Patent Application
20100308482
1. Field of the Invention
The present invention relates to a method for manufacturing an optical waveguide with a high optical transmission efficiency.
2. Description of the Related Art
Optical waveguides in which a tip of an over-cladding layer is formed in a lens shape are known (Japanese Unexamined Patent Publication No. 2008-281654 A). Referring to
First, as shown in
Secondly, as shown in
Third, as shown in
Finally, when the molding die 34 is removed, as shown in
However, it is not possible to press the molding die 34 onto the under-cladding layer 32 by the application of a high pressure in a process of
The ultraviolet curable liquid-state resin 37 having penetrated into the clearance 42 is cured by the irradiation of the ultraviolet rays 38 shown in
Referring to
In conventional methods for manufacturing optical waveguides, it is impossible to press the molding die 34 onto the under-cladding layer 32 with a high pressure because the quartz-made molding die 34 has a weak mechanical strength. This makes it easy to create the clearance 42 between the molding die 34 and the under-cladding layer 32.
When there is the clearance 42 between the molding die 34 and the under-cladding layer 32, the ultraviolet curable liquid-state resin 37 penetrates into the clearance 42 to form the burr 43 around the over-cladding layer 41. The over-cladding layer 41 has a thickness greater than the designed value, even if the burr 43 is not formed.
Thus, the center 40 in the lens 39 that is located at the tip of the over-cladding layer 41 is out of alignment from the design position. Accordingly, the light 44 emitted from the core 33 does not become the desired parallel beams 45 but becomes the diffusion light 46 when emitted from the lens 39. This lowers the optical transmission efficiency of the optical waveguide 30.
The summary of the present invention is described as follows:
In a first preferred embodiment, there is provided a method for manufacturing an optical waveguide according to the present invention which comprises: a substrate for transmitting ultraviolet rays; an under-cladding layer formed on the substrate; a core formed on the under-cladding layer; and an over-cladding layer formed on the under-cladding layer so as to cover the core. The method for manufacturing an optical waveguide according to the present invention includes the following steps A) to c): A) filling an ultraviolet curable liquid-state resin that may form an over-cladding layer in a concave portion of a die with a concave portion; B) bringing the core and the under-cladding layer into close contact with the ultraviolet curable liquid-state resin filled in the concave portion of the die; and C) irradiating ultraviolet rays from the substrate side to cure the ultraviolet curable liquid-state resin while bringing the under-cladding layer into close contact with the die by applying a pressure onto the substrate and the die, alternatively, after bringing the under-cladding layer into close contact with the die by applying a pressure onto the substrate and the die and then removing the die.
In a second preferred embodiment of the manufacturing method according to the present invention, the substrate is a cycloolefin-resin film or an ester resin film.
In a third preferred embodiment of the manufacturing method according to the present invention, a material for the die is a metal.
In a fourth preferred embodiment of the manufacturing method according to the present invention, the material for the die is any one of an aluminum, an aluminum alloy, a nickel, a nickel alloy, an iron, and a ferrous alloy.
In a fifth preferred embodiment of the manufacturing method according to the present invention, an end surface of the over-cladding layer is a long lens having a cross-sectional shape of a quarter of a circle.
In a sixth preferred embodiment of the manufacturing method according to the present invention, the pressure is 0.01 to 10 MPa.
In a seventh preferred embodiment of the manufacturing method according to the present invention, a clearance between the under-cladding layer and the die is less than 5 μm when bringing the under-cladding layer into close contact with the die.
In an eighth preferred embodiment of the manufacturing method in step B according to the present invention, a laminate including a core, an under-cladding layer, and a substrate is absorbed in a holder with at least two absorption means to release absorption of one absorption means and the core and the under-cladding layer are partially in contact with the ultraviolet curable liquid-state resin while bowing the laminate and subsequently, the other absorption means is released to bring the core and the under-cladding layer completely into contact with the ultraviolet curable liquid-state resin.
The optical waveguide obtained by the manufacturing method of the present invention is as per designed in dimensions and shape of the over-cladding layer. For instance, the dimensions of the long lens of the tip of the over-cladding layer are as per designed and the shape of the lens is formed as per designed. Accordingly, light emitted from an end of the core becomes parallel beams by the long lens when emitted from outside the optical waveguide. Thus, the optical waveguide obtained by the manufacturing method of the present invention has a high optical transmission efficiency.
For a full understanding of the present invention, reference should be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
The preferred embodiments of the present invention will now be described with reference to
As shown in
The manufacturing method of the present invention includes the following steps A to C in order. The steps A to C may include another steps.
In step A, as shown in
The die 15 is used for molding the over-cladding layer 14 in any shape (typically, a lens shape). The shape and size of the concave portion 16 in the die 15 are appropriately determined according to the shape of the over-cladding layer 14.
The die 15 to be used in the manufacturing method of the present invention needs a mechanical strength. For this reason, a metal, such as aluminum (alloy), nickel (alloy), iron (alloy) or the like is typically preferred.
The aforementioned ultraviolet curable liquid-state resin 17 is cured by the irradiation of ultraviolet rays, although the resin 17 flows in room temperature and is transformed into a stable state of being dissolved slightly and poorly soluble. The ultraviolet curable liquid-state resin 17 generally includes a photo polymerization prepolymer polymerized by photochemical functions and a reactive diluent, a photopolymerization initiator, a solvent, and a leveling agent or the like.
As shown in
The substrate 11 transmits ultraviolet rays. The substrate 11 preferably has an ultraviolet transmission efficiency of at least 65%, more preferably at least 70% at a wavelength of 365 nm. The substrate 11 preferably has a thickness of 10 to 200 μm.
A material for forming the substrate 11 is preferably a resin film with flexibility. Examples of a resin film to transmit ultraviolet rays include a cycloolefin-resin film or an ester resin film.
The under-cladding layer 12 is formed from a material having a lower reflective index than the core 13. The under-cladding layer 12 and the over-cladding layer 14 are preferably made of an identical material. The under-cladding layer preferably has a thickness of 5 to 50 μm.
The core 13 is formed from a material having a higher refractive index than the under-cladding layer 12 and the over-cladding layer 14 and high transparency at a wavelength of light that propagates. A material for forming the core 13 is preferably an ultraviolet curable resin having a higher refractive index than the under-cladding layer 12 and the over-cladding layer 14.
The maximum refractive index difference between the core 13 and the under-cladding layer 12 is preferably 0.02 to 0.2. The maximum refractive index difference between the core 13 and the over-cladding layer 14 is preferably 0.02 to 0.2. The core 13 typically has a width of 10 to 500 μm and typically has a height of 10 to 100 μm.
The core 13 is patterned in any shape according to its purpose. Examples of the method for patterning the core 13 include a dry etching method, a transfer method, an exposing/developing method, a photo-bleaching method or the like.
Although a method for bringing a laminate 18 including the core 13, the under cladding layer 12, and the substrate 11 into contact with the ultraviolet curable liquid-state resin 17 is not particularly limited, a typical example is a method shown in
First, as shown in
Secondly, as shown in
Finally, as shown in
With use of such a method, it is possible to effectively remove bubbles easily adhered to the periphery of the core 13.
As shown in
When the die 15 is removed after the curing or the partial curing of the ultraviolet curable liquid-state resin 17, as shown in
The die 15 that withstands the high pressure 23 is used in the manufacturing method of the present invention. The die 15 is attached firmly to the under-cladding layer 12 by applying the high pressure 23 between the die 15 and the substrate 11 to cure the ultraviolet curable liquid-state resin 17. This makes it possible to prevent the burr around the over-cladding layer 14 and obtain the over-cladding layer 14 with a designed thickness.
The strength of the pressure 23 is preferably 0.01 to 10 MPa, more preferably 0.1 to 1 MPa. When the pressure 23 is less than 0.01 MPa, there is a possibility of the burr having a thickness of more than 30 μm. When the pressure 23 is over 10 MPa, there is a possibility of a pressure device being too big.
As long as the clearance between the under-cladding layer 12 and the die 15 is less than 5 μm when bringing the under-cladding layer 12 into close contact with the die 15, the dimensions and shape of the over-cladding layer 14 are substantially as designed. Light emitted from an end of the core 13 becomes parallel beams when the light is emitted from outside the optical waveguide 10.
The irradiation level of the ultraviolet rays 24 is preferably 100 to 8,000 mJ/cm2 at a wavelength of 365 nm.
The die 15 is removed in a state in which the ultraviolet curable liquid-state resin 17 maintains the shape of the concave portion 16 in the die 15. The ultraviolet curable liquid-state resin 17 may be completely cured or may be partially cured when the die 15 is removed. Further curing treatment, such as irradiation of ultraviolet rays may be performed after removing the die 15 when the ultraviolet curable liquid-state resin is partially cured.
As shown in
The optical waveguide 10 is typically capable of receiving light at an end 13a of the core 13 arranged on a short side surface 10a and transmitting light to an end 13b of the core 13 near a long side surface 10b. The light 26 emitted from the end 13b of the core 13 becomes parallel beams by the long lens 25 when emitted outside from the optical waveguide 10. Accordingly, the optical waveguide 10 obtained from the manufacturing method of the present invention has a high optical transmission efficiency.
A varnish for forming cladding layer was prepared by mixing 100 parts by weight of a UV-curable epoxy-based resin having an alicyclic skeleton (EP 4080E manufactured by ADEKA CORPORATION) (Component A) and 2 parts by weight of a photo-acid-generation agent (CPI-200K manufactured by SAN-APRO Ltd.) (Component B).
A varnish for forming cores was prepared by mixing 40 parts by weight of a UV-curable epoxy-based resin having a fluorene skeleton (OGSOL EG manufactured by Osaka Gas Chemicals Co., Ltd.) (Component C), 30 parts by weight of a UV-curable epoxy-based resin having a fluorene skeleton (EX-1040 manufactured by Nagase ChemteX Corporation) (Component D), 30 parts by weight of 1,3,3-tris(4-(2-(3-oxetanyl))butoxyphenyl)butane (synthesized in accordance with Example 2 in JP 2007-070320 A) (Component E), 1 part by weight of the Component B, and 41 parts by weight of ethyl lactate.
The varnish for forming cladding layer was applied onto the surface of a polyethylene terephthalate film having an ultraviolet ray transmission efficiency of 70% at a wavelength of 365 nm. This was irradiated with 1,000 mJ/cm2 of ultraviolet rays and thermally-treated at 80° C. for 5 minutes to form an under-cladding layer with a thickness of 20 μm. The under-cladding layer had a refractive index of 1.510 at a wavelength of 830 nm.
The core-forming varnish was applied onto the surface of the under-cladding layer, and this was subjected to a heating treatment at 100° C. for 5 minutes so that a core layer was formed. The core layer was covered with a photomask and this was irradiated with 2,500 mJ/cm2 of ultraviolet rays at a wavelength of 365 nm, and further subjected to a heating treatment at 100° C. for 10 minutes. The gap between the core layer and the photomask was 100 μm.
Unirradiated portions with ultraviolet rays of the core layer were dissolved and removed by a γ-butyrolactone aqueous solution, and this was subjected to a heating treatment at 120° C. for 5 minutes so that a plurality of cores having a core width of 20 μm and a core height of 50 μm were formed. The plurality of cores respectively had a refractive index of 1.592 at a wavelength of 830 nm.
A laminate which comprises a core, an under-cladding layer, a polyethylene terephthalate film was obtained by the aforementioned steps.
The clad-forming varnish was filled in the concave portion of an aluminum die with a concave portion and placed on a stage.
The aforementioned polyethylene terephthalate film of the laminate was absorbed in a holder with two absorption means. Releasing one absorption means, the core and the under-cladding layer were attached firmly to the clad-forming varnish while bowing the laminate so as not to put air. Subsequently, the other absorption means was released and the core and the under-cladding layer were attached firmly to the clad-forming varnish.
Next, a pressure (0.1 MPa) was applied between the die and the polyethylene terephthalate film to reduce the size of a clearance between the die and the under-cladding layer down to 5 μm or so (The clearance between the die and the under-cladding layer is presumed by the thickness of the burr around the over-cladding layer). The clad-forming varnish was cured by the irradiation of ultraviolet rays from the polyethylene terephthalate film side.
The optical waveguide was completed by removing the die. The thickness of the burr around the over-cladding layer in the prepared optical waveguide was as indicated in Table 1.
As shown in
An optical waveguide was formed of the same material and under the same conditions except for the above. The thickness of the burr around the over-cladding layer in the prepared optical waveguide was as indicated in Table 1.
The polyethylene terephthalate film and the over-cladding layer+under-cladding layer were separated each other by inflecting the prepared optical waveguide. The burr of the exposed over-cladding layer was measured by using a micro gage (MF-50, manufactured by Nikon Corporation).
Although the applications of the optical waveguides obtained by the present invention are not particularly limited, the optical waveguides are preferably used for, for example, optical wiring plates, an optical connectors, substrates with optical-electric devices mixedly mounted, coordinate input devices of optical touch panels and the like.
This application claims priority from Japanese Patent Application No. 2009-136227, which is incorporated herein by reference.
It is to be understood that the present invention may be practiced in other embodiments in which various improvements, modifications, and variations are added on the basis of knowledge of those skilled in the art without departing from the spirit of the present invention. Further, any of the specific inventive aspects of the present invention may be replaced with other technical equivalents for embodiment of the present invention, as long as the effects and advantages intended by the invention can be insured. Alternatively, the integrally configured inventive aspects of the present invention may comprise a plurality of members and the inventive aspects that comprise a plurality of members may be practiced in a integrally configured manner.
There has thus been shown and described a novel method for manufacturing an optical waveguide which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-136227 | Jun 2009 | JP | national |
