JPH076867B2 - Optical fiber structure measurement method - Google Patents

Description

The present invention relates to a method for measuring the structure of an optical fiber.

<Prior Art> In recent years, the mainstream of optical fibers for communication has shifted from the graded index type fiber to the single mode fiber (SM fiber) shown in FIG. As shown in the figure, the SM fiber has a small core diameter of about 10 μm, so if the core 1 is eccentric, the transmission loss at the time of connection increases. Therefore, the required accuracy for the outer diameter and eccentricity of the SM fiber is becoming severe. Along with this, there is a high demand for the accuracy of optical fiber structure measurement, and development of a highly accurate measurement method is desired. Incidentally, 2 in FIG. 1 is a cladding,
3 is a primary coating and 4 is a secondary coating.

As a conventional example of the optical fiber structure measuring method, Fig. 8 shows the measuring method using ITV. As shown in the figure, the end surface 5a of the fiber 5 to be measured is magnified by the objective lens 6, observed by the ITV camera 7, and displayed on the monitor. ITV at this time
The fiber diameter, core diameter, fiber non-circularity, core non-circularity, core eccentricity, etc. are evaluated based on the distribution of the luminance level of.
Two types of illumination light are used. One of them is for core measurement, which is emitted from the core incidence light source 8, propagates through the dummy fiber 9 and the measured fiber 5, and is emitted from the end face 5a. On the other hand, the other one is for the cladding measurement, which is emitted from the reflected light source 10, reflected by the half mirror 11, passed through the lens 6, and reflected by the end face 5a of the fiber to be measured. Thus, in the measurement of one optical fiber, the fiber transmitted light was used for the core measurement, and the fiber end face reflected light was used for the cladding measurement.

<Problems to be Solved by the Invention> In the above-described conventional measuring method, it is difficult to improve the measurement accuracy because the measured value is easily affected by a slight deviation of the optical axis or the inclination of the fiber end to be measured with respect to the optical axis. It was.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for measuring an optical fiber structure which solves the above-mentioned problems of the prior art, improves the measurement accuracy, and improves the light incidence efficiency.

<Means for Solving Problems> The structure of the present invention that achieves such an object is to measure the structure of an optical fiber by observing the end face of the optical fiber by enlarging it with a lens and measuring the fiber as illumination light. In an optical fiber structure measuring method for measuring a core and a clad by using transmitted light, the fiber transmitted light is characterized by being incident on the inside of the clad after passing through a light scattering substance in close contact with the optical fiber. .

<Operation> Generally, it is thought that light propagates only in the core portion of the optical fiber, but actually, the light can propagate even in the cladding portion if the distance is short. Utilizing this property, in the present invention, not only the core measurement but also the cladding measurement is performed by the fiber transmitted light.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings. It should be noted that the same parts as those of the above-mentioned conventional technique are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 shows an embodiment of the present invention. As shown in the figure, a light source 12 for cladding measurement is installed above the fiber 5 to be measured and close to its end face 5a, and the light emitted from the light source 12 is incident on the cladding of the fiber 5 to be measured. Then, the light propagates through this and exits from the fiber end face 5a to be measured, and is observed by the ITV camera 7 as fiber transmitted light. This evaluates the structure for the cladding. Since the core measurement is illuminated by the above-mentioned core incidence light source 8, both the core measurement and the cladding measurement can be performed by illuminating with the fiber transmitted light. It should be noted that the observation is not limited to the ITV camera 7, but may be performed with the naked eye.

As shown in FIG. 2, the light is incident on the clad. As shown in FIG. It is a method of irradiating and passing light on and then making it enter the cladding and propagating. As the light-scattering substance 14, a substance capable of scattering light, for example, frosted glass, mending tape, vinyl tape or the like is used.

The present embodiment having the above configuration has the following effects.

That is, when the inclination angle of the fiber end face with respect to the optical axis is θ, the method of using the fiber end face reflected light as the irradiation light for the cladding measurement is shown in FIG. 3, and the method of using the fiber transmitted light is shown in FIG. It shows in comparison. As shown in both figures, the deviation of the light incident on the lens 6 as the illumination light from the optical axis is 2θ in the method shown in FIG. 3, whereas it is (θ′−θ) in the method shown in FIG. Is. Here, θ ′ is expressed by the following equation. Therefore, for example, θ = 3 °, However, n is the refractive index of fiber and n'is the refractive index of air.

In the case of n = 1.4 and n ′ = 1, 2θ = 6 °,
(Θ'-θ) = 1.2 ° and 2θ>(θ'-θ). In general, 2θ> (θ′−θ), and the optical axis of the illumination light incident on the lens 6 from the fiber end surface is smaller when using the fiber transmitted light as in the present embodiment than when using the fiber end surface reflected light. The deviation from is small. This means that considering the effects of lens aberration, etc., it is desirable that the light entering the lens enter the center of the lens parallel to the optical axis. When light is used, it means that a more distortion-free image can be obtained and accurate measurement can be performed.
Also, when using the fiber end face reflected light, the light emitted from the reflected light source 10 must be imaged cleanly on the fiber end face, and the fact that fiber transmitted light is used for core measurement etc. In particular, it is desirable to use the fiber transmitted light for the cladding measurement in order to improve the measurement accuracy.

Further, as shown in FIGS. 5 and 6, when a flaw B is present on the fiber end face, the conventional measurement method often causes light to be reflected outward, which makes measurement impossible. Since the influence when using the fiber transmitted light is small, the measurement can be performed and the measurement efficiency can be improved.

Next, referring to the table below, the results of the cladding measurement according to the present invention using the transmitted light from the fiber and the conventional method using the reflected light from the fiber end surface are illuminated. For the measurement, the diameter (μm) and the eccentricity (%) of the cladding were measured 10 times each, and the standard deviations of these values were obtained and summarized in the table as a result. As shown in Table 1 below, for all the results, the present invention has a standard deviation. The difference is small, that is, the variation is small, which shows that accurate measurement can be performed.

<Effects of the Invention> As described above in detail with reference to the embodiments, in the present invention, not only the core but also the cladding is measured by using the fiber transmitted light as the illumination light. Therefore, the illumination light has the lens center as the optical axis. It is easy to pass in parallel, so that an image without distortion can be observed and accurate measurement can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a device configuration for carrying out the present invention, FIG. 2 is a perspective view of a method of making light incident on a cladding, and FIG. 3 is a case of illuminating using end face reflected light. 4 is an explanatory view showing the optical path of the illumination light, FIG. 4 is an explanatory view showing the optical path of the illumination light in the case of illuminating using fiber transmitted light, FIG. 5 is a perspective view of the fiber end surface with scratches, and FIG. 6 is Fifth
7 is a cross-sectional view of the SM fiber, and FIG. 8 is an explanatory view of a conventional optical fiber structure measuring method. In the drawing, 5 is a fiber to be measured, 6 is a lens, 7 is an ITV camera, 8 and 12 are light sources, 9 is a dummy fiber, 13 is a fiber coating, and 14 is a light scattering substance.

Claims (1)

[Claims] 1. An optical fiber structure measuring method for measuring the structure of the optical fiber by observing the end face of the optical fiber by enlarging it with a lens and measuring the core and the clad by using fiber transmitted light as illumination light. 2. The optical fiber structure measuring method as set forth in claim 1, wherein the light transmitted through the fiber is incident on the inside of the clad after passing through a light-scattering substance in close contact with the optical fiber.