New multicompatible optical coupler produced by injection molding

#The invention relates to a process for the production of optical couplers from polymers.

#In passive optical waveguide networks, couplers serve as optical components for distributing the light signals from incoming optical waveguides to output optical waveguides. Couplers of this type comprise a transparent element which is connected to optical waveguides on the light-entry and light-exit sides. In addition to couplers produced by bonding or melting transparent moldings together with optical waveguides, couplers are also known which are produced by twisting optical waveguide bundles and stretching them at the twist point (Agarwal, Fiber Integr. Optics 6 (1), 27-53, 1987).

#However, the production of composite couplers of this type is complex and expensive; in addition, the transmission attenuation of such known couplers is difficult to reproduce, which means that the performance varies by more than 1 dB between the various output fibers.

#FIGS. 1 through 3 are respectively schematic representations of M-, N-, and X- branching units which may be produced by the process for the production of optical couplers in accordance with the teachings of the present invention.

#FIG. 4 is an exploded view illustrating a preferred embodiment of the process for producing an optical Y-coupler in accordance with the teachings of the present invention.

#FIG. 5 is a chart illustrating the dependency of the insertion attenuation D on the angle .alpha. of the optical Y-coupler of FIG. 4.

#The invention thus relates to a process for the production of optical couplers for the construction of optical waveguide systems, which comprises producing the coupler structure by injection molding, in which a hot polymer melt is injected into a pre-fabricated injection mold, which may comprise two or more parts, the melt is allowed to solidify, and the finished coupler element (mixing zone with optical waveguide ends) is subsequently removed.

#In principle, any transparent polymer is suitable for the injection-molding of couplers, but, due to the optical losses, preference is given to amorphous polymers, such as, for example, polymethyl methacrylate (PMMA), polystyrene, polycarbonates, polyolefins, polyesters, polysulfones, polyether sulfones, polyether imides, polyarylates, polyamides and polyester carbonates. It is also possible to use copolymers, for example made from methyl methacrylate and pentafluoro-n-propyl methacrylate, or polymer blends, for example PMMA/polyvinylidene fluoride.

#However, it is also possible to employ partially crystalline polymers if only slight differences in density exist between the amorphous and crystalline regions, so that the scattering losses which occur are low. An example of a suitable partially crystalline polymer of this type is poly-4-methyl-1-pentene. In general, however, it must be ensured that the molecular weights of the polymers used are suitable for processing by injection molding. Many common polymers, such as, for example, PMMA or polycarbonate, are already available on the market as specific injection-molding grades.