In this review paper, we describe the current state of the art to stabilize the output radiation of ultrashort-pulse (USP) fiber lasers and analyze passive methods to reduce the magnitude of fluctuations in the amplitude–frequency noise of output radiation. Regarding main noise characterization in mode-locked fiber lasers, we further consider the influence on laser operation of primary generation regimes starting up in cavities, such as solitons, stretched pulses, similaritons, and dissipative solitons. Then, we proceed to analyze the external and internal factors that affect the stability of the output radiation characteristics depending on the mode-locking mechanism and the resonator scheme.

We report on the experimental results of high-order soliton molecule (SM) generation in an erbium-doped oscillator. The generation of 14 solitons with an average power of 48 mW, a pulse duration of 508 fs, a separation of 2.59 ps between pulses, and a repetition rate of 19 MHz at 1560 nm central wavelength was demonstrated. The stability of this generation was also evidenced by its low relative intensity noise (0.08% in the frequency range [10 kHz–1 MHz]), and a low Allan deviation of frequency repetition rate of 1.98⋅10⁻⁹ at an interval of 1 s (during 10 h of free-running measurements). Moreover, the accurate manipulation of SM order by changing the pump power was investigated; we showed the ability to generate with four, six, seven, nine, 10, 11, 13, and 14 pulses with high stable states between solitons. The change in the number of pulses occurred repeatably by increasing and decreasing the pump power, offering a stable source of a controllable number of pulses for potential applications in quantum computing.

We demonstrate generation of both 17 fs ultrashort pulses and 862 nm spanning supercontinuum (SC) directly from an erbium-doped fiber (EDF) oscillator, utilizing extra-cavity management of nonlinearity and second-order dispersion using a combination of commercially available SMF-28 and specially developed homemade fiber with anomalous dispersion and enhanced nonlinearity. The simple but accurately designed fiber ring laser, passively mode-locked by nonlinear polarization evolution, offers a self-starting pulse generation with a dechirped duration of 51.8 fs as well as a 19.4 mW average power, 0.81 nJ pulse energy, and 13.9 kW peak power at a 23.76 MHz repetition rate and 1560 nm central wavelength. The increased extra-cavity nonlinearity enabled supercontinuum generation with visible light components corresponding to the second-harmonic generation (SHG). Implementation of a thermally stabilized case and environmental isolation resulted in highly stable self-started mode-locking operation, with a relative intensity noise of −140 dBc/Hz (at 1 MHz) and only 0.2% instability of average power during a 6 h free-running measurement.