Net 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.

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.

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.

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.

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.

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.

Bound states of dispersion-managed solitons in a fiber laser at near zero dispersion

We report on the observation of various bound states of dispersion-managed (DM) solitons in a passively mode-locked erbium-doped fiber ring laser at near zero net cavity group velocity dispersion (GVD). The generated DM solitons are characterized by their Gaussian-like spectral profile with no sidebands, which is distinct from those of the conventional solitons generated in fiber lasers with large net negative cavity GVD, of the parabolic pulses generated in fiber lasers with positive cavity GVD and negligible gain saturation and bandwidth limiting, and of the gain-guided solitons generated in fiber lasers with large positive cavity GVD. Furthermore, bound states of DM solitons with fixed soliton separations are also observed. We show that these bound solitons can function as a unit to form bound states themselves. Numerical simulations verified our experimental observations.

Period-doubling of dispersion-managed solitons in an Erbium-doped fiber laser at around zero dispersion

Period-doubling of dispersion-managed solitons in an Erbium-doped fiber ring laser operating at the near zero net cavity group velocity dispersion region was experimentally observed. The generated dispersion-managed solitons of the laser are characterized by their near Gaussian spectral profiles and no sidebands. Numerical simulations verified our experimental observations and showed that the period-doubling could occur both in the positive and negative near zero net cavity group velocity dispersion regions, which suggests that the occurrence of the period-doubling is an intrinsic feature of the mode-locking fiber lasers and independent of the concrete mode-locked pulse profile.

Coexistence and competition between different soliton-shaping mechanisms in a laser

There exist two distinctive types of soliton-shaping mechanisms in mode-locked fiber lasers: one is the balance between the fiber nonlinear Kerr effect and the linear cavity dispersion, and the other one is that caused by the laser gain saturation and dispersion. We show both numerically and experimentally that as the net cavity group velocity dispersion approaches zero, the two types of soliton-shaping mechanisms coexist in a laser. Depending on the laser operation, either of them could dominate the pulse shaping in a laser. And as a result of their competition, the stable soliton formed in the cavity dispersion regime could have different temporal and spectral profiles.