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Position weighting of fiber Bragg gratings for bandpass filtering.

A fiber Bragg grating bandpass filter with tailored refractive-index modulation is investigated. The writing method includes a position weighting technique, which provides flexible and accurate control of the index modulation along the fiber. This weighting is accomplished by adjusting the positions of a large number of overlapping subgratings to control the local grating strength. A 10-cm grating with a truncated sin(x)/x refractive-index modulation function was written and characterized with this method, showing good agreement with simulations. These types of filter are well suited for wavelength-division-multiplexing applications and can be made to have steep edges, low sidelobes, large bandwidth, and low stopband ripple.