D. Y. Tang

A graphene-based passively Q-switched polycrystalline Er:YAG ceramic laser operating at 1645?nm

Efficient passive Q-switching operation of a 1532?nm in-band pumped polycrystalline Er:YAG ceramic 1645?nm laser is demonstrated in this work. Graphene deposited on a quartz substrate was used as the saturable absorber for the Q-switching operation. Under an incident pump power of 4.14?W, an average output power of 528?mW was obtained, with the pulse energy and pulse repetition rate being 7.08??J and 74.6?kHz, respectively.

Manipulation of Group-Velocity-Locked Vector Solitons From Fiber Lasers

Manipulation of group-velocity-locked vector solitons (GVLVSs) is numerically proposed and experimentally demonstrated. A pseudo-high-order GVLVS could be generated from a fundamental GVLVS with the help of a polarization-resolved system. Specifically, a pseudo-high-order GVLVS with a two-humped pulse along one polarization and a single-humped pulse along the orthogonal polarization could be obtained. The phase difference between the two humps could be 180°.

Mechanism of Spectrum Moving, Narrowing, Broadening, and Wavelength Switching of Dissipative Solitons in All-Normal-Dispersion Yb-Fiber Lasers

We report experimental observations and numerical simulation results on the spectrum moving, narrowing, broadening, and wavelength switching of dissipative solitons (DSs) in an all-normal-dispersion Yb-fiber laser that is passively mode-locked by using the nonlinear polarization rotation (NPR) technique. We found numerically that the DS spectrum moving, together with spectrum narrowing/broadening, is caused by the effective gain profile change resulted from the moving of the artificial spectral filter. Furthermore, we show that the wavelength switching observed in the laser is a natural consequence of the effective gain switching. The moving of the artificial spectral filter could be originated from either the cavity birefringence change or the polarizer rotation. Due to the broad gain and the artificial birefringent filter introduced by the NPR technique, apart from the central wavelength shifting and bandwidth changing, wavelength switching of DSs could be obtained by simply rotating the polarizer. Numerical simulations well reproduced the experimental observations. Our results suggest that extra effort should be made for wavelength tuning if there is any polarization-dependent component in the cavity as the wavelength switching will interrupt the continuously wavelength shift.

Bound States of Vector Dissipative Solitons

We report on the first experimental observation of bound states of vector dissipative solitons (VDSs) in an erbium-doped fiber laser mode locked with a semiconductor saturable absorber mirror and operated in the normal dispersion regime. Bound states of either the coherently coupled VDSs or the incoherently coupled VDSs were obtained. No polarization evolution was observed for either of the bound VDSs. Both types of bound VDSs have a fixed soliton separation, which is invariant to the laser operation condition. Numerical simulations confirm the experimental observations.

Initial conditions for dark soliton generation in normal-dispersion fiber lasers.

We report results of numerical simulations on the various initial conditions for dark soliton generation in an all-normal-dispersion fiber laser. All the dark solitons generated are odd dark solitons. Differently from the dark soliton generation in fibers, where an arbitrary dip could evolve into a dark soliton, it is found that the dark soliton can originate only from an initial dip with a certain parameter requirement. A bright pulse with either a hyperbolic secant square, Gaussian, or Lorentz profile can be developed into a dark soliton, provided that the parameters of the initial bright pulse are selected. Dark solitons can be generated in fiber lasers only if there is a phase jump, and this phase jump can be maintained and evolve to π during the pulse evolution.

A passively Q-switched Er:LuYAG laser with a graphene saturable absorber

A stable passively Q-switched Er:LuYAG laser resonantly pumped by an Er, Yb co-doped fiber laser was demonstrated using a graphene-based saturable absorber. At an incident pump power of 5.5 W, a maximum average output power of 460 mW at a central wavelength of 1648 nm was obtained with a shortest pulse duration of 2.05 μs, a repetition rate of 78.9 kHz and a pulse energy of 5.84 μJ.

Generation of High-Order Group-Velocity-Locked Vector Solitons

We report numerical simulations on the high-order group-velocity-locked vector soliton (GVLVS) generation based on the fundamental GVLVS. The high-order GVLVS generated is characterized with a two-humped pulse along one polarization and a single-humped pulse along the orthogonal polarization. The phase difference between the two humps could be 180° It is found that, by appropriately setting the time separation between the two components of the fundamental GVLVS, the high-order GVLVS with different pulsewidth and pulse intensity could be obtained. Either type “1+2” or “2+2” high-order GVLVS could be obtained.

Impulsive stimulated Raman scattering in tetragonal GdVO4 single crystal: many-phonon Stokes and cross-cascaded lasing

For the first time we excited four-phonon impulsive stimulated Raman scattering (SRS) in tetragonal GdVO4 single crystal under near-IR femtosecond pumping. All of its recorded χ (3)-nonlinear Stokes cascaded and cross-cascaded fully coherent lasing emissions were identified at internal vibrations of the [VO4]3− units of the studied vanadate. The obtained new fundamental knowledge could significantly enrich the functional potential of this crystal, which is a host crystal for trivalent lanthanide lasants and attractive gain media for Raman laser converters and self-SRS lasers.

Compact single-frequency Tm:YAG ceramic laser with a volume Bragg grating

We demonstrated a compact high-power single-frequency Tm:YAG ceramic laser operating at 1999.7 nm. Single-frequency operation was achieved by incorporating a reflection volume Bragg grating (VBG) in a laser with a short cavity length. The laser emission has a spectral linewidth of ?10?MHz and a maximum output power of 1.4?W, which is limited by the pump-induced thermal-lens effect of the laser.

A Diode-Pumped Dual-Wavelength Tm, Ho: YAG Ceramic Laser

A diode-pumped dual-wavelength CW Tm, Ho: YAG ceramic laser was demonstrated for the first time to our knowledge. A maximum output power of ~1.2 W with a beam quality factor M2 = 1.19 has been generated from the 3at.% Tm, 0.5at.% Ho: YAG ceramic, corresponding to a slope efficiency of 16.7% with respect to the absorbed pump power. This Tm, Ho: YAG ceramic laser operated at dual-wavelengths around 2090 and 2096 nm. With the increase in the absorbed pump power and the output coupler transmittance, blue-shift of the emission wavelength was observed.