Cavity Group Velocity Dispersion Research Articles

Investigation on different type of pulses due to strong third order dispersion effect in mode-locked fiber lasers

Here we have numerically investigated the pulse property in a wavelength switchable mode-locked fiber laser which is achieved with a tunable filter. Owing to the strong third-order dispersion (TOD) of dispersion-compensating fiber, the net cavity group velocity dispersion of the proposed fiber laser can be manipulated and exhibits wavelength-dependent feature. Our findings indicate that different types of pulses, including conventional solitons, dispersion-managed solitons, and dissipative solitons, can be achieved, and switched in various wavelengths. The pulse characteristics including pulse width and spectrum bandwidth have been investigated, in addition to with the intracavity dynamics. The influence of the length of dispersion-compensating fiber is also investigated. These results provide an excellent foundation for understanding the formation dynamics of various pulse waveforms in the laser cavity and help the development of a multi-wavelength fiber laser with a strong TOD cavity.

Flat-Top Soliton Frequency Comb Generation Through Intra-Cavity Dispersion Engineering in a Brillouin Laser Cavity

Dissipative Kerr cavity soliton and optical frequency comb (OFC) can be generated in fiber cavities or microresonators with anomalous group velocity dispersion (GVD), which has achieved great breakthroughs and found significant applications in many fields. Despite recent progress in this field, it remains challenging to obtain OFCs with a flat-top spectrum and a high conversion efficiency in an optical cavity with anomalous GVD. In this paper, intra-cavity dispersion engineering is proposed to reshape the bright dissipative Kerr solitons in a Brillouin laser cavity with anomalous GVD for generating flat-top OFCs with a high conversion efficiency. By introducing a piece of optical fiber with normal GVD into the above Brillouin fiber laser cavity for making a hybrid fiber cavity with near zero net cavity GVD, the intra-cavity waveform is broadened in time-domain due to the existence of normal GVD, which conquers the pulse compression caused by four-wave mixing and anomalous GVD, and leads to the formation of bright dissipative Kerr solitons and OFCs with a flat-top profile and a high conversion efficiency, via interlocking of up-switching waves. Furthermore, flat-top OFCs with step tunable mode spacing from GHz to THz are achieved via intra-cavity dispersion engineering.

Quartic soliton dynamics and pattern formations in passive driven fiber resonators with different quartic dispersion regimes

Solitons are particle-like localized structures which can sustain characteristic shape in various nonlinear systems. Very recently, the novel concept of quartic soliton with remarkable energy scaling law arising from the interaction of quartic dispersion and Kerr nonlinearity, provides innovations in nonlinear optics and applications. Here we theoretically investigate the quartic soliton dynamics in passive driven fiber resonators from negative to positive quartic dispersion driving. In the pure negative quartic dispersion regimes, the typical energy-duration scaling relationship is sufficiently demonstrated. Worth to note that, we further investigate the dissipative quartic soliton formation in the positive quartic dispersion regimes, achieving remarkable pulse energy increase. Interestingly, echoing our previous work on the influence of cavity group-velocity dispersion on dissipative Faraday instability formation, pattern formation dynamics in the quartic dispersion driving fiber resonators is also explored. Our investigations might benefit the fundamental understanding of the quartic soliton dynamics.

Investigation into the impact of the recovery time of a saturable absorber for stable dissipative soliton generation in Yb-doped fiber lasers.

In this study, we conduct a numerical evaluation of the impact of the recovery time of a saturable absorber (SA) on the output performance of an Yb-doped fiber laser operating in the dissipative soliton regime. Particularly, we evaluate the output pulse characteristics, such as the pulse width, spectral bandwidth, pulse peak power, and pulse energy depending on the change in recovery time. Applying a too-slow SA recovery time above a certain critical value is shown to make the output pulse unstable and broken. Furthermore, we demonstrate that there is an optimum recovery time range for stable dissipative soliton pulse generation, depending on the cavity dispersion and modulation depth of the SA. Further, we perform an additional numerical simulation of the pulse compression to demonstrate the relationship between the output dechirped pulse width and SA recovery time. The optimum approach for the generation of the shortest dechirped pulses in the dissipative soliton regime will be to construct a fiber laser cavity with a small normal cavity group velocity dispersion and use an SA with an appropriate recovery time.

Numerical Investigation of the Impact of the Saturable Absorber Recovery Time on the Mode-Locking Performance of Fiber Lasers

We investigated the impact of the recovery time of a saturable absorber (SA) on the mode-locking performance of a fiber laser. This study was conducted for two types of fiber cavities with different net cavity group velocity dispersion (GVD) at a wavelength of 1.55 μm: normal and anomalous. The impact of modulation depth variation was also analyzed. It was found that the recovery time of the SA has little influence on the output pulse characteristics in the case of the anomalous net cavity GVD due to an interplay between saturable absorption-induced pulse shaping and modulation instability-induced soliton evolution, irrespective of the SA operating in the fast or slow saturable absorption regime. However, the recovery time was found to have a significant impact on the output pulse characteristics for the case of a normal net cavity GVD. An SA operating in the fast saturable absorption regime produces mode-locked pulses with symmetric temporal shapes for the normal GVD cavity, whereas asymmetric pulses are generated in the slow saturable absorption regime. From the simulation results, the optimum recovery time range for fiber laser mode-locking is discussed.

Broadband tuning of ring-type cavity-dumped femtosecond optical parametric oscillator in the near-infrared.

We report a cavity-dumped optical parametric oscillator (OPO) with a ring-type cavity configuration, which is based on periodically poled lithium niobate gain synchronously pumped by a mode-locked Ti:sapphire laser. Because of reduced cavity loss and group velocity dispersion inherent to ring-cavity employment, a wide wavelength tuning capability from 1.02 to 1.65 μm was achieved by the simple displacement of a cavity mirror. At a wavelength of 1.28 μm, the cavity-dumped system provides femtosecond pulses with 42 nJ energy and 50% dumping efficiency. The group delay dispersion (GDD) of the OPO cavity could be characterized through the wavelength tuning behavior with cavity displacement, and its validity was confirmed by the numerical GDD calculation of each optical component within the cavity.

Bound states of different pulses based on third-order dispersion.

Bound states of double pulses with different wavelengths are observed in a Tm-doped passively mode-locked fiber laser with near-zero net cavity group-velocity dispersion and strong third-order dispersion. The double pulses in the bound states exhibit different pulse durations and peak powers. Simulations show that the two pulses experience different compressing and broadening processes during the intra-cavity evolution. This demonstration reveals the existence of a new form of bound states and enriches the nonlinear dynamics of multi-pulse mode locking.

Stable dispersion-managed soliton molecules in Yb-doped polarization-maintaining fiber laser with chirped fiber Bragg grating

We present stable dispersion-managed soliton (DMS) molecules in a passively mode-locked Yb-doped polarization-maintaining fiber laser based on chirped fiber Bragg grating in the anomalous dispersion regime. The generation of DMSs are characterized by their sech2-like spectral profile with no steep spectral edges, which is distinct from those of dissipative solitons generated in Yb-doped fiber lasers with a large net positive cavity group velocity dispersion regime. The pulse width is 4.8 ps if the sech2 profile is assumed. The corresponding pulses width could be compressed to 278 fs with grating pair compressor. Furthermore, DMS molecules exhibit multiple discrete equilibrium distances and a regular spectral modulation pattern. All these DMS molecules are stable in the sense that after being obtained they can remain several days. The proposed laser proves its great potential to future practical use in high-resolution optics for coding and optical communication.

Coexistence of dissipative soliton and stretched pulse in dual-wavelength mode-locked Tm-doped fiber laser with strong third-order dispersion.

Mode-locked lasers with strong high order dispersion exhibit rich nonlinear dynamics. Here we numerically and experimentally demonstrate coexistence of dissipative soliton (DS) and stretched pulse (SP) in a dual-wavelength mode-locked Tm-doped fiber laser with strong third-order dispersion (TOD), where the DS and SP show completely different pulse duration and peak power. Wavelength-dependent feature of the net cavity group-velocity dispersion (GVD) leaded by the strong TOD plays a key role for the coexistence patterns. To our best knowledge, this is the first demonstration of the coexistence of different mode-locked pulse regimes with strong laser cavity TOD.

Simultaneous emission of Gaussian-like and parabolic-like pulse waveforms in an erbium-doped dual-wavelength fiber laser

We report on the observation of different pulse formation dynamics in a nonlinear polarization evolution (NPE)-based broadband erbium-doped fiber laser when the net cavity group-velocity dispersion (GVD) is managed to be close to zero. The fiber laser can generate pulses with a single wavelength or dual wavelengths by adjusting the waveplates. When the laser operates in dual-wavelength emission, the output pulses corresponding to the two wavelengths exhibit Gaussian- and parabolic-like waveforms, respectively, indicating that the laser can simultaneously operate in stretched-pulse and self-similar regimes. The generation of dual-wavelength emission with different pulse waveforms can be attributed to an overdriven NPE switch acting on a chirped broadband pulse and different dispersion mechanisms. These findings provide a good foundation for comprehensively studying pulse formation dynamics in laser cavities.

Bound States of Dissipative Solitons in the Single-Mode Yb-Doped Fiber Laser

We present results of our research on the observation of a bound state of double dissipative-soliton operation of a passive mode-locked Yb-doped fiber laser based on the nonlinear polarization rotation mechanism through the proper adjustment of the wave plates. The generated dissipative solitons with large net positive cavity Group Velocity Dispersion (GVD) are characterized by their spectral profile of sharp peaks near edges, which are distinct from those of the conventional solitons in fiber lasers. By using an artificial saturable absorber, we have obtained stable single and double bound-state dissipative solitons. In all-normal-dispersion Yb-doped single-mode fiber lasers, the bound state of double dissipative solitons with a full-width at half-maximum of 7 ps, and a fixed pulse separation of 8 ps independent of the experimental conditions is achieved for the first time, to the best of our knowledge. Our result once again shows that the passively mode-locked fiber laser with large normal dispersion can help to explore dissipative soliton dynamics.

Dissipative soliton operation of a diode pumped Yb:NaY(WO₄)₂ laser.

We report on the dissipative soliton operation of a diode pumped Yb:NaY(WO₄)₂ (Yb:NYW) solid-state laser. The dissipative solitons and their features as the net cavity group velocity dispersion is changed from the normal to the anomalous dispersion regime are experimentally investigated. Taking advantage of the dissipative soliton shaping of the mode-locked pulses we have generated stable near transform-limited pulses as short as 54 fs. To our knowledge, this is so far the shortest pulse directly obtained from the mode-locked Yb:NYW oscillator.

Numerical study on the minimum modulation depth of a saturable absorber for stable fiber laser mode locking

We conducted a numerical study to investigate the minimum modulation depth of a saturable absorber that is essentially required for stable optical pulses to be generated from a passively mode-locked fiber laser cavity. More specifically, an extended nonlinear Schrodinger equation was numerically solved in order to analyze the impact of the cavity group velocity dispersion (GVD), cavity χ(3) nonlinearity, and saturation gain of an active fiber on the minimum modulation depth that is required. The net cavity GVD is shown to significantly influence the required minimum modulation depth level of a saturable absorber. A cavity with little net anomalous dispersion was found to be readily mode locked through the use of a saturable absorber with a very small amount of modulation depth. Furthermore, the reason that a fiber laser cavity with a zero cavity GVD becomes unstable and needs a much higher modulation depth was investigated, and such a condition was found to be associated with the fiber χ(3) nonlinearity. The minimum modulation depth was also shown to vary according to the saturation gain level of an active fiber.

Systematical analysis of mode-locked fiber lasers using single-walled carbon nanotube saturable absorbers

The output characteristics of the Er-doped mode-locked fiber laser using a single-walled carbon nanotube saturable absorber are investigated theoretically with a nonlinear Schrödinger equation and a saturable absorption equation using realistic parameters. Stable self-starting mode-locking pulses are achieved under net normal, net zero, and net anomalous cavity group velocity dispersion (GVD) respectively. A spectrum with a flat top is obtained from the net normal cavity GVD laser while a spectrum with Kelly side-bands is obtained from the net anomalous cavity GVD laser. The characteristics of the pulse duration changing with cavity GVD and modulation depth of the single-walled carbon nanotubes are discussed. The characteristics of the mode-locking pulses from net normal, net zero, and net anomalous cavity GVD mode-locked fiber lasers are compared. These systematical results are useful for designing mode-locked fiber lasers with saturable absorbers made by different kinds of carbon nano-materials.

Numerical investigation of wavelength tuning in a graphene-based mode-locked fiber laser

We numerically demonstrate a wavelength-tunable graphene-based mode-locked fiber laser with net anomalous cavity group-velocity dispersion. It is shown that by utilizing fiber birefringence, the central wavelength of mode-locked pulses could be continuously tuned over the range from 1553 to 1566 nm. The numerical results are in agreement with the experimental observations in the literature. The mechanism of wavelength tuning may be attributed to an artificial fiber birefringence-induced filter in the cavity.

Generalized characteristics of soliton in dispersion-managed fiber lasers

The generic characteristics of dispersion-managed fiber laser are systematic investigated experimentally. When the net cavity group-velocity dispersion (GVD) is large negative or positive, it exhibits the features of fiber laser constructed by purely negative or positive components, respectively. Furthermore, we demonstrate that two types of soliton formation mechanisms simultaneously act on one mode-locked pulse as the fiber laser operates in the vicinity of zero net cavity GVD. The features of mode-locked pulse depending on the interaction and competition of cavity dispersion, fiber nonlinearity, laser gain saturation and spectral filtering. In addition, the characteristics of noise-like pulse under different net cavity GVD are also experimentally investigated.

Bright–Dark Pulse Pair in a Figure-Eight Dispersion-Managed Passively Mode-Locked Fiber Laser

We report on the generation of bright–dark pulse pair in a figure-eight dispersion-managed (DM) passively mode-locked fiber laser with net anomalous cavity group velocity dispersion (GVD). The nonlinear amplifying loop mirror (NALM) is employed in this configuration to allow for passively mode-locked operation. Through carefully adjusting the polarization controllers (PCs), the bright–dark pulse pair could be easily achieved. Furthermore, it is found experimentally that the pulse pair is formed due to the cross coupling between the bright and dark pulses, which are located at two different wavebands.

Dark pulse generation in a dispersion-managed fiber laser

We report an experimental observation of dark pulse generation in a dispersion-managed erbium-doped fiber laser with net anomalous cavity group-velocity dispersion. It is found that apart from the bright soliton pulses, dark pulses with spectral sidebands could be obtained in the laser under appropriate operating conditions. The generation of dark pulses may be attributed to soliton shaping in the cavity.

Experimental Observation of Dark Soliton Emitting with Spectral Sideband in an All-Fiber Ring Cavity Laser

The dark soliton pulse with spectral sideband is experimentally observed in a dispersion-managed all-fiber ring laser with net negative cavity group velocity dispersion. We find that, for single or multiple dark solitons, the spectral sidebands always appear and exhibit asymmetric characteristics which are similar to bright solitons. The experimental measurements of spectral sideband positions are carried out and the results are in good agreement with the calculated values. Our results show that spectral sideband effect is also an intrinsic feature of a dark soliton fiber laser.

Observation of dark pulse in a dispersion-managed fiber ring laser

The observation of dark pulse in a dispersion-managed fiber ring laser with net negative cavity group velocity dispersion (GVD) is reported. Both bright and dark pulses can be obtained in our fiber laser. When we appropriately adjust the cavity birefringence to achieve triple-wavelength mode-locked operation in the laser by rotating the polarization controller, the bright pulse could be switched to dark pulse. It is believed that the dark dispersion-managed (DM) pulse generation is caused by the linear and nonlinear intermodulation effects among the three wavelength pulses.