Domain inversion under coplanar waveguide electrodes is proposed to improve the frequency-chirping behavior of z-cut LiNbO/sub 3/ Mach-Zehnder modulators. This is achieved by introducing phase reversal electrode section in tandem with inverted ferroelectric domain section. The resulting chirp is shown to be related to the length of the inverted domain. The method opens the way to single-drive modulators with predetermined chirp parameter. The fabrication of such modulators is described, and experimental results confirm that the /spl alpha/-chirp parameter can be more than ten times smaller than that of a conventional Z-cut device.