Wavelength-Tunable PT-Symmetric Single-Longitudinal-Mode Fiber Laser with a Single Physical Loop

A wavelength-tunable parity-time (PT)-symmetric single-longitudinal-mode fiber laser with a single physical loop is demonstrated. Single-longitudinal-mode lasing with a tunable range from 1549.2 to 1550.3 nm and a linewidth of 670 Hz is achieved experimentally.