A Mach-Zehnder modulator (MZM) is horizontally integrated with a VCSEL. The horizontally-integrated MZM overcomes wavelength dependence problems of horizontally-integrated EA modulators and yet has the same advantages as horizontally-integrated EA modulators in terms of overcoming the ER and modulation range problems associated with the vertically-integrated EA and EO modulators. By overcoming these problems with the existing integrated modulators, the operation speed of the VCSEL is increased and the modulation signal range is extended to allow a wider range of modulation signals and modulation schemes, including large-signal digital modulation schemes.