Dark Pulse Generation Research Articles

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.

Domain-wall dark pulse generation with polyacrylonitrile as saturable absorber

Domain-wall dark pulse generation with polyacrylonitrile as saturable absorber

Nonlinear Multimodal Interference as Ultrafast Photonic Device for Dual-Wavelength Domain-Wall Dark Pulse Generation

Abstract In comparison to bright pulses, better stability that is not susceptible to loss makes dark pulses accessible for applications in such fields as signal processing, optics sensing, and quantum communication. Here we investigate the dual-wavelength domain-wall dark pulse generation in a graded-index multimode fiber (GIMF) based anomalous dispersion single-mode fiber (SMF) laser. By optimizing intra-cavity nonlinearity and pulse polarization, the mode-locked states can evolve each other between bright pulses, dark pulses, and bright-dark pulse pairs. The evolution mechanism among them may be relevant to the coherent mode superposition, spectral filtering, and mode selection in SMF-GIMF-SMF hybrid-fiber modulation devices that affect the pulse formation and evolution in temporal, frequency, and space domains. These results provide a valuable reference for promoting further development of nonlinear optics and ultrafast optics, in which ultrafast photonic devices, with low cost, simple manufacture as well as wide adaptability, as novel pulsed generation technique, play a vital role.

Molybdenum gallium carbide coated D-shape fiber for nanosecond dark pulse generation in erbium-doped fiber laser

Molybdenum gallium carbide (Mo2Ga2C), a material belongs to MAX phase group, has garnered significant interest in a wide range of scientific field, including material science, engineering, and laser physics. It is chemically and structurally promising since it exhibits a low shear modulus, superconducting behaviour, and high mechanical stability. Here, we prepared a saturable absorber (SA) based on Mo2Ga2C coated D-shape fiber using solution casting technique. It exhibits outstanding saturable absorption of 7.2%, allowing it to generate dark pulse laser in an erbium-doped fiber laser cavity. We analyzed the laser’s performance and obtained a dark pulse with a pulse energy, peak power, and average output power of 3.9 nJ, 27.5 mW, and 7.3 mW, respectively. This foundational work may introduce a new material as an alternative SA device in fiber laser cavity.

Harmonic domain-wall dark pulse generation using unpumped thin-core thulium fiber as interferometer

In this work, the harmonic domain-wall dark pulse is experimentally demonstrated in C-band fiber laser. The domain-wall dark pulse was self-started at pump power of 112 mW. The fundamental dark pulse repetition rate was measured as 0.96 MHz, pulse duration of 250 ns and highest average pulse energy of 3.24 nJ. As the power increased, dark pulses up to the 7th harmonic order were visualized and quantified. Pulse temporal width reduced as harmonic order increased, with the minimum pulse width of 60 ns recorded in the 7th order. The harmonic dark pulse fiber laser demonstrated adequate stability, with signal-to-noise ratios above 50 dB throughout all harmonic operations. The endeavor of harmonic dark pulse dark soliton could lay the groundwork for future sustainable industrial growth.

Domain-wall dark pulse generation with SMF-GIMF-SMF structure as artificial saturable absorber

We experimentally demonstrated the generation of domain-wall dark pulse in an Erbium-doped fiber laser using the combination of a 10 cm graded index multimode fiber sandwiched by single mode fibers as artificial saturable absorber. The interaction of phase difference in grade index multimode fiber allowed the stable dual-wavelength oscillation in the cavity. The dual-wavelength centered at 1567.2 nm and 1569.4 nm produces the topological defect in temporal domain and achieved a dark pulse formation with repetition rate of 21.5 MHz. The highest average pulse energy is calculated as 769.6 pJ with pulse width of 5 ns. Throughout the operating pump power range, the average pulse energy and output power increase linearly, with R2 of 0.9999 and achieved the laser efficiency of 9.33%. From the measurement in frequency domain, the signal-to-noise ratio is measured as 49 dB. As compared to reported DW dark pulse works, the proposed structure only required a short length of multimode fiber, which allowed the domain-wall dark pulse to achieve higher pulse repetition rate. The venture of domain wall dark pulse is potentially to pave the foundation toward sustainable industrial growth.

Dark pulse generation in mode-locked Erbium-doped fiber laser with Molybdenum Aluminium Boride coated side-polished fiber

We demonstrate the generation of dark pulses from an Erbium-doped fiber laser (EDFL) using a Molybdenum Aluminium Boride (MoAlB) as a saturable absorber for the first time. Molybdenum Aluminium Boride (MoAlB) was coated onto side-polished fiber (SPF) to improve the birefringence and nonlinearity inside the EDFL cavity with net anomalous dispersion. The soliton dark pulses are obtained from the laser cavity based on cubic-quintic nonlinear Schrödinger equation (CQNLSE) mechanism. The laser operated at 1560.6 nm with a pulse duration of 152 ns and repetition rate of 1.87 MHz as the pump power is set within 200 mW to 370 mW. At the maximum pump power, the average output power and pulse energy are recorded at 6.93 mW and 3.77 nJ, respectively. We think that this research is the first to show MoAlB 's potential for dark pulse generation.

Hyperbolic resonant radiation of concomitant microcombs induced by cross-phase modulation

A high-quality optical microcavity can enhance optical nonlinear effects by resonant recirculation, which provides a reliable platform for nonlinear optics research. When a soliton microcomb and a probe optical field are coexisting in a micro-resonator, a concomitant microcomb (CMC) induced by cross-phase modulation (XPM) will be formed synchronously. Here, we characterize the CMC comprehensively in a micro-resonator through theory, numerical simulation, and experimental verification. It is found that the CMCs spectra are modulated due to resonant radiation (RR) resulting from the interaction of dispersion and XPM effects. The group velocity dispersion induces symmetric RRs on the CMC, which leads to a symmetric spectral envelope and a dual-peak pulse in frequency and temporal domains, respectively, while the group velocity mismatch breaks the symmetry of RRs and leads to asymmetric spectral and temporal profiles. When the group velocity is linearly varying with frequency, two RR frequencies are hyperbolically distributed about the pump, and the probe light acts as one of the asymptotic lines. Our results enrich the CMC dynamics and guide microcomb design and applications such as spectral extension and dark pulse generation.

Dynamics of Dark Pulse Affected by Higher-Order Effects in Microresonators

We theoretically investigate dynamics of dark pulse and Raman-Kerr microcombs generation influenced by higher-order effects, including high-order dispersion (HOD), stimulated Raman scattering (SRS) and self-steepening (SS) effects in silicon microresonators. These three effects cause the delay of dark pulse individually, or interact with each other to alter the drift velocity and direction of pulses. HOD effect can change pulse shift direction and even cause bifurcation. The temporal drift induced by SS or SRS effects could be balanced by the simultaneous third-order dispersion (TOD) engineering. In spectral domain, stable Raman-Kerr frequency comb will be generated due to the competition between strong SRS and Kerr effects. The Raman comb components are suppressed when HOD effect coexists, while SS effect has ignorable effect on the distribution of the Raman comb. Furthermore, the SS effect will increase the total energy of the spectrum by shifting the dispersive wave (DW) generation to the longer wavelength side. Our findings could deepen the understanding of intracavity nonlinear dynamics and provide theoretical guidance to precisely control the stabilization of dark pulse and the generation of broadband mid-infrared (MIR) microcomb.

Experiments on Generation of Various Dark and Bright Pulses From an FM Mode-Locked Laser

We experimentally describe the generation of various dark and bright pulses from an FM mode-locked laser with, for example, Gaussian, secant hyperbolic (sech), double-sided exponential, rectangular, parabolic, triangular, Nyquist, and even tangent hyperbolic (tanh) shapes. The experiments were carried out by constructing a 20 GHz actively FM mode-locked erbium fiber laser. Since a continuous wave (CW) offset is needed to form a dark pulse, which can be considered the sum of a negative pulse and a rectangular pulse in one time slot. Therefore, a specific filter, which is installed in the laser cavity, consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A(\omega )$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A(\omega + n\Omega _{m})$ </tex-math></inline-formula> with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n=-\infty \sim +\infty $ </tex-math></inline-formula> and a sinc function spectrum that is newly introduced as a Fourier transformation of a rectangular pulse for describing the CW offset. Here, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega _{m}$ </tex-math></inline-formula> is the angular modulation frequency. We also generated a positive bright pulse that consists of a positive pulse with a positive CW offset. The generated optical pulses agreed well with the theory, where the spectral profiles even below −40 dB coincided well with the numerical profiles. We could also generate parabolic and triangular dark pulses in the intensity expression. Finally, we demonstrated tanh <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(t/T)$ </tex-math></inline-formula> pulse generation, which is an odd function and well known as a dark soliton solution of the nonlinear Schrödinger equation. This pulse was generated by changing the odd function into an even function by cascading positive and negative tanh <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(t/T)$ </tex-math></inline-formula> pulses at half the repetition rate.

Dark Rectangular Pulses From a Dumbbell-Shaped Mode-Locked Double-Clad Er:Yb Laser

The formation of dark rectangular pulses from a dumbbell-shaped mode-locked double-clad erbium-ytterbium fiber laser is experimentally demonstrated. The laser operates under a large net-anomalous cavity dispersion regime, with a passive mode locking mechanism that relies on a nonlinear amplifying loop mirror (NALM) along with a nonlinear optical loop mirror (NOLM). This design facilitates the control of nonlinear effects within the cavity and enables the generation of dark pulses as the dominant mode locking regime. The variations of dark-rectangular pulse emission and its spectral evolution are experimentally investigated as a function of the pump power, revealing a dependence analogous to bright dissipative soliton resonance (DSR) pulses, where the dark pulse duration increases with increasing pump power, a behavior that is opposite to previously reported dark rectangular pulses. At the maximum pump power of 9.5 W, the mode-locked fiber laser generates dark rectangular-shaped pulses with duration of 571 ns, average output power of 600 mW, fundamental repetition rate of 320 kHz.

Theory of Generation of Various Dark and Negative Pulses From an FM Mode-Locked Laser

We show theoretically that various kinds of dark pulses and negative pulses can be generated from an FM mode-locked laser. First, we classify optical pulses into two groups, namely a positive pulse group, which has an electric field with a positive amplitude, and a negative pulse group, which has an electric field with a negative amplitude. We classify them into two further groups; one has a positive offset with a CW electric field and the other has a negative offset. Therefore, we have a total of four kinds of pulses, which we denote as positive bright, positive dark, negative bright, and negative dark pulses. We show that these pulses can be successfully generated by employing FM mode-locking with specific optical filters that we newly propose here. We generate various dark pulses including Gaussian, sech, double-sided exponential, rectangular, triangular, parabolic, and even dark Nyquist pulses, where we can precisely control their width, depth, and repetition rate. We also describe dark triangular and dark parabolic pulses with an intensity expression. Finally, we generate a tanh( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t/T$ </tex-math></inline-formula> ) pulse, which is an odd function and a dark soliton solution of the nonlinear Schrödinger equation. Since this pulse has different amplitudes with ± signs on the wings, conversion from an odd function to an even function plays an important role in achieving FM mode-locking.

Stimulated Raman scattering induced dark pulse and microcomb generation in the mid-infrared

We demonstrate that strong stimulated Raman scattering in silicon and germanium microresonators can induce stable and breathing dark pulses generation circumventing traditional complex approaches such as pump modulation and mode coupling. Although multi-photon absorption shows a small influence on the detuning value for stable dark pulse excitation, the concomitant free carrier will assist dark pulse excitation and broaden the excitation area of dark pulse thus making it easier to capture stable pulse. Furthermore, dark breather dynamics in Si and Ge are also observed, which shows distinct properties from the dark soliton breathers dominated solely by Kerr effect. Finally, we show that octave spanning mid-infrared (MIR) microcomb can be generated combining with high-order dispersion engineering, which in turn affects the breathing dynamics of dark pulses. Our findings provide another way for the initiation of dark pulses in group IV materials and broadband MIR microcomb generation for spectroscopy applications.

Intra-cavity dark pulse generation through synchronized sum-frequency mixing

A Nd:YVO4 laser operating at 1064 nm generating a stable mode-locked train of 10 ps-long dark pulses with a 211 MHz repetition rate is presented. The mode-locking relies on a periodic loss modulation produced by intra-cavity sum-frequency mixing with a synchronous bright-pulse train from a mode-locked femtosecond Yb:KYW laser at 1040 nm. A modulation depth of 90% was achieved for the dark pulses, confirmed by cross-correlation measurements. The ultrafast loss modulation injects power into the Nd:YVO4 laser cavity modes beyond the laser gain bandwidth. At proper laser cavity length, the detuning interaction of these modes with the lasing modes leads to the generation of periodic ultrafast transients at frequencies above 1.5 THz.

Rectangular dark pulses in all-normal dispersion fiber oscillator

We report the generation of rectangular dark pulses (RDPs) in ytterbium (Yb) doped fiber laser using a nearly 50:50 coupler based nonlinear optical loop mirror (NOLM) in a simple linear standing wave cavity. Width of the dark pulse decreases with increase in the pump power whereas depth of the rectangular pulse profile remains constant. The nonlinear reflectance characteristics of the NOLM used in the cavity has been experimentally investigated to understand its role in formation of RDPs. Numerical simulations were performed to show the evolution of dark pulses in a fiber oscillator in all normal dispersion configuration. Both experimental and numerical simulations indicate that reverse saturable absorption supports formation of dark pulses. With increase in the saturation energy, width of RDP was found to decrease in line with the experimental observations. Further, an ansatz is proposed to model RDPs. The ansatz is used in cubic quntic Ginzburg-Landau equation to establish relationship between pulse parameters and cavity parameters. Results from analytical formalism are in accordance with the experimental measurements and numerical simulations. Detailed theoretical analysis reveals that experimentally observed RDPs do not belong to domain wall type.

Hafnium Bismuth Erbium Co-Doped Fiber Based Dark Pulses Generation With Black Phosphorus As Saturable Absorber

A dark pulse generation is demonstrated in a fiber laser configured with a 20 cm long HBEDF and multilayer Black Phosphorus as a gain medium and saturable absorber, respectively. Dark pulses fiber laser at 1.5 µm region was obtained when the pump power exceeds the threshold of 147 mW. Meanwhile, the spectrum of the dark pulse is centred at 1556.40 nm, with the 3 dB bandwidth of 0.12 nm and the separation between adjacent pulses is 1145 ns, corresponding to the cavity length of 211 m. The pulse width was measured to be around 320 ns. The radio-frequency spectrum of the dark pulse, which was measured within the 20 MHz range. More than 17 harmonics were observed within this range, which indicates the mode-locking operation of the laser. The fundamental frequency was obtained at 1.1 MHz, which agreed with the oscilloscope trace. Furthermore, it shows a signal to noise ratio of about 36.58 dB, which indicates good stability. The maximum output power of 0.78 mW and pulse energy of 0.78 nJ were obtained at 187 mW pump power.

Free carrier induced dark pulse generation in microresonators.

We theoretically demonstrate a novel, to the best of our knowledge, mechanism for dark pulse excitation in normal dispersion microresonators exploiting free carrier dispersion and free carrier absorption effects due to multi-photon absorption. Dark pulses can be generated in the three- and four-photon absorption regimes in the presence or absence of external reverse bias to control the lifetime of free carriers, respectively. Direct generation of dark pulses is proven to be feasible in both regimes with a frequency fixed laser. The dynamics of their temporal and spectral evolution have also been investigated. Our findings establish a reliable path for dark pulse and Kerr microcomb generation in related platforms with simplified controlling and tuning techniques.

Generation of dark, Q-switched and bright pulses using erbium-ytterbium-thulium co-doped fiber

We demonstrate the generation of dark and bright pulses in a Q-switched laser using an erbium-ytterbium-thulium co-doped fiber. By manipulating pump power while maintaining lasing wavelength at 1571 nm, dark and bright pulses were observed at pump power thresholds 94.1 and 1770 mW with pulse duration of 3 and 71 ns, respectively. Stability of the two regimes were also high across an operating time of 60 min. These findings may be the stepping stone towards realising a laser with flexible operating range at different pulse regimes.

Stable dark pulses produced by a graphite oxide saturable absorber in a fiber laser cavity.

In this paper, we report for the first time, to the best of our knowledge, the experimental generation of dark pulses in the 1.5 µm band from a passively $Q$Q-switched fiber laser employing graphite oxide as the saturable absorber, generating tunable microsecond pulses with kHz repetition rates. The graphite oxide samples were obtained by recycling the graphite present in Li-ion batteries used in cell phones through a chemical separation and oxidation process. Sample characterization employing x-ray diffraction, solid-state $ ^{{13}}{\rm C} $13C nuclear magnetic resonance, and Raman spectroscopy showed that the produced graphite oxide exhibited a homogeneously oxidized structure. Dark pulse emission could be observed at a relatively low pump threshold of 35 mW in a short 20 m laser cavity, indicating that the graphite oxide acted as a saturable absorber, significantly enhancing the nonlinearity of the laser cavity. Additionally, dark pulse operation was demonstrated at a high stability with a signal-to-noise ratio of 56 dB and a pulse-to-pulse timing jitter of 159.84 fs.

Bi2Te3 Topological Insulator for Domain-Wall Dark Pulse Generation from Thulium-Doped Fiber Laser

We have experimentally demonstrated domain-wall (DW) dark pulses from a thulium-doped fiber laser incorporating a topological insulator saturable absorber (SA). The bulk-structured Bi2Te3 was used as the SA, which was constructed on a fiber ferrule platform through the deposition of the Bi2Te3 mixed with distilled water. The DW dark pulses were generated from the thulium-doped fiber laser cavity with a dual wavelength at 1956 nm and 1958 nm. The dark pulse width and the repetition rate were measured as ~10.3 ns and ~20.7 MHz over the pump power of ~80 mW, respectively. To the best of our knowledge, this work is the first demonstrated generation of the DW dark pulse from a thulium-doped fiber laser using nanomaterial-based SA.