WO2005047196A1

WO2005047196A1 - Production method for grin lens and grin lens

Info

Publication number: WO2005047196A1
Application number: PCT/JP2004/015251
Authority: WO
Inventors: Hiroyoshi Matsumura; Taro Suzuki
Original assignee: Toyo Glass Co., Ltd.
Priority date: 2003-11-14
Filing date: 2004-10-15
Publication date: 2005-05-26
Also published as: JP2005145751A

Abstract

To be able to produce at low costs a GRIN lens having a large numerical aperture without variations in refractive index distribution shape. With a container having a cylindrical inner peripheral surface rotated, cylindrical silicon wet gel, formed by laminating layers different in refractive index imparting metal concentration that gradually grows toward the center, is produced on the inner peripheral surface of the container, the wet gel is dried to cylindrical dry gel, which is then sintered to form a cylindrical glass element, the glass element is heated sequentially starting at one end while being rotated to produce a cylindrical GRIN lens parent body with a closed inner diameter, and the lens parent body is heated and elongated to a specified diameter. Accordingly, the lens can be produced with a 100% yield and therefore at very low costs because a desired refractive index distribution can be uniformly imparted and an expensive refractive index imparting metal component will not be lost by elution.

Description

Specification

GRIN lens manufacturing method and GRIN lens technical field

The present invention particularly relates to a gradient index optical element applicable to optical coupling parts for optical communication, optical elements such as cameras and endoscopes, and a method for producing the same by a sol-gel method.

Background art

[0002] A refractive index distribution type optical element is a lens having a small spherical aberration used when, for example, radiated light from a semiconductor laser is incident on an optical fiber with high efficiency. Since it can provide an arbitrary focal length by changing the length of the cylinder, it has been attracting attention as an image transmission lens such as a camera. In particular, because of its small cylindrical shape, it is expected to be a highly assemblable lens with easy alignment and holding of the optical system.

[0003] The columnar refractive index distribution type optical element (Graded

Index lens, hereinafter abbreviated as "GRIN lens". ), As shown in Fig. 1, the refractive index n in the cross-sectional direction x, y

g: A constant that indicates the focusing power of the GRIN lens

n: Refractive index of GRIN lens material

0

As shown in the figure, a lens that changes continuously with an approximately squared curve, the lens action is performed by this refractive index distribution. As shown in Fig. 1, if the radius of the GRIN lens is d and the refractive index at the radius d is n,

d

g

= NA / dn where NA = (n ² —n ² ) ^1/2 (2)

0 0 d

Is represented by Here, NA is the square root of the square difference of the refractive index between the center and the periphery of the GRIN lens, and is called the numerical aperture (hereinafter abbreviated as “NA”), which is an important parameter that indicates lens performance. As is clear from equation (2), the numerical aperture NA increases as the difference between the refractive index at the center and the refractive index at the outer periphery increases. A lens with a large NA has a high light focusing ability That is, the lens has good lens characteristics. At present, NA = 0.2 is practically used, and a GRIN lens with NA≥0.4 is strongly desired.

[0004] As a method of manufacturing the GRIN lens, an ion exchange method, a gas-phase CVD (Chemical Vapor Deposition) method, a sol-gel method, and the like are known. However, since the GRIN lens made by the ion exchange method is a multi-component glass containing an alkali component, the NA cannot be large, and the glass material has a very large coefficient of thermal expansion, which is a problem due to the problem of heat resistance. He was poor in sex. In the gas phase method, NA of 0.38 (for example, literature; P.B.O 'Connor et al .:

Electron 丄 ett., 13 (1977) 170-171) has been obtained at the laboratory level. In order to obtain more NA, is the amount of additive (GeO, Ge Ο, etc.) increased? Must be

2 2 5

As a result, the thermal expansion coefficient of the glass material increased, and the base material was easily cracked, making it unstable for practical use.

[0005] On the other hand, the sol-gel method is a synthesis method at a low temperature, and is an effective method capable of precisely forming a desired concentration distribution. In the method for producing glass by the sol-gel method, an alcohol solution containing silicon alkoxide as a main component is added with an acid or a base as a solvent and hydrolyzed to form a sol. The metal component is added, and the sol is further subjected to a polycondensation reaction, so that a cross-linking reaction proceeds to produce a wet gel. Then, the obtained wet gel is dried, and after removing the solvent in the gel, it is baked to produce a dense glass.

When a GRIN lens is manufactured using a sol-gel method, a method that uses a metal alkoxide or a metal salt as a raw material of the metal component, and a molecular stuffing method, are required to form a concentration distribution in the metal component. Are known.

[0006] In the method using a metal alkoxide, a gel prepared by adding a metal alkoxide as an alcohol solution as a component for increasing the refractive index to a silicon alkoxide during the preparation of a sol is produced. In a gel using a metal alkoxide, silicon and metal atoms form a bond.Therefore, in order to form a concentration distribution in the metal component, a concentration at which the bond of silicon metal atoms can be cut and the metal component can be eluted is formed. This method involves immersing the gel in a distribution-imparting solution, washing the eluate, fixing the concentration distribution, washing, drying, and baking. However, the GRIN lens manufactured according to the above conventional method has a certain degree of decrease in the refractive index at the outer peripheral portion. However, the concentration of the metal component contributing to the formation of the refractive index distribution does not decrease sufficiently, and the refractive index difference between the central part and the outer peripheral part cannot be so large. Was unable to secure a stable price.

[0007] On the other hand, in the method of introducing a metal component for forming a refractive index distribution using a metal salt, a gel is prepared by adding the metal salt as an aqueous solution or an alcohol solution during the preparation of the sol. In such a gel, a metal salt is dissolved in a solvent in a pore that also has a skeletal force of silicon and exists. The obtained gel is immersed in a low-molecular-weight alcohol or water having a high solubility for a metal salt, or a mixed solution thereof to elute metal components contained in the gel and form a concentration distribution. However, since there is no suitable salt of metal that greatly contributes to the refractive index such as Ti, Nb, Ta, and Zr, it is very difficult to apply it to GRIN lenses with high NA. .

[0008] On the other hand, in the molecular stuffing method, Japanese Patent Publication No. 5-83332 discloses that a wet gel is dried and fired to produce a porous body, and is immersed in a Ti-containing solution or the like to add a metal component to the porous body. A method of uniformly impregnating to obtain a glass containing metal such as SiO—TiO is disclosed. Toko

twenty two

Filtration In this method, the dry gel is heat-treated to a high temperature, so that the bonds of Si—O—Si are firmly bonded and the number of reactive Si—OH groups is reduced. Power of metal components It was difficult to stably produce high NA GRIN lenses that could not be bonded to Si—O—Si.

In addition, in the methods using these metal alkoxides and metal salts, and the conventional sol-gel method to which the molecular stuffing method is applied, the concentration distribution is basically given by the diffusion of the metal component, so that the concentration distribution is precisely controlled. It was not possible to do so, and it was easy to increase the dispersion of the concentration distribution shape. Also, since the base gel is basically cylindrical, it was difficult to stabilize the quality immediately after trying to make a large-diameter gel, and the manufacturing cost was extremely high.

Patent Document 1: US Patent No. 3910677

Patent Document 2: US Patent No. 4701011

Patent Document 3: US Pat. No. 5,384,874

Patent Document 4: JP-A-8-292341 Disclosure of the invention

Problems to be solved by the invention

An object of the present invention is to manufacture a GRIN lens having a uniform distribution of concentration by precisely controlling the refractive index distribution. In particular, a GRIN lens having a large numerical aperture NA can be manufactured at low cost. It is an object to manufacture.

Means for solving the problem

(Structure 1) The present invention provides a method for rotating a container having an inner peripheral surface that is cylindrical while rotating the container on the inner peripheral surface of the container.

Forming a cylindrical wet gel of silicon in which layers having different refractive index-imparting metal concentrations are stacked so that the refractive index-imparting metal concentration is gradually increased toward the inside;

Drying the cylindrical wet gel to form a cylindrical dry gel; andsintering the cylindrical dry gel to form a cylindrical glass body;

The cylindrical glass body is heated sequentially from the end while rotating, and a cylindrical G having a closed inner diameter is formed.

Creating a RIN lens matrix;

Heating and stretching the GRIN lens body to a predetermined diameter.

[0011] The refractive index-imparting metal may be formed by laminating a plurality of layers (preferably eight or more layers) having different concentrations in a stepwise manner, or by laminating layers having different concentrations continuously.

(Structure 2) The present invention also relates to the manufacturing method according to Structure 1, wherein the raw material power for preparing the cylindrical wet gel is an alcohol solution containing silicon alkycoside as a main component, and an acid or base as a solvent. A GRIN lens comprising a refractive index-imparting metal and silicon powder.

[0013] By adding silicon powder to the raw material for producing the cylindrical wet gel, it is possible to prevent the gel from becoming too dense due to the centrifugal force caused by the rotation of the container. The average particle size of the silicon powder is desirably ultra-fine particles of 50 nm or less.

About 25% is appropriate.

(Structure 3) The present invention is the method of manufacturing a GRIN lens according to the manufacturing method of the structure 1 or 2, wherein the refractive index imparting metal is Ti or Ta.

(Structure 4) Further, the present invention provides the method according to any one of Structures 1-3, wherein A method for producing a GRIN lens, wherein the rotation speed of the container in the step of forming a wet gel is 800 rotations Z or more.

(Structure 5) In the manufacturing method according to any one of Structures 14 to 14, in the step of forming the cylindrical GRIN lens body having a closed inner diameter, the cylindrical glass body is rotated. This is a method of manufacturing a GRIN lens, characterized in that the inside of a tube of a cylindrical glass body is depressurized when heating is sequentially performed from an end.

[0017] When the inside of the tube of the cylindrical glass body is depressurized while sequentially heating the cylindrical glass body from the end while rotating the glass body, the glass body collapses into an elliptical shape when it softens, and the inside of the GRIN lens body is reduced. The refractive index distribution has an elliptical shape. In general, the shape of the laser beam is elliptical (the higher the power of the laser beam, the smaller the shape of the laser beam). Therefore, the efficiency can be further improved by matching the shape of the laser beam with the shape of the refractive index distribution of the GRIN lens. In fact, it can be a GRIN lens.

(Structure 6) Further, according to the manufacturing method of Structure 5, in the step of forming the cylindrical GRIN lens body having a closed inner diameter, the pressure in the tube of the cylindrical glass body is set to be lower than the atmospheric pressure. A method for manufacturing a GRIN lens, characterized in that the rotation speed of a cylindrical glass body is reduced by at least 50 rotations Z or more by 20 Pa or less.

[0019] As the amount of pressure reduction (difference from atmospheric pressure) in the glass body tube is increased, the refractive index distribution inside the GRIN lens becomes a crushed elliptical shape. The degree of pressure reduction and how much the ellipse will be crushed depends on the outer diameter and inner diameter of the glass body, etc. Generally, when the amount of pressure reduction is less than 20 Pa, the refractive index distribution is close to a perfect circle and the effect is small. . If the rotation speed of the glass body is low, the outer shape of the GRIN lens body becomes elliptical, which is not preferable for connection with an optical fiber. By setting the rotation speed of the glass body to be equal to or more than 50 rotations Z, the outer shape of the GRIN lens body can be made substantially circular.

(Arrangement 7) The present invention is a GRIN lens manufactured by the manufacturing method of Arrangement 16 and having a numerical aperture of 0.4 or more.

The invention's effect

According to the method of manufacturing a GRIN lens of the present invention, a large-sized (large-diameter) GRIN lens can be manufactured because a wet gel having a cylindrical shape is used instead of a cylindrical shape as in the related art, and a metal component is added. Expensive metal components disappear due to elution, etc. due to the lamination of different compositions It can be manufactured at a yield of 100% without the need for stacking, and since compositions with different amounts of metal components are laminated, precise control of the refractive index distribution is possible, and productivity is increased, resulting in extremely low cost.

Brief Description of Drawings

FIG. 1 is an explanatory diagram of a GRIN lens.

FIG. 2 is an explanatory view of a process of forming a GRIN lens.

FIG. 3 is an explanatory view of a wet gel 22 and a GRIN lens matrix 24.

FIG. 4 is an explanatory diagram showing the relationship between the rotation speed of a container and the shape of a wet gel.

FIG. 5 is an explanatory diagram of the addition amount of a refractive index imparting metal and a change in the refractive index.

FIG. 6 is an explanatory diagram of the addition amount of a metal having a refractive index and a change in a coefficient of thermal expansion.

FIG. 7 is an explanatory view of a glass body and a GRIN lens body.

Explanation of symbols

[0023] 21 containers

22 wet gel

23 Glass body

24 GRIN lens body

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is a GRIN lens having a high numerical aperture whose refractive index distribution is precisely controlled, and a method for manufacturing the same, which is manufactured as follows. First, as shown in FIG. 2 (a), a metal component (titanium or tantalum) imparted with a refractive index prepared by a sol-gel method is placed in a cylindrical rotating container (eg, tetrafluoroethylene resin tube) 21 having an inner diameter of 50 mm, for example. Sol) in which the added amount is sequentially changed is successively injected and gelled, and wet gels 22 having different concentrations of metal components are sequentially laminated on the inner wall of the container in a cylindrical shape. The wet gel 22 is dried under an atmosphere of 60 ° C. for one week to obtain a dry gel. The dry gel shrinks by about 1/2, is 26 mm in inner diameter and 13 mm in outer diameter, and has a cylindrical shape with an ellipticity of 0.04%. The temperature of the obtained dry gel was raised from room temperature to 800 ° C in an oxygen atmosphere at 150 ° C Zhr, and then heated to 1250 ° C in a helium atmosphere at 50 ° C / hr and calcined.Figure 2 (b) A transparent cylindrical glass body 23 as shown in FIG. Both ends of this cylindrical glass body 23 are fixed on a rotary lathe and heated sequentially from the end with an oxyhydrogen panner 25 at about 2000 ° C while rotating, and a cylindrical GRIN lens with a closed inner diameter is obtained. Maternal 24 is obtained. When this fiber is inserted into an electric furnace with a carbon heater and spun at an appropriate speed, a GRIN lens-like optical fiber having a desired outer diameter of, for example, 150 m is obtained. When this is cut to an appropriate length, the desired GRIN lens can be obtained.

[0025] As described above, a large-sized GRIN lens can be manufactured by the conventional manufacturing method using a cylindrical wet gel instead of a columnar one, and a high cost because a composition having a different addition amount of the metal component is laminated. It can be manufactured at a yield of 100% without extinguishment of various metal components by elution, etc., and is extremely low-cost.In addition, it is possible to control the refractive index by stacking compositions with different amounts of added metal components, and it is possible to control the NA The advantage that can be secured can be exhibited.

(Refractive index distribution): Power of refractive index distribution of cylindrical GRIN lens matrix 21 In order to obtain a refractive index distribution that decreases with a square curve as shown in equation (1), the wet gel 22 needs to be As shown in Fig. 3, the addition amount of the metal component is as follows, where a is the inner diameter of the wet gel 22, and R is the distance in the inner diameter direction.

^{{(R / a) 2 -} 1} 1/2 (3)

It should be set so that the amount of soybean curd decreases according to.

(Cylindrical shape): The refractive index distribution power of the GRIN lens body 21 is reduced concentrically by the ^ <th> power curve. In order to have a refractive index distribution, the wet gel 22 is formed into a concentric cylindrical shape that is almost a perfect circle. Must be done. The circular shape of the wet gel greatly depends on the rotation speed of the rotary container 21. Figure 4 shows the angle φ between the surface of the liquid and the centrifugal force direction when the sol is injected into the rotating container 22 with an inner diameter of 50 mm and gels 21 around the semicircle week with the rotation speed of the container as a parameter. It shows the result of the examination in. When the angle φ is 90 degrees at all circumferential angles, the gel is completely cylindrical, but when the rotation speed is low, the inner surface of the gel is knotted. From this, it was a component that it was necessary to rotate more than 800 rotations per minute in order to increase the concentricity.

[0028] (High NA metal additive component): When the refractive index of the binary silica glass was predicted using the well-known Lorentz-Lorenz equation, SiO2 was found as a candidate for the metal additive component of the GRIN lens.

2

-Bi O -In O, -Y O, — La O, — Ga O, —Sb O,

2 3 2 3 2 3 2 3 3 2 3 2

— GdO, -NbO, -SnO, TaO, -TiO and ZrO were mentioned. In this,

3 2 2 5 2 2 5 2 2

The composition containing Bi, In, Y, and La is a poorly soluble solid containing any alkoxide as an additive element, Can't make it. In the composition containing Gd and Ga, the numerical aperture (NA) of less than 0.3 was obtained in the region where the amount of additive was small (addition amount to Si was less than 20 mol%). For other yarns, for example, the additive obtained with an NA of 0.5 (that is, a refractive index of 1.54 compared to 1.4584 of quartz) has a small amount of added kneaded material. As shown in Table 2, Nb: 6 mol%, Ta: 10 mol%, Sb: 10 mol%, Ti: 12 mol%, Zr: 18 mol%, and Sn: 15 mol%.

[0029] (Cracking of wet gel during drying): In the method for producing a GRIN lens of the present invention, a sol in which the addition amount of a metal component imparting a refractive index is sequentially changed is sequentially injected into a cylindrical container. While rotating, gels with different concentration distributions of metal components are sequentially laminated on the inner wall of the container, and dried and sintered to form a cylindrical glass tube. For this reason, if the thermal expansion coefficients of the laminated glass layers are significantly different from each other, there is a high possibility that cracks at the boundary surface will occur during gel formation, drying, and sintering due to the difference in thermal expansion. For this reason, it is necessary to select a material with a small coefficient of thermal expansion even for a material that has a high NA. From our experience, to prevent cracking due to thermal expansion, the thermal expansion coefficient of SiO glass

2

It is required for 5x10- ^⁷ K ^_1 15x10- ⁷ is K ^_1 less. Figure 6 shows the results of experimentally determining the coefficient of thermal expansion when the amount of metal component added was changed.

[0030] As described above, the metal component Nb:

Among 6 mol%, Ta: 10 mol%, Sb: 10 mol%, Ti: 12 mol%, Zr: 18 mol%, and Sn: 15 mol%, Nb-Sn added glass shows the presence of a crystalline substance and has a thermal expansion coefficient. However, it was not suitable as a GRIN lens.

[0031] From the above, SiO-SbO, SiOTaO, SiOTiO and SiO-ZrO-based quartz glass are:

2 2 3 2 2 5 2 2 3 2 2

High NA and coefficient of thermal expansion almost equal to SiO glass, that is, cylindrical system

2

It turned out that it can be applied to the GRIN lens manufacturing method. However, Sb-added glass evaporates the additional element Sb during sintering of the gel.Zr-added glass undergoes a relatively rapid hydrolysis reaction in the process of gel preparation, although the amount is small in methanol, which is the solvent. When a precipitate is formed, it has process instability.

[0032] From the above examination results, it was found that SiO Sb 0, SiO Ta O, SiO Ti 0 and SiO—ZrO

2 2 3 2 2 5 2 2 3 2 2 British glass power Further, in consideration of process stability, SiO Ta 0, SiO -Ti 0 system

2 2 5 2 2 3 It was found that a GRIN lens with a high NA could be produced by adding sol-gel method to Ta: 10 mol% and Ti: 12 mol%, respectively, using quartz glass.

Example 1

[0033] 9.2 ml of 2N hydrochloric acid was added to a mixture of 76.6 ml of silicon tetramethoxide and 184.3 ml of isopropanol, and then 50 ml of ultrafine silica having an average particle diameter of 30 nm was mixed and stirred for 1 hour to partially hydrolyze. Decomposition was performed. This solution was divided into eight equal parts, and titanium tetra-n-butoxide having the concentration shown in Table 1 was added thereto to prepare eight types of sols having one to eight layers having different titanium components with time. Then, after a certain time, 0.01N aqueous ammonia was added to the mixture to prepare a sol.

First, the sol of the first layer was placed in a cylindrical polypropylene container 21 having an inner diameter of 50 mm, and rotated at a speed of 1100 rpm for 30 minutes to produce a cylindrical wet gel on the inner wall of the container. Thereafter, in a similar process, two to eight layers of sol liquids having different titanium components are sequentially put into the container 21, and concentrically formed on the inner wall of the container are formed eight layers of wet gel layers having different amounts of titanium added. Were stacked. The produced cylindrical wet gel 22 was dried at 60 ° C. for 1 week while rotating to obtain a dry gel. The dry gel was a cylinder with an inner diameter of 26 mm and an outer diameter of 13 mm and an ellipticity of 0.04% or less. The temperature of the obtained dry gel is raised to 150 ° C / hr in an oxygen atmosphere up to 800 ° C and then to 50 ° C / hr in a helium atmosphere to 1250 ° C. I got 23.

[Table 1] Titanium addition amount

1 layer 0 ml

2 layers 1.1 ml

3 layers 1.6 ml

4 layers 2.1 ml

5 layers 2.6 ml

6 layers 3.0 ml

7 layers 3.5 ml

8 layers 4.3 ml [0036] Both ends of the cylindrical glass body 23 are fixed on a rotary lathe, and heated sequentially from the ends with an oxyhydrogen panner 25 at about 2000 ° C while rotating, whereby a cylindrical GRIN having a closed inner diameter is obtained. A lens matrix 24 was obtained (Fig. 2 (c)). This GRIN lens matrix 24 was spun into a GRIN lens-like optical fiber having an outer diameter of 150 m while being inserted into an electric furnace of a carbon heater at 0.04 mm / s. . As a result of measuring the refractive index distribution of the fabricated GRIN lens-shaped optical fiber, it has a refractive index distribution that decreases from the center to the periphery in a substantially square curve, and the numerical aperture is NA = 0.53. Here, at the time of spinning at 1900 ° C. or more, the titanium component in the center part scatters slightly. Therefore, as shown in Table 1, the addition amount of titanium in the eight layers was increased to prevent a decrease in the refractive index.

Example 2

[0037] Silicon tetramethoxide l.lg and tantalum ethoxide in the eight kinds of added kneads shown in Table 2 were added and mixed, and 1.3 cc of methanol was added and mixed, followed by stirring. Thereafter, 0.3 g of ultrafine particle silica having an average particle size of 30 nm was mixed, and the mixture was stirred for 1 hour, and after a while, 1.3 cc of methanol and 0.3 cc of pure water were mixed and dropped, respectively, to prepare a sol.

First, the sol of the first layer was placed in a cylindrical polypropylene container 21 having an inner diameter of 50 mm and rotated at a speed of 1100 rpm for 30 minutes to produce a cylindrical gel on the inner wall of the container. Thereafter, in a similar process, two to eight layers of sols having different titanium components were sequentially placed in the container, and eight layers of wet gels having different tantalum concentrations were concentrically laminated on the inner wall of the container. The produced cylindrical wet gel 22 was dried at 60 ° C. for 1 week while rotating to obtain a dry gel. The dry gel was a cylinder with an inner diameter of 25 mm and an outer diameter of 14 mm and an ellipticity of 0.04% or less. The temperature of the obtained dry gel is increased from room temperature to 800 ° C in an oxygen atmosphere at 150 ° C Zhr, and then raised to 1250 ° C in a helium atmosphere at 50 ° C / hr. Got.

[Table 2] Tantalum addition amount

0 g

^{1 m1 m}

0.6 g

3 layers 0.9 g

1.2 g

1.5 g

6 layers 1.7 g

7 layers 2.0 g

8 layers 2.2 g

[0040] Both ends of this cylindrical glass body 23 are fixed on a rotary lathe, and heated sequentially from the ends with an oxyhydrogen panner 25 at about 2000 ° C while rotating, whereby a cylindrical GRIN having a closed inner diameter is obtained. A lens matrix 24 was obtained (Fig. 2 (c)). This GRIN lens matrix 24 was spun into a GRIN lens-like optical fiber having an outer diameter of 150 μm while being inserted into an electric furnace of a carbon heater at 0.04 mm / s, thereby producing a GRIN lens-like optical fiber. As a result of measuring the refractive index distribution of the fabricated GRIN lens-shaped optical fiber, the GRIN lens-shaped optical fiber had a refractive index distribution that decreased from the center to the periphery with a substantially square curve, and the numerical aperture was NA = 0.52. In the case of tantalum, there was no scattering of tantalum as described in Example 2.

Example 3

The upper part of FIG. 7 shows a cross section of the cylindrical glass body 23 produced by the method of the second embodiment, and the lower part shows a cross section of the GRIN lens body 24 produced by the method of the present embodiment. The glass body has an outer diameter of 13 mm and an inner diameter of 7.7 mm. When the cylindrical glass body was sequentially heated from the end to form a GRIN lens body, the inside of the tube of the cylindrical glass body was depressurized, and the glass body was rotated at a speed of 80 rotations Z minutes. The outline of the GRIN lens matrix was almost a perfect circle, and the refractive index was distributed in an elliptical shape. The difference between the amount of reduced pressure (difference from atmospheric pressure) and the maximum ellipticity of the isorefractive index curve was as follows. The ellipticity is (a−b) Za, where the major axis of the ellipse is a and the minor axis is b, and the larger the ellipse, the more the ellipse becomes.

Decompression amount 60Pa Maximum ellipticity 32%

Decompression amount l lOPa Maximum ellipticity 45% Decompression 200Pa Max ellipticity 68%

As shown in the lower part of FIG. 7, the iso-refractive index curve has an elliptical shape in which the central layer is most crushed, and an elliptic shape in which the outer layer is less crushed. By adjusting the amount of pressure reduction, a GRIN lens with the optimum refractive index distribution for the laser light used can be manufactured.

Industrial applicability

[0043] The GRIN lens of the present invention can be used as an optical fiber coupling component, a collimator, or the like by being welded to the tip of an optical fiber.

Claims

The scope of the claims

[1] While rotating a container having a cylindrical inner peripheral surface, a silicon layer having different refractive index-imparting metal concentrations is laminated on the inner peripheral surface of the container so that the refractive index-imparting metal concentration gradually increases toward the inside. Creating a cylindrical wet gel of

Creating a RIN lens matrix;

Heating and stretching the GRIN lens body to a predetermined diameter.

2. The production method according to claim 1, wherein the raw materials for forming the cylindrical wet gel are: an alcohol solution containing silicon alkycoside as a main component; an acid or base as a solvent; a refractive index imparting metal; and silicon powder. A method for producing a GRIN lens characterized by containing

[3] The method for producing a GRIN lens according to claim 1 or 2, wherein the refractive index imparting metal is Ti or Ta.

[4] The production method according to any one of [13] to [13], wherein the rotational speed of the container in the step of forming the cylindrical wet gel is 800 rotations Z or more.

GRIN lens manufacturing method

[5] In the manufacturing method according to any one of [1] to [4], in the step of forming the cylindrical GRIN lens body having a closed inner diameter, the cylindrical glass body is rotated while being sequentially heated from the end while rotating. A method for producing a GRIN lens, characterized by reducing the pressure inside a tube of a cylindrical glass body.

6. The manufacturing method according to claim 5, wherein, in the step of forming the cylindrical GRIN lens body having a closed inner diameter, the pressure in the tube of the cylindrical glass body is reduced by 20 Pa or more lower than the atmospheric pressure. A method for manufacturing a GRIN lens, wherein the rotation speed of the body is set to 50 rotations or more for Z minutes.

[7] G manufactured by the manufacturing method according to claim 11, wherein the numerical aperture is 0.4 or more. RIN lens