Mode-locked Fiber Ring Laser Research Articles

Mode-locking dynamics of triple attractors in a wavelength-multiplexing fiber laser

We demonstrate the coexistence of triple attractors in a mode-locked ring fiber laser with equal dual-gain-channel. Even under identical cavity conditions, quantum noise can evolve into three distinct stable states: tightly bound soliton, asynchronous dual-wavelength pulses, and loosely bound soliton. The mode-locking dynamics reveal that the final state depends on whether the dispersive wave or the residual noise pulse dominates the gain competition, which is significantly influenced by the modulation depth of the saturable absorber. By reducing the modulation depth from 70% to 5%, the probability of forming asynchronous dual-wavelength pulses increases from 33% to 90%. Our findings offer what we believe to be new insights into the dynamics of dual-gain-channel fiber laser and underscore the critical role of the saturable absorber in wavelength-multiplexing.

Generation of dark pulses in mode-locked erbium-doped fiber ring laser using Ti2SnC absorber

Abstract We report the experimental observation of domain-wall type dark solitons in an all-fiber ring cavity erbium-doped fiber laser (EDFL) mode-locked with a Titanium Tin Carbide (Ti2SnC) saturable absorber (SA). The SA, featuring a modulation depth of 8.2%, was created by incorporating Ti2SnC particles into a polyvinyl film. Dark pulse formation is attributed to cross-phase coupling resulting from cavity birefringence. The mode-locked laser operates at 1559 nm with pump power ranging from 30.9 mW to 90.0 mW, achieving a maximum pulse energy of 1.73 nJ, a repetition rate of 1.78 MHz, and a pulse width of 261.2 ns.

Hybrid Mode-Locked Fiber Ring Laser Using Graphene Saturable Absorbers to Generate 20 and 50-GHz Pulse Trains

Optical pulses at high repetition rates are generated using rational harmonic mode locking and saturable absorber made of graphene nanoparticles in a fiber laser. The pulse generation from the fiber laser is modeled by solving the Generalized Nonlinear Schrodinger Equation. The computation involved varying the various saturable absorption parameters, such as linear and nonlinear absorption coefficients. Experimentally stable pulse trains at 20 GHz and 50 GHz are generated with a pulse width of ∼ 2.7 ps. This result agrees with the simulation.

Relocking and Locking Range Extension of Partially Locked AMLL Cavity Modes with Two Detuned RF Sinusoids

Actively mode-locked fiber ring lasers (AMLLs) with loss modulators are used to generate approximately 100ps pulses with 100MHz repetition. RF detuning around the fundamental frequency, f0, causes a loss in phase lock (unlocking) of cavity modes and partial mode locking. Multiple RF inputs are shown, theoretically, to relock and extend the locking range of cavity modes in a detuned partially mode-locked AMLL. A custom-built Yb3+-doped AMLL with f0=26MHz, and operating wavelength of 1064nm, was used to experimentally verify the theoretical predictions. Two RF sinusoidal signals with constant phase and equal amplitude resulted in an extension of the range by Xn=6.4kHz in addition to the range Rn=14.34kHz with single input for the mode n=10. An increase in locking range was also observed for higher modes. Pulsewidth reduction to approximately 205ps from about 2ns was also observed in the AMLL.

Passively mode-locked dual-wavelength Ho-doped fiber laser with noise-like pulse regime

We experimentally and theoretically investigate the noise-like pulse (NLP) generation in a nonlinear polarization rotation-based mode-locked Ho-doped fiber ring laser, which can optionally operate in the dual-wavelength regime. By carefully changing the pump power and polarization state, the dual-wavelength NLP regime at 2041.9 and 2083.3 nm is finally achieved, which corresponds to a pulse energy of 11.84 nJ and a pulse duration of 849 fs. It is believed to be the first report on the dual-wavelength NLP operation from the previously reported Ho-doped fiber lasers.

Multi-soliton pulse generation in a fiber laser by using a long-period fiber grating

In this paper, multi-soliton pulse generation is realized by incorporating a long period fiber grating into an Er-doped mode-locked fiber ring laser cavity. By using nonlinear polarization rotation mode-locking technique and a long period fiber grating that plays the role of spectral filter in the laser cavity, discretely tunable multi-soliton pulses can be produced at low lasing threshold of 80 mW. The number of solitons can be controlled by simply adjusting the polarization controller in the laser cavity. It is found that Kelly sideband of the traditional mode-locked solitons become weak as a result of introducing the long period fiber grating in the laser cavity, due to the fact that the nonlinearity and dispersion in the cavity are balanced, and hence stabilizing the soliton pulses. The use of long-period fiber grating has the advantages of effectively reducing the pumping threshold for the multi-soliton pulse generation, and supporting stable laser operation.

Mode-Locked Fiber Ring Laser Using Graphene Nanoparticles as Saturable Absorbers

Mode locked fiber ring laser using graphene nanoparticles as saturable absorbers to compress the pulse width has been studied. An experimental method to demonstrate the generation of pulse train with 50 GHz repetition rate with an ultrashort pulse width has been demonstrated. This method uses a combination of rational harmonic mode-locking (RHML) and a saturable absorber in the fiber ring laser. The pulse width using saturable absorbers is shorter by about a factor of 2 compared to that without a saturable absorber. Pulse generation using fiber ring laser with a saturable absorber has been analyzed. The experimental results are in agreement with the results from the simulation.

Multi-branch erbium fiber-based femtosecond optical frequency comb for measurement of cavity ring-down spectroscopy

<sec>In this paper, we demonstrate an optical frequency comb (OFC) based on an erbium-doped-fiber femtosecond laser, for the measurement of cavity ring-down spectroscopy (CRDS) with wavelengths of 1064, 1083, 1240, 1380, 1500, 1600, 1750 and 2100 nm. We adopt a multi-branch structure to produce high power at the specific wavelengths to meet the requirement for application in the spectral measurement. The OFC is developed by using a mode-locked fiber ring laser based on the nonlinear amplifying loop mirror mechanism. The laser is self-starting by introducing a nonreciprocal phase bias in the cavity and insensitive to the environmental perturbation. Using the chirped pulse amplification and highly nonlinear fibers, the broad spectra at the specific wavelengths are obtained. By optimizing the parameters of the pulses, the power of per mode at each target wavelength is greater than 300 nW.</sec><sec>The<i> </i><i>f</i><sub>rep</sub> is obtained by detecting the output of the femtosecond laser directly, while the<i> </i><i>f</i><sub>ceo</sub> is detected by <i>f</i>-2<i>f</i> interference. The signal-to-noise ratio of the<i> </i><i>f</i><sub>ceo</sub> is about 35 dB with a 300-kHz resolution bandwidth. By controlling the intra-cavity electro-optic modulator and piezoactuator , the <i>f</i><sub>rep</sub> is stabilized with high bandwidth and large range (about megahertz bandwidth and 3 kHz range). The <i>f</i><sub>ceo</sub> is stabilized by using feedback to the pump current of the femtosecond laser dynamically. The in-loop frequency instability degree of the <i>f</i><sub>ceo</sub>, evaluated by the Allan deviation, is approximately 4.95 × 10<sup>–18</sup>/<i>τ</i><sup>1/2</sup> at 1 s and integrates down to 10<sup>–20</sup> level after 2000 s, while that of the <i>f</i><sub>rep</sub> is well below 5.85 × 10<sup>–13</sup>/<i>τ</i>. The all polarization-maintaining erbium fiber-based femtosecond optical frequency comb with multi-application branches we demonstrate in this paper is efficient and reliable for many other applications including optical frequency metrology and optical atomic clocks.</sec>

Ultralong ring laser supercontinuum sources using standard telecommunication fibre

The application of a recently demonstrated mode-locked ultralong pulsed fibre ring laser architecture (Gallazzi et al., 2021) to the inexpensive and efficient generation of supercontinuum from a pulsed output at 1.56 μm in standard single-mode telecommunication fibre is experimentally demonstrated. The impact of broadening fibre, dynamic switching between different harmonic modes and the influence of laser polarization on the properties of the generated supercontinuum are studied for three different kinds of telecommunication fibre. Flexible spectral broadening beyond 200 nm is obtained with good temporal correlation and pulse compression from 240 fs down to 50 fs.

Mitigation of the supermode noise in a harmonically mode-locked ring fiber laser using optical injection.

We report on a new, to the best of our knowledge, technique enabling mitigation of the supermode noise (and timing jitter) in a soliton harmonically mode-locked (HML) fiber laser built on the nonlinear polarization evolution (NPE). An optical injection of an external continuous wave (CW) into the HML laser cavity results in an increase of the supermode noise suppression level (SSL) by a two-three order of magnitude for harmonics between 25th and 135th. The operation mechanism involves phase-locking between the injected light and soliton pulses and exhibits strong resonant dependence on the CW laser wavelength. Our findings offer important insights into the HML laser dynamics associated with an interaction between solitons and CW background in the laser cavity.

Pulse repetition rate tuning of a harmonically mode-locked ring fiber laser using resonant optical injection.

We report on a new, to the best of our knowledge, technique enabling fine-tuning of the pulse repetition rate (PRR) of a soliton harmonically mode-locked (HML) fiber laser built on the nonlinear polarization evolution (NPE). Optical injection of an external continuous wave (CW) into the HML laser cavity is used for this purpose enabling precise PRR tuning with the elementary step equal to the fundamental PRR one-by-one. The effect exhibits strong resonance dependence on the CW laser wavelength and available in both positive and negative directions. Our findings offer important insights into the HML laser dynamics associated with the birth and annihilation of solitons in the cavity.

All-fiber saturable absorber based on nonlinear multimode interference with enhanced modulation depth.

We experimentally demonstrate a passively mode-locked fiber ring laser using a small-core fiber-graded index multimode fiber-single-mode fiber (SCF-GIMMF-SMF) structure as an effective saturable absorber based on the nonlinear multimode interference (NL-MMI) effect. A small-core fiber is used as an input single-mode fiber to improve the coupling of power into higher-order modes in a multimode fiber and to enhance the modulation depth of the structure. Stable fundamental mode-locked operation is obtained at a pump threshold of 166 mW and the output soliton pulses have a 647 fs duration at 1557.96 nm with a 5.2 nm spectral width at a repetition rate of 19.37 MHz. This NL-MMI SA can be applied to high-power mode-locked fiber lasers owing to its inherent high damage threshold, compact size, wavelength independent operation, and fabrication simplicity.

Concurrent Passive Mode-Locked and Self-Q-Switched Operation in Laser Systems.

Concurrent passive mode-locked and self-Q-switched operation of laser devices is modeled using the complex cubic-quintic Ginzburg-Landau equation. Experimental observations use a passively mode-locked fiber ring laser with a waveguide array as a fast saturable absorber. The shape of each individual self-Q-switched pulse and the periodic trains of pairs of such pulses are in a good qualitative agreement with the numerical results.

Generation and dynamics of stepped h-shaped noise-like pulses in a mode-locked thulium-doped fiber ring laser

New h-shaped pulses with stepped flattops are observed in a mode-locked thulium-doped fiber laser (251 m long cavity) by the nonlinear polarization rotation technique. The step at the end of an h-shaped pulse has a lower intensity and an almost fixed duration (~5 ns) when it is tuned in the range of several tens of ns. By incorporating simple gain dynamics and a model of saturable absorption, the h-shaped pulses are simulated from a retrieval of noise-like pulse solutions. The change regularity of pulses in experiment is basically verified and explained by the numerical results. An analysis reveals that gain depletion and mode-locking threshold are key factors to form the ‘h’ shape. It is also proposed that the step tail is a kind of noise-like square wave pulse generated at the trailing edge.

Soliton mode-locked fiber laser for distance measurements.

Absolute distance measurement is crucial for many applications including metrology, large-scale manufacturing, range finding, and surveying. In this paper, a novel, to the best of our knowledge, technique is introduced for precise distance measurement by including the distance under measurement in a soliton mode-locked fiber ring laser (SMFRL). Consequently, the measured distance can be calculated from the change in the repetition rate of the emitted pulses due to the laser cavity length change. The SMFRL technique is implemented here to measure distances up to 57.4 m with precision of less than 9 µm. Therefore, we believe that the SMRFL technique provides a relatively simple and precise technique to measure relatively long distances.

Generation of noise-like pulses and soliton rains in a graphene mode-locked erbium-doped fiber ring laser

We demonstrate the generation of noise-like pulses (NLPs) and soliton rains in a graphene saturable absorber mode-locked erbium-doped fiber laser. Typical NLPs are obtained at a proper pump power and in a cavity polarization state. The soliton rain operation with multiple solitons can be achieved by finely adjusting the cavity polarization state. In addition, distinctive multi-soliton interactions are observed and investigated, including the fundamental mode-locking and multiple pulses. The experimental results can help further understand nonlinear pulse dynamics in ultrafast optics.

Wavelength-Switchable Multiple Type Bound Solitons in a Passively Mode-Locked Er-Doped Fiber Laser

We report on the experimental observation of wavelength-switchable bound solitons in a passively mode-locked erbium-doped fiber ring laser based on a tapered graded-index multimode fiber. Due to the multimode interference filtering effect, by adjusting the polarization controller while maintaining the pump power of 158 mW at 1480 nm, the center wavelength of the fiber laser output can be switched between 1565 nm and 1595 nm. At the same time, bound soliton pairs and bound soliton triplets can be both observed in these two wavelengths. Such a simple, compact all-fiber mode-locked laser with switchable wavelength has great potential for high capacity optical communication.

Pulse-amplitude equalization in the monotonic region of the modulator of a rational-harmonically mode-locked fiber ring laser

We investigate characteristics of the modulator and classify the modulation regions to study pulse-amplitude equalization (PAE) of a rational-harmonically mode-locked fiber ring laser pulses. PAE was accomplished experimentally in a polarization-maintaining laser resonator simply by optimizing the modulator driving power without any additional devices, and stable pulse-amplitude-equalized pulses were obtained in the monotonic region of the modulator at repetition rates of 20 GH, 30 GH, and 40 GH.

Harmonic mode-locking fiber ring laser with a pulse repetition rate up to 12 GHz

We experimentally demonstrate a harmonically mode-locked Er-doped fiber laser. The distinctive feature of the laser is highly stable pulse trains generated via self-starting hybrid mode-locking triggered by frequency-shifting and nonlinear polarization evolution. A intra-cavity tunable bandpass filter allows getting a pulse repetition rate up to 12 GHz with local adjustment of the wavelength.

Characterization and experimental verification of actively mode-locked erbium doped fiber laser utilizing ring cavity

Abstract A simple active mode-locked erbium-doped fiber (EDF) ring laser is characterized and experimentally demonstrated. The active mode-locked laser can be tuned in the C-band wavelength range 1525 nm to 1565 nm using a tunable bandpass filter placed in the cavity. An intensity modulator placed inside the laser cavity is driven using a sinusoidal signal at different repetition rates. The laser can produce trains of pulses with a width that is controlled using the mode-locking order. The experiments demonstrated an active mode-locked laser that can generate pulse trains with 39 ns width at multiple cavity fundamental frequency of 0.67 MHz repetition rate. Numerical simulations are conducted to investigate the effect of the tunable filter bandwidth and the power of the EDF 980 nm pump on the mode-locking process and produced pulses width.