Noise characteristics in line-narrowed semiconductor lasers with optical feedback

Effects of optical-feedback-induced line-narrowing on low-frequency amplitude and phase noise of semiconductor lasers are reported. Free-running laser noise is compared with that of lasers operating with external mirror feedback. While less than 1 dB difference in the amplitude noise with and without feedback is observed, line-narrowed lasers exhibit 15?20 dB reduction in low-frequency wavelength instability, or phase noise.