Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1993-06-17
1996-07-30
Smith, Jeffrey T.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524287, 524315, 524317, 524319, 525265, 525277, 525306, 525932, 264 124, 264 11, 264 129, 385124, 385141, C08K 5101
Patent
active
055412475
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to optical resin materials with distributed refractive index, processes for producing the materials, and optical conductors using the materials, and more particularly, to optical resin materials of which the refractive index has a gradient in a specific direction, processes for producing the materials, and optical conductors using the materials, which conductors include optical fibers, waveguides, optical integrated circuits, and base materials (preforms) therefor having distributed refractive indexes.
BACKGROUND ART
It is already known in the art to use optical resins as materials for optical conductors of distributed refractive index type, including optical fibers, optical waveguides, optical integrated circuits, and base materials (preforms) therefor.
The optical resins used for the optical conductors of distributed refractive index type are usually required to have a high level of transparency and an accurately controlled distribution of refractive index. For instance, in a distributed refractive index type optical fiber, it is necessary to form an accurately controlled radial distribution of refractive index in a resin material having a high level of transparency, in order to realize a broad transmission band and a low loss.
The techniques conventionally known for producing optical resin materials with distributed refractive index can be roughly classified into a copolymerization method and a diffusion method. None of the presently available techniques can produce optical resin materials that fully meet the above-mentioned requirements.
The copolymerization method is a method in which two or more different monomers are copolymerized. For example, Examined Japanese Patent Publication (KOKOKU) No. 54-30301 and Unexamined Japanese Patent Publication (KOKAI) No. 61-130904 disclose optical conductors having a refractive index gradient, which are produced by utilizing the copolymerization reaction of monomers having different reactivity ratios r1 and r2, and changing the proportion of the monomer units contained in the polymers generated in the early stage and the late stage of the polymerization.
This method makes use of the difference between the copolymerization reactivity ratios r1 and r2, and therefore, the greater the difference between the values of r1 and r2, the easier it becomes to produce a difference in refractive index; however, as the difference between the values increases, the monomers are more likely to be polymerized independently, compared with the rate of the copolymerization. As a result, phase separation unavoidably takes place between the reaction products. If fluctuation in the refractive index distribution is caused due to such phase separation, then a scattering loss occurs in the resulting optical conductor.
If an intensive phase separation occurs, it is observed as a cloudy phenomenon, which possibly makes it utterly impossible to use the material for applications including optical fibers, optical waveguides, and optical integrated circuits.
In addition, increasing the difference in the reactivity ratio between monomers causes a monomer having a lower reactivity to remain as monomer until the last stage of the polymerization process, and if the polymerization process is not complete, the resulting optical device is subject to change with time, which leads to deterioration of the characteristics.
In contrast with the copolymerization method, the diffusion method is a method wherein gel is produced from a monomer; another type of monomer is poured and diffused in the gel; and then the mixture is fully polymerized.
For example, according to a method proposed in Examined Japanese Patent Publication (KOKOKU) No. 52-5857, a polymer precursor (prepolymer gel), which has a transparent and three-dimensional crosslinked structure, is prepared first; then a monomer, which forms a polymer having a different refractive index, is diffused from outside; and the mixture is subjected to post-treatment to be fully polymerized and solidified, thereb
REFERENCES:
patent: 3718383 (1973-02-01), Moore
patent: 3816160 (1974-06-01), Moore
patent: 3955015 (1978-05-01), Ohtsuka et al.
patent: 4521357 (1985-01-01), Ohtuska et al.
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