We demonstrate an all-fiber femtosecond source operating in the 1600 nm spectral window. The system architecture is based on a classic configuration comprising a master oscillator, an erbium-doped fiber amplifier (EDFA), and a dispersion-decreasing fiber (DDF) compressor. A key feature is the master oscillator operating in a stable harmonic mode-locking regime with repetition rates scalable from ∼14 MHz to 6.5 GHz, without degradation in output pulse quality at higher rates. Adiabatic soliton compression implemented within the DDF enables efficient compression of seed pulses down to 70 fs with high temporal purity. Numerical simulations closely match experimental data, confirming efficient energy transfer from the seed pulse into the Raman soliton. Combining a GHz repetition rate, clean sub-100 fs profiles, and operation in the 1600 nm window makes the proposed source highly promising for various practical applications.

We report on the control of multi-pulse soliton dynamics and the stabilization of high-order harmonic mode-locking (HML) in an all-polarization-maintaining (PM) fiber laser. Comparative numerical simulations of long-range soliton interactions are presented for two cavity architectures, contrasting a filterless system with a spectrally tailored setup. The analysis unveils that introducing an asymmetric spectral constraint via a flat-top filter forces co-drifting solitons onto a steeper gain slope, magnifying their frequency divergence and, consequently, their inverse group velocity mismatch. Such enhanced gain-mediated repulsion acts as a strong restoring force that suppresses multi-pulse jitter and locks the periodic soliton train. Appropriate adjustment of the filter detuning and bandwidth allows stable HML operation to be experimentally achieved up to a 6.16 GHz repetition rate. Compared to the reference filterless regime, the stabilized configuration utilizing the asymmetric filter exhibits a 13-27 dB improvement in supermode noise suppression, forcing the RMS (root-mean-square) timing jitter deep into the sub-picosecond domain. The convergence between experimental observations and numerical models confirms that filter-driven frequency shifting offers a scalable approach for suppressing instabilities in complex multi-soliton systems converging to the HML state.

Long-range soliton interactions governed by the gain depletion and recovery (GDR) mechanism in polarization-maintaining fiber (PMF) lasers are investigated both numerically and experimentally. We show that the direction and magnitude of the interaction forces strongly depend on the stage of cooperative evolution of solitons and dispersive waves within the gain fiber. The GDR mechanism enables control over soliton interactions by varying the position of the saturable absorber (SA) inside the cavity. In particular, placing the SA directly after the gain fiber promotes attractive forces, transforming the laser into a generator of bound solitons or soliton bunches. In contrast, selecting an optimal separation between the SA and the gain fiber enhances repulsive inter-soliton interactions and enables harmonic mode-locking (HML) with multi-GHz pulse repetition rates and improved stability. The results of numerical simulations are in good agreement with experimental observations.

In this work, we propose that the photobiological mechanisms governing the distant fate of proliferating cells involve a bystander effect following continuous-wave 1265 nm laser irradiation at a dose of $562.5 \mathrm{~J} / \mathrm{cm}^{2}$. This effect is manifested by a decrease in the viability of non-irradiated (bystander) cells within a melanoma cell culture and is absent in non-cancerous cells.

The interaction of soliton pulses through gain depletion and recovery (GDR) is one of the key processes determining the long-range dynamics of mode-locked fiber lasers. Conventionally, this mechanism has been associated solely with repulsive pulse interactions, which promote the evenly spaced pulse arrangements typical of harmonic modelocking (HML). In this work, we develop a theoretical framework and conduct numerical simulations that reveal an alternative behavior. We show that the GDR-induced interaction is significantly modified by dispersive-wave generation, the strength and phase of which can be controlled through the laser’s polarization state. Under certain conditions, this coupling leads to mutual long-range attraction between solitons. The results provide a new perspective on the mechanisms responsible for the formation and transformation of multi-soliton structures in passively mode-locked fiber lasers.

This study explores harmonic mode-locking (HML) in an Er/Yb-doped fiber laser with a sub-MHz fundamental frequency of 0.678 MHz. By tuning a polarization controller, we identified regimes where multiple soliton bunches achieved loworder HML (3rd to 8th harmonics) and a remarkable high-order HML regime at the 472nd harmonic, corresponding to a 320 MHz repetition rate. This regime demonstrated outstanding stability, with a supermode suppression level of 49 dB and timing jitter on the order of a few picoseconds. The exceptional stability is attributed to an exact optoacoustic resonance between the laser repetition rate and intrinsic fiber acoustic modes (R-06 and TR2,15). These findings represent a significant advancement in the development of fiber lasers with high repetition rates and robust pulse trains, offering practical solutions for applications in spectroscopy, telecommunications, and microwave photonics.

We present a combined numerical and experimental investigation into the role of saturable absorber positioning in polarization-maintaining (PM) fiber soliton laser based on Semiconductor Saturable Absorber Mirror (SESAM). Simulations reveal a narrow optimal cavity region where precise SESAM placement enables stable single-pulse operation at significantly higher gain levels. This configuration suppresses background continuum buildup and delays the transition to multi-pulse operation. Experiments using an Er-doped PM fiber laser confirm these predictions, demonstrating increased pulse energy, broader spectra, and improved operational robustness when the SESAM is optimally positioned. These findings highlight a physically grounded and practically effective strategy for boosting the performance of soliton fiber lasers and are particularly relevant for advanced short-wavelength infrared (SWIR) systems based on Tm- or Ho-doped fibers.

We present, to the best of our knowledge, the first demonstration of a sub-GHz harmonically mode-locked (HML) Er-doped fiber laser based on a nonlinear amplified loop mirror (NALM). This fully spliced, polarization-maintaining (PM) fiber configuration operates in a self-starting regime, delivering high-frequency pulse trains with significantly enhanced stability against environmental perturbations. The laser achieves a maximum pulse repetition rate (PRR) of ~630 MHz, corresponding to the 242nd cavity harmonic. Furthermore, we apply a supermode noise mitigation technique using continuous-wave injection from an external narrow-band source successfully stabilizing the HML operation and reducing timing jitter by more than a factor of two across the entire range of observed repetition rates. This novel design provides a robust, adjustment-free solution for high-frequency operation with exceptional stability, meeting the demands of precision and reliability required for advanced applications.

Ultra-stable, low-noise lasers are indispensable for advanced fiber sensor applications requiring high sensitivity and precision. This work presents a novel polarization-maintaining (PM) fiber laser design utilizing a fully spliced PM fiber ring cavity for self-injection locking of a distributed feedback (DFB) laser. This configuration eliminates the need for adjustments or maintenance, offering robust, environmentally resilient operation with a Lorentzian linewidth of approximately 75 Hz. Phase and intensity noise levels are suppressed to below -120 dBc/Hz (>10 kHz) and -140 dBc/Hz (>30 kHz), respectively. With an output power of similar to 8 mW and frequency drift below 0.5 MHz/min, this laser design is ideal for demanding fiber sensor applications, including distributed acoustic sensing and high-resolution interferometry, while being compact and cost-effective.

This review summarizes recent progress and emerging trends in multiparameter optical fiber sensing, emphasizing techniques that enable the simultaneous measurement of temperature, strain, acoustic waves, pressure, and other environmental quantities within a single sensing network. Such capabilities are increasingly important for structural health monitoring, environmental surveillance, industrial diagnostics, and geophysical observation, where multiple stimuli act on the fiber simultaneously. The paper outlines the physical principles and architectures underlying these systems and focuses on strategies for compensating and decoupling cross-sensitivity among measured parameters. Special attention is devoted to advanced distributed sensing schemes based on coherent optical frequency-domain reflectometry (C-OFDR), coherent phase-sensitive time-domain reflectometry (Φ-OTDR), and Brillouin optical time-domain reflectometry (BOTDR). Their theoretical foundations, their signal-processing algorithms, and the design modifications that improve parameter discrimination and accuracy are analyzed and compared. The review also highlights the roles of polarization and mode diversity and the growing application of machine-learning techniques in the interpretation and calibration of data. Finally, current challenges and promising directions for the next generation of fiber-optic multiparameter sensors are outlined, with a view toward high-resolution, low-cost, and field-deployable solutions for real-world monitoring applications.

We experimentally identify a steady-state emission regime in a soliton fiber laser that produces a flattened optical spectrum with broadened sidebands. In the multiplepulse operation domain, this spectral shape indicates the suppression of harmonic mode-locking (HML) and the appearance of closely bound soliton complexes or compact irregular bunches. Physically, the observed regime reflects conditions in which long-range attractive interactions outweigh repulsive forces across the entire cavity. The experimental findings are supported by numerical modeling, revealing that this attraction results from the combined effect of dispersivewave radiation and gain depletion and recovery dynamics in the active medium.

We have been investigated the features of broadband spectral comb formation in ring fiber harmonic mode locking configuration. The key element of proposed fiber resonator is an active Bragg grating, which combines the functions of optical filter and amplifier. It was shown that when the Bragg grating is sensitive to external mechanical (acoustical) effects and changing temperature conditions, its spectral characteristics change. This leads to a change in the repetition rate of the generated pulse sequences.

This study demonstrates the enhancement of pulse repetition rates (PRRs) in soliton fiber lasers up to 12 GHz using double harmonic mode-locking (DHML)1. By leveraging optoacoustic resonance (OAR), the laser achieves stabilization of harmonic mode-locking while enabling higher PRRs aligned with multiples of the OAR frequency. The interaction between circulating optical pulses and resonant acoustic vibrations within the cavity results in a robust pulse train with exceptional stability. The laser achieves supermode suppression ratios exceeding 40 dB and timing jitter at the picosecond level, making it a reliable source for high-frequency applications in microwave photonics, optical communications, and precision metrology.

The paper describes an erbium fiber laser mode-locked with a semiconductor saturable-absorber mirror (SESAM) and made up entirely of polarization-maintaining fiber components. With the focal spot correctly adjusted on the semiconductor mirror, the laser operates in the harmonic mode-locking (HML) regime available over the entire pump power range up to 355 mW with the supermode suppression level of less than 25 dB. In the HML regime, the laser can generate linear polarized pulses and provide a pulse repetition rate up to 1145 MHz. We have shown experimentally that by injecting radiation from an external continuous laser directly into the fiber cavity we can improve the stability of laser operation in the HML regime while the level of supermode suppression is increased by 20 or 30 dB. In addition, it is shown that external injection can extend the pump power range available for the laser in the HML regime increasing the maximum pulse repetition rate up to 2195 MHz. It is important to note that optical injection does not affect the high purity of the laser’s polarization state. The presented results of numerical modeling can qualitatively explain the effects observed experimentally.