Highly External Optical Feedback-Tolerant 1.49- $\mu$ m Single-Mode Lasers With Partially Corrugated Gratings

An InGaAsP single-mode laser diode (LD) highly tolerant to optical feedback was realized utilizing a partially corrugated grating with a window-mirror structure. The length and the coupling coefficient of the grating were properly chosen to enable moderate output power, low feedback sensitivity, and a side mode suppression ratio of 40 dB simultaneously. Under -16 dB external optical feedback, the relative intensity noise (RIN) was improved by 10 dB compared with that of a conventional DFB LD. The RIN was maintained at less than -120 dB/Hz under strong external optical feedback as high as -10 dB. These results show that the fabricated lasers are potentially useful for isolator-free optical modules.