Picosecond frequency chirping and dynamic line broadening in InGaAsP injection lasers under fast excitation

Abstract

We report the first observation of picosecond time-resolved frequency chirping within each longitudinal mode of InGaAsP injection lasers under fast excitation. This transient phenomenon is responsible for the characteristic dynamic line broadening observed in the spectra of injection lasers under modulation. The frequency chirping invariably shows a ‘‘red shift’’ during the optical pulse, and is associated with the refractive index increase due to the carrier density decrease in the process of optical pulse generation. The dynamic line broadening will limit the single-mode fiber transmission bandwidth even when single-longitudinal-mode injection lasers are used.