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Dynamic optical coupling technique based on complementary Dammann gratings

With the development of optical communication, the need of dynamic optical couplers, especially of Ν broad band couplers, becomes greater. Though some advanced fiber fusion techniques have been developed, they still have many shortcomings. We proposed a new 1×Ν dynamic coupler employing two even-numbered Dammann gratings. We divide a conventional Dammann grating into two complementary gratings. When there is no shift between them, they equal to a normal Dammann grating. The light that comes from the input fiber is diffracted into Ν spots with equal intensity and coupled into the Ν output fibers. When the two gratings have an accurate shift of a half-period, the total phase difference reduces to zero because of the complement. The light coming from the input fibers are coupled into the only one fiber which locates in the center. So they can work as a beam splitter or a combiner according to the relative shift between them. This approach has the clear advantage of realizing dynamic coupling of medium size of channels (e.g. 8×16) and is superior to the conventional methods particularly in very high Ν arrays. Experimental results of 1×8 optical dynamic coupler are presented in this paper.