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We investigate electrooptic directional-coupler modulators operating at the wavelength of 1.3 /spl mu/m, to have high linearity in their response function. The inverse Fourier transform technique was used to synthesize the spatially varying coupling function from a specified response function. The resulting coupling function was then used to determine the shape of the modulator structure. Modulators to have the response function of the form of a triangular ("linear") function have been designed, fabricated, and tested. The third-order intermodulation-limited spurious-free dynamic range, at -130-dBm normalized noise floor, of 96.2 dB/Hz/sup 2/3/ was obtained.