Detuned Grating Single-Mode Laser With High Immunity to External Optical Feedback

In this paper, we report a novel single-mode laser with high immunity to external optical feedback following the principle of active-filter-tuned oscillator. Within the conventional Fabry-Perot (FP) cavity, a high-Q bandpass filter formed by two tilted gratings with detuned Bragg wavelengths is embedded, and the resultant mode selection mechanism can purify the lasing spectrum by eliminating all but one of the FP cavity modes near the peak wavelength of the said filter. The proposed laser inherently bears the distinct feature of being robust against any small disturbances to oscillation loop. Simulation results from the large-signal dynamic model show that a stable single-mode operation has been achieved with a side-mode suppression ratio of as high as 50 dB. Further, compared with conventional index-coupled distributed feedback lasers, the proposed laser exhibits a much higher immunity to external optical feedback, even at a very high feedback level of -3 dB, and its single-mode yield is also less susceptible to variations of effective facet phases caused by cleaving in semiconductor laser fabrications.