Patent Description:
The present disclosure relates to a method for manufacturing an optical fiber.

As one of the factors that deteriorate the variation of the glass outer diameter of the optical fiber, the vibration of the drawing tower is known. <CIT> discloses a method for suppressing the variation of the outer diameter of the optical fiber glass due to the vibration of the drawing tower by providing a vibration suppressing mechanism having a time constant of <NUM> seconds or less between the drawing tower and the optical fiber preform.

The present disclosure provides a method for manufacturing an optical fiber. The method includes the features of claim <NUM>.

The foregoing and other purposes, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:.

One of the important characteristics of an optical fiber is polarization mode dispersion (PMD). <CIT> discloses a method for suppressing PMD by periodically swinging a guide roller and twisting an optical fiber. However, in the method disclosed in <CIT>, the outer diameter of the glass is varied by changing the traveling position and distance of the optical fiber. In addition, a variation in the outer diameter of the glass may specifically deteriorate under certain conditions. In such a case, in order to suppress the variation of the outer diameter of the glass, a method for remarkably reducing the drawing speed or reducing the twisting as much as possible is adopted. However, productivity and yield are severely compromised. According to the method described in <CIT>, the variation of the glass outer diameter is improved to some extent, but it is not enough. <CIT> discloses a method of accurately measuring the diameter of an optical fiber with reduced polarization mode dispersion.

An object of the present disclosure is to provide a method for manufacturing an optical fiber capable of further suppressing a variation in the outer diameter of glass without deteriorating productivity and yield.

According to the present disclosure, it is possible to provide a method for manufacturing an optical fiber capable of further suppressing a variation in the outer diameter of glass without deteriorating productivity and yield.

[Description of Embodiments of the Present Disclosure] Embodiments of the present disclosure will be described. A method for manufacturing an optical fiber according to an embodiment of the present disclosure includes: heating an optical fiber preform to draw glass fiber; measuring an outer diameter of the glass fiber to obtain a function of time; transforming the function of time into a function of frequency; identifying a first peak caused by a first drawing condition and a second peak caused by a second drawing condition in the function of frequency; and adjusting the second drawing condition so as to satisfy fn < fm - wm / <NUM> or fn > fm + wm / <NUM>, where fm is a frequency of the first peak, wm is a full width at half maximum of the first peak, and fn is a frequency of the second peak.

In this method for manufacturing an optical fiber, the second drawing condition is adjusted so that the first peak caused by the first drawing condition and the second peak caused by the second drawing condition do not overlap each other. As a result, the occurrence of a large amplitude due to the overlap of the first peak and the second peak is suppressed. Therefore, it is possible to further suppress the deterioration of the variation of the glass outer diameter without deteriorating the productivity and the yield.

A sampling time interval of the outer diameter may be <NUM> or less. In this case, it is possible to surely detect the short-period variation of the glass outer diameter.

The method for manufacturing an optical fiber further includes forming a coating layer on the glass fiber to form an optical fiber; and twisting the optical fiber using a swing guide roller. In this case, since it is necessary to swing the swing guide roller in order to twist the optical fiber, the swing frequency of the swing guide roller is the second drawing condition, and a second peak is generated by the swing frequency. Therefore, it is more effective to prevent the first peak and the second peak from overlapping each other.

The second drawing condition is a swing frequency of the swing guide roller. In this case, by adjusting the swing frequency of the swing guide roller, it is possible to further suppress the deterioration of the variation of the glass outer diameter without deteriorating the productivity and the yield.

A specific example of the method for manufacturing an optical fiber according to the present disclosure will be described below with reference to the drawings. The present invention is not limited by such examples but shown by the claims.

In the following description, the same elements in a description of the drawings are denoted by the same reference signs and an overlapping description will be omitted.

<FIG> is a configuration diagram of a manufacturing device used in the method for manufacturing an optical fiber according to the embodiment. The manufacturing device <NUM> (drawing device) shown in <FIG> is a device for manufacturing the optical fiber <NUM> from the optical fiber preform <NUM> via the glass fiber <NUM>. A manufacturing device <NUM> is provided with a gripper <NUM>, a heating furnace <NUM>, a thermal insulation furnace <NUM>, a measuring instrument <NUM>, a cooler <NUM>, a die <NUM>, an ultraviolet irradiation device <NUM>, a swing guide roller <NUM>, a capstan <NUM>, a winder <NUM>, and a controller <NUM>.

The gripper <NUM> grips the optical fiber preform <NUM> and feeds it into the heating furnace <NUM> at a constant speed. The optical fiber preform <NUM> includes a base end portion 101a gripped by the gripper <NUM> and a tip portion 101b inserted into the heating furnace <NUM>. The gripper <NUM> functions as a supplier for supplying the optical fiber preform <NUM> to the heating furnace <NUM>.

The heating furnace <NUM> includes openings 103a and 103b. The optical fiber preform <NUM> is inserted into the opening 103a. The opening 103b faces the opening 103a. The glass fiber <NUM> is drawn out from the opening 103b. The heating furnace <NUM> heats and softens the tip portion 101b of the optical fiber preform <NUM> supplied into the heating furnace <NUM>. The glass fiber <NUM> is drawn out from the tip portion 101b softened by heating. The glass fiber <NUM> is drawn out of the heating furnace <NUM> through the opening 103b.

The thermal insulation furnace <NUM> keeps the glass fiber <NUM> warm and relaxes the structure of the glass. The measuring instrument <NUM> measures the outer diameter (glass outer diameter) of the glass fiber <NUM> in a state where the glass structure is relaxed. The measuring instrument <NUM> measures the outer diameter of the glass by irradiating the glass fiber <NUM> with a laser. The sampling time interval of the outer diameter of the glass by the measuring instrument <NUM> is, for example, <NUM> or less. Depending on the drawing speed, there is a possibility that the variation of the short period of the glass outer diameter cannot be detected when the sampling interval becomes long. The measuring instrument <NUM> transmits the measured outer diameter of the glass to the controller <NUM>.

A cooler <NUM> is located after the measuring instrument <NUM> to cool the glass fiber <NUM>. The die <NUM> applies resin to the outer peripheral surface of the glass fiber <NUM> to form a coating resin. The resin includes an acrylate-based ultraviolet curable resin. The ultraviolet irradiation device <NUM> irradiates the coating resin formed on the glass fiber <NUM> with ultraviolet rays to cure the coating resin. As a result, the glass fiber is coated with the resin to form the optical fiber <NUM>.

The swing guide roller <NUM> periodically tilts its axial direction to twist the optical fiber <NUM>. The swing guide roller <NUM> is electrically connected to the controller <NUM>, and is controlled and oscillated by the controller <NUM> to impart a twist to the optical fiber <NUM>. Although a pair of fixed guide rollers may be disposed in front of and behind the swing guide roller <NUM>, it is not possible to completely prevent the swing of the swing guide roller <NUM> from being transmitted to other portions.

<FIG> is a diagram of the swing guide roller as viewed from the upstream side of the pass line (the ultraviolet irradiation device side). As shown in <FIG>, the swing guide roller <NUM> swings within the range of ± θ in the angle formed by the rotation axis M1 and the predetermined axis M2. As a result of the swing motion as the swing, when the rotational axis M1 of the swing guide roller <NUM> is inclined by an angle + Θ with respect to the predetermined axis M2, a lateral force is applied to the optical fiber <NUM>, and the optical fiber <NUM> rolls on the surface of the swing guide roller <NUM> to twist the optical fiber <NUM>. When the swing guide roller <NUM> is inclined by an angle - θ with respect to a predetermined axis M2, the optical fiber <NUM> is twisted in the opposite direction.

That is, the optical fiber <NUM> is alternately twisted clockwise and counterclockwise with respect to the traveling direction (drawing direction) by repeating a symmetrical reciprocating motion in which the swing guide roller <NUM> swings at an angle ± θ with respect to a predetermined axis M2. The swing guide roller <NUM> guides the optical fiber <NUM> to the capstan <NUM> while twisting the optical fiber <NUM>.

The capstan <NUM> pulls the optical fiber <NUM> at a predetermined speed and tension. The winder <NUM> winds the optical fiber <NUM> drawn by the capstan <NUM>. The controller <NUM> receives the glass outer diameter measured by the measuring instrument <NUM> from the measuring instrument <NUM>, and feedback-controls the swing of the swing guide roller <NUM> based on the glass outer diameter. The controller <NUM> may control the entire manufacturing device <NUM>.

The controller <NUM> may be configured as a computer system including, for example, a processor such as a CPU (Central Processing Unit), memories such as a RAM (Random Access Memory) and a ROM (Read Only Memory), input / output devices such as a touch panel, a mouse, a keyboard and a display, and a communication device such as a network card. The controller <NUM> realizes the functions of the controller <NUM> by operating each hardware under the control of the processor based on the computer program stored in the memory.

<FIG> is a flowchart showing a method for manufacturing an optical fiber according to the embodiment. The method for manufacturing the optical fiber <NUM> includes: step S1 of inserting the optical fiber preform <NUM> into the heating furnace (wire drawing furnace) <NUM>; step S2 of heating the tip portion 101b of the optical fiber preform <NUM>; step S3 of drawing the glass fiber <NUM> from the tip portion 101b; step S4 of keeping the glass fiber <NUM> warm; step S5 of measuring the outer diameter of the glass fiber <NUM>; step S6 of cooling the glass fiber <NUM>; step S7 of forming a coating layer on the glass fiber <NUM> to form the optical fiber <NUM>; step S8 of twisting the optical fiber <NUM>; and step S9 of winding the optical fiber <NUM>. The steps after step S4 are shown in the order when focusing on a certain point in the length direction of the optical fiber <NUM>.

In step S1, the optical fiber preform <NUM> is inserted into the heating furnace <NUM> at a constant speed by the gripper <NUM>. In the optical fiber preform <NUM>, the tip portion 101b is fed into the heating furnace <NUM> through the opening 103a of the heating furnace <NUM> with the base end portion 101a gripped. In step S2, the tip portion 101b is heated by the heating furnace <NUM> to be softened.

In step S3, the glass fiber <NUM> is drawn out through the opening 103b from the tip portion 101b softened by heating. The insertion speed of the optical fiber preform <NUM> in step S1 can be set according to the drawing speed of the glass fiber <NUM> in step S3.

In step S4, the drawn out glass fiber <NUM> is kept warm by the thermal insulation furnace <NUM>. This relaxes the structure of the glass. In step S5, the outer diameter of the glass fiber <NUM> is measured by the measuring instrument <NUM>. In step S6, the glass fiber <NUM> is cooled.

In step S7, first, the outer peripheral surface of the glass fiber <NUM> is coated with resin by the die <NUM> to form a coating resin. Subsequently, the coating resin is cured by ultraviolet rays irradiated from the ultraviolet irradiation device <NUM> to form a coating layer surrounding the glass fiber <NUM>. As a result, a coating layer on the outer peripheral surface of the glass fiber <NUM> is formed. Accordingly, the optical fiber <NUM> is obtained. A plurality of coating layers may be formed by repeating step S7.

In step S8, the optical fiber <NUM> is twisted by the periodic swing of the swing guide roller <NUM>. In step S9, the optical fiber <NUM> is drawn at a predetermined speed and tension by the capstan <NUM> and then wound by the winder <NUM>.

<FIG> is a flowchart showing a step of controlling a swing of the swing guide roller. The method for manufacturing the optical fiber <NUM> further includes step S10 as shown in <FIG>. Step S10 is a step of controlling the swing of the swing guide roller <NUM> based on the outer diameter of the glass measured in step S5. Step S10 is performed by the controller <NUM>. First, the controller <NUM> performs step S11 for obtaining the glass outer diameter. Specifically, the controller <NUM> receives the glass outer diameter measured in step S5 from the measuring instrument <NUM>.

Subsequently, the controller <NUM> performs step S12 of storing the obtained outer diameter of the glass as a function of time. For example, the controller <NUM> stores the outer diameter and the time in the memory in association with each other. Subsequently, the controller <NUM> performs step S13 for transforming the stored function into a function of frequency. This transform is performed by a Fourier transform.

Subsequently, the controller <NUM> performs step S14 of identifying the first peak P1 caused by the first drawing condition and the second peak P2 caused by the second drawing condition in the transformed function of frequency. The first drawing condition is, for example, the frequency caused by a vibration of the manufacturing device <NUM>, the building, or the optical fiber preform <NUM>. In the present invention the first drawing condition is the characteristic vibration frequency of the manufacturing device <NUM>. The second drawing condition is a frequency caused by a disturbance, that is a swing frequency of the swing guide roller <NUM>.

The first peak P1 has a relatively large bandwidth. The second peak P2 has a narrower bandwidth than the first peak P1.

Since the second peak P2 is a peak corresponding to the swing frequency or the half multiple swing frequency of the swing guide roller <NUM>, the controller <NUM> can identify the second peak P2 based on the swing frequency of the swing guide roller <NUM>. When the second peak P2 is identified, the controller <NUM> can identify the first peak P1 by comparing the bandwidth of the second peak P2 with a bandwidth of a peak to be identified. The full width at half maximum may be used for the comparison instead of the bandwidth.

Next, the controller <NUM> performs step S15 of adjusting the second drawing condition so as to satisfy fn < fm - wm / <NUM> or fn > fm + wm / <NUM>, where fm is the frequency of the first peak P1, wm is the full width at half maximum of the first peak P1, and fn is the frequency of the second peak P2. Since the second peak P2 corresponds to the swing frequency or the half multiple swing frequency of the swing guide roller <NUM>, there is a plurality of second peaks P2. Therefore, the second drawing condition is adjusted so as to satisfy the above relation for the frequency fn of each of the plurality of the second peaks P2.

In this embodiment, the controller <NUM> adjusts the swing frequency of the swing guide roller <NUM> as the second drawing condition. Thus, the second peak P2 can be shifted from the first peak P1 so that the second peak P2 does not overlap the first peak P1. As a result, it is suppressed that the first peak P1 and the second peak P2 are overlapped each other, and that the amplitude of the glass outer diameter variation increases. The second peak P2 overlapping the first peak P1 means that the frequency fn of the second peak P2 is within a frequency range centered on the frequency fm of the first peak P1 and having the same width as the full width at half maximum wm.

As described above, the controller <NUM> performs step S10 to control the swing of the swing guide roller <NUM>. The characteristic vibration frequency of the manufacturing device <NUM> also varies with the remaining length of the optical fiber preform <NUM>. Therefore, even if the second peak P2 is once shifted from the first peak P1 by step S10, the first peak P1 may change to overlap the second peak P2 again. Therefore, it is effective to monitor the outer diameter of the glass at all times during the manufacturing the optical fiber <NUM>, to repeatedly perform step S10, and to perform the feedback control of the second drawing condition. Step S10 may be performed, for example, every time step S5 is performed a predetermined number of times, or may be performed every predetermined time.

<FIG> is a graph showing a temporal change in a glass outer diameter variation when the glass outer diameter variation deteriorated. In <FIG>, the horizontal axis represents time, and the vertical axis represents the glass outer diameter variation (µm). The glass outer diameter variation is the difference from the target glass outer diameter. In a general optical fiber, the target glass outer diameter is set to <NUM>. In the graph of <FIG>, 3σ of the glass outer diameter variation was <NUM>.

<FIG> is a graph showing a frequency spectrum of a glass outer diameter variation when the glass outer diameter variation deteriorated. <FIG> shows the result of Fourier transform of the time variation of the glass outer diameter variation shown in <FIG>. In <FIG>, the horizontal axis represents frequency and the vertical axis represents intensity. In the frequency spectrum shown in <FIG>, there are a first peak P1 having a relatively wide bandwidth and a second peak P2 having a relatively narrow bandwidth. As described above, the first peak P1 is caused by the characteristic vibration frequency of the manufacturing device <NUM>. The second peak P2 corresponds to the frequency of the swing guide roller <NUM>, which imparts a twist, or a half multiple thereof. Here, the first peak P1 overlaps one of the second peak P2. When the first peak P1 and the second peak P2 overlap with each other in this way, the amplitude of the glass outer diameter variation increases.

Feedback control was performed by the controller <NUM>. <FIG> is a graph showing a frequency spectrum of a glass outer diameter variation when feedback control was performed by the controller. In <FIG>, the horizontal axis represents frequency and the vertical axis represents intensity. Specifically, the frequency of the second peak P2 was adjusted so that the frequency of the second peak P2 was shifted from the frequency of the first peak P1. When the swing frequency of the swing guide roller <NUM> becomes low, the frequency interval between the adjacent second peaks P2 becomes narrow, and then the second peak P2 easily overlaps the first peak P1. Therefore, in this embodiment, the swing frequency of the swing guide roller <NUM> was adjusted so as to increase.

<FIG> is a graph showing a temporal change in a glass outer diameter variation when feedback control was performed by the controller. In <FIG>, the horizontal axis represents time, and the vertical axis represents the glass outer diameter variation (µm). In the graph of <FIG>, 3σ of the glass outer diameter variation was improved to <NUM>. The drawing speed was not changed. Therefore, the productivity is maintained and the variation in the outer diameter of the glass is improved.

As described above, in the manufacturing method according to the embodiment, in step S10, the second drawing condition is adjusted so that the first peak P1 caused by the first drawing condition and the second peak P2 caused by the second drawing condition do not overlap each other. As a result, the occurrence of a large amplitude due to the overlap of the first peak P1 and the second peak P2 is suppressed. Therefore, it is possible to further suppress the deterioration of the variation of the glass outer diameter without deteriorating the productivity and the yield.

The sampling time interval of the glass outer diameter by the measuring instrument <NUM> is <NUM> or less. Therefore, it is possible to surely detect the short-period variation of the glass outer diameter.

Claim 1:
A method for manufacturing an optical fiber (<NUM>) comprising:
heating an optical fiber preform (<NUM>) to draw glass fiber (<NUM>);
measuring an outer diameter of the glass fiber (<NUM>) to obtain a function of time;
transforming the function of time into a function of frequency;
identifying a first peak (P1) caused by a first drawing condition and a second peak (P2) caused by a second drawing condition in the function of frequency;
adjusting the second drawing condition so as to satisfy fn < fm - wm / <NUM> or fn > fm + wm / <NUM>, where fm is a frequency of the first peak (P1), wm is a full width at half maximum of the first peak (P1), and fn is a frequency of the second peak (P2);
forming a coating layer on the glass fiber (<NUM>) to form an optical fiber (<NUM>); and
twisting the optical fiber (<NUM>) using a swing guide roller (<NUM>);
wherein the second drawing condition is a swing frequency of the swing guide roller (<NUM>);
wherein the first drawing condition is a characteristic vibration frequency of a manufacturing device (<NUM>).