JP3080461B2 - UV irradiation method to fiber ribbon coated with UV curable resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating an ultraviolet ray to a fiber ribbon coated with an ultraviolet curable resin (hereinafter referred to as "UV resin") in order to form a uniform thin film coating on the optical fiber ribbon with high strength. More particularly, the present invention relates to a method of irradiating a fiber ribbon coated with a UV-curable resin so that a part of the ultraviolet light can be reflected also on the back surface of the fiber ribbon on which a thin film coating is to be formed.

[0002]

2. Description of the Related Art In a typical submarine optical cable system,
Repeater stations are typically 70 to 200 km away. Optical fiber currently has a length of at most 50km
To make a longer cable, you have to connect optical fibers. Therefore, these connection parts must withstand stresses such as relatively high tensions during cable manufacturing and cable laying. In the conventional connection method, the strength of the connection point becomes very weak. Typically, the strength of the 125 μm coated original fiber is approximately 70 N (Newton), but approximately 7 N after connection.
Fall to N. The main cause is believed to be mechanical damage to bare fibers that come into contact with peripheral members such as blades for stripping, cutting blades, or alignment V-grooves.

[0003] These mechanical damages cause micro-scratching on the surface of the fiber, resulting in high local stresses. Also, if additional stresses are concentrated on these scratches during cabling or handling, the fibers are easily broken. At present, various connection technologies are being developed to obtain high strength technology. For example, Miyajima suggested that after making a conventional connection, the fiber surface would be etched with hydrofluoric acid to expose and cover the connection. This is described by Miyajima et al. In "Long distance fiber with high strength connection" (Electronic Letters, Vol. 17, pp. 670-672, September 1981).
Mon). In addition, Clause proposed flame fusion splicing using hydrogen chloride gas and preserved the joints using a UV curable material. For this, see J.M. T. `` Fiber Splices with Perfect Fiber Strengt ''
hs of 5.5 GPa V> 0.01 ”(Electronics Letters,
vol.21, N.12, Jun.6,1985 PP.533-535).

[0004] As a more general method, a non-contact method is used. The bare fiber is handled with great care during the entire connection process, from the pre-connection preparation stage to the post-connection coating, so as not to cause any mechanical damage. For example, Yamada et al., "Arc fusion splicing using high-strength low-loss submarine optical cable contour matching system" (IEEE, 1986).
In, the fiber coating is chemically removed using methylene chloride and the cladding is cleaved, aligned, and clamped for final arc fusion splicing. The connection is again covered with a UV curable resin for protection. Artha R in 1990
Tines, "Method and Apparatus for Making High-Strength Splices in Optical Fiber," U.S. Pat. No. 4,958,
No. 905), the coating of the fiber is likewise chemically removed, but the alignment is done by V-groove blocks coated with a non-frictional material and the connection is made by heating the tungsten or tantalum ribbon. I use.
Further, the connection portion is again covered with a UV curing resin for protection.

[0005] For example, K. "1.55 by Osaka etc.
Development of high-strength splicing technology that can be used in the field of μm diffusion-shifted fibers ”(IWCS Proceedings 1988)
Has proposed another non-contact method. According to this,
The fiber coating is removed by a hot stripper, and the bare fiber is coated with a UV-cured thin film to a thickness of about 5 μm except for a few mm from the cut end. Thereafter, the coated fiber is connected with a conventional arc discharge fusion splicer, and the connected fiber is reinforced with a heat shrink tube.

The methods described herein are all applicable to high strength connections to a single fiber. However, when making a high-strength connection to the fiber ribbon, the coating on the fiber ribbon cannot be removed chemically. Just one
One practical removal method is to use a hot stripper. Also, the fiber ribbon cannot clamp the sheath when aligned. At present, as a fiber alignment means applicable to multi-core fusion splicing, only a V-groove block formed with high precision is used. That is, the clad portions of a pair of fibers to be connected are arranged and aligned on the V-groove block, and the V-groove block is fixed so as not to move in any direction. Therefore, if the fiber ribbon coating is clamped without alignment using the V-groove block, excessive alignment errors (e.g., due to fiber curl) can occur for individual fibers, resulting in large splice losses. will do. Furthermore, V coated with a non-frictional material
Aligning the fiber ribbon with the groove blocks can cause mechanical damage to the bare fiber due to fine contaminants such as dust on the V-grooves and deposits of SiO ₂ vapor. This will result in micro-scratching on the fiber surface which results in a significant loss of strength.

[0007] One of the effective methods for realizing a high-strength fiber ribbon connection in consideration of the above constraint conditions is to remove a coating portion from an original fiber ribbon with a hot stripper, and then remove the coating portion from the original fiber ribbon. In order to prevent permanent damage, a UV-cured thin film with a thickness of about 5 μm is formed on the bare part where the coating has been removed, and then, when connecting, a conventional multi-core fusion method using a high-precision V-groove block for fiber alignment Connection is made using a destination connection machine. Then, the connection point is coated again with a UV-curable resin for protection.

[0008]

With a single fiber thin film coating, the uniformity of the thin film thickness is less important. This is because many available single fiber fusion machines have a core or cladding XY alignment mechanism. However, in thin film coating of fiber ribbons, thickness uniformity between individual fibers as well as uniformity between fibers in the ribbon becomes very important. Because, as already mentioned, all available multi-core fusion splicers have high precision V-groove blocks for alignment of each fiber, but an XY alignment mechanism for the individual fibers in the ribbon. Is not provided. Therefore, the non-uniformity of the thin film coating of each fiber constituting the ribbon may cause extreme eccentricity of the fiber and may cause a large connection loss.

In addition, since a single fiber is coated with a thin film or re-coated with a UV curable resin for the purpose of protecting a connection portion, a conventional ultraviolet irradiation system usually uses one ultraviolet light source (for example, a mercury xenon lamp (see FIG. 1)). Abbreviation))
As shown in FIG. 14, ultraviolet rays are guided by fiber bundles 101 and 102 (typically those having an outer diameter of 3 mm) to the vicinity of the fiber 100 to be coated. In this case, the uniformity of the thin-film coating of a single fiber is not very important, so that thin-film coating of a single fiber can be performed well with this type of illumination system. If the above irradiation system is adopted for thin film coating of fiber ribbon,
If the ultraviolet light guiding fiber bundles 101 and 102 are arranged at a distance dl from the plane formed by the fibers 100 (f1 to f8) in the ribbon, the irradiation area on each fiber surface is shown in FIG. Thus, a region having a diameter D represented by the following equation is obtained. D = d ₀ +2 dl · tan a (1) where D: diameter of irradiation area on fiber surface d ₀ : diameter of ultraviolet light guide fiber bundle dl: ribbon fiber bundle is formed from ultraviolet light guide fiber bundle Distance to plane a: Dispersion angle of ultraviolet light guide fiber bundle

The minimum width of the region L 'requiring ultraviolet irradiation can be obtained by the following equation, where P is the distance between adjacent fibers and n is the number of fibers. L ′ = (n − ／) P (2) An ultraviolet light source (for example, a mercury xenon lamp) is not usually very stable, and the ultraviolet light intensity on a plane perpendicular to the irradiation direction is uniform. Since they are not distributed, the intensity of ultraviolet light applied to each fiber of the ribbon is not constant. The non-uniformity of the ultraviolet intensity is such that L ′ and D become equal (ie, n
Is large and dl is small). For example, n = 8, d
If l = 2 mm, P = 0.25 mm, a = 14 °,
D is 3.997 m from equations (1) and (2), respectively.
m and L 'are 1.875 mm, which are of the same order of magnitude.

The ultraviolet irradiation area on the plane formed by the fibers in the ribbon has a circular shape, and the relative movement of the fibers in the ultraviolet irradiation is in the direction B as shown in FIG. 15, so that they adhere to the fibers f4 and f5, respectively. The UV curable resin thin film layers 100D and 100E are irradiated earlier than the UV curable resin thin film layers adhering to other fibers (for example, the thin film layers 100A and 100H adhering to f1 and f8, respectively).
To reach. As a result, the time during which the UV curable resin thin film layer on the fiber surface is irradiated with ultraviolet light is not the same, and the thickness of the thin film between the fibers in the ribbon becomes non-uniform. L '
And D are approximately equal (ie, n is large and dl is small),
The difference in irradiation time becomes even more significant.

If only dl, the distance from the plane formed by the fibers in the ribbon to the UV light guide fiber bundle, is increased, the diameter D of the illuminated area will be very large from equation (1). Also, the fiber bundle must be positioned much higher than the UV holder 5 to avoid premature curing of the UV curable resin film layer on the fiber surface. However, this is not preferred. This is because the distance between the fiber and the relatively upwardly moving fiber relative to the light source is increased, so that the thin film layer is cured with sufficient UV intensity. The relative speed of movement of the fiber with respect to the UV source is very low (approximately 0.07 mm / sec), and therefore the integration time required for thin film coating is very long.

The present invention has been made in view of the above-mentioned conventional drawbacks,
It is an object of the present invention to provide a method of irradiating a fiber ribbon with an ultraviolet ray to form a UV curable resin thin film layer in order to make a high-strength connection to a fiber ribbon having a uniform thickness coating on each fiber. After connecting ribbons using a conventional multi-core fusion splicer that uses a V-groove block formed with high precision for arranging fibers, the UV curable resin applied to the connection points of each fiber is uniformly cured. It is an object of the present invention to form a thin film having a uniform thickness without any unevenness in strength at the connection point.

[0014]

That is, the present invention provides a method of irradiating a fiber ribbon coated with an ultraviolet-curing resin with ultraviolet rays to irradiate ultraviolet rays to cure the resin and protect the connection points. Wherein the fiber ribbon is clamped in a vertical direction, and a slit is arranged in front of the fiber ribbon clamped at an exit surface parallel to a surface formed by each fiber in the fiber ribbon, and a fiber bundle for ultraviolet light guiding is provided. Is placed in front of the clamped fiber ribbon, and in front of the slit, parallel to the normal to the plane formed by the fiber, and at the center of all fibers passing through the center of the slit exit. Arranging the center of the ultraviolet light-guiding fiber bundle, passing the ultraviolet light-guiding fiber bundle and the exit of the slit, and forming each of the fibers; UV guided through onto a surface, a cylindrical concave mirror arranged to the rear surface of the fiber ribbon is intended to reflect the ultraviolet rays passed through the gap between the fibers on the back surface of each fiber. According to the present invention, the inner and outer surfaces of the thick and elongated flat slit are painted black, and the inner and outer surfaces of the thick and elongated flat slit have a relatively rough surface. Further, according to the present invention, in the cylindrical concave mirror, the angle θ between the mirror plane and each fiber in the fiber ribbon at the time of ultraviolet irradiation is expressed by the following equation: tan2θ = (L ₀ −L ₁ ) / d where L _0: thick distance from the exit plane slit to the top of the mirror surface L _1: distance from the exit of the thick planar slit to preferred fiber clamping position d: is intended to rotate the diameter of each fiber in the ribbon Mitsurusu so.

[0015]

[Function] The uniformity of the thin film coating thickness depends on the time for attaching the UV curable resin thin film layer to the surface of each bare fiber to be irradiated with ultraviolet light and the intensity of ultraviolet light irradiation. And the intensity of irradiation of ultraviolet rays to each fiber constituting the above. In order to achieve uniform irradiation intensity between the fibers and to prevent premature curing of the UV curable resin thin film layer deposited on the fiber surface, the present invention uses a thick and long flat slit which is very rough and black, and uses ultraviolet irradiation light. The angle of incidence is limited, and the intensity of ultraviolet light in the horizontal direction created by each fiber constituting the ribbon is completely uniformized. The use of this planar slit eliminates the need for an expensive and special cylindrical lens for guiding incident irradiation light.

According to the present invention, by using a cylindrical concave mirror, it is possible to irradiate the back surface of a bare fiber, which is not directly radiated from an ultraviolet ray source, with reflected ultraviolet light. Therefore, only one ultraviolet ray is required as the ultraviolet ray for guiding and irradiating the fiber bundle. Since a typical UV source typically emits two UV's to guide it to the fiber bundle, the use of two fiber bundles for two fiber ribbons simultaneously allows the use of both fibers on both sides. A thin film can be coated. This can reduce the average coating time of the thin film by almost half. According to the present invention, in order to obtain a uniform irradiation area and a uniform light intensity on both sides of each fiber, according to the present invention, the thickness dimension of the plane slit, the position of the fiber ribbon to be clamped, the radius and the minimum dimension of the cylindrical concave mirror, and furthermore, The location of the concave mirror must be carefully determined. In addition, the concave mirror needs to be rotated so that a certain angular relationship exists between the plane formed by the mirror surface and the plane formed by the fibers constituting the ribbon. These parameters are closely related to each other, and the relationship can be determined geometrically.

[0017]

An embodiment of the present invention will be described below with reference to the accompanying drawings. For details of the method for forming the thin film coating on the fiber ribbon, see the specification of Japanese Patent Application No. 218015/1990 filed on August 21, 1991. FIG. 1 shows a method of irradiating a fiber ribbon coated with an ultraviolet curable resin according to the present invention with ultraviolet rays. In this method, a fiber ribbon 1 (for example, 8
(Composed of the present fiber ribbon), the first coating is removed from one end by hot stripping, and the bare fibers f1 to f8 are exposed. Then, the fiber ribbon 1 is vertically clamped by the clampers 2 and 3. Next, the UV curable resin material 4 is applied to the UV resin holder 5. Then, the slot 6 and the UV curable resin material 4 move smoothly in the downward direction A at a constant speed. The UV curable resin thin film layer 7 remains on the surface of the bare fiber, and the thin film layer 7 is cured by the ultraviolet rays 8 and 9.

The thickness of the thin film coating formed by the above-described method depends on the following factors. 1. 1. viscosity of UV curable resin 2. Surface tension of UV curable resin 3. Moving speed of holder 5 downward. The longer the attachment time of the UV curable resin thin film layer to the surface of the fiber to be irradiated with ultraviolet light, the thinner the coating becomes. Note that it is pulled down by the acting surface tension or falls down by its own gravity.) 5. UV intensity (because it affects the curing rate) Under stable operating temperatures, the surface tension and viscosity of the UV curable resin are almost constant, and the thickness of the thin film coating usually moves down the holder 5 It can be controlled by adjusting the speed.

Therefore, the uniformity of the thickness of the thin film coating between each fiber of the ribbon depends on the following conditions. 1. 1. The linearity of the exposed portion of the bare fiber to be coated 2. Uniformity of bare fiber spacing exposed from ribbon. 3. The time during which the UV curable resin thin film layer is attached to the surface of each bare fiber exposed to ultraviolet light. Intensity of ultraviolet light applied to each fiber in the ribbon As described above, the thickness of the thin film applied between the fibers in the ribbon should be as uniform as possible. This is to prevent excessive eccentricity for each fiber, resulting in large splice loss. Therefore, in order to obtain a uniform thin film coating thickness, the above four conditions must be satisfied between each fiber in the ribbon. The first two conditions can be sufficiently achieved by employing a good fiber clamp system as described below. Therefore, an object of the present invention is to provide an ultraviolet irradiation method (system) that maintains the third and fourth conditions between the fibers in the ribbon as uniformly as possible.

FIG. 2 shows an embodiment of an ultraviolet irradiation system in which the method of irradiating an ultraviolet ray to a fiber ribbon coated with an ultraviolet curable resin according to the present invention is applied. In the ultraviolet irradiation system of this embodiment, the fiber ribbon 1 (the original coating is partially removed from one end to remove the bare fibers f1 to f8)
Are exposed and the ribbon is clamped perpendicular to a plane (not shown) parallel to the YZ plane formed by each fiber) to form a uniform thin film coating at the connection points. A thick and elongated flat slit 11 for irradiating ultraviolet rays and having an exit surface 11A parallel to the YZ plane.
And the center of the fiber bundle is parallel to the X axis, passes through the center of the exit surface 11A of the slit 11, and exposes the fiber f1.
A single fiber bundle 15 for guiding ultraviolet light passing through the entire center of the optical fiber f8, a cylindrical concave mirror surface 16 for reflecting a part of the ultraviolet irradiation light from the fiber bundle 15 to one end of the fibers f1 to f8 facing the mirror surface. It is composed of In the present invention, the thick and elongated planar slit 11 limits the incident angle of ultraviolet rays, and the horizontal direction (XY) crossing the plane (YZ plane) formed by the fibers f1 to f8 in the ribbon 1.
Direction) is used to accurately and consistently maintain the ultraviolet intensity. As the thick and long plane slit 11, a solid block (for example, an aluminum block) having a long and narrow groove machined with high precision is used, or two thick planes in which planes facing each other are provided at a small distance. Use a solid block. The slit 11 formed in this way must have a sufficient thickness and a sufficient length in the Y direction as compared with the width of the fiber ribbon 1 to be coated. As a result, the light after passing through the slit 11 When considering a small area in the Y direction to be considered, the intensity can be considered to be substantially constant in the same direction.

FIG. 3 is a longitudinal sectional view of the thick plane slit 11 in the ZX plane, and is composed of two slit blocks 12 and 13. The inner surfaces 12A and 13A of the slit blocks 12 and 13 are relatively rough and painted black. Incident light (for example, 20A and 20B) that does not collide with the inner surfaces of the slit blocks 12 and 13 can pass freely without any obstacle. However, if the incident light (eg, 20)
If the light travels in such a direction as to impinge on the inner surfaces of the slit blocks 2, 13, most of the energy will be absorbed because the inner surfaces of the slit blocks 12, 13 are painted black. The remaining energy of the incident light will be scattered and reflected as shown in FIG. This is because the inner surface is considerably rough. The scattered light will strike the inner surfaces of the slit blocks 12, 13 many times. Therefore, if the ultraviolet rays collide with the inner surfaces of the slit blocks 12 and 13 before reaching the slit outlets 11A, they are continuously scattered and reflected several times on the inner surfaces of the slit blocks 12 and 13 and then the slit outlets 11A. The magnitude of the light intensity of the ultraviolet light that can pass through is negligible.

According to the above concept, according to FIG. 5, an arbitrary point P on the slit outlet 11A is delimited by two straight lines 20C and 20D respectively forming angles α ₁ and α ₂ with respect to the X axis. It can be regarded as a point light source having emitted light that can travel in a direction. The two angles with the X axis are obtained from the following equation. α ₁ = tan ⁻¹ [(S + Z) / L] (3) α ₂ = −tan ⁻¹ [(S−Z) / L] (4) where S: width of the plane slit 11 Half L: thickness of the plane slit 11 Z: distance from the X axis to P The two angles α ₁ and α ₂ are maximum when Z is equal to S or −S, and the value at this time is | α ₁ | = | α ₂ | = α = tan ⁻¹ (2S / L) (5) The angle α shown in FIG. 6 is the maximum dispersion angle of the corresponding thick planar slit 14. The maximum dispersion angle can be adjusted to be extremely small by setting S and L to optimal values.

The width of the thick plane slit 11 (2S) is extremely large as compared with the wavelength λ of ultraviolet rays (for example, S = 0.
Assuming that the wavelength is 4 mm and the wavelength of the ultraviolet light is 365 nm, 2S / λ> 20
00). Therefore, the amount of light follows Fresnel diffraction, and diffraction angles larger than ± α can be ignored. Under such conditions, the pattern of light passing through the plane slit 11 is
It can be obtained by using geometric optics.

According to the present invention, the cylindrical concave mirror surface 16 is provided.
Are used to reflect a portion of the ultraviolet radiation to the exposed fiber side opposite the mirror surface 16. The cylindrical concave mirror surface 16 is a conventional cylindrical concave mirror or a metal surface polished well for low reflection loss. As shown in FIG. 7, all rays passing through the slit outlet 11A collide with the mirror surface 16 and are reflected backward. All the reflected lights after passing through a certain point are bounded by the reflected light rays 20E 'and 20F' corresponding to the incident light rays 20E and 20F, respectively. Incident ray 2
0E and 20F are plane slits 1 with a propagation angle about the X axis.
Equal to the maximum possible dispersion angle ± α of unity. The point mentioned above is equal to the image I at the slit exit O formed by the cylindrical concave mirror 16 when the parallel axis theory of the concave mirror is used.
The position of this image can be calculated from the well-known concave mirror formula shown below. (1 / U) + (1 / V) = 1 / (2R) (6) where, U: a vertex P _{0 of the} mirror surface 16 from the exit O of the slit.
V: distance from image I to vertex P ₀ of mirror surface 16 R: radius of mirror surface 16

Calculation errors from the actual position of the image I under the conditions of the parallel axis theory (the radius R is large and the incident ray is close to the principal axis) will not be affected by the present invention. .
This is because the point of most interest in the present invention is position 30 in FIG. This position 30 is the preferred position of the fiber ribbon to be clamped vertically in a direction perpendicular to the plane formed by the fibers in the ribbon parallel to the X axis. At this preferred fiber clamp position 30, the illuminated area is substantially similar on the front and back as well as the total intensity illuminated on the front and back of each fiber of the ribbon. Therefore, the above conditions 3, 4 for making the thin film coating of the fiber ribbon uniform (that is, the object of the present invention) are satisfied. This condition 3,
Note also that some other assumptions and practical considerations are needed to satisfy 4 as much as possible. As one of the conditions to be considered, the outer surface of the plane slit 11 facing the mirror surface 16 absorbs the ultraviolet light reflected by the mirror surface 16,
Alternatively, they should be rough and black to scatter and collide on the outer surfaces 12B, 13B.

According to the present invention, the thick planar slit 11
And the preferred clamping location 30 for the fiber,
The mirror surface 16 located to be placed a minimum height and the radius R ₁ of the cylindrical concave mirror 16, has become very important to obtain a uniform ultraviolet irradiation in each fiber on both sides in to be coated ribbon.

FIG. 8 shows the maximum dispersion angle ± α of the slit 11.
And shows the clamping positions obtained by the intersection of the corresponding incident rays 20E, 20F with the reflected rays 20E ', 20F', respectively, reflected by the mirror surface 16. The relationship between the design parameters is as follows. Definitions: S: half width of thick plane slit 11 L: thickness of thick plane slit 11 L ₀ : distance from thick plane slit 11 to vertex P _{0 of} mirror surface 16 L ₁ : preferable fiber clamp position from thick plane slit 11 distance to 30 L _2: preferred fiber distance from the clamping position to the plane of the reflection point PR1 and PR2 of the mirror 16 X _0: distance from the reflection point PR1, PR2 is formed plane to the vertex P ₀ of the mirror 16 C: mirror Center of 16 R: Radius of mirror surface 16 H1: Length of half of minimum height of mirror surface 16 H2: Half length of irradiation area of fiber surface α: Maximum dispersion angle of thick plane slit 11 b: Incident ray 20D Angle formed between perpendicular C-PR1 γ: Angle formed between reflected ray 20E 'and a plane formed by PR1 and PR2

Now, if the parameters S, L, L ₁ , L ₂
If can be specified, other design parameters can be easily calculated geometrically, and the following relationship is obtained. α = tan ⁻¹ [(2S) / L] (from ∵ (5)) H1 = S + (L ₁ + L ₂ ) tan α (7) H2 = S + L ₁ tan α (8) γ = tan ⁻¹ [ L ₂ / (H1 + H2)] ...... (9) b = (π / 4) - [(α + γ) / 2] ...... (10) R = H1 / sin (α + b) ...... (11) X 0 = R [ 1−cos (α + b)] (12) L ₀ = L ₁ + L ₂ + X ₀ (13) In short, if the size of the thick plane slit (S and L),
Preferred fiber clamp position 30 (L ₁ ), mirror surface 16
If the reflection point position (L ₂₎ is determined at the optimum radius R, the minimum height of the cylindrical concave mirror 16 (2H2), the optimum position (L ₀₎ is obtained from the above equation. As described above, in order to satisfy the object of the present invention (that is, the above conditions 3 and 4) as much as possible, some other assumptions and practical considerations are necessary. This additional assumption or practical consideration is one feature of the present invention, namely, the mirror surface 1 at an angle θ about the Z axis.
6 rotates.

Next, as shown in FIG. 8, the irradiation light beam passes through the fibers f1 to f8. Each fiber f1 to f8
Irradiation light passing by the side advances straight on the mirror surface 16. Irradiation light beam EW passing through each of the fibers f1 to f8
Is refracted twice at the interface between the front and back surfaces 31 and 32 of each fiber and air, and is dispersed at a large scattering angle. Since the surface of the fibers f1 to f8 has the UV curable resin, the surface 3
Most of the light beam directly illuminating 1 will be absorbed. On the other hand, the luminous flux remaining without being absorbed is represented by fibers f1 to f
8, the light is refracted at least twice and finally passes through the fibers f1 to f8 and is dispersed. As a result, the back surface 32 of the fiber cannot be sufficiently irradiated with the direct light beam incident on the front surface 31. The weak scattered light passing through the fibers f1 to f8 advances on the mirror surface 16 and is reflected to
Will return to 2. However, the intensity of these reflected light beams is very weak and widely dispersed. Therefore, the amount of energy of the light illuminating the back surface 32 with these reflected light beams can be ignored.

In order to sufficiently irradiate the ultraviolet light on the back surface 32 of the fibers f1 to f8, the mirror surface 16 is set to Z as shown in FIG.
Rotate about the axis by an angle θ. Here, tan2θ = (L ₀ −L ₁ ) / dd: The diameters L ₀ and L ₁ of the exposed bare fibers f ₁ to f ₈ have the same meanings as before. As shown in FIG. And back 32
In considering the ultraviolet beam to be irradiated, the surface 31 is directly irradiated from the ultraviolet beam Ed ₁ to Ed _n, whereas the rear surface 32 is illuminated by the light beam reflected mirror 16 from the incident light beam Er ₁ to Er _n. Gap d 'between fibers
Is equal to the diameter d of the fiber, so that all the required parameters are properly determined, as before, the following conclusions can be reached. That is, the irradiation intensity and the irradiation area on both the front and back surfaces of each fiber in the ribbon are substantially the same, and the object of the present invention is achieved.

However, before reaching this conclusion, the following condition must be further satisfied. 1. The maximum dispersion angle α of the thick slit 14 is very small. 2. The radius R of the mirror surface 16 is the minimum height of the mirror surface 16 (2H
It is larger than 1). 3. The rotation angle θ of the mirror surface 16 about the Z axis is very small. The reasons for requiring these special conditions are described below. Since the reflecting surface used is a cylindrical concave mirror and not a plane mirror, the pattern of the reflected light beam is such that the reflecting surface is rotated in a direction such that an angle exists between the incident light beam and a plane perpendicular to the reflecting surface. Then distortion will occur. At its simplest, the flat and parallel (in the XZ plane) incident rays from I ₁ to I _n and their corresponding R ₁ to R _n
11 are shown in FIG. I ₁ to I
The pattern of incident light up to _n is a straight line when observed from the X direction. However, the patterns of the reflected light rays from R ₁ to R _n are curved (ie, distorted) when viewed from the same X direction. In addition, R ₁ to R
The pattern of reflected light up to _n (for example, pattern 1 (Pat.
1), Pattern 2 (Pat. 2), Pattern 3 (Pat. 3))
It changes when observed on various surfaces apart from the surface forming the reflecting mirror surface 16.

In the present invention, the incident ultraviolet rays are not parallel. For a flat incident light beam (with respect to the XZ plane) entering from the exit 11A of the slit, the propagation angle of the incident light beam from the X axis changes from O to ± α, which corresponds to the Z coordinate of the point light source already described. Dependent. As a result, the reflection pattern of these flat incident light beams is even more complex. This situation can be simulated using a computer. As a result, reflection patterns observed on various planes are shown in FIGS. The parameters in this simulation are shown below. L = 40 mm Thickness of the plane slit 11 S = 5 mm Half the width of the plane slit 11 R = 45 mm Radius of the reflecting mirror surface 16 L ₀ = 60 mm Distance from the slit outlet 11A to the vertex P _{0 of the} mirror surface 16 viewing plane L ₁ and the rotation angle θ is changed.

As shown in FIGS. 12A to 12F,
Reflection pattern distortion is less of a problem for small angles of rotation of the concave mirror. If the propagation angle of the incident light beam with respect to the X axis is small (ie, the maximum dispersion angle α of the plane slit 11 is small, so that the minimum height 2H of the mirror surface 16 is small).
If it is necessary that 1 be small), the distortion of the reflection pattern is also of little concern. For the irradiation system actually used for coating the fiber ribbon thin film, the maximum dispersion angle α ₁ of the plane slit 11 can be controlled with a very small value, and the rotation angle of the concave mirror is very small. To illustrate whether the effects of reflection pattern distortion are significant or not, the design of the UV illumination system was actually performed once with a full simulation, and the results are shown in FIG. The parameters used in this design are: S = 0.4 mm L = 20 mm L ₁ = 12 mm L ₀ = 27.03 mm R = 15.12 mm θ = 0.24 ° Here, these symbols have the same meaning as before.

In FIG. 13, the regions Reg1 to Reg8 indicate the irradiation regions of the fibers f1 to f8, respectively. A region surrounded by a thick line is an irradiation region on the surface of the fibers f1 to f8, and a region filled with a thin line is an irradiation region on the back surface of the fibers f1 to f8. Under the conditions of the above practical design parameters, no significant distortion occurs in the reflection pattern. Therefore, the following conclusions are obtained. That is, the total irradiation intensity and the total irradiation area on the front and back surfaces of the fiber in the ribbon to be coated with the thin film can be made substantially constant by selecting the optimum one as the whole design parameter. The present invention focuses on a technique for obtaining uniform irradiation conditions on both the front and back surfaces of a fiber ribbon to be coated with a thin film of a UV curable resin. Any of the techniques described herein can be used when coating a fiber with a UV curable resin using the present invention.

[0035]

As described above, according to the method of irradiating the ultraviolet ray to the fiber ribbon coated with the ultraviolet curable resin according to the first aspect of the present invention, the ultraviolet irradiation light is incident on the fiber ribbon using the flat slit. The corner is limited,
Ultraviolet rays can be irradiated so that the light intensity becomes uniform in the horizontal direction across the plane formed by each fiber of the fiber ribbon, so that the UV curing resin layer attached to the fiber surface is prevented from being cured at an early stage. The thin film of the cured resin can be uniformly formed at the fiber connection portion, and thus, high-strength fusion splicing of the fiber ribbon becomes possible.

According to the method of irradiating the ultraviolet ray to the fiber ribbon coated with the ultraviolet curable resin according to the third aspect of the present invention, the cylindrical concave mirror reflects the ultraviolet light passing through the gap between the fibers, thereby directly irradiating the fiber. Ultraviolet rays can be applied to the back side of the fiber, which cannot be used. Therefore, only one ultraviolet ray bundle is required as the ultraviolet rays for guiding and irradiating the (all) fibers. In other words, by carefully determining the dimensions of the slit, the position of the fiber ribbon to be clamped, the radius and the minimum dimension of the cylindrical concave mirror, and the arrangement position of this concave mirror, uniform irradiation on both the front and back surfaces of each fiber in the ribbon is achieved. An area and a uniform light intensity are obtained.

[Brief description of the drawings]

FIG. 1 is an overall view showing a method for forming a thin film coating on a fiber ribbon according to the present invention.

FIG. 2 is a schematic diagram showing an irradiation system of the present invention.

FIG. 3 is a longitudinal sectional view showing a thick planar slit according to the present invention.

FIG. 4 is an explanatory diagram showing a state in which light collides and is diffusely reflected on the inner surface of a thick planar slit.

FIG. 5 is an explanatory view showing a direction in which light can travel at an arbitrary point on a slit exit plane.

FIG. 6 is an explanatory diagram showing a maximum diffusion angle in a thick plane slit.

FIG. 7 is an explanatory diagram showing a limit of reflected light on a mirror surface.

FIG. 8 is an explanatory diagram showing the relationship among the dimension of a thick planar slit, a preferred clamping position of a fiber, the diameter and minimum height of a concave mirror, and the position where a concave mirror is to be arranged.

FIG. 9 is an explanatory diagram showing a relationship between a fiber and irradiation light.

FIG. 10 is a view for explaining the reason for rotation of the concave mirror about the Z axis.

FIG. 11 is an explanatory diagram showing the influence of distortion of a reflection pattern when a concave mirror is rotated at a fixed angle with respect to the Z axis.

FIGS. 12A to 12F are explanatory diagrams showing patterns reflected on various observation surfaces when the mirror surface of the concave mirror is rotated at different angles around the Z axis.

FIG. 13 is an explanatory diagram showing irradiation regions on both front and back surfaces of each fiber according to one embodiment of the thin film coating irradiation system.

FIG. 14 shows a thin film coating or UV protection for connection points.
FIG. 2 is a conventional diagram showing an ultraviolet irradiation system for performing recoating of a cured resin on an optical fiber.

FIG. 15 is an explanatory diagram showing an irradiation area on a fiber surface using a conventional ultraviolet irradiation system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fiber ribbon 2, 3 Clamp 4 UV curable resin material 5 UV resin holder 6 Slot 7 UV curable resin thin film layer 8, 9 Ultraviolet rays 11 Slit 11A Slit outlet 15 Fiber bundle 16 Cylindrical concave mirror surface f1 to f8 Fiber

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-62-229202 (JP, A) JP-A-63-156042 (JP, A) JP-A-5-181032 (JP, A) Patent 229684 (JP, A) B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00-6/54 B05C ⁷ /00-21/00

Claims (3)

(57) [Claims] 1. A method of irradiating a fiber ribbon coated with an ultraviolet curable resin with ultraviolet rays to irradiate ultraviolet rays to cure the resin and protect the connection point, thereby irradiating the fiber ribbon with ultraviolet rays. Clamping on the surface of each fiber in the fiber ribbon, the exit surface of a thick and thin slit is arranged, and the ultraviolet light guiding fiber bundle is arranged in front of the clamped fiber ribbon, A front surface, parallel to a normal of a plane formed by the fiber,
And, the center of the ultraviolet light guiding fiber bundle is arranged at the center of all the fibers passing through the center of the slit outlet, and the surface of each fiber passes through the ultraviolet light guiding fiber bundle and the outlet of the slit. A method of irradiating a fiber ribbon coated with an ultraviolet curable resin, the method comprising: guiding ultraviolet light upward, arranging a cylindrical concave mirror on the back surface of the fiber ribbon, and reflecting the ultraviolet light on the back surface of each fiber. 2. The ultraviolet curable resin according to claim 1, wherein the inner and outer surfaces of the thick and elongated flat slit are painted black, and the inner and outer surfaces of the thick and elongated flat slit have a relatively rough surface. A method of irradiating a fiber ribbon coated with UV with ultraviolet rays. 3. The cylindrical concave mirror has a relationship tan2θ = (L ₀ −L ₁ ) / d in which the angle θ between the mirror plane and each fiber in the fiber ribbon at the time of ultraviolet irradiation is expressed by the following equation. L ₀ : distance from the exit of the thick plane slit to the vertex of the mirror surface L ₁ : distance from the exit of the thick plane slit to the preferred fiber clamp position d: rotating so as to satisfy the diameter of each fiber in the ribbon Claim 1 or 2
A method for irradiating a fiber ribbon coated with the ultraviolet-curable resin according to the item 1 to ultraviolet light.