JP2005289766A - Preform for optical element, optical element manufactured using the same, and method for manufacturing preform for optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a preform for an optical fiber with small possibility of occurrence of defects on the interface between a core and a clad even for a wide range of combination of core/clad materials, solving problems possessed by every manufacturing method of an optical fiber having optical functionality. <P>SOLUTION: This preform glass for an optical fiber is such that the interface between a core part to be the core of the optical fiber and a clad part to be the clad thereof is composed of three or more planes parallel to the direction to be the optical axis of the optical fiber. The sectional shape of the interface between the core part and the clad part is preferably a polygon such as a quadrangle or a hexagon, while the sectional shape of the outer periphery of the clad part is preferably a circle or a polygon such as a quadrangle or a hexagon. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical element used in the field of optical communication, and more particularly to an optical fiber type functional element and a manufacturing method thereof.

  In recent years, the proportion of optical communication systems using optical fibers in information communication is large. For general information transmission, silica glass fibers are usually used, but various other optical functions are provided in the form of optical fibers. Examples are optical fiber amplifiers and optical fiber diffraction gratings. Therefore, various methods have been devised as a method for producing an optical fiber made of glass containing various components other than silica glass or a preform thereof (glass base material for an optical element).

  Among them, typical methods for obtaining a preform having a structure in which the refractive index changes stepwise (so-called step index type) include a gas phase synthesis method such as the VAD method, a built-in casting method, and a rod-in-tube method. Is known. It is actually used.

  Vapor phase synthesis is widely used in the manufacture of silica glass fibers. In this case, silicon tetrachloride is mixed with the burning oxyhydrogen burner flame to change to silicon dioxide, and the silicon dioxide fine particles are deposited to form a base material.

  In the build-in casting method, after the melt that forms the cladding is cast into a cylindrical mold, the melt in the central part is poured out before the melt in the central part is solidified, and the core is formed in the cavity. This is a method of casting a melt (see Non-Patent Document 1).

The rod-in-tube method is a method in which a pipe (tube) is formed by drilling a cladding glass lump, and a core glass rod (rod) that has been processed into a size that fits the hole is inserted.
T.A. T. Miyashita, 1 other person, IEEE Journal of Quantum Electronics, (USA), IEEE, 1982, QE Vol. 18, No. 10, p. 1432-1450

  However, in the gas phase synthesis method, the raw material of the component constituting the preform needs to be a gas or a liquid that can be easily vaporized, and as a result, the chemical composition of the preform falls within a very narrow range. Limited. In addition, the manufacturing equipment is very large and the turning is not effective, so it is not suitable for high-mix low-volume production. Therefore, it is not necessarily suitable for the production of optical fibers having optical functionality other than silica glass fibers.

  In the built-in casting method, when a melt that constitutes a clad is cast into a cylindrical mold, the melt is solidified from a portion in contact with the mold. That is, the cavity formed by pouring the melt of the central portion before the melt of the central portion is solidified has a shape that narrows toward the bottom of the mold. Therefore, the preform in which the melt that constitutes the core is cast into the hollow portion can only be obtained with a core dimension that decreases toward the bottom of the mold, and the core dimension is not uniform. There is a point.

  Furthermore, the rod-in-tube method manufactures a pipe from a glass lump for cladding, but it is difficult to finish the inner surface of the pipe to a smooth and clean surface. There is a disadvantage that defects are easily generated.

  The present invention has been made paying attention to such problems in the prior art, and the object is to produce defects at the interface between the core and the clad even in a wide range of core / clad material combinations. An object of the present invention is to provide a base material for an optical element with a low possibility.

  The optical element base material of the present invention includes a core and a clad having a hollow columnar structure in which a core part having a columnar structure can be inserted, having a core and a clad closely surrounding the outer periphery thereof and having a refractive index smaller than that of the core. The inner surface facing the outer surface of the core part of the part is composed of three or more planes parallel to the axial direction of the hollow columnar structure.

  Here, the “core part” of the optical element base material refers to a part of the optical element base material that finally becomes the core part of the optical element when the optical element is manufactured. The same applies to the “cladding portion”.

  In other words, the structure of the base material for an optical element is a structure in which a columnar cladding portion has a hollow portion having a polygonal cross section, and a core portion of a different material is inserted into the hollow portion. In the case of such a structure, the material of the core part and the clad part can be selected independently, the degree of freedom of the cross-sectional shape is high, and the material can be selected freely. For this reason, not only can the refractive index difference between the core and the clad be easily set, but also a material having characteristics preferentially required for each of the core and the clad can be used. For this reason, for example, a material having excellent optical functionality can be selected for the core, and a material having excellent weather resistance, chemical resistance, and devitrification resistance can be selected and used for the cladding. .

  The core part and the clad part are preferably joined, but may be joined at the stage of forming the optical element, or the core part may be inserted into the clad part at the stage of the optical element base material.

It is preferable that the core part has a columnar shape, and the cross-sectional shape perpendicular to the axial direction is substantially circular or polygonal. In the case of a polygon, a quadrangle or a hexagon is desirable.
In the case of a circular shape, an optical element manufactured from this base material is convenient when combined with another optical element having a circular outer shape, such as a lens or an optical fiber. In particular, in the case of a polygonal shape, it is preferable that the cross-sectional shape of the inner surface of the clad portion be the same.

  As a result, the smoothness and cleanliness of the surface of the cladding base material adjacent to the core base material can be easily increased. This can reduce defects such as foreign matter at the interface between the core and the clad in the optical element manufactured from the base material. When the optical element is an optical fiber, the light propagating through the optical fiber can be reduced. This means that the transmission loss can be reduced more easily.

  The clad portion preferably has a hollow columnar structure in which at least the central portion where the core portion is located is hollow, and the outer peripheral shape of the cross section perpendicular to the axial direction is substantially circular or polygonal. In the case of a polygon, a quadrangle or a hexagon is desirable.

  When the outer peripheral shape of the cladding part is substantially circular, connection with other optical fibers or the like can be facilitated. Further, when the outer peripheral shape of the cladding part is a quadrangle or a hexagon, the degree of freedom of rotation in the optical axis direction can be limited when the optical element is arranged. Furthermore, when arranging, the optical elements can be arranged without a gap.

  At least one of the core portion and the clad portion of the optical element base material of the present invention is made of an inorganic glass material, and the optical element of the present invention is preferably formed by stretching the optical element base material along the axial direction. .

  By forming the base material for an optical element with an inorganic glass material, a stretching technique can be applied, and an optical element utilizing a long fiber shape can be formed. Since the dimensional change from the optical element base material to the optical element in the drawing process can be accurately controlled, the drawing technique is suitable for mass-producing fiber type optical elements.

  For example, an optical amplifying element can be realized by adopting a glass material having optical amplifying properties for the core. Since glass having functionality as well as optical amplification is used as a core, and a material to be clad can be independently selected, the present invention provides an optical waveguide type or optical fiber type having such functionality. It is particularly suitable for the production of optical elements.

The manufacturing method of the optical element base material of the present invention includes the following steps.
(1) A step of processing and shaping each of a core base material having a columnar structure serving as a core portion and a columnar base material for cladding having a lower refractive index than the core base material,
(2) A step of assembling a clad portion having a hollow columnar structure by combining a plurality of clad base materials,
(3) a step of inserting a core portion made of a core base material into a hollow portion of the clad portion;
It is. further,
(4) A step of joining the clad part and the core part inserted therein may be added.

  In the present invention, in order to freely select the combination of the core and the clad, when the base material for the optical element is manufactured, the member that becomes the core part and the member that becomes the clad part are different members. Therefore, the member that becomes the core portion and the member that becomes the cladding portion are referred to as a core base material and a clad base material, respectively. The same applies hereinafter.

  The clad base material is preferably composed of a plurality of flat members. The flat plate member is easy to manufacture, and it is also easy to surround a core base material by combining a plurality of flat members. Furthermore, it is desirable that the clad base material is a tubular member in which the plate-like members are joined together in advance so that the core base material can be inserted along the axial direction of the columnar structure.

In this case, it is also possible to take a method in which the inner peripheral shape of the clad base material is processed into a desired shape, and the core base material is inserted into a plurality of parts.
The core base material may be a columnar member obtained by previously joining a plurality of members.

  It is desirable that the core base materials, the clad base materials, or the core base material and the clad base material be bonded in a state in which at least one base material is heated to a temperature higher than the temperature at which the base material is deformed by its own weight.

  Since the optical element base material of the present invention has a core / clad interface with few defects and contamination, an optical element having excellent characteristics can be produced. In addition, since the core base material and the clad base material can be combined with materials having greatly different compositions, an optical element having a new function can be realized.

Hereinafter, embodiments of the present invention will be described in detail.
1A to 1G schematically show typical shapes of the optical element base material of the present invention. Both are columnar members in which the clad portions 12a to 12g surround the core portions 10a to 10g at the center.

  A typical example of the material that can be used as the base material for the optical element of the present invention is glass. When glass is used as the base material, the core base material (hereinafter referred to as the core base glass) and the cladding base material (hereinafter referred to as the base glass for cladding) are joined by some means to form the base for the optical element. A material (hereinafter referred to as an optical element base glass) can be produced. The outline of the manufacturing process of this optical element base glass is shown in FIG.

  In the optical element base material of the present invention, as shown in FIG. 1, the inner surfaces of the clad portions 12a to 12g facing the outer peripheral surfaces of the core portions 10a to 10g are all flat. However, the outer peripheral surface of the core glass is not necessarily a flat surface, and the cross section perpendicular to the axial direction may be substantially circular as shown in FIG. However, if possible, it is desirable that both surfaces be flat or substantially flat. If the surface forming this interface is a substantially flat surface, shaping, polishing and cleaning are easy, and a surface with few defects and contamination and high dimensional accuracy can be easily obtained.

  By using such a core glass and a cladding glass, it is possible to easily obtain a core / cladding interface with few defects and contamination, and an optical element suitable for manufacturing a high-performance optical element. The base material glass can be easily obtained. In particular, when the optical element is an optical fiber, it has a great effect on prevention of disconnection during spinning of the optical fiber due to heat drawing, improvement of the stability of the outer diameter of the spun optical fiber, and improvement of the optical functional characteristics of the optical fiber. is there.

  In addition, since the base material is composed of separately manufactured core base glass and cladding base glass, it is possible to obtain a base material having core and cladding portions made of glasses having significantly different physical and chemical properties. it can. This feature makes it possible to simultaneously satisfy the required characteristics for each of the core and the clad by combining glass having more suitable characteristics, and can greatly contribute to the improvement of the optical functional characteristics of the optical element.

  The cross-sectional shape of the inner surface of the clad part of the optical element base material of the present invention is not particularly limited as long as it is a closed shape. However, in practice, as shown in FIG. 1, it is preferable to have a shape that can be regarded as a polygon composed of only three or more straight lines. In particular, a quadrangle or a hexagon is desirable as shown in FIGS. 1A to 1D, but in the case of a quadrangle, a regular hexagon is preferable in the case of a rectangle, rhombus, square, or hexagon.

  The reason is that it is easy to increase the dimensional accuracy of the base glass for the core and the base glass for the clad, and thus the core shape of the base material to be manufactured can be made more accurate, and optical. This is because when the element is an optical fiber, the mode of light propagating through the optical fiber can be controlled more easily.

  When the number of sides exceeds 4, for example, as shown in FIG. 1 (e) or (f), the internal angle of two adjacent sides may exceed 180 ·. In such a case, the core base material may be prepared by being divided into a plurality of members.

  The cross-sectional shape of the core portion is not necessarily similar to the inner surface of the cladding portion, and there may be a gap between the core portion and the cladding portion of the optical element base material. Accordingly, the cross-sectional shape of the core portion may be a shape different from the cross-sectional shape of the inner surface of the clad portion, such as a circle. However, the cross-sectional shapes of the outer periphery of the core part and the inner surface of the clad part are preferably similar in shape to the core part side being slightly smaller.

  Moreover, the cross-sectional shape of the outer periphery of the clad portion of the optical element base material of the present invention may be any shape, but in practice, it is preferably any of a substantially circular shape, a square shape, or a hexagonal shape. The reason is that it is convenient for assembling with other optical elements to be combined when the optical element is assembled as an optical component or an optical device, such as a lens, an optical fiber, and a planar optical waveguide. In particular, when the optical element is an optical fiber, such a characteristic of the outer periphery shape of the cladding is important.

  When the outer peripheral shape of the cladding part is substantially circular, the combination with other optical fibers is very easy. In addition, since there are already a wide variety of optical fiber components that can be used as they are, it is easy to handle the optical fiber and the manufacturing cost of the apparatus using the optical fiber can be reduced.

  Moreover, when the clad outer peripheral shape is a quadrangle or a hexagon, the degree of freedom of rotation in the axial direction of the optical fiber is limited when the optical fiber is disposed. This feature is useful, for example, in preventing inadvertent application of torsional stress to the optical fiber in an apparatus using the optical fiber. Conversely, when it is necessary to apply a torsional stress to the optical fiber, a constant torsion can be easily applied and held.

  Furthermore, when the optical fibers having a quadrangular or hexagonal cross-sectional shape on the outer periphery of the cladding can be arranged without gaps, the optical fibers can be arranged with no gap. This feature is advantageous for improving the alignment accuracy when manufacturing an optical fiber array in which a plurality of optical fibers are arrayed. Further, according to this feature, since the core interval between the two optical fibers can be accurately defined, one of the optical fibers arranged without a gap is provided when the optical fiber is provided with a function of light emission (especially laser oscillation) or optical amplification. It becomes easy to inject excitation light from one core to the other core through the clad.

  As described above, the cross-sectional shape of the cladding outer periphery of the optical element base material of the present invention is such that both base materials can realize a predetermined outer peripheral shape when the core base glass and the cladding base glass are combined. Although the glass may be shaped, it is preferable that the outer periphery is processed into a predetermined shape after the above-described fusing process. The processing can be performed by grinding or polishing.

  The planes, straight lines, circles, polygons, squares, hexagons, rectangles, rhombuses, squares, regular hexagons, etc. described above do not mean mathematically exact ones. In the range of processing accuracy and the range that does not have a serious adverse effect on the characteristics of the optical element to be manufactured, it is interpreted as including a deviation and error with respect to a mathematically exact shape.

  Next, the optical element of the present invention, its base material, and its manufacturing method will be described with examples of optical fibers.

[Example 1]
(Manufacture of optical fiber preforms)
The core matrix glass composition was produced by a conventional melting method. That is, a glass raw material mixed with necessary components is melted to produce a glass composition (glass lump) (“melting” step in FIG. 2A). Table 1 shows the glass composition and typical physical properties. The main components for both the core and the cladding are SiO ₂ , Al ₂ O ₃ , and Li ₂ O, and 1 mol% of Bi ₂ O ₃ is added only to the core glass.

According to the inventors' research, it has been clarified that this glass composition added with a small amount of Bi ₂ O ₃ emits red light and has a light amplification property in the infrared region. In other words, this example is intended to produce an optical fiber amplifier using this Bi ₂ O ₃ -containing glass. In order to confine light in the core, the refractive index (1.524) of the core glass is adjusted to be larger than the refractive index (1.512) of the cladding glass.

  This glass composition is cut and ground by applying a mechanical processing method to ordinary glass to obtain a 2 mm square × 150 mm square prism, and optical polishing is performed on four sides of the square pillar (FIG. 2). A core preform glass having a smooth and clean surface was obtained (through the “shape processing” step in (a)). The direction of the central axis of this quadrangular column coincides with the direction of the optical axis of the optical fiber to be manufactured.

The clad matrix glass composition was also produced by the usual melting method. The glass composition and typical physical properties are also shown in Table 1. The glass is processed in the same way as the core glass, and four square columns of 16 mm x 14 mm x 150 mm are produced. Further, two adjacent side surfaces of the square column are optically polished to obtain a smooth and clean surface. A base metal glass for a clad having a thickness of 5 was obtained.
In the above processing, the processing was performed so that the dimensional accuracy other than the longitudinal direction had an error of 10 μm or less.

  Four clad base glass are assembled so as to surround the regular quadrangular prism side surface of the core base glass. As shown schematically in FIG. 3A, the cross-section of the assembled prism is such that the four cladding glass members 13a are symmetrical with respect to the center on the side surface of the regular square column of the core glass 11a. Has been placed. In this case, the surfaces subjected to optical polishing come into contact with each other.

  Next, a very small amount of adhesive was applied to the end face of the joint glass of the cladding base glass, and the glass was temporarily fixed. The main purpose of this fixing is to ensure that the assembly does not break before the subsequent process is completed. Therefore, it is not preferable that a large amount of the adhesive soaks into the glass joint, and the amount of the adhesive applied is preferably within a few mm from the end surface in the region where the adhesive penetrates the glass joint.

  Furthermore, it is preferable that the adhesive does not penetrate between the core matrix glass and the cladding matrix glass. Also, the adhesive layer is preferably thin, and it is preferable that the adhesive layer evaporates or decomposes and vaporizes in the subsequent heating step. Therefore, the adhesive is preferably an organic adhesive having a low viscosity. The cyanoacrylate adhesive used was used. The above is the “assembly” process in FIG.

  For example, the temporary fixing method can be used without using an adhesive using a holding jig or the like, but in this case, since the subsequent process includes a heating process, the holding jig and the base material are used. Careful attention should be paid to the fact that the temporary fixing is not loosened in the heating process due to the difference in the coefficient of thermal expansion of the glass or unnecessary stress is not applied to the base material.

  Next, in order to join the temporarily fixed glass, it was set in a jig for heat fusion. This jig has a structure in which the temporarily fixed glass can be held horizontally in the axial direction of the prism and tilted in the cross-sectional direction. Further, the jig was entirely made of refractory, and the surface touched by the glass was covered with 95% platinum-5% gold alloy foil.

The jig used here is
-By tilting in the cross-sectional direction, pressure due to the weight of the glass is applied to all the surfaces where the glasses are in contact, and the contact between the glasses can be maintained.
・ Because it is made of refractory, there is no change in the material and dimensions at the temperature of the heat fusion process.
・ Platinum-gold alloy has poor glass wettability and can be easily removed.
It is suitable for the production method of the present invention.
It should be noted that although the jig may be made of other materials such as metal or carbon material, the requirements for the jig are sufficiently satisfied.

  Next, the temporarily fixed glass set on the jig was subjected to heat fusion (“heat fusion” step in FIG. 2B). This glass was inserted into a room temperature electric furnace and heated from room temperature to a temperature exceeding the yield point by 80 ° C. at a rate of 5 ° C./min. After maintaining the temperature for 2 hours, the electric furnace was turned off, allowed to cool to room temperature, and gradually cooled. The cooling rate during this slow cooling is about 2 ° C./min.

  The heat fusion process was performed in a normal air atmosphere, but it is more preferable to perform in a vacuum atmosphere. The holding temperature is preferably 40 to 120 ° C. higher than the yield point, but the higher the temperature, the easier the fusion, while the larger the deformation, there is an appropriate range combined with the holding time. . It is important that the heating rate and the slow cooling rate are set so as not to give a thermal shock or leave thermal stress in the finished glass base material.

  The optical fiber (optical element) base material manufactured in this way is completely fused without containing foreign matter or bubbles between the core part and the clad part, and the interface between the base glass for the clad is It disappeared completely, and the trace could not be confirmed. The optical fiber preform was ground to have a cylindrical shape with an outer periphery of 25 mm in diameter, and its surface was gloss polished (the “outer shape processing step in FIG. 2 (a)) as the final form.

(Manufacture of optical fiber)
The optical fiber preform manufactured in the above process is fixed in an optical fiber spinning apparatus equipped with a normal resistance heating type electric furnace, heated and drawn so that the outer diameter of the clad becomes 125 μm, and spun. Manufactured.

  This optical fiber was coated with a normal UV curable resin to prevent damage caused by contact with the glass fiber surface and to protect the optical fiber from breaking. As shown schematically in FIG. 3B, this optical fiber has a structure in which a square core 16a having a side of 10 μm is surrounded by a circular cladding 18a having a diameter of 125 μm.

(Optical amplification characteristics of optical fiber)
FIG. 4 shows a schematic diagram of an optical amplification characteristic measuring apparatus. The basic configuration is a so-called reverse-pumped optical fiber amplifier, in which the signal light to be amplified is incident on the optical fiber, while the pumping light serving as the energy source for optical amplification is the opposite end of the optical fiber, that is, the signal The light is incident from the light exit end to cause optical amplification in the fiber.

  In the present invention, a laser beam obtained from a signal light source 36 composed of two types of semiconductor lasers with wavelengths of 1064 nm and 1314 nm is used as the signal light 30, and a semiconductor laser (LD) pumped Nd-YAG green laser is used as the pumping light 20. Continuous light having a wavelength of 532 nm emitted from the excitation light source 26 is used. Further, wavelength selective reflecting mirrors 74 and 72 were used for multiplexing and demultiplexing the signal light and the excitation light.

  The measurement of optical amplification was performed as follows. The above-mentioned optical fiber was cut into a length of 1 m, and installed as a test optical fiber 100 at a predetermined position of the measuring apparatus. The optical system was adjusted, and the signal light 30 and the excitation light 20 were collected by the lenses 54 and 52, respectively, and aligned so as to be well incident on the core of the optical fiber 100.

  First, only signal light having a wavelength of 1314 nm was made incident on the optical fiber 100, and the intensity of the signal light 32 transmitted through the optical fiber was converted into an electric signal by the light detection system 80 and measured by the oscilloscope 90. Next, the excitation light 20 is simultaneously incident on the optical fiber 100 in that state, and the intensity of the signal light 32 transmitted through the optical fiber 100 is measured. The intensity of the signal light is compared with that of the signal light alone. As a result, the effect of light amplification was confirmed.

  When the same experiment was performed by changing the wavelength of the signal light to 1064 nm, the intensity of the signal light was approximately twice that of the signal light alone by simultaneously making the excitation light incident on the optical fiber. The effect of light amplification was confirmed.

  In addition, since the emission wavelength at which the core glass of the optical fiber has maximum light emission is about 1140 nm and is between 1064 nm and 1314 nm where the amplification gain is confirmed, optical amplification is performed at least in the wavelength range of 1064 nm to 1314 nm. It is possible.

[Example 2]
(Manufacture of optical fiber preforms)
The core glass and clad base glass compositions were produced by the melting method in the same manner as in Example 1. The glass composition and typical physical properties are listed in Table 1. The main components for both the core and the cladding are P ₂ O ₅ , Al ₂ O ₃ and MgO, and Bi ₂ O ₃ is added in an amount of 0.3 mol% only to the core glass.

According to the studies by the inventors, this glass composition to which a small amount of Bi ₂ O ₃ is added exhibits red light emission like the glass composition of Example 1 and has light amplification in the infrared region. . The purpose of this example is also to produce an optical fiber amplifier using this Bi ₂ O ₃ -containing glass. In order to confine light in the core, the refractive index (1.504) of the core matrix glass is adjusted to be larger than the refractive index (1.490) of the cladding matrix glass.

  The core glass is cut and ground in the same manner as in Example 1 to obtain a 2.4 mm square × 150 mm regular square column, and optical polishing is performed on four sides of the square column to have a smooth and clean surface. A core glass was obtained. The direction of the central axis of this quadrangular column coincides with the direction of the optical axis of the optical fiber to be manufactured.

As the base metal glass for cladding, two square columns each having 30 mm × 13.8 mm × 150 mm and 2.4 mm × 13.8 mm × 150 mm were produced. A cladding base material having a smooth and clean surface by optically polishing one side of the former square column with the larger area and three sides (the front and back sides and one side) of the side surfaces of the latter square column Glass was produced.
In the above processing, the dimensional error between the thickness of the core base glass and the thickness of the latter clad base glass was set to have an error of 10 μm or less.

  The core base glass 11b and the two types of clad base glasses 13b and 13c were each assembled so that the surfaces subjected to optical polishing were in contact with each other. The cross section is schematically shown in FIG. 5A, but this method has few parts that require high dimensional accuracy, and as a result, an optical fiber preform having a high dimensional accuracy core can be obtained. There are features.

  Next, a very small amount of an adhesive was applied to the end face of the seam of the base glass for cladding, and the glass was temporarily fixed by the same procedure as in Example 1. Thereafter, the core glass was taken out to make only the clad glass. The above is the “assembly” process of the base glass for cladding in FIG.

Next, in order to join the temporarily-fixed base glass for clad, it was set in a heat-welding jig in the same manner as in Example 1 and heat-sealed (the base glass for clad in FIG. 2B). "Heat fusion" process).
In this base material, the interface between the base glass for cladding disappeared completely, and the traces could not be confirmed.

  After that, the core preform glass is inserted into the pipe-shaped clad preform glass produced by the heat-sealing process, and the final form of the preform for the optical fiber (optical element) is obtained (FIG. 2B). “Insertion” process).

  In addition, although the process shown in parentheses in FIG. 2B is not performed in this embodiment, it may be inserted as necessary. After the clad base glass is heat-fused into a pipe shape, the outer shape may be processed and shaped (“outer shape processing step of the clad base glass in FIG. 2B)”.

  If a core glass is required, a plurality of members may be assembled and integrated by heating and fusing ("assembly" or "heating fusing" of the core glass in FIG. 2B). Process). Furthermore, in the above-mentioned process, the core base glass is inserted into the pipe-shaped cladding base glass, and the final form is used. After the insertion, the optical fiber base is integrated by heating and melting before spinning. It is also possible (the last “heat fusion” step in FIG. 2B).

(Manufacture of optical fiber)
The optical fiber preform manufactured as described above is fixed in an optical fiber spinning apparatus equipped with a normal resistance heating type electric furnace, heated and drawn so that one side of the clad becomes 125 μm, and spun. Manufactured. As schematically shown in FIG. 5B, this optical fiber has a square core 16b having a side of 10 μm surrounded by a square clad 18b having a side of 125 μm.

(Optical amplification characteristics of optical fiber)
The optical amplification characteristics were measured in the same manner as in Example 1. However, in this example, the optical fiber was wound into a circular shape with a diameter of 100 mm, and a resin coating was applied thereto. This optical fiber could be easily aligned and wound without twisting.

  Also in the optical fiber of this embodiment, the effect of optical amplification can be confirmed at both wavelengths of 1314 nm and 1064 nm, and optical amplification can be performed at least in the wavelength range of wavelengths from 1064 nm to 1314 nm.

  As described above, the optical fiber preform of the present invention has a core / cladding interface with few defects and contamination, and the characteristics of the manufactured optical fiber are improved. Moreover, the manufacturing method of the base material has a feature that it is simple and can combine a core glass and a clad glass having different characteristics.

  In the above embodiments, an optical fiber having an optical amplifying property is described as an example of the optical element. However, the present invention also provides light having various optical functionalities such as a core having a material having nonlinear optical characteristics. It can also be applied to fiber.

  Moreover, it is applicable not only to optical fibers but also to optical elements such as flat optical waveguides and various light guides. In this case, the spinning step is not necessarily required, and there may be a case where a desired optical element can be produced by a process such as cutting to a predetermined length and polishing the end face after the outer shape processing of the optical element base material.

  Further, in the above embodiment, the core base material and the clad base material are both made of glass, separately shaped, and then heat-sealed to obtain an optical fiber base material. However, the present invention is not limited to glass materials, but can be applied to resins, other dielectric materials, and combinations thereof, and the integration of the core base material and the clad base material is also a method by heat fusion. Is not limited.

  For example, it is possible to apply a sol-form organic silicate compound as a clad base material around a glass core base material, and fire it to obtain an optical element base material. Alternatively, it is possible to apply a resin having fluidity as a base material for clad and cure it by heating or irradiation with light such as ultraviolet light. A resin or an inorganic dielectric can also be used for the core base material.

It is a schematic diagram which shows the shape of the preform | base_material for optical elements of this invention. It is a flowchart which shows an example of the manufacturing process of the preform | base_material for optical elements of this invention. It is sectional drawing of (a) base material glass for optical fibers of Example 1, and (b) optical fibers. It is a figure which shows the measuring apparatus of an optical amplification characteristic. It is sectional drawing of (a) preform | base_material glass for optical fibers of Example 2, and (b) optical fiber.

Explanation of symbols

10a, 10b, 10c, 10d, 10e, 10f, 10g Core parts 11a, 11b Core glass for cores 12a, 12b, 12c, 12d, 12e, 12f, 12g Clad parts 13a, 13b, 13c Clad base glass 16a, 16b Core 18a, 18b Clad 26 Excitation light source 36 Signal light source 52, 54 Lens 72, 74 Wavelength selective reflector 80 Photodetection system 90 Oscilloscope 100 Optical fiber

Claims (20)

A base material for an optical element for manufacturing an optical element having a core and a clad closely surrounding the outer periphery thereof and having a refractive index smaller than that of the core, and at least light propagates in the core. An inner surface of the clad portion having a hollow columnar structure into which the core portion having the inner surface can be inserted is configured by three or more planes parallel to the axial direction of the hollow columnar structure. Base material for optical elements. The base material for an optical element according to claim 1, wherein the core portion and the clad portion are joined. 2. The optical element base material according to claim 1, wherein the core portion has a substantially circular cross-sectional shape perpendicular to the axial direction of the columnar structure. The base material for an optical element according to claim 1, wherein the core portion has a polygonal cross-sectional shape perpendicular to the axial direction of the columnar structure. The base material for an optical element according to claim 4, wherein the polygon is a quadrangle. The base material for an optical element according to claim 5, wherein the polygon is a hexagon. The base material for an optical element according to any one of claims 1 to 6, wherein the clad portion has a substantially circular outer peripheral shape in a cross section perpendicular to the axial direction of the hollow columnar structure. The base material for an optical element according to any one of claims 1 to 6, wherein the cladding portion has a polygonal outer peripheral shape in a cross section perpendicular to the axial direction of the hollow columnar structure. The base material for an optical element according to claim 8, wherein the polygon is a quadrangle. The base material for an optical element according to claim 8, wherein the polygon is a hexagon. The base material for an optical element according to any one of claims 1 to 10, wherein at least one of the core part and the clad part is made of an inorganic glass material. An optical element, wherein the optical element base material according to claim 11 is formed by stretching along an axial direction thereof. The optical element according to claim 12, wherein the core has an optical amplification property. A core serving as the core of the optical element, which is used to manufacture an optical element that has a core and a clad that is in close contact with the outer periphery of the core and has a refractive index smaller than that of the core and that propagates light at least in the core And a method of manufacturing a base material for an optical element having a cladding portion to be the cladding, wherein the core base material has a columnar structure to be the core portion, and a columnar shape having a smaller refractive index than the core base material. A step of processing and shaping each of the cladding base materials having a structure, a step of assembling a cladding portion having a hollow columnar structure by combining a plurality of the cladding base materials, and a core portion made of the core base material of the cladding portion. And a step of inserting the hollow element into the hollow part. In addition to the process of Claim 14, the process of joining the said clad part and the said core part inserted in it is implemented, The manufacturing method of the base material for optical elements characterized by the above-mentioned. The method for manufacturing a base material for an optical element according to claim 14, wherein the clad portion includes a plurality of base materials for a clad plate. The method for manufacturing a base material for an optical element according to claim 14, wherein a plurality of flat clad base materials are joined together in advance to form a clad portion having the hollow columnar structure. The method for manufacturing a base material for an optical element according to claim 14, wherein a plurality of columnar core base materials are bonded together in advance to form the core portion having the columnar structure. The method for manufacturing a base material for an optical element according to claim 17 or 18, wherein the clad base material or the core base material is fusion-bonded in a state where the clad base material or the core base material is heated to a temperature at which it is deformed by its own weight. . 16. The method of manufacturing an optical element base material according to claim 15, wherein the core base material and the clad base material are fusion-bonded in a state where at least one of them is heated to a temperature at which at least one of them is deformed by its own weight. .

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