Compact wide-band tunable narrow-linewidth laser based on BOA-driven PT-symmetry

In semiconductor gain-enhanced long cavities, conventional mode-selection techniques face significant challenges in achieving single-longitudinal-mode operation. In contrast, parity-time (PT) symmetry based approaches exhibit higher gain contrast and wavelength-independent characteristics compared to traditional methods, holding greater promise for application in widely tunable semiconductor lasers. In this paper, a theoretical framework for a polarization-based PT-symmetric laser is constructed. The PT symmetry of a single resonator semiconductor optical amplifier (SOA) laser is verified in a long-cavity laser with a semiconductor amplifier as the gain medium. By enhancing the polarization-dependent gain characteristics of the SOA and the polarization-coupled output of the polarization beam splitter, polarization duality is constructed in the laser loop, achieving wide tuning performance and narrow-linewidth output. Experimental results show that under the condition of PT-symmetry breaking, a narrow-linewidth laser output with a linewidth of 6.5 kHz, a tuning range of 140 nm, and a signal-to-noise ratio of 59 dB is achieved. This research shows promise for application in wide-range highly coherent swept lasers.