JP2001281482A - Optical waveguide and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide easy in manufacturing and high in a yield. SOLUTION: In the optical waveguide having structure wherein a core 3 consisting of resin is held between a pair of clads 21, 22 consisting of resin having a refractive index lower than that of the core 3, the core 3 exists within a groove formed in one side of clad 21, the width of the groove is not increased as the depth from the surface of one side of clad 21 is increased in the cross section orthogonal to the propagating direction of light, and moreover at least a part of the contour of the groove is composed of a curved line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide which is used for optical passive components such as a demultiplexer, a multiplexer and an optical switching element in an optical communication field, and which can be applied to an optical integrated circuit. It relates to a manufacturing method.

[0002]

2. Description of the Related Art With the practical use of optical communication, optical waveguides have attracted attention. The optical waveguide is formed by covering a core made of a high refractive index material with a clad made of a low refractive index material.

As a method for manufacturing an optical waveguide, for example, a method in which a thin film forming method such as a sputtering method, a CVD method, or a vacuum evaporation method is used in combination with a fine processing technique such as photolithography is well known. Thus, a core having a rectangular cross section with a clear boundary can be formed. However, in these methods, it is necessary to repeat the formation and etching of the thin film, so that the number of steps is increased and the cost is increased.

[0004] As an optical waveguide that can significantly reduce the manufacturing cost, an optical waveguide in which a core and a clad are made of resin has been proposed. For example, in Japanese Patent Publication No. 7-9492, a substrate (cladding) made of resin and having a groove having a rectangular cross section is manufactured by injection molding, casting, compression molding, or the like.
A method of manufacturing an optical circuit board (optical waveguide) by filling a resin of a core material into the groove is described.

[0005]

SUMMARY OF THE INVENTION The above Japanese Patent Publication No. 7-949.
As described in Japanese Patent Laid-Open No. 2 (1993) -2000, if the groove for burying the core is integrally formed at the time of manufacturing the clad, the manufacturing process can be significantly simplified.

However, according to the experiments by the inventors of the present invention, when a clad is formed by injection molding or the like using a mold in which a ridge having a rectangular cross section corresponding to the core size is formed,
It was found that when the clad was released from the mold, chipping occurred in the vicinity of the groove and the yield was reduced.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical waveguide which is easy to manufacture and has a high yield.

[0008]

The above object is achieved by the following (1).
This is achieved by the present invention of (4). (1) An optical waveguide having a structure in which a core made of a resin is sandwiched between a pair of clads made of a resin having a lower refractive index than the core, wherein the core is present in a groove formed in one of the clads, and light is propagated. In a cross section perpendicular to the direction, the groove does not increase in width with an increase in the depth from the one clad surface, and at least a part of a profile of the groove is formed of a curve. Optical waveguide. (2) At least a part of the contour of the groove has a radius of curvature of 5
The optical waveguide according to the above (1), which is constituted by a curve of not less than μm. (3) The optical waveguide according to (1) or (2), wherein an angle between a depth direction of the groove and a tangent to a contour of the groove is 1 degree or more in a cross section perpendicular to the light propagation direction. (4) A method for manufacturing the optical waveguide according to any one of the above (1) to (3), wherein a step of forming one clad having a groove, a step of filling a core material in the groove, Laminating the other clad on the surface of one clad on which the grooves are formed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1E shows a cross section perpendicular to the light propagation direction of a conventional optical waveguide. This optical waveguide has a structure in which a core 3 is sandwiched between a pair of claddings each having a plate-like lower cladding 21 and an upper cladding 22. The core 3 is embedded in a groove formed in the lower clad 21. Both the clad and the core are made of resin. In FIG. 1E, the groove in which the core 3 is embedded has a rectangular cross section. For this reason, as described above, when the lower clad 21 is manufactured by injection molding or the like and is released from the mold, the lower clad is likely to be chipped near the groove.

FIG. 1 shows an example of the configuration of an optical waveguide according to the present invention.
(A), FIG. 1 (B), FIG. 1 (C) and FIG. 1 (D).

In FIG. 1A, the groove in which the core 3 is embedded has a constant width regardless of the depth. The boundary between the upper surface of the lower clad 21 and the groove and the boundary between the side surface of the groove and the bottom surface of the groove are formed by curves.

In FIG. 1B, the groove in which the core 3 is buried has a contour whose width decreases as the depth increases. The boundary between the upper surface of the lower cladding 21 and the groove is formed by a curve, and all other groove contours are formed by a curve.

In FIG. 1C, the groove in which the core 3 is buried has a contour whose width decreases as the depth increases. The boundary between the upper surface of the lower clad 21 and the groove and the boundary between the side surface of the groove and the bottom surface of the groove are formed by curves.

As described above, the groove in the present invention does not increase in width as the depth from the cladding surface increases, and at least a part of the groove contour is formed by a curve. Therefore, when releasing the clad from the mold,
The boundary between the upper surface of the clad and the groove and the boundary between the side surface of the groove and the bottom surface of the groove are not easily chipped. In addition, the inventors have found that introducing a curve into at least a part of the contour of the core hardly affects the propagation loss.

FIG. 1A, FIG. 1B and FIG.
In the example shown in (C), the boundary between the upper surface of the clad and the groove is constituted by a curve, and the boundary between the side surface of the groove and the bottom of the groove or the entire contour of the groove is constituted by a curve. 1
As shown in (D), only the boundary between the clad upper surface and the groove may be a curve, or only the boundary between the groove side surface and the groove bottom may be a curve, or the boundary between the clad upper surface and the groove may be formed as a curve. Only the entire groove contour excluding may be a curve.
However, it is preferable that at least the boundary between the upper surface of the clad and the groove is formed by a curved line because the chip is most likely to occur.

The curve forming at least a part of the groove preferably has a radius of curvature of 5 μm or more, more preferably 10 μm or more. If the radius of curvature is too small,
The effect of preventing breakage of the clad during mold release tends to be insufficient.

In the illustrated cross section, the angle between the depth direction of the groove and the tangent to the contour of the groove is preferably at least 1 degree, more preferably at least 3 degrees. This angle is the angle θ exemplified in FIG. By forming at least a part of the groove with a curved line and setting the angle θ in this manner, the effect of preventing the clad from being damaged at the time of releasing the mold is significantly increased. However, if the angle θ is too large, the function of the optical waveguide as a core is impaired. Therefore, the angle θ is preferably 20 degrees or less, more preferably 10 degrees or less.

The resin constituting each of the core and the cladding is not particularly limited, and may be appropriately selected so that the cladding has a lower refractive index than the core. The refractive index difference between the two is
What is necessary is just to set suitably according to various conditions, such as a use mode. It is generally preferable to use a thermoplastic resin, a thermosetting resin, or a photocurable resin for the clad constituent material, and to use a photocurable resin for the core constituent material.

In the present invention, the dimensions of the core are not particularly limited. For example, the present invention can be applied to a single mode optical waveguide having a core diameter of about 5 to 10 μm and a multimode optical waveguide having a core diameter of about 50 μm to 1 mm.

[0020] The optical waveguide of the present invention comprises a step of forming one clad having a groove, a step of filling a core material in the groove, and a step of forming the other clad on the surface of the one clad where the groove is formed. And a step of stacking. Others are not particularly limited, but usually,
It is preferable to manufacture by the method described below.

In this method, first, a lower clad and an upper clad are formed. The groove for burying the core is also
It is formed integrally during clad molding. Injection molding is preferred as a means for molding the clad, but any of casting molding, pressurized heat molding and the like may be used.

Although there is no particular limitation on the method for forming the groove provided in the clad in the sectional shape defined by the present invention, for example, the method described below can be used.

At the time of the cladding molding, a metal master (stamper) having a ridge that serves as a matrix pattern of a groove is provided in a molding space to form a mold, or a ridge is formed on a mold itself constituting the molding space. Or to form. The ridge is generally formed by photolithography. In photolithography, if the exposure conditions and development conditions are appropriately controlled,
Since the corners of the rectangular cross section of the ridge can be blunted, the ridge corresponding to the groove shape defined in the present invention can be formed.

Further, even if the ridge provided on the mold has a rectangular cross section with sharp corners, the groove having the shape limited by the present invention is deliberately lowered by intentionally lowering the transfer accuracy during molding. Can be formed. For example, if the molding conditions are set such that a predetermined amount of air remains near the base of the ridge during injection molding, a clad having a curved boundary between the upper surface of the clad and the groove can be obtained. Also, if the mold temperature during injection molding is set relatively low, the resin will be cooled on the mold surface and the fluidity will decrease, and as a result, the resin will completely enter the base of the ridge. Disappears. As a result, a clad in which the boundary between the upper surface of the clad and the groove is curved is obtained. The method of lowering the mold temperature has the effect of improving productivity because the molding cycle can be accelerated.

After the clad is formed in this manner, the resin for the core is filled in the groove provided in the lower clad. For filling the resin, application or pouring can be used. At this time, since it is necessary to fill up to the upper end of the groove, the resin usually spreads to the lower clad surface. When the upper clad is laminated in this state, a resin layer (resin layer 31 shown) continuous to the upper end of the core exists between the lower clad and the upper clad. The thicker the resin layer, the greater the propagation loss of the optical waveguide. Therefore, if necessary, at least a part of the resin spread on the lower clad surface is removed by a squeegee or the like.

Next, an upper clad is laminated on the lower clad. When a photocurable resin is used as the core material, curing light is irradiated after laminating the upper clad. By curing the core and the resin layer continuous with the upper end thereof, the upper clad and the lower clad are adhered to complete the optical waveguide.

The upper clad can be formed by applying or pouring a resin.

[0028]

EXAMPLE A thermoplastic acrylic resin was prepared as a cladding material, and an ultraviolet curable acrylic resin was prepared as a core material.

The stamper on which the ridges were formed was placed in a molding space of a molding apparatus, and a lower clad was formed by injection molding. The cross section of the ridge was a rectangle having a width of 50 μm and a height of 50 μm. The temperature of the stamper during molding was 70 ° C. As a result, a lower clad 21 having the shape shown in FIG. 1D was obtained. The radius of curvature of the curve existing on the contour of the groove was 7 μm. When this lower clad was released from the stamper, the rate of chipping was 5%.

On the other hand, for comparison, the temperature of the stamper was set to 9
Injection molding was performed at 0 ° C. to obtain a lower clad 21 having the shape shown in FIG. When this lower clad was released from the stamper, the rate of chipping was 60%.

A core material was poured into the grooves of the lower clad, and then the upper clad formed by injection molding was adhered to produce an optical waveguide sample. When the insertion loss was measured for these samples, the increase of the insertion loss in the sample of the present invention was as small as about 1 dB as compared with the comparative sample having a rectangular core cross section.

[0032]

According to the present invention, since the cross section of the groove for burying the core provided in the clad has a predetermined shape, it is possible to prevent the clad from being damaged when the mold is released from the mold.

[Brief description of the drawings]

FIGS. 1A, 1B, 1C, and 1D are cross-sectional views illustrating a configuration example of an optical waveguide of the present invention, and FIG. 1E is a cross-sectional view illustrating a configuration example of a conventional optical waveguide. It is.

[Explanation of symbols]

 21 Lower clad 22 Upper clad 3 Core 31 Resin layer

Claims (4)

[Claims] 1. An optical waveguide having a structure in which a core made of a resin is sandwiched between a pair of clads made of a resin having a lower refractive index than the core, wherein the core exists in a groove formed in one of the clads, In a cross section perpendicular to the light propagation direction, the groove does not increase in width with an increase in the depth from the one clad surface, and at least a part of a profile of the groove is formed of a curve. Optical waveguide. 2. The optical waveguide according to claim 1, wherein at least a part of the contour of the groove is formed by a curve having a radius of curvature of 5 μm or more. 3. The optical waveguide according to claim 1, wherein an angle between a depth direction of the groove and a tangent to a contour of the groove is 1 degree or more in a cross section perpendicular to the light propagation direction. 4. The method for manufacturing an optical waveguide according to claim 1, wherein one of a clad having a groove is formed, and a core material is filled in the groove. Laminating the other clad on the surface of the clad formed with the grooves.