JP2893048B2 - Carbon coated optical fiber inspection method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon-coated optical fiber inspection method and apparatus capable of continuously measuring the thickness of a carbon layer of a communication carbon-coated optical fiber. .

[Conventional technology]

As shown in FIG. 4, the carbon coated optical fiber is
The structure is such that the surface of a quartz optical fiber for communication 20 having an outer diameter of 0.125 mm and having a fiber core 23 is coated with an amorphous carbon layer 21 having a thickness of about 400 Å, and a resin layer 22 is coated around the amorphous carbon layer 21. The resin is usually soft inside and hard outside, and the material is generally UV-curable urethane, or a combination of thermosetting silicone and nylon, and the outer diameter of the coating is from 0.25 mm. 1mm
It is about. The carbon-coated optical fiber having such a structure has no change in transmission loss even when used in a hydrogen atmosphere because the carbon layer 21 has excellent shielding properties against moisture and hydrogen, and when used in water. Has excellent features such as little mechanical strength degradation observed. This feature is provided by the carbon layer 21.

[Problems to be solved by the invention]

By the way, in the above-mentioned product inspection of the carbon-coated optical fiber, it is necessary to confirm that the carbon layer 21 is continuously coated without interruption in the longitudinal direction of the optical fiber. The coating of the carbon layer 21 is performed by a CVD (Chemical Vapor Deposition) furnace. If the supply of the raw material gas for the carbon layer 21 is momentarily interrupted or the drawing speed fluctuates in the CVD furnace, the carbon layer 21 may be interrupted. However, there is no non-destructive method for inspecting the presence or absence of minute pinholes to the extent that hydrogen molecules generated in the carbon layer 21 can penetrate, and there is no method for online inspection at the time of manufacturing, which is a serious problem in terms of quality assurance. Was.

The present invention has been made in view of the above circumstances, and can continuously measure the thickness of a carbon layer at the time of manufacturing, thereby non-destructively determining the presence or absence of minute pinholes generated in the carbon layer, and It is an object of the present invention to provide a method of inspecting a carbon-coated optical fiber that can be detected online and an apparatus therefor.

[Means for solving the problem]

The present invention covers the optical fiber drawn from the optical fiber spinning furnace with a carbon layer, and after changing the direction with a pulley,
In the process of manufacturing the carbon coated optical fiber leading to the winding machine, the optical fiber preform in the optical fiber spinning furnace is continuously irradiated with an optical signal, and the optical fiber bent from the bent portion of the optical fiber is bent by the pulley. The thickness of the carbon layer coated on the optical fiber is continuously measured by measuring the amount of radiation.

[Action]

According to the above configuration, the optical signal is continuously incident on the optical fiber preform to be drawn, whereby the optical signal incident on the optical axis of the core at the center of the optical fiber is transmitted in the longitudinal direction of the fiber, and the optical signal is transmitted by the pulley. The light is emitted to the outside from the bent portion of the fiber. For example, a carbon layer having a thickness of 400 angstroms gives a transmission loss of about 5 dB for light having a wavelength of 1.3 microns. Therefore, when the optical signal is continuously measured, the light receiving power varies in the order of several dB depending on the presence or absence of the carbon layer, so that a defect of the carbon layer can be accurately detected online.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a view showing a configuration of a carbon coated optical fiber production line to which an embodiment of the present invention is applied. In this figure, an optical fiber 2a drawn from a quartz fiber preform 2 in an electric furnace 3 as an optical fiber spinning furnace passes through a CVD furnace 7 and a resin coating device 8 provided immediately below the optical fiber 2a, and is horizontally pulled by a pulley 9. After being bent in the direction, it is wound on a bobbin by a winder. In some cases, a fiber outer diameter measuring device, a cooling device, or the like is installed between the CVD furnace 7 and the resin coating device 8. The CVD furnace 7 is provided with a raw material gas supply port 5 and an exhaust port 6 for the carbon layer 21 and seal gas supply ports 4 and 4. About 400 Å of amorphous carbon is deposited on a quartz surface having a surface temperature of about 1000 ° C. immediately after drawing. The thickness is tightly coated. The resin coating device 8 includes a die for coating urethane resin and the like, an ultraviolet curing furnace, a heat curing furnace, and the like, and is usually installed continuously so as to cover two layers of soft and hard resins. In FIG. 1, only one die is shown.

Now, in this embodiment, the light source 1 is installed with the optical axis aligned with the central axis of the fiber preform 2. Specifically, a fiber preform 2 is fixed, a through hole 12a for an optical signal is formed at the center of a preform clamp 12 having an elevating function, and a light source 1 is installed above the through hole 12a. The wavelength of the light source 1 is not particularly limited, but it is advantageous to select a wavelength at which the transmission loss of the optical fiber 2a is low. The transmission wavelength of a normal quartz fiber for communication is 1.3 or 1.55 microns, and as the light source 1, an LED (light emitting diode), an LD (laser diode) having this wavelength, or a high-output YAG ring laser can be used. When it is desired to visually confirm the leak light, a helium neon laser of visible light may be used.

On the other hand, a photodetector 10 is provided below the CVD furnace 7 so as to continuously measure the leakage light power by a bending method. In this embodiment, as an example, the pulley 9 is used as a method for giving a bend to the optical fiber 2a. In this case, the smaller the diameter of the pulley 9, the higher the optical power radiated from the optical fiber 2a. As the light receiver 10, a photodiode of Ge (germanium) or Si (silicon) or the like is used. Depending on the thickness of the resin layer 22, the radiated light power may be greatly attenuated. In this case, a photon counter or an integrating sphere may be used to improve the light receiving sensitivity. Further, a dark box 11 covering the pulley 9 and the light receiver 10 is for removing the influence of disturbance light, and is used as needed.

Here, FIG. 2 shows the measurement results of the amount of light attenuation when transmitting only the carbon film. In this figure, the horizontal axis is the carbon film thickness, and the vertical axis is the attenuation when passing through the carbon film. Also, the optical fiber used is for a wavelength of 1.3 microns,
Single-mode optical fibers for 1.55 microns, each coated with amorphous carbon. An optical signal was incident on the core of this fiber, and the optical power of the leaked light from the portion bent to a bending diameter of 14 mm was measured. The two solid lines indicate the width of the variation. As can be seen from FIG. 2, in the case of a carbon film of 400 Å as an example, a transmission loss of 5 to 8 dB occurs. Therefore, when the power of the photodetector 10 is continuously measured by the measurement system shown in FIG. 1, the received light power changes between the portion where the carbon layer 21 is coated and the portion where the coating is defective, and the defective coating can be sensed with high sensitivity.

Next, FIG. 3 shows a measurement result by the measurement system of the above-described embodiment. In this case, a YAG ring laser (wavelength: 1.32 microns) with an output of 35 mW was used as the light source 1, and the length was 50
While covering the optical fiber preform 2 for the 1.3 micron centimeter with a carbon film having a thickness of 400 Å,
The light receiving power meter was continuously measured with a power meter using a Ge diode as the light receiving device 10, and the drawing speed was 120 meters per minute. A point A shown in the figure is a place where supply of the raw material gas for the carbon layer 21 was intentionally stopped for one second, and a change of the received light power of 2 dB was detected at this place. Therefore, the effectiveness of this test method could be confirmed.

In the above-described embodiment, the pulley 9 and the photodetector 10 are arranged one by one. However, in the circumferential direction, any one of the pulleys 9 and the photodetectors 10 may be disposed in the circumferential direction with respect to a carbon film coating defect such as a pinhole. A plurality of pulleys 9 and a plurality of light receivers 10 may be provided so that a pinhole at a location can also be detected.

〔The invention's effect〕

As described above, according to the present invention, the presence or absence of minute pinholes generated in the carbon layer during the production of the carbon-coated optical fiber can be inspected nondestructively and continuously online during the production. Therefore, an excellent effect can be obtained in terms of quality assurance of the carbon coated optical fiber.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a carbon-coated optical fiber manufacturing line to which an embodiment of the present invention is applied, FIG. 2 is a graph showing an amount of optical power attenuation when passing through a carbon layer, and FIG. FIG. 4 is a graph showing a measurement result according to one embodiment. FIG. 4 is a cross-sectional view showing a configuration of a carbon-coated optical fiber. DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Optical fiber preform, 2a ... Optical fiber, 3 ... Electric furnace, 7 ... CVD furnace, 9 ... Pulley, 10 ... Receiver, 20 ... Optical fiber, 21 ... ... carbon layer.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01M 11/00 G02B 6/44 C03B 37/12 C03C 25/02

Claims (2)

(57) [Claims] 1. After coating an optical fiber drawn from an optical fiber spinning furnace with a carbon layer and changing the direction with a pulley,
In the process of manufacturing the carbon coated optical fiber leading to the winding machine, the optical fiber preform in the optical fiber spinning furnace is continuously irradiated with an optical signal, and the optical fiber bent from the bent portion of the optical fiber is bent by the pulley. A carbon-coated optical fiber inspection method, wherein the thickness of the carbon layer coated on the optical fiber is continuously measured by measuring the amount of radiation. 2. After coating an optical fiber drawn from an optical fiber spinning furnace with a carbon layer and changing the direction with a pulley,
In the apparatus for manufacturing a carbon-coated optical fiber to be guided to a winder, a light source for continuously irradiating an optical signal to an optical fiber preform in the optical fiber spinning furnace, and a bent portion of the optical fiber bent by the pulley Light detecting means for detecting the amount of radiation emitted from the optical fiber, and continuously measuring the film thickness of the carbon layer coated on the optical fiber based on the detection result of the light detecting means. Fiber inspection equipment.