Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2000-03-27
2004-03-09
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S394000, C430S290000, C385S123000, C385S124000, C385S143000, C385S145000
Reexamination Certificate
active
06703188
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating an optical waveguide structure by use of light and a photo-curable liquid resin. More particularly, the present invention relates to a method of fabricating an optical waveguide structure by use of light and a mixture of two types of photo-curable liquid resins having different curing initiation wavelengths and different refractive indexes, in which the core portion of the optical waveguide structure is formed through curing of one photo-curable liquid resin, and the cladding portion of the optical waveguide structure is formed through curing of both the photo-curable liquid resins.
The present invention further relates to a method of fabricating an optical waveguide structure in which an optical fiber is dipped into the above-described liquid mixture in order to form an optical waveguide structure which continues from the optical fiber and is excellent in terms of straightness and parallelism.
The present invention is applicable to optical connectors for interconnection, optical splitters, and optical mixers which are used in optical communications and which are inexpensive and involve lowered loss.
2. Description of the Related Art
Recently, there has been widely noticed a technique for forming an optical waveguide at a tip end of an optical fiber by use of a photo-curable liquid resin. Japanese Patent Application Laid-Open No. 4-165311 discloses an exemplary method for fabricating an optical waveguide structure. Briefly, in a first step, one end of an optical fiber is dipped into a photo-curable liquid resin containing fluorine-based monomers. In a subsequent step (second step), light having a wavelength suitable for curing the liquid resin is radiated from the tip end of the fiber.
When a laser beam having, for example, a wavelength close to a UV range or a shorter wavelength is caused to radiate from the tip end of the optical fiber, a portion of the photo-curable liquid resin adjacent to the tip end cures through photopolymerization. Thus, a so-called core portion is formed at the tip end of the fiber in accordance with the power distribution of the laser beam. The formation of the core portion enables the laser beam to propagate farther, so that the core portion is extended. As a result, an optical waveguide is formed.
In a third step, the optical fiber is removed from the photo-curable liquid resin and is subjected to cleaning or a like process in order to remove a portion of the photo-curable liquid resin which remains in an uncured state. Subsequently, in a fourth step, the core portion is coated with light-transmissive resin in order to protect the core portion from dust and prevent damage to the core portion. In a final, fifth step, the tip end surface of the thus-formed core portion is ground in order to form a light output surface of the waveguide.
As described above, an optical waveguide continuous from an optical fiber is formed in five steps.
However, when such an optical waveguide is formed by the conventional method, a resultant optical waveguide meanders, while the cross-sectional area of the path increases gradually. The term “meander” means that the radius periodically changes along a Z-axis or optical axis. This phemomenon occurs due to mismatch in refractive index between the core portion of the optical fiber and a photo-curable liquid resin. As a result, there is formed a graded-index-type optical waveguide having an widened beam aperture.
In such a graded-index-type optical waveguide, light meanders in accordance with refractive index. That is, the focal distance changes depending on the length of the waveguide. Therefore, in the final step for grinding the end surface, the grinding amount must be determined while the focal distance is measured. This results in an extremely high fabrication cost.
In addition, the waveguide length of the core portion formed by the conventional method is limited to 8.5 mm. When end surface treatment is performed, the waveguide length decreases further. Therefore, such a conventional method is difficult to apply to cases in which a split mirror is inserted in a waveguide in order to fabricate an optical splitter or combiner, although it can be applied to connectors for connecting optical fibers.
There has also been reported that a tapered optical waveguide is formed at the tip end of an optical fiber. Formation of such a tapered optical waveguide also stems from mismatch in refractive index between the core portion of the optical fiber and a photo-curable liquid resin. When such a tapered optical waveguide is used in an optical combiner or splitter, its loss increases due to an increase in cross-sectional area.
Further, the above-described method has a drawback in that if the cladding layer is cured as is, the refractive index of the cladding layer becomes the same as that of the core portion. Accordingly, in order to obtain a step-index-type optical waveguide, an additional step for replacing the material for fabricating the cladding portion with any other material is required, resulting in deterioration in productivity.
SUMMARY OF THE INVENTION
The present invention was accomplished in order to solve the above-described problems, and an object of the present invention is to provide a method of fabricating an optical waveguide structure which facilitates formation of core and cladding portions by use of a liquid mixture of two types of photo-curable liquid resins and which enables the core portion to extend straight. The term of “a liquid mixture of two types of photo-curable liquid resins” herein means that the liquid mixture should contain a plurality of photo-curable liquid resins which are not identical in curing initiation wavelength and refractive index, as hereinafter described. Hence, the photo-curable liquid resins to be used are not necessarily of two kinds.
Another object of the present invention is to provide a method of fabricating an optical waveguide structure in which the refractive index of the liquid mixture is adjusted in accordance with an optical fiber to be used to thereby enable formation of an optical waveguide which extends straight from a light output end of an optical fiber, regardless of the type of the optical fiber.
Still another object of the present invention is to provide a method of fabricating an optical waveguide structure which can greatly reduce assembly cost and parts cost in order to render the optical waveguide structure inexpensive.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided a method of fabricating an optical waveguide structure in which light of a predetermined wavelength is introduced into a photo-curable liquid resin in order to cure the photo-curable liquid resin along an opticalaxis to thereby form an optical waveguide structure continuing from an area through which the light is introduced. The photo-curable liquid resin is a liquid mixture of a first photo-curable liquid resin and a second photo-curable liquid resin having a curing initiation wavelength shorter than that of the first photo-curable liquid resin. A light beam of a wavelength capable of curing only the first photo-curable liquid resin is radiated into the liquid mixture so as to form a core portion having a rod-like shape. Subsequently, light of a wavelength capable of curing both the first and second photo-curable liquid resins is radiated into the liquid mixture from an area surrounding the liquid mixture so as to form a hardened cladding portion surrounding the core portion. The core portion has a refractive index greater than that of the cladding portion.
In the fabrication method according to a second aspect of the present invention, the refractive index of the first photo-curable liquid resin after curing is greater than the refractive index of the liquid mixture.
In the fabrication method according to a third aspect of the present invention, the beam of light having the predetermined wavelength is radiated from a tip end of a
Ito Hiroshi
Kagami Manabu
Takeda Yasuhiko
Yamashita Tatsuya
Angebranndt Martin
Kabushiki Kaisha Toyota Chuo Kenkyusho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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