optical fiber ferrule manufactured according to the present invention is butt-connected at an optical axis inclination angle of 8 °,
The deviation of the optical axis point between the optical fibers is small, indicating that good physical contact is maintained.

[0024]

[Table 1]

Next, the chamfer angle is 30 °, the radius of curvature Rmm
When the center point of the oblique convex spherical surface and the optical axis point, which occur when the truncated conical oblique convex spherical ferrules are butt-connected at an inclination angle of 8 °, and the curvature eccentricity Δl is 70 μm,
Table 2 shows the results obtained by calculating the curvature eccentric angle α ° with respect to each curvature radius R from the equation (1). As described above, if the values of the curvature eccentric angles α ° at the respective curvature radii R are summarized in a table, it is convenient to set the processing inclination angle of the ferrule in performing the oblique convex spherical surface polishing work.

[0026]

[Table 2]

[0027]

According to the method for polishing the end face of an optical fiber connector of the present invention, the inclination angle between the straight line connecting the center point of curvature of the oblique convex spherical surface and the optical axis point of the optical fiber and the center axis of the optical fiber of the ferrule is θ. When the oblique convex spherical surface of the optical fiber ferrule used at a setting of ° is polished, the polishing angle formed by the optical fiber center axis of the ferrule and the vertical axis of the polishing plate is α ° larger than the inclination angle θ ° by (θ + α) °. By using a very simple method of simply holding and polishing the optical fiber connector, the deviation of the optical axis of the optical fiber when the oblique convex spherical ferrules are butt-connected is eliminated, and a good physical contact is maintained. Therefore, it is possible to provide an optical fiber connector having excellent connection characteristics with less connection loss and reflected return light.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of a ferrule showing one embodiment of a process in an end face polishing method for an optical fiber connector of the present invention. (A) shows a smooth polishing step of the tip of the ferrule.
(B) shows an oblique plane polishing step of the ferrule tip.
(C) shows an oblique convex spherical surface polishing step (elastic polishing step) at the tip of the ferrule.

FIG. 2 is an explanatory sectional view showing a state in which an oblique convex spherical ferrule formed by the method of the present invention is inclined by θ ° and joined to a plane X.

FIG. 3 is an explanatory diagram showing a state in which optical fiber ferrules having obliquely convex spherical surfaces are butt-connected.

FIG. 4 is an explanatory front view showing a tip shape of a ferrule.

FIG. 5 is an explanatory sectional view of a ferrule showing steps of a conventional method for polishing an end face of an optical fiber connector. (A) shows a smooth polishing step of the tip of the ferrule. (B) shows an oblique plane polishing step of the ferrule tip. (C) shows an oblique convex spherical surface polishing step of the ferrule tip.

FIG. 6 is an explanatory cross-sectional view showing a state where an oblique convex spherical ferrule formed by a conventional method is inclined by θ ° and joined to a plane X.

[Explanation of symbols]

 Reference Signs List 1 optical fiber 2 oblique convex spherical ferrule 2 'truncated conical ferrule θ inclination angle α curvature eccentric angle R radius of curvature RC center of curvature △ l curvature eccentricity G interval S central axes of optical fiber P1, P' optical axis point F1 oblique plane FC Center point of oblique plane Q1 Oblique convex sphere QC Center point of oblique convex sphere V Vertical axis H Adhesive X Plane 20A Polishing plate 20B Polishing plate 20C Elastic polishing plate

Claims (3)

[Claims] 1. An end face of a truncated conical ferrule in which an optical fiber is inserted and fixed to a central axis is formed as an oblique convex spherical surface having a radius of curvature R having a center of curvature at a position off the optical fiber central axis of the ferrule. To form an oblique convex spherical ferrule, and the two oblique convex spherical ferrules define a tilt angle between a straight line connecting the center point of curvature of the oblique convex spherical surface of the two ferrules and the optical axis of the optical fiber and the central axis of the optical fiber. A method of polishing an end face of an optical fiber connector which is butt-connected and used at an angle θ °, wherein the vertical rotation of the elastic polishing plate is performed while holding the frusto-conical ferrule at a required polishing processing angle and pressing against the elastic polishing plate. In the elastic polishing step of polishing the tip end surface of the ferrule into an oblique convex spherical surface by relatively rotating around the axis, the optical fiber center axis of the frusto-conical ferrule and End surface polishing method of the optical fiber connector, characterized by polishing the holding eggplants grinding angle between the vertical axis (θ + α) in ° ferrule sexual polishing plate. 2. The method for polishing an end face of an optical fiber connector according to claim 1, wherein said α ° is an angle determined by equation (1). α ≒ tan ⁻¹ (△ l / R) ─── (1) where, △ l represents curvature eccentricity, and R represents a radius of curvature. 3. The method for polishing an end face of an optical fiber connector according to claim 1, wherein the radius of curvature R is in a range of 5 mm to 12 mm.