JP2005284248A - Optical waveguide having micromirror formed by laser beam machining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide having means for performing optical coupling with high efficiency at an arbitrary position in an optical circuit substrate including an optical-electrical circuit board. <P>SOLUTION: A projected part 12a of the optical waveguide is irradiated with a high output laser beam 15 such as an excimer laser or a carbon dioxide gas laser through an optical waveguide film at an angle of 45° and a hole is made at an angle of 45° with respect to the waveguide face. The hole is used as a micromirror and the light beam is combined with a light receiving element or the like. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a polymer optical waveguide capable of changing an optical path, and more particularly to a method of manufacturing an optical integrated circuit, an optical component for optical interconnection, an opto-electric hybrid board, and the like.

  As base materials for optical components or optical fibers, inorganic materials such as quartz glass and multicomponent glass, which have the characteristics of low light propagation loss and wide transmission band, are widely used. System materials have also been developed and are attracting attention as materials for optical waveguides because they are superior in processability and price compared to inorganic materials. For example, a flat plate type having a core-clad structure in which a polymer having excellent transparency such as polymethyl methacrylate (PMMA) or polystyrene is used as a core and a polymer having a refractive index lower than that of the core material is used as a cladding material. An optical waveguide is produced (Patent Document 1). On the other hand, a low-loss flat optical waveguide is realized using polyimide, which is a transparent polymer with high heat resistance (Patent Document 2).

  Surface emitting lasers (VCSEL) are being mounted in the field of optical interconnection due to demands for cost reduction, etc., but laser light emitted perpendicular to the substrate is incident on an optical waveguide that is horizontal to the substrate. Sometimes, an optical path change of about 90 ° is required. The polymer optical waveguide is cut at about 45 ° by a dicing saw to enable 90 ° optical path conversion (Patent Document 3). However, when a dicing saw is used, unnecessary portions are cut out at 45 °. Therefore, it can be said that if a dicing saw is used, it is impossible to form an optical coupling for optical path conversion at an arbitrary location in the substrate.

  On the other hand, a technique for forming a circular hole using an excimer laser on an optical printed circuit board has also been reported (Non-patent Document 1). When the hole is circular, it is equivalent to the formation of a microlens. Normally, light diverges and coupling efficiency is greatly deteriorated. In order to improve the coupling efficiency, complicated asymmetric coupling optical systems are required, and they must be arranged on the order of a micron or less. This is unrealistic in an opto-electric hybrid board.

In recent years, there has been an increasing demand for miniaturization of optical components using optical waveguides. Therefore, it is necessary to bend, branch, and multiplex light at a short distance. Further, in the opto-electric hybrid board, it is necessary to wire light at various points in the shortest distance. However, in the case of the conventional bent optical waveguide and the multiplexed / demultiplexed optical waveguide, the optical waveguide that can be manufactured due to the limitation of the relative refractive index difference cannot be less than a certain size or length. Therefore, an optical waveguide that can make such a circuit small has been demanded.
JP-A-3-188402 JP 04-9807 Japanese Patent Laid-Open No. 10-300961 IEICE Transactions 2001/9 Vol.J84-C No.9 724-725

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide provided with means capable of optically coupling at an arbitrary position in an optical circuit board including an opto-electric hybrid board in order to avoid the above-described problems. It is another object of the present invention to provide an optical waveguide that realizes a small optical waveguide that performs steep optical path conversion and multiplexing / demultiplexing in an optical circuit.

As a result of intensive studies, the present inventor has found that the above-mentioned problems can be solved by performing drilling using a laser at an arbitrary position of the optical waveguide, and has completed the present invention. That is, the present invention is an optical waveguide having a core and a cladding layer, and an optical waveguide in which at least a part of the core formed by cutting at least a part in the thickness direction of the core by laser irradiation is a mirror surface. It is a waveguide.

  Here, in one preferable aspect, the laser irradiation is in a direction perpendicular to the optical waveguide surface, and the mirror surface is perpendicular to the optical waveguide surface and inclined with respect to the core extending direction. This makes it possible to change the optical path in the optical waveguide plane without providing a separate micromirror or the like.

  In another preferred embodiment, the laser irradiation is oblique with respect to the optical waveguide surface, and the mirror surface is inclined with respect to the extending direction of the core. This makes it possible to change the optical path in the out-of-plane direction of the optical waveguide, for example, in the direction perpendicular to the plane, without providing a micromirror or the like.

  Further, in the present invention, a projection reflecting the shape of the core is formed on the upper surface of the clad layer, the cutting direction by the laser irradiation is oblique to the core passing through the projection, and the mirror surface is preferably a curved surface. . As a result, a lens effect can be further obtained when changing the optical path in addition to the in-plane.

  The present invention is also an optical waveguide having a core and a clad layer, wherein the end surface of the core is a curved mirror surface for performing optical path conversion. This enables optical path conversion with a lens effect.

  These optical waveguides are preferably provided on one surface of a circuit board on which an electric circuit is mounted to constitute a mixed optical / electric board.

  The present invention further includes a step of forming the first cladding layer with a transfer mold having a protrusion corresponding to the core, a step of peeling the first cladding layer from the transfer mold, and a contact with the transfer mold of the first cladding layer. A step of filling a core material in a recess formed on the first surface, a step of forming a second cladding layer on the first surface of the first cladding layer, and forming on the outer surface of the first cladding layer And a step of irradiating a part of the protrusion along the core with a laser obliquely to the core to cut at least a part in the thickness direction of the core. is there.

  A method combining photolithography and dry etching is also conceivable as a method for forming a hole for optical coupling at an arbitrary position. However, a thickness of several tens of microns must be dry etched, which is impractical in terms of productivity and cost.

  A hole is formed at an arbitrary position in the surface of the optical waveguide, and a mirror surface is formed on the cut surface in the middle of the core, and as shown in FIG. 8, the end of the optical waveguide 41 provided with the core 42 is applied to the end of the core. As described above, it is possible to make the mirror wall surface 43 of the core formed by irradiating the laser and cutting the outermost end portion of the optical waveguide. Further, the wall surface obtained by cutting the entire core in the thickness direction with a laser can be used as a mirror surface, and in this case, all the light propagating through the core can be converted into an optical path. On the other hand, if a wall surface obtained by cutting halfway through the thickness of the core is used as a mirror surface, a part of the light propagating through the core can be converted into an optical path and the other part can be moved straight.

  In the present invention, it goes without saying that the laser beam is stationary relative to the optical waveguide during laser irradiation.

     According to the present invention, since optical coupling can be easily performed at an arbitrary place and with various core patterns, the degree of freedom in designing an optical circuit is remarkably increased. Further, by using a laser, the hole wall can be easily formed into a smooth mirror surface at the same time as the hole is formed by laser irradiation. Further, the optical path can be changed or branched at an arbitrary angle, and the optical waveguide size can be greatly reduced. This effect is particularly suitable for an opto-electric hybrid board. In particular, when the core wall surface is a curved mirror surface, coupling efficiency is high and light coupling can be easily performed with respect to a light receiving element having a small light receiving diameter or a light emitting element having a large spread angle (numerical aperture).

  Hereinafter, the present invention will be described in detail. Here, a polyimide optical waveguide will be described as an example, but it is of course possible to form a structure for optical path conversion by using an optical material resin other than polyimide as the material of the optical waveguide. Further, an electric circuit or another optical circuit may be formed on the surface or inside of the substrate on which the optical waveguide of the present invention is formed.

  First, a lower clad layer made of polyimide is formed on a silicon wafer. A polyimide layer partially having a core and a resist layer are sequentially formed thereon. Next, the resist pattern used as a mask is formed by exposing using the mask pattern in which the desired core pattern was drawn. Using this resist pattern as a mask, a layer whose core is partly dry is etched with oxygen plasma. Next, the resist of the mask is removed with a stripping solution. Next, an upper clad layer made of polyimide is formed thereon. Then, the multi-layered silicon wafer is immersed in a hydrofluoric acid aqueous solution, and the multi-layer that becomes the optical waveguide is peeled from the silicon wafer. Thus, a film-like optical waveguide having an optical waveguide formed is obtained.

  By irradiating the laser at an angle of 45 degrees from the optical waveguide plane within a plane perpendicular to the optical waveguide plane and including the extending direction of the core, the core of the optical waveguide is 45 degrees with respect to the extending direction of the core. An inclined reflecting surface can be formed. The optical path can be converted in the direction perpendicular to the surface of the optical waveguide through the 45-degree reflecting surface. A metal layer having a high reflectivity may be provided on the 45 ° reflective surface as necessary. When this reflecting surface is used, it is not necessary to separately provide a micromirror as an individual component.

  In this manner, an opto-electric hybrid board that can be optically coupled at an arbitrary place can be manufactured by forming an electric circuit, an optical element, or an optical circuit in the optical waveguide, or by attaching the optical circuit to the electric circuit board.

  In the optical waveguide of the present invention, both the clad layer and the core layer are preferably made of resin, and particularly preferably made of polyimide resin or epoxy resin. By using the resin, the wall surface of the hole formed by laser irradiation can be easily obtained as a smooth mirror surface.

  Next, a forming method in which the reflecting surface becomes a curved surface will be described with reference to FIGS. First, a transfer mold 11 on which a desired core pattern is formed is prepared (FIG. 2 (a)). On top of that, a polyamic acid solution, which is a precursor of polyimide to be the clad layer 12, is applied by spin coating or the like. Next, imidization is performed by heat treatment. At this time, by appropriately adjusting the resin concentration of the polyamic acid solution, a raised protrusion 12a reflecting the core pattern is formed on the surface of the clad layer above the core pattern (FIG. 2B). Next, the polyimide film is peeled from the transfer mold (FIG. 2 (c)). The peeled polyimide film is turned upside down, and a polyamic acid solution, which is a polyimide precursor to be the core 13, is applied so as to be embedded in the groove, and is heated and imidized (FIG. 2D). Next, a polyamic acid solution, which is a polyimide precursor that will become the lower clad layer 14, is applied and heated to imidize. In this way, an optical waveguide having a protrusion 12a formed by raising a clad layer at a location where the core 13 is present can be produced (FIG. 2 (e)).

  From the top of the optical waveguide film thus obtained, as shown in FIG. 3A, it is inclined 45 degrees toward the projection 12a and with respect to the optical waveguide surface, and the high-power laser beam 15 such as an excimer laser or a carbon dioxide gas laser is used. Is drilled at an angle of about 45 degrees with respect to the waveguide surface. At this time, a mask (not shown) having a square window opened is used. By irradiating a laser beam from the side of the upper clad layer having the raised protrusion 12a toward the protrusion, a hole 16 for cutting the core is formed. At this time, a smooth spherical surface or cylindrical surface can be easily obtained on the wall surface 17 of the hole 16 that crosses the core of the optical waveguide (FIG. 3B). At this time, even if the formed hole is slightly displaced in the direction perpendicular to the core pattern direction, there is no problem because it is formed in the raised portion of the cladding. When a flat optical waveguide without a raised cladding layer is used, a curved mirror surface can be obtained by using a mask in which a desired curve is formed instead of a square.

  FIG. 4 shows a state of light propagation using a micromirror having a curved core cut surface. Only the core part and the mirror part are shown here. The propagating light 22 propagating through the optical waveguide 21 is reflected by a micro mirror 24 processed at an angle of about 45 degrees. In this case, the light converges so that the reflected light 25 is focused at a distance half the radius of curvature of the spherical surface. In this way, the light can be narrowed down. For example, if a light receiving element is arranged above, light can be received efficiently.

  Next, an optical waveguide having a function of changing the optical path within the plane of the optical waveguide or branching the optical path will be described. An optical waveguide is used in which the core pattern is patterned in a T-shape, L-shape or Y-shape, depending on the purpose.

  From above the optical waveguide, an excimer laser is irradiated in a direction perpendicular to the surface of the optical waveguide and at a portion where the core is bent, and a through hole is formed therein. That is, when the excimer laser is irradiated onto the core portion of the optical waveguide using a hole-shaped mask, a part of the core is cut to form a hole. The cut surface of the core formed by the hole becomes a reflection surface that is an interface between air and the core, and light is reflected by this reflection surface, so that steep optical path conversion or branching is possible. It is also possible to cover the cut surface of the core with a highly reflective material, or to fill the hole with a material having a lower refractive index than the cladding.

  FIG. 5 shows the shape of the hole 31 for branching the single light 33 coming from the top to the left and right in the shape of the core 31 that is created. In FIG. 5A, a hole 32 is formed so as to be reflected and branched at a plane of 45 degrees with respect to the optical axis. FIG. 5B shows a through hole 34 for reflecting and branching the optical interface at the two-folded surface, and FIG. 5C shows reflecting and branching so that the optical interface has a curved surface. A through hole 35 is formed. In the case of FIG. 5, the branching ratio can be changed depending on the position of the through hole in the lateral direction. Further, the light can be multiplexed by reversing the traveling direction of the light.

  FIG. 6 shows each shape of the hole for changing the optical path to the L-shape. In FIG. 6A, a hole 36 is formed in a portion bent at a right angle of the core so as to change the optical path at a right angle so that a reflecting surface inclined at 45 degrees with respect to the optical axis appears. FIG. 6 (b) shows a hole 37 for changing the optical path in a two-fold plane, and FIG. 6 (c) shows a curved hole 38 for changing the optical path. In this way, various small optical waveguides can be produced simply by changing the shape of the hole.

  In FIG. 7, a through hole 40 for changing the optical path is formed immediately on the Y branch 39 of the core having a Y branch shape before the T-shape. Since the branching can be performed at the Y branching portion, even if the lateral position error of the through hole is large, the 1: 1 branching can be performed more accurately.

(Example 1)
2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2-bis (trifluoromethyl) -4,4'-diaminobiphenyl (TFDB) on a 5-inch silicon wafer ) Is used as the upper and lower cladding layers, and polyimide formed from 6FDA and 4,4′-oxydianiline (ODA) is used as the core layer sandwiched between the upper and lower cladding layers. The core on the lower clad layer is patterned by known photolithography and dry etching techniques, and then the upper clad layer is formed to form a film-like optical waveguide. Here, a plurality of core layers whose length directions are parallel to each other are formed to form a multi-array optical waveguide. Thereafter, the silicon wafer on which the optical waveguide was formed was immersed in a 5 wt% hydrofluoric acid aqueous solution, and the optical waveguide was peeled off from the silicon wafer to produce a film-shaped optical waveguide. The thickness of the film-shaped optical waveguide was 80 μm.

In FIG. 1, a film-like optical waveguide provided with a core layer 3 was produced using this fluorinated polyimide. Drilling was performed by irradiating the excimer laser 2 while tilting the film-shaped optical waveguide 1 by 45 degrees with respect to the optical axis of the excimer laser (FIG. 1 (a)). At this time, the wall surface 4 crossing the core of the formed hole was at an angle of 45 degrees with respect to the film-shaped optical waveguide surface (FIG. 1 (b)). The irradiation conditions were a total irradiation energy of 0.4 J / pulse, an irradiation energy density to the optical waveguide of 1 J / (cm ² · pulse), and a repetition frequency of 200 pulses / second for 2 seconds. When a laser beam is irradiated onto the reflection surface at 45 degrees from a surface emitting laser (not shown in the drawing, from below the film-shaped optical waveguide) from the direction perpendicular to the optical waveguide surface, the core of the optical waveguide along the optical axis 5 is irradiated. The light output could be observed from the end face (Fig. 1 (c)). A metal film may or may not be formed on the 45 ° reflective surface. When the metal film is formed, an arbitrary resin can be embedded in the formed hole without considering the refractive index.

  A hole whose wall surface is inclined by 45 degrees can be formed in any number of places, and the degree of freedom in designing an optical circuit is high. Further, since it is not necessary to provide a micromirror as an individual part in the hole, it is easy to align the optical axis.

  (Example 2) A core pattern on a ridge having a width of 50 μm and a height of 40 μm is formed on a 5-inch silicon wafer by dry etching. This is a transfer mold. Formed thereon from 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2-bis (trifluoromethyl) -4,4'-diaminobiphenyl (TFDB) The resulting polyamic acid solution is spin coated and heated to imidize. At this time, the concentration of the polyamic acid solution was set to 25%. On the upper surface of the clad layer above the core pattern, a raised protrusion is formed along the core pattern. Next, the clad layer of polyimide is detached from the silicon wafer by immersing it in distilled water. Next, the groove is formed by spin-coating and heat-treating into a groove formed with a copolymerized polyimide composed of 6FDA, 4,4′-oxydianiline (ODA) and 6FDA / TFDB. Further, a cladding layer made of 6FDA / TFDB is formed thereon. In this way, a film optical waveguide was produced. The thickness of the film waveguide was 90 μm.

Next, an excimer laser, a mask made of a copper alloy plate on its optical axis and having a 0.15 mm square window on one side, and a film optical waveguide were disposed. The optical waveguide was inclined 45 degrees with respect to the optical axis of the laser. Excimer laser was irradiated toward the projection of the film waveguide, and the through hole was formed obliquely with respect to the optical waveguide. The irradiation conditions were a total irradiation energy of 0.4 J / pulse, an energy density of 1 J / (cm ² · pulse), and a repetition frequency of 200 pulses / second for 2 seconds. At this time, the processed surface crossed by the core was a spherical surface having a curvature radius of about 0.8 mm in both the in-plane direction and the thickness direction of the optical waveguide.

  When light having a wavelength of 850 nm was inserted into the optical waveguide from one end surface of the film optical waveguide, reflected light on the micromirror surface could be observed. When reflected light was received with an optical fiber of 100 μmφ, it was found that the received light intensity was about 70%.

(Example 3)
2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2-bis (trifluoromethyl) -4,4'-diaminobiphenyl (TFDB) on a 5-inch silicon wafer Multi-mode optical waveguide film using known photolithography and dry etching techniques with polyimide formed from) as the upper and lower cladding layers and polyimide formed from 6FDA and 4,4′-oxydianiline (ODA) as the core layer Form. At this time, patterning was performed in a T shape. Thereafter, the silicon wafer on which the optical waveguide was formed was immersed in a 5 wt% hydrofluoric acid aqueous solution, and the optical waveguide was peeled off from the silicon wafer to produce a film optical waveguide. The thickness of the film waveguide was 80 μm.

Next, square through holes were formed at the intersections of the T-shapes using a reduction optical system / mask projection type KrF excimer laser processing apparatus. The irradiation conditions were a total irradiation energy of 0.4 J / pulse, an energy density of 1 J / (cm ² · pulse), and a repetition frequency of 200 pulses / second for 2 seconds. Two branches in the 90 degree direction with a branching loss of 1 dB were achieved at a wavelength of 850 nm.

Example 4
Up to now, the example of laser processing was shown so that the core was cut in the entire thickness direction, but by cutting the laser irradiation before penetrating the core part, the cut surface could be moved to an arbitrary position in the thickness direction of the core. Can be formed. As a result, it is possible to distribute the light guided through the core. By making the laser irradiation time half of the time required to penetrate the core, the processing depth can be halved. For example, in FIG. 9, when it is necessary to irradiate the excimer laser 51 at 200 pulses / second for 2 seconds to form a through hole in a polyimide optical waveguide film having a thickness of about 100 μm, the irradiation time is 1 second. By doing so, it is possible to form the hole 54 machined to a half position. In this case, the light 55 propagating through the upper part of the core 53 undergoes optical path conversion at the cut surface, and the light 56 propagating through the lower part of the core propagates as it is. When processing is stopped at a position half the core height, light can be distributed at a ratio of approximately 1: 1. The distribution ratio can be changed by changing the laser processing depth. In this way, not only can the total light quantity be taken in and out, but light can be taken in and out at a certain ratio of the total light quantity.

  Further, as shown in FIG. 10, even when a mirror surface perpendicular to the optical waveguide surface is formed, the light can be distributed by stopping the laser processing in the middle. 10A is a plan view seen from above, and FIG. 10B is a cross-sectional view of an optical waveguide composed of a core 61 and a cladding layer 62. FIG. A hole 63 is formed partway through the core by irradiating a laser beam perpendicular to the optical waveguide surface. The light 64 propagating through the upper part of the core has its path changed at a right angle while remaining parallel to the optical waveguide surface at the wall surface 63a of the hole 63. On the other hand, the light 65 propagating under the core travels straight. Also at this time, the distribution ratio can be changed by changing the hole depth by laser processing.

  The present invention is particularly applicable to optical integrated circuits, optical components for optical interconnection, opto-electric hybrid boards and the like.

The figure which shows an example of the manufacturing process using the oblique irradiation laser processing of invention. The figure which shows an example of the manufacturing method of the optical waveguide which forms the micro mirror with a lens function of this invention. The figure which shows an example of the formation process of the micro mirror with a lens function of this invention. The figure which shows an example of the micro mirror with a lens function of this invention. The figure which shows an example of the T-shaped light branch using the optical waveguide with a through-hole of this invention. The figure which shows an example of the L-shaped optical path conversion using the optical waveguide with a through-hole of this invention. The figure which shows an example of the Y-shaped light branch using the optical path conversion by the through-hole of this invention. Diagram of the end of the optical waveguide cut out with a laser Illustration of an optical waveguide cut halfway through the core Illustration of an optical waveguide cut halfway through the core

Explanation of symbols

1 .... Film optical waveguide, 2 .... Excimer laser, 3..Core layer,
4 .... Wall, 5 .... Optical axis, 11 .... Transfer type, 12 .... Clad layer,
12a ... projection, 13 ... core, 14 ... lower clad layer,
15. ・ Laser beam, 16. ・ Hole, 17. ・ Wall 21 ・ ・ Optical waveguide
22 ... Propagating light, 24 ... Micro mirror, 25 ... Reflected light
31 ・ ・ Core, 32 ・ ・ Hole, 33 ・ ・ Light 34 ・ ・ Through hole
35 ・ ・ Through hole, 36, 37, 38, 40 ・ ・ Hole, 39 ・ ・ Y branch,
41 ... Optical waveguide, 42 ... Core, 43 ... Wall
51 ・ ・ Excimer laser, 52 ・ ・ Clad layer, 53 ・ ・ Core
54 ... Core, 55, 56 ... Optical, 61 ... Core 62 ... Cladding layer
63 ... Hole, 64, 65 ... Light

Claims (7)

An optical waveguide comprising a core and a cladding layer, wherein a wall surface crossing at least a part of the core formed by cutting at least a part of the core in the thickness direction by laser irradiation is a mirror surface Waveguide. The optical waveguide according to claim 1, wherein the laser irradiation is perpendicular to the optical waveguide surface, and the mirror surface is perpendicular to the optical waveguide surface and inclined with respect to the core extending direction. The optical waveguide according to claim 1, wherein the laser irradiation is oblique with respect to the optical waveguide surface, and the mirror surface is inclined with respect to the extending direction of the core. The optical waveguide according to claim 1, wherein a projection reflecting the shape of the core is formed on an upper surface of the cladding layer, a cutting direction by the laser irradiation is oblique to the core through the projection, and the mirror surface is a curved surface. . An optical waveguide comprising a core and a cladding layer, wherein an end surface of the core is a curved mirror surface for performing optical path conversion. An optical / electrical hybrid board, wherein the optical waveguide according to claim 1 is provided on one surface of a circuit board on which an electric circuit is mounted. Forming a first clad layer with a transfer mold having a protrusion corresponding to the core, peeling the first clad layer from the transfer mold, and a first surface of the first clad layer in contact with the transfer mold A step of burying a core material in the recess formed in the step, a step of forming a second cladding layer on the first surface of the first cladding layer, and a core formed on the outer surface of the first cladding layer. And a step of irradiating a part of the projection along the core obliquely with a laser to cut at least a part in the thickness direction of the core.

Images