Normal Dispersion Regime Research Articles

Turn-key, high-efficiency Kerr comb source.

We demonstrate an approach for automated Kerr comb generation in the normal group-velocity dispersion (GVD) regime. Using a coupled-ring geometry in silicon nitride, we precisely control the wavelength location and splitting strength of avoided mode crossings to generate low-noise frequency combs with pump-to-comb conversion efficiencies of up to 41%, which is the highest reported to date for normal-GVD Kerr combs. Our technique enables on-demand generation of a high-power comb source for applications such as wavelength-division multiplexing in optical communications.

Kerr Frequency Comb Generation in Microbottle Resonator With Tunable Zero Dispersion Wavelength

In this letter, we report an optical frequency comb (OFC) generated in a whispering-gallery-mode microbottle resonator, and present a convenient and simple method for adjustment of the zero dispersion wavelength (ZDW). The ZDW tunability of the microbottle resonator realized by exciting modes with different axial mode numbers is predicted theoretically and demonstrated experimentally by changing the coupling position of a tapered fiber. Cascaded four-wave mixing (FWM)-based frequency combs are investigated by pumping the resonator in different dispersion regimes. The results show that the OFC based on degenerated FWM could be generated under the anomalous dispersion, while Raman or Raman-assisted OFC are obtained in the normal dispersion regime.

A variety of optical solitons for nonlinear Schrödinger equation with detuning term by the variational iteration method

This work addresses a variety of Schrödinger equations (NLS) with detuning term in the anomalous and normal dispersive regimes. We operate the variational iteration method (VIM) for obtaining a set of diverse types of exact bright and dark soliton solutions. Singular and periodic solutions are derived as well. The presented analysis shows the pertinent features of the VIM in the presented analysis.

Midinfrared Pulse Generation by Pumping in the Normal-Dispersion Regime of a Gas-Filled Hollow-Core Fiber

Based on numerical simulations, the authors offer a midinfrared pulse source that uses hollow-core optical fiber filled with gas. Such a source could find applications across a large variety of sectors in science and technology (particularly biomedical), due to its conceptual simplicity. The approach taken in this work resolves all major issues related to pulse generation in the midinfrared spectral region. The system promises to be highly robust against noise, and has a major advantage over existing devices, in using a pump in the 1-$\ensuremath{\mu}$m wavelength range, which is readily available.

Soliton-comb structures in ring-shaped optical microresonators: generation, reconstruction and stability

Characteristic features of soliton-comb structures in optical microresonators are investigated in normal and anomalous dispersion regimes, when the detuning parameter is varied over a broad range of values. The study rests on the assumption that soliton combs are self-organized ensemble of co-propagating coherently entangled states of light, and depending on the group-velocity dispersion they can result from space-division multiplexing of single-bright and single-dark solitons. Their analytical and numerical reconstruction schemes are discussed, while a linear-stability analysis leads to a $2\times 2$ Lam\'e eigenvalue problem whose boundstate spectrum is composed of a Goldstone-type translation mode and stable internal modes, as well as unstable decaying modes and growing modes. A power-spectral analysis of the three distinct possible soliton crystals enables us probe their inner structures in the frequency domain, and unveil the existence of structural defects in their power spectra.

Observation of vector solitons supported by third-order dispersion

We report on the experimental observation of dark-bright and antidark-bright vector solitons supported by third-order dispersion in a weakly birefringent cavity fiber laser. Using a cavity dispersion and birefringence management technique we constructed a weakly birefringent cavity fiber laser with near-zero net cavity dispersion. Operating the fiber laser in either the net normal or net anomalous dispersion regime, we found that both dark-bright and antidark-bright vector solitons could be simultaneously formed as a result of incoherent cross-polarization phase modulation. Our experimental results confirm the existence of antidark-bright vector solitons and the coexistence of dark-bright and antidark-bright vector solitons in a real physical system.

Bright and dark optical solitons for (2+1)-dimensional Schrödinger (NLS) equations in the anomalous dispersion regimes and the normal dispersive regimes

We operate the variational iteration method (VIM) for obtaining bright and dark optical solitons for (2+1)-dimensional nonlinear Schrödinger (NLS) equations, that appear in the anomalous dispersion regimes and the normal dispersive regimes respectively. We derive diverse types of solutions that contain bright optical solitons and dark optical solitons, which are very important from a physical point of view of nonlinear optics and electro magnetic wave propagations. The VIM, that will be employed here, demonstrates the solutions in a rapidly convergent series structure.

Wavefront shaping for optimized many-mode Kerr beam self-cleaning in graded-index multimode fiber.

We report experimental results, showing that the Kerr beam self-cleaning of many low-order modes in a graded-index multimode fiber can be controlled thanks to optimized wavefront shaping of the coherent excitation beam. Adaptive profiling of the transverse input phase was utilized for channeling the launched power towards a specific low-order fiber mode, by exploiting nonlinear coupling among all guided modes. Experiments were carried out with 7 ps pulses at 1064 nm injected in a five meters long multimode fiber operating in the normal dispersion regime. Optimized Kerr beam self-cleaning of five different LP modes is reported, with a power threshold that increases with the mode order.

Dynamics of soliton molecules in a normal-dispersion fiber laser

Soliton molecules have been extensively investigated in mode-locked anomalous-dispersion fiber lasers by virtue of real-time measurement technologies. However, in the normal-dispersion regime, it is unclear how a soliton molecule evolves. Here, we first present, to the best of our knowledge, experimental investigations on the dynamics of soliton molecules in the normal-dispersion regime. We observe aperiodical evolutions of two dissipative solitons within a soliton molecule. They exchange energies during propagation. In particular, the large dissipative soliton splits when energy exchange occurs. Rogue waves are first revealed in the spectral domain of soliton molecules. High-resolution time-stretch technique, field autocorrelation analysis, and spatiotemporal intensity measurements allow us to reveal these critical behaviors of soliton molecules.

Modulation instability induced by intermodal cross-phase modulation in step-index multimode fiber.

Based on linear stability analysis, we theoretically investigate the onset condition and gain spectrum of intermodal cross-phase modulation-induced noise-seeded modulation instability taking place in the normal dispersion regime of step-index multimode fiber, specially designed to support four modes (LP01, LP11, LP21, LP02) at 1064nm. For the case of total power being distributed equally in certain bimodal combinations, the peak sideband frequency scales as the square root of total power, and peak gain increases linearly with total power. For the case of total power being distributed unequally, there exists an optimal power ratio to obtain peak gain, which does not depend on total power significantly. When the mode group velocity mismatch is considered, the range and peak values of gain spectra are notably increased.

Monolithic all-fiber mid-infrared supercontinuum source based on a step-index two-mode As2S3 fiber**Project supported by the National Natural Science Foundation of China (Grant Nos. 61435009, 61235008, and 61405254).

We demonstrate efficient supercontinuum generation extending into mid-infrared spectral range by pumping a two-mode As2S3 fiber in the normal dispersion regime. The As2S3 fiber is fusion spliced to the pigtail of a near-infrared supercontinuum pump source with ultra-low splicing loss of 0.125 dB, which enables a monolithic all-fiber mid-infrared supercontinuum source. By two-mode excitation and mixed-mode cascaded stimulated Raman scattering, a supercontinuum spanning from to is obtained. Over 70% of the supercontinuum power is converted to wavelengths beyond m. This is the first experimental report with respect to the multimode mid-infrared supercontinuum generation in a step-index two-mode chalcogenide fiber.

1.8–13 μm supercontinuum generation by pumping at normal dispersion regime of As–Se–Te glass fiber

AbstractMid‐infrared (MIR) band supercontinuum (SC) light source has highly important application prospects in aerospace, biomedicine, MIR sensing, and pollutant monitoring. As–Se–Te glass has high nonlinear refractive index, wide MIR transmission range and weak crystallization ability. As40Se40Te20 glass fiber is suitable for producing wide MIR–SC spectrum. In this study, purified As40Se40Te20 glass was prepared and unclad and step‐index fibers were drawn. An unclad As40Se40Te20 glass fiber with minimum loss of 1.7 dB/m at 8.8 μm was obtained. By pumping the unclad fiber in the normal dispersion region at 5 μm, we recorded the broadest SC generation spectrum, which covered 1.8–13 μm with a 30 dB spectral flatness, from a fiber with 15 cm length. Besides, As40Se40Te20/As40Se42Te18 step‐index fiber with minimum loss of 5.6 dB/m at 5 μm was drawn from isolation extruded preform. The step‐index fiber was pumped in the normal dispersion region at 5 μm, and the SC spectrum, covering 2.1–11.2 μm with a 40 dB spectral flatness, was recorded from a fiber with 15 cm length. The SC spectrum, which was achieved by pumping the As40Se40Te20 fiber, covered almost all the transparent range of material.

Dissipative soliton resonance and its depression into burst-like emission in a holmium-doped fiber laser with large normal dispersion.

We report on dissipative soliton resonance (DSR) and its transformation into a type of burst-like emission in a holmium-doped fiber (HDF) laser in the large normal dispersion regime. A nonlinear amplifying loop mirror incorporating ∼118 m large normal dispersion fiber acts as an artificial saturable absorber. To the best of our knowledge, the HDF laser has the largest net normal dispersion so far. As the pump power is increased from ∼1.72 W to ∼4.80 W, the produced single pulse linearly broadens from ∼6.7 ns to ∼68.0 ns, while the output pulse peak power is clamped around ∼180.5 mW due to the peak-power-clamping effect with DSR. The sharp spectral peak indicates that DSR is realized with a large normal dispersion. With further manipulation of the polarization state, DSR can evolve into a type of burst-like emission. It is further revealed that this burst-like emission could be caused by a type of peak-power-depressing effect, which results from the competition between DSR and soliton formation.

Cross-phase modulation instability under delayed response and walk-off effects in the anomalous regime of dispersion

The dynamics of the modulation instability induced by cross phase modulation is studied by considering the influence of the walk-off and noninstantaneous response effects for two copropagating optical fields travelling in the anomalous regime of dispersion. To do so, we make use of extensions of the nonlinear Schrdinger equation jointly with the Debye model for polarization, which is shown to be effective and simplified when compared to the implementation of other methods for the noninstantaneous nonlinear response. In analyzing the sideband formation, two bands are observed with different behaviors with respect to the way the maximum gain and the respective frequency vary with increasing phase mismatch. Further, we also show the manner in which the maximum gain as well as its corresponding frequency scale with the delay parameter τ is substantially different from the cases of both fields experiencing the normal group-velocity dispersion regime and the case of mixed regimes. These facts may give rise to many new possibilities for the evolution of the modulated wave when compared to the nonanomalous cases studied in the literature.

Lax pair, Darboux transformation, vector rational and semi-rational rogue waves for the three-component coupled Hirota equations in an optical fiber

The optical fiber communication system is one of the supporting systems of the modern internet age. In this paper, we study the three-component coupled Hirota equations, which govern the simultaneous propagation of three fields in the normal dispersion regime of an optical fiber. We derive a Lax pair and construct the corresponding Darboux transformation. Via the Darboux transformation, rogue wave solutions with the corresponding characteristic polynomial admiting a quadruple root and two/one double roots are obtained. Via such solutions, we depict the first-order vector rational rogue wave with the two components containing the four-petaled rogue wave, and the other component containing one eye-shaped rogue wave; increasing the value of the real parameter which denotes the integrable perturbation, we observe that the range of the first-order vector rational rogue wave along an axis increases; we display the first-order vector rational rogue waves with each component containing two/three merged and separated rogue waves. The second-order rogue waves are graphically displayed, with each component containing five, seven or nine rogue waves, which form the pentagon, triangle, clawlike, hexagon, arrow, line or trapezoid structures. The first- and second-order vector rational/semi-rational rogue waves are graphically exhibited. Two types of the vector semi-rational rogue waves are presented: the one with each component containing the rogue waves and line breathers, and the other with each component containing the rogue waves and Y-shaped breathers.

Optical solitons for nonlinear Schrödinger (NLS) equation in normal dispersive regimes

We operate variational iteration method for obtaining exact analytical solutions for nonlinear Schrödinger (NLS) equation with normal dispersive regimes. A set of diverse types of solitons that contains optical dark solitons are furnished with significant physical perspective. VIM gives the solution in a rapidly convergent series structure. The current analysis under study depicts pertinent attributes of considered method. Additionally, improved G′G expansion method is employed to NLS equation, generating soliton solutions having rich spatial-temporal configuration along with abundant free parameters.

Metallic carbon nanotube-based saturable absorbers for holmium-doped fiber lasers.

In 2003, carbon nanotubes opened a new field of research on nanomaterial-based mode-locked fiber lasers. They maintain popularity in the ultrafast laser community due to their broadband operation, relatively high damage threshold, and tunable optical properties. Here we show that metallic carbon nanotube-based thin film fabricated by vacuum filtration technique can be used as a saturable absorber in holmium-doped fiber laser operating in anomalous and normal dispersion regimes. Scaling the absorbers modulation depth by adjusting the film thickness was observed. The Fourier transform limited 6.65 nm wide optical solitons in anomalous dispersion regime were generated. Utilizing stretched-pulse regime greatly improves the laser performance - 212 fs pulses reach the energy of 3.79 nJ.

Cross-phase modulation instability in an elliptical birefringent positive-negative index coupler with self-steepening and intrapulse Raman Scattering effects

In this paper, we investigate the modulational instability (MI) in an elliptical birefringent positive-negative index coupler. Also, we derive the general expression for instability gain by taking into account cross-phase modulation (XPM), self-steepening (SS) and intrapulse Raman scattering. The instability gain is attained. Using standard linear stability analysis, particularly, we study different configurations of the birefringence with self-steepening or intrapulse Raman scattering effects on MI for both normal and anomalous group velocity dispersion regimes. We observe that the instability gain exhibits significant changes due to the effects of the cross-phase modulation. Finally, we show that efficient control of the MI can be realized by adjusting the self-steepening and intrapulse Raman scattering term, even in the presence of different configurations of the birefringence.

Various soliton molecules in fiber systems.

Generation and propagation of various soliton molecules (SMs) in fiber systems are reviewed. SMs can survive either in fibers or fiber lasers. A dispersion-managed (DM) fiber link is the only platform for SM demonstration, while various fiber lasers can support different SMs. The fundamental unit of SMs can be conventional solitons generated in an anomalous dispersion regime, stretched pulses in DM fiber lasers, parabolic pulses, or gain-guided solitons in a normal dispersion regime. SMs with typically close soliton separation are presented. In addition, we demonstrate a new kind of SM with nanosecond soliton separation. The narrow spectral filtering is required for the generation of SMs with such long-distance interaction.

Ultrabroadband and coherent mid-infrared supercontinuum generation in Te-based chalcogenide tapered fiber with all-normal dispersion.

We demonstrated an ultrabroadband supercontinuum (SC) generation with high coherence property in all-normal-dispersion (ANDi) Te-based chalcogenide tapered fiber. The fibers made of Ge20As20Se15Te45 core and Ge20As20Se20Te40 cladding glasses were fabricated via isolated stacked extrusion. The waist diameter and length can be accurately controlled by a homemade tapering platform. When the core diameter of the waist was ≤14 μm, the fiber showed an ANDi characteristic in the wavelength range of 1.7-14 μm. A coherent SC generation covered 1.7-12.7 μm was generated in a 7-cm-long tapered fiber, pumped at 5.5 μm. To the best of our knowledge, this is the first SC experimental demonstration in Te-based step-index tapered fiber and the broadest SC generation in chalcogenide tapered fiber when pumped in the normal dispersion regime so far.