JP2005022943A - Method for manufacturing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a low-loss optical fiber having a long size and a uniform dispersion property. <P>SOLUTION: Eighteen holes 13, each having an inner diameter of 3 mm, are perforated at a prescribed interval in a glass rod 14 by using an ultrasonic drill 9. Then, capillaries 16, each having a hole diameter of 3 mm and an outer diameter of 3.5 mm, are arranged at the outer periphery of the glass rod 14. In a PCF, a defective part 15 free from the hole is arranged at the central part so as to impart waveguide property. After cleaning the inner faces of the holes 13 with hydrofluoric acid and drying the faces, the glass rod 14 having the perforated holes 13 is heated in an electrical furnace and drawn into an optical fiber having a diameter of 125 μm. After drawing the optical fiber, the optical fiber is cut, and the hole diameters d and the intervals A between holes are measured with an electron microscope. The optical fiber having perforated holes analogous to the shape of the holes of the original glass rod having the perforated holes can be obtained. Further, it is possible to process several to several hundreds of holes almost free from deviation in the diameter at an equal hole interval. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical fiber manufacturing method, and more particularly to an optical communication network and an optical fiber manufacturing method as a transmission medium used for optical signal processing.

  FIG. 1 is a diagram showing a general structure of a conventional optical fiber. In FIG. 1, reference numeral 1 denotes a core portion of the optical fiber, and 2 denotes a cladding portion of the optical fiber. As shown in FIG. 1, the conventional optical fiber has a structure in which a clad portion 2 having a low refractive index is disposed outside a core portion 1 having a high refractive index.

  FIG. 2 is a view showing PCF (Photonic Crystal Fibers) among conventional optical fibers, in which 3 is a hole, 4 is pure silica glass, and 5 is a defect. As shown in FIG. 2, a hole is periodically formed in a single glass, for example, pure quartz glass 4. The intervals between adjacent holes 3 are all equal. However, the defect portion 5, that is, the portion without the hole 3 is arranged at the center of the optical fiber. The defect 5 functions as a core and functions to confine light (for example, see Non-Patent Document 1).

  FIG. 3 is a view showing a method of manufacturing the conventional PCF shown in FIG. 2, in which reference numeral 6 denotes a glass rod, 7 denotes an inner glass pipe, and 8 denotes an outer glass pipe. A hexagonal glass rod 6 without a hole 3 is provided at the center, and a hexagonal inner glass pipe 7 with a hole 3 is provided outside thereof, and these are further inserted into the outer glass pipe 8. Later, the optical fiber was drawn at a high temperature of about 200 ° C.

J.C.Knight, T.A.Birks, P.St.J.Russell, and D.M.Atkin, “All-silica single-mode optical fiber with photonic crystal cladding,” Opt. Lett. 21, 1547-1549 (1996)

However, the conventional manufacturing method described above has the following problems.
1) Since the hexagonal glass rod is deformed by heat when it is made into an optical fiber, the interval and size of the holes are deformed, and the holes are not designed as designed, so that an optical fiber cannot be manufactured with a high yield. .
2) When a glass pipe is bundled and heated and stretched, the hole diameter and position of the glass pipe are greatly deformed from the initial values, and therefore, a hole of an arbitrary size cannot be formed at an arbitrary position.
3) When manufacturing a hexagonal glass pipe, it is necessary to grind the side surface of the glass pipe. However, the occurrence of scratches during processing and inconsistencies in the interface when the glass pipes are bundled are unavoidable. Therefore, when the bundled glass pipes are integrated, they are taken into the glass as bubbles before the scratches disappear. This adds a hole in the PCF, which has been a big problem in PCF production.
The present invention has been made in view of such problems, and an object of the present invention is to provide a method for producing a long, low-loss optical fiber having a constant dispersion characteristic.

  The present invention has been made in order to achieve such an object. The invention according to claim 1 is directed to a core portion through which light is guided, and a wavelength of light disposed around the core portion. In an optical fiber composed of a plurality of gaps having the same diameter, after arranging a capillary on the outer periphery of a glass rod in which several to several hundreds of the gaps that are the basis of the optical fiber are opened by an ultrasonic drill, The optical fiber is drawn.

  According to a second aspect of the present invention, in the first aspect of the invention, the glass rod having the holes is heated and stretched, and a glass pipe is fitted outside the glass rod, and then the optical fiber is attached. It is characterized by drawing.

  Further, the invention described in claim 3 is the invention described in claim 1, wherein glass fine particles serving as a clad portion are formed on the outside of the glass having the holes formed therein, and then heated to form a transparent glass. It is characterized by.

  Thus, in the present invention, a hole is made with an ultrasonic drill in a glass rod that is a starting point of an optical fiber. For example, when a hole with an inner diameter of 3 mm is opened in a glass with an ultrasonic drill, the hole can be opened with an accuracy of an inner diameter of 3 ± 0.01 mm. The number of holes is around 10. After that, a capillary is disposed on the outer peripheral portion and integrated at a high temperature, and then converted into an optical fiber. Therefore, since the number of holes is about one-tenth compared with the conventional tens to hundreds, the time for drilling is reduced, which contributes to cost reduction.

Further, when the perforated rod is stretched in a heating furnace, the shape of the hole hardly changes even after the wire is drawn if the temperature distribution of the electric furnace is kept uniform. Therefore, since the hole shape after the optical fiber can be maintained as designed, an optical fiber having the characteristics as designed can be produced with high yield.
Fields of application of the present invention include devices that compensate for dispersion and use nonlinear effects, and optical fibers that maintain polarization.

  As described above, according to the present invention, in an optical fiber comprising a core portion where light is guided and a plurality of air gaps arranged around the core portion and having the same diameter as the wavelength of light, After the capillary is placed on the outer periphery of a glass rod with several to several hundreds of gaps, which are the basis of the optical fiber, drawn to the optical fiber, it is drawn to the optical fiber, so there is little change in diameter (about μm). Several to several hundreds of holes, and the hole interval can be equally processed. After that, by performing normal drawing, the hole size interval and the like are deformed similarly to the initial hole shape, so that an optical fiber as designed can be easily manufactured.

  Moreover, since there is no glass connection between the holes, there is no loss due to structural irregularities. For this reason, a long, low-loss optical fiber can be manufactured with high yield as designed.

Embodiments of the present invention will be described below with reference to the drawings.
The dispersion characteristics and MFD characteristics of PCF are determined by the hole diameter d and the hole interval A. In order to manufacture PCF with high yield, reproducibility such as hole diameter d and hole interval A is important. In order to realize a low-loss PCF, 1) the starting glass loss (Rayleigh scattering loss, infrared absorption loss, etc.) is low, and 2) the hole shape is maintained in the longitudinal direction of the optical fiber. 3) It is necessary to reduce the surface roughness of the holes, and 4) to reduce impurities inside and inside the holes.

FIG. 4 is a diagram showing the wavelength dependence of dispersion when d / A = 0.5.
When the hole interval A is 1.6 μm, the zero dispersion wavelength is 1.2 μm, and when A is 1.9 μm, the zero dispersion wavelength is 1.68 μm. As the hole spacing A increases by 0.3 μm, the zero dispersion wavelength increases by 0.48 μm.

FIG. 5 is a diagram showing the wavelength dependence of dispersion when A = 1.6 μm.
For example, when the pore diameter d increases from 0.8 μm to 0.9 μm, the zero dispersion wavelength changes from 1.2 μm to 1.4 μm. That is, when the pore diameter d changes by 11%, the zero dispersion wavelength changes by 200 nm. Therefore, in order to suppress the change of the zero dispersion wavelength to about 10 nm, the pore diameter variation must be 0.5% or less.

  FIGS. 6A and 6B are views showing Example 1 of the optical fiber manufacturing method according to the present invention, and FIG. 6B is a cross-sectional view of FIG. In the figure, reference numeral 9 is an ultrasonic drill, 13 is a hole, 14 is a glass rod, 15 is a defective portion, and 16 is a capillary. Eighteen holes 13 having an inner diameter of 3 mm were formed in the glass rod 14 having an outer diameter of 40 mm and a length of 200 mm with an ultrasonic drill 9 at intervals of 5 mm. Next, a capillary 16 having a hole diameter of 3 mm and an outer diameter of 3.5 mm was disposed on the outer periphery of the glass rod 14.

  By using this capillary 16 in combination, the number of holes in the perforated glass rod 14 is 18. Conventionally, for example, in order to effectively confine light in the core portion, it was necessary to open 60 or more holes. For this reason, in the present invention, the time required for drilling can be reduced to one third or less, and the time required for conventional drilling can be greatly shortened. Further, although light propagates through the core portion 15, the portion where the outer capillary 16 is disposed is sufficiently attenuated as compared with the central portion, so that excessive loss occurs due to the accuracy and contamination of the capillary 16. It never happened.

  In the PCF, a defect portion 15 having no hole is disposed in the center portion in order to provide waveguide characteristics. A part of the glass rod 14 after the hole 13 was opened was cut, and the shape of the hole 13 was measured. The hole diameter d was within 3 mm ± 10 μm. The hole interval A was within 5 mm ± 10 μm.

  Next, the inner surface of the hole 13 was washed with hydrofluoric acid and dried, and then the glass rod 14 having the hole 13 was heated in an electric furnace and drawn into an optical fiber having a diameter of 125 μm. The length of the produced optical fiber was 10 km. After drawing the optical fiber, the optical fiber was cut, and the hole diameter d and the hole interval A were measured with an electron microscope. The hole diameter d after drawing the optical fiber is 9.4 μm, the hole interval A is 15.6 μm, and a perforated optical fiber similar to the shape of the hole in the original glass hole can be realized. There was no change in shape over the entire length.

  In addition, in PCF, light is confined in the hole at the center, so if the hole at the center is opened with high accuracy and in the absence of cracks, the outer hole does not significantly affect the transmission characteristics. It has been. In this optical fiber, the optical loss was as low as 1 dB / km at a wavelength of 1.3 μm and 0.5 dB / km at a wavelength of 1.55 μm.

  FIG. 7 is a view for explaining Example 2 of the optical fiber manufacturing method according to the present invention, and the same reference numerals are given to components having the same functions as those in FIG. 18 holes 13 with a hole diameter d of 1.4 mm and a hole interval A of 2.9 mm were formed in a glass rod having an outer diameter of 40 mm and a length of 200 mm.

  The perforated glass rod 14 thus produced was washed and dried, and then stretched to an outer diameter of 8 mm with a burner. Thereafter, 72 capillaries 16 were arranged on the outer periphery to make the number of holes 90. As shown in FIG. 7, both the glass rod 14 and the capillary 16 were inserted into a glass pipe 10 having an outer diameter of 40 mm and an inner diameter of 12 mm, and drawn into an optical fiber having a diameter of 125 μm. The optical fiber length was 5 km, the hole diameter after drawing the optical fiber was 0.9 μm, the hole interval was 1.8 μm, and the entire length of the optical fiber was constant. The loss was 1 dB / km at a wavelength of 1.3 μm, and 0.6 dB / km at a wavelength of 1.55 μm.

The zero dispersion wavelength of the PCF thus produced was 1.55 μm, and the dispersion slope at the wavelength of 1.55 μm was −0.1 ps / km / nm ² . This PCF was used to compensate the dispersion at a wavelength of 1.55 μm of a dispersion-shifted fiber having a 1.55 μm zero dispersion. As a result, the dispersion value at a wavelength of 1.5 to 1.6 μm could be ± 0.1 ps / km / nm ² .

  FIG. 8 is a view for explaining Example 3 of the optical fiber manufacturing method according to the present invention, in which reference numeral 11 indicates a burner, and 12 indicates glass particles. In addition, the same code | symbol is attached | subjected about the component which has the same function as FIG. As shown in Example 1 described above, 18 holes having an outer diameter of 40 mm, a hole diameter of 1.3 mm, and a hole interval of 2.8 mm were drilled using an ultrasonic drill.

  After stretching the apertured glass rod 14 to an outer diameter of 10 mm, glass fine particles 12 are formed on the outer peripheral portion of the apertured glass rod 14 by the glass synthesis burner 11 using the VAD method, and then 1700 in an electric furnace. Heated to ° C., a starting glass base material having an outer diameter of 50 mm and a hole diameter of 0.33 mm was formed. This perforated glass material was heated by an optical fiber drawing furnace to produce an optical fiber having a diameter of 125 μm and 10 km.

The hole diameter d after drawing the optical fiber was 0.83 μm, and the hole interval A was 1.8 μm. The hole diameter d and the hole interval A were constant over the entire length of the manufactured optical fiber. The loss of the manufactured optical fiber was 2 dB / km at a wavelength of 1.3 μm, and 0.5 dB / km at a wavelength of 1.55 μm. The zero dispersion wavelength was 1.31 μm, and the dispersion slope at the wavelength of 1.31 μm was −0.1 ps / km / nm ² .

This optical fiber was used to compensate for dispersion of a conventional SMF at a wavelength of 1.3 to 1.4 μm. As a result, the dispersion value at a wavelength of 1.3 to 1.4 μm could be ± 0.1 ps / km / nm ² .

  The present invention relates to an optical fiber manufacturing method that is a transmission medium used for an optical communication network and optical signal processing, and can provide a method for manufacturing an optical fiber that is long, has constant dispersion characteristics, and has low loss.

It is a figure which shows the general structure of the conventional optical fiber. It is a figure which shows PCF (Photonic Crystal Fibers) among the conventional optical fibers. It is a figure which shows the manufacturing method of the conventional PCF shown in FIG. It is a figure which shows the wavelength dependence of dispersion | distribution in case d / A = 0.5. It is a figure which shows the wavelength dependence of dispersion | distribution at the time of setting A = 1.6micrometer. It is a figure which shows Example 1 of the manufacturing method of the optical fiber which concerns on this invention, (b) is sectional drawing of (a). It is a figure for demonstrating Example 2 of the manufacturing method of the optical fiber which concerns on this invention. It is a figure for demonstrating Example 3 of the manufacturing method of the optical fiber which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core part of optical fiber 2 Clad part of optical fiber 3 Hole 4 Pure quartz glass 5 Defect part 6 Glass rod 7 Inner glass pipe 8 Outer glass pipe 9 Ultrasonic drill 10 Glass pipe 11 Burner 12 Glass particulate 13 Hole 14 Glass rod 15 Defect 16 Capillary

Claims (3)

  In an optical fiber composed of a core portion where light is guided and a plurality of voids having a diameter of the same diameter as the wavelength of the light disposed around the core portion, an ultrasonic wave is applied to the void that is the source of the optical fiber. A method of manufacturing an optical fiber, comprising: arranging a capillary on the outer periphery of a glass rod opened by several to several hundreds with a drill, and then drawing the optical fiber.   2. The method of manufacturing an optical fiber according to claim 1, wherein the glass rod having the hole is heated and stretched, and a glass pipe is fitted on the outside of the glass rod, and then drawn to the optical fiber. The method for producing an optical fiber according to claim 1, wherein glass fine particles serving as a clad portion are formed outside the glass having the holes formed therein, and then heated to form a transparent glass.

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