Normal Cavity Dispersion Research Articles

280 GHz dark soliton fiber laser.

We report on an ultrahigh repetition rate dark soliton fiber laser. We show both numerically and experimentally that by taking advantage of the cavity self-induced modulation instability and the dark soliton formation in a net normal dispersion cavity fiber laser, stable ultrahigh repetition rate dark soliton trains can be formed in a dispersion-managed cavity fiber laser. Stable dark soliton trains with a repetition rate as high as ∼280 GHz have been generated in our experiment. Numerical simulations have shown that the effective gain bandwidth limitation plays an important role on the stabilization of the formed dark solitons in the laser.

Bright and Dark Square Pulses Generated From a Graphene-Oxide Mode-Locked Ytterbium-Doped Fiber Laser

The observation of the bright pulses and dark square pulses in a graphene-oxide saturable absorber (GOSA) passively mode-locked ytterbium-doped fiber laser has been investigated experimentally. Bright pulses are achieved at a pump power of ~ 200 mW. However, the dark-square-pulse generation starts at a much higher pump power of ~ 450 mW. At the maximum pump power of 600 mW, the dark-square-pulse bunches and harmonic mode locking (HML) can be also obtained by tuning the polarization controller (PC) to different orientations. It is the first demonstration of the bunches and HML of dark square pulses in a GOSA passively mode-locked ytterbium-doped fiber laser with large normal dispersion cavity.

Experimental studies of multiple pulses in a passively ytterbium-doped fiber laser based on graphene-oxide saturable absorber

The different multiple pulse phenomena are experimentally studied in a passively mode-locked ytterbium-doped fiber laser based on graphene-oxide saturable absorber (GOSA) with net normal dispersion cavity. At the same pump power with different polarization orientations, we observe the multiple pulse phenomena, including harmonic mode-locking of rectangular pulses, dissipative solitons, quasi-harmonic mode-locking, periodical peak modulation, multipulse bunches, multipulse cluster, and chaotic multipulse. The inserted 2 nm narrow bandwidth filter is important for limiting the gain bandwidth and shaping pulses. Adjusting the polarization controller is equivalent to changing the gain in the laser cavity, which is the main reason for the formation of different multiple pulses states. This is the first time that different multiple pulses states have been observed in an-normal-dispersion Yb-doped fiber laser with graphene-oxide saturable absorber. These results could extend the understanding of multiple pulse dynamics in GOSA mode-locked fiber lasers.

Soliton rains in a graphene-oxide passively mode-locked ytterbium-doped fiber laser with all-normal dispersion

We experimentally investigated soliton rains in an ytterbium-doped fiber (YDF) laser with a net normal dispersion cavity using a graphene-oxide (GO) saturable absorber (SA). The 195 m-long-cavity, the fiber birefringence filter and the inserted 2.5 nm narrow bandwidth filter play important roles in the formation of the soliton rains. The soliton rain states can be changed by the effective gain bandwidth of the laser. The experimental results can be conducive to an understanding of dissipative soliton features and mode-locking dynamics in all-normal dispersion fiber lasers with GOSAs. To the best of our knowledge, this is the first demonstration of soliton rains in a GOSA passively mode-locked YDF laser with a net normal dispersion cavity.

132 μm mode-locked bismuth-doped fiber laser operating in anomalous and normal dispersion regimes

We demonstrate a 1.32 μm mode-locked bismuth fiber laser operating in both anomalous and normal dispersion regimes. In anomalous dispersion regime, achieved by using 13 nm/cm linearly chirped fiber Bragg grating, the laser exhibits multiple soliton operation with pulse duration of 2.51 ps. With the net normal cavity dispersion, the single-pulse operation with higher power has been obtained by avoiding the limitations generic to conservative soliton systems.

Numerically Analysis on the Role of the Modulation Depth in an All-Fiber Erbium-Doped Laser with Normal Cavity Dispersion

We numerically solve the Haus master equation by split Fourier transform method under Fortran and MATLAB environment to investigate the role of the modulation depth in a mode-locked all-fiber erbium laser with normal cavity dispersion. Through our simulation, we have demonstrated that the modulation depth of the saturable absorber (SA) significantly affects the mode-locking energy, per pulse energy, pulse duration and spectral bandwidth at the laser output for a given cavity design.

Sub-50 fs Yb-doped laser with anomalous-dispersion photonic crystal fiber

We report on the generation of 42 fs pulses at 1 μm in a completely fiber-integrated format, which are, to the best of our knowledge, the shortest from all-fiber-integrated Yb-doped fiber lasers to date. The ring fiber cavity incorporates anomalous-dispersion, solid-core photonic crystal fiber with low birefringence, which acts as a broadband, in-fiber Lyot filter to facilitate mode locking. The oscillator operates in the stretched-pulse regime under slight normal net cavity dispersion. The cavity generates 4.7 ps long pulses with a spectral bandwidth of 58.2 nm, which are dechirped to 42 fs via a grating pair compressor outside of the cavity. Relative intensity noise (RIN) of the laser is characterized, with the integrated RIN found to be 0.026% in the 3 Hz-250 kHz frequency range.

Observations of bound states of two and three dissipative solitons in a figure-eight laser in a normal dispersion regime

Dissipative bound-state solitons exhibiting a trapezoid spectral profile and a regular modulation pattern are observed experimentally in a figure-eight fiber laser with large normal cavity dispersion for the first time, to the best of the author’s knowledge. The soliton pairs have a pulse duration T0 of about 800 fs and a peak-to-peak separation of about 8T0. With the appropriate increase of the pumping strength, the proposed laser generates a bound state of three solitons with a pulse duration T0 of about 460 fs and a separation between adjacent pulses of about 15T0. Experimental results show that the bound-state solitons are strongly stable and suggest that they are formed by direct soliton interaction.

Control over the performance characteristics of a passively mode-locked erbium-doped fibre ring laser

We report an all-fibre ultrashort pulse erbium-doped ring laser passively mode-locked by single-wall carbon nanotubes dispersed in carboxymethylcellulose-based polymer films. Owing to intracavity dispersion management and controlled absorption in the polymer films, the laser is capable of generating both femto- and picosecond pulses of various shapes in the spectral range . We have demonstrated and investigated the generation of almost transform-limited, inversely modified solitons at a high normal cavity dispersion.

Transform-limited pulse generation in normal cavity dispersion erbium doped single-walled carbon nanotubes mode-locked fiber ring laser

We demonstrate an erbium doped fiber ring laser mode-locked with a carboxymetylcellulose high-optical quality film with dispersed single-walled carbon nanotubes (SWCNT). The laser with large normal net cavity dispersion generates near bandwidth-limited picosecond inverse modified soliton pulses at 1.56 µm.

Dissipative soliton generation from a graphene oxide mode-locked Er-doped fiber laser

We demonstrated dissipative soliton obtained from a graphene oxide mode-locked Er-doped fiber laser, which operated in normal dispersion cavity by employing the dispersion compensation fiber. The highly chirped pulses at the repetition rate of 19.5 MHz can be compressed from 11 ps to 542 fs by using single mode fiber. Numerical simulations were in good agreement with the experimental results. The hydrophilic graphene oxide with easier fabrication shows great potential to be a novel low-cost saturable absorber in reliable and compact mode-locked fiber laser system.

Ultrafast Raman laser mode-locked by nanotubes

We demonstrate passive mode-locking of a Raman fiber laser using a nanotube-based saturable absorber coupled to a net normal dispersion cavity. This generates highly chirped 500 ps pulses. These are then compressed down to 2 ps, with 1.4 kW peak power, making it a simple wavelength-versatile source for various applications.

Experimental observation and analysis of novel pulse properties in erbium-doped fiber ring laser with normal cavity dispersion

We demonstrate the experimental observation of different operation states in erbium-doped fiber ring laser with normal cavity dispersion. The Q-switching, Q-switching mode-locking (QML), continuous wave mode-locking (CML), harmonic mode-locking (HML), double-pulse and multiple-pulse operation states can be manipulated by only adjusting the polarization controller with the same pump power. The output spectral bandwidth and pulse width of operation states are measured. The central wavelength dynamics of different operation states achieved by adjusting the polarization controller are also observed and analyzed. It is shown that pulse width, polarization, chirp and stability of different operation states are diverse by using nonlinear polarization rotation technique.

All-fiber Er-doped dissipative soliton laser based on evanescent field interaction with carbon nanotube saturable absorber

We report on an Er-doped fiber pulse laser at large net normal dispersion cavity by employing a dispersion compensating fiber in combination with a single-walled carbon nanotube (SWCNT) saturable absorber. A SWCNT/polymer composite film uniformly spin-coated on the side-polished fiber is prepared for robust and efficient nonlinear interaction with evanescent fields in the waveguide expecting increase of optical and thermal damage threshold compared to previously reported direct coating of SWCNTs on fiber ferrules. The fabricated dissipative soliton fiber laser exhibits high average output power of 55.6 mW, corresponding to pulse energy about 2.35 nJ. Highly chirped 5.8 ps pulses are generated with a spectral bandwidth of 13.9 nm and compressed down to 226 fs using additional length of conventional optical fiber at extra-cavity.

Statistical properties of partially coherent cw fiber lasers

We perform a detailed quantitative numerical analysis of a partially coherent quasi-cw fiber laser on the example of a high-Q normal dispersion cavity Raman fiber laser. The key role of precise spectral performances of fiber Bragg gratings forming the laser cavity is clarified. It is shown that cross-phase modulation between the pump and Stokes waves does not affect the generation. Amplitudes of different longitudinal modes strongly fluctuate, obeying the Gaussian distribution. As the intensity statistics is noticeably nonexponential, longitudinal modes should be correlated.

Experimental investigation of square dissipative soliton generation and propagation

We have experimentally investigated the generation and propagation of square dissipative solitons emitted from an erbium-doped fiber laser with large normal cavity dispersion. The square pulse exhibits an approximately Gaussian spectral profile and large frequency chirp on its edges. When the square pulse propagates through a segment of single-mode fiber (SMF), it can be shaped to a Gaussian pulse and the corresponding spectrum will have a redshift with a prolonged wing on the longer wavelength. Our experiments show that the pulse evolution in the SMF is determined by the combined effects of the fiber dispersion, intrapulse Raman scattering, and the pulse initial chirps.

Investigation of soliton pairs in an erbium-doped fiber laser with large normal dispersion

We experimentally investigate the soliton pairs in a passively mode-locked erbium-doped fiber laser with large normal cavity dispersion. By adjusting the polarization state, four different kinds of soliton pairs are achieved. The pulses in soliton pairs exhibit different temporal separations, and show randomly distributed spikes on the top-flat of spectra. The pulse–pulse interactions in the soliton pairs are investigated, and it is suggested that the pulse separation, pulse duration, and their relative intensities all determine the strength of pulse interactions.

Multistability evolution and hysteresis phenomena of dissipative solitons in a passively mode-locked fiber laser with large normal cavity dispersion

We report on the experimental observations of multiple dissipative solitons in a passively mode-locked fiber laser with large normal cavity dispersion. The dynamic evolution of solitons as a function of the pump power is demonstrated, alternately evolving on the stable and unstable states. The proposed laser produces the multiple solitons of up to ten for the pump power of about 406 mW. Multistability and hysteresis phenomena observed in this report are qualitatively distinct from those observed in the large net-anomalous-dispersion conventional-soliton fiber lasers. The experimental results suggest that the accumulation of excessive pulse chirps together with the nonlinear polarization effect play key roles in the multistability operation of dissipative solitons.

Impact of spectral filtering on a weak breathing laser based on AS-Yb-PBGF with large net normal dispersion cavity

We have investigated numerically the effects of the spectral filtering on the temporal and spectral properties of the pulse with large net normal cavity dispersion in a weak breathing passively mode-locked ring laser based on all-solid Yb-doped photonic bandgap fiber (AS-Yb-PBGF), which gives the laser gain and anomalous dispersion simultaneously. The specific range of spectral filter bandwidth is indispensable for obtaining high-peak-power pulse in a given highly chirped pulse laser system under a fixed pump level. The shortening of the pulse durations and the shaving of the sharp peaks at the steep edges of the spectrum by the spectral filter are demonstrated. Moreover, the advantage of the weak breathing fiber laser by introducing the AS-Yb-PBGF for scaling up the peak power and shortening the pulse width is investigated, and the effect of third-order dispersion induced by AS-Yb-PBGF on the pulse shape is also discussed.

High‐energy femtosecond fiber lasers based on pulse propagation at normal dispersion

AbstractThe generation and stable propagation of ultrashort optical pulses tend to be limited by accumulation of excessive nonlinear phase shifts. The limitations are particularly challenging in fiber‐based devices, and as a result, short‐pulse fiber lasers have lagged behind bulk solid‐state lasers in performance. This article will review several new modes of pulse formation and propagation in fiber lasers. These modes exist with large normal cavity dispersion, and so are qualitatively distinct from the soliton‐like processes that have been exploited effectively in modern femtosecond lasers but which are also quite limiting. Self‐similar evolution can stabilize high‐energy pulses in fiber lasers, and this leads to order‐of‐magnitude increases in performance: fiber lasers that generate 10 nJ pulses of 100 fs duration are now possible. Pulse‐shaping based on spectral filtering of a phase‐modulated pulse yields similar performance, from lasers that have no intracavity dispersion control. These new modes feature highly‐chirped pulses in the laser cavity, and a theoretical framework offers the possibility of unifying our view of normal‐dispersion femtosecond lasers. Instruments based on these new pulse‐shaping mechanisms offer performance that is comparable to that of solid‐state lasers but with the major practical advantages of fiber.