Patent Description:
In general, a quartz glass-based optical fiber is manufactured by drawing an optical fiber preform made of quartz glass. The optical fiber preform is manufactured by, after forming a porous layer by depositing glass particulates on the outer circumference of a target (starting material), vitrifying the porous layer by dehydrating and sintering. Here, the porous layer is formed by an outside vapor deposition (OVD) apparatus or the like.

In the OVD apparatus, a flammable gas, a combustion supporting gas, and a glass material are introduced into a glass-particulate synthesizing burner provided in a reaction chamber, and glass particulates generated by flame hydrolysis reaction are deposited in the radial direction of a rotating target. As a result, a porous layer is formed on the outer circumference of the target, and an optical fiber porous preform (hereinafter also referred to as a porous preform) to be a base of an optical fiber preform is manufactured. When manufacturing this porous preform, it has been known to use, in addition to the glass-particulate synthesizing burner, auxiliary burners that perform heating for sintering both end portions of the porous preform (see Patent Literature <NUM>). Sintering the end portions of the porous preform by using the auxiliary burners makes it possible to suppress cracking (crack) of the deposited porous layer and peeling from the target.

<CIT> discloses a method for producing an optical fiber preform having a large size soot porous body (cf. abstract) and that this method comprises the following steps: a) mounting a rod on the chucks of a movable lathe provided with means to rotate the rod onto its own longitudinal axis, means to traverse the rod along its own longitudinal axis, one or more soot forming burners provided with means to traverse the burner along the longitudinal axis of said rod and supply means to supply reactant gases, and one or more heating means provided towards opposite ends of said rod, wherein the heating means are provided with means to supply oxygen and fuel gases, which in-turn are provided with means to control the flow rate of oxygen and fuel gases and/or means to control the amount of oxygen and fuel gases; b) rotating said rod onto its own longitudinal axis by said means to rotate and traversing said rod along its own longitudinal axis by said means to traverse; and c) directing glass forming soot materials from the soot forming burner to get deposited on the surface of said rod till desired amount of soot particles is deposited on said rod to have soot porous body of desired diameter which is transferred to a sintering furnace wherein the optical fiber preform (cf.

<CIT> discloses a burner for forming fine powder of optical glass (cf. claim <NUM>) and that in the burner wherein the fine powder of optical glass prepared by the chemical reaction of vapor-phase raw material through oxyhydrogen flame is piled on the powder deposit position in the reactor equipped with the exhaust vent, the hood to regulate the extent of flame is set at the outer periphery of the tip of the burner, and the protection member to protect flame from air flow in the reactor is laid at the outside of the hood (cf.

<CIT> discloses a device of producing a preform for optical fibers (cf. abstract) and that a plurality of the clad burners have cylindrical burner hoods at their tips, and a part or the whole of the clad burners is provided with a glass particulate sticking prevention part at the tip of each burner hood (cf.

<CIT> discloses that an apparatus for producing the glass parent material is equipped with a blocking plate which detours the air current supplied from the air supply port to avoid direct contact with the target and leads the current to the air exit (cf.

However, in a vitrification process after manufacturing the porous preform, cracks may occur in the porous preform to be vitrified. The inventor has diligently studied the causes of cracks and found that one of the causes is that the flames of the auxiliary burner are fanned by supply air wind in the reaction chamber of the OVD apparatus when manufacturing the porous preform. The supply air wind is an airflow that is flowed in the reaction chamber so as to discharge surplus glass particulates that have not deposited on the target while being generated in the reaction chamber to the outside of the reaction chamber. When the flames of the auxiliary burner are fanned by this airflow, the end portion of the porous preform is unevenly heated, which may cause insufficient sintering. If the sintering of the porous preform is insufficient, in the subsequent vitrification process, the porous preform may be unable to withstand the stress generated when the porous preform shrinks, and cracks may occur.

The present invention has been made in view of the foregoing, and an objective of the present invention is to provide a manufacturing apparatus and a manufacturing method for an optical fiber porous preform that are capable of sufficiently sintering an end portion of the optical fiber porous preform while suppressing the flames of an auxiliary burner from being fanned and are capable of suppressing the occurrence of cracks in the optical fiber porous preform in a subsequent vitrification process. Solution to Problem.

In order to solve the above disadvantage and to achieve the objective, the present invention provides a manufacturing apparatus for an optical fiber porous preform according to claim <NUM> and a manufacturing method for an optical fiber porous preform according to claim <NUM>. Further embodiments of the present invention are described in the dependent claims.

With the manufacturing apparatus and the manufacturing method for an optical fiber porous preform of the present invention, the airflow guiding unit provided in the circumference of the auxiliary burner can suppress the flames of the auxiliary burner from being greatly fanned, so that it is possible to sufficiently sinter the end portion of the optical fiber porous preform and to suppress the occurrence of cracks in the optical fiber porous preform in the vitrification process that is a post-process.

The following describes an exemplary embodiment of the present invention with reference to the accompanying drawings. The invention, however, is not intended to be limited by the following embodiment. In each of the drawings, identical or corresponding constituent elements are denoted by identical reference signs as appropriate, and redundant explanations are omitted as appropriate. Furthermore, it needs to note that the drawings are schematic and that the relation of dimensions of respective elements and the like may be different from reality. Between the drawings also, portions that the relation of dimensions and the ratios are different from one another may be included.

First, a manufacturing apparatus and a manufacturing method for an optical fiber porous preform according to one embodiment of the present invention will be described. <FIG> illustrates an outside vapor deposition (OVD) apparatus, which is a manufacturing apparatus for an optical fiber porous preform according to this embodiment. <FIG> is an enlarged view of an enclosed portion A in <FIG>.

As illustrated in <FIG>, an OVD apparatus <NUM> includes a reaction chamber <NUM>, a glass-particulate synthesizing burner <NUM>, an auxiliary burner <NUM> on which a wind guard <NUM> is arranged, an auxiliary burner <NUM> on which a wind guard <NUM> is arranged, and a gas supply unit <NUM>.

The reaction chamber <NUM> is configured to be able to carry in and accommodate a target <NUM> and dummy rods <NUM>. In the reaction chamber <NUM>, provided are an air inlet 11a for introducing clean air from the outside or a predetermined air supply unit (not depicted), and an exhaust duct 11b for discharging gas in the reaction chamber <NUM>. As the clean air is introduced into the reaction chamber <NUM> via the air inlet 11a and discharged from the exhaust duct 11b, airflow <NUM> going toward the exhaust duct 11b from the air inlet 11a is generated in the reaction chamber <NUM>. By the airflow <NUM>, the surplus glass particulates floating in the reaction chamber <NUM> during the manufacturing of a porous preform <NUM> can be discharged from the exhaust duct 11b.

The glass-particulate synthesizing burner <NUM>, which is a main burner, is made up of at least a single concentric multi-tube burner for depositing glass particulates on the target <NUM> as a starting material, or for performing sintering. In the glass-particulate synthesizing burner <NUM>, simultaneously introduced from the gas supply unit <NUM> are a main raw material gas such as silicon tetrachloride (SiCl<NUM>), hydrogen (H<NUM>) gas, which is a flammable gas, oxygen (O<NUM>) gas, which is a combustion supporting gas, argon (Ar) gas as a blanketing gas, or the like, for example. The dummy rods <NUM> are portions that are connected to both ends of the target <NUM> and are grasped by grasping units (not depicted) for driving to rotate and driving to elevate the target <NUM>. In the deposition of the glass particulates, a gas composed of vaporized SiCl<NUM> gas, H<NUM> gas, and O<NUM> gas is supplied while being ignited and burned in the glass-particulate synthesizing burner <NUM>. The SiCl<NUM> that is subjected to hydrolysis reaction in the flames is turned into silica particulates and deposited around the target <NUM>. Along with this, while the target <NUM> is being rotated, the glass-particulate synthesizing burner <NUM> is made to repeatedly reciprocate along the longitudinal direction of the target <NUM> (arrows B in <FIG>). As a result, the glass particulates are uniformly deposited on the outer circumference of the target <NUM>, and a porous layer <NUM> in the porous preform <NUM> is formed. The target <NUM> is made up of a portion to be a core when made into an optical fiber, and a portion to be a cladding formed therearound. The porous layer <NUM> turns into a cladding portion that is integrated with a portion to be the cladding of the target <NUM> when made into an optical fiber later.

As illustrated in <FIG>, each of the auxiliary burners <NUM> and <NUM> is provided in the vicinity of the end portion along the longitudinal direction of the target <NUM>. The positions of the auxiliary burners <NUM> and <NUM> are immovable with respect to the end portions of the target <NUM>. This configuration enables the auxiliary burners <NUM> and <NUM> to be able to heat both end portions of the porous preform <NUM> to be manufactured. In the auxiliary burners <NUM> and <NUM>, from a predetermined combustion gas supply unit (not depicted), a flammable gas such as H<NUM> gas and a combustion supporting gas such as O<NUM> gas are introduced, for example. The flammable gas and the combustion supporting gas are ignited and burned in the auxiliary burners <NUM> and <NUM>, and the end portions of the target <NUM> are heated.

<FIG> are respectively a side view and a top view of the wind guards <NUM> and <NUM> in this embodiment. As illustrated in <FIG>, <FIG>, the wind guards <NUM> and <NUM> serving as an airflow guiding unit in this embodiment are respectively provided in the vicinity of the auxiliary burners <NUM> and <NUM>. In the wind guards <NUM> and <NUM>, at least an emission side of the flames is open that the auxiliary burners <NUM> and <NUM> emit. Furthermore, each of the wind guards <NUM> and <NUM> has a shape covering, with respect to the auxiliary burners <NUM> and <NUM>, the side opposite to the emission side of the flames, and lateral sides as viewed from the emission side. Specifically, in this embodiment, the shape of the wind guards <NUM> and <NUM> in a lateral view (see <FIG>) seen from the plane in <FIG> (hereinafter referred to as a lateral surface shape) is in a trapezoidal shape having a tapered portion corresponding to the shape of the end portion of the porous preform <NUM>. Furthermore, the shape of the wind guards <NUM> and <NUM> in <FIG> in top view (see <FIG>) seen from the upper portion (hereinafter referred to as an upper surface shape) is in a U-shape that covers and guards the lateral sides of the auxiliary burners <NUM> and <NUM>. The wind guards <NUM> and <NUM> are made of titanium (Ti) or a Ti alloy, for example. Ti and Ti alloys are preferable, from the viewpoint of being excellent in corrosion resistance and durability, as the material of the wind guards <NUM> and <NUM> that are arranged in the vicinity of the auxiliary burners <NUM> and <NUM>. For the material of the wind guards <NUM> and <NUM>, it is also possible to employ materials such as quartz glass, which is excellent in corrosion resistance and heat resistance and is easy to process.

As illustrated in <FIG>, with respect to the auxiliary burner <NUM>, the wind guard <NUM> is located on the upstream side of the airflow <NUM> generated in the reaction chamber <NUM> and, on the downstream side of the airflow, the open portion of the wind guard <NUM> is located. As a result, it is configured such that the airflow <NUM> does not directly blow against the auxiliary burner <NUM>. Furthermore, as illustrated in <FIG>, as the airflow <NUM> is guided by lateral surfaces 20a of the wind guard <NUM> on the lateral sides of the auxiliary burner <NUM>, the airflow <NUM> can be restrained from going around toward the open portion of the wind guard <NUM>. This configuration prevents the airflow <NUM> from going toward the flames of the auxiliary burner <NUM>. Accordingly, the flames of the auxiliary burner <NUM> can be restrained from being fanned greatly by the airflow <NUM>, and the flames can be stabilized. Thus, it is possible to perform heating of the end portions of the porous preform <NUM> stably and to perform sintering sufficiently. In addition, because the gas flow rate of the glass-particulate synthesizing burner <NUM> is larger as compared with the auxiliary burners <NUM> and <NUM>, the possibility of being fanned greatly by the airflow <NUM> is low.

Next, first to seventh modifications of the wind guard in the embodiment of the present invention will be described.

<FIG> is a side view illustrating a wind guard <NUM> according to a first modification of the present invention. As illustrated in <FIG>, the lateral surface shape of the wind guard <NUM> in the first modification is in a rectangular shape, for example.

<FIG> is a side view illustrating a wind guard <NUM> according to a second modification of the present invention. As illustrated in <FIG>, the lateral surface shape of the wind guard <NUM> in the second modification is a tetragon for which the upper portion has a tapered shape corresponding to the shape of the end portion of the porous preform <NUM> and the side on the porous preform <NUM> side of the wind guard <NUM> has a tapered shape expanding toward the lower portion.

<FIG> is a side view illustrating a wind guard <NUM> according to a third modification of the present invention. As illustrated in <FIG>, the lateral surface shape of the wind guard <NUM> in the third modification has a shape for which the corner of the upper portion in the lateral surface shape of the wind guard <NUM> in the above-described embodiment is rounded.

<FIG> is a top view illustrating a wind guard <NUM> according to a fourth modification of the present invention. As illustrated in <FIG>, the upper surface shape of the wind guard <NUM> in the fourth modification has a C-shape for which the emission side of the flames from the auxiliary burner <NUM> or <NUM> is open and has a shape covering, with respect to the auxiliary burner <NUM> or <NUM>, the side opposite to the emission side, and the lateral sides as viewed from the emission side.

<FIG> is a top view of a wind guard <NUM> according to a fifth modification of the present invention. As illustrated in <FIG>, the upper surface shape of the wind guard <NUM> in the fifth modification has an L-shape for which the emission side of the flames from the auxiliary burner <NUM> or <NUM> is open and has a shape covering, with respect to the auxiliary burner <NUM> or <NUM>, the side opposite to the emission side, and the lateral sides as viewed from the emission side.

<FIG> is a top view of a wind guard <NUM> according to a sixth modification of the present invention. As illustrated in <FIG>, the upper surface shape of the wind guard <NUM> in the sixth modification is in a shape for which, in a shape of an even-numbered polygon, for example, in a hexagonal shape, one side on the emission side of the flames of the auxiliary burner <NUM> or <NUM> is open. As a result, the wind guard <NUM> has a shape covering, with respect to the auxiliary burner <NUM> or <NUM>, the side opposite to the emission side, and the lateral sides as viewed from the emission side.

<FIG> is a top view of a wind guard <NUM> according to a seventh modification of the present invention. As illustrated in <FIG>, the upper surface shape of the wind guard <NUM> in the seventh modification is in a shape for which, in a shape of an odd-numbered polygon, for example, in a pentagonal shape, one side on the emission side of the flames of the auxiliary burner <NUM> or <NUM> is open. As a result, the wind guard <NUM> has a shape covering, with respect to the auxiliary burner <NUM> or <NUM>, the side opposite to the emission side, and the lateral sides as viewed from the emission side.

The lateral surface shape (<FIG>) and the upper surface shape (<FIG>) in the embodiment, the lateral surface shapes by the first to the third modifications (<FIG>), and the upper surface shapes by the fourth to the seventh modifications (<FIG>) in the foregoing can be selected and combined as appropriate. Specifically, the wind guard can be in various shapes, such as a wind guard having the lateral surface shape by the embodiment (see <FIG>) and having the upper surface shape by the fourth modification (see <FIG>), a wind guard having the lateral surface shape by the second modification (see <FIG>) and having the upper surface shape by the seventh modification (see <FIG>), and the like, for example.

The embodiment of the present invention in the foregoing enables the wind guards <NUM> and <NUM> serving as an airflow guiding unit to prevent the airflow <NUM> in the reaction chamber <NUM> from directly blowing against the flames of the auxiliary burner <NUM>, and thus the flames are not greatly fanned by the airflow <NUM> are stabilized, the sintering of the end portions of the porous preform <NUM> can be performed sufficiently. Thus, in the vitrification process performed after manufacturing the porous preform <NUM>, the occurrence of cracks in the porous preform <NUM> can be suppressed.

In the foregoing, the embodiment of the present invention has been explained concretely. However, the present invention is not limited to the above-described embodiment. For example, the numerical values presented in the above-described embodiment are mere examples, and different numerical values may be used as needed.

While, in the above-described embodiment, the example using SiCl<NUM> as the glass material has been illustrated, for the glass material, SiHCl<NUM>, SiHCl<NUM>, and the like may be used, for example, and for Ge raw material as a dopant, GeCl<NUM> may further be used. Moreover, a glass material such as siloxane may be used. Furthermore, as the flammable gas, in addition to H<NUM>, a short-chain hydrocarbon such as CH<NUM>, C<NUM>H<NUM>, C<NUM>H<NUM>, C<NUM>H<NUM>, and the like may be used, for example.

In the above-described embodiment, the glass-particulate synthesizing burner <NUM> has been made to reciprocate along the longitudinal direction of the target <NUM>. However, the glass-particulate synthesizing burner <NUM> and the porous preform <NUM> only need to reciprocate relatively, and the porous preform <NUM> can be made to reciprocate with the glass-particulate synthesizing burner <NUM> standing still.

Furthermore, in the above-described third modification, an example of a shape for which the upper corner is rounded in the lateral surface shape of the wind guard <NUM> by the embodiment has been illustrated. However, it may be a shape for which the upper corner is rounded in the lateral surface shape of the wind guard <NUM> by the first modification or in the lateral surface shape of the wind guard <NUM> by the second modification.

Claim 1:
A manufacturing apparatus for an optical fiber porous preform comprising:
a reaction chamber (<NUM>) having an air inlet (11a) and an exhaust duct (11b);
a gas supply unit (<NUM>) that supplies a raw material gas and a flammable gas;
at least one main burner (<NUM>), provided in the reaction chamber (<NUM>), that ignites and burns the flammable gas and the raw material gas to synthesize glass particles and supplies the synthesized glass particles to a starting material (<NUM>) while being moved relative to the starting material (<NUM>) to deposit the particulates generated by reaction of the gases on an outer circumference of the starting material (<NUM>) to form a porous preform (<NUM>); and
at least one auxiliary burner (<NUM>) that heats an end portion of the porous preform, wherein a position of the auxiliary burner (<NUM>) with respect to the starting material (<NUM>) is immovable,
characterized in that
the manufacturing apparatus further comprises an airflow guiding unit (<NUM>) that prevents an air flow from the air inlet (11a) to the exhaust duct (11b) from directly blowing against the auxiliary burner (<NUM>), the airflow guiding unit (<NUM>) being provided in a vicinity of the auxiliary burner (<NUM>),
the airflow guiding unit (<NUM>) has a shape for which an emission side of flames that the auxiliary burner (<NUM>) emits is open and a shape covering, with respect to the auxiliary burner (<NUM>), a side opposite to the emission side, and lateral sides as viewed from the emission side,
an open portion of the airflow guiding unit is located on an exhaust duct (11b) side of an airflow generated in the reaction chamber (<NUM>).