JP4146810B2 - Manufacturing method of glass optical device, manufacturing method of fiber type optical device and manufacturing apparatus thereof - Google Patents

Description

  The present invention relates to a glass optical device manufacturing method including a fiber optical device and an optical waveguide optical device, and a fiber optical device manufacturing apparatus.

As a method for manufacturing a fiber-type optical device in which a local refractive index profile is formed in the core, it is known that a method of manufacturing a Ge-doped silica fiber by irradiating with ultraviolet rays is effective. A fiber grating in which a grating is formed on a core by this method has already been put into practical use. In ordinary Ge-doped silica fibers, the difference in refractive index of 10 ⁻⁴ or more necessary for device development cannot be induced by ultraviolet irradiation. Therefore, the Ge addition concentration is increased or B or Sn are co-added. Various ideas have been made (for example, see Non-Patent Document 1). As the most effective high sensitivity method, there is a method of filling an optical fiber with hydrogen under high pressure and adding it (for example, see Patent Document 1).

JP 7-244210 A Masayuki Yamane, et al., “Glass Optical Handbook”, Asakura Shoten, July 5, 1999, p. 548

However, processes such as hydrogenation for realizing a refractive index difference of 10 ⁻⁴ or more are complicated in process and costly. In addition, the writing of the refractive index distribution by ultraviolet irradiation shows a relaxation phenomenon in which the refractive index approaches the value before irradiation after irradiation, and there is also a problem in terms of long-term stability (lifetime) of the device. Furthermore, in the fiber type optical device manufacturing method, the refractive index distribution writing process needs to be performed separately after the drawing process, which also causes an increase in cost.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, to easily form a refractive index distribution in the core, and to produce a device having excellent long-term stability. An object of the present invention is to provide a method for manufacturing a type optical device and an apparatus for manufacturing the same.

To achieve the above object, the invention of claim 1, an optical fiber, or in the manufacturing method of glass optical device for forming a local refractive index distribution in the optical waveguide, pure silica glass, or the concentration of 10 After performing the heat treatment for reducing the fictive temperature of the optical fiber or the optical waveguide using Ge-doped silica glass of less than 1% to 1400 ° C. or less, the fictive temperature of the predetermined portion of the optical fiber or the optical waveguide after the heat treatment to raise 100 ° C. or higher than a locally rapidly heated glass made light device manufacturing method of the predetermined portion by irradiating the infrared laser beam.

According to a second aspect of the invention, in the method for manufacturing a fiber type optical device to form a refractive index distribution in the optical fiber and drawing by melting the base metal in a melting furnace, pure silica glass was drawing from the melting furnace, or concentration After heat treatment for reducing the fictive temperature of optical fiber using 10% or less Ge-added silica glass to 1400 ° C. or lower, the fictive temperature at a predetermined position of the optical fiber is raised by 100 ° C. or higher than after the heat treatment. A method of manufacturing a fiber-type optical device, wherein a refractive index profile is formed by irradiating an infrared laser beam in order to rapidly heat the predetermined portion locally.

According to a third aspect of the present invention, there is provided a melting furnace for melting a base material, and a line for drawing an optical fiber using pure silica glass or Ge-doped silica glass having a concentration of 10% or less by dropping and freezing the molten base material. An annealing furnace for lowering the fictive temperature to 1400 ° C. or less is provided immediately below the melting furnace, and an infrared laser beam is used to increase the fictive temperature by 100 ° C. or more to the optical fiber that has passed through the annealing furnace. Is a fiber-type optical device manufacturing apparatus provided with a laser oscillation device for forming a refractive index distribution by local rapid heating treatment by irradiating.

  According to the present invention, it is possible to easily form a refractive index distribution in the core, and to produce an excellent effect that a glass optical device having excellent long-term stability can be manufactured.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The inventors of the present invention have described that “in a pure silica glass and a Ge-added silica glass having a concentration of 10% or less, if the fictive temperature difference is 100 ° C. or more, the refractive index difference is 10 ⁻⁴ or more” and “1400 ° C. or less It is possible to write a refractive index difference of 10 ⁻⁴ or more in the core by irradiating an optical fiber having a virtual temperature with infrared rays for a short time to increase the local virtual temperature by 100 ° C. or more. The present invention has been reached.

  FIG. 1 is a schematic diagram of a fiber type optical device manufacturing apparatus according to the present embodiment.

  As shown in FIG. 1, a fiber-type optical device manufacturing apparatus 10 includes a melting furnace 11 that melts a fiber preform, an annealing furnace 12 that heat-treats the optical fiber, a coating device 13 that coats the surface of the optical fiber, and an optical fiber. And a laser oscillation device 14 for irradiating infrared laser light. In the configuration, an annealing furnace 12 is provided immediately below the melting furnace 11 of the drawing line of the optical fiber, a laser oscillation device 14 is provided so as to irradiate the drawing line under the annealing furnace 12 with infrared laser light, A coating device 13 is provided on the drawing line.

  Next, a manufacturing method of the fiber type optical device will be described.

  The optical fiber preform is melted in the melting furnace 11, and the molten preform is dropped and solidified from the melting furnace 11 to be drawn into an optical fiber 15 that has been reduced in diameter and stretched. The optical fiber 15 formed here is a Ge-added silica glass fiber in which 4.5% concentration of Ge is added to the core. The drawn optical fiber 15 is heat-treated in the annealing furnace 12 to reduce the fictive temperature of the optical fiber 15.

  The fictive temperature is a temperature that indicates how many times the supercooled liquid is in a thermal equilibrium state and is a good indicator of the structure frozen in the glass (solidified Glass has a different fictive temperature depending on its structure), and glass having a different fictive temperature has a different refractive index.

  Next, the optical fiber 16 that has passed through the annealing furnace 12 is locally irradiated with infrared laser light to form a portion having a high virtual temperature. Immediately after the virtual temperature of the optical fiber is lowered by the heat treatment, local rapid heating and rapid cooling are performed by short-time irradiation of the infrared laser light pulsed by the laser oscillation device 14 to form a region where the virtual temperature is higher than the surroundings. Since the irradiated laser beam is an infrared laser beam pulse-oscillated from the laser oscillation device 14, the drawn optical fiber has a portion where the infrared laser beam is irradiated and a portion where the infrared laser beam is not irradiated. A fiber-type optical device 17 having a refractive index distribution in which different portions are alternately formed is obtained. Further, in addition to pulsed laser light, continuously oscillated infrared laser light may be used to irradiate the optical fiber with a chopper or the like with a short time interval. In this case, the wavelength of the continuously oscillated laser beam is adjusted to be the same as the wavelength of the infrared laser beam.

  Finally, the fiber type device 17 in which the refractive index profile is formed is coated with a coating resin or the like to protect the surface, and the fiber type optical device 18 is obtained.

  In the manufacturing method of the fiber type optical device 18, the virtual temperature distribution of the fiber core for comparing the case where the heat treatment is not performed (annealing furnace OFF) and the case where the heat treatment is performed (annealing furnace ON) is shown. It is shown in 2.

Here, the virtual temperature evaluation method includes a method using infrared spectroscopy and a method using Raman scattering. Since the change in peak position near 2260 cm ^{-1 in} infrared absorption and the change in peak intensity called D1 and D2 lines in Raman scattering have a very good correlation with the virtual temperature, the virtual temperature is obtained by these measurements. Can do. In the case of measurement of an optical fiber, a microspectroscopic method is required, but since the spatial resolution cannot be increased by infrared spectroscopy, the virtual temperature of the optical fiber is determined by microscopic Raman spectroscopy.

  As shown in FIG. 2, in the optical fiber 16 manufactured by turning on the annealing furnace 12, the fictive temperature is lowered to about 1250 ° C., and the fictive temperature is raised to around 1400 ° C. only in the portion irradiated with the infrared laser light. There is a difference of 100 ° C. or more with and without infrared laser light irradiation. On the other hand, the optical fiber manufactured with the annealing furnace 12 turned off has a fictive temperature of 1500 ° C. or higher, and there is almost no temperature difference from the portion irradiated with the infrared laser light. Therefore, since the virtual temperature of the portion irradiated with the infrared laser light is around 1400 ° C., the virtual temperature by the heat treatment should be 1400 ° C. or less in order to make a difference in the virtual temperature depending on whether or not the infrared laser light is irradiated. Preferably, it is 1000-1400 degreeC more preferably. The heat treatment is performed under conditions of 1100 to 1400 ° C.

  If an annealing furnace 12 is installed in the optical fiber manufacturing apparatus and the optical fiber 15 is subjected to heat treatment to promote structural relaxation of the glass, an optical fiber 16 having a low fictive temperature of 1400 ° C. or lower is manufactured. The core can be rapidly heated and cooled locally by short-time irradiation of infrared rays by the oscillation device 14 to increase the local virtual temperature and write the refractive index distribution to the core. Here, the heat treatment for continuously lowering the fictive temperature was performed during the drawing of the optical fiber, but the optical fiber 16 having a low fictive temperature may be separately heat-treated after the drawing. .

  In addition, since the refractive index distribution is written in the core during the drawing of the optical fiber by the heat treatment and the local heat treatment by the infrared laser light irradiation, the cost is much lower than the conventional method in which the ultraviolet irradiation is performed after the drawing. Is advantageous. Note that the fiber type optical device of the present embodiment can also write the refractive index distribution by irradiating infrared rays in a state where travel of the drawing line is stopped after drawing the optical fiber. In that case, a slit or the like may be provided between the optical fiber and the laser oscillation device, and the refractive index distribution may be written by irradiating infrared rays in the form of interference fringes.

FIG. 3 is a diagram showing the relationship between the fictive temperature and the refractive index of the core of a pure silica fiber (containing about 1000 ppm of chlorine for dehydration). This is an actual measurement of the refractive index of a fiber-type optical device formed at a fictive temperature within 1000 to 1500 ° C. As shown in FIG. 3, there is a relationship in which the refractive index and the virtual temperature rise at the same ratio, and the refractive index changes by 1 × 10 ⁻⁴ every time the virtual temperature changes by 100 ° C. FIG. 4 is a diagram showing the relationship between the fictive temperature and the refractive index in a Ge-added silica fiber (Ge concentration 4.5%). Like FIG. 3, the refractive index is 1 every time the fictive temperature changes by 100 ° C. It shows that it changes by × ^10-4 .

As described above, in order to change the refractive index of 10 ⁻⁴ necessary for functioning as an optical device, a change in the virtual temperature is required to be 100 ° C. or more. Further, referring to FIG. Accordingly, a fiber-type optical device having a refractive index distribution with a refractive index change of 10 ⁻⁴ or more can be manufactured.

  According to the glass optical device manufacturing method of the present embodiment, a virtual temperature difference at the time of forming an optical fiber is used, and a sufficient refractive index difference can be obtained without performing a hydrogenation process or the like. In addition, the obtained refractive index difference is considered from the structure relaxation time, and the fiber type manufactured by the manufacturing method of this embodiment is shorter than the time when the refractive index distribution of the fiber type optical device manufactured by the conventional manufacturing method deteriorates. The time during which the refractive index distribution of the optical device deteriorates is longer, does not deteriorate at room temperature, and is excellent in long-term stability.

  Furthermore, although the fiber type optical device manufactured in this embodiment uses a 4.5% Ge-doped silica fiber, it can also be applied to glass of other compositions, preferably a Ge-doped silica having a concentration of 10% or less. It can be applied to fiber or pure silica core fiber.

  In the present embodiment, the fiber type optical device manufacturing method in which the refractive index profile is formed in the optical fiber has been described. However, the present invention is not limited to the fiber type optical device, but also applies to glass optical devices including other optical waveguide type devices. It is. In a manufacturing method of an optical waveguide, a manufacturing method for forming a refractive index distribution by performing a heat treatment for lowering the virtual temperature of the optical waveguide and changing the virtual temperature by locally heating the core of the optical waveguide. Can be applied. Moreover, according to the manufacturing method, it has the same effect as the manufacturing method of the above-mentioned fiber type optical device.

It is the schematic which shows the manufacturing apparatus of the fiber type optical device of this Embodiment. It is a figure which shows the virtual temperature distribution of each core at the time of ON / OFF of annealing treatment. It is a figure which shows the relationship between the fictive temperature and refractive index of the core of a pure silica fiber. It is a figure which shows the relationship between the fictive temperature and refractive index of the core of Ge addition silica fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fiber type optical device manufacturing apparatus 11 Melting furnace 12 Annealing furnace 15 Optical fiber 18 Fiber type optical device

Claims (3)

In a method of manufacturing a glass optical device for forming a local refractive index profile in an optical fiber or an optical waveguide, an optical fiber or optical fiber using pure silica glass or Ge-doped silica glass having a concentration of 10% or less After heat treatment for lowering the fictive temperature of the waveguide to 1400 ° C. or lower, infrared laser light is irradiated so as to raise the fictive temperature of the optical fiber or a predetermined portion of the optical waveguide by 100 ° C. or higher than after the heat treatment. A method for manufacturing a glass optical device, wherein the predetermined portion is subjected to rapid heat treatment locally. In a fiber-type optical device manufacturing method for forming a refractive index distribution in an optical fiber drawn by melting a base material in a melting furnace, pure silica glass or Ge having a concentration of 10% or less is drawn from the melting furnace After performing heat treatment to lower the fictive temperature of the optical fiber using silica glass to 1400 ° C or lower, irradiate infrared laser light to raise the fictive temperature of the predetermined part of the optical fiber by 100 ° C or higher than after the heat treatment. A method of manufacturing a fiber-type optical device, wherein the refractive index distribution is formed by locally rapidly heating the predetermined portion. A melting furnace for melting the base material is provided, and the virtual base material is dropped and frozen to create a virtual fiber directly below the melting furnace in a line for drawing an optical fiber using pure silica glass or Ge-added silica glass having a concentration of 10% or less. An annealing furnace for lowering the temperature to 1400 ° C. or lower is provided, and the optical fiber that has passed through the annealing furnace is locally irradiated with an infrared laser beam to raise the fictive temperature by 100 ° C. or more than the heat treatment. fiber-type optical device manufacturing apparatus characterized in that a laser oscillating apparatus for forming a refractive index distribution and rapid heat treatment.

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