JP3866696B2 - Optical fiber manufacturing method - Google Patents

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, it was drawn into an optical fiber at a high temperature.

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 is a big problem in the production of PCF because it adds unnecessary holes in the PCF.
4) In addition, with the conventional drilling methods, it is difficult to accurately drill all of tens to hundreds of holes, and cracks occur on the inner surfaces of some of the holes. And the yield of the PCF is poor, which increases the manufacturing cost.

  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-length, low-loss optical fiber having a constant dispersion characteristic.

The present invention has been made in order to achieve the above object, a first aspect of the present invention, a core portion which is guided light is plurality disposed around the core portion, of the light In a method of manufacturing an optical fiber having a hole having a diameter approximately equal to the wavelength and formed in parallel with the light guiding direction, a single glass rod is formed when integrated to form a light guiding direction. are prepared glass rod part having a cross-section parallel, the parallel to the light propagation direction in the ultrasonic drill glass rod part open multiple pores, and superimposed the cross section of the glass rod part, the glass rod consisting of the assembly we are said core portion and said plurality of holes, heated to integrated, characterized in that drawing the optical fiber.

According to a second aspect of the present invention, there are provided a core portion through which light is guided, a plurality of core portions arranged around the core portion, having a diameter approximately equal to the wavelength of light, In a manufacturing method of an optical fiber comprising holes opened in parallel, a glass rod part having a cross section parallel to the light guiding direction is prepared by forming a glass rod when integrated, and the glass rod A glass composed of the core part and the plurality of holes assembled by opening a plurality of holes in the part in parallel with the light guiding direction with an ultrasonic drill and overlapping the cross sections of the glass rod parts. After the glass pipe is fitted on the outside of the rod, the optical fiber is drawn.

According to a third aspect of the present invention, there are provided a core portion through which light is guided, a plurality of core portions arranged around the core portion, having a diameter approximately equal to the wavelength of light, In a manufacturing method of an optical fiber comprising holes opened in parallel, a glass rod part having a cross section parallel to the light guiding direction is prepared by forming a glass rod when integrated, and the glass rod A glass composed of the core part and the plurality of holes assembled by opening a plurality of holes in the part in parallel with the light guiding direction with an ultrasonic drill and overlapping the cross sections of the glass rod parts. The rod is heated and integrated, and glass fine particles serving as a clad portion are formed on the outside of the integrated glass rod , and then heated to form a transparent glass, and then drawn to the optical fiber. To do.

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. Thereafter, the glass rods with holes are stretched, and the resulting holed glass rods are bundled and integrated into a PCF preform. Since the number of glass rods to be bundled at a time is smaller as the number of glass rods to be bundled is smaller, it is possible to produce a PCF that is low in cost and has no failure in drilling.
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, an optical fiber comprising a core portion through which light is guided and a plurality of air gaps having a diameter approximately the same as the wavelength of light disposed around the core portion. In the method, prepare a plurality of glass rods in which a plurality of gaps that form the basis of the optical fiber are opened with an ultrasonic drill, superimpose the side surfaces of the plurality of glass rods, and use the superposed glass rod as an outer diameter of the glass rod. After being inserted into a glass pipe having the same inner diameter as that of the optical fiber, the optical fiber is drawn. Therefore, since the number of holes in one glass rod is small, the number of holes is reduced and the PCF production yield is increased. For this reason, it is possible to process several to hundreds of accurate holes with a small change in diameter (about μm) and the hole interval equally at low cost. 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 loss of the starting glass (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 the hole interval 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.

  FIG. 6 is a view showing Example 1 of the optical fiber manufacturing method according to the present invention, in which reference numeral 13 denotes a hole, 14 (14a to 14c) denotes a glass rod, and 15 denotes a defect portion. A glass rod 14 having an outer diameter of 40 mm and a length of 200 mm was divided into three, and holes 3 having an inner diameter of 3 mm were opened at intervals of 5 mm in each glass rod 14a to 14c with an ultrasonic drill. Thereafter, the three divided glass rods 14a to 14c were integrated with an oxyhydrogen burner to form a perforated glass rod 14 having a circular cross section.

  When a hole 13 is cracked when the hole 13 is opened, the optical loss after drawing the optical fiber increases. For example, even if a crack occurs in one of the 18 holes 13, the optical loss after drawing to the optical fiber increases, so that the perforated glass rod 14 cannot be used. As in the present invention, the number of holes in the three divided glass rods 14a to 14c is 3, 12, and 3, respectively, as shown in FIG. 6, and the probability of occurrence of cracks on the inner surface of the hole is greatly reduced.

  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. The optical loss of this optical fiber was as low as 0.5 dB / km at a wavelength of 1.3 μm and 0.3 dB / km at a wavelength of 1.55 μm.

  FIG. 7 is a view for explaining Example 2 of the method for manufacturing an optical fiber according to the present invention, and reference numeral 9 in the drawing denotes a glass pipe. In addition, the same code | symbol is attached | subjected to the component which has the same function as FIG. A glass rod 14 having an outer diameter of 40 mm and a length of 200 mm was divided into three, and holes 13 having a hole diameter d of 1.4 mm and a hole interval A of 2.9 mm were formed in each of the glass rods 14a to 14c. However, there is no hole in the center.

  After the perforated glass rod 14 thus prepared was washed and dried, it was stretched to 25 times in an electric furnace and then divided into three glass rods 14a to 14c having an outer diameter of 40 mm and an inner diameter of 9 mm. It was inserted into the pipe 9 and drawn into an optical fiber having a diameter of 125 μm. The optical fiber length was 5 km, the hole diameter d after drawing the optical fiber was 0.9 μm, and the hole interval A was 1.8 μm, which was constant over the entire length of the optical fiber. 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, the glass rod 14 is divided into three parts, and holes 13 having a hole diameter d of 1.3 mm and a hole interval A of 2.8 mm are formed in each glass rod 14a to 14c using an ultrasonic drill. Opened.

  The perforated glass rod 14 was stretched to an outer diameter of 10 mm and then integrated with an oxyhydrogen burner. Next, after the glass fine particles 12 are formed on the outer peripheral portion of the integrated apertured glass rod 14 by the glass synthesis burner 11 using the VAD method, the glass fine particles 12 are heated to 1700 ° C. in an electric furnace, and the outer diameter is 50 mm. A starting glass matrix of 0.33 mm was formed. This perforated glass material was heated by an optical fiber drawing furnace to produce an optical fiber 10 km having a diameter of 125 μm.

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. 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 Glass pipe 11 Burner 12 Glass particulate 13 Hole 14 (14a-14c) Glass rod 15 Defects

Claims (3)

Light consisting of a core portion through which light is guided and a plurality of holes arranged around the core portion, having a diameter approximately the same as the wavelength of the light and opened in parallel to the light guiding direction In the fiber manufacturing method, when integrated, a glass rod is formed, and a glass rod component having a cross section parallel to the light guiding direction is prepared, and the glass rod component is guided in the light guiding direction by an ultrasonic drill. parallel opened a plurality of pores, and superimposed the cross section of the glass rod part, a glass rod consisting of the assembly we are said core portion and said plurality of holes, and integrated heated, A method of manufacturing an optical fiber, wherein the optical fiber is drawn. Light consisting of a core portion through which light is guided and a plurality of holes arranged around the core portion, having a diameter approximately the same as the wavelength of the light and opened in parallel to the light guiding direction In the fiber manufacturing method, when integrated, a glass rod is formed, and a glass rod component having a cross section parallel to the light guiding direction is prepared, and the glass rod component is guided in the light guiding direction by an ultrasonic drill. A plurality of holes in parallel with each other, and the cross-section of the glass rod component is overlapped, and a glass pipe is fitted on the outside of the glass rod composed of the assembled core part and the plurality of holes. A method of manufacturing an optical fiber, wherein the optical fiber is drawn. Light consisting of a core portion through which light is guided and a plurality of holes arranged around the core portion, having a diameter approximately the same as the wavelength of the light and opened in parallel to the light guiding direction In the fiber manufacturing method, when integrated, a glass rod is formed, and a glass rod component having a cross section parallel to the light guiding direction is prepared, and the glass rod component is guided in the light guiding direction by an ultrasonic drill. A plurality of holes are formed in parallel with each other, the cross sections of the glass rod parts are overlapped, and the assembled glass rod composed of the core part and the plurality of holes is heated and integrated, and the integrated A method for producing an optical fiber , comprising: forming glass fine particles to be a clad portion on the outer side of the converted glass rod , and then heating to form a transparent glass, followed by drawing to the optical fiber.

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