| 摘要 |
A coupler (FIG. 4) comprising a pair of interwined monomode fibers optically coupled along a portion of their length. The diameter of one fiber is significantly smaller than that of the other and this fiber is thus wound helically. A helical pitch not exceeding 10 mm is chosen. For such pitch, the smaller diameter fiber is appreciably longer. The following inequality thus holds: lambda cxL/ DELTA L</=Lc: where lambda c is the design wavelength, DELTA L/L is the difference in fiber lengths per unit length, and Lc is the interaction length of the coupler. The signal coupling of the coupler is than a strongly peaked function of wavelength. The coupler is suited to wavelength multiplex/demultiplex applications.
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