Enhanced frequency modulation in cleaved‐coupled‐cavity lasers is analyzed and results for frequency deviation per unit modulator current and lasing spectra are presented. Strong sensitivity to gap spacing and bias point are reported and nonlinearities are shown to limit distortionless analog frequency modulation. In a typical case, a 40‐&mgr;A peak modulation current produces a 200‐MHz maximum frequency deviation with 2% distortion.