Soliton Pulse Generation Research Articles

Two-color flat-top solitons in microresonator-based optical parametric oscillators

We studied numerically the generation of the two-color flat-top solitonic pulses, platicons, in the microresonator based doubly resonant optical parametric oscillator. We revealed that if the signs of the group velocity dispersion (GVD) coefficients at interacting harmonics are opposite, platicon excitation is possible via pump amplitude modulation or controllable mode interaction approach. Upon pump frequency scan generation of platicons was observed at positive pump frequency detunings for the normal GVD at pump frequency and at negative detunings in the opposite case. Interestingly, we found the effect of the transformation of the flat-top platicon profile at half-frequency into the bell-shaped bright soliton profile upon frequency scan. For platicon excitation one needs simultaneous accurate matching of the microresonator free spectral ranges at interacting harmonics and resonant eigenfrequencies. Excitation conditions and platicon generation domains were found for the different generation methods, and properties of the generated platicons were studied for various combinations of the medium parameters.

Tungsten trioxide (WO3) film absorber for generating soliton mode-locked pulses in erbium laser

We proposed a new type of passive saturable absorber (SA) based on tungsten trioxide (WO3)- polyvinyl alcohol (PVA) film for generation of soliton mode-locked pulse in the erbium-doped fiber laser (EDFL) cavity. The WO3-PVA has a modulation depth of 20% with a saturable intensity of 0.04 W/cm2. The new SA film was integrated into the cavity to realize a stable mode-locked pulses operating at 1565.08 nm within a pump power range from 50 mW to 225 mW. The pulse repetition rate and pulse width of the soliton laser was 1.85 MHz and 2.69 ps, respectively. The pulse energy of 1.14 nJ and peak power of 0.67 kW were obtained at the maximum input pump power of 225 mW. These results indicate that WO3 is a promising nonlinear optical material for application in generating ultra-fast mode-locked laser. This is the first time that WO3 was utilized as SA in the 1.5 μm region.

Optical soliton through induced cesium doppler broadening medium

In this article we have controlled and modified the absorption, dispersion, reflection and transmission spectrum within a cesium atomic medium under the Doppler broadening effect. The Doppler and inverse Doppler effect show significant influence on the absorption and dispersion as well as the corresponding transmission and reflection spectrum. The output pulses intensity show no losses in the medium. The distortion free pulse propagation is investigated by taking into account Doppler and inverse Doppler broadening effect and Rabi oscillations. The dispersive and nonlinear effects cancellation has been achieved in the medium, which show soliton pulse propagation in the medium with the strength of Rabi oscillation and inverse Doppler broadening. The results obtained could have potential applications in soliton radar technology.

Optical solitons with Kudryashov's model by a range of integration norms

This paper recovers optical solitons for the newly proposed Kudryashov’s equation which governs soliton pulse propagation through optical fibers and photonic crystal fibers. A spectrum of soliton solutions are obtained from a wide range of integration norms. The existence criteria for such solitons are enlisted. Finally, couple of numerical simulations make the paper rounded.

Highly stable and repeatable femtosecond soliton pulse generation from saturable absorbers based on two-dimensional Cu3-xP nanocrystals.

Heavily doped colloidal plasmonic nanocrystals have attracted great attention because of their lower and adjustable free carrier densities and tunable localized surface plasmonic resonance bands in the spectral range from near-infra to mid-infra wavelengths. With its plasmon-enhanced optical nonlinearity, this new family of plasmonic materials shows a huge potential for nonlinear optical applications, such as ultrafast switching, nonlinear sensing, and pulse laser generation. Cu3-xP nanocrystals were previously shown to have a strong saturable absorption at the plasmonic resonance, which enabled high-energy Q-switched fiber lasers with 6.1 μs pulse duration. This work demonstrates that both high-quality mode-locked and Q-switched pulses at 1560 nm can be generated by evanescently incorporating two-dimensional (2D) Cu3-xP nanocrystals onto a D-shaped optical fiber as an effective saturable absorber. The 3 dB bandwidth of the mode-locking optical spectrum is as broad as 7.3 nm, and the corresponding pulse duration can reach 423 fs. The repetition rate of the Q-switching pulses is higher than 80 kHz. Moreover, the largest pulse energy is more than 120 µJ. Note that laser characteristics are highly stable and repeatable based on the results of over 20 devices. This work may trigger further investigations on heavily doped plasmonic 2D nanocrystals as a next-generation, inexpensive, and solution-processed element for fascinating photonics and optoelectronics applications.

MXene: two dimensional inorganic compounds, for generation of bound state soliton pulses in nonlinear optical system

Abstract MXene are a class of metal carbide and metal nitride materials with a two-dimensional layered structure. MXene Ti3C2Tx has the characteristics of good metal conductivity and adjustable chemical composition, which has attracted the attention of scientists. Recently, Mxene have shown strong nonlinear photonics and optoelectronic effect, which can be used to generate ultrashort pulsed laser. However, soliton molecules pulse in laser cavity based on Mxene have not been reported at present. In this article, MXene have been characterized systematically, and the nonlinear optical characters were measured. In addition, we combined MXene with taper fiber to make a saturable absorber device for an erbium-doped fiber laser. The modulation depth and saturation absorption intensity of MXene are 10.3% and 197.5 MW/cm2, respectively. Thanks to the outstanding character of MXene, a three-order soliton molecules pulse were generated in laser cavity. The center wavelength, pulse interval and spectral modulation period of soliton molecules are 1529.4 nm, 15.5 ps and 0.5 nm, respectively. The above experimental results show that MXene have broad application prospects in the fields of optical fiber communication, laser material processing and high-resolution optics.

Analysis of solitonic pulse propagation in metamaterials implemented in photonic crystals

ABSTRACT In this paper we present the analysis of soliton propagation in photonic crystal metamaterials. Current analysis considers the case of the complex refractive index for double negative (DNG) materials and for regular metamaterials. The analytical solution of the nonlinear Schrödinger (NLS) partial differential equation is realized through the traveling wave model. The analysis reveals the existence of soliton pulse propagation under specific constraint conditions necessary for the existence of the soliton solutions. The analytical solutions are validated by the results obtained through simulations. The analysis results give design guidance of waveguide structures able to support undistorted soliton wave propagation.

Switchable generation of a sub-200 fs dissipative soliton and a noise-like pulse in a normal-dispersion Tm-doped mode-locked fiber laser.

We report on the switchable generation of a dissipative soliton (DS) pulse and a noise-like pulse (NLP) in an all-fiberized Tm-doped fiber laser in the normal-dispersion region. Mode-locking operation is achieved through a nonlinear polarization rotation component, and the cavity dispersion is compensated using ultra-high numerical aperture (UHNA4) fiber that is easy to integrate and low in cost. At a pump threshold of 510 mW, DS operation can first be achieved without additional filter. The 3 dB spectrum bandwidth of the DS pulse is greater than 50 nm, and the duration of the de-chirped pulse is 193 fs. By increasing the pump power to 880 mW, the mode-locking state can evolve into NLP operation with proper cavity polarization state. The 3 dB spectrum bandwidth and duration of de-chirped coherence spike are 105.6 nm and 121 fs, respectively. Meanwhile, ultra-broadband NLP (over 150 nm considering 3 dB spectrum width) can also be observed with the appropriate cavity parameters. All the proposed pulse patterns present good capacity for achieving narrow pulse width and withstanding high pulse energy.

Solitons and Turbulence in Solar Wind at 1 au: Multi-satellite Data and FDTD Simulations

Abstract During 2015 January 1–31 multi-satellite data at 1 au showed the propagation of single soliton pulses, the formation of soliton trains, and their ultimate development into the turbulence in solar wind magnetic field, density, speed, temperature, and dynamic pressure. This work is motivated by a basic research question: what are the differences in the conditions for excitation of soliton pulse, soliton train, and turbulence in the solar wind? To answer this question, a convective and dispersive system is considered and simulated via the finite difference time domain (FDTD) method. It is found that when a system is initially driven by a weak shock wave only a single soliton pulse will propagate. When the convection coefficient is smaller than or equal to the dispersion coefficient and system is driven by a strong shock then soliton trains are formed. The development of turbulence occurs when the convective coefficient dominates the dispersion coefficient and the system is driven by a stronger shock. Combining the findings of FDTD simulations with the Hall magnetohydrodynamic model, it is concluded that an enhanced interplanetary magnetic field in the magnetic sheath and the declining ion density after corotation interaction region interface provide favorable conditions for the solitons formation. Contrarily, the declining magnetic field in ejecta provides pertinent conditions for the evolution of Alfvénic turbulence. Our findings are critical for understanding the wave development into turbulence in solar wind.

Graphene and Mo2C vertical heterostructure for femtosecond mode-locked lasers [Invited

Two-dimensional (2D) materials, which commonly have much higher optical nonlinearity and faster carrier dynamics than their bulk counterparts, hold huge potential for use in nonlinear optical devices, especially in ultrafast mode-locked fiber lasers. Graphene has ultrafast carrier dynamics but the optical absorption is low and the modulation depth is small. It is nontrivial to combine graphene with other 2D materials so as to form a heterostructure with improved optical properties. In particular, recent research has shown that the 2D transition metal carbide (TMC) Mo2C has a very large nonlinear absorption coefficient and can be used as a saturable absorber for mode-locking pulse generation. However, the nonlinear optical properties of the graphene-Mo2C heterostructure have not been investigated. In this work, by directly growing Mo2C nanosheets on the monolayer graphene film and forming the heterostructure, a new kind of saturable absorber was prepared with considerate nonlinear absorption coefficient and large modulation depth. Such a new saturable absorber was evanescently interacted with the side-polished fiber and successfully delivered femtosecond pulse generation at 1550 nm. The combination of two semi-metal 2D materials has enabled the ease of mode locking and stable soliton state pulse generation.

Generation and dynamics of solitonic pulses due to pump amplitude modulation at normal group-velocity dispersion

We studied generation and dynamics of solitonic pulses, platicons, at normal group velocity dispersion due to the pump amplitude modulation. We proposed, that if the required frequency of amplitude modulation is too large for available modulators, it is possible to use subharmonic phase modulation for platicon generation. It was also demonstrated that it is possible to control the repetition rate of platicons by tuning modulation frequency. Tuning range for platicons was found to be much wider than for bright solitons. We also studied the influence of the high-order dispersion on platicon properties. It was shown that both third-order dispersion and pump modulation govern platicon dynamics making it quite different from dynamics of dissipative Kerr solitons. Third-order dispersion was also shown to affect significantly the optimal conditions for the platicon generation and repetition rate tuning range.

Study of the propagation of solitary waves produced by an assembly of quantum dots through optical fibers

In this research, the potential use of semiconductor nanostructures as optical field sources to optimize the propagation of lossless pulses along non-linear optical fibers is studied. During this investigation, we propose the external excitation of a set of semiconductor SQD points through a source of optical pulses, giving rise to the generation of solitonic pulses that propagate through an optical fiber with non-linear optical characteristics. Theoretically, soliton formation studied from the non-linear interaction between SQD and external optical excitation. In the study, the non-linear Schrödinger NLSE equation solved numerically using the Fourier Split-Step method to understand the evolution of the soliton emitted for SQD within an optical fiber with real physical parameters.

The Unified Transform Method to Initial-Boundary Value Problem for a Coupled Cubic–Quintic Nonlinear Schrödinger System

In this study, we consider a coupled cubic–quintic nonlinear Schrodinger (CCQNLS) system, which is an important model in fiber-optic communication since this system can be used to describe the effect of quintic nonlinearities on the propagation of ultrashort optical soliton pulses in non-Kerr media. We solved the initial-boundary value problem of the CCQNLS system on the half-line by virtue of the unified transform method. And we manifest that the solution of the CCQNLS system can be represented by the unique solution of a $$3\times 3$$ matrix Riemann–Hilbert problem formulated in the complex $$\lambda $$ -plane. Furthermore, we demonstrate that a slice of spectral functions are not independent of each other, but rather to satisfy a paramount relations (so-called global relationship).

Application of ethanol infiltration for ultra-flattened normal dispersion in fused silica photonic crystal fibers

This paper proposes a new design for an ultra-flattened normal dispersion photonic crystal fiber (PCF) with ethanol infiltration. The optimization process allow us to achieve a symmetric ultra-flat (1 ps/nm/km) normal dispersion in the range of over 500 nm, which is not possible with standard air hole silica fiber. This fiber allows for supercontinuum (SC) generation in the normal dispersion regime. Numerical simulations show that a PCF fiber of length 20 cm, with the pump wavelength of 1550 nm, pulse energy of 4 nJ and duration of 80 fs can generate 945 nm of flattened broadband SC spectrum in the infrared wavelength range; the output pulse peak is also very stable. In addition, the same optical fiber with air holes and under the same stimulated conditions generates the SC spectrum in the anomalous dispersion regime. The proposed PCF structure could be very helpful in large-scale engineering applications, such as dispersion compensation, ultra-short soliton pulse propagation, spectroscopy applications etc.

Nonlinear compression of temporal solitons in an optical waveguide via inverse engineering

We propose a novel method based on the so-called shortcut-to-adiabatic passage techniques to achieve fast compression of temporal solitons in a nonlinear waveguide. We demonstrate that soliton compression could be achieved, in principle, at an arbitrarily small distance by inverse-engineering the pulse width and the nonlinearity of the medium. The proposed scheme could possibly be exploited for various short-distance communication protocols and may be even in nonlinear guided wave-optics devices and generation of ultrashort soliton pulses.

Black phosphorus saturable absorber for dual-wavelength polarization-locked vector soliton generation

We report the usage of few-layered black phosphorus (BP) as saturable absorbers (SAs) to achieve dual-wavelength vector solitons mode locking in an erbium-doped fiber laser for the first time, to our knowledge. The SA is fabricated based on liquid exfoliation method by incorporating BP nanosheets with polyvinyl alcohol. We have demonstrated that the saturable absorption of BP is polarization independent. The laser is capable of generating dual-wavelength polarization-locked vector solitons centered at ~1533 and ~1558 nm with the bandwidths of ~3.7 and ~6.9 nm simultaneously. The results indicate the potential applications of few-layered BP as broadband SAs in vector soliton pulses generation.

Large-area highly crystalline WSe2 atomic layers for ultrafast pulsed lasers.

Large-area and highly crystalline transition metal dichalcogenides (TMDs) films possess superior saturable absorption compared to the TMDs nanosheet counterparts, which make them more suitable as excellent saturable absorbers (SA) for ultrafast laser technology. Thus far, the nonlinear optical properties of large-scale WSe2 and its applications in ultrafast photonics have not yet been fully investigated. In this work, the saturable absorption of chemical vapor deposition (CVD) grown WSe2 films with large-scale and high quality are studied and the use of WSe2 films as a broadband SA for passively mode-locked fiber lasers at both 1.5 and 2 μm ranges is demonstrated. To enhance the light-material interaction, large-area WSe2 film is tightly transferred onto the side wall of a microfiber to form a hybrid structure, which realizes strong evanescent wave interaction between light and WSe2 film. The integrated microfiber-WSe2 device shows a large modulation depth of 54.5%. Using the large-area WSe2 as a mode-locker, stable soliton mode-locked pulse generation is achieved and the pulse durations of 477 fs (at 1.5 μm) and 1.18 ps (at 2.0 μm) are demonstrated, which suggests that the large-area and highly crystalline WSe2 films afford an excellent broadband SA for ultrafast photonic applications.

CsPbBr_3 perovskite quantum dots: saturable absorption properties and passively Q-switched visible lasers

This work presents the saturable absorption (SA) properties of CsPbBr3 perovskite quantum dots (QDs). The perovskite QDs show excellent SA performance with a nonlinear absorption coefficient of −35×10−2 cm/GW and a figure of merit of 3.7×10−14 esu cm. Further, their use as saturable absorbers in a passively Q-switched visible solid-state laser for the generation of soliton pulses is demonstrated. These results demonstrate the potential for the perovskite QDs to act as saturable absorbers.

Femtosecond mode-locking of an ytterbium-doped fiber laser using self-assembled gold nanorods

We experimentally demonstrate the use of a saturable absorber (SA) based on self-assembled gold nanorods (GNRs) for femtosecond mode-locking of an ytterbium-doped fiber-based 1 µm laser. A novel type of SA was made by implementation of an end-to-end GNRs self-assembly technique through hot-air induced rapid drying of the GNRs in a deionized water suspension, which enabled us to enhance optical absorption in the 1.06 µm wavelength region. By incorporating this novel SA into an ytterbium-doped fiber-based ring cavity under dispersion-managed conditions, we were able to readily generate mode-locked, soliton pulses having a temporal width of 840 fs at 1063.9 nm. To the best of our knowledge, this is the first demonstration of the effectiveness of a GNRs-based SA for the generation of femtosecond soliton pulses operating in the 1 µm range.

Soliton Pulse Propagation in the Presence of Disorder-Induced Multiple Scattering in Photonic Crystal Waveguides.

We introduce a new coupled mode theory to model nonlinear Schrödinger equations for counterpropagating Bloch modes that include disorder-induced multiple scattering effects on nonlinear soliton propagation in photonic crystal waveguides. We also derive subunit-cell coupling coefficients and use these to introduce a generalized length scale associated with each coupling effect. In particular, we define a multiple-scattering length scale that quantifies the spatial extent of a disorder-induced cavity mode. Our numerical simulations of nonlinear pulse propagation are in excellent qualitative agreement with recent experiments and provide insight into how structural disorder inhibits soliton propagation and other nonlinear propagation effects in photonic crystal waveguides.