Mode-locked Fiber Laser Research Articles

Reinforcement Learning for Efficient Identification of Soliton System Parameters Across Expansive Domains

Abstract Optical solitons in mode-locked fiber lasers and optical communication links have a wide range of applications. A crucial step in studying the transmission modes of optical solitons is to investigate the relationship between equation parameters and soliton evolution using deep learning techniques. However, current identification models have a limited parameter domain search range and are greatly influenced by initialization, often leading to divergence towards incorrect parameter values. This research harnesses reinforcement learning to revamp the iterative process of the parameter identification model. Through the development of a two-stage optimization strategy, the model is capable of conducting an accurate parameter search across arbitrary domains. The investigation encompasses a series of experiments on various standard and higher-order equations, illustrating that the innovative model overcomes the impact of initialization on the parameter search, and the identified parameters are guided towards their correct values. The enhanced model markedly improves experimental efficiency and holds significant promise for advancing the research of soliton propagation dynamics and addressing intricate scenarios.

Low-noise 2-GHz figure-9 fiber laser based on passive harmonic mode-locking

We have proposed and demonstrated the generation of a high-repetition-rate ultrashort pulse with long-term stability and low noise based on a harmonic mode-locked (HML) figure-9 fiber laser. Different HML orders from the 2nd to the 13th are generated by adjusting the pump power, net dispersion, and wave plate angles. A 2-GHz HML pulse is obtained with a 155-MHz fundamental repetition rate in a Yb-doped fiber laser, and the corresponding supermode suppression level is as high as 50 dB. The average power of the output pulse is nearly 200 mW, and the compressed pulse duration is 535 fs. To the best of our knowledge, 2 GHz and 196 mW represent, respectively, the highest repetition rate and output power in a figure-9 fiber laser. This work offers a potential pathway to achieve high-repetition-rate ultrashort pulses in the GHz range with high power and low noise levels.

Mamyshev oscillation self-starting mode-locked fiber laser based on a self-feedback amplifying sub-cavity

The Mamyshev oscillator (MO) boasts unparalleled modulation depth advantages in establishing mode-locking. However, this also significantly inhibits the self-starting of mode-locking. This Letter addresses the issue by constructing a self-feedback mechanism for regenerative oscillation. By amplifying noise cycles during the initial pumping phase to introduce periodic fluctuations in light intensity, we successfully achieve self-starting mode-locking at 1550 nm in an MO with a single gain arm structure at the pump power threshold of 76 mW. This self-starting mode-locking mechanism based on self-feedback sub-cavity amplification demonstrates excellent stability and repeatability in a single-arm MO structure. It provides what we believe to be a new approach for developing simple, reliable, and high repetition rate mode-locked lasers.

InAs/GaSb superlattice SESAM mode-locked fluoride fiber laser at 2.8 µm

We demonstrate a mode-locked fluoride fiber laser operating at 2.8 µm using an InAs/GaSb superlattice (SL) semiconductor saturable absorber mirror (SESAM). Z-scan measurements show that the SL saturable absorber layer possesses off-bandgap nonlinearity near 2.8 µm, with a saturation fluence of 15.9 µJ/cm2, a single-pass modulation depth of 2.4%, and a damage threshold of 10.4 mJ/cm2. Using this high-damage-threshold SESAM, we achieved a maximum average output power of 1.16 W from the 2.8 µm mode-locked Er:ZBLAN fiber laser, with a pulse duration of 28.1 ps. Continuous mode-locking operation at an average power of 224 mW was sustained for 36 h without interruption, demonstrating the reliability of the InAs/GaSb SL SESAM for the development of mid-infrared mode-locked fluoride fiber lasers.

Diverse and controllable soliton molecules in a fiber laser based on PbBi4Te7 saturable absorber

With the advancement of optical communication, optical encoding, and optical storage technologies, the demand for tunable mode-locked fiber lasers (MLFL) with soliton molecules is continuously increasing. The novel ternary two-dimensional topological insulator PbBi4Te7 provides an effective pathway for realizing tunable soliton molecules in MLFL. This study employs a combined liquid phase exfoliation (LPE) and optical deposition methods (ODMs) to prepare PbBi4Te7 saturable absorbers (SAs). In the same MLFL, conventional soliton (CS), controllable soliton molecules with adjustable soliton numbers and intervals, as well as multi-soliton complexes are obtained. Among them, a fundamental frequency CS pulse at 22.778 MHz with a signal-to-noise ratio (SNR) of up to 71 dB is achieved. By adjusting the pump power, 2nd-, 3rd-, 4th-, 9th-, and 11th-order soliton molecules were obtained. By tuning the polarization controller (PC), switching of the soliton interval for 2nd-, 3rd-, and 4th-order soliton molecules was achieved. Additionally, we obtained three unequally spaced multi-soliton complexes: 2 + 1 soliton molecule, 2 + 2 soliton molecule complex and 2 + 2 + 1 soliton molecule complex. The results indicate that PbBi4Te7-SA exhibits outstanding nonlinear optical performance.

Nonlinear polarization rotation based 635 nm praseodymium doped mode-locked fiber laser

We demonstrated a mode-locked fiber laser oscillator using nonlinear polarization rotation as a saturable absorption system. The fiber laser generates mode-locked pulses by adjusting four waveplates. A single-clad Pr3+-doped single mode fluoride fiber with a 425 mW threshold pump power serves as the foundation for the ring cavity, which operates in the dissipative soliton resonance regime. The radio frequency signal-to-noise ratio of the pulses at 634.9 nm is 60 dB, maximum output power of 5.5 mW, and repetition rate of 34.5 MHz. These findings provide a foundation for the advancement of photonic applications in the visible spectrum.

Deep learning method for predicting the complex nonlinear dynamics of passively mode-locked fiber laser

The dynamic evolution processes are highly complicated nonlinear dynamic processes in passively mode-locked fiber laser systems. Here, an artificial intelligence (AI) model is employed to predict the complex dynamic processes, which uses the long short-term memory network method, serving as an alternative to the numerical calculation of the nonlinear Schrödinger equation (NLSE). We specifically emphasize the complex evolution processes under different gain saturation energies, comparing the results predicted by the AI model with those simulated by the NLSE. The predicted results of the AI model are in good agreement with the simulated results of NLSE. The root mean square errors of test samples in this study are all below 0.15. Furthermore, with GPU acceleration, the AI model achieves a mean simulation time of 0.452 s for 6000 roundtrips, approximately 2391 times faster than the numerical solution of NLSE executed on a CPU.

L-band wavelength-switchable bound states in a hybrid mode-locked fiber laser

L-band wavelength-switchable bound states in a hybrid mode-locked fiber laser

1 GHz fundamental repetition rate thulium-doped all-polarization maintaining modelocked fiber laser

Abstract In this work, we present a passively modelocked all-fiber laser that fully retains polarization with a fundamental repetition rate of 1 GHz. The whole cavity consists of a 106-mm-long highly-Tm-doped polarization-maintaining fiber with a dichroic mirror on one end and a semiconductor saturable absorber mirror on the other. We experimentally characterized the output of this laser, which emits a train of transform-limited light pulses with a temporal width of 520 fs at the central optical wavelength of 1.96 μm. The high stability of this laser was also experimentally verified. Together with this, a detailed theoretical model was developed, confirming the experimental results.

Intelligent multi-parameter control of rectangular pulse in a passively mode-locked fiber laser

Intelligent multi-parameter control of rectangular pulse in a passively mode-locked fiber laser

Study of complex instability in a Thulium-doped figure-eight fiber laser including a polarization-imbalanced NOLM with no polarization control.

This study proposes a Thulium-doped figure-eight (F8) fiber laser design to be used as a platform to explore complex dynamics in passively mode-locked fiber laser systems. The proposed scheme incorporates a polarization-imbalanced nonlinear optical loop mirror (PI-NOLM) without a polarizer in the ring section. The absence of a polarizer prevents controlling the polarization state at the PI-NOLM input, which in turn allows the PI-NOLM switching power to vary dynamically during the laser operation. This leads to an intermittent noise-like pulse (NLP) operation, which is affected by complex instability in the form of non-periodic Q-switched-like behavior. Using real-time time-domain mapping techniques, we get a deep insight into the laser intricate dynamics, which involves not only NLPs, but also solitons and quasi-continuous-wave components with their subtle interactions. This study highlights the importance of the PI-NOLM in F8 laser schemes for the study and understanding of complex dynamics in Thulium-doped fiber lasers, which have been less extensively studied compared to other rare-earth-doped lasers. Our findings will contribute to the optimization and design of advanced laser systems for various scientific and industrial applications.

Generation of stable dual-wavelength mode-locked pulses using boron nitride saturable absorber in all-polarization-maintaining Er-doped fiber laser

This work demonstrates the generation of stable dual-wavelength mode-locked pulses using boron nitride (BN) as a novel saturable absorber within a polarization-maintaining (PM) Er-doped fiber laser cavity. BN was chosen due to its exceptional properties, including high thermal stability, wide bandgap, and excellent mechanical strength. A drop-casting technique was employed to fabricate the BN-based saturable absorber. The laser generated high-quality dual-wavelength pulses centered at 1566.3 nm and 1575.6 nm with a repetition frequency of 25.3 MHz and a pulse width of 900 ps. The generated laser exhibited excellent stability and a high degree of polarization (DOP) of 99.8 %. These findings contribute to the advancement of dual-wavelength mode-locked fiber laser technology and open new avenues for applications such as dual-frequency comb spectroscopy.

Spatiotemporal dissipation dynamics: a route to high-beam-quality and high-peak-power spatiotemporal mode-locked fiber lasers

Spatiotemporal mode-locking (STML) opens a new avenue for implementing high-energy, high-peak-power mode-locked fiber oscillators. However, the compromised beam quality poses a critical limitation to their broader applications. This study presents a method for enhancing the beam quality of STML fiber lasers by employing spatiotemporal dissipation involving the quenching and reabsorption effects of multimode erbium-doped fibers. The proposed technique introduces spatiotemporal saturable absorption, achieving high beam quality without the stringent conditions required for Kerr beam self-cleaning (BSC). Integrating spatiotemporal dissipation with Kerr BSC, we demonstrate an all-anomalous-dispersion Er-doped STML fiber laser, which produces solitons with 6.7 nJ pulse energy (the intracavity solitons with 25.8 nJ pulse energy and >52.8kW peak power), sub-500 fs pulse duration, and beam quality with M x 2/M y 2=1.23/1.20. To our knowledge, it is a record peak power for 1.5 µm band soliton lasers. Additionally, the approach enables the generation of noise-like pulses with M x 2/M y 2=1.04/1.13. This work not only advances our understanding of spatiotemporal dissipation dynamics in STML fiber lasers, but also paves the way toward high-performance STML fiber lasers, rendering them very attractive for applications.

Passively Mode-Locked Erbium-Doped Fiber Laser and Application in Laser Thrombolysis

Fiber lasers have been widely used in surgery with the development of fiber photonics. Since the human body is prone to myocardial infarction caused by blood clots, laser thrombolysis was proposed as a safe and efficient treatment. Mode-locked fiber lasers have high peak power and narrow pulse width. In order to observe the effect of laser thrombolysis with mode-locked fiber lasers, a 1.5 µm mode-locked fiber laser based on carbon nanotubes was built, showing a pulse width of 1.46 ps, a 3 dB bandwidth of 1.65 nm, and a repetition rate of 29.5 MHz. The output pulses were amplified by an erbium-doped fiber amplifier to the hundred-milliwatt level and were applied to the surface of a self-made thrombus. The influences of lasing power and time on the damage diameter of the thrombus surface were evaluated. A low threshold damage power of 45 mW was observed, which resulted from the high peak power of the mode-locked pulses. These results demonstrate that high ablation efficiency can be achieved by using mode-locked pulses with a narrow pulse width and high peak power.

Hybrid inverse design of mode-locked fiber lasers

Hybrid inverse design of mode-locked fiber lasers

Mode-locked soliton pulse generation using copper phthalocyanine absorber in long erbium-doped fibre laser cavity

We present the development of a mode-locked erbium-doped fibre laser (EDFL) utilizing Copper Phthalocyanine (CuPc) as a saturable absorber (SA). CuPc exhibits unique optical properties, including its high nonlinear optical response and rapid recovery time. To seamlessly integrate CuPc into the laser cavity, we employed a simple embedding technique within a polymer film. The SA demonstrates a modulation depth of 3.1% and a saturation intensity of 17 MW/cm2. Operating within a pump power range of 90.6 to 122.9 mW, the laser achieves mode-locked operation, producing a soliton pulse train with a fundamental frequency of 1.82 MHz and a pulse width of 6.4 ps at a wavelength of 1561.5 nm. It attains a maximum output power of 13.97 mW and a pulse energy of 7.67 nJ. These results underscore CuPc's potential as a promising material for generating mode-locked pulses, suggesting new avenues in ultrafast laser development for diverse applications.

Wavelength-Switchable Ytterbium-Doped Mode-Locked Fiber Laser Based on a Vernier Effect Filter

A wavelength-switchable ytterbium-doped mode-locked fiber laser is reported in this article. Two Mach–Zehnder interferometers (MZIs, denoted as MZI1, MZI2) with close free spectral ranges (FSRs) are connected in series to form a Vernier effect sensor. By utilizing the filtering effect of the Vernier effect sensor, the wavelength-switchable output of an ytterbium-doped mode-locked fiber laser is realized. When the 3 dB bandwidth of the Vernier effect filter is set to be 5.31 nm around 1073.42 nm, stable dissipative solitons are obtained. Stretching MZI1 horizontally, the central wavelengths of the pulses can be switched among 1073.42 nm, 1055.38 nm, and 1036.22 nm, with a total tunable central wavelength range of 37.2 nm. When the 3 dB bandwidth of the Vernier effect filter is set to be 4.07 nm, stable amplifier similaritons are obtained. Stretching MZI1 horizontally, the central wavelengths of the pulses are switchable among 1072.71 nm, 1060.15 nm, 1048.92 nm, and 1037.26 nm, with a total tunable central wavelength range of 35.15 nm. Compared with traditional fiber interference filters, the Vernier effect filter has a higher sensitivity, making wavelength switching more convenient and providing a wider tuning range for the ytterbium-doped mode-locked fiber laser.

Passively mode-locking fiber laser based on Cr2Si2Te6 saturable absorber

This paper reports on the generation of third-order harmonic mode-locking, double-pulse phenomena, and conventional solitons in an erbium-doped fiber laser using Cr2Si2Te6 as a saturable absorber (SA). The double-balance probing method was employed to examine the nonlinear characteristics of Cr2Si2Te6-SA. Its modulation depth is 2.35 %, and its saturation intensity is 29.74 MW/cm2. We discovered conventional soliton functioning with a center wavelength of 1561.8 nm at a pump power of 34.76 mW. It has a repetition frequency of 6.76 MHz and a signal-to-noise ratio of 45 dB. As the pump power increased, the traditional soliton was able to maintain its existence in the range of 34.76 mW to 80.96 mW. The maximum output power reaches 1.1 mW when the pump power is 80.96 mW, and the maximum single-pulse energy of the conventional soliton is 0.16 nJ. Furthermore, we observed third-order harmonic mode-locking and double-pulse phenomena at pump outputs of 53.65 mW and 71.16 mW. The experimental findings demonstrate the excellent nonlinear effect of the SA based on Cr2Si2Te6. In ultrashort-pulse fiber lasers, Cr2Si2Te6 nanosheets can be employed as an efficient saturable absorption material.

All–polarization maintained erbium-doped nonlinear amplifying loop mirror mode-locked fiber laser for optical frequency comb application

All–polarization maintained erbium-doped nonlinear amplifying loop mirror mode-locked fiber laser for optical frequency comb application

Intelligent controllable ultrafast fiber laser via deep learning and adaptive optimization algorithm

Ultrafast fiber lasers based on nonlinear polarization rotation can generate femtosecond pulses with different pulse durations and high peak powers, which are powerful tools for engineering applications and scientific research. However, achieving a precise and repeatable polarization state for generating the ultrashort pulses with the shortest pulse duration remains a significant challenge. In this paper, we extend the use of recurrent neural networks and adaptive optimization algorithms, specifically designed to optimize repetitive processes in optical systems, to facilitate intelligent search and control aimed at achieving the minimum pulse duration within a mode-locked fiber laser cavity. Our multi-algorithm-based intelligent system can fully simulate and optimize the processes involved in hands-on experiments. Our intelligent system identified a mode-locked fiber laser with the shortest pulse duration of 465 fs, which was experimentally verified. The proposed intelligent algorithm not only identifies the shortest pulse but also holds significant potential for selecting related laser characteristic parameters. We believe this work opens up a novel avenue for exploration and optimization in mode-locked lasers and the intelligent laser can find practical applications in engineering and scientific research.