MEASUREMENTS AND MODELING OF THE HARMONIC DISTORTION IN INGAASP DISTRIBUTED FEEDBACK LASERS

We report measurements of the second harmonic distortion in 1.3 µm InGaAsP distributed feedback lasers. At low modulation frequencies (~50 MHz), the second harmonic distortion exhibits a minimum at a certain bias current. The minimum, in general, is not observed at high modulation frequencies (~ 1 GHz). A model of the harmonic distortion, based on the equivalent electrical circuit of the laser, is presented to explain the observed behavior. The model predicts that the minimum occurs at a bias current of (1 + Rl/Ra) l1, and the minimum exists only if ωτ ≪ 1, where Rl, Ra are series resistances in the leakage and active laser paths, Il is the leakage current, and τ is the lifetime of excess minority carriers at the leakage-current blocking layer. The model also predicts that the second harmonic distortion increases with larger Il, ω and τ, and is strongly dependent on Rl/Ra. The spatial hole burning effect in the active region introduces additional nonlinearity, its effects can be significant compared to that of the leakage path. © 1990 IEEE