JP2000155223A - Spinneret and method for inspecting optical fiber using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make light efficiently incident on the inside of optical fibers and to enable the execution of the measurement of transmission loss, etc., with high accuracy without degrading the productivity of optical fibers by forming the light exit ends of light exit parts which emit the light into optical fiber spinning holes and directly introduce the light into fiber materials on the flow passage wall surfaces of the optical fiber spinning holes. SOLUTION: The light exit part comprises a light guide 10 bundled with the many optical fibers and a light guide rod 11 connected and fixed to this light guide 10 and light transmission member 13. The light guide rod 11 is held in the upper part of the light guide member 13 through a light guide member retainer 12 of a cylindrical shape. The bottom end of the light guide member 13 is the light exit end 19. This light exit end 19 is formed on the wall surface of the fiber material flow passages 14. The light exit end 19 is formed on the same plane as the plane of the fiber material flow passage wall surface 18 perpendicular to the central axis 17 of the optical fiber spinning hole 16 in order to more efficiently make the light incident on the inside of the optical fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for in-line inspection of an optical fiber during continuous production of the optical fiber, and a spinneret suitable for the method.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring transmission loss in-line during continuous production of an optical fiber, as disclosed in Japanese Patent Application Laid-Open No. 61-6609, a production line after shaping is used. There is a method in which inspection light is incident on the optical fiber by irradiating light from the side while bending the optical fiber to a certain curvature or more.

However, in this method, a sheath portion of light incident on an optical fiber at a predetermined angle (light incident in the opposite direction through an optical path when light propagating in the optical fiber leaks due to bending) is used. Only the light component that reaches the core without being reflected and absorbed by the optical fiber, and the light component that is incident at an angle other than a predetermined angle and reaches the core, is changed to an angle that can be propagated by scattering inside the optical fiber. It could not be taken into the optical fiber and the incidence efficiency of the inspection light was very poor. As described above, when the amount of light propagating in the optical fiber decreases, the absolute amount of light lost by the propagation decreases, and the light leaked from the side of the optical fiber detected by the photodetectors arranged at a plurality of locations. When the transmission loss of the optical fiber is to be measured based on the difference in light amount, the difference in light amount between the photodetectors becomes small, and the measurement error of the transmission loss becomes large. Therefore, when the transmission loss of the optical fiber is measured by using the method of JP-A-61-6609, the inspection light is incident, and the light amount difference of the light detected by the photodetectors arranged at a plurality of locations is measured. In order to reduce the measurement error, it is necessary to increase the distance between the photodetectors and increase the attenuation of light propagating in the optical fiber to increase the difference in the amount of light detected by the photodetectors. there were. Also,
When an inspection of a multi-core optical fiber or the like is performed by this method, light cannot be uniformly incident on all the cores. Further, a guide or the like that bends the optical fiber with a small curvature in order to make the inspection light incident is required, and this guide may cause damage to the surface of the optical fiber in some cases.

[0004]

To solve these drawbacks, Japanese Patent Publication No. 8-12129 discloses an optical fiber extruding process in which a light source connected to a light source in a flow of resin for a core material. A method has been proposed in which a transmission element is directly inserted and light is directly incident on the core of an optical fiber.

However, in this method, since the optical transmission element is formed so as to protrude into the flow path of the resin for the core material, the optical transmission element is damaged or the resin for the core material stays and deteriorates around the optical transmission element. Therefore, it is difficult to use the extruder head for a long period of time, and the replacement of the extruder head causes a reduction in optical fiber productivity due to the cleaning operation. That is, an object of the present invention is to perform an optical characteristic inspection of an optical fiber in-line, without impairing the productivity of the optical fiber, and efficiently measure light, such as transmission of light, into the optical fiber with high accuracy. It is an object of the present invention to provide a spinneret and an optical fiber inspection method that can be performed.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a spinneret for an optical fiber which extrudes a plurality of materials having different refractive indices and performs composite spinning. A light emitting portion for directly introducing light therein is provided, and a light emitting end of the light emitting portion is provided in a spinneret formed on a channel wall surface of the optical fiber spinning hole.

Further, the gist of the present invention is to use the above-mentioned spinneret to spin out an optical fiber while directly introducing light from a light emitting portion into a core material of the optical fiber, and to prevent light leaking from a side surface of the optical fiber. An inspection method for an optical fiber detected by using a photodetector.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an optical fiber inspection method according to the present invention will be described. FIG. 2 shows a schematic diagram of one embodiment.

A plurality of materials having different refractive indices melted from an extruder 40 are measured by a gear pump 42, supplied to a spinneret 43 described later, and subjected to composite spinning. As the material, a transparent resin is preferably used, but a transparent inorganic material or the like can also be used as long as it is a material capable of composite spinning. Known polymers such as polymethyl methacrylate (PMMA) can be used as the transparent resin. In the case of composite spinning, the light source device 4
The light emitted from 1 is guided into the spinneret, directly introduced into the core material, and propagates through the optical fiber as inspection light. On the other hand, the spun optical fiber is introduced into a drawing furnace 46 and heated using hot air, steam, or the like. At this time, the rotation speed of the nip roll 45 after the stretching furnace is set to the nip roll 4 before the stretching furnace.
Since the rotation speed is higher than the rotation speed of No. 4, the optical fiber is drawn. The stretching ratio is not particularly limited, but is usually 1.
It is about 5 to 3.0 times. The heat-stretched optical fiber passes through the detection positions of two photodetectors 47 and 48 arranged at a predetermined distance (in this embodiment, 20 m), and light leaking from the side surface is detected. Taken. As described above, in the present invention, the inspection can be performed while the optical fiber is continuously manufactured. The optical fiber can be run linearly between the photodetectors, or can be run in a state of being bent by a guide having a large curvature that does not damage the fiber. The distance between the photodetectors when traveling in a bent state is the traveling distance of the optical fiber between the photodetectors.

Light leaking from the side of the optical fiber is detected by photodetectors 47 and 48. The photodetector is an integrating sphere that averages the intensity of leaked light emitted from the side of the optical fiber in various directions, a light guide that extracts and transmits leaked light from the integrating sphere, and receives light transmitted by the light guide. And an amplifier for amplifying the sensor output. In addition, at the fiber entrance and exit of the photodetector, a light-shielding portion that blocks light so that external light does not enter the integrating sphere is arranged. The photodetector is not limited to this, and a known photodetector can be used.

A transmission loss is calculated by a transmission loss calculating device 50 based on the amount of leaked light detected by the photodetectors 47 and 48. In the present embodiment, the difference in the light amount between the leaked light detected by the photodetector 47 and the leaked light detected by the photodetector 48 corresponds to a transmission loss of an optical fiber of 20 m.

The amount of light leaking from the side of the optical fiber is
Since the change also occurs due to a change in the diameter of the optical fiber or a flaw on the side surface (hereinafter, these are simply referred to as “defects”), a defect in the optical fiber can be inspected simultaneously by detecting a change in the amount of leaked light.

In this case, since the optical fiber passes through the photodetector in a short time, an optical sensor having a high response speed capable of detecting a short-time change in the amount of light due to a change in diameter or a flaw on a side surface is used. Is preferred.

Further, in the integrating sphere in the photodetector, since the leakage light from all side surfaces of the optical fiber is averaged, even if a defect exists in a part of the optical fiber passing through the integrating sphere. Since the detected light amount is an average value of the light amounts of the light leaked from both the normal part and the defect, the fluctuation is small. For this reason, in order to detect a small change in the amount of light caused by a defect with high sensitivity, the integrating sphere is so reduced that the difference between the total area of the outer periphery of the optical fiber inside the integrating sphere and the area of the portion where the defect exists is small. It is preferable to reduce the total area of the internal optical fibers. That is, it is preferable to use a photodetector provided with a small integrating sphere.

The dimensions of the integrating sphere for inspecting the optical fiber for defects are appropriately selected depending on the period of the diameter variation to be detected and the size of the flaw on the side surface. Is preferably 10 times or less the diameter of the optical fiber.

In this embodiment, two photodetectors are provided, and the transmission loss of the optical fiber is measured from the detected light amounts. However, the present invention is not limited to this.
For example, foreign matter and structural irregularities in the optical fiber can be detected by detecting the bright spot of the optical fiber using one photodetector.

Further, by providing the light source device with a sensor for detecting the intensity of the emitted light and a dimming device for maintaining the intensity of the emitted light at a set value according to the output of the sensor, the light detector due to deterioration of the light source lamp or the like can be provided. It is also possible to prevent a decrease in the amount of leaked light detected by the above.

Hereinafter, each part will be described in more detail. FIG. 1 shows an example of the spinneret of the present invention. In FIG. 1, the spinneret has a symmetrical structure, and an optical fiber 20 having two core-sheath structures is spun. The melted core material flows through the core material channel 14, and the melted sheath material supplied from the sheath material channel 15 is coated on the outer periphery of the core material and discharged as an optical fiber.

The light emitting portion is composed of a light guide 10 in which a number of optical fibers are bundled, a light guide rod 11 connected to and fixed to the light guide, and a light guide member 13. The light guide member 13 is held above the light guide member 13 through the light guide member holder 12 having a cylindrical shape. In the figure, the lower end of the light guide member 13 is a light emitting end 19 of a light emitting portion, and the light emitting end 19 is
Is formed on the wall surface. The light emitting end 19 is provided on the core material channel wall surface 1 perpendicular to the central axis 17 of the optical fiber spouting hole 16 in order to make the light enter the optical fiber more efficiently.
8 is preferably formed on the same plane.

A male screw-shaped groove is provided on the outer periphery of the light guide member holder 12, and the light guide member holder 1 of the spinneret is provided.
Since a female screw-shaped groove corresponding to this male screw is provided in a portion in contact with the outer peripheral portion of 2, the light guide holder 12 is moved up and down by rotating the light guide holder 12.

The lower half of the light guide member 13 is tapered. The light guide member 13 is inserted into the light guide member insertion hole of the spinneret conforming to this shape, and has a heat-resistant elastic cylindrical Teflon resin or an upper portion. Spacer 21 made of metal spring
Is pressed against the spinneret by the light guide member. Therefore, even when a difference in expansion occurs due to a difference in thermal expansion coefficient between the spinneret and the light guide member 13, the light guide member 13 slides in the light guide member insertion hole due to the elasticity of the spacer 21. 13 can be prevented from being damaged by compression, and leakage of resin and formation of a stagnant portion due to generation of a gap between the spinneret and the light guide member 13 can be prevented. The light emitting portion is not limited to this, and may have another configuration.

It is preferable that the light guide rod 11 has a structure that can be easily separated from the light guide member 13 so that the spinneret can be easily attached to and detached from the spinning device.

The light guide member 13 is preferably made of a material that can withstand the shaping temperature of the optical fiber and transmit light, and examples thereof include multi-component glass, quartz glass, sapphire, and diamond. The light guide 10 also preferably has high heat resistance. For example, a glass optical fiber bundle or a glass rod can be used. The light guide rod 11 is also preferably one having high heat resistance, for example, a large-diameter optical fiber made of glass or one whose outer periphery is protected by a metal tube can be used.

One end of the light guide 10 is connected to a light source device (not shown), and the other end is connected to the light guide member 13, so that light from the light source device is transmitted to the light guide 10, the light guide rod 11, and the light guide. It is introduced into the core through the member 13. By connecting a plurality of light guides 10 to one inspection light source, it is possible to supply inspection light to a plurality of spinnerets or a plurality of light emitting portions in one spinneret.

The tip of the light guide 10 and the light guide member 1
3 is arranged so that its central axis coincides with the central axis of the optical fiber spun hole, so that light is incident substantially toward the central axis of the optical fiber, and light is efficiently introduced into the optical fiber. You. Therefore, it is possible to easily increase the light amount of the inspection light, and particularly to shorten the distance between the photodetectors when measuring the transmission loss using a plurality of photodetectors arranged at a predetermined distance. Is possible, and the amplification factor of the output of the photodetector can be reduced, so that the amplification error can be reduced.

Although only the spinneret for an optical fiber having a core-sheath structure has been described here, the present invention can be applied to a spinneret for an optical fiber having another structure. For example, using a spinneret for concentrically laminating three or more types of materials having different refractive indices, and using a spinneret, an optical fiber whose refractive index changes continuously from the center to the outer periphery, or light that changes stepwise is used. The case where a fiber is manufactured is mentioned. When an optical fiber is manufactured using three or more types of materials, it is preferable to provide a light emitting end on the channel wall surface of the material constituting the central layer. Further, when manufacturing a sea-island type optical fiber in which a large number of islands are integrated in a state of being separated from each other by the sea, when the island is a single layer, it is formed on the channel wall surface of the material constituting the island. When the island portion has a multilayer structure, it is preferable to provide a light emitting end on the channel wall surface of the material constituting the central layer.

In order to reduce the attenuation of the inspection light due to the light scattering loss in the molten core material and the absorption loss at the core material channel wall surface, the distance from the light emitting end to the sheath is shortened as much as possible. It is desirable to make it. It is also possible to apply a coating or the like to the wall surface of the core material flow path and reflect, diffuse, and propagate the inspection light introduced into the core material with the coating material.

The light source device is not particularly limited as long as the light from the lamp can enter the light emitting portion. Known lamps can be used for the light source device, and for example, LEDs and the like can be used, but high-intensity lamps, such as high-pressure, ultra-high-pressure mercury lamps, tungsten lamps, and xenon lamps, are placed in the optical fiber. It is desirable to increase the amount of light that can be incident. For example, when inspecting an optical fiber having a diameter of 0.75 mm, the optical fiber is cut at the detection position of the photodetector located at the farthest end, and the inspection light whose amount of light emitted from the end face is about 1 mw is transmitted through the optical fiber. , The ambient light or the like of the production line is incident on the optical fiber and disturbed light propagates to a negligible level. Therefore, there is no need to shield the disturbance light during the inspection and to provide a special mechanism for distinguishing the disturbance light from the inspection light, and there is no need to use a high-sensitivity, high-precision photodetector, which is simple and inexpensive. Since a simple photodetector can be used, the inspection cost can be reduced.

As the light source device, for example, the one shown in FIG. 3A can be used. In the light source device 60, the light emitted from the light source lamp 61 is reflected directly or by the reflecting mirror 62, collected by the lens 63, converted into substantially parallel light by the lens 67, and introduced into the light guide 10. A motor 65 is provided between the lens 63 and the lens 67.
A disk 64 that is rotatable is installed. Lens 6
The light passing through 3 collects on the outer periphery of the disk 64. FIG. 3B is an enlarged view of the disk 64. In order to use the disk 64 as a shutter for transmitting and blocking the light from the light source lamp 61, openings 68 are provided at regular intervals in the circumferential direction at positions on the outer periphery of the disk where the light passing through the lens 63 is collected. When the wavelength of the light emitted from the light source device 60 is switched, the light source device shown in FIG.
FIG. 4 is an enlarged view of a disk 64 of the light source device 60 and FIG.
As shown in (b), the opening 68 provided in the disk 64
, A plurality of specific wavelength light transmission filters 69 of different types are attached.

That is, the light from the lens 63 passes through the opening 68 arranged on the disk, reaches the lens 67, and is emitted from the light source device 60.
The motor 65 determines whether or not the opening 68 is disposed on the optical path from the lens 3 to the lens 67 and which of the two or more types of specific wavelength light transmitting filters 69 attached to the opening 68 is disposed on the optical path. Can be selected by rotating the disk 64 with. That is, the light source device 60
In the above, light can be emitted from the light source device 60 by arranging the opening 68 on the optical path by rotating the motor 65, and if the specific wavelength light transmission filter 69 is attached to the opening 68, Since the specific wavelength light transmission filter 69 is disposed in front of the light source lamp 61, the color of light emitted from the light source device 60 can be changed to the color of light having the wavelength transmitted by the filter 69. Also, the signal detector 66 can detect whether an opening is disposed on the optical path from the lens 63 provided on the disk 64 to the lens 67 and which of the specific wavelength light transmission filters 69 is disposed. Preferably, a mark is provided on the disk. In the present embodiment, since the transmission type optical sensor is used as the signal detector, the detection hole 70 is provided at the detection position of the optical sensor on the disk. Detection hole 7
Since the number and position of 0 are changed depending on the type of the filter 69, the signal detector can output a signal depending on the number and position of the detection holes 70. A known color filter or the like can be used as the specific wavelength light transmission filter.

In the method of the present invention, the inspection light is reduced at regular intervals using the light source device of FIG. 3, and the leakage light detected by the photodetector when the inspection light is incident on the optical fiber from the light source device. By subtracting the amount of leakage light detected by the photodetector when the inspection light is not incident on the optical fiber, that is, the amount of leakage light generated only by disturbance light such as illumination from the light source device, Since the amount of leakage light generated by the incident inspection light can be known, the inspection accuracy is further improved.

Further, in the case of an optical fiber that uses all wavelengths in the visible light range, such as for a lighting application, even if only the transmission loss of a certain wavelength changes, the color of emitted light changes. When performing the inspection, it is preferable to perform the inspection using light of a plurality of wavelengths. In the light source device 60 of FIG. 4, two or more types of specific wavelength light transmission filters 69 are attached to the opening 68 of the rotatable disk 64, so that the disk 64 is rotated to set the wavelength of the inspection light at predetermined intervals. Can switch. Then, the wavelength of light emitted from the light source device is determined based on the signal output from the signal detector of the light source device, and the amount of light for each wavelength is detected, thereby reducing the transmission loss for each wavelength. Can be calculated. As the light source device used in such an inspection method, the light source device shown in FIG. 4 is preferable, but it is also possible to use a lamp that uses two or more types of lamps having different wavelengths and switches a lamp for introducing light into the light guide. is there.

The light source device shown in FIG. 3 in which an opening 68 is provided in the disk 64 has only a shutter mechanism, and a specific wavelength light transmitting filter 69 is provided in the opening 68 of the disk.
The light source device shown in FIG. 4 in which are sequentially attached includes both a switching mechanism of the specific wavelength light transmission filter 69 and a shutter mechanism. Depending on the purpose of inspection, a light source device having only a switching mechanism can be configured.

[0034]

The present invention will be described below with reference to examples. (Example 1) PMMA as a core material and vinylidene fluoride / tetrafluoroethylene as a sheath material were 80/20 (mo).
1%) of the copolymer was melted by an extruder and metered by a gear pump and fed to a spinneret as shown in FIG. The light guide 10 is a bundle fiber obtained by converging a plurality of quartz optical fibers, the light guide rod is a glass optical fiber having a large diameter and a metal tube arranged around the outer periphery thereof, and the light guide member 13 is quartz. The light guide rod made from was used. A 500 W halogen lamp was used as a lamp of the light source device. An optical fiber having a diameter of 1.06 mm spun from a spinneret was made to have a diameter of 0.75 mm by a hot drawing treatment, and was then placed in a nip roll downstream of the drawing furnace by 2 mm.
The optical fiber was cut at a point separated by 0 m, and the amount of light emitted from the end face was measured.
μw.

Using this spinneret, the transmission loss of the optical fiber was measured as shown in FIG. By increasing the amount of the inspection light to be introduced to such a degree that the influence of the external light can be ignored, it was possible to accurately detect the transmission loss of the optical fiber even when the optical fiber was exposed to the external light. Further, this spinneret was usable for a long period of time.

(Embodiment 2) A light source device shown in FIG. 3 having a shutter mechanism capable of blocking light emitted from a lamp and a mechanism indicating the open / closed state of the shutter is used.
Calculates the difference between the amount of light leaked from the optical fiber when the shutter is open and the amount of light leaked from the optical fiber when the shutter is closed, according to an output signal indicating the open / closed state of the shutter from the light source device. The transmission loss of the optical fiber was measured in the same manner as in Example 1 except that a light source device was used and a halogen lamp of 250 W was used as the light source lamp of the light source device. Even when the amount of light incident on the optical fiber was small and the optical fiber was exposed to external light, the transmission loss of the optical fiber could be accurately detected as in the first embodiment.

(Embodiment 3) As light source devices, 6
A shutter mechanism and a switching mechanism capable of blocking outgoing light and switching the wavelength of outgoing light to 650 nm and 570 nm using two types of specific wavelength light transmitting filters transmitting 50 nm and 570 nm light; The apparatus shown in FIG. 4 having a mechanism for indicating the open / close state and the wavelength of the emitted light is used. Accordingly, the transmission loss of the optical fiber at two wavelengths was measured in the same manner as in Example 2 except that a device having a mechanism for calculating the difference in the amount of light leaked from the fiber when the shutter was opened and closed according to the wavelength was used. . Even when the optical fiber was exposed to external light, it was possible to accurately detect the transmission loss of the optical fiber at two wavelengths.

(Comparative Example 1) An optical fiber having a diameter of 1.06 mm spun from a spinneret and having a diameter of 0.75 mm was subjected to a hot drawing process without introducing inspection light from the spinneret.
Downstream of the nip roll after the drawing furnace, the optical fiber is held in a state of being bent at a curvature of 30 mm, light is irradiated from the side of the optical fiber with a 500 W ultra-high pressure mercury lamp, and the optical fiber is cut at a distance of 20 m from the irradiated part. When the amount of light emitted from the end face was measured, the measured value was about 1 μw.
Met. Further, the transmission loss of the optical fiber was measured in the same manner as in Example 1 except that the inspection light was incident by the method described above. However, the amount of light leaked from the fiber is small,
When the optical fiber was exposed to external light, the measurement accuracy of the transmission loss of the optical fiber was poor due to the effect of the external light.

[0039]

According to the spinneret of the present invention, light can be efficiently incident on an optical fiber and can be used for a long period of time. Further, the inspection method of the present invention can perform an optical fiber inspection in-line without lowering the productivity of the optical fiber.

[Brief description of the drawings]

FIG. 1 is a view showing an example of a spinneret of the present invention.

FIG. 2 is a diagram showing one embodiment of the inspection method of the present invention.

FIG. 3 is a diagram illustrating an example of a light source device having a shutter mechanism.

FIG. 4 is a diagram illustrating an example of a light source device having a shutter and a filter wavelength switching mechanism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light guide 11 Light guide rod 12 Light guide member holding 13 Light guide member 14 Core material channel 15 Sheath material channel 16 Spinning hole 17 Spindle hole central axis 18 Core material channel wall surface 19 Light emitting end 20 Optical fiber 40 Extruder 41 Light source device 42 Gear pump 43 Spinneret 44 Nip roll 45 Nip roll 46 Drawing furnace 47 Photodetector 48 Photodetector 49 Winding device 50 Transmission loss calculation device 60 Inspection light source device 61 Lamp 62 Reflecting mirror 63 Lens 64 Disk 65 Motor 66 signal detector 67 lens 68 opening 69 specific wavelength light transmission filter 70 detection hole

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Yasuteru Tahara 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory F-term (reference) 2G086 CC05 KK01 KK06 2H038 AA01 AA52 AA61 BA23 2H050 AA13 AB43Z 4L045 AA05 BA03 BA52 BA60 CA20 CB16 CB40

Claims (8)

[Claims] 1. A spinneret for an optical fiber for extruding a plurality of materials having different refractive indices and performing composite spinning, wherein the light emitting portion emits light to an optical fiber spinning hole and directly introduces light into a core material. And a light emitting end of the light emitting portion is formed on a flow path wall surface of the optical fiber spinning hole. 2. A light emitting portion of the spinneret according to claim 1, wherein a light source lamp, a shutter mechanism having an openable / closable shutter for blocking light from the light source lamp, and an open / closed state of the shutter are shown. A spinneret with a light source device connected to a light source device having a mechanism. 3. A spinneret with a light source device, wherein a light source device in which a light source lamp and a specific wavelength light transmission filter are sequentially arranged is connected to the light emitting portion of the spinneret according to claim 1. 4. A light source device having two or more types of specific wavelength light transmission filters, a switching mechanism for selecting one type of specific wavelength light transmission filter and arranging the same in front of the light source lamp, and a switching mechanism arranged in front of the light source lamp. The spinneret with a light source device according to claim 3, wherein the light source device includes a mechanism indicating the type of the specific wavelength light transmission filter. 5. An optical fiber is spun out by using the spinneret according to claim 1, while light is directly introduced into the core material of the optical fiber from the light emitting portion, and light leaks from a side surface of the optical fiber. Inspection method for detecting an optical fiber using a photodetector. 6. After the spun optical fiber is subjected to a heat drawing process, the amount of light leaking from a side surface of the optical fiber by passing the optical fiber to a detection position of a plurality of light detectors is detected.
6. The optical fiber inspection method according to claim 5, wherein a transmission loss is calculated from a difference between a detected light amount from each photodetector and a detection position of the photodetector. 7. A light amount when the spin detector according to claim 2 is used as a spinneret, and a signal indicating that the shutter is open is output from a mechanism indicating an open / close state of the shutter to the photodetector. 6. The light according to claim 5, wherein a light amount when a signal indicating that the shutter is closed is output is detected, and a transmission loss is calculated based on the difference in light amount. Fiber inspection method. 8. The spinneret according to claim 4 as a spinneret, and the photodetector outputs a signal indicating the type of the specific wavelength light transmission filter from a mechanism indicating the type of the specific wavelength light transmission filter disposed. 7. The optical fiber inspection method according to claim 6, wherein the amount of leaked light is separately detected in response to the detection, and the transmission loss is obtained for each light having a wavelength transmitted by each specific wavelength light transmission filter.