Optical fiber measurement device and method for bending optical fiber

An optical fiber measurement device includes a light source, a light detector, a direction-changing member, and a tension-applying member. The light source emits light toward an optical fiber. The light detector receives the light that has propagated through the optical fiber. The optical fiber is hung on the direction-changing member. The direction-changing member changes an extending direction of the optical fiber to extend downward, the optical fiber being optically connected to the light source and the light detector at each of two end parts of the optical fiber. The tension-applying member applies a tension to the optical fiber hanging from the direction-changing member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2019-166336, filed Sep. 12, 2019, the contents of which are hereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an optical fiber measurement device and a method for bending an optical fiber.

BACKGROUND

Patent Document 1 discloses an optical fiber measurement device including a light source, a photodetector, and a roller that bends an optical fiber. In the optical fiber measurement device, components such as the light source, the photodetector, and the roller are disposed on substantially the same plane.

CITATION LIST

Patent Document

SUMMARY

In the configuration of Patent Document 1, when the optical fiber is hung around the roller, the position of the optical fiber in an up-down direction is likely to vary because of the weight of the optical fiber, or the optical fiber is likely to be obliquely wound around the roller. In such a manner, when it is difficult to set the optical fiber, the posture (position) of the optical fiber with respect to the roller is likely to vary. As a result, the radius of curvature of bending of the optical fiber may vary from setting to setting, and the accuracy of measurement may become unstable.

One or more embodiments of the present invention provide an optical fiber measurement device or a method for bending an optical fiber capable of improving the ease of setting the optical fiber and of stabilizing the accuracy of measurement.

According to one or more embodiments of the present invention, there is provided an optical fiber measurement device including: a light source that emits light toward an optical fiber; a light-receiving portion (i.e., detector) that receives the light that has propagated through the optical fiber; a direction-changing member on which the optical fiber is hung, and which changes an extending direction of the optical fiber downward, the optical fiber being optically connected to the light source and the light-receiving portion at both end parts of the optical fiber; and a tension-applying member that applies a tension to the optical fiber hanging from the direction-changing member.

According to one or more embodiments of the present invention, there is provided a method for bending an optical fiber, the method including: hanging the optical fiber on a direction-changing member, both end parts of the optical fiber being fixed; applying a tension to the optical fiber hanging from the direction-changing member using a tension-applying member; and bending the optical fiber using a plurality of mandrels disposed between the direction-changing member and the tension-applying member.

According to one or more embodiments of the present invention, the optical fiber measurement device and the method for bending an optical fiber can be provided which are capable of improving the ease of setting the optical fiber and of stabilizing the accuracy of measurement.

DETAILED DESCRIPTION

First Embodiment

Hereinafter, an optical fiber measurement device and a bending method according to a first embodiment will be described with reference to the drawings.

As shown inFIGS.1A to1C, an optical fiber measurement device (hereinafter, referred to as a measurement device10A) includes a stage S, a light source1, a light-receiving portion2, a direction-changing member3, a tension-applying member4, and the like. The measurement device10A is a device that bends an optical fiber F and measures a characteristic of the optical fiber F. Incidentally, the light source1and the light-receiving portion2may be provided inside one analysis device.

In the present embodiment, an X-Y-Z Cartesian coordinate system is set, and a positional relationship between configurations will be described. In each drawing, a Z axis represents an up-down direction, an X axis represents one direction orthogonal to the up-down direction, and a Y axis represents a direction orthogonal to both the Z axis and the X axis. Hereinafter, a Z-axis direction is referred to as the up-down direction, an X-axis direction is referred to as a left-right direction, and a Y-axis direction is referred to as a front-back direction. In addition, a +Z side in the up-down direction indicates an upper side, and a −Z side indicates a lower side. One side (+X side) in the left-right direction is referred to as a right side, and the other side (−X side) is referred to as a left side. One side (+Y side) in the front-back direction is referred to as a front side, and the other side (−Y side) is referred to as a rear side.

The optical fiber F to be measured may be a single mode fiber. The specific type of the optical fiber F can be appropriately changed.

The stage S is a desk or the like. The light source1and the light-receiving portion2are placed on the stage S. The light source1and the light-receiving portion2are disposed at an interval in the left-right direction. The light source1is disposed on the left side, and the light-receiving portion2is disposed on the right side. Incidentally, the positions of the light source1and the light-receiving portion2may be reversed.

The light source1emits light toward the optical fiber F. A first end part of the optical fiber F is optically connected to an emitting side connection portion1aof the light source1. The wavelength of the light emitted by the light source1and the like are appropriately changed according to the characteristic to be measured of the optical fiber F. Namely, the light source1is configured to be capable of appropriately changing the wavelength of light or the like. Incidentally, the emitting side connection portion1aand the first end part of the optical fiber F may be directly connected to each other, or may be connected to each other via another optical path (optical fiber or optical waveguide). In either case, the optical fiber F and the light source1are optically connected to each other.

The light-receiving portion2receives the light that has propagated through the optical fiber F. A second end part of the optical fiber F is optically connected to an incident side connection portion2aof the light-receiving portion2. The light-receiving portion2is configured to be capable of analyzing a characteristic of the optical fiber F based on the received light. Incidentally, the incident side connection portion2aand the second end part of the optical fiber F may be directly connected to each other, or may be connected to each other via another optical path (optical fiber or optical waveguide). In either case, the optical fiber F and the light-receiving portion2are optically connected to each other.

The direction-changing member3is located in front of the light source1and the light-receiving portion2. A part of the optical fiber F connected to the light source1and the light-receiving portion2is hung on the direction-changing member3. Accordingly, the direction-changing member3changes a direction, in which the optical fiber F extends forward from the light source1and the light-receiving portion2, downward. The direction-changing member3extends along the left-right direction. A left end portion of the direction-changing member3is located on a left side of the emitting side connection portion1a, and a right end portion of the direction-changing member3is located on a right side of the incident side connection portion2a. Namely, the direction-changing member3is disposed across the emitting side connection portion1aand the incident side connection portion2ain the left-right direction. The direction-changing member3is fixed to the stage S. However, the direction-changing member3may be fixed to a member other than the stage S (for example, floor surface or the like).

The direction-changing member3of the present embodiment is formed in a columnar shape. In addition, a diameter of the column is smaller than φ280 mm, and a part of the optical fiber F is bent along an outer peripheral surface of the direction-changing member3. For this reason, the optical fiber F is bent at a radius of curvature smaller than 140 mm by the direction-changing member3. Generally, bending at a radius of curvature of 140 mm or more is not regarded as bending when a characteristic of the optical fiber F is measured. The reason is that such bending at a small curvature is unlikely to affect the characteristic of the optical fiber F. Conversely, the direction-changing member3of the present embodiment intentionally bends the optical fiber F to a size to be considered when a characteristic of the optical fiber F is measured.

The tension-applying member4is located below the direction-changing member3. As shown inFIG.1B, the position of the tension-applying member4in the front-back direction coincides with the position of a front end portion of the direction-changing member3. The tension-applying member4is configured to be movable in the up-down direction with respect to the stage S and the direction-changing member3. When the optical fiber F is measured, the tension-applying member4is suspended by the optical fiber F hanging downward from the direction-changing member3. The tension-applying member4applies a tension to the optical fiber F by means of, for example, its weight. The tension can be appropriately changed, but may be, for example, 20 gf or less.

The tension-applying member4is formed in a substantially disk shape. As shown inFIG.1B, a groove4ais formed in a central portion of the tension-applying member4in the front-back direction. The optical fiber F passes through the inside of the groove4a. The position of the optical fiber F is regulated by the groove4a, so that the posture of the optical fiber F is stable, and the optical fiber F can be prevented from coming off from the tension-applying member4.

A diameter of a bottom surface of the groove4ashown inFIG.1Cis smaller than φ280 mm, and a part of the optical fiber F is bent along the bottom surface of the groove4a. For this reason, the optical fiber F is bent at a radius of curvature smaller than 140 mm by the tension-applying member4. Namely, similarly to the direction-changing member3, the tension-applying member4also bends the optical fiber F to a size to be considered when a characteristic of the optical fiber F is measured. Incidentally, the tension-applying member4may not include the groove4a. In this case, the radius of an outer peripheral surface of the tension-applying member4is set to coincide with the desired radius of curvature of the optical fiber F.

In the present embodiment, a tension is applied to the optical fiber F only by the weight of the tension-applying member4having a disk shape. However, the configuration for applying a tension, the shape of the tension-applying member4, and the like can be appropriately changed.

For example, as shown inFIG.1D, a spring4bmay be provided so as to apply an upward force to the tension-applying member4. In this case, a difference obtained by subtracting an elastic force of the spring4bfrom the weight of the tension-applying member4is a tension of the optical fiber F. Further, a so-called constant load spring may be used as the spring4b. The constant load spring is a spring of which the load does not change according to the amount of deformation. When a constant load spring is used, the tension of the optical fiber F can be made constant regardless of the position of the tension-applying member4in the up-down direction.

In addition, a balance structure7as shown inFIG.1Emay be adopted. The balance structure7includes a balance pole7a, a support portion7b, and a weight7c. The balance pole7ais supported by the support portion7bso as to be rotatable around a fulcrum C. A first end portion of the balance pole7ais rotatably fixed to the tension-applying member4, and the weight7cis attached to a second end portion of the balance pole7a. According to this configuration, a difference obtained by subtracting an upward force from the weight of the tension-applying member4is a tension of the optical fiber F, the upward force being applied to the tension-applying member4by the weight7c.

According to the configuration ofFIG.1D, the tension of the optical fiber F can be easily changed by changing the strength of the spring4b. In addition, when a load sensor is provided which detects a load applied to the spring4b, a tension applied to the optical fiber F can be monitored.

According to the configuration ofFIG.1E, the tension of the optical fiber F can be easily changed by changing the position or the mass of the weight7c. In addition, when a load sensor is provided below the weight7cor a torque sensor is provided which detects a torque around the fulcrum C, a tension applied to the optical fiber F can be monitored.

In addition, a tension applied to the optical fiber F can also be changed by attaching or removing a weight to or from the tension-applying member4itself.

Alternatively, the weight of the tension-applying member4can be changed and a tension applied to the optical fiber F can be changed by changing the shape of the tension-applying member4, such as forming the tension-applying member4in a semi-circular shape.

Next, a method for bending the optical fiber F in the present embodiment will be described.

First, the optical fiber F to be measured is cut to a predetermined length.

Next, both end parts of the optical fiber F are connected to the emitting side connection portion1aof the light source1and the incident side connection portion2aof the light-receiving portion2. At this time, both end parts of the optical fiber F are fixed to the emitting side connection portion1aand the incident side connection portion2asuch that the optical fiber F is not pulled out from the emitting side connection portion1aand the incident side connection portion2aby a tension applied by the tension-applying member4.

Next, the optical fiber F of which both end parts are connected to the light source1and the light-receiving portion2is hung on the direction-changing member3from above, and hangs downward because of its weight. Accordingly, the direction in which the optical fiber F extends forward from the light source1and the light-receiving portion2toward the direction-changing member3is changed downward.

Next, the tension-applying member4is brought closer to the optical fiber F from above, the optical fiber F hanging from the direction-changing member3. In the present embodiment, since the tension-applying member4includes the groove4a, the optical fiber F is inserted into the groove4a. A predetermined tension is applied to the optical fiber F by the tension-applying member4, and the optical fiber F is bent along the direction-changing member3and the tension-applying member4.

Next, light for measurement is emitted from the light source1. The light is incident on the light-receiving portion2through the optical fiber F. When the light passes through parts of the optical fiber F which are bent by the direction-changing member3and the tension-applying member4, the intensity of the light or the like changes. Therefore, the characteristic of the optical fiber F related to bending can be evaluated by analyzing the light incident on the light-receiving portion2.

As described above, the measurement device10A of the present embodiment includes: the light source1that emits light toward the optical fiber F; the light-receiving portion2that receives the light that has propagated through the optical fiber F; the direction-changing member3on which the optical fiber F is hung, and which changes an extending direction of the optical fiber F downward, the optical fiber F being optically connected to the light source1and the light-receiving portion2at both end parts of the optical fiber F; and the tension-applying member4that applies a tension to the optical fiber F hanging from the direction-changing member3.

According to this configuration, in the up-down direction, the positions of parts where the optical fiber F contacts with and is bent by the direction-changing member3and the tension-applying member4are unlikely to vary because of the weight of the optical fiber F or the like. For this reason, the optical fiber F is easily set. Therefore, the radius of curvature of bending of the optical fiber or the like is stable, so that the accuracy of measurement can be stabilized.

In addition, the groove4athat regulates the position of the optical fiber F is formed in the tension-applying member4. Accordingly, the ease of setting the optical fiber F on the tension-applying member4is more improved. In addition, since the shape of a part of the optical fiber F which is bent along the tension-applying member4is stable, the accuracy of measurement can be more stabilized.

Second Embodiment

Next, a second embodiment according to the present invention will be described, but a basic configuration is the same as that in the first embodiment. For this reason, the same configurations are denoted by the same reference signs, a description thereof will be omitted, and only different points will be described.

As shown inFIGS.2A and2B, a measurement device10B of the present embodiment includes a plurality of mandrels5and a position detection unit (i.e., position detector)6in addition to the stage S, the light source1, the light-receiving portion2, the direction-changing member3, the tension-applying member4.

The position detection unit6shown inFIG.2Bis configured to detect the position of the tension-applying member4in the up-down direction.

The plurality of mandrels5are disposed between the direction-changing member3and the tension-applying member4. The plurality of mandrels5are configured to bend the optical fiber F. As shown inFIG.2A, in part of the optical fiber F located on a left side of the tension-applying member4, some mandrels5are disposed to interpose the part of the optical fiber F therebetween in the left-right direction. In addition, in part of the optical fiber F located on a right side of the tension-applying member4, the remaining mandrels5are disposed to interpose the part of the optical fiber F therebetween in the left-right direction. In addition, the same number of the mandrels5may be disposed on the right side and the left side of the tension-applying member4. Further, the positions of the mandrels5disposed on the left side of the tension-applying member4and the positions of the mandrels5disposed on the right side of the tension-applying member4in the up-down direction may coincide with each other.

In addition, at least one mandrel5disposed on the left side of the tension-applying member4and at least one mandrel5disposed on the right side of the tension-applying member in the left-right direction may be provided.

When the plurality of mandrels5are disposed in such a manner, a pass line of the optical fiber F can be compactly arranged. Namely, it is possible to shorten the dimension of the optical fiber measurement device in the up-down direction.

As shown inFIG.2B, the position of each of the mandrels5in the front-back direction coincides with the position of the tension-applying member4in the front-back direction. In the example ofFIG.2A, the diameter of each of the mandrels5is smaller than the diameter of the tension-applying member4. However, the diameter of each of the mandrels5may be the same as the diameter of the tension-applying member4, or may be larger than the diameter of the tension-applying member4. In other words, the bending (diameter) of each part can be appropriately set according to the characteristic that is desired to be measured.

FIGS.3A to3Ceach show one example of a shape of the mandrel5.

As shown inFIG.3A, the mandrel5may have a columnar shape (disk shape) without a groove. When the mandrel5ofFIG.3Ais used, the optical fiber F is bent along an outer peripheral surface of the mandrel5. In this case, a radius of the outer peripheral surface of the mandrel5is set to coincide with a desired radius of curvature of the optical fiber F. In this case, a diameter of the outer peripheral surface of the mandrel5is smaller than φ280 mm.

As shown inFIG.3B or3C, the mandrel5may include a groove (mandrel groove)5a. When the mandrel5ofFIG.3BorFIG.3Cis used, the optical fiber F is bent along a bottom surface of the groove5a. In this case, a radius of the bottom surface of the groove5ais set to coincide with a desired radius of curvature of the optical fiber F. In this case, the diameter of the bottom surface of the groove5ais smaller than φ280 mm.

In addition, when both the mandrel5and the tension-applying member4include a groove, the position of the groove5aof the mandrel5in the front-back direction and the position of the groove4aof the tension-applying member4in the front-back direction coincide with each other. Accordingly, parts of the optical fiber F which are in contact with the mandrel5and the tension-applying member4are prevented from being unnecessarily bent in the front-back direction. In addition, the grooves of both the mandrel5and the tension-applying member4can prevent a pass line of the optical fiber F from being misaligned in the front-back direction.

As shown inFIG.3C, the mandrel5may include a cutout portion5b. When the mandrels5ofFIG.3Care used, the mandrels5can be prevented from coming into contact with each other. Incidentally, the shape of the mandrel5is not limited to those ofFIGS.3A to3C, and can be appropriately changed. For example, the cutout portion5bas shown inFIG.3Cmay be formed in the mandrel5ofFIG.3A.

In addition, a combination of the mandrels5shown inFIGS.3A to3Cmay be used as the plurality of mandrels5provided in the measurement device10B.

Next, a method for bending the optical fiber F in the present embodiment will be described.

First, similarly to the first embodiment, the optical fiber F of which both end parts are connected to the light source1and the light-receiving portion2is hung on the direction-changing member3and hangs downward. In addition, a tension is applied to the optical fiber F by the tension-applying member4. The loosening of the optical fiber F is removed by application of the tension.

Next, as shown inFIG.4A, the mandrels5are moved to interpose the optical fiber F therebetween. InFIG.4A, each of the mandrels5is moved in the left-right direction, but a movement direction of the mandrel5may be appropriately changed. When the mandrel5includes the groove5a, the optical fiber F enters the inside of the groove5a.

As shown inFIG.4B, the mandrels5are moved, so that the optical fiber F is bent along each of the mandrels5. Accordingly, the optical fiber F is bent at a desired radius of curvature based on the radius of the outer peripheral surface of the mandrel5or of the bottom surface of the groove5a.

In the example ofFIG.4B, among five mandrels5disposed on the left side of the tension-applying member4, the optical fiber F is bent at a degree of 90° along the upper mandrel5and the lower mandrel5. In addition, the optical fiber F is bent at an angle of 180° along each of three mandrels5disposed between the upper mandrel5and the lower mandrel5. Similarly, the optical fiber F is also bent by five mandrels5disposed on the right side of the tension-applying member4.

In such a manner, the mandrels5that bend the optical fiber F at an angle of 90° and the mandrels5that bend the optical fiber F at an angle of 180° are combined, so that the optical fiber F can be bent at a desired angle. Accordingly, the angle of bending of the optical fiber F can be easily adjusted. In addition, a path (pass line) of the optical fiber F from the light source1to the light-receiving portion2is easily designed.

Incidentally, the angle of bending of the optical fiber F may be adjusted by either of the mandrels5that bend the optical fiber F at an angle of 90° and the mandrels5that bend the optical fiber F at an angle of 180°.

Since the mandrels5are in contact with the optical fiber F in a state where the optical fiber F is tensioned by the tension-applying member4, loosening or twisting of the optical fiber F can be prevented from remaining in the optical fiber F.

Light is emitted from the light source1in this state, and the light is analyzed in the light-receiving portion2, so that the characteristic of the optical fiber F related to bending can be measured.

Here, for example, as shown inFIG.4C, when the optical fiber F is not properly hung around some mandrels5, the tension-applying member4is located below a predetermined position. Therefore, the position of the tension-applying member4is detected by the position detection unit6, so that it can be determined whether or not the optical fiber F is properly hung around all the mandrels5.

In addition, the disposition of the mandrels5can be appropriately changed, and for example, disposition as shown inFIG.5Amay be adopted. Here, when the lower mandrel5is moved parallel to the left-right direction as shown inFIG.5Bin order to obtain the state shown inFIG.5A, the mandrels5may come into contact with each other. Such a situation is likely to occur particularly when the groove5ais formed in the mandrels5. Therefore, as shown inFIG.5C, an oblique movement of the mandrel5with respect to the left-right direction can prevent the mandrels5from coming into contact with each other. In the example ofFIG.5C, as viewed from the front, the lower mandrel5is inclined and moved in a +Z-axis direction with respect to the left-right direction.

As described above, the measurement device10B of the present embodiment includes the plurality of mandrels5that bend the optical fiber F. Accordingly, the optical fiber F can be bent to a greater extent.

Incidentally, in the case of the present embodiment, since the optical fiber F can be bent by the mandrels5, it is not essential to apply bending to be measured to the optical fiber F by the direction-changing member3and the tension-applying member4. Namely, in the present embodiment, the diameter of the outer peripheral surface of the direction-changing member3, of the outer peripheral surface of the tension-applying member4, or of the bottom surface of the groove4amay be larger than φ280 mm.

In addition, the groove (mandrel groove)5athat regulates the position of the optical fiber F may be formed in at least one of the plurality of mandrels5. In this case, the position of the optical fiber F bent by the mandrel5including the groove5acan be more stabilized. Therefore, the accuracy of measurement can be more stabilized.

In addition, the positions of the groove4aand the mandrel groove5ain the front-back direction may coincide with each other, where the front-back direction is a direction orthogonal to both the up-down direction and the left-right direction in which the plurality of mandrels5face each other with the optical fiber F interposed therebetween as viewed in the up-down direction. Accordingly, parts of the optical fiber F which are in contact with the mandrel5and the tension-applying member4are prevented from being unnecessarily bent in the front-back direction. In addition, the grooves of both the mandrel5and the tension-applying member4can prevent a pass line of the optical fiber F from being misaligned in the front-back direction.

In addition, at least one of the plurality of mandrels5may be movable obliquely with respect to the left-right direction in which the plurality of mandrels5face each other with the optical fiber interposed therebetween as viewed in the up-down direction. In this case, the mandrels5can be prevented from coming into contact with each other.

In addition, the measurement device10B of the present embodiment includes the position detection unit6that detects the position of the tension-applying member4in the up-down direction. With this configuration, it is possible to determine whether or not the optical fiber F is properly hung around the mandrels5. Therefore, it is possible to prevent in advance from being measured under an erroneous bending condition when measuring the characteristic of the optical fiber F.

In addition, the plurality of mandrels5may include at least one mandrel5disposed on the left side of the tension-applying member4in the left-right direction and at least one mandrel5disposed on the right side of the tension-applying member4in the left-right direction. Accordingly, the pass line of the optical fiber F can be compactly arranged, and the dimension of the optical fiber measurement device in the up-down direction can be shortened.

In addition, the plurality of mandrels5may include the mandrels5that bend the optical fiber F at an angle of 90° and the mandrels5that bend the optical fiber F at an angle of 180°. Since the plurality of mandrels5are combined in such a manner, the optical fiber F can be bent at a desired angle and thus, the angle of bending of the optical fiber F can be easily adjusted. In addition, a path (pass line) of the optical fiber F from the light source1to the light-receiving portion2is easily designed.

In addition, the method for bending an optical fiber according to the present embodiment includes: hanging the optical fiber F on the direction-changing member3, both end parts of the optical fiber being fixed; applying a tension to the optical fiber F hanging from the direction-changing member3using the tension-applying member4; and bending the optical fiber F using the plurality of mandrels5disposed between the direction-changing member3and the tension-applying member4. According to this configuration, in the up-down direction, the positions of parts where the optical fiber F contacts with and is bent by the direction-changing member3and the tension-applying member4are unlikely to vary. Further, since the mandrels5come into contact with the optical fiber F to which a tension is applied in advance by the tension-applying member4, loosening or twisting of the optical fiber F can be prevented from remaining in the optical fiber F in contact with the mandrels5. Therefore, the ease of setting the optical fiber F can be improved, and the accuracy of measurement can be more stabilized.

EXAMPLES

Hereinafter, the above embodiments will be described with reference to specific examples. Incidentally, the present invention is not limited to the following examples.

A measurement device10C as shown inFIG.6Awas prepared. The measurement device10C included the light source1, the light-receiving portion2, the direction-changing member3, the tension-applying member4, three mandrels5, the position detection unit6(not shown), and the balance structure7. A diameter of an outer peripheral surface of each of the three mandrels5was set to φ20 mm. The tension-applying member4included the groove4a, and the diameter of the bottom surface of the groove4awas φ280 mm. In the measurement device10C, bending to be measured was applied to the optical fiber F by the three mandrels5. The bending of the optical fiber F by the tension-applying member4was not a measurement target since the radius of curvature is 140 mm. In addition, since the diameter of the direction-changing member3was also φ280 mm or more, the bending of the optical fiber F by the direction-changing member3was not a measurement target.

As shown inFIG.6A, the optical fiber F was set in the measurement device10C, and then the mandrels5were moved to be in the state shown inFIG.6B. As shown inFIG.6B, the optical fiber F was bent at an angle of 90° by each of the upper and lower mandrels5. In addition, the optical fiber F was bent at an angle of 180° by the central mandrel5. Therefore, the optical fiber F was bent at a radius of curvature equivalent to 10 mm×360° using the measurement device10C. This bending condition was the same as that in the case where the optical fiber F was wound one wrap around a cylinder having a diameter of φ20 mm.

As shown in Table 1, the tension applied to the optical fiber F by the tension-applying member4was changed in a range of 1 gf to 20 gf. The tension was adjusted by changing the position and the weight of the weight7c. φ shown in Table 1 represents the magnitude (standard deviation) of measurement variations under each condition. Hereinafter, a more detailed description will be provided.

In Comparative Example 1, the optical fiber F in a linear state was connected to the light source1and the light-receiving portion2, and a transmitted power P1was measured by the light-receiving portion2. The measurement wavelength was set to 1,625 nm. Thereafter, the optical fiber F was manually wound one wrap around a cylinder having a diameter of φ20 mm, light was emitted from the light source1in this state, and a transmitted power P2was measured by the light-receiving portion2. In Comparative Example 1, there is no tension data due to manual winding, but it is considered that the tension is approximately 10 gf. A value A of a loss caused by winding the optical fiber F around the mandrel can be calculated by the following mathematical formula (1).
Δ=10 Log(P1/P2)  (1)

When this measurement was performed 10 times and a standard deviation of the values of Δ was calculated, φ=1.52 dB.

In Example 1-1, a tension of 20 gf was applied to the optical fiber F by the tension-applying member4and the balance structure7. The measurement wavelength was set to 1,625 nm as in the comparative example, and the transmitted power P1was measured in the state shown inFIG.6Aand then the transmitted power P2was measured in the state shown inFIG.6B. When the transmitted power P2was measured, the position detection unit6confirmed that the tension-applying member4was at a predetermined position. Namely, it was confirmed that the optical fiber F was properly wound around three mandrels5. In Comparative Example 1 and Example 1-1, the bending conditions of the optical fiber F were substantially the same.

Also in Example 1, Δ was calculated by mathematical formula (1). When this measurement was performed 10 times and a standard deviation of the values of A was calculated, the standard deviation φ=0.56 dB.

Also in Examples 1-2 to 1-7, φ was calculated in the same procedure as that in Example 1-1. However, the position and the weight of the weight7cwere changed to adjust appropriately the tension as shown in Table 1.

As shown in Table 1, in each of Examples 1-1 to 1-7, the values of φ are significantly smaller than those in Comparative Example 1. The reason will be thoughtfully reviewed. In Comparative Example 1, since the optical fiber F is manually wound around the cylinder, the posture of winding of the optical fiber F around the cylinder is likely to vary. For example, the optical fiber F is likely to be wound around the cylinder in a twisted state, or the optical fiber F is likely to be wound obliquely with respect to an axial direction of the cylinder.

In such a manner, when the posture of winding around the cylinder varies, the radius of curvature of bending of the optical fiber F also varies. Therefore, in Comparative Example 1, it is considered that a variation of A is large and the value of φ is also large.

On the other hand, in Examples 1-1 to 1-7, since the measurement device10C is used, the optical fiber F can be stably bent. Therefore, it is considered that the variation of Δ is small and the value of φ is also small.

In Examples 1-1 to 1-7, there was no significant difference in the value of φ. Therefore, when the tension applied to the optical fiber F is 20 gf or less, the value of φ can be suppressed to be a small value. There is no data on the case where the tension is less than 1 gf, but when the tension is too small, it is considered that the loosening of the optical fiber F cannot be sufficiently removed.

Based on the above considerations, it can be said that the tension may be 20 gf or less and may also be 1 gf or more and 20 gf or less.

Next, a measurement device10D as shown inFIG.7was prepared. The measurement device10D included the light source1, the light-receiving portion2, the direction-changing member3, the tension-applying member4, 22 mandrels5, the position detection unit6(not shown), and the balance structure7. 11 mandrels5were disposed to interpose the optical fiber F on the −X side therebetween, and the remaining 11 mandrels5were disposed to interpose the optical fiber F on the +X side therebetween. The diameter of the outer peripheral surface of each of the mandrels5was set to φ30 mm. The tension-applying member4included the groove4a, and the diameter of the bottom surface of the groove4awas φ280 mm.

Here, the same number of a plurality of the mandrels5were disposed on both sides in the left-right direction to interpose the tension-applying member4therebetween. Since the plurality of mandrels5are disposed in such a manner, a pass line of the optical fiber F can be compactly arranged and thus, measurement can be stably performed.

In the measurement device10D, bending (equivalent to a radius of curvature of 15 mm×3,600°) to be measured was applied to the optical fiber F by the 22 mandrels5. The bending of the optical fiber F by the tension-applying member4was not a measurement target since the radius of curvature is 140 mm. In addition, since the diameter of the direction-changing member3was also φ280 mm or more, the bending of the optical fiber F by the direction-changing member3was not a measurement target.

As shown in Table 2, the tension applied to the optical fiber F by the tension-applying member4was changed in a range of 1 gf to 20 gf. The tension was adjusted by changing the position and the weight of the weight7c. Incidentally, in Comparative Example 2 and Examples 2-1 to 2-7 shown in Table 2, the measurement wavelength was set to 1,550 nm. Other points were the same as those in Table 1.

As shown in Table 2, there was no significant difference in the value of φ in Examples 2-1 to 2-7. Similarly to the results in Examples 1-1 to 1-7, it can be said that the tension may be 20 gf or less and may also be 1 gf or more and 20 gf or less.

In addition, in Examples 2-1 to 2-7, the bending diameters are larger than those in Examples 1-1 to 1-7 and the values of a bending loss are smaller than those in Examples 1-1 to 1-7. In such a manner, even when the bending condition was changed, it could be confirmed that setting the tension in a range of 1 gf to 20 gf was effective.

(Measurement of Cutoff Wavelength by Bending Method)

In order to measure a cutoff wavelength in a bending condition in which the optical fiber F was wound one wrap around a cylinder of φ60 mm, similarly to the above-described bending loss measurement, the measurement device10C shown inFIG.6Awas prepared. The measurement device10C was the same as the measurement device10C used for the bending loss measurement except that the diameter of the mandrel5was φ60 mm. As shown in Table 3, in Comparative Example 3 and Examples 3-1 to 3-7, the cutoff wavelength of the optical fiber F was measured 10 times under each condition. The cutoff wavelength was measured according to IEC 60793-1-44.

In Comparative Example 3, the optical fiber F was bent by manually winding the optical fiber F one wrap around a cylinder of φ60 mm.

In Examples 3-1 to 3-7, the optical fiber F was bent using the measurement device10C. In Comparative Example 3 and Examples 3-1 to 3-7, the bending conditions of the optical fiber F were substantially the same.

The column φ in Table 2 shows the values of a standard deviation of the cutoff wavelengths measured 10 times under each condition.

As shown in Table 3, in Examples 3-1 to 3-7, the values of the standard deviation φ could be more significantly reduced than those in Comparative Example 3.

Similarly to the results in Table 1, it was confirmed that the accuracy of measurement of the cutoff wavelength could be improved by using the measurement device10C. Also, when the cutoff wavelength is measured, it can be said that the tension may be 20 gf or less and may also be 1 gf or more and 20 gf or less.

(Measurement of Cutoff Wavelength by Multi-Mode Method)

The cutoff wavelength was measured by a multi-mode method using the measurement device10A shown inFIG.1A. The measurement device10A included the light source1, the light-receiving portion2, the direction-changing member3, and the tension-applying member4. A cylinder having a diameter of φ280 mm was used as the direction-changing member3. The tension-applying member4included the groove4a, and the diameter of the bottom surface of the groove4awas φ280 mm.

As shown in Table 4, in Comparative Example 4 and Examples 4-1 to 4-7, the cutoff wavelength of the optical fiber F was measured 10 times under each condition by the multi-mode method.

The cutoff wavelength was measured by the multi-mode method as follows.

In Comparative Example 4, both ends of the optical fiber F were set in the light source1and the light-receiving portion2, and the optical fiber F was bent by manually winding the optical fiber F one wrap around a mandrel of φ280 mm.

In Examples 4-1 to 4-7, bending was applied using the measurement device10A. The optical fiber F was bent at φ280 mm×360° by the direction-changing member3and the tension-applying member4, and other parts were not bent. Namely, in Comparative Example 4 and Examples 4-1 to 4-7, the bending conditions of the optical fiber F were substantially the same.

In both Comparative Example 4 and Examples 4-1 to 4-7, in a state where the optical fiber F was bent, light from the light source1was incident on the optical fiber F, and a transmitted power P1(λ) was measured by the light-receiving portion2. Next, the optical fiber F was removed from the measurement device10A, a multi-mode fiber was connected to the light source1and the light-receiving portion2, and a light-receiving power P2(λ) of the light that had passed through the multi-mode fiber was measured. The cutoff wavelength by the multi-mode method was calculated using P1(λ) and P2(λ) according to IEC-60793-1-44.

As shown in Table 4, in Examples 4-1 to 4-7, the values of the standard deviation (φ) could be more significantly reduced than those in Comparative Example 4. In such a manner, it was confirmed that the accuracy of measurement of the cutoff wavelength using the multi-mode method could be improved by using the measurement device10D. In addition, also when the cutoff wavelength is measured using the multi-mode method, it can be said that the tension may be 20 gf or less and may also be 1 gf or more and 20 gf or less.

(Measurement of Cutoff Wavelength by Bending Method)

Next, the bending condition was changed, and the cutoff wavelength by the bending method was measured using a measurement device10E shown inFIG.8A. The measurement device10E included the light source1, the light-receiving portion2, the direction-changing member3, the tension-applying member4, four mandrels5, three mandrels5A, the position detection unit6(not shown), and the balance structure7. A cylinder having a diameter of φ80 mm was used as the direction-changing member3. The diameter of the outer peripheral surface of each of the four mandrels5was set to φ80 mm. The diameter of the outer peripheral surface of each of the three mandrels5A was set to φ60 mm. The tension-applying member4included the groove4a, and the diameter of the bottom surface of the groove4awas φ80 mm.

Here, regarding the four mandrels5, the same number of the mandrels5were disposed on both sides in the left-right direction to interpose the tension-applying member4therebetween, and the three mandrels5A were disposed only on the left side. In such a manner, when at least one mandrel5disposed on the left side of the tension-applying member4and at least one mandrel5disposed on the right side of the tension-applying member4in the left-right direction are provided, the dimension of the optical fiber measurement device in the up-down direction can be shortened.

According to the measurement device10E, bending to be measured was applied to the optical fiber F by the direction-changing member3, the tension-applying member4, and the four mandrels5. The positions of the emitting side connection portion1aand the incident side connection portion2ain the up-down direction coincided with the position of an upper end of the direction-changing member3. For this reason, each of parts of the optical fiber F along the direction-changing member3was bent at a radius of curvature of 40 mm×90° (refer toFIG.8B). The optical fiber F was bent at two places by the direction-changing member3. Therefore, the bending of the optical fiber F by the direction-changing member3corresponded to a radius of curvature of 40 mm×180°.

Each of the four mandrels5bent the optical fiber F at a radius of curvature of 40 mm×90°. In addition, the tension-applying member4bent the optical fiber F at a radius of curvature of 40 mm×180°. The three mandrels5A bent the optical fiber F at a radius of curvature of 30 mm×(90°+180°+90°).

Summing up the above, the measurement device10E bent the optical fiber F at a radius of curvature equivalent to 40 mm×720° (two wraps) and at a radius of curvature equivalent to 30 mm×360° (one wrap).

As shown in Table 5, in Comparative Example 5 and Examples 5-1 to 5-7, the cutoff wavelength of the optical fiber F was calculated 10 times under each condition using the bending method. The cutoff wavelength was calculated using transmitted powers before and after bending equivalent to a radius of curvature of 40 mm×720° was performed by the mandrels5of the measurement device10E and bending equivalent to a radius of curvature of 30 mm×360° (one wrap) was performed by the mandrels5A under the bending condition.

In Comparative Example 5, the optical fiber F was bent by manually winding the optical fiber F around a cylinder of φ80 mm two wraps. The transmitted power P1was measured in that state. Next, in addition to the state where the optical fiber F was wound two wraps around a cylinder of φ80 mm, the optical fiber F was bent one wrap around a cylinder of φ60 mm. The transmitted power P2was measured in that state. The cutoff wavelength was measured using P1and P2obtained in such a manner.

In Examples 5-1 to 5-7, the optical fiber F was bent using the measurement device10E. Specifically, the transmitted power P1was measured in a state where the optical fiber F was bent at a radius of curvature equivalent to 40 mm×720° by the mandrels5. Next, the transmitted power P2was measured in a state where the optical fiber F was bent at a radius of curvature equivalent to 30 mm×360° by the mandrels5A in addition to being bent by the mandrels5. The cutoff wavelength was measured using P1and P2obtained in such a manner.

In Comparative Example 5 and Examples 5-1 to 5-7, the bending conditions of the optical fiber F were substantially the same.

The column σ in Table 5 shows the values of a standard deviation of the cutoff wavelengths measured 10 times under each condition.

As shown in Table 5, in Examples 5-1 to 5-7, the values of the standard deviation σ could be more significantly reduced than those in Comparative Example 5.

In such a manner, it was confirmed that the accuracy of measurement of the cutoff wavelength could be improved by using the measurement device10E. In addition, also when the bending condition is changed and the cutoff wavelength is measured, it can be said that the tension may be 20 gf or less and may also be 1 gf or more and 20 gf or less.

(Measurement of Mode Field Diameter)

In order to measure a mode field diameter under a bending condition in which the optical fiber F was wound one wrap around a cylinder of φ60 mm, similarly to the above-described bending loss measurement, the measurement device10C shown inFIG.6Awas prepared. The measurement device10C was the same as the measurement device10C used for the bending loss measurement except that the diameter of the mandrel5was φ60 mm. As shown in Table 6, in Comparative Example 6 and Examples 6-1 to 6-7, the mode field diameter was measured 10 times under each condition. The mode field diameter was measured according to IEC 60793-1-45.

In Comparative Example 6, the optical fiber F was bent by manually winding the optical fiber F one wrap around a cylinder of φ60 mm.

In Examples 6-1 to 6-7, the optical fiber F was bent using the measurement device10C. In Comparative Example 6 and Examples 6-1 to 6-7, the bending conditions of the optical fiber F were substantially the same.

The column ≐ in Table 6 shows the values of a standard deviation of the mode field diameter measured 10 times under each condition.

As shown in Table 6, in Examples 6-1 to 6-7, the values of the standard deviation σ could be more significantly reduced than those in Comparative Example 6.

In such a manner, it was confirmed that the accuracy of measurement of the mode field diameter could be improved by using the measurement device10C. In addition, also when the mode field diameter is measured, it can be said that the tension may be 20 gf or less and may also be 1 gf or more and 20 gf or less.

Incidentally, the technical scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above examples, the bending loss, the cutoff wavelength, and the mode field diameter have been provided as an example of the characteristic to be measured of the optical fiber F. However, when a characteristic of the optical fiber F other than the above characteristics is measured, the measurement devices10A to10E of the present embodiment or the bending method of the present embodiment can also be adopted. When the characteristic requires the bending of the optical fiber F during measurement, the accuracy of measurement can be improved by applying the present embodiment.

In addition, the disposition of the mandrels5is not limited to the examples of the measurement devices10B to10E, and can be appropriately changed.

In addition, the emitting side connection portion1aand the incident side connection portion2amay not necessarily face forward (+Y side). For example, the emitting side connection portion1aand the incident side connection portion2amay face upward or backward. Alternatively, the emitting side connection portion1amay face leftward, and the incident side connection portion2amay face rightward. In these cases, an optical path (optical fiber, optical waveguide, or the like) may be connected to each of the emitting side connection portion1aand the incident side connection portion2a, and ends of the optical path may be disposed at the positions of the emitting side connection portion1aand the incident side connection portion2ashown inFIG.1Aand the like. Then, in the case of a configuration in which both end parts of the optical fiber F are connected to the ends of the optical path and the extending direction of the optical fiber F is changed downward by the direction-changing member3, the same effects as those in the above embodiments can be obtained. Even in these cases, there is no difference in that the direction-changing member3changes the extending direction of the optical fiber F downward, both end part of the optical fiber F being optically connected to the light source1and the light-receiving portion2.

In addition, a distance in the left-right direction between the emitting side connection portion1aand the incident side connection portion2aor a distance in the left-right direction between the ends of the optical path which are connected to the emitting side connection portion1aand the incident side connection portion2amay be adjusted such that the optical fiber F is not obliquely wound around the direction-changing member3. For example, inFIG.1A, the distance in the left-right direction between the emitting side connection portion1aand the incident side connection portion2amay be equal to the diameter of the bottom surface of the groove4aof the tension-applying member4.

In addition, the positions of the emitting side connection portion1aand the incident side connection portion2ain the up-down direction may be different from each other.

In addition, the components in the above-described embodiments can be appropriately replaced with known components without departing from the concept of the present invention, and the embodiments or the modification examples described above may be appropriately combined.

For example, the mandrel5having the shapes shown inFIGS.3A to3Cmay be adopted as the mandrels5and5A of the measurement devices10B to10E.

In addition, the spring4bshown inFIG.1Dmay be applied to the measurement devices10B to10E.

In addition, in the measurement devices10B to10E, the spring4bmay be used instead of the balance structure7. Alternatively, in the measurement devices10B to10E, a tension may be applied to the optical fiber F by merely the weight of the tension-applying member4instead of using the spring4bor the balance structure7.

REFERENCE SIGNS LIST