Precise characterization of the frequency chirp in directly modulated DFB lasers

We report on results from the characterization of the frequency chirp characteristics of distributed feedback (DFB) lasers under direct modulation conditions. Parameters describing transient and adiabatic chirp effects are measured for a DFB laser from the ratio of phase to amplitude modulation factors when modulated with sine waves using a high-resolution optical spectrum analyzer. Transient and adiabatic chirp effects produced under digital non-return to zero (NRZ) amplitude modulation are also analyzed using the emitted optical spectrum. Finally, results from the measurement technique are compared with those obtained from measured optical spectra.