Deyuan Shen

Dark soliton fiber lasers.

Dark soliton formation and soliton dynamics in all-normal dispersion cavity fiber ring lasers without an anti-saturable absorber in cavity is studied both theoretically and numerically. It is shown that under suitable conditions the dark solitons formed could be described by the nonlinear Schrödinger equation. The dark soliton formation in an all-normal-dispersion cavity erbium-doped fiber ring laser without an anti-saturable absorber in cavity is first experimentally demonstrated. Individual dark solitons are experimentally identified. Excellent agreement between theory and experiment is observed.

Room temperature continuous-wave laser performance of LD pumped Er:Lu 2 O 3 and Er:Y 2 O 3 ceramic at 2.7 μm

We report the demonstration of continue wave operation of diode end-pumped Er:Y2O3 and Er:Lu2O3 ceramic lasers operating at 2.7 μm at room temperature. The maximum output power of 320 mW and 611 mW was obtained from the Er:Y2O3 and Er:Lu2O3 ceramic lasers, with slope efficiency of 6.5% and 7.6%, respectively. Characteristics of Red-shift in lasing wavelength of the ceramic lasers was investigated and discussed. The study indicates that under 967 nm and 976 nm LD pumping, 15 at.% Er-doped Lu2O3 ceramic exhibit a better performance than that of Y2O3 at room temperature.

Simultaneous pulse generation of orthogonally polarized dual-wavelength at 1091 and 1095 nm by coupled stimulated Raman scattering

Intracavity coupled Raman conversions in KTP and KTA driven by a laser diode (LD) pumped Nd:YAG/Cr(4+):YAG 1064 nm laser is demonstrated in this paper. Simultaneous pulse generation of orthogonally polarized dual-wavelength at 1091 and 1095 nm are achieved by balancing the Raman gain of KTP and KTA. Under the LD pump power of 8.1 W, the maximum average output powers at 1091 and 1095 nm are 170 and 150 mW, respectively. The corresponding pulse width and repetition rate are measured to be 3.3 ns and 11.2 kHz, with the pulse peak powers calculated to be 4.6 and 4.1 kW, respectively. The laser source with such small wavelength separation and orthogonal polarization provides the interest for terahertz generation in the 1 THz range. Our study provides a simple and flexible method to achieve orthogonally polarized dual-wavelength laser source by Raman-based intracavity coupled nonlinear frequency conversions.

Vector Soliton Generation in a Tm Fiber Laser

Vector soliton generation is experimentally demonstrated in an all-fiber Tm/Ho-doped fiber laser operated at 1951 nm. To the best of our knowledge, it is the first clear evidence of group-velocity-locked vector soliton formation around 2 μm. Numerical simulation well reproduces the experimental observation and suggests that the central wavelength shift between the two orthogonal polarized components of the vector soliton is determined by the cavity birefringence. The central wavelength shift increased with the increasing of the cavity birefringence. However, the vector solitons become linearly polarized if the cavity birefringence is too strong. Experimental observation and numerical simulations both suggest that the vector soliton generation is wavelength independent.

Sub-80 femtosecond pulses generation from a diode-pumped mode-locked Nd:Ca 3 La 2 (BO 3 ) 4 disordered crystal laser

We experimentally demonstrated a diode-pumped sub-80 fs Nd:Ca3La2(BO3)4 disordered crystal laser. Pumping by an 808 nm fiber coupled laser diode, stable continuous-wave mode-locked pulses as short as 79 fs were achieved with a semiconductor saturable absorber mirror (SESAM). The ultrashort pulses had a repetition rate of ∼98.9  MHz at the central wavelength of about 1068 nm. To the best of our knowledge, this is the first demonstration of sub-100 fs pulses and the shortest mode-locked pulses generated from the Nd3+-doped crystal lasers.

Nanosecond nonlinear Čerenkov conical beams generation by intracavity sum frequency mixing in KTiOAsO 4 crystal

Nanosecond Čerenkov-type conical beam at 628 nm is obtained by intracavity sum frequency mixing (SFM) of 1064 and 1534 nm in KTiOAsO(4) (KTA) crystal. The 1534 nm signal generated by the KTA optical parametric oscillation (OPO), respectively, interacts with the orthogonally polarized 1064 nm radiations by the nonlinear Čerenkov SFM, emitting two red rings with cone angles of 11.4° and 16.0°, respectively. Multidomain structure observed in the KTA crystal can account for the corresponding phenomenon. The KTA crystal simultaneously serves as OPO medium and Čerenkov radiation emitter in this experiment, indicating that it is a promising multifunctional nonlinear crystal material. Furthermore, the naturally grown crystal combined with intracavity Čerenkov-type configuration will provide a simple and compact approach, opening a door for the wide application of nonlinear Čerenkov radiation sources due to its cost-effectiveness.

High efficiency Tm:YAG slab laser with hundred-watts-level output power.

We report on a hundred-watts-level high power Tm:YAG slab laser system operating at room temperature. The laser has a threshold pump power of 46.7 W, benefiting from the good mode matching of an end-pumping scheme and the excellent heat-dissipation capability of our cooling system. At 350 W of incident pump power, 100 W of output power at ∼2015  nm has been generated, corresponding to a slope efficiency of 33.6% with respect to the incident pump power and an optical-to-optical conversion efficiency of 28.6%. As far as we know, this is the highest optical-to-optical conversion efficiency so far achieved in a high power Tm:YAG laser system operating at a hundred-watts level.

Soliton-dark pulse pair formation in birefringent cavity fiber lasers through cross phase coupling.

We report on the experimental observation of soliton-dark pulse pair formation in a birefringent cavity fiber laser. Temporal cavity solitons are formed in one polarization mode of the cavity. It is observed that associated with each of the cavity solitons a dark pulse is induced on the CW background of the orthogonal polarization mode. We show that the dark pulse formation is a result of the incoherent cross polarization coupling between the soliton and the CW beam and has a mechanism similar to that of the polarization domain formation observed in the fiber lasers.

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.

Optical properties of Ho:YAG and Ho:LuAG polycrystalline transparent ceramics

Lutetium Aluminum Garnet (LuAG) is a garnet isostructure similar to Yttrium Aluminum Garnet (YAG). High quality Ho3+ doped YAG and LuAG transparent polycrystalline ceramics were fabricated successfully by a reactive sintering method under vacuum. The microstructures, absorption spectrum, fluorescence spectrum and the laser performances of Ho:YAG and Ho:LuAG ceramics were systematically investigated. The in-line transmittances of Ho:YAG ceramic in the visible and infrared region are higher than 82% and 84%. The absorption coefficient of 1.0 at.% Ho:LuAG is 0.88 cm−1 at 1906 nm and its absorption cross section is 0.62 × 10−20 cm2.