JPH11199265A - Inspection apparatus for preform for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate the straightness of a preform for an optical fiber in order to lessen the eccentricity defect of the optical fiber. SOLUTION: A laser beam released from a red semiconductor laser 22 of a light projector 21 of a laser outside diameter measuring instrument 20 is made into parallel beams by a light projecting lens 23 and these parallel beams are projected to the preform 10 for the optical fiber which is hung down in a perpendicular direction and is rotated from the side of the preform. This projected light 24 is made incident through an optical band-pass filter 27 on a CCD image sensor 28 built in a light receiver 26. The edge part position of an image (projected image) shaded by being shielded by the preform 10 for the optical fiber is detected. The fluctuation width when this edge part position fluctuates concurrently with the rotation of the preform 10 is determined and the straightness of the preform 10 for the optical fiber is evaluated by this fluctuation width.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting the straightness of an optical fiber preform suitable for use in an optical fiber manufacturing process or the like.

[0002]

2. Description of the Related Art In general, a silica glass optical fiber is produced by using a gas phase reaction process to generate glass particles of silicon dioxide in a flame of an oxyhydrogen burner and deposit the glass particles to form a porous soot preform. (Glass particle deposit) is produced, and the porous soot preform is subjected to a heat treatment to be transparently vitrified into a base material for an optical fiber, and the base material is drawn and spun in a spinning furnace. When spinning a longer optical fiber from a single optical fiber preform, when increasing the size of the preform, the soot preform made by the VAD method or the like is first made into a transparent glass, which is then used as the starting material. As a material, a glass fine particle deposition layer serving as a clad is formed around the material (external method), and thereafter, a vitrification is performed.

[0003] This secondary cladding step is carried out by mounting the starting base material on a lathe in which the centering adjustment is sufficiently performed, and depositing glass particles around the starting base material. At this time, a glass support rod is jointed to both ends of the starting base material, and the support rod portion is held by a chuck of a lathe.

[0004]

However, if the straightness of the optical fiber preform immediately before spinning the optical fiber or the starting preform before the secondary cladding is not sufficient, the fiber is spun from such a preform. The resulting optical fiber has a problem that the amount of eccentricity of the core (the amount of displacement of the core from the center of the clad) is large.

That is, if a secondary cladding is performed on a starting base material having insufficient straightness, the axis of the starting base material does not coincide with the axis of the cladding layer formed by the secondary cladding. However, there is a tendency that the eccentricity of the core of the optical fiber obtained by spinning this from a transparent vitrified base material becomes large. In addition, during the vitrification process after the secondary cladding process, the joint between the optical fiber base material and the support rod is bent if the heat history of the glass fine particle deposition layer in the electric furnace is not optimal. In some cases, when the base material in which the bend is generated in the transparent vitrification process is sent to the spinning furnace and spun, the eccentricity of the core of the optical fiber obtained therefrom increases.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to prevent an optical fiber having an eccentricity defect by removing a bent optical fiber preform before secondary cladding or spinning or by interrupting the manufacturing process. An object of the present invention is to provide an optical fiber preform inspection apparatus capable of reliably and easily inspecting the straightness of an optical fiber preform before secondary cladding or spinning, which is suitable for I do.

[0007]

In order to achieve the above object, an apparatus for inspecting an optical fiber preform according to the present invention is characterized in that the upper end of an optical fiber preform to be inspected is gripped vertically. Gripping means for supporting and rotating, light projecting means for projecting light from the side of the held optical fiber preform, and light arranged to face the light projecting means with the optical fiber preform interposed therebetween Light receiving means for obtaining a projected image of the fiber preform, and means for detecting a position variation width due to the rotation of the edge of the projected image of the optical fiber preform obtained from the light receiving means. Has become.

A moving means for moving the light projecting means and the light receiving means opposed thereto in the vertical direction with respect to the optical fiber base material supported in the vertical direction may be further provided.

When the optical fiber preform is bent, if the optical fiber preform is rotated, the position of the edge of the projected image of the optical fiber preform fluctuates in a sinusoidal manner. Then, the fluctuation range represents the amount of eccentricity from the rotation center axis, which is a bent amount at all, and corresponds to non-straightness. Therefore, it is possible to evaluate the straightness based on the position variation width of the edge portion of the projected image. Since the optical fiber preform is supported and rotated in the vertical direction, the straightness can be accurately evaluated without bending the preform. (If the optical fiber preform is horizontally supported and rotated, the central The part bends downward).

When the light projecting means and the light receiving means opposed thereto are moved in the vertical direction with respect to the optical fiber base material supported in the vertical direction, the position at each position in the length direction of the optical fiber base material is changed. The edge portion position fluctuation width of the projected image of the optical fiber preform can be detected, and the straightness at each position in the length direction of the optical fiber preform can be evaluated.

[0011]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, an optical fiber preform 10 is suspended in a direction (vertical direction) perpendicular to the plane of the paper, and the outer diameter is measured by a laser outer diameter measuring device 20. That is, the projection light 24 from the light projector 21 is projected from the side of the optical fiber preform 10, and the projection light 24 is made to enter the light receiver 26, and the image of the shadow of the optical fiber preform 10 (projection image) Is caught. The light projector 21 is provided with a red semiconductor laser 22, and the laser light emitted from the red semiconductor laser 22
Is converted into parallel light and projected toward the optical fiber preform 10. With the optical fiber base material 10 interposed, the light projector 2
A light receiver 26 is disposed so as to face the light receiving device 1, and the projected light 24 passes through an optical band-pass filter 27,
The light is incident on the D image sensor 28.

The CCD image sensor 28 has an array of detection cells so that at least a one-dimensional horizontal projected image of the optical fiber preform 10 can be obtained. The projection light 24 may have a planar shape corresponding to this and spread only in the horizontal direction. An image signal representing a horizontal one-dimensional projected image of the optical fiber preform 10 is output from the CCD image sensor 28. Since the projection light 24 is blocked by the optical fiber preform 10, a shadow corresponding to the outer shape of the preform 10 is generated, and an image signal representing the shadow portion (projected image of the preform 10) is output.

When the optical fiber preform 10 is rotated, the position of the edge portion of the projected image becomes sinusoidal as shown by a dotted line in FIG. 2 when the optical fiber preform 10 is bent. fluctuate. If the difference between the maximum value and the minimum value of the data of the edge portion position is determined for a certain period of time, the variation width W can be obtained. The fluctuation width W indicates the degree of bending, that is, the larger the fluctuation width W, the more the optical fiber preform 10 is bent. This means that the straightness of the preform 10 is smaller if the fluctuation width W is smaller. It means good.

FIG. 3 shows the overall configuration. The optical fiber preform 10 is vertically suspended with its upper end gripped by the chuck 12 of the rotation support device 11 and rotated as indicated by the arrow. The laser outer diameter measuring device 20 including the light emitter 21 and the light receiver 26 is provided with a moving device 30.
Is moved in the vertical direction. A nut portion 29 is attached to the laser outer diameter measuring device 20, and the nut portion 29 is engaged with a pole screw 32. When the pole screw 32 is rotated by the motor 31, the nut portion 29 moves in the axial direction of the pole screw 32, that is, in the vertical direction, whereby the laser outer diameter measuring device 20 moves in the vertical direction.

The vertical movement distance is determined by the pole screw 3
The rotation is detected by a rotation detector 33 that detects the rotation of the second rotation and a pulse counter 36 that counts the pulses. A disk 34 provided with a slit is attached to the lower end of the pole screw 32, and the slit is detected by a slit detector 35. The slit detector 35 can be constituted by, for example, an optical detector that utilizes the fact that the light beam is blocked by portions other than the slit of the rotating disk 34 and is not blocked by the slit. If the pulse counter 36 counts the detection signal for each slit output from the slit detector 35, the rotation of the pole screw 32 is known, and the vertical movement distance of the laser outer diameter measuring device 20 is known.

The image signal from the laser outer diameter measuring device 20 is sent to an edge display 42 and an outer diameter display 43 via a branch adapter 41, and the position of the edge portion of the projected image and the length of the projected image (shadow portion) Length) is displayed. The signal indicating the position of the edge portion and the signal indicating the length of the projected image are taken into the computer 45 via the network adapter 44. The computer 45 controls the rotation of the optical fiber preform 10 by controlling the rotation of the rotation support device 11, and controls the rotation of the motor 31 by giving a command to the sequencer 46 to control the rotation of the motor 31. 20 vertical positions, and
The position is confirmed by taking in the output of the pulse counter 36 through the sequencer 46.

Therefore, in this computer 45,
The variation width W of the edge portion position can be calculated for each position over the entire length of the optical fiber preform 10, and the preform 1
It is possible to evaluate straightness over the entire length of 0. Others
The outer diameter at each position along the entire length of the optical fiber preform 10 can also be measured.

The optical fiber preform 10 is rotated with the upper end thereof being held by the chuck 12 and suspended in the vertical direction, so that the optical fiber preform 10 does not bend due to the weight of the optical fiber preform 10 itself. Assuming that the optical fiber preform 10 is supported and rotated in the horizontal direction, the central portion is bent downward by its weight. In order to support and rotate the optical fiber preform 10 in the vertical direction in this manner, the preform 1
Accurate evaluation of straightness can be performed without sagging 0.

With this configuration, the optical fiber preform before the secondary cladding step is inspected so that the variation width W becomes 0.3 mm or less over the entire length, and the optical fiber preform before spinning varies. 4.0 over the entire length
mm or less, the eccentricity failure of the optical fiber after spinning could be reduced by about 40%. From these results, it can be seen that the use in the optical fiber manufacturing process is suitable for removing a bent optical fiber base material before secondary cladding or spinning.

The above shows only one embodiment of the present invention, and it is a matter of course that the present invention is not intended to be limited to these descriptions. For example, a configuration in which the optical fiber preform 10 is gripped at the upper end and rotated while being suspended, a configuration in which the laser outer diameter measuring device 20 is moved in the vertical direction, and a configuration in which the rotation and movement are controlled by the computer 45 are other. Configuration.

[0021]

As described above, according to the optical fiber preform inspection apparatus of the present invention, the straightness of the optical fiber preform before secondary cladding or spinning can be reliably and easily inspected. This is effective in removing bent portions and preventing the production of optical fibers with eccentricity.

[Brief description of the drawings]

FIG. 1 is a schematic view of a projector / light receiver portion according to an embodiment of the present invention.

FIG. 2 is a graph showing a change in an edge position of a projection image of an optical fiber preform.

FIG. 3 is an overall schematic diagram of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Base material for optical fiber to be measured 11 Rotation support device 12 Chuck 20 Laser outer diameter measuring device 21 Projector 22 Red semiconductor laser 23 Projection lens 24 Projection light 26 Receiver 27 Bandpass filter 28 CCD image sensor 29 Nut portion 30 Moving device Reference Signs List 31 motor 32 pole screw 33 rotation detector 34 disk 35 slit detector 36 pulse counter 41 branch adapter 42 edge display 43 outer diameter display 44 network adapter 45 computer 46 sequencer

Claims (2)

[Claims] 1. A gripping means for gripping an upper end of an optical fiber preform to be inspected and supporting and rotating the optical fiber preform in a vertical direction, and light for projecting light from a side of the gripped optical fiber preform. Projecting means, light receiving means arranged to face the light projecting means with the optical fiber preform interposed therebetween to obtain a projected image of the optical fiber preform, and projection of the optical fiber preform obtained from the light receiving means Means for detecting a position variation width of the edge portion of the image accompanying the rotation. 2. The apparatus according to claim 1, further comprising moving means for moving the light projecting means and the light receiving means opposed thereto in the vertical direction with respect to the optical fiber preform supported in the vertical direction. An inspection apparatus for an optical fiber preform according to the above.