Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1999-03-01
2000-12-26
Sanders, Kriellion
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
526 62, 526 64, 526 88, 526245, C08L 8300, C08F 200, C08F 1820
Patent
active
061661074
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for producing an optical rod-shaped graded-index polymer preform by making the composition of the preform near the core (or centre) differ from the composition of the shell (or cladding) of the preform by polymerization with rotation of the mixture containing the starting substances. The present invention furthermore relates to optical rod-shaped graded-index polymer preform and optical lenses and optical fibres obtained by using such a preform.
A similar method for producing a graded-index polymer preform is known from the article "Review Polymer Optical Fibres", Emslie, C., Journal of Materials Science, 23 (1988), pages 2281-2293. The cross-sectional refractive index gradient of the preform described in said article has been obtained as a result of the fact that the chemical composition of the copolymer gradually changes in cross-sectional direction. The preform is made by transferring a mixture consisting of two monomers and an ultraviolet-sensitive initiator added thereto to a glass tube. Said tube is externally irradiated by ultraviolet light and slowly rotated in order to achieve a uniform irradiation over the circumference of the tube. As a consequence of the limited penetration depth of the ultraviolet light the polymerization process starts near the outside of the tube. The reactivity ratios of the monomers are selected such that one of the monomers preferably polymerizes near the outside of the tube during the early part of the polymerization process. Then the rest of the polymerization process proceeds from the outside of the preform towards the centre thereof, whereby a decreasing amount of the first monomer and an increasing amount of the second monomer is being polymerized. The chemical composition of the preform gradually changes from the outside of the preform towards the centre of the preform, therefore, and the preform consists of a very large number of different copolymers of different chemical compositions. In addition to that it is possible to further optimize the optical properties of the preform by using a third monomer, as a result of which a more uniform refractive index profile is obtained. The maximum diameter of the rod-shaped preform produced in accordance with said method is limited, because the second monomer must diffuse inwardly during polymerization. As a result of this the polymerization process must take place slowly, which in practice limits the maximum diameter.
The international application WO 92/10357 relates to method and apparatus for in situ preparing a plastic lens element having a gradient index of refraction. According to this method first and second monomer-containing compositions, each having a different index of refraction, are injected into a centrifugal mould at a controlled ratio to produce a lens element having a gradient index of refraction. Precise control of the gradient index is achieved by varying the ratio of the two monomers over a predetermined number of steps during the filling process. After filling of the central cavity, the spin mould is irradiated with ultraviolet light (UV) to induce photopolymerization and to form a hardened lens. According to this method a gradient index lens element measuring 9.5 mm long by 7.58 mm diameter was obtained.
The German patent DE-C1-42 14 259 relates to a method for in situ preparation of optical preforms having a gradient index of refraction. A homogeneous mixture of components with different molecular weights is melted in a mould and subsequently rotated to cause a separation of the molecular components due to the rotation forces. After achieving the intended distribution the temperature is decreased and the gradient is fixed. This patent does not mention a reaction between the components.
The international application WO 87/01071 relates to a preform with a graded refractive index and a method for construction of the same. According to this application a graded index is obtained by bringing together monomers with almost identical reaction parameters and solubility
REFERENCES:
patent: 4956000 (1990-09-01), Reeber et al.
Bastiaansen Cornelis Wilhelmus Maria
van Duijnhoven Franciscus Gerardus Henricus
Sanders Kriellion
Technische University Eindhoven
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