JP5760859B2 - Method for producing glass particulate deposit, glass preform for optical fiber, and optical fiber - Google Patents

Description

  The present invention relates to a method for producing a glass fine particle deposit as a material for an optical fiber glass preform, and to an optical fiber glass preform and an optical fiber comprising the glass fine particle deposit.

In the method for producing a glass fine particle deposit, a gas of Ge (germanium) compound (for example, GeCl ₄ : germanium tetrachloride) and Si (silicon) compound (for example, SiCl ₄ : silicon tetrachloride), which are glass raw materials, are introduced into a burner. While the burner is reciprocatingly traversed relative to the starting material along the growth axis direction, glass fine particles (hereinafter referred to as “soot”) generated on the outer peripheral surface of the starting material rotating about the axis are deposited (hereinafter referred to as “soot”). A manufacturing method (OVD method) manufactured by “sooting” is known. Further, a multi-burner multi-layering method (MMD method) is known in which a plurality of burners are sooted while being reciprocally traversed relative to a starting material.

  The glass base material for optical fibers of a cylindrical transparent glass body can be manufactured by sintering the glass fine particle deposit body manufactured by the above-described manufacturing method while heating in a sintering furnace.

  Such a glass preform for optical fiber is measured by a preform analyzer (hereinafter referred to as “PA measurement”) in order to confirm whether or not a predetermined refractive index distribution can be formed in the core equivalent part before the drawing operation. ) May be performed.

  In the method for producing a glass fine particle deposit by the ordinary OVD method and MMD method, as described above, the starting material reciprocates at a constant speed relative to the burner, and the starting material rotates at a constant speed. The soot deposited during one traverse and one rotation becomes one layer, and the soot body deposited becomes a layer. Since the traverse speed and rotation speed are usually constant, the thickness of one layer is also almost constant, and the optical fiber glass preform made of the glass fine particle deposit is manufactured according to the traverse period and rotation period of the starting material. Striped streaks (streaks) occur.

  Such striae is that the concentration and bulk density of dopants (Ge, etc.) added to control the refractive index of the optical fiber glass preform by changing the temperature of the deposited portion during one traverse, one rotation, etc. A periodic refractive index change is generated in the optical fiber glass preform in which the striae are considered to occur due to fluctuations.

  In PA measurement, laser light is incident from the side surface of the glass base material and the refractive index distribution is measured by measuring the pattern of the transmitted laser light. If the glass base material has a periodic refractive index change, this PA Since the measurement laser light is diffracted, the diffracted higher-order mode light interferes with the zero-order light, and a part of the measured refractive index distribution is disturbed. This disturbance causes an error in a characteristic value (cutoff wavelength or the like) calculated from the PA measurement result.

  In order to accurately perform the above-mentioned PA measurement, as described in Patent Document 1, the incident PA measurement is performed by the slit passing on the optical axis of the light that has passed through the optical fiber glass preform. There has been proposed a method of measuring the refractive index distribution by detecting only the 0th-order light, excluding the higher-order diffracted light generated by the interaction between the laser light and the periodic change in the optical fiber glass preform. Yes.

  Further, as described in Patent Document 2, a method for measuring the refractive index distribution while changing the beam diameter of the PA measurement laser beam intermittently in accordance with the periodic change and structure of the glass preform for optical fiber has been proposed. ing.

  Further, as described in Patent Document 3, a method of eliminating the influence of striae by PA measurement by reducing the thickness of a layer deposited per rotation and per traverse has been proposed.

JP-A-6-347372 JP-A-8-201221 Japanese Patent Laid-Open No. 11-199263

  However, in the prior art of Patent Document 1, it is difficult to selectively extract only the 0th-order light unless the width and direction of the slit are appropriately designed. For example, if the slit width is too large, even higher-order diffracted light is transmitted, and if the slit width is too small, even the 0th-order light that is signal light is blocked.

  Further, in the prior art of Patent Document 2, the striae of the optical fiber glass base material is basically very fine and complicated, so that the optimum beam diameter of the PA measurement laser beam is selected according to the structure. It is very difficult to perform PA measurement, and there is a problem that complicated control is required.

  In addition, the technique disclosed in Patent Document 3 has a problem in that, since the thickness of the layer deposited per rotation is reduced per rotation, the manufacturability is sacrificed and the manufacturing cost is increased.

  This invention makes it an example of a subject to cope with such a problem. That is, it is possible to prevent the occurrence of interference due to diffraction of incident PA measurement laser light, to be able to perform PA measurement of an accurate refractive index structure by preventing the occurrence of interference due to diffraction of PA measurement laser light, and to provide an accurate refractive index structure. An object of the present invention is to reduce the error of the characteristic value calculated from the PA measurement result by performing the PA measurement.

  In order to achieve such an object, a method for producing a glass particulate deposit according to the present invention comprises the following arrangement.

While rotating a starting material that rotates or a burner that jets a flame relatively reciprocally traverses along the growth axis direction, the glass raw material gas containing GeCl ₄ and the flame forming gas are heated by the flame to generate glass particles, A method for producing a glass particulate deposit by depositing the glass particulates on the starting material,
The thickness of the glass fine particle layer deposited for each traverse is deposited to be different between adjacent layers, the relative refractive index difference is 0.8% or more, and an irregular period striae is formed. .

  By varying at least one of the starting material or the traverse speed of the burner, the supply amount of the glass raw material gas, and the supply amount of the flame forming gas, the thicknesses of the glass fine particle layers deposited for each traverse are adjacent to each other. It is preferable to deposit the layers differently.

  Moreover, it is preferable to change the thickness of the glass fine particle deposition layer regularly in a cycle of at least two or more layers.

  Moreover, it is preferable to change at least one of the starting material or the traverse speed of the burner, the supply amount of the glass raw material gas, and the supply amount of the flame forming gas between two or more set values.

  The set value is preferably changed in accordance with a binary pseudorandom number sequence, and the binary pseudorandom number sequence is preferably an M sequence.

  Furthermore, it is preferable to change the rotational speed of the starting material during the traversing of the starting material or the burner.

  It is preferable that the glass fine particle deposit is one that synthesizes a core portion or a jacket portion of a glass preform for an optical fiber.

  Moreover, it is a glass base material for optical fibers, characterized by being produced by the glass fine particle deposit produced by the above production method.

  Further, the optical fiber is formed by drawing the optical fiber preform.

  By having such characteristics, the present invention has the following effects. In other words, since the thickness of the glass particle layer deposited for each traverse is deposited differently in adjacent layers, the striae period (layer thickness) becomes random, and diffraction of incident PA measurement laser light is performed. It is possible to prevent the occurrence of interference due to. By preventing the occurrence of interference due to diffraction of the PA measurement laser beam, an accurate refractive index structure can be measured, and the error of the characteristic value calculated from the PA measurement result can be reduced.

It is a schematic diagram which shows the manufacturing method which manufactures a glass fine particle deposit body by the external chemical vapor deposition method (OVD method). (a) is a schematic diagram which shows an example of the striae structure (comparative example) in the glass preform for optical fibers manufactured from the glass particulate deposit manufactured by the conventional manufacturing method, and (b) is the present invention. It is a schematic diagram which shows an example of the striae structure (Example) in the glass preform | base_material for optical fibers manufactured from the glass fine particle deposit body manufactured by this manufacturing method. (a) shows an example of the refractive index distribution measurement result of the glass preform for optical fibers of the comparative example. (b) shows an example of the refractive index distribution measurement result of the glass preform for optical fiber of the example. (a1) is a schematic diagram which shows the detail of an example of the striae structure in the glass preform | base_material for optical fibers of a comparative example, (a2) is an enlarged view of a1. (b1) is a schematic diagram showing details of an example of a striae structure in the glass preform for an optical fiber of the example, and (b2) is an enlarged view of b1. (c1) is the schematic diagram which shows the detail of another example of the striae structure in the glass preform | base_material for optical fibers of an Example, (c2) is an enlarged view of c1. (d1) is a schematic diagram showing details of another example of the striae structure in the glass preform for optical fiber of the example, and (d2) is an enlarged view of d1.

The starting material of the present invention is called a starting rod, a target rod, or the like, and is a rod or pipe made of ceramic such as alumina or quartz glass. The glass raw material of the present invention is, for example, high-purity GeCl ₄ and high-purity SiCl ₄ . The flame forming gas of the present invention is a gas in which, for example, O ₂ (oxygen) gas, H ₂ (hydrogen) gas, N ₂ (nitrogen) gas, or the like is mixed.

  Hereinafter, an embodiment of a method for producing a glass fine particle deposit according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a production method for producing a glass fine particle deposit by an external chemical vapor deposition method (OVD method).

  In this manufacturing method, in a reaction vessel (not shown) having an exhaust device (not shown), at least a glass raw material gas and a flame forming gas are supplied to the burner 1, and the oxyhydrogen flame ejected by the burner 1 is used. The soot is generated at the same time, and the generated soot is applied to the outer peripheral surface of the starting material 2 rotating around the axis while the burner 1 is reciprocally traversed along the growth axis direction. Manufacturing method.

  A glass optical fiber preform (not shown) is produced by heating and sintering the glass particulate deposit 3 thus produced. Before drawing the optical fiber glass preform, Then, PA measurement is performed to confirm whether or not a predetermined refractive index profile can be formed in the core equivalent part.

  In the following, the refractive index distribution of a glass preform for optical fiber (hereinafter referred to as “Example”) manufactured from the glass particle deposit 3 manufactured by the manufacturing method according to the present invention, and the glass particles manufactured by the conventional manufacturing method. The refractive index distribution of a glass preform for optical fiber (hereinafter referred to as “comparative example”) manufactured from the deposit is measured by PA measurement, and the result of comparison between the two is described.

The glass base materials for optical fibers of Examples and Comparative Examples are both obtained by the OVD method shown in FIG. 1 using GeCl ₄ and high-purity SiCl ₄ as glass raw materials and O ₂ and H ₂ as flame forming gases. This is a glass preform for an optical fiber produced by producing a glass particulate deposit 3 and heating and sintering the glass particulate deposit 3.

  2A and 2B show striae structures appearing as fluctuations in the relative refractive index difference (Δn) in the optical fiber glass preform manufactured from the glass fine particle deposit 3 manufactured in this way. The results of PA measurement of the glass base material are shown in FIGS. 3 (a) and 3 (b).

  In the manufacturing method of the comparative example, the traverse speed of the starting material 2 at the time of sooting is unified to 1000 mm / min, and the glass mother for optical fiber is formed from the glass fine particle deposit 3 formed by adding Ge so that Δn≈1%. The material is manufactured. Since this glass preform for optical fiber has a constant traverse speed of the starting material 2 at the time of sooting, as shown in FIG. 2 (a), adjacent layers are uniformly arranged with a thickness of 10 μm. The striae of a fixed period have occurred.

  As a result of PA measurement of such a glass preform for optical fiber, it is shown that crushing A occurs at the center of the refractive index distribution as shown in FIG. This crush A causes striae with a period of 10 μm in the glass preform for optical fiber, and the PA measurement laser light incident by this periodic refractive index change is diffracted at the time of PA measurement. It can be judged that it was caused because it was not performed.

  Therefore, the glass particulate deposit 3 manufactured by the manufacturing method of the comparative example causes interference due to diffraction of the incident PA measurement laser beam, and a glass base material for an optical fiber that cannot measure a correct refractive index distribution is manufactured. It is.

  In contrast to the manufacturing method of the comparative example, the manufacturing method of the example is a glass in which the traverse speed is alternately changed between 1200 mm / min and 800 mm / min in a two-layer cycle, and Ge is added so that Δn≈1%. An optical fiber glass preform is produced from the particulate deposit 3. In this optical fiber glass preform, the traverse speed is changed alternately at 1200 mm / min and 800 mm / min in a two-layer cycle, so that adjacent layers are alternately arranged as shown in FIG. It repeats with the thickness of 8um and 12um, and the striae of the period where the thickness of the layer changes every two layers are generated.

  As a result of PA measurement of such a glass preform for optical fiber, it was shown that there was no collapse A in the refractive index distribution as shown in FIG. That is, when the incident beam diameter of the PA measurement laser beam is about 20 μm, the striae period is irregular within the beam diameter, so that interference due to diffraction is less likely to occur, and the refractive index distribution is crushed A. Therefore, it can be judged that the PA measurement was accurately performed.

  4 (a1), (a2), FIG. 5 (b1), (b2), FIG. 6 (c1), (c2), FIG. 7 (d1), and (d2) are the examples 1 to 3 and the comparative example. FIG. 3 schematically shows a striae structure that appears as a change in relative refractive index difference (Δn) in a glass preform for optical fiber, and in either case, the starting material 2 rotates 8 times while the burner 1 traverses 2 times. This shows what kind of striae occur when manufactured with

  FIGS. 4A1 and 4A2 show the striae structure generated in the glass preform for an optical fiber of the comparative example. This glass base material for optical fiber has a constant traverse speed and a constant rotation speed, and is produced by rotating the starting material 2 four times while one soot layer is formed in one traverse. It is manufactured from the body 3.

  FIG. 4 (a1) shows a striae in a range formed by four traverses, and a layer having a thickness of 10 um is formed by one traverse, and four striations due to rotation are repeated for each layer. It is.

  FIG. 4 (a2) shows an enlarged view of the range formed by two traverses, where the traverse speed is constant and four revolutions are performed at a constant speed during one traverse. This striae is repeated eight times at a constant cycle of the same thickness (2.5 um).

  FIGS. 5B1 and 5B2 show the striae structure generated in the optical fiber glass preform of the first embodiment. This glass preform for optical fiber is produced from a glass particulate deposit 3 produced at a constant speed, with two kinds of traverse speeds being changed alternately for each layer, and the rotational speed is the same as in the comparative example. It is.

  FIG. 5 (b1) shows the striae in the range formed by 4 traverses, and the traverse speed is changed at a cycle of 2 layers for each layer. A layer having a thickness of 12 μm is repeated in one traverse, and eight striae are repeated during two traverses.

  FIG. 5 (b2) shows the striae in a range formed by two traverses in an enlarged manner, and the striae caused by rotation is generated 8 times with a constant period of the same thickness (2.5 um). Yes.

  6 (c1) and 6 (c2) show the striae structure generated in the glass preform for optical fiber of the second embodiment. This glass preform for optical fiber is manufactured from a glass particle deposit 3 manufactured by alternately changing two kinds of traverse speeds for each layer and changing the rotational speed between two values during traverse. It is.

  FIG. 6 (c1) shows the striae in the range formed by 4 traverses, and the traverse speed is alternately changed every 2 layers in a cycle of 2 layers. A layer having a thickness of 12 μm is repeated in one traverse, and eight striae are repeated during two traverses.

  FIG. 6 (c2) shows the striae in a range formed by two traverses in an enlarged manner, and the striae caused by rotation are generated so as to be repeated eight times alternately at a thickness of 2 um and 3 um. .

  FIGS. 7D1 and 7D2 show the striae structure generated in the optical fiber glass preform of Example 3. FIG. This optical fiber glass preform is manufactured from a glass particulate deposit 3 manufactured by alternately changing two kinds of traverse speeds for each layer and changing the rotational speed between four values during traverse. It is.

  FIG. 7 (d1) shows the striae of the range formed by 4 traverses, and the traversing speed is alternately changed every two layers at a cycle of 2 layers. A layer having a thickness of 12 μm is repeated in one traverse, and eight striae are repeated during two traverses.

  FIG. 7 (d2) shows an enlarged view of the striae in the range formed by 2 traverses, and the striae due to rotation is 1.5 um, 3.5 um, 2 um, 3 um in thickness, a total of 8 times. It is happening to be repeated.

  Therefore, in the manufacturing methods of Examples 1 to 3, since the thickness of the glass fine particle layer to be deposited is different between adjacent layers by changing the traverse speed of the burner 1, a constant period as in the comparative example is obtained. Periodic changes due to striae are disrupted, and irregular striae can be formed in the optical fiber glass preform. Further, the periodicity can be further broken by changing the rotation period as in the second and third embodiments.

  Therefore, the manufacturing method of the embodiment can prevent the occurrence of interference due to the diffraction phenomenon of incident PA measurement laser light, and can manufacture the glass fine particle deposit 3 capable of performing PA measurement of an accurate refractive index structure.

  In addition, since the optical fiber glass preform manufactured from the glass fine particle deposit 3 manufactured by the manufacturing method of the embodiment can measure an accurate refractive index structure by PA, the characteristic value calculated from the PA measurement result can be obtained. The error can be reduced.

  Examples of the method for changing the traverse speed of the starting material 2 and the rotation speed of the starting material 2 at the time of sooting in Examples 1 to 3 include a method using a binary pseudorandom number sequence other than the M series and the M series.

  The M series is a pseudo random pattern that generates pseudo white noise, and is a simple pattern. That is, when the rotational speed of the starting material 2 and the traverse speed of the burner 1 are changed as in the embodiment, adopting this M series can be easily equipped in equipment for performing sooting work. .

  It should be noted that the present invention is not limited to the illustrated embodiments, and can be implemented with configurations within a range that does not deviate from the contents described in the respective claims.

  For example, by changing the traverse speed of the burner 1 and the rotational speed of the starting material 2, it is limited to a manufacturing method that forms striae with an indefinite period and causes irregular refractive index changes due to the striae with the indefinite period. First, by changing the input amount of the source gas and changing the flow rate of the flame-forming gas, an irregular cycle striae is formed, and irregular refractive index changes are caused by the irregular cycle striae. It may be a manufacturing method (not shown).

  In addition, the traverse speed of the burner 1 and the rotation speed of the starting material 2 are changed according to the M sequence according to other conditions, the rotation speed of the starting material 2 is changed according to a binary pseudorandom number sequence other than the M series, By changing the traverse speed and the rotation speed of the starting material 2 by a finite number of set values of 3 or more, an irregular cycle stria is formed, and irregular refractive index changes due to this irregular cycle striae It is good also as a manufacturing method to produce (not shown).

  Further, the method is not limited to the manufacturing method of the glass fine particle deposit by the external method such as the OVD method, but the MCVD method (internal chemical vapor deposition method), the PCVD method (plasma activated chemical vapor deposition method), etc. It is also possible to adopt a manufacturing method (not shown) in which a glass fine particle deposit is produced by depositing glass fine particles inside the glass tube by an internal method.

  Further, the produced glass fine particle deposit body is not limited to the one that produces the core portion of the optical fiber glass preform, and may be one that produces the jacket portion of the optical fiber glass preform (not shown). ).

    1: Burner 2: Starting material 3: Glass particulate deposit

Claims (10)

While rotating a starting material that rotates or a burner that jets a flame relatively reciprocally traverses along the growth axis direction, the glass raw material gas containing GeCl ₄ and the flame forming gas are heated by the flame to generate glass particles, A method for producing a glass particulate deposit by depositing the glass particulates on the starting material,
The thickness of the glass fine particle layer deposited for each traverse is deposited to be different between adjacent layers, the relative refractive index difference is 0.8% or more, and an irregular period striae is formed. A method for producing a glass particulate deposit.   By varying at least one of the starting material or the traverse speed of the burner, the supply amount of the glass raw material gas, and the supply amount of the flame forming gas, the thicknesses of the glass fine particle layers deposited for each traverse are adjacent to each other. 2. The method for producing a glass particulate deposit according to claim 1, wherein the layers are deposited differently.   3. The method for producing a glass fine particle deposit according to claim 1, wherein the thickness of the glass fine particle deposit layer is regularly changed in a cycle of at least two or more layers.   At least one of the starting material or the traverse speed of the burner, the supply amount of the glass raw material gas, and the supply amount of the flame forming gas is changed between two or more set values, The method for producing a glass fine particle deposit according to claim 2.   The method for producing a glass particulate deposit according to claim 4, wherein the set value is changed according to a binary pseudorandom number sequence.   6. The method for producing a glass particulate deposit according to claim 5, wherein the binary pseudorandom number sequence is an M series.   The method for producing a glass particulate deposit according to any one of claims 1 to 6, further comprising changing the rotational speed of the starting material during traversing of the starting material or the burner. .   The method for producing a glass fine particle deposit according to any one of claims 1 to 7, wherein the glass fine particle deposit is one that synthesizes a core portion or a jacket portion of a glass preform for an optical fiber.   9. An optical fiber glass preform manufactured by the glass fine particle deposit manufactured by the manufacturing method according to claim 1.   An optical fiber comprising the optical fiber preform according to claim 9 drawn.

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