# Patent

## Title
Sub-mount for mounting optical component and light transmission and reception module

## Abstract

A sub-mount includes a recess for holding a polymer optical waveguide film and recesses for embedding and holding a light emitting element and a light detecting element. The sub-mount further has an adhesive filling groove formed adjacent to respective recesses. When mounting the polymer optical waveguide film, the light emitting element, and the light detecting element onto the sub-mount, an adhesive is accurately applied and is prevented from flowing out as the adhesive filling grooves are provided.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority under 35 USC 119 from Japanese patent document, No. 2005-207178, the disclosure of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sub-mount and to a light transmission and reception module, more specifically, to a sub-mount mounted in a package of an optical device and to a light transmission and reception module using the same.
2. Description of the Related Art
Recently, in IC technique or LSI technique, optical wiring between equipments, between boards in the equipments, or in a chip is given attention instead of the electrical wiring at high density to enhance the operating speed or integration degree.
In Japanese Patent Application Laid-Open No. 2000-39530, for example, an optical element including a light emitting element and a light detecting element in a core clad stacking direction of a polymer optical waveguide including the core and the clad surrounding the core, and further including an incident side mirror where light emitted from the light emitting element is coupled and a emission side mirror emitting the light to the light detecting element. In the publication, the optical element is disclosed in which the clad layer is formed into a concave shape at locations corresponding to the light paths from the light emitting element to the incident side mirror, and from the emission side mirror to the light detecting element, at where the light from the light emitting element and the light from the emission side mirror converge.
Further, in Japanese Patent Application Laid-Open No. 2000-39531, an optical element is disclosed in which light from a light emitting element is coupled at a core end surface of a polymer optical waveguide including the core and a clad surrounding the core. In the optical element, the end surface of the core is formed into a convex surface towards the light emitting element so that the light from the light emitting element is converged and a wave loss is suppressed.
Further, in Japanese Patent Application Laid-Open No. 2000-235127, an optoelectronic integrated circuit is disclosed in which the polymer optical waveguide circuit is directly assembled on the circuit integrating the electronic elements and optical elements.
When the above elements are packaged in an optical wiring and can be incorporated into a device, the assembling flexibility of the optical wiring can be increased. As a result, a light transmission and reception element with compact shape can be manufactured.
However, the methods proposed so far requires a mirror to be embedded to form a 90° return mirror, and requires positioning at high precision when laminating the waveguide and the light transmission and reception element, and thus the cost required for mounting becomes large.
A polymer optical waveguide module equipped with light emitting and detecting elements including a polymer optical waveguide film was disclosed by the present inventors (Japanese Patent Application No. 2004-139041, Japanese Patent Application FE04-04966). In the disclosure, the polymer optical waveguide film includes a light path conversion mirror surface and an abutting surface on the same end.
A semiconductor laser device in which a mirror surface is formed on a sub-mount of a semiconductor laser, wherein a light path of the laser light is converted by such mirror surface is disclosed in Japanese Patent Application Laid-Open No. 2000-114655.
However, when mounting a light emitting element or a light detecting element and a waveguide element in the sub-mount, an adhesive must be applied to a predetermined position at excellent precision in case that the adhesive (including electrically conductive paste) is used for fixation. Further, the adhesive may flow out from a recess for mounting when the element is mounted.
The present invention provides a sub-mount for mounting an optical component in which the adhesive is applied to a predetermined position at excellent precision and is prevented from flowing out, and in which the optical component is easily and reliably mounted; and a light transmission and reception module using the same.
SUMMARY OF THE INVENTION
The first aspect of the present invention provides a sub-mount for mounting optical component comprising a recess for mounting for embedding and mounting the optical component, and an adhesive filling groove formed adjacent to the recess for mounting.
The second aspect of the present invention provides a light transmission and reception module comprising an optical waveguide film formed with an optical waveguide; a light transmitting section having a light emitting element and a sub-mount for holding the light emitting element, that holds one end of the optical waveguide film on the sub-mount so that light emitted from the light emitting element enters into an incident end surface of the optical waveguide; and a light detecting section having a light detecting element and a sub-mount for holding the light detecting element, that holds the other end of the optical waveguide film on the sub-mount so that light emitted from an emission end surface of the optical waveguide is detected by the light detecting element. Each sub-mount includes a recess for mounting for embedding and mounting an optical component and an adhesive filling groove formed adjacent to the recess for mounting.



BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will be described in detail based on the following figures, wherein:
FIGS. 1A to 1F are views showing manufacturing steps of a sub-mount of the present invention;
FIGS. 2A to 2D are views showing another manufacturing steps of a sub-mount of the present invention;
FIG. 3 is a schematic configuration view of a light transmission and reception module according to the present embodiment;
FIGS. 4A and 4B are views showing follow-up property to deformation of the light transmission and reception module according to the present embodiment;
FIG. 5A is a perspective view of an end portion of a polymer optical waveguide film of the light transmission and reception module according to the embodiment, FIG. 5B is a sectional view taken along A-A of FIG. 5A, and FIG. 5C is a sectional view taken along B-B of FIG. 5B;
FIGS. 6A to 6I are views showing manufacturing steps of the polymer optical waveguide film of the light transmission and reception module according to the embodiment;
FIG. 7A is a perspective view of the sub-mount of the light transmission and reception module according to the present embodiment, FIG. 7B is a plan view of the sub-mount of the light transmission and reception module according to the present embodiment, and FIG. 7C is a sectional view taken along C-C of FIG. 7B;
FIG. 8A is a plan view of an optical transmission and reception section of the light transmission and reception module according to the present embodiment, FIG. 8B is a sectional view taken along D-D of FIG. 8A, and FIG. 8C is a partially magnified view showing an optical coupler in FIG. 8B in an enlarged manner;
FIG. 9 is a schematic view showing a configuration of the light transmission and reception module according to the present embodiment;
FIG. 10A is a perspective view of a sub-mount of another light transmission and reception module according to the present embodiment, FIG. 10B is a plan view of the sub-mount, and FIG. 10C is a sectional view taken along C′-C′ of FIG. 10B;
FIG. 11A is a plan view of an optical transmission and reception section of another light transmission and reception module according to the present embodiment; FIG. 11B is a cross sectional view taken along D′-D′ of FIG. 11A; FIG. 11C is a partially magnified view showing an optical coupler in FIG. 11B in an enlarged manner; and
FIG. 12 is a schematic view showing a configuration of another light transmission and reception module according to the present embodiment.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Sub-Mount and Its Manufacturing Method
The sub-mount of the present invention has a recess for embedding and mounting optical components and an adhesive filling groove arranged adjacent to the recess for mounting. Noted that “the filling groove arranged adjacent” means inner spaces of the recess and the filling groove are communicated each other.
The sub-mount of the invention can be obtained by a manufacturing method comprising the steps of (1) a mold production step for producing a mold for duplication having projections and recesses for replicating the surface configuration of a sub-mount, (2) a filling step for filling the produced mold with curing material, (3) a curing step for curing the applied curing material, and (4) a releasing step for separating a duplicated sub-mount from the mold.
Methods of producing a mold (Step (1) above) include (A) a method by curing liquid silicon rubber on a master plate of the sub-mount, (B) a method by etching a silicon substrate, and (C) a method by casting a metal. The manufacturing method of the sub-mount using the mold produced in the method (A) will be referred to as “the duplication method using silicon resin” hereinafter, and the manufacturing method of sub-mount using the mold produced by the method (B) or (C) will be referred to as “the stamper method” hereinafter.
Duplication Method Using Silicon Resin
An overall picture of duplication method using silicon resin is explained by referring to FIGS. 1A to 1F. FIG. 1A shows a silicon substrate 50. Projections and recesses are formed on the main surface of the silicon substrate 50 by RIE, and a master plate 52 of a sub-mount is produced (see FIG. 1B). By precision processing technology such as RIE, the master plate 52 of the sub-mount is produced precisely. Projections and recesses corresponding to a plurality of sub-mounts are formed in the master plate, and by using this mater plate, a plurality of the sub-mounts can be duplicated simultaneously.
Liquid silicone rubber is applied or poured onto the projection and recess formed surface of the master plate 52, and cured (see FIG. 1C). Then the silicone resin layer 54A is peeled off, and a silicone resin mold 54 having projections and recesses is obtained, in which projections and recesses replicate the surface configurations of the sub-mount (see FIG. 1D). Due to the adhering and releasing properties of the liquid silicone rubber, projections and recesses of the master plate 52 are duplicated accurately. These steps correspond to the mold production step.
The mold 54 is filled with ultraviolet curable resin and cured by ultraviolet irradiation (see FIG. 1E). These steps correspond to the filling step and curing step. Then, by separating the cured resin layer 56 from the mold 54, projections and recesses of the sub-mount surface are reproduced. This step corresponds to the releasing step. By dicing this duplicate (not shown) into individual sub-mount, sub-mounts 58 of ultraviolet cured resin having projections and recesses on the surface are obtained (see FIG. 1F).
The principal steps of the duplication method using silicon resin are more specifically described below.
(Production of Master Plate)
The above example is for producing the master plate of the sub-mount by etching the silicon substrate by RIE method. However, the material of master plate is not limited to silicon substrate but may be glass substrate such as quartz glass substrate and metal substrate such as nickel (Ni) substrate and the like. For production of the master plate, conventional methods such as photolithography may be employed without any limitation. Moreover, the electrodeposition or photoelectrodeposition previously filed by the present applicant (Japanese Patent Application No. 2002-10240) is also applicable for production of the master plate.
(Production of Mold)
In the duplication method using silicone resin, as mentioned above, liquid silicone rubber is applied or poured onto the projection and recess formed surface of the produced master plate, dried if necessary, and cured, and a silicone resin layer is formed. By separating the silicone resin layer from the master plate, a mold replicating the surface configuration of the sub-mount is produced.
The thickness of the silicone resin layer is properly determined in consideration of handling convenience of the mold, but in general it is suitably set to be about 0.1 to 50 mm. Preferably, the master plate should be coated in advance with releasing agent or the like to facilitate releasing from the mold.
The liquid silicone rubber is curing organopolysiloxane, which becomes silicone rubber after curing, and the term “liquid” includes paste or viscous substances. The liquid silicone rubber preferably contains methyl siloxane group, ethyl siloxane group, or phenyl siloxane group in its molecule. Among liquid silicone rubber materials, liquid dimethyl siloxane rubber (polydimethyl siloxane: PDMS) is particularly preferable from the viewpoint of adhesion, releasing property, strength and hardness.
The liquid silicone rubber is excellent in both adhesion and separation, which are contradictory properties, and has a capability of replicating fine configuration. Accordingly, the mold using silicone rubber is capable of replicating the master plate at high precision, and it is easy to separate the mold from ultraviolet curable resin for forming the sub-mount described later. Advantages of liquid silicone rubber mold include sufficient mechanical strength and dimensional stability as mold (which is to be used repeatedly), and stiffness (hardness) for retaining the projected and recessed configurations. From this mold, therefore, sub-mounts retaining the shape at high precision can be reproduced very easily.
The liquid silicone rubber is preferred to be of two-pack type used together with hardening agent. The addition type liquid silicone rubber is preferred because it is cured uniformly both at the surface and the inside in a short time, free from byproducts or produces few byproducts, is excellent in releasing property and small in shrinkage rate. As required, various additives may be used in the liquid silicone rubber.
Since the liquid silicone rubber can be applied or poured on the surface of the master plate and the projections and recesses formed on the master plate must be duplicated accurately, the viscosity is preferred to be less than a certain level. The viscosity of the liquid silicone rubber is preferred to be about 500 mPa.s to 7000 mPa.s, or more preferably about 2000 mPa.s to 5000 mPa.s. For adjusting the viscosity, a solvent may be added slightly so as not to express adverse effects of the solvent.
The surface energy of mold is 10 dyn/cm to 30 dyn/cm, preferably 15 dyn/cm to 24 dyn/cm, from the viewpoint of adhesion to the resin. The surface energy can be analyzed by measuring the contact angle between solid and liquid, and hence it is measured by a specified contact angle measuring apparatus. Share rubber hardness of the mold is 15 to 80, preferably 20 to 60, from the viewpoint of patterning performance, retaining of the recess shape and separation. Share rubber hardness can be measured by using spring type rubber durometer for measuring an amount of deformation when a surface of the object is pushed by a needle and made deformed. Surface roughness of mold (maximum height: Ry) is set to be 0.2 μm or less, preferably 0.1 μm (100 nm) or less, from the viewpoint of patterning performance. Surface roughness Ry is a value expressing a maximum height defined by the difference of a maximum value and a minimum value of roughness curve, and can be measured by probe type film thickness gauge.
The mold is preferred to be light transmittable in ultraviolet ray region and/or visible ray region. When the mold is light transmittable in visible ray region, the state of filling the mold with the resin can be observed and completion of filling is easily confirmed. When the mold is light transmittable in ultraviolet ray region, ultraviolet curing is achieved by making ultraviolet transmit through the mold. The transmittance of the mold in ultraviolet ray region (250 nm to 400 nm) is preferred to be 80% or more.
(Duplication of Sub-Mount)
In the duplication method using silicon resin, as mentioned above, the mold replicating the surface configuration of the sub-mount is filled with ultraviolet curable resin for forming a sub-mount, the applied resin is cured, and the cured resin layer is separated from the mold, so that a sub-mount forming projections and recesses on the surface can be duplicated.
As the ultraviolet curable resin for forming a sub-mount, a resin of high heat resistance is preferred, and epoxy based and polyimide based UV curable resins are preferably used. Also, monomer, oligomer, or mixture of monomer and oligomer of ultraviolet curing type may be preferably used.
The ultraviolet curable resin is required to be sufficiently low in viscosity so as to fill up the projections and recesses of the mold. The viscosity of ultraviolet curable resin is preferably 10 mPa.s to 2000 mPa.s, more preferably 20 mPa.s to 1000 mPa.s, and most preferably 30 mPa.s to 500 mPa.s.
To reproduce the projections and recesses formed on the master plate at high precision, it is required that the volume change is small before and after curing of the ultraviolet curable resin. The volume change is preferred to be 10% or less, or more preferably 6% or less. It is preferred to avoid lowering the viscosity by using a solvent because the volume change before and after curing becomes large.
To reduce volume change (shrinkage) after curing of the ultraviolet curable resin, a polymer may be added to the ultraviolet curable resin. The polymer to be added is preferably compatible with the ultraviolet curable resin and dose not have adverse effects on the resin refractive index, elasticity and light-transmitting properties thereof. By adding the polymer, not only the volume change can be decreased, but also the viscosity or glass transition point of the cured resin can be effectively controlled at advanced level. The polymer includes acrylic system, methacrylic acid system, epoxy system, and many others.
To cure the ultraviolet curable resin, light is emitted from ultraviolet ray lamp, ultraviolet ray LED, UV irradiation apparatus, in an ultraviolet region (250 nm to 400 nm).
Stamper Method
A general picture of the stamper method is explained by referring to FIGS. 2A to 2D. In the stamper method, the mold is used as a stamp. FIG. 2A shows a silicon substrate 60. Projections and recesses are formed on the main surface of the silicon substrate 60 by RIE, and a silicon mold 62 is produced (see FIG. 2B). This mold has projections and recesses duplicated corresponding to a plurality of sub-mounts, and by using this mold, a plurality of sub-mounts can be reproduced simultaneously. By precision processing technology such as RIE, the mold 62 accurately replicating the projections and recesses of the sub-mount can be produced precisely. These steps correspond to the mold production step.
Thermoplastic resin is tightly fitted to the mold 62, heated and pressurized, and cured by being cooled gradually (see FIG. 2C). These steps correspond to the filling step and curing step. Then, by separating the cured resin layer 64 from the mold 62, projections and recesses of the sub-mount surface are reproduced. This step corresponds to the stripping step. By dicing this duplicate (not shown) into individual sub-mount, sub-mounts 66 of thermoplastic resin having projections and recesses on the surface are obtained (see FIG. 2D).
The principal steps of the stamper method are more specifically described below. Hereinafter, in order to distinguish from the mold employed in the duplication method using silicone resin, the mold produced by the Stamper method is herein called the stamper.
(Production of Stamper)
The above example is for producing a stamper by etching a silicon substrate by RIE method. However, the material of the stamper is not limited to silicon substrate, but may be glass substrate such as quartz glass substrate, and metal substrate such as nickel (Ni) substrate. For production of the stamper, conventional methods such as photolithography may be employed without any limitation. The stamper can be produced also by the electrodeposition or photoelectrodeposition previously filed by the present applicant (Japanese Patent Application No. 2002-10240). The production precision of the mold is enhanced by employing photolithography or RIE.
(Duplication of Sub-Mount)
In the stamper method, as mentioned above, the stamper replicating the surface configuration of the sub-mount is tightly fitted to thermoplastic resin for forming the sub-mount, heated and pressurized, and slowly cooled to ordinary temperature until cured. By releasing the cured resin layer from the mold, a sub-mount having projections and recesses on the surface can be produced.
The thermoplastic resin for forming the sub-mount is desired to be high in heat resistance, and unsaturated polyester resin-based, epoxy resin-based, polyimide-based, PPS (polyphenylene sulfide)-based thermoplastic resins are, in particular, preferably used. Further, ultraviolet curing monomer, oligomer, or mixture of monomer and oligomer may be used. A resin for precision molding obtained by mixing fillers into thermosetting resin is also used preferably. An example of such resin is BMC resin obtained by mixing fillers such as glass fiber in unsaturated polyester resin so as to suppress shrinkage.
The thermoplastic resin preferably has high dimensional precision with a shrinkage rate of 1% or less, thermal deformation starting temperature of 200 deg. C. or more, is close to metal in coefficient of linear expansion, and is easily combined with metal parts (smaller than in aluminum).
To form projections and recesses on the thermoplastic resin, the thermoplastic resin adhered to the stamper is heated to a temperature about glass transition point (Tg) +50 deg. C., and pressurized at pressure of about 10 N.
In the stamper method, low-melting glass which is molten by heating, such as glass which is softened (molten) at, for example, 600 deg. C. or less can be used instead of thermoplastic resin. The low-melting glass is heated to about 500 deg. C. and a metallic die is used as “stamper”, so that a sub-mount made of glass can be reproduced. Even a glass material whose melting point is high, namely, 800 deg. C. such as PyrexTM is pressurized under heating temperature of about 650 deg. C., the glass material is deformed so that a sub-mount can be reproduced by the stamper method. As the low-melting glass, hard glass mainly containing SiO2 and B2O3 can be properly applied.
Light Transmission and Reception Module
FIG. 3 is a schematic structural diagram of light transmission and reception module in the embodiment. As shown in FIG. 3, the light transmission and reception module is composed of a belt-shaped polymer optical waveguide film 10 and optical transmission and reception sections 12, 14 for transmitting and receiving an optical signal through an optical waveguide formed in the polymer optical waveguide film 10.
The optical transmission and reception section 12 has a sub-mount 22, and one end of the polymer optical waveguide film 10 is held on the sub-mount 22. The optical transmission and reception section 14 has a sub-mount 24, and the other end of the polymer optical waveguide film 10 is held on the sub-mount 24.
The polymer optical waveguide film 10 consists of a transparent resin film having flexibility, and has a follow-up property to deformation such as “bend” or “twist”, as shown in FIG. 4A and FIG. 4B. Thus, even if the film is in a deformed state, the optical signal transmitted from the optical transmission and reception section 12 is guided through the optical waveguide formed in the polymer optical waveguide film 10 and received by the optical transmission and reception section 14. The polymer optical waveguide film 10 preferably has a flexibility of a curvature radius of 3 mm or less. The curvature radius is a value that, when the microscopic portion of a curve formed on the inner side of the film when the film is bent approaches a circle, indicates the length of the radius of such circle, and the acceptable value thereof is measured according to ASTM D-2176. The resin materials used for the polymer optical waveguide film 10 will be hereinafter explained.
The polymer optical waveguide film 10 is preferred to have a thickness in a range of 50 μm to 300 μm in order to enhance the follow-up property to deformation, and a more preferable range is 100 μm to 200 μm. For the same reason, the width of the film is preferred to be in a range of 0.5 mm to 10 mm, or more preferably 1 mm to 5 mm.
Polymer Optical Waveguide Film.
With referring to FIGS. 5A to 5C, the configuration of the polymer optical waveguide film 10 will be described. FIG. 5A is a perspective view of an end portion of the polymer optical waveguide film 10, FIG. 5B is a sectional view of A-A (section along optical axis of optical waveguide) of FIG. 5A, and FIG. 5C is a sectional view of B-B of FIG. 5B.
As shown in the drawing, the polymer optical waveguide film 10 is composed of square cores 18 extending in film length direction, and cladding 16 and 20 surrounding the cores 18. In the polymer optical waveguide film 10, plural cores 18 are disposed parallel in the film width direction and plural optical waveguides are formed in the film. In this example, two optical waveguides are formed in the film 10.
At the end of the polymer optical waveguide film 10, a mirror 10b is disposed at an angle of 45 degrees to the optical axis of optical waveguide. The mirror 10b functions as optical path converter for converting the optical path of the light guided in the optical waveguide. That is, the light guided in the optical waveguide has an optical path thereof changed by 90 degrees on the mirror 10b and is emitted from the film side 10c of the light incident and exit surface. The leading end of the cladding 16 forming the mirror 11b is cut off and an abutting surface 10a orthogonal to the optical axis of optical waveguide is formed. The abutting surface 10a is a surface abutting against the sub-mount and is utilized in positioning on the sub-mount at the time of mounting.
The polymer optical waveguide film 10 can be manufactured, for example, in the following steps (1) to (6): (1) a step of preparing a mold formed of a cured layer of curable resin for forming a mold, having recesses corresponding to the optical waveguide core portions and two or more through-holes each penetrating through both ends of the respective recess, (2) a step of tightly adhering a plastic film base material for cladding to the mold, the plastic film is capable of contacting tightly with the mold, (3) a step of filling the through-hole at one end of the respective recess of the mold with a curable resin for forming a core and evacuating and sucking from the through-hole at the other end of the respective recess resulting in each recess of the mold filled with the curable resin, (4) a step of curing the filled curable resin for forming a core, and separating the mold from the plastic film base material for cladding, (5) a step of forming a cladding layer on the plastic film base material on which the cores are formed, and (6) a step of forming the 45-degree mirror and the abutting surface at the end of the obtained polymer optical waveguide film.
The manufacturing processes of the above mentioned polymer optical waveguide film will now be further explained in detail with reference to FIG. 6A to FIG. 6I. To simplify the explanation, that in which one optical waveguide is arranged will be explained. FIG. 6A shows a master plate 100 and numeral 120 denotes a projection corresponding to the core of the optical waveguide. The curable resin for forming a mold is applied or poured on the projection formed surface of the master plate 100 and then cured (refer to FIG. 6B). In FIG. 6B, 200a denotes a curable resin layer. Thereafter, when the curable resin layer 200a is peeled off, the curable resin layer 200a formed with a recess is obtained (not shown). The through-holes 260 and 280 communicating to the recess 220 are formed in the curable resin layer 200a by punching etc. at both ends of the recess to obtain a mold 200 (refer to FIG. 6C).
As shown in FIG. 6D, a plastic film base material for cladding 300 is adhered to the mold. A curable resin for forming a core is poured into the through-hole 260 at the one end of the mold recess 220. The mold recess 220 is filled with the curable resin for forming a core by evacuating and sucking from the through-hole 280 at the other end of the mold recess 220. After the resin is cured, the mold is parted and a core 320 is formed on the plastic film base material for cladding 300 as shown in FIG. 6E.
Forming a cladding (upper cladding layer) 400 (see FIG. 6F), the resin portions cured inside the through-holes 260 and 280 are cut off by a dicer or the like, and a polymer optical waveguide film 10 is obtained (see FIG. 6G).
Finally, using a dicing saw having a 45-degree angle blade, the end of the polymer optical waveguide film 10 is diced, and a 45-degree mirror 10b is formed at the end of the film 10 (see FIG. 6H). Further, using the dicing saw, the leading end of the 45-degree mirror is cut off at right angle with respect to the longitudinal direction of polymer optical waveguide film by a specified length including only the cladding portion, whereby an abutting surface 10a is formed (see FIG. 6I).
The each step of forming the polymer optical waveguide film 10 is specifically explained below.
(1) A Step of Preparing a Mold
Preferably, the mold is prepared by using a master plate having projecting portions corresponding to the optical waveguide cores but it is not limited to this. A method of using a master plate is explained below.
(Production of Master Plate)
To produce the master plate having projecting portions, a conventional method, for example, photolithography can be used without any limitation. Also the method previously proposed by the present inventers for producing a polymer optical waveguide by electrodeposition or photoelectrodeposition (Japanese Patent Application No. 2002-10240) is also applicable for production of the master plate.
The size of the projecting portions corresponding to the optical waveguide formed in the master plate is determined properly depending on the application of the polymer optical waveguide. For example, in the case of optical waveguide for single mode, a core of about 10 μm square is generally used, or in the case of optical waveguide for multimode, a core of about 50 to 100 μm square is used, and depending on the applications, an optical waveguide having much larger core of about hundreds of μm may be used.
(Production of Mold)
As an example of production of mold, a layer of curable resin for forming a mold is formed on the projecting portion formed surface of the master plate produced as mentioned above by applying or pouring curable resin for forming a mold thereon. The layer is dried and cured as required, then the cured resin layer is separated from the master plate and a die having recesses corresponding to the projecting portions are formed. The through-holes each communicating from one end to the other end of the recess are formed in the die. The through-holes can be formed by punching the die in a specified shape. Even if the through-holes are formed by punching, the contact tightness between the mold and the film base material for cladding is excellent so that no gap to the film base material for cladding is formed except for the recess of the mold. Accordingly, the curable resin for forming a core will not permeate into other portion than the recesses.
The thickness of the die (resin cured layer) is properly determined in consideration of handling capability of the mold, but generally it is suitably set to be about 0.1 to 50 mm. Preferably, the master plate should be preliminarily coated with releasing agent or the like to facilitate releasing from the mold.
The through-hole provided at a supply side of the curable resin for forming a core functions as a reservoir for liquid (curable resin for forming a core). The through-hole provided at a discharge side of the resin is used for evacuation and suction to evacuate the recess so that the recess is filled with the resin. The shape and size of the supply side through-hole are not particularly specified as far as the through-hole communicates with the supply side of the recess and functions as the liquid reservoir. The shape and size of the discharge side through-hole are also unlimited particularly as long as the through-hole communicates with the discharge end of the recess and can be used for evacuating and sucking.
Since the supply side through-hole functions as the reservoir for the curable resin for forming a core, a section of the through-hole is preferably formed to be made larger at the side contacting with the base material for cladding and smaller as away from the base material, so that it is easier to separate the mold and base material after filling the recess with the curable resin for forming a core and curing. The sectional configuration of the discharge side through-hole is not particularly specified as the discharge side through-hole does not function as the reservoir.
As other example of producing the mold, the master plate is provided not only with projecting portions corresponding to the optical waveguide cores but also with projecting portions for forming through-holes (the height of the projecting portions are higher than the thickness of the cured layer of curable resin for forming a mold), and the curable resin for forming a mold is applied to the master plate so that the projecting portions for forming the through-holes poke through the resin layer. After the resin layer is cured, the cured resin layer is separated from the master plate.
The curable resin for forming a mold is required to have appropriate properties, including ease of peeling of the cured matter from the master plate, sufficient mechanical strength and dimensional stability as mold (to be used repeatedly), stiffness (hardness) for retaining the recess shape, and adhesion to the film base material for cladding. As required, various additives may be added to the curable resin for forming a mold.
The curable resin for forming a mold can be applied or poured to the surface of the master plate and is required to replicate accurately the projecting portions corresponding to the individual optical waveguide cores formed on the master plate. Therefore, it is preferred to have viscosity below a certain limit, for example, about 500 to 7000 mPa.s. (The curable resin for forming a mold used in the invention includes a material becoming elastic rubber like body after curing.) For control of viscosity, a solvent may be added slightly so as not to cause adverse effects of the solvent
As the curable resin for forming a mold, a curable organopolysiloxane, which becomes silicone rubber (silicone elastomer) or silicone resin after curing is preferably used from the viewpoint of releasing property, mechanical strength and dimensional stability, hardness and adhesion with base materials for cladding as stated above. The curing organopolysiloxane is preferred to contain methyl siloxane group, ethylene siloxane group, or phenyl siloxane group in its molecule.
The curing organopolysiloxane may be either one-pack type or two-pack type to be used together with hardener, or may be either hot curing type or cold curing type (for example, cured by moisture in air). Or other hardener (ultraviolet curing agent) may be also used.
The curable organopolysiloxane is preferred to become silicone rubber after curing. So-called liquid silicone rubber can be used (the term “liquid” includes paste or highly viscous substances herein) and the two-pack type to be used together with hardener is preferred. Above all, the addition type liquid silicone rubber is especially preferred because it is cured in short time uniformly both on surface and inside thereof, free from byproducts or produce few byproducts, and excellent in releasing property and small in shrinkage rate.
Among liquid type silicone rubbers, liquid dimethyl cyclohexane rubber is particularly preferable from the viewpoint of adhesion, separation, strength and hardness. The cured substance of liquid dimethyl cyclohexane rubber is generally low in refractive index of about 1.43, and a mold made from this substance can be preferably used as cladding layer directly, which does not cause separation from the base material for cladding. In this case, it is required to have proper means to prevent peeling of applied core forming resin and base material for cladding from the mold.
The viscosity of liquid silicone rubber is preferably about 500 to 7000 mPa.s, or more preferably about 2000 to 5000 mPa.s, from the viewpoint of accurate replicating of projecting portions corresponding to the optical waveguide cores and the position regulating portions of the power supply wire, ease of defoaming by limiting entry of foams, and obtaining mold size of several millimeters in thickness.
A surface energy of the mold is in a range of 10 dyn/cm to 30 dyn/cm, preferably 15 dyn/cm to 24 dyn/cm from the viewpoint of the adhesion with the base material film. The surface energy is measured by a method of measuring a critical surface tension using a Zisman method. Share rubber hardness of the mold is 15 to 80, or preferably 20 to 60 from the viewpoint of profiling performance, maintenance of the recess shape and separation. The share rubber hardness can be measured according to JIS K 6253 by using a durometer.
A surface roughness of the mold (an arithmetic mean roughness Ra) is 0.2 μm or less, or preferably 0.1 μm or less from the viewpoint of profiling performance. The arithmetic mean roughness Ra can be measured according to JIS B 0601.
The mold is preferred to be light transmittable in ultraviolet ray region and/or visible ray region. When the mold is light transmittable in visible ray region, positioning is easier when adhering the mold to the film base material for cladding at step (2) below, and filling of mold recess with curable resin for forming a core can be observed at step (3) so that completion of filling can be easily known.
When the mold is light transmittable in ultraviolet ray region, ultraviolet curing is to be achieved by transmitting ultraviolet through the mold in case that ultraviolet curable resin is used to form a core. Preferably, the transmittance of the mold in ultraviolet ray region (250 nm to 400 nm) is 80% or more.
The curable organopolysiloxane, in particular, liquid silicone rubber which becomes silicone rubber after curing is excellent in both of the contradictory properties of adhesion and separation with respect to the film base material for cladding and has a capability of replicating nano configuration, and also works to prevent entry of liquid when silicone rubber and cladding base material are adhered.
As the mold using such silicone rubber copies the master plate accurately and adheres to the cladding base material, it fills only the recess between the mold and cladding base material efficiently with the core forming resin, and the mold can be separated easily from the cladding base material. Therefore, polymer optical waveguides retaining the configurations thereof at high precision can be produced very easily.
(2) A Step of Tightly Adhering a Plastic Film Base Material for Cladding to the Mold
Since an optical device (a light transmission and reception module) produced from the polymer optical waveguide of the invention is used in optical wiring in various layers, the material of the plastic film base material for cladding is properly selected in consideration of refractive index, light permeability and other optical characteristics, mechanical strength, heat resistance, adhesion with mold, flexibility and others, depending on the applications of the optical device.
Examples of the film include alicyclic acrylic resin film, alicyclic olefin resin film, triacetic cellulose film, and fluorine containing resin film. The refractive index of film base material is preferably 1.55 or less, or more preferably 1.53 or less, in order to keep enough difference in refractive index from the core.
The alicyclic acrylic resin film is, for example, OZ-1000, OZ-1100 (Hitachi Chemical Co., Ltd.) manufactured by introducing tricyclodecane or other alicyclic hydrocarbon in ester substituent.
The alicyclic olefin resin film is one having norbornene configuration in the main chain, and one having norbornene configuration in the main chain and having polar group such as alkyl oxycarbonyl group (alkyl group having 1 to 6 carbon atoms or cycloalkyl group) in the side chain. Above all, the alicyclic olefin resin having norbornene configuration in the main chain and having polar group such as alkyloxycarbonyl group in the side chain as mentioned above is particularly suited to production of optical waveguide sheet of the invention because it is excellent in optical characteristics, having low refractive index (refractive index being about 1.50, assuring a sufficient difference in refractive index between core and cladding) and high light permeability, excellent in adhesion to the mold, and excellent in heat resistance.
A thickness of the film base material is properly selected in consideration of flexibility, rigidity and ease of handling, and is generally about 0.1 mm to 0.5 mm.
(3) A Step of Filling a Curable Resin for Forming a Core in the Recess of the Mold
At this step, the through-hole provided at the supply side of the resin is filled with curable resin for forming a core, and by evacuating and sucking through the through-hole provided at the discharge side of the resin, the gap (i.e., the recess of the mold) formed between the mold and the film base material for cladding is filled with the resin. By evacuating and sucking, the adhesion of the mold and the film base material for cladding is enhanced, and entry of foams can be avoided. For evacuating and sucking, a suction pipe connected to a pump is inserted into the through-hole at the discharge side.
The curable resin for forming a core includes resins of radiation curing type, electron curing type and heat curing type, and above all the ultraviolet curable resin and thermosetting resin are preferably used. As the ultraviolet curable resin and thermosetting resin for forming a core, ultraviolet curing type and thermosetting type monomer, oligomer, or mixture of monomer and oligomer may be preferably used. Ultraviolet curable resins of epoxy system, polyimide system, and acrylic system may also be preferably used.
The curable resin for forming a core is filled in gaps (the recesses of mold) formed between the mold and the film base material by capillarity, and the curable resin for forming a core is required to be sufficiently low in viscosity for realizing such filling. Therefore, the viscosity of the curable resin is 10 mPa.s to 2000 mPa.s, preferably 20 mPa.s to 1000 mPa.s, or more preferably 30 mPa.s to 500 mPa.s.
Besides, in order to reproduce the original shape of the projecting portion corresponding to the optical waveguide core formed on the master plate at high precision, it is important that the volume change is small before and after curing of the curable resin. For example, decrease in volume leads to conduction loss. Therefore, the curable resin for forming a core is desired to be small in volume change as far as possible, for example, 10% or less, or preferably 6% or less. It is recommended to avoid lowering of viscosity by using a solvent as the volume change becomes large before and after curing.
To reduce the volume change (shrinkage) after curing of the resin, a polymer may be added to the resin. Such a polymer is preferred as being compatible with curable resin for forming a core, not having adverse effects on the resin refractive index, elasticity or permeability. By adding the polymer, not only the volume change can be decreased, but also it is effective to control the viscosity or glass transition point of the cured resin at an advanced level. The polymer includes acrylic system, methacrylic system, epoxy system, and many others.
The refractive index of the cured matter of curable resin for forming a core is required to be larger than that of the film base material as the cladding (including the cladding layer in step (5) below), and is 1.50 or more, preferably 1.53 or more. The difference in refractive index between the cladding (including the cladding layer in step (5) below) and the core is 0.01 or more, preferably 0.03 or more.
(4) A Step of Curing the Applied Resin for Forming a Core and Separating the Mold from the Film Base Material for Cladding
At this step, the applied curable resin for forming a core is cured. To cure the ultraviolet curable resin, ultraviolet lamp, ultraviolet LED, UV irradiation equipment or the like is used, and to cure the thermosetting resin, it is heated in an oven or the like.
The mold used at steps (1) to (3) may be directly used as the cladding layer as far as the conditions such as refractive index are satisfied, and in such a case, separation of the mold is not required. In this case, it is preferred to treat the mold in ozone in order to enhance the adhesion between the mold and core material.
(5) A step of Forming a Cladding Layer on the Plastic Film Base Material for Cladding
A cladding layer is formed on the film base material on which the cores are formed. The cladding layer to be used may be the film base material for cladding used in above step (2), a layer formed by applying and curing a curable resin for cladding, and a polymer film obtained by applying and drying a solvent solution of polymer membrane. As the curable resin for cladding, ultraviolet curable resin or thermosetting resin is used preferably, and for example, monomer, oligomer or mixture of monomer and oligomer of ultraviolet curing type or thermosetting type may be used.
To reduce a volume change (shrinkage) after curing of the resin, the resin may be blended with a polymer (for example, methacrylic system, epoxy system), which is compatible with the resin and does not have adverse effects on resin refractive index, elasticity or permeability.
When using a film as cladding layer, an adhesive may be used. The refractive index of the adhesive is desired to be closer to the refractive index of the film. As the adhesive, the ultraviolet curing type resin or thermosetting resin is used preferably. For example, monomer, oligomer or mixture of monomer and oligomer of ultraviolet curing type or thermosetting type may be used. To reduce the volume change (shrinkage) after curing of ultraviolet curable resin or thermosetting resin, the same type polymer added to the cladding layer may be used.
The refractive index of the cladding layer is desired to be 1.55 or less, preferably 1.53 or less in order to assure a sufficient difference in refractive index from the core. From the viewpoint of entrapping the light, the refractive index of the cladding layer is preferred to be similar to the refractive index of the film base material.
(6) A Step of Forming a 45-degree Mirror and an Abutting Surface on an End Surface of the Obtained Polymer Optical Waveguide Film
The obtained polymer optical waveguide film is constituted so that the 45-degree mirror and the abutting surface are formed on the film end surface by using, for example, a dicing saw. The core portion is exposed from the mirror.
Since the plastic film base material exhibits favorable adhesion to the mold, no gap except for the recess configuration formed in the mold is allowed between the mold and the cladding base material without fixing them by using special means but adhering the plastic film base material for cladding tightly to the mold. Accordingly, the curable resin for curing a core can be provided only in the recess.
Therefore, the manufacturing process is extremely simplified and the polymer optical waveguide film can be manufactured at an extremely low cost.
In this manufacturing method, through-holes are provided in the mold and the discharge side of the recess of the mold is evacuated and sucked through the through-holes so that the adhesion of the mold and the film base material is further enhanced, and entry of foams can be avoided. Further, although performing such a simple method, the obtained polymer optical waveguide film has small conduction loss and high precision, and can be mounted in various devices.
Optical Transmission and Reception Section
Referring to FIGS. 7A to 7C and FIGS. 8A to 8C, a configuration of an optical transmission and reception section 12 having a sub-mount 22 is explained. As a sub-mount 24 is same as the sub-mount 22 in configuration and an optical transmission and reception section 14 is the same as the optical transmission and reception section 12 in configuration, the detailed description of the sub-mount 24 and the optical transmission and reception section 14 will be omitted.
First, referring to FIGS. 7A to 7C, the configuration of the sub-mount 22 is explained. FIG. 7A is a perspective view of the sub-mount 22, FIG. 7B is a plan view of the sub-mount 22, and FIG. 7C is a sectional view C-C of FIG. 6B.
The sub-mount 22 is made of a rectangular parallelepiped substrate. This sub-mount 22 has a recess 26 (a recess for mounting optical components) for mounting a polymer optical waveguide film 10, and recesses 28a and 28b (recesses for mounting optical components) for fitting and holding (mounting) a light detecting element and a light emitting element, respectively. In this embodiment, two recesses 28a and 28b are formed to mount the respective element, however, one recess may be formed to mount both of a light detecting element and a light emitting element. The recess 26 includes an applied surface 26a attached to the abutting surface 10a of the polymer optical waveguide film 10, and a mounting surface 26b for mounting a film surface 10c of the polymer optical waveguide film 10.
Adhesive filling grooves 27, 29a and 29b are formed adjacent to each of the recesses 26, 28a, and 28b serving as recesses for mounting optical component, respectively.
In part of the surface of the sub-mount 22, electrode films 30a, 30b, 30c, 30d are formed for electrical wiring with the light detecting element and the light emitting element. In this example, the electrode films 30a, 30b are patterned so as to be extended to the top surface of the sub-mount 22 from the bottom surface of the recess 28 by way of the side surface.
The electrode films 30c, 30d are patterned on the top surface of the sub-mount 22 so as to be insulated from the electrode films 30a, 30b. By forming the electrode films at the sub-mount 22, electrical wiring is easily provided to the light detecting element and the light emitting element when installing the light transmission and reception module in a package.
The sub-mount 22 is produced at a high precision by the manufacturing method using the above-mentioned duplication method with the mold. The electrode films 30a, 30b, 30c, 30d are, for example, formed by vapor-depositing a metal film of gold (Au), aluminum (Al) or the like on the surface of sub-mount 22, and patterning this metal film by the technology of photolithography.
Referring next to FIGS. 8A to 8C, a mounting state of an optical transmission and reception section 12 is explained. FIG. 8A is a plan view of the optical transmission and reception section 12, FIG. 8B is a sectional view taken along D-D (sectional view along the optical axis of optical waveguide) of FIG. 8A, and FIG. 8C is a partially magnified view showing an optical coupler in FIG. 7B.
When mounting the light transmission and reception module, a surface emission type semiconductor laser diode (LD) 32 as the light emitting element, a photo diode (PD) 34 as the light detecting element, and the polymer optical waveguide film 10 are held on the sub-mount 22 of the optical transmission and reception section 12.
The end of the polymer optical waveguide film 10 is fitted into the recess 26 of the sub-mount 22. The abutting surface 10a abuts against the applied surface 26a of the sub-mount 22 and is positioned at specified location. The film surface 10c of the light incident and exit side is mounted on the sub-mount 22 so as to oppose to the mounting surface 26b of the sub-mount 22. Thus, holding the polymer optical waveguide film 10 on the mounting surface 26b, the flexible polymer optical waveguide film 10 can be held stably.
The film surface 10c is adhered to the opposing mounting surface 26b, the LD 32 and the PD 34 with the adhesive 36 filled from the adhesive filling groove 27. A light curable adhesive such as ultraviolet curable resin, a heat curable adhesive or the like is used as the adhesive 36, but the same curable resin used for the clad 16 of the polymer optical waveguide film 10 is preferably used to reduce light loss.
The LD 32 and the PD 34 are fitted in the recesses 28a and 28b of the sub-mount 22, respectively and are fixed at the bottom surface of the recesses 28a and 28b. By fitting the LD 32 and the PD 34 in the recesses 28a and 28b, the optical transmission and reception section 12 is made compact. In this example, the electrode films 30a and 30b are formed in the bottom surfaces of the recesses 28a and 28b. Therefore, the back electrode of the LD 32 and the electrode film 30a, and the back electrode of the PD 34 and the electrode film 30b are fixed at the bottom surfaces of the recesses 28a and 28b by conductive solder (electroconductive paste) or the like which is filled through the adhesive filling grooves 29a and 29b so as to conduct with each other electrically.
The other electrode of LD 32 is electrically connected to the electrode film 30c by wire 38a, and the other electrode of PD 34 is electrically connected to the electrode film 30d by wire 38b. 
The LD 32 and PD 34 are disposed at specified positions, depending on the abutting position of the abutting surface 10a, so that the emitter 32a of the LD 32 is opposite to the end surface (incident end surface) of the core 18 of the optical waveguide for transmission of polymer optical waveguide film 10, and that the detector 34a of the PD 34 is opposite to the end surface (exit end surface) of the core 18 of optical waveguide for reception of polymer optical waveguide film 10.
Herein, the optical waveguide for transmitting an optical signal from the optical transmission and reception section 12 is described as the optical waveguide for transmission, and the optical waveguide for receiving an optical signal from the optical transmission and reception section 12 is described as the optical waveguide for reception. As seen from the optical transmission and reception section 14, needless to say, the optical waveguide for transmission and optical waveguide for reception are inverted.
The optical transmission and reception section 12 can be assembled easily, by fitting the LD 32 and PD 34 in the recesses 28a and 28b of the sub-mount 22 and fitting the polymer optical waveguide film 10 in the recess 26 of the sub-mount 22.
In this embodiment, the polymer optical waveguide film 10 is composed of a transparent resin, and the position of end of the core 18 of the optical waveguide can be observed through back surface reflection of the mirror 10b. Therefore, by using the back surface reflection image on the mirror 10b, alignments of LD 32 and PD 34 become easy to be mounted in high precision by passive alignment.
Operation of Light Transmission and Reception Module
Referring to FIG. 9, the operation of the light transmission and reception module of the embodiment is explained. FIG. 9 is a view schematically showing a structure of light transmission and reception module. Herein, the optical waveguide for transmitting an optical signal from the optical transmission and reception section 12 is designated as the optical waveguide for transmission, and the optical waveguide for receiving an optical signal from the optical transmission and reception section 12 is designated as the optical waveguide for reception.
In the light transmission and reception module of the embodiment, when transmitting an optical signal from the optical transmission and reception section 12 to the optical transmission and reception section 14, the light emitted from the LD 32 held on the sub-mount 22 of the optical transmission and reception section 12 enters into the incident end surface of the core 18 of the optical waveguide for transmission, and is guided in the optical waveguide for transmission formed in the polymer optical waveguide film 10. The light emitted from the exit end surface of the core 18 of the optical waveguide for transmission is received in the PD 34 held in the sub-mount 24 of the optical transmission and reception section 14.
Similarly, when receiving an optical signal transmitted from the optical transmission and reception section 14 by the optical transmission and reception section 12, the light emitted from the LD 32 held in the sub-mount 24 of the optical transmission and reception section 14 enters into the incident end surface of the core 18 of the optical waveguide for reception, and is guided in the optical waveguide for reception formed in the polymer optical waveguide film 10. The light emitted from the exit end surface of the core 18 of optical waveguide for reception is received in the PD 34 held in the sub-mount 22 of the optical transmission and reception section 12.
As explained above, in the light transmission and reception module of the embodiment, two way light communications are performed between a set of optical transmission and reception sections as mentioned above. The flexible belt-shaped polymer optical waveguide film has a property of following up the deformation such as bending, folding or twisting, so that even if the film is deformed, optical signal can be transmitted and received by way of the optical waveguide formed in the polymer optical waveguide film. Therefore, it can be used in optical wiring of often-bent-or-folded connection of cellphone, slim personal computer or other mobile appliance.
In the light transmission and reception module of the embodiment, since the electrode film is formed in the sub-mount, when installing the light transmission and reception module in a package, electrical wiring can be easily provided in the light detecting element and in the light emitting element of the optical transmission and reception section.
In the light transmission and reception module according to the present embodiment, since the sub-mount including adhesive (including electrically conductive paste) filling grooves 27, 29a and 29b adjacent to the recesses 26, 28a and 28b for mounting optical component is used as described above, the adhesive is evenly applied to the bottom surfaces (component mounting surface) of the recesses 26, 28a and 28b by being poured from the adhesive filling grooves 27, 29a and 29b. When the optical components are mounted to the recesses 26, 28a and 28b, the adhesive filling grooves 27, 29a and 29b function as the reservoir thereby preventing the adhesive from flowing out.
Another Arrangement of Electrode
In the embodiment, it is explained that the electrode film is formed so as to extend from the bottom surface of the recess formed on the sub-mount via the side surface to the top surface of the sub-mount and the rear electrodes of LD and PD and the electrode films are electrically conductive, but the forming pattern of the electrode films is not limited to this.
For example as shown in FIGS. 10A to 10C, FIGS. 11A to 11C and FIG. 12, electrode films 40a, 40b, 40c and 40d which are insulated from each other are formed on the top surface of the sub-mount 22. When the light transmission and reception module is mounted, the electrode films 40a and 40b may be electrically connected to the electrodes of the LD 32 by wires 42a and 42b, and the electrode films 40c and 40d may be electrically connected to the electrodes of the PD34 by wires 42c and 42d. 
Another Constitution of Module
In the embodiment, it is explained that the light transmission and reception module of two way optical communications having the light transmission and reception sections respectively mounted with both the light emitting element and the light detecting element. However, the light transmission and reception module may be one way type which is constituted with a light transmission section having a light emitting element and a light reception section having a light detecting element.
EXAMPLES
The invention is more specifically described below by referring to examples, but the invention is not limited to these examples alone.
Example 1
Sub-mounts are produced with “Duplication Method using Silicone Resin” and the light transmission and reception module shown in FIG. 3 is produced.
(Production of Polymer Optical Waveguide Film)
After an Si substrate is coated with a thick film resist (trade name: SU-8, manufactured by Microchemical) according to a spin coat method, it is prebaked at 80 deg. C., is exposed through a photomask and is developed so that four projections having a quadrate section (width: 50 μm, height: 50 μm, length: 80 mm) are formed. Each gap between the projections is set to 250 μm. The Si substrate coated with the thick film resist is post-baked at 120 deg. C., so that a master plate for manufacturing a polymer waveguide is produced.
A releasing agent is applied on the master plate, and a mixture of thermosetting liquid dimethyl siloxane rubber (product name: SYLGARD184 manufactured by Dow-Corning Asia, viscosity 5000 mPa.s) and its hardening agent is poured in, and heated and cured for 30 minutes at 120 deg. C. After releasing, a die (die thickness: 5 mm) having recesses corresponding to the projections of a rectangular section is produced.
Further, through-holes of circular top view, having a section tapered in mold thickness direction are formed by punching to communicate with the recesses at both ends of each recess, whereby a mold is produced.
This mold is adhered tightly to a film base material for cladding (product name: Arton Film manufactured by JSR Co., refractive index 1.510) of film thickness of 50 μm, which is one size larger than the mold.
A few drops of ultraviolet curable resin of viscosity of 500 mPa.s are dropped into supply side through-hole of the mold, and the discharge side (i.e., the evacuating and sucking side) through-hole is evacuated and sucked, such that the recess is filled with the ultraviolet curable resin in 10 minutes. It is cured by emitting ultraviolet light of 50 mW/cm2 irradiated from outside of the mold for 5 minutes, and the mold is separated from Arton Film, whereby cores of same shapes as projecting portions of the master plate are formed on the Arton Film.
The ultraviolet curable resin with the same refractive index of 1.510 after curing as that of the Arton film is applied to the core formed surface of the Arton film, and the film base materials for cladding of 50 μm are laminated. The ultraviolet curable resin is cured by emitting ultraviolet light of 50 mW/cm2 for five minutes so that two films are adhered, thereby a belt-shaped polymer optical waveguide film with width of 1.5 mm and thickness of 180 μm is obtained.
Using a dicing saw with a Si blade angled by 45 degrees, both ends of this polymer optical waveguide film are cut off at an angle of 45 degrees with respect to the optical axis, such that each core having a 45-degree mirror surface is exposed. Each cladding portion of the 45-degree mirror surfaces is cut off vertically to the optical axis at a position of 50 μm inside from the leading end, and a polymer optical waveguide film having 45-degree mirror surfaces and vertical cut sections at both ends is obtained.
(Production of Sub-Mount)
On Si substrate of 600 μm in thickness, two recesses for mounting light emitting element and light detecting element are formed by RIE. The depth of recess is 250 μm. Further, to mount the polymer optical waveguide film, a recess of 50 μm in depth having an applied surface opposing to the vertical cut section of the polymer optical waveguide film is formed by RIE method. Adhesive filling grooves in which conductive paste or adhesive is poured are formed adjacent to these recesses, respectively. The Si master substrate having the recesses is prepared as a master plate of the sub-mount. In this master plate, recesses for a plurality of sub-mounts are formed and, at each recess, portions corresponding to the filling grooves for the adhesive or the conductive paste are formed. By using this master plate, a plurality of sub-mounts can be reproduced simultaneously.
On this master plate, a mixture of thermosetting liquid dimethyl siloxane rubber (product name: SYLGARD184, manufactured by Dow-Corning Asia, viscosity 5000 mPa.s) and its hardening agent is poured in, and heated and cured for 30 minutes at 120 deg. C. After releasing the cured layer, a silicone resin mold (die thickness: 5 mm) having projections and recesses corresponding to the projections and recesses of the master plate on its surface is produced.
Ultraviolet curable resin (of NTT-AT) with viscosity of 3000 mPa.s is applied, and ultraviolet light of 50 mW/cm2 is irradiated from outside of the mold for 5 minutes to cure, and the cured resin layer is released from the mold. After vapor-depositing Au in a thickness of 200 nm on the cured resin layer, the Au electrodes are patterned by photolithography, whereby electrode pads for lower electrodes extending from a bottom surface to a side surface of each recess up to a top surface of the sub-mount, electrode pads for upper electrodes insulated from the electrode pads for lower electrodes, and electrode pads for the electric supply wires are formed. By cutting the cured resin layer having electrode pads by using a dicer, a plurality of sub-mounts A made of ultraviolet curable resin are formed.
Dimensional difference of projections and recesses as seen from the master plate of the sub-mount (the master substrate) is within 100 nm, and sub-mounts A made of ultraviolet curable resin can be produced at high precision.
(Mounting of Module)
The recess for the light emitting element of the sub-mount A is filled with conducting paste (trade name: SA-0425, manufactured by FUJIKURA KASEI CO., LTD.) through the adhesive filling groove by a dispenser, and a VCSEL element (manufactured by Fuji Xerox, Co., Ltd.) is placed. The recess for the light detecting element of the sub-mount A is filled with the conducting paste (product name: SA-0425, manufactured by FUJIKURA KASEI CO., LTD.) through the adhesive filling groove by a dispenser, and a photodiode element is placed. After each element is disposed, the sub-mount A is heated to 180 deg. C. for 30 minutes so that the VCSEL element and the photodiode element are fixed to the predetermined recesses of the sub-mount A, respectively. As a result, each lower electrode of the VCSEL element and the photodiode element is electrically connected to the electrode pad. Thereafter, the respective upper electrode of the VCSEL element and the photodiode element and the electrode pads are bonded by using an Au wire.
Both ends of the polymer optical waveguide film having 45-degree mirrors are respectively fitted into the recesses of the sub-mounts A, each of the vertical cut section is positioned by abutting against the applied surface of the sub-mount A, and polymer optical waveguide film is fixed to sub-mount A by using ultraviolet curing agent (adhesive) which is filled through the adhesive filling groove. As a result, a two-way light transmission and reception module having a pair of optical transmission and reception sections and polymer optical waveguide film is obtained.
(Evaluation of Communication Performance)
Light transmission and reception performance of a two-way light transmission and reception module which is obtained according to Example 1 was evaluated by using a sampling oscilloscope (product name: Agilent 86100C, manufactured by Agilent Technologies) and a pulse pattern generator. As a result, satisfactory eye pattern could be measured at up to 3.125 Gbps.
Example 2
The sub-mount made of resin is produced through “Stamper Method”, and the light transmission and reception module shown in FIG. 3 is produced. The light transmission and reception module is produced using the method similar to Example 1 except that producing the sub-mount with “Stamper Method”.
(Production of Sub-Mount)
The master substrate made of Si is produced similar to Example 1. The master substrate is used as the stamper (mold) and the thermoplastic bulk molding compound (BMC) resin is adhered to the stamper, heated for two minutes under a pressure of 100 N and at a temperature of 250 deg. C., and thereafter, stood to cool to cure the epoxy resin. The cured layer is then stripped from the stamper, thereby producing the cured resin layer (thickness of mold: 5 mm), which surface includes projections and recesses corresponding to the projections and recesses of the stamper.
Next, after vapor depositing Au on the cured resin layer at a thickness of 200 nm, Au electrode patterning is performed with photolithography, thereby forming an electrode pad for the lower electrode extending from the bottom surface of each recess to the upper surface of the sub-mount through the side surface, and an electrode pad for the upper electrode insulated from the electrode pad for the lower electrode. The cured resin layer formed with the electrode pads is cut with a dicer to form a plurality of sub-mounts C made of epoxy resin.
Dimensional difference of projections and recesses as seen from the stamper (the master substrate) is within 100 nm, and sub-mounts C made of ultraviolet curable resin can be produced at high precision.
(Mounting of Module)
A two-way light transmission and reception module comprising a pair of optical transmission and reception sections and a polymer waveguide film is obtained by mounting in a manner similar to Example 1 with the sub-mount C.
(Evaluation of Communication Performance)
Light transmission and reception performance of a two-way light transmission and reception module which is obtained according to Example 2 was evaluated by using a sampling oscilloscope (product name: Agilent 86100C, manufactured by Agilent Technologies) and a pulse pattern generator. As a result, satisfactory eye pattern could be measured at up to 3.125 Gbps.
Example 3
A sub-mount made of glass is produced through “Stamper Method”, and the light transmission and reception module shown in FIG. 3 is produced. The light transmission and reception module is produced using the method similar to Example 2 except that producing the sub-mount made of glass through “Stamper Method” using a metal die, as explained below.
(Production of Sub-Mount)
A die (a master substrate) made of Ni including a recess having a depth of 250 μm for mounting the light emitting element and the light detecing element, and a recess having a depth of 50 μm for mounting the polymer waveguide film is molded. Using the die as the stamper (mold), low melting glass (made from Sumita Optical Glass Inc., “K-PG375” (Vidron), Tg: 343 deg. C., Yielding point: 363 deg. C.) is adhered to the stamper, heated for five minutes under a pressure of 10 Pa and at a temperature of 375 deg. C., and thereafter stood to cool to cure the low melting glass. The cured glass layer is then stripped from the stamper, thereby producing the cured glass layer (thickness of mold: 5 mm), which surface includes projections and recesses corresponding to the projections and recesses of the stamper.
After vapor-depositing Au in a thickness of 200 nm on the cured glass layer, the Au electrodes are patterned by photolithography, whereby electrode pads for lower electrodes extending from a bottom surface to a side surface of each recess up to a top surface of the sub-mount, electrode pads for upper electrodes insulated from the electrode pads for lower electrodes are formed. By cutting the cured glass layer having electrode pads by using a dicer, a plurality of sub-mounts E made of glass are formed.
Dimensional difference of projections and recesses as seen from the stamper (the master substrate) is within 100 nm, and sub-mounts E made of glass can be produced at high precision.
(Mounting of Module) A two-way light transmission and reception module having a pair of optical transmission and reception sections and a polymer waveguide film is obtained by mounting in a manner similar to Example 1 with the sub-mount E.
(Evaluation of Communication Performance)
Light transmission and reception performance of a two-way light transmission and reception module which is obtained according to Example 3 was evaluated by using a sampling oscilloscope (product name: Agilent 86100C, manufactured by Agilent Technologies) and a pulse pattern generator. As a result, satisfactory eye pattern could be measured at up to 3.125 Gbps.
The above embodiment of the present invention provides examples of a sub-mount and a light transmission and reception module having the sub-mount; however, the present invention is not limited to the embodiments, but various modifications can be made. It is obvious for the skilled person in the art that such modifications are also included in the scope of the invention.
A sub-mount according to the present invention has an adhesive filling groove formed adjacent to a recess for embedding and mounting optical components. A light transmission and reception module according to the present invention includes the sub-mount having the adhesive filling groove.
According to the above aspects, the adhesive is poured in from the adhesive filling groove arranged adjacent to the recess for mounting thereby allowing the adhesive to be evenly applied to a bottom surface (component mounting surface) of the recess for mounting when mounting the optical component to the recess for mounting. Further, the adhesive filling groove functions as a reservoir for liquid to prevent the adhesive from flowing out.
The light transmission and reception module uses the sub-mount including the adhesive filling groove adjacent to the recess for mounting to allow the optical components such as the light detecting element or the light emitting element to be easily and reliably mounted to the sub-mount. The light transmission and reception module of the present invention is thus precise, excels in mass production, and is of low cost.
The sub-mount of the invention may be manufactured by producing a mold for duplication formed with projections and recesses in order to replicate a surface configuration of the sub-mount, filling a curable material into the produced mold for duplication, curing the curable material and separating the duplicated sub-mount from the mold for duplication.
According to the above, the sub-mount can be produced precisely and inexpensively.
The mold for duplication may be manufactured by applying or pouring liquid silicone rubber into the master plate of the sub-mount to be cured. The mold for duplication may be manufactured by performing etching or ion reactive etching on a silicon substrate, or casting a metal.
A heat resistant resin, a light curable heat resistant resin, a thermoplastic heat resistant resin and the like may be applied as the curable material. Epoxy resin, polyimide resin and the like may be applied as the heat resistant resin. A low-melting glass which is molten by heating can be used. As the low-melting glass, a hard glass mainly containing SiO2 and B2O3 can be properly applied.
According to the above, the sub-mount can be produced precisely and inexpensively.
An electrode pattern for electric wiring may be formed at the sub-mount of the invention.
An inner space of the recess for mounting is communicated with an inner space of the adhesive filling grove in the sub-mount of the invention.
As explained above, since the adhesive filling groove is provided adjacent to the recess for mounting in the sub-mount, the adhesive can be applied to the predetermined location precisely and prevented from flowing out. Accordingly, the sub-mount of the invention allows easy and reliable mounting of optical components at satisfactory precision. Further, the sub-mount of the invention is precise and excels in mass production and is inexpensive as they are manufactured by producing the mold for duplication, filling the curable material into the mold for duplication and curing the curable material. The light transmission and reception module of the invention includes the sub-mount for mounting the optical components having the adhesive filling groove thereby, the optical components such as light detecting element or light emitting element are easily and reliably mounted to the sub-mount at high precision. The light transmission and reception module of the invention is also excel in mass production with a low cost.

## Claims

1. A light transmission and reception module, comprising:
an optical waveguide film formed with an optical waveguide;
a light transmitting section having a light emitting element and a sub-mount for holding the light emitting element, that holds one end of the optical waveguide film on the sub-mount so that light emitted from the light emitting element enters into an incident end surface of the optical waveguide; and
a light detecting section having a light detecting element and a sub-mount for holding the light detecting element, that holds the other end of the optical waveguide film on the sub-mount so that light emitted from an emission end surface of the optical waveguide is detected by the light detecting element; wherein,
each sub-mount includes a recess for mounting for embedding and mounting an optical component and an adhesive filling groove formed adjacent to the recess for mounting.

2. The light transmission and reception module according to claim 1, wherein an inner space of the recess for mounting is communicated with an inner space of the adhesive filling grove.