Improved intrinsic dynamic distortions in directly modulated semiconductor lasers by optical injection locking

Abstract

Abstract—The effects of optical injection locking on the nonlin-ear distortions of directly modulated semiconductor distributed feedback (DFB) lasers are investigated experimentally. The sec-ond harmonic distortion (SHD) and third harmonic distortion (THD), as well as the third-order intermodulation distortion (IMD3), are measured as functions of modulation frequency for both the free-running and injection-locked lasers. Under strong injection locking with 8-dB injection ratio, the SHD and THD of the DFB laser have been suppressed by 15 dB from 2 to 4 GHz. Moreover, nearly 15-dB reduction in IMD3 has been observed from 1.4 to 3.0 GHz with the same injection conditions. We also found that the injection locking is not effective in reducing the low-frequency distortions. Index Terms—Detuning frequency, harmonic distortion, in-jection-locked semiconductor lasers, injection ratio, intermodu-lation distortion, resonant frequency, stable locking range. I