JP5941430B2 - Method for producing porous glass preform for optical fiber - Google Patents

Description

  The present invention relates to a transparent vitrification method for a porous preform for optical fibers having through holes, and a transparent glass preform for optical fibers using the same.

With the technical progress of optical fibers, optical fibers having a special structure have been realized (see Patent Documents 1 to 11). An optical fiber having the special structure is shown in FIG. (A) Hole assist fiber, (b) photonic crystal fiber, (c) multi-core fiber, and (P) panda fiber (PANDA (Polarization-maintaining AND Absorption-) reducing) fiber). In these optical fibers, the process of manufacturing the optical fiber preform is complicated compared to other general optical fibers, and is composed of a plurality of processing steps that are very laborious and costly.

  That is, the hole assist fiber is manufactured as follows. First, as shown in FIG. 22, a porous mother is formed by forming a core 102 and a clad 103 covering the outer periphery of a seed rod 101 of quartz glass by a VAD method (Vapor phase Axial Deposition method). Material 104 is produced. Next, as shown in FIG. 23, the porous base material 104 is fed into the quartz glass reaction vessel 106 heated at the high temperature electric furnace 105 at a predetermined speed in the direction indicated by the arrow 107, and at the same time, into the quartz glass reaction vessel 106. While flowing a mixed gas of He gas and chlorine gas from the direction of arrow 108-1, the gas is exhausted in the direction of arrow 108-2. As a result, the porous preform 104 is made into a transparent glass, and an optical fiber preform 114 (hereinafter referred to as a transparent glass preform 114) in which the outer periphery of the core 112 as shown in FIG. Is obtained).

  Thereafter, in order to open a through-hole in the transparent glass base material 114, as shown in FIG. 25, the upper and lower ends of the transparent glass base material 114 are cut with a glass cutting machine to form a flat upper surface 115 and a flat lower surface. 116 is formed (FIG. 25B). Thereafter, a plurality of through holes 117 extending in the longitudinal direction of the transparent glass base material 114 are opened in the transparent clad 113 of the transparent glass base material 114 by drilling or cutting with ultrasonic waves (FIG. 25). (C)), an optical fiber preform 114 with a through hole is manufactured. In this method, a through-hole is formed using a drill or ultrasonically cut, so that cleaning, dehydration, drying, and heating steps must be performed after the through-hole is formed. After passing through the above steps, a hole assist fiber preform is completed, and then the preform is drawn to obtain a hole assist fiber.

  The photonic crystal type fiber of FIG. 21B is also manufactured by the same method as the hole assist fiber. First, a porous base material 104 is manufactured by forming a core 102 and a clad 103 covering the outer periphery of a seed rod 101 made of quartz glass. Next, an optical fiber preform 114 obtained by converting the porous preform 104 into a transparent glass using the method shown in FIG. 25 is obtained. Thereafter, an optical fiber preform 114 having holes (through holes) 117 is obtained using the method of FIGS. 21A to 21C in the same manner as the hole assist fiber preform. Even in this method, cleaning, dehydration, drying, and heating processes must be performed after the through holes are formed. Thereafter, the base material is drawn to obtain a photonic crystal type fiber. As another method for producing a photonic crystal fiber, a method of drawing a bundle of a plurality of glass capillaries and integrating them is also used.

In the multi-core fiber shown in FIG. 21 (c), a porous preform made of SiO ₂ rod is first manufactured by the VAD method described above. Next, the porous base material is made into transparent glass by the above-described method, and flattening is performed by cutting the upper surface and the lower surface of the base material. Thereafter, a plurality of through-holes 117 extending in the longitudinal direction at a predetermined interval are formed in the base material, as described above, by using a drill or by cutting with an ultrasonic wave to form a core insertion through-hole. The optical fiber glass base material (glass molded body with through holes) is produced. After that, the core base materials 117-1 to 117-7 manufactured in another step are inserted into the through holes through the steps of washing, dehydrating, drying and heating the base material, and fused to form a multi-core. Use fiber base material. A multi-core fiber is manufactured by drawing the base material.

According to Non-Patent Document 1, the panda fiber shown in FIG. 21 (d) also produces a porous preform having a core and a clad by the VAD method in the same manner as described above, and thereafter, the porous preform is made into a transparent glass. Do. Then, the upper and lower surfaces of the transparent glass base material are cut and flattened, and then two through-holes extending in the longitudinal direction at predetermined intervals in the clad 113 surrounding the core 112 of the base material are drilled. Or by cutting with ultrasonic waves. As a result, a glass preform for optical fiber (a glass molded body with a through hole) having a glass rod insertion through hole serving as a stress applying portion is manufactured. Then, after passing through the optical fiber preform cleaning, dehydration, drying, and heating steps, the stress applying portion made of SiO ₂ glass added with B ₂ O ₃ manufactured in another step in the through hole. Glass rods 118-1 and 118-2 are inserted and subjected to high-temperature heat treatment to fuse and integrate the base material and the rod. In this manner, the target panda fiber preform is manufactured. Thereafter, the panda fiber preform is drawn to obtain a panda fiber.

JP 2003-040637 A Japanese Patent Laid-Open No. 2003-342031 Japanese Patent Laid-Open No. 2003-342032 JP 2004-339004 A JP 2005-263576 A JP 2006-044950 A JP 2006-069871 A JP 2007-072251 JP 2008-310034 A JP 2009-149470 JP 2010-173917

Arai, et al .: Polarization-maintaining optical fiber, Furukawa Electric Times, Vol. 109, pp.5-10, January 2002

  Thus, all of the above optical fibers are complicated and very laborious and costly in the manufacturing process of the optical fiber preform (manufacture of porous preform, transparent vitrification of the preform, preform) Flattening by cutting the upper surface and lower surface of the metal, forming a through-hole by cutting with a drill or ultrasonically, then cleaning, dehydrating, drying, heating process of the base material, and subsequent drawing process of the base material ). In particular, since a through hole is formed in a transparent glass-made optical fiber preform in a later step, moisture and impurities are always mixed in the through hole. In order to remove moisture, it must be removed by heating at a high temperature while flowing He gas and chlorine gas over a long period of time, but part of the moisture in the through holes diffuses into the vitrified core and cladding, Since it has penetrated into OH groups, it has been difficult to get out of the optical fiber preform, causing an increase in optical loss.

  In addition, a through hole for inserting a core provided in the transparent glass base material, a through hole for lowering the refractive index in the cladding, a through hole for realizing a photonic crystal structure, and a glass rod serving as a stress applying portion Unless the inner diameter of the through hole for insertion is slightly smaller than the outer diameter of the glass rod to be inserted, the shrinkage rate of the transparent glass base material is higher than the shrinkage rate of the glass rod due to high temperature heating. Since it is small, a gap is generated between the through hole and the glass rod to be inserted, and scattering loss is induced. However, in reality, it is difficult to manufacture by controlling the dimensions of the through hole and the glass rod with high accuracy. In addition, there are also problems such as the inner surface roughness of the through hole being large, the roundness and straightness of the through hole being poor, and low scattering loss by inserting and fusing the glass rod into the through hole with good adhesion. It was difficult to realize the optical fiber.

  In order to realize a long optical fiber, it is desirable to use a base material that is as long as possible. However, in the conventional method of forming a through hole using a drill, a plurality of through holes are precisely mechanically opened in the longitudinal direction of a long optical fiber base material (first base material) having a length of 50 cm or more, It is difficult to polish the inner surfaces of these through holes. This is because it is extremely difficult to manufacture a drill with a length of 50 cm or more with good dimensional accuracy, straightness and roundness, and the drill hole is drilled through the base material while rotating the drill. This is because as the length becomes longer, rotation unevenness is more likely to occur, and when the straightness and roundness of the drill are poor, the dimensional accuracy of the through hole becomes extremely poor. After all, conventionally, the length of the base material is shortened and a through hole is formed with a short drill, and the outer diameter of the base material is increased instead.

  However, when the outer diameter of the preform is increased, it is necessary to use a high-temperature electric furnace equipped with a large-diameter core tube in the drawing process of the optical fiber preform after forming the through hole. It is difficult to use such a high-temperature electric furnace under the present circumstances. Eventually, before drawing, the optical fiber preform must be stretched to reduce the outer diameter. It was also difficult to realize a long optical fiber with a single optical fiber preform. In addition, since the end face of the optical fiber preform manufactured by the VAD method has a conical shape, the upper and lower surfaces of the preform are cut into a polished flat surface when opening the through hole. There must be. Since this cutting and polishing work takes a lot of time, the manufacturing cost is high. Moreover, even if the upper surface and the lower surface of the base material are flat, it has been difficult to successfully open the through hole with high dimensional accuracy.

Furthermore, in order to manufacture a multi-core fiber, an important core preform for propagating light must be inserted into the through hole. Moreover, in order to manufacture a panda fiber, a glass rod serving as a stress applying portion must be inserted into the through hole.
In order to insert a core base material and a glass rod into a plurality of mechanically opened through holes and bring them into close contact with each other, the through holes must be formed with good straightness and roundness. In particular, in the case of a long optical fiber, the long core base material and the glass rod must be inserted into the long through hole, and the through hole is formed with higher straightness and higher roundness. There is a need. In addition, the inner surface of the through-hole that has been mechanically opened has a large surface roughness, and moisture and impurities adhere to it, so as to reduce the surface roughness and remove moisture and impurities, the polishing process of the inner surface of the through-hole, The cleaning process, dehydration, and heating process must be performed carefully. Also, after inserting the core preform or glass rod into the through hole, to eliminate the gap between the through hole and the core preform, or the through hole and the glass rod, to make a solid optical fiber preform A fusing process of heating at a high temperature must be performed. In particular, in the case of a panda fiber, when the fiber is bent with a small bending radius, the surface roughness in the through hole causes a large scattering loss. Therefore, after the through hole is mechanically opened, the inner surface of the through hole is polished, cleaned, and dehydrated. The heating process must be done carefully and thoroughly. In order to eliminate the gap between the through hole and the glass rod after inserting the glass rod for forming the stress applying portion, a fusion process for heating to a higher temperature must be performed. These multiple processes require significant equipment and costs. In addition, much time is required for the polishing process, the cleaning process, the dehydrating process, and the fusing process of the inner surface of the through-hole so as not to add a light loss factor. Even in such a case, the residue of OH group in the optical fiber preform in the cleaning step causes a problem of a large increase in loss.

  The next problem is the cause of light loss during each process (cause of scattering loss due to the roughness of the inner surface of the through hole, cause of absorption loss due to adhesion of impurities during the process of forming the through hole on the inner surface of the through hole, There is an incentive to absorption loss due to adhesion of impurities to the outer periphery of the core rod and the outer periphery of the stress application portion, and so on, so that the optical loss increases at the stage of the optical fiber. Furthermore, as mentioned above, in order to open a through-hole with a drill or ultrasonic waves in a long base material of 50 cm or longer, the upper surface or the lower surface of the base material must be cut and polished so as to be flat. Moreover, even if the upper surface or the lower surface is flat, it is not easy to drill through holes with high straightness and roundness, good surface smoothness, and high dimensional accuracy from the upper surface side or the lower surface side with a drill or ultrasonic waves. It is not. After drilling, the inner surface of the through hole is polished with a polishing agent, chemically etched, de-OH group treatment, etc. to increase the dimensional accuracy of the through hole or reduce the roughness of the inner surface. However, it is very difficult to polish the inner surface with a small hole diameter, it is difficult to achieve a good inner surface by etching, and it is difficult to reduce the loss. It takes a lot of work. In short, it is difficult to open through holes with high dimensional accuracy, small surface roughness, good straightness and roundness in the longitudinal direction of a long optical fiber preform, and as a result it is long with low scattering and low absorption loss. It is difficult to manufacture optical fiber.

  In addition, the core diameter of each optical fiber preform of the hole assist fiber, photonic crystal fiber, multi-core fiber, and panda fiber manufactured by the VAD method, the outer diameter of the stress applying portion, and the shape in the longitudinal direction thereof There is also a problem that it is difficult to control accurately. As described above, the conventional optical fiber preforms of hole assist fiber, photonic crystal fiber, multi-core fiber, and panda fiber have many problems in terms of scattering loss, surface roughness, and dimensional accuracy. In addition, since the production method is extremely low, the price of the manufactured optical fiber has become very expensive. In addition, the outer diameter, the core diameter, and the ratio between the outer diameter and the core diameter, the core interval, the hole diameter, the hole interval, the position of the stress applying part, the position of those stresses, and other important structural parameters for the optical fiber are highly dimensioned. It was difficult to control with precision and reproducibility was low. Further, it has been difficult to manufacture the long optical fiber preforms.

  Therefore, an object of the present invention is to efficiently remove OH groups contained in a transparent glass preform for optical fiber obtained by converting the porous glass preform into a transparent glass, and to reduce the relative refractive index difference of the fiber. To make it even bigger.

  The present invention has been made in order to achieve the above-mentioned object. A through-hole that is difficult to manufacture by a conventional method is intentionally provided in a porous glass base material, and the porous This is a transparent glass base material in which OH groups and impurities in the glass base material are efficiently removed. As a result, the relative refractive index difference of the fiber can be further increased and the numerical aperture can be increased, so that the bending loss can be bent with a small bending radius, which is not obtained by the conventional method, and the light to the core is further reduced. A fiber with good confinement can be realized.

Specifically, the method for producing a transparent glass preform for an optical fiber according to the first embodiment of the present invention,
A porous glass base material having a through-hole extending in the longitudinal direction,
This is a method for producing a transparent glass preform for optical fibers by converting the porous glass preform into a transparent glass by heating at a high temperature while flowing a mixed gas of helium gas and chlorine gas through the through-hole.

Moreover, the method of manufacturing the transparent glass preform for optical fiber according to the second embodiment of the present invention,
Place the metal rod in the container,
Clad layer mixed liquid containing curable resin and SiO ₂ particles, and a curing agent for solidifying the mixed liquid by self-curing reaction is injected into the container,
After the mixed liquid for the cladding layer is solidified, the container and the metal rod are detached from the solidified body to form a porous glass base material having a through hole,
This is a method for producing a transparent glass preform for optical fibers by converting the porous glass preform into a transparent glass by heating at a high temperature while flowing a mixed gas of helium gas and chlorine gas through the through-hole.

In the production method of the second aspect, wherein as the high temperature heated by the porous glass preform is vitrified to contract 80% to 90%, and curable resin and SiO2 particles in the clad layer mixture It is preferable that it is blended.

  In both the first and second methods, the high temperature heating is preferably performed by moving the porous glass base material at a constant speed in a high temperature electric furnace.

  In this case, the through hole is preferably composed of a core hole located in the center of the porous glass base material and a plurality of pores having a diameter smaller than that of the core hole located around the core hole.

  Further, when a quartz glass tube is attached to one end portion or both end portions of the porous glass base material so as to surround the through hole, and the mixed gas flows through the quartz glass tube to the through hole, The mixed gas can surely flow through the holes.

  It is also a good method to arrange a heat-resistant protective tube in a high-temperature electric furnace and heat the porous base material at a high temperature in a state where the protective tube is in a chlorine gas atmosphere.

  Furthermore, it is preferable to control the flow rate of the mixed gas flowing through the through hole of the porous glass base material when heated at a high temperature.

  Further, when the porous glass base material has a plurality of through holes, a glass rod having a refractive index higher than the refractive index of the porous glass base material is formed in a part of the plurality of through holes during high-temperature heating. It is preferable to insert and flow a mixed gas of helium gas and chlorine gas into the remaining through holes at a constant flow rate.

Furthermore, the porous glass base material has a through hole located in the center of the porous glass base material, two through holes located on both sides thereof, and a through hole located in another porous glass base material. In the case of having a hole, during high-temperature heating, a glass rod having a refractive index higher than the refractive index of the porous glass base material is inserted into the central through-hole and the through-holes on both sides of the glass rod are A SiO ₂ glass rod added with B having a refractive index lower than that of the porous glass base material is inserted, and a mixed gas of helium gas and chlorine gas is allowed to flow from one of the other through holes toward the other. It is good to make it.

Optical fiber transparent glass preform according to the present invention is a transparent glass preform for an optical fiber produced by the production method of Zureka to be above.

  In this case, the transparent glass preform for optical fiber preferably has a plurality of through holes, and a core glass through which an optical signal propagates is inserted into a part of the through holes.

Furthermore, it is preferable that a SiO ₂ glass layer to which F is added is provided on the outer periphery of the core glass.

Furthermore, as most of the outer periphery of the SiO ₂ glass layer added the F is covered with voids, the SiO ₂ glass layer obtained by adding the F has a structure in contact with the inner surface with at least three of the through hole Is preferred.

  The present invention relates to various types of transparent glass preforms for fibers such as transparent glass preforms for fibers having various shapes such as circular and polygonal shapes, and transparent glass preforms for fibers having through-holes having a circular or polygonal cross-sectional shape. Applicable to materials.

  The present invention sinters the porous glass base material by heating the porous glass base material having a through-hole extending in the longitudinal direction at a high temperature while flowing a mixed gas of helium gas and chlorine gas through the through-hole, This is a method for producing a transparent glass preform for optical fiber by forming into transparent glass.

  Conventionally, since the porous glass base material has no through-holes, there is a method for removing moisture and impurities in the porous glass base material by flowing helium gas and chlorine gas around the outer periphery of the porous glass base material. In this method, helium gas and chlorine gas enter the porous glass base material from the outer peripheral side, and then return to the outer peripheral side of the porous glass base material. Since the water and impurities were discharged, the water and impurities could not be removed sufficiently.

  On the other hand, in the production method of the present invention, the mixed gas is flowed into the through hole to make the inside of the through hole have a positive pressure, and the mixed gas is flowed from the through hole toward the outer peripheral side of the porous glass base material. Since the moisture and impurities in the porous glass can be diffused and released, the moisture and impurities can be easily removed. For this reason, a transparent glass preform for optical fiber having a low OH group and high purity can be produced.

In this case, a metal rod is placed in the container, and a mixed solution for a cladding layer containing a curable resin and SiO ₂ particles and a curing agent for solidifying the mixed solution by a self-curing reaction are injected into the container. Then, after the mixed liquid for the clad layer is solidified, the container and the metal rod are detached from the solidified body to form a porous glass base material having a through hole. A porous glass base material can be formed without going through a polishing process. For this reason, mixing of the loss factor from the outside with respect to a porous glass base material can be suppressed few.

  Further, a metal rod having a high roundness and mirror-polished and having a length of at least 50 cm or more (can be realized even at 1000 cm) in the longitudinal direction, an upper lid having a flat lower surface, and a lower lid having a flat upper surface A through hole having a high roundness can be formed by arranging straightly in a state of being pulled at both ends in the center of a container having a sealable structure. At this time, the porous glass base material and the through hole can be manufactured with high dimensional accuracy by increasing the mechanical accuracy of the container and the metal rod.

  In the above method, just by changing the shape of the container, the outer shape of the porous glass preform can be made into an arbitrary shape such as a circle or a polygon. A desired shape such as a square or a polygon can be easily obtained. For this reason, it can be used for various applications such as optical communication, medical use, and processing, and there has been no conventional performance, such as high numerical aperture (NA) characteristics, large capacity transmission, and low bending loss characteristics. Thus, an optical fiber preform having a plurality of excellent characteristics can be realized.

  Furthermore, in the above method, the shape of the through hole can be changed to a desired shape such as a circle or a polygon simply by changing the shape of the metal rod disposed in the container. When the shape of the through hole is circular, or a polygon such as a square or hexagon, a metal bar with high dimensional accuracy, small surface roughness, and excellent roundness and straightness is easily available. By using it, a porous base material having through holes with high dimensional accuracy can be realized. Furthermore, the through-hole can be composed of a core hole located at the center of the porous glass base material and a plurality of pores having a smaller diameter than the core hole located around the core hole.

  Further, by increasing the size of the container (in the case of a circular container, its inner diameter and length (height)), a porous glass base material having a large diameter and a long length (at least 50 cm in the longitudinal direction) can be obtained. It can be manufactured easily, whereby a long optical fiber can be obtained.

Furthermore, since the SiO ₂ cladding layer is formed by contacting and solidifying the liquid mixture for the cladding layer in the liquid state on the outer periphery of the metal rod, the outer peripheral surface of the metal rod and the SiO ₂ cladding layer are in close contact, and A uniform component SiO ₂ cladding layer can be formed on the outer periphery of the metal rod. Here, the outer peripheral surface of the metal rod is mirror-polished so that the surface roughness is 0.2 μm or less, preferably 0.01 μm to 0.03 μm, and high straightness (0.1 mm / 1000 mm), If a stainless steel rod with a high roundness (0.05 mm / 1000 mm) and a length of at least 50 cm is used, the rod is placed straight in the container while being pulled at both ends. When the curing agent is injected into the container and the mixed liquid for the clad layer is solidified by a self-curing reaction, the surface roughness of the inner surface of the through hole (hole) can be reduced to at least 3 μm or less in the longitudinal direction. Both straightness and roundness can be made excellent. As for the container, the inner surface is 0.2μm or less surface roughness is mirror polished, preferably by using a container of 0.03μm stainless steel long from 0.01 [mu] m (at least 50cm above), SiO ₂ The surface roughness of the outer peripheral surface of the cladding layer can be made extremely smooth with 3 μm or less.

  Conventionally, a through-hole is mechanically opened in a porous glass preform made into a transparent glass, and then the inner surface of the through-hole is subjected to polishing using a polishing agent, chemical etching, de-OH group treatment, and the like. It was. In this method, de-OH grouping and high purity in the vitrified base material are extremely difficult, and it is the actual situation that the loss of the optical fiber in the 1.3 μm band and 1.55 μm band cannot be kept low. If the porous glass base material obtained by the above-described method is used, these problems can be solved.

Moreover, as transparent glass to contract the porous glass preform 80% to 90% by the high temperature heating and a curing resin and SiO2 particles in the clad layer mixture is less shrinkage Therefore, cracks and cracks can be reduced in the porous glass base material during sintering. Further, a transparent glass rod having an outer diameter taking into account the inner diameter of the pores after being shrunk due to the transparent vitrification of the porous glass preform is inserted into a part of the through hole (hole) of the porous glass preform. If sintered, the transparent glass rod can be uniformly integrated with good adhesion within the pores of the transparent glass preform for optical fiber.

  When the porous glass base material is heated at high temperature while being moved into the high temperature electric furnace at a constant speed, the mixed gas can be poured into the through holes of the porous glass base material at a constant speed. Transparent vitrification of the base material can be progressed uniformly.

  In addition, if a heat-resistant protective tube is disposed in the high-temperature electric furnace and the porous glass base material is heated and sintered at a high temperature in a state where the protective tube is in a chlorine gas atmosphere, the outer periphery of the porous glass base material Is protected with a heat-resistant protective tube and chlorine gas, so that a transparent glass preform for optical fiber with very few impurities both inside and outside can be manufactured. Here, a glassy carbon tube, an alumina tube, a quartz glass tube or the like can be used as the heat-resistant protective tube.

  Also, a quartz glass tube is attached to one end or both ends of the porous glass base so as to surround the through hole, and a mixed gas of helium gas and chlorine gas is allowed to flow into the through hole through the quartz glass tube. Then, since the mixed gas can be reliably guided and flowed into the through hole, moisture and impurities contained in the porous glass base material can be efficiently diffused and released. Moreover, the quartz glass tube can be used as a holding tube for the base material when the transparent glass base material for optical fibers is inserted into the high-temperature electric furnace in the drawing process, and as a guide tube for drawing.

  In addition, when the flow rate of the mixed gas flowing through the through hole of the porous glass base material is controlled when heating at a high temperature, the inner diameter of the through hole is made uniform in the length direction during the sintering of the porous glass. In addition, the roundness and straightness of the through hole can be kept uniform. As a result, the outer diameter of the base material is also kept uniform.

The porous glass base material has a plurality of through holes, and a glass rod having a refractive index higher than a refractive index of the porous glass base material in a part of the plurality of through holes during the high temperature heating. Inserting and flowing a mixed gas of helium gas and chlorine gas into the remaining through-holes at a constant flow rate, the glass rod is fused in the through-holes with good adhesion to produce a transparent glass preform for optical fibers. it can. In this case, if a glass rod having a diameter considering the shrinkage rate due to sintering of the porous glass base material is inserted into the through hole, the glass rod can be fused into the through hole with better adhesion. it can. As the glass rod having a refractive index higher than that of the quartz glass, an SiO ₂ glass rod to which at least one additive for increasing the refractive index such as GeO _2, P ₂ O ₅ , or TiO ₂ is added is used.

The porous glass base material has a through hole located in the center of the porous glass base material, two through holes located on both sides thereof, and a through hole located in another porous glass base material. During high temperature heating, a glass rod having a refractive index higher than that of the porous glass base material is inserted into the central through hole, and the porous glass mother is inserted into the through holes on both sides of the glass rod. When a SiO ₂ glass rod added with B having a refractive index lower than that of the material is inserted and a mixed gas of helium gas and chlorine gas is allowed to flow from one of the other through holes to the other, A panda fiber preform with dimensional accuracy, low scattering loss, and low bending loss can be manufactured.

  In addition, according to the manufacturing method of the present invention, characteristic hole assist fibers, multi-core fibers, panda fibers, photonic crystal fibers, and photonic crystal fibers having a high NA and low bending loss and having through holes are obtained. be able to.

  Since the transparent glass preform for optical fiber according to the present invention is manufactured by the manufacturing method described above, it can have excellent characteristics as described above.

  The transparent glass preform for optical fiber has a plurality of through holes, and by inserting a core glass through which an optical signal propagates into a part of the through holes, optical communication, medical use, processing use, illumination use, Transparent glass base material for optical fiber that can be used in various applications such as for light guides. In terms of performance, several excellent properties such as high NA characteristics, large capacity transmission, and low bending loss characteristics that did not exist in the past It becomes a transparent glass base material for optical fibers having

When a SiO ₂ glass layer added with F is provided on the outer periphery of the core glass, a transparent glass base material for optical fiber having a high NA characteristic can be obtained. Further, the outer periphery of the SiO ₂ glass layer added with F can be obtained. If a structure in which the SiO ₂ glass layer added with F is in contact with the inner surface of the through-hole at least at three places is adopted so that most of the glass is covered with voids, a transparent glass preform for optical fiber with higher NA can be obtained. Can be realized.

The left view (a), the front view (b), and the right view (c) of the porous preform for the hole assist fiber according to the first embodiment of the present invention. The left side view (a), front view (b), and right side view (c) of the transparent glass preform for hole-assisted optical fiber according to the first embodiment of the present invention. It is a figure for demonstrating the method to manufacture a porous preform | base_material by die cutting using a metal container and a metal rod, the front view (a) which has arrange | positioned the metal rod in a metal container, AA sectional drawing (b) ). The figure which shows the state in which the quartz glass tube is fusion-connected to one end of the porous base material, and the figure (b) showing the state in which the quartz glass tube is fusion-connected to one end of the transparent glass base material. Explanatory drawing of the process of transparentizing a porous base material. The left view (a), the front view (b), and the right view (c) of the transparent glass preform | base_material for hole assist fibers which concern on 2nd Example of this invention. Sectional view (a) of a porous preform for a multi-core fiber according to a third embodiment of the present invention and a transparent glass preform for a multi-core fiber obtained by sintering with a core glass rod inserted into the porous preform. Sectional drawing (b). Sectional view (a) of a porous preform for a multi-core fiber according to a fourth embodiment of the present invention and a transparent glass for a high NA multi-core fiber obtained by sintering with a core glass rod inserted into the porous preform. Sectional drawing (b) of a base material. Sectional view (a) of a porous preform for panda fibers according to a fifth embodiment of the present invention and a transparent glass preform for panda fibers obtained by sintering with a glass rod inserted into the porous preform. Sectional drawing (b). Sectional drawing of the transparent glass preform | base_material for hole assist fiber for high NA which concerns on 6th Example of this invention. Sectional drawing of the transparent glass preform | base_material for hole assist fiber for high NA which concerns on 7th Example of this invention. Sectional drawing of the transparent glass preform | base_material for multi-core fibers for high NA which concerns on 8th Example of this invention. Sectional drawing of the transparent glass preform | base_material for hole assist fiber for super-high NA which concerns on 9th Example of this invention. It is a figure which shows the other example of the optical fiber base material which turned into the transparent glass of this invention, (a) is a transparent glass base material for hole assist fibers, (b) is a transparent glass base material for multi-core fibers, (c) Is a transparent glass base material for panda fiber, (d) is a transparent glass base material for photonic crystal fiber, (e) is a transparent glass base material for multi-core fiber, and (f) is a transparent glass for hole assist fiber for ultra-high NA. Sectional drawing of a base material. Sectional drawing of the porous preform | base_material of the state which attached the quartz glass tube which concerns on 10th Example of this invention. Sectional drawing of the porous preform | base_material of the state which attached the quartz glass tube which concerns on 11th Example of this invention. The figure which shows the apparatus which melt-connects a quartz glass tube to the porous preform | base_material which concerns on 12th Example of this invention. The figure which shows the method of transparent vitrification of the porous preform | base_material which concerns on 13th Example of this invention. The figure which shows the method of transparent vitrification of the porous preform | base_material which concerns on 14th Example of this invention. The figure which shows the method of transparent vitrification of the porous preform | base_material which concerns on 15th Example of this invention. The figure which shows the method of drawing the transparent glass base material which concerns on 16th Example of this invention. Sectional drawing of the conventional optical fiber preform | base_material is shown, (a) is the transparent glass preform | base_material for hole assist fibers, (b) is the transparent glass preform | base_material for photonic crystal fibers, (c) is the transparent glass preform | base_material for multi-core fibers (D) is a cross-sectional view of a transparent glass preform for panda fiber. The front view (a) and sectional drawing (b) of the conventional porous preform for optical fibers. Explanatory drawing of the method of making the conventional porous preform | base_material transparent. The front view (a) and sectional drawing (b) of the transparent glass preform | base_material for the conventional optical fiber. The Example of the method of transparentizing the porous base material of this invention. The figure which shows the process of forming a through-hole (hole) in the conventional transparent glass base material.

  Several embodiments of the present invention will be described below with reference to the drawings.

A first embodiment in which the present invention is applied to a porous preform and a transparent glass preform for hole assist fibers will be described. FIG. 1A shows the configuration of the porous base material 50 according to this embodiment, and FIG. 1B shows the configuration of the transparent glass base material 60. The transparent glass base material 60 is obtained by sintering the porous base material 50 into a transparent glass. (A) of each figure is a left view, (b) is a front view, (c) is a right view.
The porous base material 50 and the transparent glass base material 60 both reduce the equivalent refractive index of the cladding 1 made of SiO ₂ , the core glass insertion hole 2 provided in the center of the cladding 1, and the cladding 1. In order to make this happen, it has a hole 3 and a hole 4 provided around the hole 2. Both end surfaces 5 and 6 of the porous base material 50 and the transparent glass base material 60 are flat surfaces, and have the same cross-sectional shape from one end surface to the other end surface.

As shown in FIG. 2, the porous base material 50 is manufactured by die cutting using a long metal container and a long metal rod. The metal container 11 is a stainless steel cylindrical container having an inner diameter D ₀ of 152 mm and a length L ₀ of 60 cm, and an upper cover and a lower cover (both not shown) are mounted on the upper and lower surfaces, respectively. ing. The metal container 11 has a halved structure so that the porous base material 50 can be taken out from the inside. The inner surface of the metal container 11, the lower surface of the upper lid, and the upper surface of the lower lid are all mirror-polished so that the surface roughness is about 0.01 μm to 0.03 μm. The inner diameter tolerance of the metal container 11 is + 0.08 / −0.010 mm.

  The metal rod is composed of one metal rod 12 for forming the hole 2, eight metal rods 13 for forming the hole 3, and eight metal rods 14 for forming the hole 4. . Each of them has a length of about 1000 mm and has an outer diameter corresponding to the inner diameter of each hole. The outer peripheral surfaces of the metal rods 12 to 14 are mirror-polished so that the surface roughness is about 0.01 μm to 0.03 μm. In addition, the metal rods 12 to 14 have a straightness of 0.06 / 1000 mm, an outer diameter tolerance of + 0 / −0.00 mm, and a roundness of 5 μm / 2000 mm, dimensional accuracy of the outer diameter, surface roughness, and straightness. It consists of a metal rod with excellent roundness. Since the pores 2 to 4 of the porous base material 50 have a circular cross section, a metal rod having a circular cross section was used, but the cross sectional shape of the pores 2 to 4 was a polygon (square, hexagon, etc.) In this case, the cross-sectional shape of the metal rod is also a polygon (square, hexagon, etc.).

The porous base material 50 is manufactured by the following method.
First, the metal rods 12, 13, and 14 are respectively arranged at predetermined positions inside the metal container 11. The metal rods 12 to 14 are arranged in a state of being pulled straight at both ends of the metal container 11. Thereby, the straightness of the metal rods 12 to 14 is further improved.

Subsequently, a mixed solution 16 of a quartz glass solution containing a curable resin and a curing agent is poured into the metal container 11.
In this example, a silica glass solution in which silica powder having a particle size of 2 μm or less (preferably 1 μm or less) was added to a mixture of a dispersant (tetramethylammonium hydroxide solution) and distilled water was used. Denacol EX512 (Nagase ChemteX Corporation), which is a liquid resin, was used as the curable resin. Triethylenetetramine was used as the curing agent. The compounding ratio (wt%) of the quartz glass solution containing the curable resin was 87% silica powder, 21.2% distilled water, 2.7% dispersant, and 10.1% curable resin. By increasing the amount of silica powder, without cracking or crack during sintering, low shrinkage Kusuru (i.e., suppress the amount of shrinkage) can. In order to keep the shrinkage amount small, the blending amount of the silica powder can be increased to about 90%.

  Next, after the quartz glass solution is solidified by a self-curing reaction, the metal rods 12 to 14 and the mold container 11 are detached from the solidified body and dried. Thereby, the porous preform | base_material 50 which has the void | holes 2-4 is obtained. The porous base material 50 obtained in this way is a smooth base material whose upper and lower surfaces are flat, and whose upper, lower and outer peripheral surfaces have small surface roughness. Further, the surface roughness of the inner surfaces of the holes 2 to 4 is small, and the base material is excellent in straightness and roundness.

The porous base material 50 obtained by the above method is sintered and made into a transparent crow by the following method.
First, as shown in FIG. 3A, the lower end of the quartz glass tube 21 is fused and connected to the upper end of the porous base material 50. The inner diameter of the quartz glass tube 21 is substantially the same as the outer diameter of the porous base material 50, and a small-diameter quartz glass tube 23 is attached to the inside thereof. The quartz glass tube 23 is fixed to the upper end of the quartz glass tube 21, and the lower end of the quartz glass tube 23 is located slightly above the lower end of the quartz glass tube 21. Accordingly, when the quartz glass tube 21 is fused and connected to the porous base material 50, the lower end portion of the quartz glass tube 23 is separated from the upper end portion of the porous base material 50.

Subsequently, as shown in FIG. 4, the protective tube 25 (glassy carbon tube, alumina furnace core tube, quartz glass tube) is heated to a temperature of 1600 ° C. to 1750 ° C. in the high temperature electric furnace 26, The porous preform 50 is inserted together with the quartz glass tubes 21 and 23 from the top to the bottom at a predetermined speed (set to a value selected from the range of 50 mm / h to 120 mm / h), and sintering is performed. . The quartz glass tube 21 can be used as a guide tube for inserting the porous base material 50.
When the porous base material 50 is inserted, a mixed gas of He gas and chlorine gas (chlorine gas partial pressure is set to a value selected from the range of 0.03 mmHg to 60 mmHg) is caused to flow through the small-diameter quartz glass tube 23. As a result, the mixed gas passes through the pores 2 to 4 of the porous base material 50 and enters the protective tube 25, and is discharged from the outlet 27 of the protective tube 25. Further, an inert gas (preferably He gas, total flow rate 5 L / min to 8 L / min) is introduced into the protective tube 25 from the inlet 28. The inert gas introduced into the protective tube 25 passes around the porous base material 50 and is discharged from the outlet 27 of the protective tube 25 as indicated by an arrow F5. In FIG. 4, the flow of the mixed gas is indicated by arrows F1 to F3, and the flow of the inert gas is indicated by arrows F4 to F5.

  As a result, the mixed gas flows inside the porous base material 50, and sintering is performed in a state where the outer periphery is covered with the inert gas (He gas). Therefore, the diffusion rate of OH groups and impurities in the porous base material 50 is increased, and these OH groups and impurities move from the inside of the porous base material 50 to the outer periphery together with the mixed gas, and are discharged into the inert gas. The As a result, the OH group and impurities are removed from the transparent glass base material 60 obtained by sintering the porous base material 50 and converting it into a transparent glass.

  In this embodiment, a porous base material 50 having an outer diameter of 25 mm and a length of 540 mm, an insertion speed of 90 mm / h, a temperature of the high-temperature electric furnace 26 at 1650 ° C., and a total He gas flow rate into the high-temperature electric furnace 26 Was sintered at a partial pressure of chlorine of 40 mm / Hg of the mixed gas of He gas and chlorine gas put into the porous base material 50 and reduced to about 82% of the porous base material 50. A glass base material 60 was obtained. Further, the straightness of the holes 2 to 4 of the transparent glass base material 60 was less than 0.1 / 500 mm, and the roundness was less than 1.6 μm / 500 mm.

  On the other hand, when the temperature of the high-temperature electric furnace 26 was 1600 ° C., a part of the sintered base material was insufficiently transparent. When the chlorine gas partial pressure was 0.2 mmHg or less, the absorption loss due to OH groups in the obtained base material increased. Further, when the flow rate of He gas flowing from the inlet 28 in the direction indicated by the arrow F3 was 2 L / min or less, an opaque portion was generated near the center of the base material. Such a phenomenon is thought to be because the temperature of the outer periphery of the base material has increased, and the sintering has progressed before the vicinity of the center.

  Thus, in this embodiment, it is possible to obtain the transparent glass base material 60 having excellent straightness and roundness of the holes 2 to 4. Moreover, the transparent glass base material 60 with few impurities, such as CH group and OH group, can be obtained.

  In this embodiment, the porous base material 50 inserted into the protective tube 25 is sintered while being moved from the top to the bottom. However, the porous base material 50 is lowered to the lowermost portion in the protective tube 25. Alternatively, sintering may be performed while moving from the bottom to the top. When sintering is performed in this manner, the sintering progresses efficiently from the vicinity of the fused portion between the quartz glass tube 21 and the porous base material 50, so that transparent vitrification can be easily performed. Further, it is also preferable that impurities and moisture contained in the porous base material 50 are difficult to enter the base material again after being diffused and released to the outside of the porous base material 50.

FIG. 5 shows a transparent vitrification base material for hole assist fiber according to a second embodiment of the present invention. This transparent vitrified base material 61 is obtained by sintering into a transparent glass state with the core glass rod 7 inserted into the pores 2 of the porous base material 50 shown in FIG. 1A. The core glass rod 7 is made of glass in which about 20 mol% of GeO ₂ is added to SiO ₂ .

As shown in the first embodiment, the porous preform 50 by sintering the transparent glass preform 60 shrinks to about 82%. Therefore, the core glass rod 7 having an outer diameter almost equal to the inner diameter of the air hole 2 after being contracted to about 82% is inserted. Accordingly, the core glass rod 7 is inserted into the air holes 2 with a slight gap, but when the quartz glass tube 21 is fused to the porous base material 50, the porous base material 50 is contracted at that portion. And the core glass rod can be tightly fixed to the fused portion of the base material. As a result, the core glass rod 7 does not fall out of the air holes 2 when the porous preform 50 is inserted into the protective tube 25.

FIGS. 6A and 6B are left side views of a porous preform and a transparent glass preform for a multi-core fiber according to a third embodiment of the present invention. The porous preform 52 has seven holes 2-1 to 2-7 of the core glass layer necessity in the cladding 2 made of SiO _2. The porous base material 52 is also formed by die cutting using a metal container and a metal rod, like the porous base material 50 for the hole assist fiber.

The transparent glass base material 62 is sintered in a state in which the core glass rods 7-1 to 7-7 are inserted into the seven holes 2-1 to 2-7 of the porous base material 52, respectively. It was obtained by converting. The core glass rod is made of glass obtained by adding about 20 mol% of GeO ₂ to SiO ₂ . Also in this embodiment, a core glass rod having an outer diameter corresponding to about 82% of the inner diameter of the hole is used.

7A and 7B show a porous preform 53 and a transparent glass preform 63 for a multi-core fiber according to a fourth embodiment of the present invention. The porous base material 53 includes holes 2-1 to 2-7 for core insertion in the SiO ₂ cladding 1 and a plurality of pores provided around the holes 2-1 to 2-7. 8. This porous preform 53 is also formed by die cutting using a metal container and a metal rod, like the porous preform 50 for the hole assist fiber.

The transparent glass base material 63 is sintered in a state in which the core glass rods 7-1 to 7-7 are inserted into the seven holes 2-1 to 2-7 of the porous base material 53, respectively. It was obtained by converting. Also in this embodiment, the core glass rod is made of glass obtained by adding about 20 mol% of GeO ₂ to SiO ₂ and has an outer diameter corresponding to about 82% of the inner diameter of the pores.

  The pore 8 is provided in order to lower the equivalent refractive index of the clad 1 and is provided in the vicinity of the hole in a range not in contact with the holes 2-1 to 2-7, thereby transmitting an optical signal in the core. More tightly confined and transmitted. Thus, also in the present embodiment, a plurality of pores and pores can be easily provided at the stage of manufacturing the porous base material 53.

FIGS. 8A and 8B show a panda fiber porous base material 54 and a transparent glass base material 64 with high NA according to the fifth embodiment of the present invention. The porous base material 54 includes a core glass rod insertion hole 2 provided at the center of the SiO ₂ clad 1, holes 2-1 and 2-2 provided on both sides thereof, and a peripheral portion. It has a plurality of pores 8 provided. The pore 8 is provided in order to lower the equivalent refractive index of the clad 1. As a result, a high NA panda fiber can be realized for the first time, and a fiber with a low loss increase can be obtained even when bent with a small bending radius.

In the transparent glass base material 64, the core glass rod 7 is inserted into the hole 2 of the porous base material 54, and the glass rods 7-1 and 7-2 are inserted into the hole 2-1 and the hole 2-2. It was obtained by sintering to glass. The core glass rod 7 is made of glass in which about 20 mol% of GeO ₂ is added to SiO ₂ and has an outer diameter corresponding to about 82% of the inner diameter of the air holes 2. The glass rods 7-1 and 7-2 are made of SiO ₂ glass to which B (boron) is added, and have outer diameters corresponding to about 82% of the inner diameters of the holes 2-1 and 2-2. Things are used.

FIG. 9 shows a transparent glass preform 65 for hole-assisted fiber aiming at ultra-high NA according to the sixth embodiment of the present invention. Similar to Example 1, this transparent glass base material 65 is obtained by sintering a porous glass base material (not shown) into a transparent glass, and is provided at the center of the SiO ₂ clad 1 having a circular outer shape and the center thereof. The through hole 31 has a rectangular cross section, the core 32 has a circular cross section disposed in the through hole 31, and the SiO ₂ layer 33 to which F is added to cover the outer periphery of the core 31. The SiO ₂ layer 33 to which F is added is arranged so that the outer periphery thereof is in contact with the inner peripheral surface of the through hole 31 at four locations. As a result, the SiO ₂ layer 33 to which F is added and the SiO ₂ cladding 1 There are voids between them. Further, a plurality of holes 3 for lowering the equivalent refractive index of the cladding 2 are provided in the cladding 1 around the through hole 31, thereby enabling the ultra-high NA hole assist fiber to be manufactured at low cost. This can be realized without an unnecessary increase in loss accompanying the formation of the holes 3. In the conventional method, in order to obtain the hole assist fiber in which the hole 3 is formed, the hole is mechanically formed with a drill after obtaining the transparent glass base material. For this reason, providing a large number of holes increases the loss such as the scattering loss of the fiber, so it has been difficult to realize.

In the optical fiber formed from the transparent glass preform 65 of the present embodiment, the outer periphery of the core 32 is covered with the SiO ₂ layer 10 to which F is added, so that the optical signal is confined to the core 32 and F is further added. The presence of a gap between the outer periphery of the SiO ₂ layer 10 and the SiO ₂ cladding 1 makes it possible to confine the optical signal more strongly in the core 7. In addition, since the voids 3 are provided in the clad 2 to lower the equivalent refractive index of the clad 1, the optical signal into the core 7 of the optical fiber can be strongly confined. Furthermore, since there are holes and voids in the SiO ₂ cladding 1, an increase in loss can be suppressed even when the fiber is bent with a small bending radius, and a fiber that is extremely resistant to bending can be realized.

FIG. 10 shows another transparent glass preform 66 for hole-assisted fiber aiming at ultra-high NA according to the seventh embodiment of the present invention. Similar to the sixth embodiment, the porous glass base material of the transparent glass base material 66 is made into a transparent glass by sintering, and the outer shape of the SiO ₂ cladding 1 having a circular shape and the cross-sectional shape provided at the center thereof are as follows. It is composed of a circular through hole 31, a high refractive index rectangular core 32 disposed in the through hole 31, and a SiO ₂ layer 33 to which F is added to cover the outer periphery of the core 32. The SiO ₂ layer 33 to which F is added is arranged so that the outer periphery thereof is in contact with the inner peripheral surface of the through hole 31 at four locations. As a result, the SiO ₂ layer 33 to which F is added and the SiO ₂ cladding 1 There are voids between them. In addition, a plurality of holes 3 for lowering the equivalent refractive index of the cladding 2 are provided in the cladding 1 around the through hole 31.

In the optical fiber formed from the transparent glass preform 66 of the present example, since the outer periphery of the core 32 is covered with the SiO ₂ layer 10 to which F is added, the optical signal is confined to the core 32 and F is further added. The presence of a gap between the outer periphery of the SiO ₂ layer 10 and the SiO ₂ cladding 1 makes it possible to confine the optical signal more strongly in the core 7. In addition, since the voids 3 are provided in the cladding 1 to lower the equivalent refractive index of the cladding 1, the optical signal into the core 7 of the optical fiber can be strongly confined. Furthermore, since there are holes and voids in the SiO ₂ cladding 1, an increase in loss can be suppressed even when the fiber is bent with a small bending radius, and a fiber that is extremely resistant to bending can be realized.

FIG. 11 shows a transparent glass preform 67 for multi-core fiber aiming at high NA (NA> 0.5) according to the eighth embodiment of the present invention. The transparent glass preform 67 is obtained by realizing the multi-core fiber structures by providing seven structure around the core of the transparent glass preform 65 showing the SiO ₂ cladding 1 in FIG. Therefore, even in the multi-core fiber formed from the transparent glass preform 67, it is possible to realize a fiber in which an optical signal can be strongly confined and transmitted in each core 7 and interference between the cores is extremely reduced. Can do. Therefore, it is possible to transmit information with a very large capacity and a very high speed with a single fiber. Moreover, it can connect with the fiber connected to the both ends of a multi-core fiber with a low connection loss. Note that the number of cores 32 provided in the clad 1 is not limited to seven, and for example, about 13 may be provided. Further, as in the transparent glass base material 65 shown in FIG. 9, a plurality of holes for lowering the equivalent refractive index of the cladding 1 may be provided around the through hole.

  FIG. 12 shows a transparent glass preform 68 for a hole-assisted fiber aimed at achieving a very high NA (NA:> 0.6) according to the ninth embodiment of the present invention. This is the one in which the outer shape of the transparent glass base material 65 for the hole assist fiber shown in FIG. 9 is changed from a circle to an octagon, and the other configurations are the same. By making the outer shape octagonal, the fibers can be easily connected to each other, and the fibers can be stably fixed when the fibers are laid. In the case where the outer shape is an octagon, when the transparent glass base material 68 is drawn to form a fiber, the corner is likely to be round, but the fiber may have a round corner.

  The present invention can be applied to a porous preform and a transparent glass preform for optical fibers other than the above-described embodiments, and an example is shown in FIG. The figure (a) is the porous preform | base_material 69 for void | hole assist fibers which made the bending loss small, and the figure (b) is the porous preform | base_material 70 for multi-core fibers which strengthened the confinement of the light in a core. (c) is a panda fiber porous base material 71 in which confinement of light in the core is strengthened and bending loss is reduced, and FIG. (d) is a porous base material 72 for photonic crystal type fiber. e) is a porous base material 73 for multi-core fibers that facilitates laying and connection between fibers, and FIG. 5 (f) is a porous base material 74 for hole-assisted fibers that facilitates laying and connection between fibers. . Since these porous base materials all have through-holes, a mixed gas of helium gas and chlorine gas can flow through the through-holes during sintering, so OH groups and CH groups, impurities, etc. It can be discharged efficiently.

FIG. 14 shows another embodiment of a quartz glass tube attached to a porous base material during sintering. As shown in FIG. 14, a quartz glass tube 21 and a quartz glass tube 211 are attached to an upper end portion and a lower end portion of the porous base material 50, respectively.
The quartz glass tube 211 is effective for directing the mixed gas sent from the quartz glass tube 21 through the pores 2 to 4 of the porous base material 50 to the outlet 27 (see FIG. 4) of the protective tube 25. Thus, deformation of the holes 2 to 4 can be suppressed. Further, the quartz glass tube 211 can be used when the transparent glass base material is drawn and drawn while being inserted into the high-temperature electric furnace.

  FIG. 15 shows another embodiment of a quartz glass tube attached to a porous base material during sintering. Unlike the quartz glass tube 21 shown in the first embodiment, this quartz glass tube 212 does not have a double tube structure. Even when such a quartz glass tube 212 is used, a mixed gas can flow into the porous base material 50 during sintering.

  FIG. 16 shows an apparatus for fusion-bonding quartz glass tubes to both ends of a porous base material 50. This chucks the quartz glass tubes 21 and 211 on the glass lathe 800 and inserts and holds both ends of the porous base material 50 in the quartz glass tubes 21 and 212. Then, an inert gas is allowed to flow from one quartz glass tube 21 side through a rotary joint 81 and a pipe 82 as indicated by an arrow 83, and the inert gas is discharged to the opposite quartz glass tube 211 side while quartz glass is discharged. The pipe 211 and the porous base material 50 are fused by flowing oxygen 85 and hydrogen 86 through an oxyhydrogen burner 84 to generate a flame 87. Both quartz glass tubes are rotated in the direction of the arrow on a lathe.

  FIG. 17 shows a method for forming a porous base material into transparent glass. In this embodiment, a protective tube 29 is used instead of the protective tube 25. This protective tube 29 is different from the protective tube 25 shown in the first embodiment in that the inlets 28 for introducing the inert gas are provided in two upper and lower stages. By increasing the number of the inlets 28 in this way, the inside of the protective tube 29 can be kept in an inert gas atmosphere as much as possible. Thereby, the temperature of the outer periphery of the porous base material 50 can be lowered, and sintering can be performed from the center of the porous base material 50.

  FIG. 18 shows another method for forming a porous base material into transparent glass. This embodiment is different from the first embodiment in that the porous base material 50 is inserted into the protective tube 25 in a state where the outer periphery of the porous base material 50 is covered with the quartz glass tube 213. When heated and sintered in the high-temperature electric furnace 26, usually, sintering from the outer periphery of the base material is likely to proceed, and the center part of the base material is often not sufficiently sintered. On the other hand, by covering the outer periphery of the porous preform 50 with the quartz glass tube 213, it becomes easy to sinter from the center of the porous preform 50 by radiant heat, and a transparent optical fiber preform can be obtained. .

FIG. 19 shows still another method for forming a porous base material into a transparent glass. This embodiment is different from the first embodiment in that the porous base material 50 is sintered in a high-temperature electric furnace 26 while being pulled up from the lower side of the protective tube 25 to the upper side at a predetermined speed to be converted into a transparent glass.
An inert gas (preferably He gas) flows from the lower inlet 28 into the protective tube 25 and exhausts from the upper outlet 27. The mixed gas of He gas and chlorine gas fed into the small-diameter quartz glass tube 23 passes through the holes in the porous base material 50 and is discharged from the outlet 27 of the protective tube 25.

FIG. 20 is a diagram illustrating a method of drawing a transparent glass base material. In this method, the transparent glass preform 60 is drawn from the lower end side of the preform 60 while being fed into the high-temperature electric furnace 31 at a predetermined speed. The optical fiber 33 after drawing is wound around a drum 35. When drawing, an inert gas (preferably He gas, or Ar, N ₂ gas may be used) is fed into the small-diameter quartz glass tube 23 as indicated by an arrow F6 and is caused to flow into the transparent glass base material 60. The transparent glass base material 60 is always set to a desired pressure as compared with the external pressure. Thereby, a fixed pressure is applied to the transparent glass base material 60, and as a result, the shape of the holes 2 to 4 of the transparent glass base material 60 can be controlled. Applying a certain pressure is extremely important for keeping the shape of the air holes 2 to 4 in the transparent glass fiber 60 uniform.
In addition, while drawing the said transparent glass base material 60, as shown by the arrow F7, an inert gas is poured on the outer periphery of this base material 60. FIG. Further, an inert gas is allowed to flow through the lower end side of the high-temperature electric furnace 31 as indicated by an arrow F8 and is discharged together with the inert gas as indicated by an arrow F9.

  The transparent glass preform obtained by the method of the present invention is drawn while being fed into a high-temperature electric furnace at a predetermined speed to obtain an optical fiber having an outer diameter of 125 μm, a core diameter of 10 μm, and a length of about 10 km. Scattering loss was measured. In the present invention, an optical fiber having a maximum length of about 800 km can be obtained by drawing a transparent glass preform. Here, loss (scattering loss, absorption loss, absorption loss due to impurities such as OH groups) is obtained. For the purpose of measurement, the length was about 10 km.

As a result, the loss was 0.27 dB / km at a wavelength of 1.55 μm. When the breakdown of the loss was examined, the Rayleigh scattering loss was 0.16 dB / km, the scattering loss due to structural irregularity was 0.03 dB / km, the intrinsic absorption in the infrared part and the ultraviolet part and the absorption loss due to impurities were 0.08 dB / km. km. The loss at the wavelength of 1.39 μm is significantly lower than the loss (about 8 dB / km) of the fiber obtained by drawing the base material manufactured by the conventional method, and is reduced to 2 dB / km. I found out. As described above, the scattering loss due to the structural irregularity is extremely low, and the absorption loss due to the impurities is low. The result is that the interface between the glass rod inserted into the hole 2 and the SiO ₂ cladding layer is uniform, and The result confirmed that the deOH group was efficiently performed by He gas and chlorine gas flowing in the pores. Such a low OH group cannot be realized with a base material in which He gas and chlorine gas are flown through a transparent glass base material as in the prior art. In addition, it has confirmed that there was no loss by CH group and Si-H group.

  Thus, in the present Example, the favorable result which was difficult to implement | achieve with the conventional transparent vitrification method and the sol gel method which flow an inert gas only to the outer periphery of a base material was able to be obtained. It can also be seen that the base metal outer dimensions can be easily controlled by the dimensions of the metal container.

In addition, this invention is not limited to the said Example.
In the above embodiment, after the porous base material (solidified body) is dried, the core glass rod is inserted into the pores of the porous base material and heated in this state to obtain a transparent glass base material. However, after obtaining a transparent glass base material by converting the porous base material into a transparent glass, a core glass rod is inserted into the pores of the transparent glass base material, and the transparent glass base material is heated from the outer periphery to a high temperature. By heating, the core glass rod may be fused in the transparent glass base material.

By the way, the above-mentioned sol-gel method is one of the methods for producing an optical fiber preform. In the sol-gel method, an optical fiber preform is manufactured by pouring a liquid source material (sol) into a mold container, forming a gel state, drying, sintering, and vitrifying. It is similar to the method for manufacturing the porous base material described in the first embodiment and the like in that the liquid raw material is injected into the mold container.
However, in the sol-gel method, quartz glass is generated by a hydrolysis reaction with an organic oxysilane (for example, tetraethoxysilane) solution and pure water, and it is difficult to control the shape. In contrast, in this example, as described above, since a quartz glass solution containing a curable resin is used, the shape can be controlled extremely easily compared to the sol-gel method, and cracks and cracks are generated. There is almost no.

  The sol-gel method produces quartz glass by a hydrolysis reaction, and the production rate of the quartz glass is low. Furthermore, in the sol-gel method, the difference in shrinkage between the radial direction and the axial direction of the optical fiber preform due to sintering is greatly different from 30% to 60%, so that cracks and cracks are likely to occur. Therefore, it is difficult to manufacture a large optical fiber preform. Furthermore, in the sol-gel method, cracks and cracks are likely to occur unless a hydrolysis reaction is caused over a long period of one day or more, and cracks and cracks occur unless drying and high-temperature heating are performed over a long period of 10 days or longer. Happens.

On the other hand, in this example, silica powder is put into a mixed liquid of a dispersant and distilled water to solidify, and the solidified body is dried and heated. Therefore, the shrinkage in the radial and axial directions during drying and heating is reduced. Since the difference is small and the shrinkage rate is as small as about 18% (= (100−82 ) % ) , there is almost no occurrence of cracks or cracks. Therefore, it can be solidified in a time of 1/10 or less of the sol-gel method, and drying can be performed in a time of 1/2 or less of the sol-gel method and at a low temperature of 50 ° C to 120 ° C. Note that, when the above solution is vacuum degassed into the metal container, bubbles are hardly mixed in, and voids are hardly formed in the solidified glass base material.

  In the sol-gel method, tetramethyl orthosilicate (TMOS) or tetraethyl orthosilicate (TEOS) is usually reacted with water to form silica gel. However, this silica gel contains a hydroxy group (OH group). In addition, CH groups and Si—H groups are also included in the silica gel as in the case of OH groups. Since it is difficult to remove OH groups, CH groups, and Si-H groups in the process from drying and sintering to vitrification of silica gel, optical fiber preforms obtained by the sol-gel method are OH groups, CH groups, Si An optical fiber including a —H group and made from such an optical fiber preform has a large loss in a wavelength band used for optical communication.

  On the other hand, in this example, sintering is performed while flowing He gas and chlorine gas from the pores of the porous base material toward the outer periphery, so that the glass is formed into transparent glass. Things can be easily evaporated and removed. For this reason, it is possible to obtain an optical fiber that hardly contains CH groups, Si—H groups, and OH groups in the transparent glass base material and suppresses optical loss due to these.

As described above, since the shrinkage due to vitrification of the solidified body is about 18% (= (100-82 ) % ) , the outer diameter of the obtained glass preform for optical fiber is 125 mm, the length is 533 mm, The inner diameter of the holes was 10 mm. Further, the variation in the outer shape of the glass preform for optical fiber was 0.5% or less, and the surface roughness was 0.5 μm or less. Low profile change, the uniformity of the contour in other words, the inner surface was produced glass preform for an optical fiber using a stainless steel container of 0.03μm from 0.01μm mirror polished with surface roughness It was obtained by this. The uniformity of the outer shape of the optical fiber glass preform is extremely effective in realizing an optical fiber having a uniform shape. Also, the small surface roughness is extremely effective in improving the mechanical strength of the optical fiber. Furthermore, the structural parameters (core diameter, outer diameter, etc.) of the optical fiber can be set accurately. That is, in the optical fiber glass molded body of the present example, both the radial direction and the axial direction are slightly reduced almost uniformly, so that the structural parameters can be easily designed.

You may use what added the high refractive index additive and rare earth elements to the center part of the glass rod for cores. As the rare earth element, Er, Nd, Pr, Ce, Yb, or the like can be used. Also, an additive for increasing the refractive index of SiO ₂ such as Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , TiO _{2 is} added as a co-additive material other than rare earth elements in the central portion of the core glass rod. You may do it. Thus, by adding rare earth elements, Al ₂ O ₃ , GeO ₂ , and P ₂ O ₅ , an optical fiber preform capable of realizing an optical amplifier or a laser can be obtained.

The material of the metal container, the metal rod, and the metal tube may be a material such as Au, Ni, or Cu other than stainless steel.
The blending ratio of the glass raw material solution of SiO ₂ containing the curable resin is limited to the above-described examples (silica powder 87%, distilled water 21.2%, dispersant 2.7%, curable resin 10.1%). Is not to be done. The present invention is characterized in that the amount of silica powder is overwhelmingly increased. This amount may be 80% or more, and can be increased to about 92%.

  The inner diameter Do and the length Lo of the metal container 7 are not limited to the above values, and the inner diameter Do can be about 30 mm to 300 mm, and the length Lo can be about 20 mm to 1000 mm. The longer the inner diameter Do and the length Lo, the longer the optical fiber can be realized.

The diameter Dc of the core hole and the core glass rod can be about 10 mm to about 100 mm. Further, the number of holes provided around the central portion of any glass base material for hole assist fiber, photonic crystal fiber, multi-core fiber, and panda fiber is not limited, and ranges from 4 to 30 You can choose from. The inner diameter of the holes is preferably in the range of 0.5 μm to 5 μm. The interval between the holes can be selected from a range of 1 μm to 6 μm.
The outer diameter dimension of the glass molded body for optical fibers of the present invention is not particularly limited.

1 ... core holes 2 ... pore inner surface 3 ... SiO ₂ cladding layer 4 ... SiO ₂ cladding layer of the outer peripheral portion 5 ... metal rod 6 ... curable mixture of resin laden silica glass solution and the curing agent 7 ... metal container 8 ... inner surface 9 ... thin holes 10 ... glass rod 12 ... SiO ₂ glass thin layer for small diameter metal rods 11 ... core metal container

Claims (9)

Place the metal rod in the container,
Clad layer mixed liquid containing curable resin and SiO ₂ particles, and a curing agent for solidifying the mixed liquid by self-curing reaction is injected into the container,
After the mixed liquid for the cladding layer is solidified, the container and the metal rod are detached from the solidified body to form a porous glass base material having a through hole,
A method for producing a transparent glass preform for an optical fiber by converting the porous glass preform into a transparent glass by heating at a high temperature while flowing a mixed gas of helium gas and chlorine gas through the through hole. The curable resin and SiO ₂ particles are blended in the mixed liquid for the clad layer so that the porous glass base material shrinks to 80% to 90% by the high temperature heating and becomes transparent glass. The manufacturing method of the transparent glass preform | base_material for optical fibers of Claim 1 . The method for producing a transparent glass preform for optical fiber according to claim 1 or 2 , wherein the high temperature heating is performed by moving the porous glass preform at a constant speed in a high temperature electric furnace. The said through-hole is comprised from the core hole located in the center of a porous glass base material, and several pores smaller in diameter than the said core hole located in the circumference | surroundings. The manufacturing method of the transparent glass preform | base_material for optical fibers in any one of 1-3 . 2. A quartz glass tube is attached to one end of the porous glass base material or to both ends so as to surround the through hole, and the mixed gas is allowed to flow through the quartz glass tube into the through hole. the method for producing a transparent glass preform for optical fiber according to any one of 1-4. The heat-resistant protective tube is placed into the high-temperature electric furnace, the protective tube while the chlorine gas atmosphere, according to any one of claims 1 to 5, characterized in that a high temperature heating the porous glass preform Of manufacturing a transparent glass preform for optical fiber. The method for producing a transparent glass preform for an optical fiber according to any one of claims 1 to 6 , wherein the flow rate of the mixed gas flowing through the through hole of the porous glass preform is controlled at high temperature. . The porous glass base material has a plurality of through-holes;
During the high temperature heating, a glass rod having a refractive index higher than the refractive index of the porous glass base material is inserted into a part of the plurality of through holes, and helium gas and chlorine gas are mixed into the remaining through holes. The method for producing a transparent glass preform for optical fiber according to any one of claims 1 to 7 , wherein gas is flowed at a constant flow rate. The porous glass base material has a through hole located in the center of the porous glass base material, two through holes located on both sides thereof, and a through hole located in another porous glass base material. And
During the high temperature heating, a glass rod having a refractive index higher than the refractive index of the porous glass base material is inserted into the central through hole, and the porous glass base material is inserted into the through holes on both sides of the glass rod. A SiO ₂ glass rod added with B having a refractive index lower than the refractive index is inserted, and a mixed gas of helium gas and chlorine gas is allowed to flow from one of the other through holes toward the other. Item 8. A method for producing a transparent glass preform for optical fiber according to any one of Items 1 to 7 .

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