JP2725620B2 - Evaluation method of physical properties of optical fiber coating - 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 for evaluating a coating material of a coated optical fiber for optical transmission and a method for evaluating physical properties of an optical fiber coating used for product inspection of a manufactured coated optical fiber.

[0002]

2. Description of the Related Art Coating of a coated optical fiber affects optical transmission characteristics and lateral pressure characteristics. Therefore, it is particularly necessary to control the physical properties of the first coating layer (primary layer).

As a method for evaluating the shear modulus and the tensile modulus of the first coating of the coated optical fiber, for example, Intern
ational Wire & Cable Symposium Proceedings 1993,
The one described on p.864 is known. In this evaluation method, a part of the coating of the coated optical fiber was removed, a sample was formed in which only the light transmitting member, that is, the glass portion was protruded, and a tensile load was applied to the light transmitting member with the outer peripheral portion of the coated optical fiber fixed. The addition causes shear elastic deformation of the material constituting the first coating layer, measures the shear elastic modulus of this material, and converts it into a tensile elastic modulus.

[0004]

However, in order to fabricate a sample of this conventional evaluation method, it is necessary to protrude only the light transmitting member while leaving the coating layer of the prescribed size, so that high dimensional accuracy is obtained. It is very difficult to make a sample. In other words, the process of removing the coating layer by a cut plane that is exactly perpendicular to the center line of the coated optical fiber and has good flatness must be performed while leaving the light transmitting member at the center, but this is very difficult. . Also,
Even if processing is possible, the dimensions of each sample often differ, and the measurement results of the shear modulus and the tensile modulus vary from sample to sample, resulting in poor measurement accuracy.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for evaluating the physical properties of a coating of a coated optical fiber in which a sample can be easily prepared with high accuracy and the shear modulus and tensile modulus can be measured with high precision. It is in.

[0007]

In order to achieve the above object, the invention according to claim 1 is directed to a light transmitting member, a first covering layer surrounding the light transmitting member and being an elastic body, and a light transmitting member. A method for evaluating physical properties of a first coating layer of a coated optical fiber having a second coating layer surrounding a first coating layer and having a tensile modulus higher than that of the first coating layer, the method comprising: Cutting the coated optical fiber by a plane perpendicular to the central axis direction of the sample to produce a sample whose both end faces are parallel; holding the sample by fixing the second coating layer; and a light transmitting member. Applying a load by pushing only the first member to apply a displacement to the light transmitting member and causing the first coating layer to undergo shear elastic deformation; and, based on the displacement amount of the light transmitting member and the added load value, And a step of calculating a shear modulus or tensile modulus of the coating layer.

Preferably, the direction in which the load is applied is a vertical direction.

Furthermore, a plurality of samples can be arranged in such a manner that their both end faces coincide with each other to form a sample aggregate, and a load can be successively applied to the plurality of samples.

[0010]

[0011]

According to the present invention, the coated optical fiber is cut by a plane perpendicular to the central axis direction of the light transmitting member of the coated optical fiber to prepare a sample whose both end surfaces are parallel, and the second coating layer is fixed. By applying a load by pressing the light transmitting member in the state, a shear elastic deformation is caused in the first coating layer,
The tensile modulus of the material constituting the first coating layer is calculated based on the displacement amount and the added load value.

In addition, by bundling a plurality of samples into a sample assembly and applying a load to those samples one after another, the tensile modulus of the first coating material can be quickly and accurately determined for the plurality of samples. Can be evaluated.

[0013]

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same or corresponding parts have the same reference characters allotted.

FIG. 1 is an explanatory diagram showing a method for evaluating physical properties of an optical fiber coating constituted according to the present invention.
1A shows a state before a load is applied to the coated optical fiber sample 2 by the indenter 1, and FIG. 1B shows a state where a load is applied.

Here, the coated optical fiber has a light transmitting member 3 made of glass having a circular cross section at the center, and a first coating layer (primary layer) having a constant thickness around the light transmitting member 3.
The first coating layer 4 is surrounded by a second coating layer (secondary layer) 5 having a constant thickness. Generally, the first coating layer 4 is made of a soft elastic material, and the second coating layer 5 is made of a hard material that can be regarded as a rigid body.

The first coating layer 4 is made of a soft material,
For example, a UV-curable urethane acrylate resin (UV
(A resin) or a relatively soft material such as a silicone resin.

The second coating layer 5 has a tensile modulus of 1
0~200kg / mm ² about, or 50~180k
It is made of a hard material of about g / mm ^2. For example, a polymer material such as an ultraviolet-curable urethane acrylate resin (UV resin) or an ultraviolet-curable resin such as epoxy acrylate or ester acrylate can be used.

Although such a coated optical fiber is long, the coated optical fiber is cut along a plane perpendicular to the axial direction of the coated optical fiber, that is, the center axis of the light transmitting member (slicing and polishing). ) To produce a sample 2 whose both end faces are parallel and separated by several mm. That is, the thickness of the sample 2 is several mm. Since the sample 2 does not require a process of leaving the light transmitting member 3 unlike the sample used in the conventional evaluation method, the sample 2 can be easily manufactured and the dimensions can be made highly accurate. Further, the risk that the sample end face is physically and chemically changed is smaller than that of the sample of the conventional evaluation method.

After preparing such a sample, the coated optical fiber 2 is held by fixing the outer peripheral portion of the hard second coating layer 5 by holding means (not shown). The light transmitting member 3 is displaced by pushing the light transmitting member 3 vertically downward by the indenter 1 to apply a load. The area of the tip of the indenter 1 is reduced, and a load can be accurately applied to the center of the light transmitting member 3. At this time, since the second coating layer 5 is made of a material that can be regarded as a rigid body as compared with the first coating layer 4, the deformation of the second coating layer 5 is negligibly small. Therefore, as much as the light transmitting member 3 is displaced downward, FIG.
As shown in b), the first coating layer 4 undergoes shear elastic deformation.

The reason why the load is applied in the vertical direction is to minimize the influence of gravity.

Here, the thickness of the sample 2, that is, the distance between the reference points is L (mm), and the diameter of the light transmitting member 3 is Df (μm).
m), the outer diameter of the first coating layer 4 is Dp (μm), the applied load is W (g), and the displacement of the light transmitting member 3 is Z (μm). Shear modulus G (kg / m
m ² ) is represented by the following conversion formula (1).

[0023]

(Equation 1)

Here, if the Poisson's ratio of the first coating layer is ν, the following relational expression (2) holds between the tensile modulus and the shear modulus. Here, the Poisson's ratio ν can be assumed to be about 0.5.

[0025]

(Equation 2)

Therefore, the tensile modulus E of the first coating layer 4
(Kg / mm ² ) is represented by the following conversion formula (3).

[0027]

(Equation 3)

Since the displacement and the load value from the microhardness tester can be monitored as digital signals, extremely accurate measurement can be performed.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 2 shows a coated optical fiber sample 2.
1 shows a sample assembly 6 having a plurality of.
This sample assembly 6 is produced as follows.

First, a length of about 6 cm, an inner diameter of 4 mm, and an outer diameter of 8
A coated optical fiber cut to a length of about 10 cm is inserted into an acrylic pipe 7 mm in diameter, and the gap is filled with an epoxy resin and cured for about one day. After curing, the pipe 7 into which the coated optical fiber has been inserted is cut into a length of L + α (L is the distance between the reference points and α is a minute amount).
Polish both end faces. This polishing is performed using a 12 μmφ diamond solution.

The sample assembly 6 does not require processing to protrude only the light transmitting member 3 unlike the sample used in the conventional evaluation method, and further has a diameter of 8 mm.
Since it has a certain size of mm, it is easy to manufacture. In addition, since the individual samples 2 are manufactured simultaneously by the manufacturing process performed at the same time, the characteristics of all the samples 2 are uniform. In FIG. 2, a cured epoxy resin 8 exists in a portion between each sample 2 and the pipe 7.

The sample assembly 6 manufactured as described above is sandwiched from the side with a vise (not shown), and a load speed of 1.1 × 10 is applied by an indenter (not shown) of a microhardness tester.
⁻³ gf / s is sequentially and continuously applied to the light transmitting members 3 in the individual samples 2. The application of the load speed one after another is performed by moving the sample assembly 6 back and forth and right and left by an XY stage (not shown). Then, the displacement amount and the load value of the light transmitting member 3 at this time are measured and stored. Based on this measurement, the conversion formula (
The shear modulus G of the first coating layer 4 of each sample 2 is calculated by 1), and each sample 2 is calculated by the conversion formula (3).
The tensile modulus E of the first coating layer 4 is calculated in order.

Therefore, data on a plurality of samples 2 can be obtained quickly. In addition, each sample 2
Is uniform as described above, the variation in the tensile modulus E of the first coating layer 4 obtained for each sample 2 is reduced, and highly accurate measurement is possible.

Next, another embodiment will be described with reference to FIGS. As shown in FIG.
One layer of the coated optical fiber 11 is wound around the bobbin 10 to which the # 1000 sandpaper 9 based on IS is attached. The winding tension at this time is set to 100 g.
The outer diameter of the body of the bobbin 10 is 28 cm. The coated optical fiber 1 thus wound around the bobbin 10
The length of one becomes about 500 m. This coated optical fiber 1
The light transmission loss L3 per km at a wavelength of 1.55 μm is measured by a cutback method within 30 minutes immediately after winding.

Here, the cutback method is one of the methods for measuring light loss. Hereinafter, the cutback method will be described. As shown in FIG. 4, light enters the optical fiber 12 via the light source 13 and the incident optical system 14, and the power P <b> 1 (λ) of the transmitted light is measured by the photodetector 15. Next, the optical fiber 12 is cut at a distance of 1 to 2 m from the incident end, and the optical power P0 (λ) is measured in the same manner. That is why this procedure is called cutback. From these two measurements, the loss α (λ) is calculated by the following equation (4).

[0036]

(Equation 4)

For details of the cutback method, for example, see Katsuhiko Okubo, “Optical Fiber Technology in the Age of ISDN”, Rigaku Kogyo (1989), pp. (3-15) to (3-16). . In the measurement by the cutback method of the present embodiment, an OMLEX FML-100 wavelength loss measuring instrument (including a power meter) is used as a spectroscope.
Was used.

Apart from the measurement of the optical transmission loss L3, the wavelength 1.5 in the bundle state of the same optical fiber 1000m, that is, the state in which the optical fiber is not wound around a bobbin or the like.
An optical transmission loss L4 per 1 km of 5 μm is measured by a cutback method.

The optical transmission loss L4 in the bundle state is subtracted from the optical transmission loss L3 in the winding state measured in this way, and the difference (L3-L4) is defined as a loss increment. The loss increment is one of the lateral pressure characteristics. It is preferable that the coated optical fiber has a loss increment of the optical transmission loss at a wavelength of 1.55 μm of 1.0 dB / km or less.

Table 1 below shows the correlation between the lateral pressure characteristic (loss increment) for the bobbin 10 and the shear modulus of the first coating layer 4, and the lateral pressure characteristic (loss increment) and the first coating layer 4. 1 shows a correlation with the tensile modulus of the sample. In addition, the left column of Table 1 shows the tensile modulus of the first covering layer 4 of the sheet (in the sheet state).

[0041]

[Table 1]

As shown in Table 1, there is not much correlation between the tensile modulus of the sheet and the pressure characteristic against the bobbin. For example, if the tensile modulus of the sheet is 0.
For a constant 30 kg / mm ² , the loss increment is 0.8
When it fluctuates more than three times from 6 dB / km to 2.61 dB / km, and when the tensile modulus of the sheet is constant at 0.20 kg / mm ² , the loss increment becomes
It fluctuates about 0.7 times from 0.71 dB / km to 2.06 dB / km. Therefore, it is almost impossible to determine the value of the pressure characteristic against the bobbin on the basis of the value of the tensile elasticity of the sheet.

On the other hand, the shear modulus of the first coating layer 4 measured by the method of the above embodiment (that is, by cutting the coated optical fiber by a plane perpendicular to the central axis direction of the light transmitting member, the both end faces are parallel). A sample aggregate is prepared by arranging a plurality of samples in such a manner that their both end faces are coincident with each other. By holding the sample aggregate, the second coating layer of the sample included in the sample aggregate is formed. The light transmitting member is fixed, and the light transmitting member is pressed against the plurality of samples to continuously apply a load, thereby displacing the light transmitting member, causing the first coating layer to undergo shear elastic deformation, and further displacing the light transmitting member. And the shear modulus of the first coating layer when the shear modulus of the first coating layer is calculated based on the added load value), and the loss of the transmission loss with respect to the bobbin at a wavelength of 1.55 μm. Between the minute, there is a correlation as shown in FIG. Therefore, it is possible to estimate a loss increment of the transmission loss with respect to the bobbin based on the shear modulus measured by the above method.

Similarly, between the tensile modulus of the first coating layer 4 measured by the method of the above embodiment and the loss increment of the transmission loss with respect to the bobbin at a wavelength of 1.55 μm, as shown in FIG. There is a correlation. Therefore, it is possible to estimate a loss increment of the transmission loss with respect to the bobbin from the tensile modulus thus measured.

As described above, it is preferable that the loss increment of the optical transmission loss at the wavelength of 1.55 μm is 1.0 dB / km or less. The line of 1.0 dB / km is shown by a dotted line in FIGS. Therefore, from FIG. 5, it is desirable that the shear modulus of the first coating layer 4 is about 0.05 kg / mm ² or less. Further, from FIG. 6, it is desirable that the tensile modulus of the first coating layer 4 is about 0.15 kg / mm ² or less. Thus, the first coating layer 4 is formed by the above method.
When the shear modulus was evaluated, the shear modulus was 0.1.
If it is not more than 05 kg / mm ² , the loss increment of the coated optical fiber can be estimated to be not more than 1.0 dB / km. Similarly, when the tensile modulus of the first coating layer 4 was evaluated by the above method, the tensile modulus was 0.1%.
If it is 5 kg / mm ² or less, the loss increment of the coated optical fiber can be estimated to be 1.0 dB / km or less.

[0046]

As described above, according to the present invention, by cutting the coated optical fiber by a plane perpendicular to the central axis direction of the light transmitting member, a step of preparing a sample whose both end faces are parallel to each other is provided. Holding the sample by fixing the coating layer of No. 2 and applying a load by pressing only the light transmitting member, thereby displacing the light transmitting member and causing the first coating layer to undergo shear elastic deformation. Calculating the shear modulus and the tensile modulus of the first coating layer based on the amount of displacement of the light transmitting member and the applied load value. Thus, it is possible to obtain a method for evaluating the physical properties of an optical fiber coating that can measure the shear modulus and the tensile modulus of the first coating layer with high accuracy.

Further, by arranging a plurality of samples in a state where their both end surfaces are coincident with each other to form a sample aggregate, and applying loads to the plurality of samples one after another,
Many homogeneous samples can be produced, and the shear modulus and tensile modulus of a plurality of samples can be measured quickly.

[0048]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a method for evaluating physical properties of an optical fiber coating constituted according to the present invention.

FIG. 2 is an explanatory view showing another embodiment of a method for evaluating physical properties of an optical fiber coating constituted according to the present invention.

FIG. 3 is a perspective view showing a state where the pressure on the bobbin is measured.

FIG. 4 is a perspective view for explaining a cutback method.

FIG. 5 is a graph showing a relationship between a shear modulus of a first coating layer and a loss increment of bobbin transmission loss.

FIG. 6 is a graph showing a relationship between a tensile modulus of the first coating layer and a loss increment of bobbin transmission loss.

[Explanation of symbols]

2 sample, 3 light transmitting member, 4 first coating layer, 5
... second coating layer, 6 ... sample aggregate.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroo Matsuda 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (56) References JP-A-63-2008 (JP, A)

Claims (3)

(57) [Claims] 1. A light transmitting member, a first covering layer surrounding the light transmitting member and being an elastic body, and surrounding the first covering layer and having a tensile modulus of elasticity higher than that of the first covering layer. A method for evaluating physical properties of a first coating layer of a coated optical fiber having a high second coating layer, wherein the coated optical fiber is cut by a plane perpendicular to a central axis direction of the light transmitting member. Thereby, a step of preparing a sample having both parallel end faces, a step of holding the sample by fixing the second coating layer, and pressing only the light transmitting member to apply a load,
Applying a displacement to the light transmitting member and causing a shear elastic deformation in the first coating layer; and a shear elasticity of the first coating layer based on a displacement amount of the light transmitting member and an added load value. Calculating a modulus or tensile modulus of elasticity. 2. The method for evaluating physical properties of an optical fiber coating according to claim 1, wherein the direction in which the load is applied is a vertical direction. 3. The method according to claim 1, wherein a plurality of the samples are arranged in a state where their both end surfaces coincide with each other to form a sample aggregate, and the load is successively applied to the plurality of the samples. Or the physical property evaluation method of the optical fiber coating according to 2.