Abstract

Most 1550-nm analog transmission systems use external modulation as it is expected that the chirp generated will be zero. However, external modulators can generate chirp.¹ In normal Mach-Zehnder (MZ) modulators chirp is zero when the two arms of the interferometer are balanced, and equal and opposite phase modulation is applied to both. In analog CATV application single-stage modulators cannot be used directly because the nonlinear transfer function causes unacceptable distortion. An alternative design based on a two-stage MZ modulator has been reported'; we have used such a modulator in the following. The modulator layout is shown in Fig. 1; RF drive is applied to both sets of electrodes in a ratio k = 0.5. Bias electrodes (not shown) are constantly adjusted to minimize composite-second-order (CSO) distortion at the transmitter.

© 1996 Optical Society of America