| 摘要 |
A fused fiber filter coupler is disclosed characterized in that a long perio d grating is written in at least a portion of the waist of the coupler. The two fibers wh ich make up the coupler have respective propagation constants .beta.fiber1 and .beta.fib er2 which are different and both fibers are singlemode at the wavelength of operation. In order for an e fficient grating to be written in the waist of the coupler, the coupler must be photo sensitive in at least a region of the waist. Since the propagation constant is a function of the wavelength and the period of the grating is given by the expression ~ = 2.pi .(.beta.fiber1 - .beta.fiber2), the filter may be tuned to a particular wavelength by adjusti ng the period of the grating. The filter so constructed acts in transmission and can discriminate wavelengths of the order of 1 nm. The filter is particularly useful in wavelength-rich o ptical communications networks to extract a particular wavelength from a signal or to add a particular wavelength to a signal (i.e. multiplexing and demultiplexing).</S DOAB>
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