JPS6019107A - Manufacture of optical waveguide - Google Patents

Abstract

PURPOSE:To manufacture an optical waveguide whose core part has a nearly square refractive index distribution by irradiating ultraviolet light twice under different timing conditions on the surface of a film of a transparent photopolymerizable soln. which changes its refractive index when exposed to ultraviolet light. CONSTITUTION:A casting soln. is poured in a container 10, gaseous nitrogen is fed, and after feeding monomer vapor, part of a monomer is evaporated to form a sheetlike transparent semisolid film 14. Ultraviolet rays 13 are inrradiated on the film 14 with an ultraviolet-ray exposer 12 to provide a nearly square refractive index distribution in the thickness direction. Gaseous nitrogen and monomer vapor are further fed, a photomask 15 is placed on the film 14, and ultraviolet rays 13 are irradiated to provide a nearly square refractive index distribution in the lateral direction. The refractive index of the central part of the resulting optical waveguide in the lateral direction is highest, and the refractive index is gradually reduced toward the peripheral part.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a method for manufacturing a leading waveguide, particularly a multimode refractive index optical waveguide which can be connected to a graded index optical fiber.

(b) Prior art and its problems Conventionally, in order to create an optical waveguide, a two-selective photopolymerization method is used to obtain a polymer optical waveguide. However, the optical waveguide obtained by the abundant light polymerization method is a step-index type with a constant refractive index in the core, so it is compatible with step-index type optical fibers, but it is a graded-index type for broadband optical transmission. When connecting to an optical fiber, there are problems such as poor compatibility, increased connection loss, and transmission delay due to dispersion of optical modes.

That is, the conventional optical waveguide is made of a film 1 formed by casting, for example, as shown in Figure 1(a).
A mask 2 having a width corresponding to the width of the optical waveguide to be created is placed on top of the mask 2, and ultraviolet light 3 is irradiated from above to form a shiffred portion by photopolymerization on the part of the film 1 that is not blocked by the mask 2. 4, and in the portion of the film 1 that is shielded from light by the mask 2, a core portion 5 with a high refractive index, which is the same as the base material, is formed, since photopolymerization does not occur. In this optical waveguide, the refractive index difference distribution seen in the X-Y section in the depth direction is substantially constant as shown in FIG. 1(b). The refractive index distribution seen in the width direction x'-y' cross section is still shown in Figure 1 (
As shown in c), the refractive index is approximately constant in the width direction as well9.
．． It can be seen that this optical waveguide is of a step index type.

By the way, optical waveguides are generally used for high-speed optical transmission.

When performing optical information processing, it is necessary to use a gray rad index fiber with a refractive index distribution (square distribution) in the core portion as the optical fiber to reduce mode dispersion of light. However, as mentioned above, the conventional leading waveguide is of the step-index type, so when coupled with a gray-rad index fiber, the refractive index distribution of the core part cannot be matched, resulting in large mode dispersion, resulting in a delay in the optical transmission signal and a waveform. The disadvantage was that the strain increased.

(c) Purpose of the Invention In view of the above, an object of the present invention is to provide a method for manufacturing an optical waveguide that can manufacture an optical waveguide in which the refractive index distribution in the core portion of the optical waveguide is approximately a square distribution. .

B) Structure and effect of the invention In order to achieve the above object, the method for manufacturing an optical waveguide of the present invention applies ultraviolet light to the surface of a film-like film of a transparent photopolymerization solution whose refractive index changes when irradiated with ultraviolet light. to form a refractive index distribution in the film thickness direction of the film-like film, and then irradiate the surface of the film-like film with ultraviolet light having an intensity distribution that is weak in the center and strong enough to reach the periphery. Light is irradiated to form a refractive index distribution also in the horizontal width direction of the film-like film, and the film-like film forms a leading waveguide.

According to this invention, the photopolymerization timing by ultraviolet light can be adjusted to 2 times.
Firstly, a refractive index distribution is formed in the film thickness direction by using the degree of attenuation of ultraviolet light in the depth direction, and a refractive index distribution is formed in the width direction by using the strength and weakness of the ultraviolet light. It is a thing,
This is because such a film-like membrane is used to construct the leading waveguide.

An optical waveguide having a refractive index distribution of approximately square distribution can be obtained. Furthermore, when the optical waveguide obtained in this way is coupled to a gray rad index fiber, the refractive index distribution of the core can be matched.

Splice loss is reduced, and optical signal delay waveform distortion due to optical mode dispersion is reduced. Therefore, the optical waveguide obtained by implementing the present invention can be widely used in optical fiber sensors, high-speed optical transmission, high-speed optical information processing, etc.

Next, the principle of adoption of this invention will be explained in Figures 2 to 4.
A little explanation will be given with reference to the figure.

FIG. 2 shows the relationship between the change in refractive index after photopolymerization and the evaporation time of the casting solution.

As shown in the figure, the shorter the evaporation time and the smaller the amount of evaporation of the solvent and monomer, that is, the larger the amount of monomer contained,
The larger the change Δn in the refractive index after photopolymerization is, and conversely, the longer the evaporation time, the smaller the change Δn in the refractive index. That is, for the evaporation time TI<T2<T6, the refractive index change is △nl
) Δn2) Δn3.

In addition, the shorter the evaporation time, the greater the change in the refractive index on the film surface after photopolymerization, but the larger the scattering due to phase separation between the base material and monomer, the more the ultraviolet light does not reach deep, so the refractive index near the back surface of the film increases. Changes decrease rapidly. Now, the 6th
As shown in Figure (a).

Figure 6 (b) shows the refractive index distribution in the depth and width directions of the leading waveguide obtained by photopolymerizing the same film as in Figure 1 (a) but with a very short evaporation time. ).

The result is as shown in FIG. 6(c). As is clear from FIG. 6(b), the refractive index difference distribution at the interface between the core portion 5 and the cladding portion 4 is large near the surface, and rapidly decreases near the back surface. In other words, the refractive index distribution in the depth direction has a shape approximately similar to a square distribution. On the other hand, the refractive index distribution in the width direction of the core portion 5 is constant as shown in FIG. 6(C), and has a step index shape.

FIG. 4 shows the relationship between the amount of ultraviolet light irradiation and the photopolymerization rate α. As shown in the figure, the larger the irradiation amount, the larger the photopolymerization rate α. As the amount of ultraviolet light irradiation increases, the rate of polymerization between the base material and the monomer increases, and the change in refractive index after photopolymerization of the base material also increases. That is, the refractive index can be controlled by the amount of ultraviolet light irradiated.

This invention has been described above. In photopolymerization after a short evaporation time,
A refractive index distribution of approximately square distribution occurs in the depth direction, and the photopolymerization rate changes when the amount of ultraviolet light irradiation is changed.

Two principles are used: the refractive index is also different.

(e) Description of examples Hereinafter, this invention will be explained in more detail with reference to Examples.

FIG. 5 is a sectional view showing one process of the embodiment of the present invention. In the figure, 10 is a cast container.

11 is a level for keeping the casting solution in the casting container 10 horizontal; 12 is an ultraviolet exposure device that generates parallel ultraviolet rays 16;

First, a squared refractive index distribution is formed in the depth direction (film thickness direction) of the optical waveguide. Therefore, the casting solution is placed in the casting container 10. The casting container 10 is pre-cleaned, for example with methylene chloride CHZC4z, before containing the casting solution. As a casting solution, for example, bisfe/-/l/Z-based polycarbonate PC is used as the base material.
Z 70 Methyl acrylate/l/M'A as L monomer
42. ysl, methylene chloride CH2Cl as solvent
A blend of 21,000 f, benzoin ethyl ether/L/BZEE2.1 f as a photosensitizer, and 0.07 g of hydroquinone HQ as an inhibitor is used.

The amount of casting solution is adjusted so that the film thickness is 100 μIl+. Further, the liquid level is leveled by adjusting the spirit level 11.

Next, the cast container 10 is semi-sealed, nitrogen gas is flowed at 1001/min for 100 minutes, and monomer vapor is then flowed for 20 minutes to evaporate a portion of the solvent and monomer.
A sheet-like transparent semi-solid film 14 is created.

Next, the ultraviolet exposure device 12 is activated to generate ultraviolet light 13 and irradiate the film 14 for about 5 minutes.

The film 14 subjected to the above treatment is shown in FIG. 6(a),
As shown in (b), the vicinity of the front surface iJa of the film 14 is strongly photopolymerized, while the vicinity of the back surface 14b is hardly affected by ultraviolet light, and therefore the refractive index is extremely small near the front surface 14a.

Near the back surface 14b, the refractive index is not equal to that of the base material PO2, and the refractive index distribution therebetween is approximately a square distribution.

In Figure 5, after exposure to ultraviolet rays, 1 liter of nitrogen gas is added.
00#Il/min for 50 minutes, then the monomer vapor was
Run for 0 minutes to further evaporate some of the solvent and monomer.

Next, a process of forming a square distribution refractive index distribution in the width direction of the optical waveguide will be explained.

FIG. 8 is a cross-sectional view for explaining this process. In addition to what is shown in FIG. 5, a photomask plate 15 having a double mask pattern 16 is placed on the film 14.

The mask pattern 16 of this mask plate 15 is shown in FIG.
), the transmittance is configured to increase sequentially from the center to the periphery with respect to the width of the core portion of the guiding waveguide. Therefore, the amount of ultraviolet light transmitted is shown in Figure 7(b).
As shown in the figure, the center is small and it gets larger towards the periphery. Such a mask pattern is realized by forming shading by a combination of chrome mask patterns having a diameter of, for example, about 01 μm.

In FIG. 8, with a sufficiently long evaporation time, the ultraviolet exposure device 12 is operated, and from above the mask plate 15,
Ultraviolet light 16 is irradiated. As a result, the central portion of 9.37 parts undergoes little photopolymerization, while the one peripheral portion undergoes photopolymerization to a large extent, resulting in a large change in the refractive index of the first peripheral portion relative to the base material. In other words, the refractive index is highest near the center of the width of the optical waveguide, and is the smallest at the periphery, so that an approximately square-law distribution of refractive index is formed in the width direction.

After the above exposure is completed, as a post-processing, the cast material is left at room temperature for 60 minutes or more, and then transferred to a vacuum dryer (not shown) every 20 minutes, and dried at 90° C. for about 10 hours. Next, the surface is barcoded with a low refractive index coating agent to a thickness of 10 μm to form a coating layer 21 (see FIG. 9(a)), and dried in a hot air dryer at 90° C. for 5 hours.

Furthermore, 2 optical waveguides created by steps 1 or more 22゜23
are superimposed as shown in FIG. 9(a). This results in
The refractive index distributions in the depth and width directions are shown in Figure 9(b) and ((
1) A leading waveguide 24 of 200×200 μm as shown in
can be obtained. Since this optical waveguide 24 has a refractive index distribution of approximately square distribution, it can be matched well with a graded index fiber having a core diameter of 200 μfilO.

In the above embodiments, the case where the film was produced by a casting method was explained, but other methods,
For example, one kanji may be created using centrifugal force using a spinner or the like.

Further, in the above embodiment, a mask plate is used to form the refractive index distribution in one width direction, but it is also possible to selectively scan the laser beam by modulating and deflecting the laser beam. good.

In the above embodiment, the case where two optical waveguides are finally bonded together has been described, but a gradient index optical waveguide may be integrally formed by simultaneously exposing one surface and the back surface.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a conventional optical waveguide manufacturing method, and FIG. 1(a) is a cross-sectional view of the conventional optical waveguide. Figure 1(b) is a diagram showing the refractive index distribution in the depth direction of the optical waveguide, Figure 1(C) is a diagram showing the refractive index distribution in the width direction of the leading waveguide, and Figure 2 is a diagram showing the refractive index distribution in the width direction of the leading waveguide. FIG. 6 is a diagram illustrating changes in refractive index with respect to evaporation time, and FIG. 6 is a diagram illustrating changes in refractive index when the evaporation time is shortened. FIG. (b) is a diagram showing the refractive index distribution in the depth direction, FIG. 6 (C) is a diagram showing the refractive index distribution in the width direction, and FIG. 4 is a diagram showing the relationship between light illumination 1A4 desire and photopolymerization rate. , FIG. 5 is a sectional view explaining one process of an embodiment of the present invention, and FIGS. 6(a) and 6(b) are diagrams showing the refractive index distribution of the film obtained in the same process. FIG. 7(a) is a diagram showing the mask pattern of a mask plate used in an embodiment of the present invention, FIG. 7(b) is a diagram showing the light transmission characteristics of the same mask plate, and FIG. FIG. 9 (11) is a sectional view illustrating another part of the embodiment of the invention, and FIG.
b) is a diagram showing the refractive index distribution in the depth direction of the optical waveguide, and FIG. 9(C) is a diagram showing the refractive index distribution in the width direction of the leading waveguide. 10: Cast container, 12: Ultraviolet exposure device. 16: Ultraviolet light, 14: Film membrane. 15: Mask board, 16: Mask pattern. Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] (1) By irradiating ultraviolet light onto the surface of a film-like film of a transparent photopolymerization bath liquid whose refractive index changes when irradiated with ultraviolet light,
A refractive index distribution is formed in the thickness direction of the film-like film, and then the surface of the film-like film is irradiated with ultraviolet light having an intensity distribution that is weak at the center and stronger at the periphery. A method for manufacturing an optical waveguide, characterized in that a refractive index distribution is also formed in the horizontal width direction of the film, and a leading waveguide is configured with the film-like film.