Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1998-10-20
2001-10-09
Kim, Ellen E. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S039000, C385S146000, C385S147000
Reexamination Certificate
active
06301411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a link structure for connecting a plastic optical fiber, mainly used for high-speed communications, to a light receptor. The invention is also concerned with a light-relay element used in the link structure and a method of manufacturing the light-relay element.
2. Description of Background Information
A plastic optical fiber has a core portion, the diameter of which is usually greater than that of the other types of fiber such as a quartz-based optical fiber. This provides a benefit in that the plastic optical fiber can easily be connected to another piece of the same fiber, or to another kind of optical element. For this reason, the components used for the connection require no stringent accuracy. Such a plastic optical fiber provides an economical communications device, which can easily be aligned optically.
In the past when optical communications were mainly carried out at a relatively low speed, the common practice was to put the light-receiving face of a light receiver such as photo-diode unit, directly against the end face of the plastic optical fiber.
Recently, however, as the research into high speed optical communications using a plastic optical fiber has progressed, the connection between the fiber and a light receiver such as photo-diode unit began to create problems.
As is known, the response speed of a photo-diode unit is determined by the time in which the electrons, excited by the light entering into the light-receiving face of the light-receiving portion of the photo-diode unit, reach the electrode inside the photo-diode. In order to obtain a response speed applicable to high-speed optical communications exceeding several hundreds of Mbps, the light-receiving portion of the photo-diode unit must be miniaturized, so that the light-traveling time can be reduced.
Conversely, the miniaturized light-receiving portion can receive only a portion of the light emitted from the end face of plastic optical fiber, so that the connection loss between the fiber and the photo-diode unit is increased.
SUMMARY OF THE INVENTION
The present invention is intended to solve the above-mentioned problem and provides a link structure connecting a plastic optical fiber to a light receptor, enabling minimizing the connection loss therebetween. Other aspects of the press invention include a light-relay element used in the connection structure, as well as a method of preparing the light-relay element.
To this end, there is provided a link structure including a light-relay element formed of a cylindrical tube and a core portion having a refractive index. The light-relay element is interposed between a plastic optical fiber having a light-emitting end face on the one hand, and a light receptor having a light-receiving face which is smaller than the light-emitting end face of the optical fiber on the other. In this structure, the core portion has a diameter decreasing gradually from the light-emitting end face toward the light-receiving face and including a radial direction along which the refractive index is graded.
Further, the core portion may include an axial direction along which the refractive index is also graded.
Preferably, the core portion of the light-relay element has a diameter at one end substantially corresponding to that of the light-emitting end face of the plastic optical fiber, and the core portion has a diameter at the other end substantially corresponding to that of the light-receiving face of the light receptor.
There is also provided a light-relay element includes a cylindrical tube and a core portion having a refractive index. The light-relay element is adapted to be interposed between a plastic optical fiber having a light-emitting end face on the one hand, and a light receptor having a light-receiving face which is smaller than the light-emitting end face on the other. In the light-relay element, the core portion has a diameter decreasing gradually from the light-emitting end face towards the light-receiving face and includes a radial direction along which the refractive index is graded.
The core portion may include an axial direction along which the refractive index is also graded.
Preferably, the core portion of the light-relay element has a diameter at one end substantially corresponding to that of the light-emitting end face of the plastic optical fiber, and the core portion has a diameter at the other end substantially corresponding to that of the light-receiving face of the light receptor.
There is further provided a method of preparing a light-relay element including a cylindrical tube and a core portion having a graded refractive index. The light-relay element is adapted to be interposed between a plastic optical fiber having a light-emitting end face on the one hand, and a light receptor having a light-receiving face which is smaller than the light-emitting end face on the other. The method includes: preparing the cylindrical tube from a polymer having a refractive index, whereby the cylindrical tube includes an inner cylindrical wall having a diameter, and an inner space, the diameter decreasing gradually from the light-emitting end face toward the light-receiving face; putting into the inner space of the cylindrical tube a mixture including a monomer constituting the polymer and a non-polymerizable compound having a refractive index higher than that of the polymer; and polymerizing the monomer while dissolving the inner cylindrical wall of the cylindrical tube.
Preferably, the polymer, monomer and non-polymerizable compounds are a poly (methyl methacrylate), methyl methacrylate and benzyl benzoate, respectively.
REFERENCES:
patent: 3832028 (1974-08-01), Kapron
patent: 4521070 (1985-06-01), Sottini et al.
patent: 4946239 (1990-08-01), Garmon
patent: 5071217 (1991-12-01), Birch
patent: 6169008 (1986-04-01), None
patent: 6323106 (1988-01-01), None
Greenblum & Bernstein P.L.C.
Kim Ellen E.
Sumitomo Wiring Systems Ltd.
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