All-Polarization-Maintaining Figure-9 Mode-Locked Tm-Doped Fiber Laser With Amplitude Noise and Timing Jitter Suppression

An all-polarization-maintaining (PM) figure-9 mode-locked Tm-doped fiber laser that leverages a nonlinear amplifying loop mirror (NALM) incorporated with a chirped fiber Bragg grating (CFBG) for dispersion management is experimentally demonstrated. A dual output is obtained at the transmission and reflection arm of the NLAM loop, with a center wavelength of 1950 nm and 3 dB bandwidth of, respectively, 8.6 nm and 30 nm. The corresponding pulse repetition rate is 30.6 MHz with an average power of, respectively, 6.5 mW and 2 mW for the two outputted pulses. By utilizing an extra-cavity amplification, the output of the transmission arm experiences nonlinear pulse evolution and its pulse width is directly compressed to 123 fs (almost approaches the calculated Fourier transform limited duration of 114 fs), along with the scaling of the average power to 80 mW. Moreover, through characterizing the noise properties of the laser, it is found that the phase noise, intensity noise and the signal-to-noise ratio (SNR) of the fundamental repetition frequency at the transmission arm manifests a better performance than at the reflection arm. With an integration frequency of [3 kHz, 1 MHz], an optimal timing jitter and relative intensity noise of 164 fs and 0.006% are, respectively, obtained. The noise suppression mechanism is attributed to the interaction between the transmission curve of the NALM and the pulse peak power fluctuations, as well as the dispersion management of the cavity. In addition, the stable operation of the laser is further verified by monitoring the long-term stability.