JPH085877A - Coated optical fiber - Google Patents

Abstract

(57) [Summary] [Object] To provide a coated optical fiber having a thin coating while maintaining optical transmission characteristics. A coated optical fiber comprising an optical transmission fiber and a coating disposed on the outer periphery of the fiber; the coating being a first coating layer disposed on the outer periphery of the optical transmission fiber. And a second coating layer disposed on the outer periphery of the first coating layer, and the second coating layer is 1.
The stress retention rate when applying 0% tensile strain is 50% of the initial value.
A coated optical fiber made of resin whose time (stress relaxation time) decreases to 48 hours or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated optical fiber for optical transmission, and more particularly to a coated optical fiber capable of thinning the coating while maintaining good lateral pressure resistant optical transmission characteristics.

[0002]

2. Description of the Related Art In recent years, in order to meet the diversification of communication demand and the increase in communication volume, optical fiber has been promoted to subscriber lines mainly in urban areas. In the optical communication system for subscribers at present, the number of optical fibers required is limited because the leased line system that handles large-capacity communication such as images and the multiplexing system that handles telephone and low-speed digital communication are mainly used. Has been.

However, in the future, if communications dealing with large-capacity information such as images become generalized and spread to households, the present subscriber line network composed of copper wires will be replaced with optical fibers. Therefore, it is predicted that it will be necessary to meet the demand of users.

In order to realize such an all-optical fiber concept (Fiber To The Home; FTTH concept) of the subscriber line network, a cable (multicore optical fiber cable) in which many optical fibers are assembled is necessary. Becomes As an optical fiber cable to be replaced with the copper wire cable currently used, it has an outer diameter that can be accommodated in the current copper wire cable laying conduit (inner diameter 75 mm), and a copper wire cable (3600 pairs) The same number of cores (eg 4000
The introduction of a super multi-fiber optical fiber cable having a core) is under consideration (Tomida et al., 1991 Spring Conference of the Institute of Electronics, Information and Communication Engineers, B-871).

In order to realize this super multi-core optical cable, the outer diameter of the coated optical fiber (currently about 1000 cores, the outer diameter of one core wire is 250 μm) is made thin (thinning).
Is essential.

The coated optical fiber usually comprises a fiber for optical transmission and a resin coating provided on the outer circumference of the fiber. This resin coating has the function of absorbing pressure from the outside to prevent bending of the optical transmission fiber and maintaining the transmission characteristics of the fiber, and at the same time has the important function of preventing external damage to the optical transmission fiber. are doing. Since it is difficult to change the outer diameter of the standardized optical transmission fiber itself, it is necessary to thin the coating in order to reduce the diameter of the coated optical fiber.

[0007]

However, such a reduction in the diameter of the coated optical fiber or a reduction in the thickness of the coating causes the problem of the quality of the optical fiber, particularly the problem of deterioration of the fiber strength (mechanical characteristics). May occur. This deterioration in fiber strength not only significantly reduces the manufacturability of the fiber, but also causes a serious problem in quality assurance of the optical fiber cable.

Therefore, in order to reduce the diameter of the coated optical fiber, it is necessary to make the coating thinner while maintaining the optical transmission characteristics and mechanical characteristics of the coated optical fiber. With the recent demand for development of a multi-fiber optical fiber cable, the importance of thinning such a coating is increasing more and more.

In order to improve the mechanical properties of the thin-walled coated optical fiber, it is effective to increase the Young's modulus of the resin constituting the coating. On the other hand, if the resin used for this coating is the same, it is generally known that the larger the coating diameter (that is, the larger the coating thickness), the better the optical fiber strength. Therefore, it is not desirable to increase the diameter of the coating.

As described above, theoretically, it is considered that the diameter of the coated fiber can be reduced by increasing the Young's modulus of the material forming the coating (making it harder). However, according to the study by the present inventors, in the thin-coated optical fiber, when the Young's modulus of the resin forming the coating is simply increased, the optical transmission characteristics of the optical fiber are rather deteriorated. Was given.

It is an object of the present invention to provide a coated optical fiber which eliminates the above-mentioned drawbacks of the prior art.

Another object of the present invention is to provide a coated optical fiber having a thin coating while maintaining the optical transmission characteristics.

Still another object of the present invention is to provide a coated optical fiber having a thin coating while maintaining the mechanical characteristics (particularly fiber side pressure characteristic, bobbin side pressure characteristic).

[0014]

As a result of earnest research by the present inventors, the deterioration of the optical transmission characteristics when the outermost coating of the coated optical fiber is simply increased in Young's modulus is caused by the stress relaxation in the outermost coating. It was found that it was due to the delay. As a result of further research by the inventors, in order to reduce the thickness of the coating while maintaining the optical transmission characteristics and / or the mechanical characteristics, the coating has a multilayer structure and a stress relaxation specific to the outermost layer coating. It has been found that imparting properties is extremely effective.

The coated optical fiber of the present invention is based on the above findings, and more specifically, a coated optical fiber comprising an optical transmission fiber and a coating arranged on the outer periphery of the fiber; Includes at least a first coating layer disposed on the outer periphery of the optical transmission fiber and a second coating layer disposed on the outer periphery of the first coating layer;
In addition, the second coating layer is made of a resin whose time (stress relaxation time) for which the stress retention rate when a tensile strain of 1.0% is applied is reduced to 50% of the initial value is 48 hours or less. To do.

[0016]

According to the experiments conducted by the present inventors, when the resin forming the outermost coating of the coated optical fiber is simply made to have a high Young's modulus, the pressure characteristic against the fiber (to be described later when the coated optical fibers are stacked and wound) In addition, the resistance of one coated fiber to the lateral pressure received from another coated fiber was significantly reduced. According to the experiments conducted by the present inventor, it is estimated that the cause of the decrease in the fiber side pressure characteristic is that the conventional outer layer resin has an insufficient elastic deformation capability (relaxation behavior) when an external stress is applied. . When the external coating is soft (Young's modulus is low) when external stress is applied to the coated fiber, the strain due to the external stress must be absorbed quickly and sufficiently by the relaxation ability of the resin that constitutes the coating. Is possible. On the other hand, according to the knowledge of the present inventor, when the outer layer coating is hard (Young's modulus is high), the coated optical fibers holding the external stress that cannot be completely absorbed are contacted (pressed) to each other. , The strain due to the stress is mutually applied to the glass fiber inside the coating (that is, a certain coated optical fiber itself is also a perpetrator and a victim), and light loss based on microbending (microbending). It is estimated that the loss has occurred and that the loss has increased. It has been found that such a phenomenon is particularly remarkable in a small-diameter fiber that requires the use of a coating having a very high Young's modulus (hard).

On the other hand, in the above-described coated optical fiber of the present invention, since the resin forming the outermost layer coating (second coating layer) has a specific stress relaxation ability, the stress or the stress is not applied even when an external stress is applied. It is possible to absorb the strain due to the stress to a considerable extent in a short time. Therefore, according to the present invention, it is possible to obtain a coated optical fiber having good pressure resistance to the fiber side and / or pressure resistance to the bobbin side even if the outermost layer coating is hard (high Young's modulus).

Conventionally, after actually manufacturing a coated optical fiber using various high Young's modulus materials, the optical transmission characteristics (fiber side pressure characteristic, bobbin side pressure characteristic, etc.) of the coated fiber are evaluated. That is, by trial and error, a thin-walled coated optical fiber having good optical transmission characteristics was obtained. On the other hand, according to the present invention, after the suitable material to be used for the outermost layer coating is efficiently screened in advance, the coated optical fiber can be produced, so that the optimum material is selected according to the application, cost, etc. Thus, it is possible to easily obtain a thin-coated optical fiber having good optical transmission characteristics.

Hereinafter, the present invention will be described in detail with reference to the drawings as necessary.

(Coated Optical Fiber) The structure of the coated optical fiber of the present invention is not particularly limited as long as it has a structure in which a coating composed of at least two coating layers is arranged on the outer periphery of the optical transmission fiber. From the viewpoint of the balance between the thinning of the entire coating and the microbend resistance of the coated optical fiber,
The coating preferably comprises at least two layers including a first coating layer (inner layer having relatively low hardness) having a function of a buffer layer and a second coating layer (outer layer) having relatively high hardness. . It is preferable that each of these first and / or second coating layers is made of a polymer compound and further a curable resin. It is particularly preferable that the curable resin is made of an ultraviolet curable resin (for example, an ultraviolet curable urethane resin or the like).

FIG. 1 is a partial schematic perspective view showing one embodiment of the structure of the coated optical fiber core wire (or strand) of the present invention.

Referring to FIG. 1, this coated optical fiber is
It is composed of an optical transmission glass fiber 1, a first coating layer 2 provided on the outer periphery of the fiber 1, and a second coating layer 3 provided on the outer periphery of the first coating layer 2. The optical transmission glass fiber 1 is usually composed of a core (not shown) and a clad (not shown) provided outside the core. The outer diameter of the optical transmission glass fiber 1 is usually 125.
It is preferably μm.

(Stress Relaxation Property) In the present invention, the second coating layer 3 is made of a resin having a specific stress relaxation property. That is, when a tensile strain of 1.0% is applied to the resin, the time until the stress retention rate decreases to 50% (or less) of the initial value due to the stress relaxation behavior of the resin itself (hereinafter, "Stress relaxation time") is 4
8 hours or less.

Whether or not the resin has such a stress relaxation characteristic can be more specifically determined by the following "stress relaxation characteristic confirmation test".

That is, first, the resin used for the second coating layer 3 was placed in a normal air atmosphere at a humidity of 50% RH,
In a temperature-controlled room at a temperature of 23 ° C. (under the same condition as that to be used as the coating layer 3)
A cured sheet is obtained by curing it into a sheet having a size of 60 × 5 mm and a thickness of 200 μm. When the resin is an ultraviolet curable resin, for example, an ultraviolet irradiation lamp (manufactured by Eye Graphics Co., trade name: Metal Halide Lamp Mo
The cured sheet may be obtained by irradiating ultraviolet rays with an irradiation light amount of 1.0 J / cm ² using 15-L312).

Next, the above cured sheet was mounted on an Instron type testing machine (manufactured by Toyo Bold Co., Ltd., trade name: Universal Tensile Testing Machine) as shown in the schematic side sectional view in FIG. Under the RH measurement environment, the above-described tester is used to pull the cured sheet at a predetermined strain rate until a tensile strain of 1.0% is reached. Here, the Instron crosshead is stopped, the Instron load cell, and the amplifier and LOG electrically connected to the load cell.
The decrease in load (stress) is continuously read by TIMER (logarithmic digital printer), and the time when the stress becomes 50% of its initial value (stress relaxation time) is measured. In FIG. 2, 11 is an original length adjusting dial, 12 is a load cell, 13 is a radiator plate, 14 is a constant temperature tank balance, 15 is a heat insulating material, 16 is a sample to be measured, 17 is a chuck, 18 is a constant temperature tank, and 19 is cooling. Holes, 10 are stoppers, 21 is a strain imparting device, 22 is an air cylinder, 23 is a horizontal adjust, 24 is a sample chamber, and 25 is a cooling hole.

The thickness of the first coating layer 2 is preferably about 7 to 50 μm. Young's modulus of the material (after curing) constituting the coating layer 2 of the said first, 0.04~0.30kg / mm ² approximately, more 0.05~0.20kg / mm ² approximately, in particular 0.07 It is preferably about 0.15 kg / mm ² .

The thickness of the second coating layer 3 is preferably about 5 to 40 μm. The Young's modulus of the material forming the second coating layer 3 (after curing) is 50 kg / mm ² or more (further 10
0 kg / mm ² or more) is preferable. This Young's modulus is usually 200 kg / mm ² or less (further 170 kg / mm ²
The following) are preferable.

When the coated optical fiber of the present invention is used as a core wire (or strand) of an ultra-multicore optical fiber cable,
The outer diameter of the outermost coating (second coating layer 3) is 220 μm.
It is preferably m or less, more preferably 200 μm or less (particularly 180 μm or less).

In the above, the embodiments of the present invention in which the inner layer and the outer layer constituting the coating are each one layer (that is, the first coating layer 2 and the second coating layer 3) have been described. In the coated optical fiber of the present invention having the resin coating layer consisting of at least two layers on the outer periphery of the fiber 1, as long as the resin forming the outermost coating layer has the stress relaxation characteristics described above, the same as in the above-mentioned aspect The effect of can be obtained.

(Pressure-to-fiber side pressure characteristic) In the coated optical fiber of the present invention, the loss increment of the optical transmission loss (wavelength 1.55 μm) is 0.06 dB / km or less, and further 0.03 dB / k.
It is preferable to have a fiber side pressure characteristic of m or less.

In the present invention, this fiber-to-fiber side pressure characteristic can be measured as follows.

That is, referring to the schematic perspective view of FIG.
Three layers of the coated optical fiber 31 are wound on the bobbin 32 (outer diameter of the body part: 28 cm) with a winding tension of 100 g. As shown in FIG. 4, which is an enlarged cross-sectional view of the portion indicated by “A” in FIG. 3, the portion in which the three layers are wound is a dummy fiber portion in which measurement is not performed. Then, the same coated optical fiber 31 as the three layers is wound on the three layers of the dummy fiber portion with a winding tension of 100 g to further wind three layers to form a measurement fiber portion (FIG. 4).

The optical transmission loss L ₁ (wavelength 1.55 μm) of only the upper three layers (measurement fiber portion) wound around the bobbin 22 in this way is cut back within 30 minutes from the winding (this cut back method). For more information, see Katsuhiko Okubo, "Optical Fiber Technology in the ISDN Era," Rigakusha, 1989.
Year, see pages (3-15) to (3-16)). In the measurement by the cutback method, the following conditions can be preferably used.

Spectrometer: Operex, trade name: FM
L-100 wavelength loss measuring device (including power meter) In addition to the above-mentioned measurement of the optical transmission loss L ₁ , a bundle state of the same optical fibers (a state not wound around a bobbin, about 1)
Optical transmission loss L ₂ (wavelength 1.55 μm) at 000 m)
Is measured by the above-mentioned cutback method. From the optical transmission loss L ₁ in the wound state to the optical transmission loss L ₂ in the bundled state
And the difference (L ₁ −L ₂ ) is taken as the loss increment (to the fiber side pressure characteristic).

(Bobbin Side Pressure Characteristics) The coated optical fiber of the present invention has a loss increment of the optical transmission loss (wavelength of 1.55 μm) of 1.5 dB / km or less, more preferably 1.0 dB / km or less. It is preferable to have characteristics.

In the present invention, this pressure characteristic against the bobbin side can be measured as follows.

That is, referring to the schematic perspective view of FIG.
A bobbin 34 with a JIS-based # 1000 sandpaper 33 attached to the body (outer diameter of the body: 28c
A layer of the coated optical fiber 35 is wound on m) with a winding tension of 100 g. The optical transmission loss L ₃ (wavelength 1.55 μm) of the coated optical fiber 35 (length: about 500 m) wound around the bobbin 32 in this way is cut back by the cutback method within 30 minutes immediately after winding. To measure.

Apart from the measurement of the optical transmission loss L ₃ described above,
Optical transmission loss L ₄ (wavelength 1. W in a bundle state of the same optical fiber (state not wound around bobbin, etc., about 1000 m)).
55 μm) is measured by the above cutback method. The optical transmission loss L ₄ in the bundled state is subtracted from the optical transmission loss L ₃ in the wound state, and the difference (L ₃ −L ₄ ) is defined as the loss increment (bobbin side pressure characteristic).

(Manufacturing Method of Coated Optical Fiber) The manufacturing method of the coated optical fiber of the present invention is not particularly limited, but the coated optical fiber is obtained by using, for example, a drawing apparatus as shown in the schematic sectional view of FIG. It can be suitably manufactured.

That is, referring to FIG. 6, the optical fiber preform 41 is drawn in the drawing furnace 42 to obtain the glass optical fiber 1. Then, the glass optical fiber 1 is passed through the first resin coating device 43a to form a first coating layer (not shown) made of an ultraviolet curable resin on the fiber 1 and then the fiber 1 The first coating layer 2 made of the above-mentioned ultraviolet-curable resin is cured by passing it through the first ultraviolet irradiation device 44a to form the first coating layer 2 (FIG. 1) on the fiber 1. The first ultraviolet irradiation device 44a includes a hollow cylindrical body 45a through which the glass optical fiber 1 should pass and an ultraviolet lamp 46 for irradiating the coating layer of the ultraviolet curable resin with ultraviolet rays.
a and a reflecting mirror 47a that reflects the ultraviolet rays.

Then, the optical fiber 1 on which the first coating layer 2 is formed is passed through the second resin coating device 43b,
After a second coating layer (not shown) made of an ultraviolet curable resin is provided on the fiber 1, the fiber 1 is passed through a second ultraviolet irradiation device 44b to make a first layer made of the ultraviolet curable resin. 2 is cured to form the first coating layer 2
The second coating layer 3 (FIG. 1) is formed on the top surface of the optical fiber to obtain the coated optical fiber 48 having the configuration shown in FIG. The second ultraviolet irradiation device 44b is the first ultraviolet irradiation device 44.
Similar to a, it includes a hollow cylindrical body 45b through which the glass optical fiber 1 should pass, an ultraviolet lamp 46b that irradiates the coating layer of the ultraviolet curable resin with ultraviolet rays, and a reflecting mirror 47b that reflects the ultraviolet rays. There is.

The coated optical fiber 48 obtained as described above is then wound by the winder 49.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples do not limit the scope of the present invention in any way.

[0045]

EXAMPLE Using the drawing apparatus shown in FIG. 6, an optical fiber preform 41 was drawn in a drawing furnace 42 to form a glass optical transmission consisting of a core and a clad arranged around the core. Fiber 1 (normal single mode, outer diameter 125 μm) was obtained. Then, the optical fiber 1 is attached to the first resin coating device 4
After passing through 3a, a coating layer made of a UV-curable urethane acrylate resin (which gives a soft coating layer after curing) is provided on the glass fiber 1, and then the first UV irradiation is further provided with an UV irradiation lamp 46a. The coating layer of the ultraviolet curable resin was cured by passing through the device 44a to form the first coating layer 2 (FIG. 1) on the glass fiber 1. The Young's modulus of the first coating layer 2 (inner layer or buffer layer) thus formed is 0.1 kg / m.
m ^2, and its thickness (coating diameter) were as shown in Table 1 below.

Then, the fiber 1 on which the first coating layer 2 has been formed as described above is passed through the second resin coating device 43b, and the ultraviolet curing type (which gives a hard coating after curing) on the glass fiber 1. A coating layer made of a urethane acrylate resin is provided, and the coating layer of the ultraviolet curable resin is cured by passing it through a second ultraviolet irradiation device 44b equipped with an ultraviolet irradiation lamp 46b to form a first coating on the glass fiber 1. Two coating layers 3 were formed to obtain a coated optical fiber 48 having the structure shown in FIG. This second coating layer 2
The (outer layer or protective layer) was formed by using a plurality of UV-curable urethane acrylate resins that provide coatings having different stress relaxation times and different Young's moduli as shown in Table 1 below. The outer coating diameter of the second coating layer was as shown in Table 1 below.

The parameters of each coated optical fiber obtained above are such that the mode field diameter is about 9.5 μm (NFP (near
field pattern) method), the cutoff wavelength is about 1.
25 μm (according to “bending method”). For details of the "NFP method" and the "bending method" used here, see, for example, Katsuhiko Okubo, "Optical Fiber Technology in the ISDN Era", Rikagakusha (1989), Nos. (3-5) to (3-12). ) You can refer to the page.

Optical transmission characteristics of each coated optical fiber obtained as described above (pressure characteristic against fiber, pressure characteristic against bobbin)
Was evaluated. The results are summarized in Table 1 below.

[0049]

[Table 1]

"Pressure-to-fiber side pressure characteristics" shown in Table 1 above.
Was measured as follows.

That is, as shown in FIGS. 3 and 4,
Three layers of the coated optical fiber 31 are wound on the bobbin 32 with a winding tension of 100 g (dummy fiber portion), and the optical fiber 31 is further wound on the three layers of dummy fiber portions with a winding tension of 100 g. Further, three layers were wound to form a measurement fiber portion. Bobbin 3 in this way
The optical transmission loss L ₁ (wavelength 1.55 μm) of only the upper 3 layers (measurement fiber portion) wound around 2 is 30 after winding.
It was measured by the cutback method within minutes. The following conditions were used in the measurement by this cutback method.

Spectrometer: Operex, trade name: FM
L-100 wavelength loss measuring device (including power meter) In addition to the above-mentioned measurement of the optical transmission loss L ₁ , a bundle state of the same optical fibers (a state not wound around a bobbin, about 1)
Optical transmission loss L ₂ (wavelength 1.55 μm) at 000 m)
Was measured by the above-mentioned cutback method. The optical transmission loss L ₂ in the bundled state was subtracted from the optical transmission loss L ₁ in the wound state described above, and the difference (L ₁ −L ₂ ) was used as the loss increment (fiber side pressure characteristic).

On the other hand, the above-mentioned "bobbin side pressure characteristic" was measured as follows.

That is, as shown in FIG. 5, the bobbin 3 having the # 1000 sandpaper 33 attached to the body portion
The coated optical fiber 35 is wound on the surface of the optical fiber 4 by one layer with a winding tension of 100 g, and the optical transmission loss L ₃ (wavelength 1.55 μm) of the coated optical fiber 35 (length: about 500 m) wound in this way is Within 30 minutes immediately after the winding, the measurement was performed by the cutback method as described above.

Apart from the above measurement of the optical transmission loss L ₃ ,
Optical transmission loss L ₄ (wavelength 1. W in a bundle state of the same optical fiber (state not wound around bobbin, etc., about 1000 m)).
55 μm) was measured by the above-mentioned cutback method. Subtracting the light transmission loss L ₄ in the bundle state from the optical transmission loss L ₃ in the wound state described above, and this difference (L ₃ -L ₄₎ loss increment (vs. bobbin lateral pressure characteristics).

The stress relaxation time was measured by the following method.

That is, the resin used for the second coating layer 3 was applied under normal air atmosphere at a humidity of 50% RH and a temperature of 2%.
UV irradiation lamp (Product name: Metal Halide Lamp Mo15, manufactured by Eye Graphics Co., Ltd.) in a constant temperature bath at 3 ° C.
-L312) and irradiating ultraviolet rays with an irradiation light amount of 1.0 J / cm ² to obtain a size of 60 × 5 mm and a thickness of 2
A cured sheet was obtained by curing to a sheet state of 00 μm.

Then, the cured sheet was mounted on an Instron type testing machine (manufactured by Toyo Bold Co., Ltd., trade name: Universal Tensile Testing Machine) as shown in the schematic side sectional view in FIG. Under the RH measurement environment, the above-mentioned test machine was used to pull the above-mentioned cured sheet at a predetermined strain rate until a tensile strain of 1.0% was reached. At this point, the Instron crosshead is stopped, the decrease in load (stress) is continuously read by the load cell 12 of the Instron, and the amplifier and LOGTIMER (logarithmic digital printer) electrically connected to the load cell 12, and the stress is reduced. Was measured to be 50% of its initial value (stress relaxation time).

As shown in Table 1 above, the outer layer (second layer)
As the Young's modulus of the coating was increased, the pressure characteristic against the bobbin was rapidly improved. When the coated optical fiber may come into contact with something extremely hard as compared with its own coating, it was effective to make the outer layer coating harder (high Young's modulus) and block the external force. This increase in Young's modulus was particularly effective in a thin coated optical fiber having a thin coating layer.

However, simply increasing the Young's modulus of the outer layer coating as described above significantly reduced the fiber side pressure characteristic, as shown in Table 1 (Samples A to D).

The cause of the deterioration of the fiber side pressure characteristic is that the conventional ultraviolet curable resin for outer layer has an insufficient elastic deformation ability (relaxation behavior) when an external stress is applied, according to the study of the present inventor. It is estimated that it was because. When external stress is applied to the coated fiber, or when the outer layer coating is soft (Young's modulus is low), the strain due to external stress must be absorbed quickly and sufficiently by the relaxation ability of the resin that constitutes the coating. Is possible. On the other hand, according to the knowledge of the present inventor, when the outer layer coating is hard (Young's modulus is high),
When the coated optical fibers that retain the external stress that cannot be completely absorbed contact (push) with each other, strain due to the stress is applied to the glass fibers inside the coating (mutually), and light based on the microbend is applied. It is presumed that the loss (microbend loss) occurs, which causes an increase in loss.

On the other hand, in the coated optical fibers of the present invention (Samples E to J in Table 1) in which the ultraviolet curable resin having a specific stress relaxation characteristic is used for the outer layer coating, the stress relaxation behavior of the outer layer coating is Based on the improvement, even if the outer layer coating is hard (Young's modulus is high), it is presumed that good pressure characteristics against the fiber were obtained.

As described above, according to the present invention, by using an ultraviolet curable resin having a high Young's modulus and a specific stress relaxation characteristic for the outer layer coating, the thin coated fiber (220 μmφ, 200 μmφ, 180 μm
It has been confirmed that even with respect to φ), good optical transmission characteristics can be obtained as well as a conventional coated optical fiber having a thick coating.

[0064]

As described above, according to the present invention, a glass fiber for optical transmission, a first coating layer arranged on the outer circumference of the fiber, and a first coating layer arranged on the outer circumference of the first coating layer. And a second coating layer, wherein the second coating layer is made of a resin having a specific stress relaxation characteristic.

The coated optical fiber of the present invention having the above-mentioned structure is based on a combination of a coating composed of a plurality of layers and an outermost layer (second layer) having a specific stress relaxation characteristic, and is caused by the stress retention in the coating. By preventing bend loss, the coating can be thinned while maintaining the optical transmission characteristics.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing one aspect of a configuration of a coated optical fiber of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a tensile tester that can be used to evaluate stress relaxation characteristics in the present invention.

FIG. 3 is a schematic perspective view for explaining a method for measuring a fiber side pressure characteristic in the present invention.

FIG. 4 is an enlarged schematic cross-sectional view showing a part (portion A) of FIG.

FIG. 5 is a schematic perspective view for explaining a method for measuring the pressure characteristic against the bobbin side in the present invention.

FIG. 6 is a schematic cross-sectional view showing an example of a method for manufacturing a coated optical fiber according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass fiber for optical transmission, 2 ... 1st coating layer, 3 ...
Second coating layer, 12 ... Load cell, 16 ... Sample, 17 ...
Chuck 18 ... Constant temperature bath, 31 ... Coated optical fiber, 32 ...
Winding bobbin, 33 ... Sandpaper, 34 ... Winding bobbin, 35 ... Coated optical fiber, 41 ... Optical fiber base material, 42 ... Drawing furnace, 43a, 43b ... Resin coating device, 4
4a, 44b ... UV irradiation device, 48 ... Coated optical fiber, 49 ... Winding machine.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroo Matsuda 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (7)

[Claims] 1. A coated optical fiber comprising an optical transmission fiber and a coating arranged on the outer circumference of the fiber, wherein the coating is a first optical fiber arranged on the outer circumference of the optical transmission fiber. At least a coating layer and a second coating layer disposed on the outer periphery of the first coating layer; and the second coating layer has a stress retention rate when a tensile strain of 1.0% is applied. The coated optical fiber is characterized by comprising a resin whose time (stress relaxation time) for decreasing to 50% of the initial value is 48 hours or less. 2. The coated optical fiber according to claim 1, wherein the resin forming the second coating layer has a Young's modulus of 100 kg / mm ² or more. 3. The coated optical fiber according to claim 1, wherein the outer diameter of the second coating layer is 220 μm or less. 4. The coated optical fiber according to claim 1, wherein the resin forming the second coating layer is a curable resin. 5. The coated optical fiber according to claim 4, wherein the resin forming the second coating layer is an ultraviolet curable resin. 6. The coated optical fiber according to claim 1, wherein the resin forming the first coating layer is a curable resin. 7. The coated optical fiber according to claim 6, wherein the resin forming the first coating layer is an ultraviolet curable resin.