JP2946651B2 - Anomaly point detection method for cladding for optical fiber coating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for detecting an abnormal point in a cladding for coating an optical fiber.

<Conventional technology> In a silica-based optical fiber or a multi-component glass-based optical fiber used for optical communication, etc., after a core having a high refractive index portion in a central portion is drawn, a core for preventing propagation of light that does not contribute to transmission is drawn. It is a common practice to form an optical fiber by coating a cladding of plastic or the like having a higher refractive index. Coating of the clad is performed immediately after drawing, thereby preventing the growth of scratches generated during fiberization and the occurrence of cracks due to exposure to air. As the plastic for cladding, energy ray-curable resins such as thermosetting silicone resin, ultraviolet-curable resin (hereinafter referred to as UV resin), and radiation-curable resin have been adopted. The demand for fast UV resins is increasing.

FIG. 6 shows an example of a manufacturing process of a silica-based optical fiber. In the figure, reference numeral 1 denotes a preform as a base material, which is supplied to the heating furnace 2 from a preform supply device (not shown).
The preform 1 is heated and melted by a heater 3 in a heating furnace 2 and drawn as a core 4. The drawn core 4 is cooled in a cooling cylinder 5 and further coated with a coating die 6.
The optical fiber strand 7 is coated with the UV resin cladding.
Becomes Subsequently, the optical fiber 7 is irradiated with ultraviolet rays by an ultraviolet lamp 9 in an ultraviolet irradiation device 8 to solidify the clad. The optical fiber 7 is then
For example, a secondary coating of, for example, UV resin is applied, and the optical fiber is wound into a winding device (not shown) as an optical fiber to form a reel.

<Problems to be Solved by the Invention> Incidentally, in the above-described manufacturing process, coating irregularities, eccentricity and uneven thickness of the cladding, and bubbles in the cladding due to deviation of the coating die 6, mixing of air, vibration, and the like. Generation and irregularities in the outer diameter (undulation) may occur.
Since an abnormal coating causes a transmission loss in optical communication and a reduction in mechanical strength, that is, a reduction in reliability, it has been attempted to detect this during the manufacturing process and perform online control. As a detection method, non-contact is required in consideration of damage to the cladding. For example, JP-A-61
The invention described in Japanese Patent No. 44336 discloses a technique in which an output signal of a photodiode array is swept, and eccentricity and uneven thickness of a clad are detected and controlled by a scattered light pattern.

Thus, the detection of the coating abnormality by the scattered light pattern is effective for eccentricity and uneven thickness, but the variation of the scattering pattern is extremely small for abnormal points such as bubbles in the clad and irregular outer diameters. Therefore, it has been difficult to detect this.

<Means for Solving the Problem> In order to solve this problem, the present invention detects an abnormal point of a clad formed of a transparent material having a different refractive index from the core, which is coated on an optical fiber core. The optical fiber travels in the axial direction, irradiates light from an external light source and propagates in the cladding, and leaks from an abnormal point of the cladding by light receiving means provided near the optical fiber. Detecting an abnormal point of the cladding for optical fiber coating by detecting the scattered light received by the light receiving means and observing the scattered light received by the light receiving means with a light detecting means. In addition to proposing a method, in an optical fiber drawing apparatus that coats and coats a core of an ultraviolet curable resin on a core, a coating die and an ultraviolet lamp are used. A light receiving means is installed in between, and an abnormal point of the clad is detected by using a phenomenon in which bubbles in the clad or irregularities in the clad surface caused by coating abnormality scatter light emitted from the ultraviolet lamp and emit light. It was made.

<Operation> Normally, light from an external light source propagates in the cladding.
If an abnormal point exists, it is scattered and leaks out of the clad. Therefore, an abnormal point is detected by observing the amount and wavelength of the scattered light.

<Embodiment> An embodiment of the present invention will be specifically described with reference to the drawings.
In the description of the embodiments, the same members as those in the conventional example described above are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 and FIG. 2 are perspective views each showing an essential part of an embodiment of an optical fiber manufacturing apparatus to which the method for detecting an abnormal point of an optical fiber cladding according to the present invention is applied.
FIG. 3 shows the principle of the present invention, and FIGS. 4 and 5 show abnormality detection charts in the embodiment.

In FIG. 1, reference numeral 10 denotes a bundle fiber serving as a light receiving means, and a light receiving portion 10a is attached near the optical fiber 7 immediately after the coating die 6. The bundle fiber 10 is connected to a high-precision photon counter 11 serving as a light detecting unit, and the number of photons received from the light receiving unit 10a, that is, the light amount and the wavelength are digitally detected. The measurement interval of the photon counter 11 in this embodiment is 10 ms. In the figure, 12 is a photon counter 1
Is a recorder that records the number of detected photons. In this embodiment, the outer diameter of the core 4 of the optical fiber 7 is 125 nm, and the running speed is 10 m / s. In addition, a cladding was formed with a thickness of 200 μm using an ultraviolet-curable urethane acrylate resin as a UV resin.

 Hereinafter, the operation of the present embodiment will be described.

When the optical fiber 7 is irradiated with light from an external light source (ultraviolet lamp 9), as shown in FIG. 3, the refractive index of the clad 13 is higher than the refractive index of the core 4, so that this light is Propagates while repeating total reflection. However,
If bubbles 14 exist in the cladding 13 or irregularities 15 occur on the surface, the propagating light scatters at these abnormal points and leaks to the outside. Then, the leaked light is sent from the bundle fiber 10 to the photon counter 11, and an abnormality is detected from the number of photons and the wavelength.

Since propagation light is used for detecting an abnormal point, it is preferable that direct light from the light source is not received by the bundle fiber 10, but in this embodiment, the ultraviolet lamp 9 below is used as a light source, and the abnormal point is detected. Is ideally done. Since the measurement interval of the photon counter 11 of this embodiment is 10 ms, the traveling speed of the optical fiber 7 is 10 m / m.
Even at a high speed of s, an abnormal point with an error of about 10 cm can be detected. It is desirable that the wavelength detected by the photon counter 11 coincides with the wavelength of ultraviolet light as a light source.
The following short wavelength light is easily absorbed by UV resin. Therefore, in this embodiment, visible light having a wavelength of 400 to 540 nm is measured.

FIG. 4 shows a photon counter chart when bubbles 14 in the clad 13 are detected. Bubbles 14 are generated by applying mechanical disturbance to the UV resin in the coating die 6. When the measurement was performed at a wavelength of 539 nm, as shown in the figure, when bubbles were mixed, light emission (a change in the amount of light) of 50 or more in terms of the number of photons was detected for about 150 seconds.

On the other hand, FIG. 5 shows a photon counter chart when an irregularity 15 on the surface of the clad 13 is detected. The irregularities are caused by increasing the application temperature of the UV resin. When the measurement was performed at a wavelength of 528 nm, light emission of 200 counts or more (peak value) in Faton number as shown in the figure
Was detected intermittently. Although the figure also shows the results of measurement of the cladding diameter using a conventional optical outer diameter measuring device, no large fluctuations could be observed.

The method described above is a method for detecting an abnormal point using the ultraviolet lamp 9 for curing the clad. However, in the manufacturing method using no light source for curing, as shown in FIG. By providing the external light source 16, the present invention can be adopted.

This concludes the description of a specific embodiment, but embodiments of the present invention are not limited to this embodiment. For example, in the above-described embodiment, the method of detecting an abnormal point in the case where the clad 13 has one layer has been described. However, the present invention is applied when there is no large difference in the refractive index between the clads 13 even when there are two or more layers. It is possible. Further, naturally, it is also possible to detect an abnormal point in the clad 13 formed of a material other than the UV resin by the above method.

<Effect of the Invention> According to the present invention, the optical fiber coating clad is irradiated with light from an external light source and propagated in the clad, and the leakage of scattered light is observed to detect an abnormal point. There is an effect that point detection can be performed with high accuracy.

[Brief description of the drawings]

FIGS. 1 and 2 are perspective views showing the main parts of an embodiment of an optical fiber manufacturing apparatus to which the method for detecting an abnormal point of an optical fiber coating clad according to the present invention is applied. Also, the third
FIGS. 4A and 4B are explanatory diagrams showing the principle of the present invention, and FIGS. 4 and 5 are abnormality detection charts in the embodiment. FIG. 6 is an explanatory view showing an example of a manufacturing process of a silica-based optical fiber. In the drawing, 4 is a core, 6 is a coating die, 7 is an optical fiber, 9 is an ultraviolet lamp, 10 is a bundle fiber, 11 is a photon counter, 12 is a recorder, 13 is a clad, 14 is a bubble, and 15 is irregular. Reference numeral 16 is an external light source.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-63037 (JP, A) JP-A-2-90825 (JP, A) JP-A-48-71257 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) G01M 11/00 G01N 21/84-21/90

Claims (2)

(57) [Claims] 1. A method for detecting an abnormal point of a clad formed of a transparent material having a refractive index different from that of a core coated on a core of an optical fiber. Light is emitted from a light source and propagated in the clad, and scattered light leaked from an abnormal point of the clad is received by light receiving means provided near the optical fiber, and scattered light received by the light receiving means is received. An abnormal point detecting method for an optical fiber coating clad, wherein an abnormal point of the clad is detected by observing with an optical detecting means. 2. An optical fiber drawing apparatus for coating and coating an ultraviolet-curable resin clad on a core, wherein a light-receiving means is provided between the coating die and the ultraviolet lamp, and air bubbles in the clad caused by abnormal coating are provided. 2. The optical fiber coating according to claim 1, wherein an irregular point on the clad surface is detected by utilizing a phenomenon that irregularities on the clad surface scatter light propagating from the ultraviolet lamp to emit light. For detecting abnormal points in cladding for steel.