JP2003294968A - Method for manufacturing optical transmission path - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily manufacture a straight optical transmission path at the front end of an optical fiber. <P>SOLUTION: The optical molding method comprises using the optical fiber and photosetting resin solutions. A solution mixture 100 is filled in a transparent container 110. The solution mixture 100 is prepared by mixing two kinds of the photosetting resin solutions varying in the initiation points of curing and refractive indices. The refractive indices are regulated by component ratios according to the exit angle from the optical fiber. One end of the optical fiber 200 is put into the solution mixture 100 and the one photosetting resin solution in the solution mixture 100 is cured by emitting short wavelength light of λ<SB>1</SB>from the end face of the fiber. As a result, a core section 105 is formed. In the case of the step index optical fiber of the refractive indices changing stepwise at the boundary between the core and the clad, the optical fiber is so formed as to satisfy (n<SB>f1</SB>)<SP>2</SP>-(n<SB>f2</SB>)<SP>2</SP>≤(nA<SB>2</SB>)<SP>2</SP>-(nC<SB>1</SB>)<SP>2</SP>when the refractive index of the core is defined as n<SB>f1</SB>, the refractive index of the clad as n<SB>f2</SB>, the refractive index of the optical transmission path as nA<SB>2</SB>, and the refractive index of the photosetting resin solution as nC<SB>1</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical transmission line manufactured by using a photocurable resin solution and light.
In particular, a photocurable resin solution is used as a mixed solution of two kinds having different curing start wavelengths and different refractive indexes, and one photocurable resin solution is used to form the core of the transmission line and both photocurable resin solutions to form a clad portion. The present invention relates to a method of manufacturing a transmission line. The present invention also relates to a method of manufacturing an optical transmission line in which an optical fiber is dipped in the above mixed solution and continuously connected to the optical fiber with good linear parallelism. The present invention provides an inexpensive and low-loss optical interconnection in optical communication,
It can be applied to optical demultiplexers or multiplexers.

[0002]

2. Description of the Related Art In recent years, a technique for forming an optical transmission line at the tip of an optical fiber using a photocurable resin solution has been attracting attention. For example, there is a method of manufacturing an optical waveguide disclosed in JP-A-4-165311. Briefly, first
In the step, one end of the optical fiber is dipped in a photocurable resin solution made of, for example, a fluorine-based monomer. Then, light having a wavelength that cures the solution is emitted from the tip of the fiber (second step). For example, when a laser beam having a wavelength close to the ultraviolet region or a short wavelength laser beam is irradiated, the photocurable resin solution at the tip portion is cured by a photopolymerization reaction.
A so-called core portion is formed at the emission end according to the power distribution. When the core portion is formed, the above light is further propagated to form the core portion one after another, and as a result, the optical transmission line is formed.

Then, as a third step, the photocurable resin solution is removed from the photocurable resin solution and the remaining photocurable resin solution is removed by washing or the like. Next, as a fourth step, the translucent resin is coated again. This is for the purpose of coating the core surface and protecting it from dust and scratches. Then, as a final fifth step, the tip end surface of the formed core portion is polished to form the emission surface of the transmission path. In this way, an optical transmission line continuous with the optical fiber was formed in about 5 steps.

[0004]

However, in the above-mentioned conventional example, the optical transmission line is meandering as a result. Meandering means that when the z axis is taken in the optical axis direction, the radius periodically differs with respect to the value of z. This is due to a mismatch in the refractive index between the core of the optical fiber and the photocurable resin solution. As a result, the outgoing spread becomes large and a gradient index optical transmission line is formed.

In the gradient index transmission line, light meanders according to the refractive index. That is, depending on the length of the transmission line,
Its focal length changes. For this reason, in the end face polishing in the final step, it is necessary to determine the polishing amount while measuring the focal length, and there is a drawback that a great manufacturing cost is required. Further, according to the above-mentioned conventional example, the transmission path length of the formed core portion is 8.5 mm. If the end surface treatment is applied, the size will be further reduced. This can be applied as a connector for connecting optical fibers, but it is difficult to insert a branching mirror or the like into the transmission line to form a demultiplexer / multiplexer. There are also reports that a tapered optical transmission line is formed at the tip of an optical fiber. The formation of the tapered optical transmission line is also caused by the mismatch of the above-mentioned refractive indexes. When this tapered optical transmission line is applied to the multiplexer / demultiplexer, there is a drawback that the loss increases due to its spread. Further, in the case of the above method, when the cladding is cured as it is, the refractive index becomes the same as that of the core. Therefore, in order to obtain a step index type optical transmission line, a separate step of replacing the fiber clad with another material is required.
There was a problem of poor productivity.

The present invention has been made in order to solve the above problems, and an object thereof is to easily prepare a core portion and a clad portion by using a photocurable resin solution, and the core portion is linear. To provide an extended optical transmission line. Moreover, it is providing the manufacturing method. Another object is to provide an optical transmission line that is linearly extended from the exit regardless of the type of optical fiber by adjusting the refractive index of the photocurable resin solution according to the optical fiber used. Is. Still another object is to provide an inexpensive optical transmission line manufacturing method in which assembly costs and component costs are significantly reduced.

[0007]

In order to achieve this object, according to the method of manufacturing an optical transmission line of the present invention, the tip of an optical fiber is dipped in a photocurable resin solution, and the optical fiber is dipped. A method of manufacturing an optical transmission path for producing a continuous optical transmission path from the optical fiber tip by emitting light of a predetermined wavelength from the tip and curing the photocurable resin solution in the optical axis direction, The optical fiber is a step index type optical fiber in which the refractive index changes stepwise at the boundary between the core portion and the cladding portion, and the refractive index of the core portion is n _f1 ,
When the refractive index of the cladding portion is n _f2 , the refractive index of the formed optical transmission line is n _A2 , and the refractive index of the photocurable resin solution is n _C1 ,
It is characterized in that the refractive index of the photocurable resin solution is adjusted so as to satisfy the condition of the expression (3).

(N 3) (n _f1 ) ² − (n _f2 ) ² ≦ (n _A2 ) ² − (n _C1 ) ² (3)

According to the method of manufacturing an optical transmission line of the present invention, the optical fiber is a graded index type optical fiber having a refractive index gradient in a radial direction with a predetermined function. The maximum refractive index at the center of the core of the optical fiber is n _f1 , the diameter of the core is 2 a _f , the refractive index of the cladding is n _f2 , the refractive index of the formed optical transmission line is n _A2 , and the refractive index of the photocurable resin solution is when to the n _C1, p an integer, in conditions satisfying the diameter 2a _w of the optical transmission line to be fabricated with (4), the refractive index of the photocurable resin solution, characterized in that it is adjusted.

2 a _w = 2a _f [1 / (2Δ) · (n _A2 ² −n _C1 ² ) / n _A2 ² ] ^{1 / p} where Δ = (n _f1 ² −n _f2 ² ) / (2n _f1 ² ) ・ ・ ・ (4)

[0009]

FUNCTION AND EFFECT First, a method of manufacturing an optical transmission line using a mixed solution in which two kinds of photocurable resin solutions are mixed will be described. It consists of a mixture of a first photocurable resin solution and a second photocurable resin solution having a property that the curing start wavelength is shorter than that of the first photocurable resin solution. Further, the refractive index of the first photocurable resin solution at the time of curing is set to be higher than the refractive index of the mixed solution at the time of curing. This mixed solution is put in, for example, a rectangular parallelepiped transparent container.

The first photocurable resin solution is added to the mixed solution.
Wavelength range to be cured λ_w(Λ₂<Λ_w<Λ₁Bee the light
Inject it in a muzzle shape. Where wavelength λ₁Is the first photocurable
The wavelength at which the resin solution begins to cure, and the wavelength λ₂Is the second light hard
It is that of the volatile resin solution. In addition, the above wavelength band λ_wLight of
Is short-wavelength laser light such as He-Cd. this
Causes only the first photocurable resin solution in the mixed solution to emit light.
It is cured by a polymerization reaction to form a linear core portion.
At this time, two kinds of photocurable resin solutions were applied to the outer periphery of the core.
The remaining mixed solution remains. Then around this mixed solution
The wavelength band λ that cures both photocurable resin solutions _c(Λ
_c<Λ₂) Light from, for example, an ultraviolet lamp.
Then, the residual solution is solidified by the photopolymerization reaction. This
As a result, the clad portion is formed around the core portion. Also,
By setting the above-mentioned refractive index, at this time the refractive index of the core part
It is higher than the refractive index of the head. That is, the step index
A box-shaped optical transmission line is formed. In this way, with the core part
Step index type optical transmission line having a clad part
Are formed by light irradiation in two steps. Therefore, extremely efficient
This is a good method for manufacturing an optical transmission line.

At this time, the transparent container for the mixed solution may have any shape. As a result, the clad portion has an arbitrary shape and can be manufactured, for example, according to the shape of the product. That is, the clad portion can be directly fixed to the product. Therefore, the optical transmission line is extremely convenient. Further, the optical transmission line is collectively molded by only irradiating the light in the predetermined wavelength bands λ _w and λ _c . Therefore, the manufacturing method has a low assembly cost.

Further, as described in Japanese Patent Application No. 10-152157, an optical element such as a half mirror is inserted into the container, and the above steps are followed to form the optical transmission line and the half mirror in close contact with each other. It is also possible to manufacture optical demultiplexers.

It is also known that the phase of the light wave changes when the optical transmission line is distorted. Since the above-mentioned manufacturing method enables an arbitrary clad shape, various physical quantities such as stress, electric field, magnetic field, and ultrasonic wave can be easily applied to the transmission line. This makes it possible to easily apply stress, that is, a phase change in various forms, and to form an optical element such as a phase modulation element. Therefore, the above manufacturing method is a basic technique for forming the basic structure of various optical elements having an optical transmission path.

If the refractive index of the first photocurable resin solution at the time of curing is adjusted to be higher than the refractive index of the mixed solution, the first
The photocurable resin solution of _{No. 2} is cured when irradiated with light in the wavelength band λ ₁ , and has a higher refractive index than that of the mixed solution. That is, a step index type optical transmission line is formed in the mixed solution.
Since it is a step index type, all the incident light is totally reflected, and the optical transmission lines can be sequentially formed efficiently. Therefore, the incident light does not have to be, for example, a laser light having good straightness. It allows the use of, for example, ultraviolet light, which is incident at an angle at which total internal reflection occurs. Therefore, the method of manufacturing the optical transmission line can use various light sources.

It is also possible to immerse the tip of the optical fiber in a mixed solution so that light of a predetermined wavelength is emitted from the tip so that the optical transmission line is continuously manufactured from the tip of the optical fiber. . The predetermined wavelength is, for example, short wavelength laser light. The short-wavelength light sequentially causes a photopolymerization reaction with respect to the photocurable resin solution in the optical axis direction. As a result, the core portion of the optical transmission line is in close contact with the core portion of the optical fiber and is continuously formed in a linear shape. Therefore, it is not necessary to align the optical axes of the optical fiber and the optical transmission line. Further, the tip of the optical fiber is firmly fixed in the clad of the optical transmission line by the light irradiation of the wavelength λc. Therefore, the degree of freedom in arranging the optical transmission line is increased, and the handling is simplified. Therefore, the optical transmission line is extremely convenient.

The refractive index of the optical fiber is the core part.
At the boundary between the clad and the clad part
Up-index type optical fiber, with its core refraction
Rate n _f1, Clad part refractive index n_f2, Refraction of core of optical transmission line
Rate n_A2, And the refractive index n of the mixed solution_C1Is the formula (3)
You can meet the requirements. This conditional expression is
Satisfies the conditions for total reflection inside the Tep index type optical fiber
Light propagates through the core of the optical fiber.
Refracted at the boundary of the core of the transmission path, and the refracted light is transmitted again.
It is a condition that propagates while satisfying the total reflection condition in the road as well.
It

The refractive index of the mixed solution is adjusted so as to satisfy the conditional expression (3). Although it is possible to form an optical transmission line even when the conditional expression (3) is not satisfied, there are problems that the shape of the optical transmission line becomes non-uniform and the propagation loss due to light leakage increases. By satisfying the conditional expression (3),
All light propagating through the optical fiber is refracted at the boundary,
Similarly, it is propagated to the optical transmission line by total reflection. Total reflection in the optical transmission line means that the optical transmission line is continuously formed. That is, an optical transmission line is formed in which the core of the step index type optical fiber is linearly extended. As a result, a linear optical transmission line directly connected to the tip of the step index type optical fiber can be manufactured.

The optical fiber is a gradient index optical fiber having a refractive index gradient in a radial direction with a predetermined function, and has a maximum refractive index n _{f1 at} the center of the core of the optical fiber, a core diameter 2a _f , and a cladding. The _partial refractive index n _f2 , the core refractive index n _{A2 of} the optical transmission line, the refractive index n _C1 of the mixed solution, and the core diameter 2 a _w of the transmission line to be manufactured should satisfy the above formula (4). it can. However, p is an integer. This equation (4) is defined by the refractive index n _C1 of the mixed solution and the diameter 2 of the optical transmission line.
It shows that a _w can be controlled. The refractive index n _C1 can be adjusted by the mixing ratio of the above two types of photocurable resin solutions.

The refractive index of the mixed solution is selected so as to satisfy the equation (4). Therefore, the light that has propagated in the vicinity of the optical axis of the optical fiber with good straightness due to refraction is extracted through a smaller aperture. The light thus extracted has a better linearity and similarly forms a step index type optical transmission line in the mixed solution. Therefore, the optical transmission line manufacturing method can be applied to a graded index optical fiber used for high-speed communication.

According to the method of manufacturing the optical transmission line of the first aspect, the tip of the step index type optical fiber is dipped in the photo-curable resin solution, and light of a predetermined wavelength is emitted from the tip of the optical fiber. It The predetermined wavelength is, for example, short wavelength laser light. The short-wavelength light sequentially causes a photopolymerization reaction with respect to the photocurable resin solution in the optical axis direction. As a result, a shaft-shaped optical transmission line (core portion) that is in close contact with the core portion of the optical fiber and is continuously formed is obtained. Therefore, also in this case, it is not necessary to align the optical axis of the optical fiber with the optical axis of the optical transmission line. In the above description, the core part and the clad part of the optical transmission line are formed by light irradiation in two steps, and the core part and the clad part are called the optical transmission line. However, it is intended to form a linear optical transmission path (only the core portion) with one or more kinds of photocurable resin solutions. Therefore, in claims 1 and 2, the optical transmission line and the core portion thereof have the same meaning.

Further, according to the above manufacturing method, the refractive index n _f1 of the core of the step index type optical fiber, the refractive index n _{f2 of the} cladding, the refractive index n _{A2 of} the optical transmission line formed in the photocurable resin solution, The refractive index n _C1 of the photocurable resin solution satisfies the condition of the above formula (3). This conditional expression is that all the light propagating in the step index type optical fiber that satisfies the condition of total reflection is refracted at the boundary surface between the core part of the optical fiber and the optical transmission line, and the refracted light is photocured again. It is a condition that propagates while satisfying the total reflection condition in the optical transmission line in the organic resin solution.

The refractive index of the photocurable resin solution is adjusted so as to satisfy the conditional expression (3). Therefore, all the light propagating through the optical fiber is propagated to the optical transmission line, and the optical transmission line is sequentially formed while being totally reflected. That is, according to the manufacturing method of the present invention, an optical transmission line having good linear parallelism is formed in which the core portion of the step index type optical fiber is linearly extended as it is.

Incidentally, the refractive index of the photocurable resin solution becomes higher than that of the solution by curing, and if a solution satisfying the condition of formula (3) can be selected, even one kind of photocurable solution can be selected. It is feasible. In addition, when the core portion of the optical transmission line is formed with a plurality of kinds of solutions, the refractive index of one kind of solution that is selectively photocured is made higher than the refractive index of another kind of solution that is not photocured. It is possible to increase the difference between the refractive index of the core part and the refractive index of the mixed solution, and easily (3)
It is possible to select the solution so as to satisfy the condition of the formula. Therefore, the solution may be a single kind or a mixture of plural kinds. At this time, the periphery of the optical transmission line is an uncured photocurable resin solution (liquid), but the periphery of the optical transmission line is not particularly limited in actual use. It may be any other medium such as gas, other liquid, or solid. It suffices that their refractive index is smaller than that of the optical transmission line. For example, in actual use, it is taken out from the photocurable resin solution, washed, and used. At this time, the circumference of the optical transmission line is air, and its refractive index is higher than that of the surroundings. Therefore,
The condition of total reflection is maintained, and a step index type optical transmission line with less transmission loss is obtained. Further, if the surrounding area is a liquid, the optical transmission line has a liquid as a clad, and if it is a solid, a solid as a clad.

Further, the above-mentioned optical transmission line is a highly flexible shaft-shaped optical transmission line. This can be directly arranged on, for example, the emission port of a semiconductor laser element formed on a semiconductor substrate or a light receiving element having a small opening. Therefore, the manufacturing method of the optical transmission line is highly convenient for inputting and outputting light.

According to the method of manufacturing the optical transmission line of the second aspect, the optical fiber immersed in the photocurable resin solution has a gradient index optical fiber having a gradient of the refractive index with a predetermined function in the radial direction. The fiber has a maximum refractive index n _{f1 at} the center of the core of the optical fiber, a core diameter 2a _f , and a cladding refractive index n.
_f2, the refractive index n _A2 of the optical transmission path formed, the refractive index n _C1 of the photocurable resin solution, the diameter 2a _w of the optical transmission line to be formed,
The above formula (4) is satisfied. However, p is an integer. This equation (2) shows that the diameter 2a _w of the optical transmission line can be controlled by the refractive index n _C1 of the mixed solution. Refractive index n _C1
Can be adjusted by the mixing ratio of the above two kinds of photocurable resin solutions.

The refractive index of the photocurable resin solution is selected so as to satisfy the conditional expression (4). Therefore, the light that has propagated in the vicinity of the optical axis of the optical fiber with good straightness due to refraction is extracted through a smaller aperture. The light thus extracted has a better straight traveling property, and similarly forms a step index type optical transmission line in the photocurable resin solution. Therefore, the optical transmission line manufacturing method can be applied to a graded index optical fiber used for high-speed communication. Also in this case, as described above, one kind of solution can be used with a plurality of kinds of mixed solutions.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific embodiments. The present invention is not limited to the examples below. (First Embodiment) A method of manufacturing an optical transmission line according to the present invention will be described with reference to FIG. The manufacturing method is a so-called movable molding method having no movable part, which uses a photocurable resin which is a liquid monomer and a short wavelength laser which cures the resin. Moreover, the figure is a schematic view of a manufacturing apparatus. The manufacturing method of the present invention includes one of a mixed solution 100 in which two types of photocurable resin solutions having different curing start wavelengths and different refractive indexes after curing are mixed, a transparent container 110 holding the mixed solution, and a mixed solution. Short wavelength laser 120 that linearly cures the components, and mixed solution 100
It is composed of, for example, an ultraviolet lamp 130 which cures the whole. The optical transmission line includes the core portion 10 formed in the linear shape.
5 and a clad portion formed around the core portion 105 by curing the entire mixed solution 100.

A feature of the present invention is that two kinds of photocurable resin solutions having different curing start wavelengths and post-curing refractive indexes are mixed, and the mixed solution is used as a photocurable resin solution for stereolithography. . By irradiating light with different wavelength bands in two steps, a so-called step index type optical transmission line in which the refractive index of the core is higher than that of the surroundings is manufactured. Therefore,
First, a method for producing the above mixed solution and then a method for producing an optical transmission line using the same will be described.

The mixed solution is composed of, for example, an epoxy high refractive index photocurable resin solution having a refractive index of 1.49 and an acrylic low refractive index photocurable resin solution having a refractive index of 1.34. The spectral sensitivity characteristics of both are shown in FIG. The horizontal axis represents wavelength and the vertical axis represents relative sensitivity. Curve A is the spectral sensitivity characteristic of the epoxy high refractive index photocurable resin solution, and curve B is the spectral sensitivity characteristic of the acrylic low refractive index photocurable resin solution. As shown in the figure, the photocurable resin solution has a short-wavelength laser 12 whose curing start wavelength is used for curing.
It is selected so as to sandwich the wavelength λ ₁ of zero. Hereinafter, this photocurable resin solution having a high refractive index will be referred to as solution A, and that having a low refractive index will be referred to as solution B.

Generally, when solutions A and B having different refractive indexes are mixed, the refractive index n _c1 of the mixed solution is expressed by the equation (5) (Yamaguchi, “Refractive Index” Kyoritsu Shuppan (1981)).

N _C1 = [(2M (C _A ) +1) / (1−M (C _A ))] ^1/2 M (C _A ) = C _A (ρ / ρ _A ) (n _A1 ² −1) ) / (N _A1 ² +2) + (1-C _A ) (ρ / ρ _B ) (n _B1 ² -1) / (n _B1 ² +2) (5) Here, ρ: density of the mixed solution , [rho _a: density of the solution a, ρ _B: density of the solution B, n _A1: refractive index of the solution a n _B1: refractive index of the solution B, C _a: is the weight percent of the solution a. That is, if the photocurable resin solution having a high refractive index n _A1 and that having a low refractive index n _B1 are mixed at a certain ratio, a mixed solution 100 having a refractive index n _C1 with n _B1 <n _C1 <n _A1 is obtained. . Then, by selecting the parameters of the Ro～C _A, the mixture refractive index n _C1 of is uniquely determined. The refractive index n _C2 after curing is n _B2 <n _C2 <n _A2
Becomes Here, n _A2 and n _B2 are the refractive indexes of the solutions A and B after curing, respectively.

An optical transmission line is manufactured using such a mixed solution 100. The manufacturing process will be described below. First,
A transparent container 110 is filled with this mixed solution 100. next,
Laser light 125 is incident from the short wavelength laser 120. This short wavelength laser 120 has a wavelength λ ₁ = 32, for example.
It is a He-Cd (helium cadmium) laser of 5 nm. This wavelength is shorter than the curing start wavelength of the solution A and longer than that of the solution B as described above. Therefore, only solution A is cured. Further, since it is a laser beam, the beam 125 travels almost straight. Therefore, the linear core portion 105 is formed in the mixed solution 100. At this time, the solution B on the optical axis is pushed to the surroundings.

After the core portion 105 is formed, the ultraviolet ray lamp 130 irradiates the ultraviolet ray 135 having the wavelength λ ₂ uniformly from the surroundings. As shown in FIG. 2, this wavelength is shorter than the curing start wavelength of both solutions A and B. Therefore, both solutions are cured. As a result, around the core portion 105,
That is, the entire mixed solution 100 is cured to form the clad portion. At this time, when the refractive index of the clad portion before curing is n _C1 and that after curing is n _C2 , the refractive index n _{A2 of the} core portion 105 is
Have the following relationships:

(6) n _A2 > n _C2 > n _C1 (6) This is because the core refractive index n _A2 is the peripheral cladding refractive index n _C2.
This means a higher step index type optical transmission line. Therefore, other laser light introduced into this transmission line or other light introduced at an angle satisfying the condition of total reflection described later propagates while being totally reflected in the core portion 105 of the optical transmission line.

As described above, by mixing two kinds of photocurable resin solutions having different curing start wavelengths and different refractive indexes after curing and irradiating light having different wavelengths in two steps, it is possible to easily perform step index type optical transmission. A road can be formed. Further, the shape of the container, that is, the clad portion, can be arbitrarily determined depending on, for example, a product to be mounted. Therefore, the manufacturing method of the optical transmission line is extremely convenient. Further, the above-mentioned clad portion shape can be formed in accordance with various actuators such as piezoelectric elements that generate stress. This makes it possible to provide a basic optical element that measures various physical quantities based on the phase difference or a basic optical element that measures a chemical quantity based on the amount of absorbed light. Therefore, the above manufacturing method is a basic technique for manufacturing a useful optical element having an optical transmission path.

(Second Embodiment) FIG. 3 shows a second embodiment formed by using a step index type optical fiber.
The figure is a manufacturing process diagram. The method of forming the core portion and the clad portion by dividing the light irradiation into two steps is the same. The different point is that the tip of the step index type optical fiber is immersed in the mixed solution to form an optical transmission line integrated with the optical fiber. In addition, the refractive index of the mixed solution is adjusted according to the refractive index of the optical fiber in order to form a linear optical transmission line in close contact with the optical fiber.

In the first step (a) of FIG. 3, the tip of the step index type optical fiber 200 is immersed in the mixed solution 100. At this time, the refractive index n _C1 of the mixed solution is adjusted under a certain condition according to the refractive index of the inserted optical fiber as described later. In the second step (b), the short-wavelength light having the wavelength λ ₁ is introduced into the step index type optical fiber 200, and the core portion 10 is introduced into the emission port by the same mechanism as in the first embodiment.
5 is formed. In the third step (c), light irradiation with the wavelength λ ₁ is continued to allow the core portion 105 to reach the bottom of the transparent container 110. In the fourth step (d), the light irradiation with the wavelength λ ₁ is stopped, and instead, the ultraviolet light with the wavelength λ ₂ is irradiated from an ultraviolet lamp (not shown). Thereby, the core unit 1
The clad portion 106 is formed around 05. At this time, the tip of the optical fiber 200 is fixed in the clad 106. Therefore, an optical transmission line integrated with an optical fiber is formed without the need for optical axis alignment.

FIG. 4 is a horizontal sectional view of the optical transmission line formed in FIG. Centering around the core part 105, the transparent container 11
The clad 106 corresponding to the shape of 0 is formed. Also,
The horizontal axis shows the distance, and the vertical axis shows the refractive index distribution between AA ′ with the refractive index. The refractive index of the core part 105 is constant n _A2 (up to 1.
5), and that of the clad portion 106 is also constant n _C2 (~
1.4). Since n _A2 > n _C2 as described above, the step index type optical transmission line is the same type as the inserted optical fiber 200.

Further, the mixed solution 100 in the step (a)
The index of refraction is strictly adjusted. This is because, depending on the refractive index, the light emitted from the core of the optical fiber 200 is diffused to form a tapered optical transmission line with large propagation loss. Therefore, as shown in FIG. 5, in order to prevent light from diffusing at the interface between the core portion 205 and the core portion 105 of the transmission line, the refractive index n of the mixed solution 100 is adjusted under the conditions described below.
_C1 is adjusted.

The refractive index of the core portion 205 of the optical fiber inserted in the mixed solution 100 is n _f1 , the refractive index of the cladding portion 206 is n _f2 , and the refractive index of the core portion 105 of the optical transmission line to be formed is n _A2. Assuming that the refractive index of the mixed solution 100 is n _C1 , the adjustment condition is the expression (7).

[Formula 7] n _C1 ≤ [n _A2 ² −n _f1 ² + n _f2 ² ] ^1/2 (7)

This is because all the light propagating in the optical fiber 200 is mixed with the core portion 105 of the optical transmission line and the mixed solution 10.
It is derived from the condition of total reflection again at the interface with 0. Specifically, the total reflection condition (Equation (8)) at point A in FIG.
It is derived from the refraction condition at the point (Equation (9)) and the total reflection condition at the point C (Equation (10)).

(8) sin ⁻¹ (n _f2 / n _f1 ) = θ (8)

[Formula 9] n _f1 · sin (π / 2−θ) = n _A2 · sin θ _p (9)

Sin ⁻¹ (n _C1 / n _A2 ) ≦ π / 2−θ _p (10) where θ is the propagation angle and θ _p is the refraction angle corresponding to θ (FIG. 5). . From the above equations (8), (9), (10), θ, θ
_{If p} is eliminated, a relational expression (7) of the refractive index n _{C1 of the} mixed solution, the refractive indices n _f1 and n _{f2 of the} inserted optical fiber, and the refractive index n _A2 of the core portion of the formed optical transmission line is derived. .

When the refractive index n _C1 of the mixed solution 100 does not satisfy the above expression (7) but the expression (11), that is, the core portion 105 and the cladding portion 106 of the optical transmission line do not satisfy the total reflection condition. There are cases. In such a case, the core portion 10
Although a higher-order mode component leaks from 5 to the cladding portion 106, a substantially linear core portion 105 can be obtained at a distance of several cm from the optical fiber.

[N 11] [n _A2 ² −n _f1 ² + n _f2 ² ] ^1/2 <n _C1 <n _A2 (11)

As described above, in this embodiment, the mixed solution 100 is used.
The refractive index of the mixed solution is determined in consideration of the refractive index of the optical fiber 200 inserted in. As a result, the light emitted from the optical fiber goes straight, and the core portion 105 of the formed optical transmission line is not tapered unlike the conventional example. Therefore, according to the method of manufacturing the optical transmission line of the present embodiment, a step index type optical transmission line that is linearly extended from the emission port of the optical fiber along the optical axis can be obtained. Therefore, it is possible to manufacture a highly convenient optical transmission line that can be coupled to other optical elements.

(Third Embodiment) In the second embodiment, an optical transmission line of the same type is formed at the tip of the step index type optical fiber 200. The third embodiment is characterized in that a graded index type optical fiber having a refractive index distributed in the radial direction is adopted instead of the above optical fiber. The manufacturing process is the same as in the second embodiment. The difference is that the refractive index of the mixed solution is adjusted according to the refractive index of the graded index type optical fiber. According to this
An optical transmission line can be formed at the tip of the graded index type optical fiber.

Since the manufacturing process is the same as that of the second embodiment, the description thereof is omitted. Here, a method of determining the refractive index of the mixed solution will be described. FIG. 6 shows a cross-sectional view of the graded index type optical fiber 300 cut out along the optical axis and its refractive index distribution in the radial direction. The horizontal axis is the distance in the radial direction, and the vertical axis is the refractive index. The graded index optical fiber 300 includes a core portion 305 having a gradient in refractive index and a clad portion 306 that protects the core portion 305. The refractive index n _f (r) of the core portion 305 can be expressed by equation (12), where r is the distance from the center of the core portion 305. This equation (12) is, for example, (7.1), (7.1) on pages 117 to 123 of an introduction to optical fiber communication (Yasuharu Suematsu, Kenichi Iga, Ohmsha Publishing, 1975).
It is widely known as equation (2).

[Equation 12]   n_f ²(R) = n_f1 ²[1-2 (r / a_f)^p・ △]   △ = (n_f1 ²-N_f2 ²) / (2n_f1 ²) (12) Where a_fIs a graded index optical phi
Radius of the core portion 305 of the bar 300, n_f1Is in the core part 305
Maximum refractive index of the heart, n_f2Is the refractive index of the cladding portion 306, p
Is an integer representing the distribution type. For example, p = 2 is used
It Δ is called relative refractive index difference. Equation (12)
Is n when r = 0_f(0) = n _f1, R = a_fof
If n_f(A_f) = N_f2Meets

Conversely, when the radius r is obtained as a function of the refractive index n _f from the equation (12), the equation (13) is obtained.

R (n _f ) = a _f [1 / (2Δ) · (n _f1 ² −n _f ² ) / n _f1 ² ] ^{1 / p} Δ = (n _f1 ² −n _f2 ² ) / ( 2n _f1 ² ) (13) The above formula is the graded index optical fiber 3
It also holds at the interface between 00 and the mixed solution 100. FIG. 7 is an enlarged view of the vicinity of the interface. At this interface, when the radius of the core portion 105 formed as shown in FIG. 7 is a _W ,
The refractive index at that point is n _C1 (boundary condition in the radius r direction). Therefore, r (n _C1 ) = a _w . Therefore, (1
Expression 3) is given as the ratio of the optical fiber having the relative refractive index Δ and the arbitrary refractive index difference (that is, the relative refractive index difference given by n _f1 and n _f ) in this optical fiber. By substituting the relative refraction difference, the radius a _w of the optical transmission line connected to the optical fiber can be obtained as shown in the equation (14).

[Mathematical formula-see original document] a _w = a _f [1 / (2Δ) · (n _A2 ² −n _C1 ² ) / n _A2 ² ] ^{1 / p} Δ = (n _f1 ² −n _f2 ² ) / (2n _f1 ² (14) where n _A2 is the refractive index of the formed core portion 105.

From this boundary condition, the radius a of the core portion 105
By determining _W , the refractive index n _C1 of the mixed solution 100 can be determined. For example, n _f1 = 1.46, n _f2 = 1.
44, a _W = 24.9 μm, a _f = 50 μm, n _A2 =
When 1.49 and p = 2, the refractive index of the mixed solution is n _C1 = 1.
It becomes 485. This is the refractive index n _A1 , n _B1 of the solutions A and B.
And its weight% are adjusted to prepare. By adjusting in this way, it is possible to extract the light that has gone straight in the vicinity of the optical axis of the core portion 305 of the graded index type optical fiber 300 by further reducing the opening. Therefore, the light emitted from the core portion 305 goes straight better and forms the core portion 105 of the step index type optical fiber in the mixed solution 100.

FIG. 8 shows the outer diameter and the length of the core portion 105 of the optical transmission line produced by using the mixed solution 100 adjusted according to the above conditional expression. The horizontal axis represents the transmission path length, and the vertical axis represents the diameter. The transmission path length reached about 40 mm. Also,
A substantially constant diameter is maintained when the transmission path length is 0 mm to 10 mm.

As described above, in this embodiment, the refractive index of the mixed solution is determined in consideration of the refractive index of the graded index type optical fiber used. As a result, the core portion of the optical transmission line does not have a tapered shape, but extends straight from the core portion 305 with good straightness. Therefore, it is a useful optical transmission line manufacturing method applicable to a graded index type optical fiber used for high-speed communication. Further, the optical transmission line can be coupled with other optical elements without loss.

(Fourth Embodiment) In the second and third embodiments, a core of an optical transmission line linearly extended by using a mixed solution in which two kinds of photocurable resin solutions are mixed. Although the part was prepared, the linear core part can be formed by one type of photocurable resin solution and one kind of light, and the clad part can be formed by other means. Alternatively, if an inert gas is used as a medium surrounding the core portion to prolong the life, formation of the clad portion can be omitted. Therefore, the core section and the optical transmission line are used interchangeably herein.

For example, when a step index type optical fiber is used as the optical fiber, one type of photocurable resin solution whose refractive index n _C1 satisfies the above formula (7) is used.
The manufacturing process is the same as that of the second embodiment except for the final process of FIG. Since the refractive index n _C1 of the photocurable resin solution is adjusted so as to satisfy the expression (7), the mechanism described in the second embodiment works. As a result, a linear optical transmission line having a diameter substantially equal to that of the core of the step index type optical fiber is formed in the photocurable resin solution.

When a graded index type optical fiber is used as the optical fiber, one type of photocurable resin solution whose refractive index n _C1 satisfies the above formula (14) is used. The manufacturing process is the same as that of the second embodiment except for the final process of FIG. Since the refractive index n _C1 of the photocurable resin solution is adjusted so as to satisfy the expression (14),
The mechanism described in the third embodiment operates. As a result, a linear optical transmission line unit having a diameter smaller than the core diameter of the graded index type optical fiber is formed in the photocurable resin solution. Since these optical transmission lines have small diameters and flexibility, they can be directly arranged in the light emitting portions of LED elements and semiconductor laser elements formed on a semiconductor substrate. Therefore, it is a method of manufacturing an optical transmission line that enables flexible arrangement in other optical elements.

Incidentally, if a solution is selected so that the refractive index after photo-curing becomes higher than the refractive index of the solution and the formula (7) or the formula (14) is satisfied, one kind of light is generated as described above. It is also possible to use a curable solution. However, it may be a mixed solution of a photo-curable solution that cures with light of a certain wavelength and another photo-curable solution that has a smaller refractive index than the solution and that does not cure with light of that wavelength. In this case, the difference between the refractive index of the core portion after curing and the refractive index of the mixed solution can be increased, and the refractive index n _C1 of the mixed photocurable solution is expressed by the formula (7), (14).
It can be set to easily satisfy the formula. This makes it possible to easily form a core portion having a high linear parallelism that does not spread in a tapered shape. It is assumed that the optical transmission line has no clad portion, but the clad portion may be formed around the optical transmission line depending on the application. that is,
It is formed by the following procedure. For example, a photocurable resin solution having a refractive index n _C1 satisfying the above formula (7) or (14) is selected according to the optical fiber used. Then, it is used as a first photocurable resin solution and is cured to form the linear optical transmission line at the tip of the optical fiber. Then, the first photocurable resin solution is washed and immersed in the second photocurable resin solution. Then, the second photocurable resin solution may be cured. By doing so, the second embodiment and the third embodiment
A blocked clad portion equivalent to that of the example is formed. In addition, the second photocurable resin solution is not cured, and the second
After taking it out from the photocurable resin solution of 1., it may be left on the surface without being washed to be cured. If you do this,
A flexible optical transmission line can be formed with a small clad diameter. Further, the clad portion may not be completely cured. That is, it may be in a gel state or may be in a liquid state. Further, a gas such as air may be used. The refractive index of the optical transmission line is
The cladding can take different forms for different applications, as long as it is larger than that of the surrounding medium.

(Modifications) Although the embodiments showing the present invention have been described above, various modifications can be considered. For example, the first
A helium-cadmium laser (λ = 325 nm) was used as the short-wavelength laser in the examples, but an argon ion laser (λ = 488 nm) or an ultra-high pressure mercury lamp (λ = 380 nm) may also be applied depending on the photocurable resin solution. Is.

In the first to third embodiments, the mixed solution is an epoxy-based high refractive index photocurable resin solution having a refractive index of 1.49 and an acrylic low-refractive index having a refractive index of 1.34. Although it is composed of a photo-curable resin solution, other material systems may be used as long as the curing start wavelength and the refractive index after curing are different. For example, a fluorine-based monomer or a silicon-based material in which a photoreaction initiator is mixed may be used. It suffices if the above-mentioned spectral sensitivity characteristics and refractive index conditions are satisfied.

Although the step index type optical fiber and the graded index type optical fiber are used in the above embodiment, other fibers may be used. A polarization maintaining fiber, a single mode fiber or the like may be used.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a method for manufacturing an optical transmission line according to a first embodiment.

FIG. 2 is a spectral sensitivity characteristic diagram of the mixed solution according to the first embodiment.

FIG. 3 is a configuration diagram of a method for manufacturing an optical transmission line according to a second embodiment.

FIG. 4 is a cross-sectional view of an optical transmission line according to a second embodiment.

FIG. 5 is an explanatory diagram of propagation conditions in the optical transmission line of the second embodiment.

FIG. 6 is an explanatory diagram of a refractive index distribution related to the optical fiber according to the third embodiment.

FIG. 7 is a relational diagram regarding the core diameter of the optical fiber and the optical transmission line according to the third embodiment.

FIG. 8 is a relationship diagram of a core diameter and a core length of the optical transmission line according to the third example.

[Explanation of symbols]

100 mixed solution 105, 205, 305 core part 106, 206, 306 clad part 110 transparent container 120 short wavelength laser 125 short wavelength laser light 130 ultraviolet lamp 135 ultraviolet light 200 step index type optical fiber 300 graded index type optical fiber

Continued front page    (72) Inventor Hiroshi Ito             Aichi Prefecture Nagachite Town Aichi District             Ground 1 Toyota Central Research Institute Co., Ltd. (72) Inventor Yasuhiko Takeda             Aichi Prefecture Nagachite Town Aichi District             Ground 1 Toyota Central Research Institute Co., Ltd. F term (reference) 2H047 KA03 KA15 MA05 PA02 PA22                       PA28 QA05                 2H050 AA13 AA14 AA17 AC03 AC05

Claims (2)

[Claims] 1. An optical fiber tip is dipped in a photocurable resin solution, and light of a predetermined wavelength is emitted from the optical fiber tip,
In a method of manufacturing an optical transmission line in which a continuous optical transmission line is produced from the tip of the optical fiber by curing the photocurable resin solution in the optical axis direction, the optical fiber has a refractive index of a core portion and a clad portion. Is a step index type optical fiber that changes stepwise at the boundary of the core part, the core part refractive index is n _f1 , the cladding part refractive index is n _f2 , the refractive index of the optical transmission line is n _A2 , and the photocurable resin solution is The method of manufacturing an optical transmission line in which the refractive index of the photocurable resin solution is adjusted so that the condition of the expression (1) is satisfied when the refractive index of the above is n _C1 . [Equation 1] (n _f1 ) ² − (n _f2 ) ² ≦ (n _A2 ) ² − (n _C1 ) ² (1) 2. An optical fiber tip is dipped in a photocurable resin solution, and light of a predetermined wavelength is emitted from the optical fiber tip,
In a method of manufacturing an optical transmission line, in which a continuous optical transmission line is produced from the tip of the optical fiber by curing the photocurable resin solution in the optical axis direction, the optical fiber is refracted in a radial direction by a predetermined function. A graded index optical fiber having a refractive index gradient, wherein the maximum refractive index at the center of the core of the optical fiber is n _f1 , the core diameter is 2 a _f , the cladding refractive index is n _f2 , and the refractive index of the optical transmission line is N _A2 , the refractive index of the photo-curable resin solution is n _C1 , and p is an integer, the photo-curable resin solution is prepared under the condition that the diameter 2a _w of the optical transmission line to be manufactured satisfies the expression (2). A method for manufacturing an optical transmission line, characterized in that the refractive index of is adjusted. 2 a _w = 2a _f [1 / (2Δ) · (n _A2 ² −n _C1 ² ) / n _A2 ² ] ^{1 / p} where Δ = (n _f1 ² −n _f2 ² ) / (2n _f1 ² ) ・ ・ ・ (2)