The control of the modal linewidth broadening enhancement factor by a laterally coupled-cavity waveguide has been analyzed. It is found that when the coupling is weak and the fluctuations of injected nonequilibrium carriers due to spontaneous radiative recombination in the two cavities are independent, the modal linewidth broadening enhancement factor may approach zero, thus making the linewidth decrease by about an order of magnitude or more. The near- and far-field distributions and the modal discrimination between inphase and out-of phase modes are discussed.