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Mode separator and delay equalizer for multimode optical fiber transmission systems
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Inventors: Uchida, Teiji; Ueki, Atsufumi;
Assignee: Nippon Electric Company, Ltd. (Tokyo, JA)
Primary Examiner: Corbin; John K.
Assistant Examiner: Hille; Rolf
Attorney, Agent or Firm: Hopgood, Calimafde, Kalil, Blaustein & Lieberman
The invention contemplates an improved light-mode separator for orientation in axially offset adjacency to an end of an optical fiber, in a plane perpendicular to the fiber axis; separate concentric regions of the separator about the fiber axis have different light-converging properties such that the convergence point for each light-converging region is (a) offset with respect to the convergence point for each remaining light-converging region, and is also (b) independently externally accessible for focused-energy utilization without masking interference with any other converging light from the separator. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As prior art background, FIG.
1, schematically shows the construction of a delay equalizer proposed by Y.
Suematsu et al.
in the above mentioned paper, in which a light pulse signal propagated along a multimode optical fiber 1 emerges from an output end 2.
The lower-order mode ray is directed to the center area of a composite lens 3 which is a constituent element of the mode separator; and the higher-order mode ray is directed to the peripheral area thereof.
Thd focal length of the lens 3 differs in the regions of its center and peripheral areas.
Hence the output rays from the optical fiber 1 are converged at positions 4, 5 and 6 through the lens 3 and thus form cone-shaped converging light rays 41, 51 and 61, respectively.
Since the optical axes of the individual regions of the lens 3 are made coincident with those of the optical fiber 1, the converging point 4 of the low-order mode ray is located within converging cones 51 and 61 formed by the higher-order mode rays.
At the convergence points 4, 5 and 6, input ends of optical fibers 7, 8 and 9 different in length from each other are fixed respectively by a supporting member (not shown).
The mode rays coupled to the optical fibers 7, 8 and 9 are delayed by an appropriate amount relative to each other so as to compensate for the dispersion introduced in the multimode optical fiber 1.
The mode rays are then applied to a photodetector 10 in which they are converted into an electric signal.
Appropriate delays are given by suitably determining the relative lengths of the optical fibers 7, 8 and 9, i.
e.
, a lower-order mode ray is forced to propagate a longer optical fiber than a higher-order mode ray does.
In this prior art mode separator, however, the converging point 4 of the lower-order mode ray is located within the converging cones 51 and 61 formed by the higher-order mode rays, while the input end of the optical fiber 7 must securely be supported in order to attain a higher light coupling efficiency
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