200 MHz Repetition-Rate 1550 nm SESAM-Based Polarization-Maintaining Linear-Cavity Femtosecond Fiber Laser

In this study, we develop a fiber-based femtosecond laser system operating stably at the 1550 nm wavelength band by employing a semiconductor saturable absorber mirror (SESAM) based mode-locking technique. The system demonstrates strong robustness against environmental variations over extended operation times and offers a wide frequency tuning range. A piezoelectric transducer (PZT) and motorized stage are used to precisely control the cavity length, thereby enabling extended repetition rate modulation. Experimental results confirm long term stability of mode-locking, even under external disturbances such as temperature fluctuations and mechanical vibrations. Dispersion compensation using dispersion-compensating fiber (DCF) minimized the pulse duration. The baseline output denotes the oscillator output before amplification; it was measured at the 10% monitoring port and scaled to the full-output level, exceeding 1.5 mW, while the amplified output was between 90 and 95 mW. The pulse duration is confirmed to be 73.4 fs through autocorrelation measurements. The Allan deviation analysis reveals a fractional frequency stability of 8×10⁻¹⁴ at 1-hour integration time. These results experimentally demonstrate the long-term stability and optical tunability of the fiber femtosecond laser system, providing a promising foundation for future ultrafast photonic applications.