Cnoidal waves and their soliton limits in single mode fiber lasers

Cnoidal waves are a type of nonlinear periodic wave solutions of the nonlinear dynamic equations.They are well known in fluid dynamics,but it is not the case in optics.In this paper we show both experimentally and numerically that cnoidal waves could be formed in a fiber laser either in the net normal or net anomalous cavity dispersion regime,especially because,as the pump power is increased,the formed cnoidal waves could eventually evolve into a train of bright(in the net anomalous cavity dispersion regime)or dark(in the net normal cavity dispersion regime)solitons.Numerical simulations of the laser operation based on the extended nonlinear Schrödinger equation(NLSE)have well reproduced the experimental observations.The result not only explains why solitons can still be formed in a fiber laser even without mode locking but also suggests a new effective way of automatic stable periodic pulse train generation in lasers with a nonlinear cavity.

Monolayer Graphene as a Saturable Absorber in a Mode-Locked Laser

We demonstrate that the intrinsic properties of monolayer graphene allow it to act as a more effective saturable absorber for mode-locking fiber lasers when compared to multilayer graphene. The absorption of monolayer graphene can be saturated at lower excitation intensity compared to multilayer graphene, graphene with wrinkle-like defects, or functionalized graphene. Monolayer graphene has a remarkably large modulation depth of 65.9%, whereas the modulation depth of multilayer graphene is greatly reduced due to nonsaturable absorption and scattering loss. Picosecond ultrafast laser pulses （1.23 ps） can be generated using monolayer graphene as a saturable absorber. Due to the ultrafast relaxation time, larger modulation depth and lower scattering loss of monolayer graphene, it performs better than multilayer graphene in terms of pulse shaping ability, pulse stability, and output energy.

On-chip photonic Fourier transform with surface plasmon polaritons

The Fourier transform(FT),a cornerstone of optical processing,enables rapid evaluation of fundamental mathematical operations,such as derivatives and integrals.Conventionally,a converging lens performs an optical FT in free space when light passes through it.The speed of the transformation is limited by the thickness and the focal length of the lens.By using the wave nature of surface plasmon polaritons(SPPs),here we demonstrate that the FT can be implemented in a planar configuration with a minimal propagation distance of around 10 mm,resulting in an increase of speed by four to five orders of magnitude.The photonic FT was tested by synthesizing intricate SPP waves with their Fourier components.The reduced dimensionality in the minuscule device allows the future development of an ultrafast on-chip photonic information processing platform for large-scale optical computing.

A stable and efficient La-doped MIL-53(Al)/ZnO photocatalyst for sulfamethazine degradation

Photocatalytic technology can solve various environmental pollution problems,especially antibiotic pollution.A novel La-doped MIL-53(Al)/ZnO composite material was successfully synthesized by a combination of hydrothermal method and calcination,showing high photocatalytic degradation percent of sulfamethazine(SMT).The 2 mol%La MIL-53(Al)/ZnO photocatalyst shows the highest degradation efficiency toward SMT(92%)within 120 min,which is 4.1 times higher than pure ZnO(increased from 18%to 92%).In addition,the degradation analysis of SMT by high performance liquid chromatography proves that the products are CO_(2) and H_(2)O.The improved photocatalytic activity is mostly caused by the following factors.(1)Doping La ions can decrease the band gap of ZnO,enhance light response,and effectively enhance the separation rate of photo-generated holes and electrons.(2)MIL-53(Al)can adsorb SMT and promote the separation of electron.This work shows that the synthesized La-doped MIL-53(Al)/ZnO photocatalyst is expected to be used as a green and effective method for treatment of environment water pollution.

High transparency Pr:Y_(2)O_(3) ceramics:A promising gain medium for red emission solid-state lasers

Highly transparent 0.5 and 1.0 at%Pr-doped Y_(2)O_(3)ceramics were fabricated by vacuum sintering plus hot isostatic pressing(HIP)treatment.The selection of suitable pre-sintering temperatures and right microstructures before HIP was critical to obtain high density of the final sintered bodies.The well-densified ceramics had pore-free microstructures with an average grain size of about 1μm.It was also found that the charge states of the Pr ions could be changed through regulating the annealing atmospheres,resulting in different absorption and emission characteristics in the visible wavelength region.Annealing in reducing atmosphere(5%H_(2)/95%Ar)favored the formation of Pr^(3+),resulting in stronger red emissions,while annealing in oxygen atmosphere led to the rise of lattice constant due to the concentration increase of oxygen interstitials.The H_(2)/Ar-annealed 0.5 at%Pr:Y_(2)O_(3)ceramics exhibited strong red emission at 600–675 nm,which may be a promising gain material for red solid-state lasers.

Tunable and switchable harmonic h-shaped pulse generation in a 3.03 km ultralong mode-locked thulium-doped fiber laser

We experimentally demonstrated a type of tunable and switchable harmonic h-shaped pulse generation in a thulium-doped fiber(TDF) laser passively mode locked by using an ultralong nonlinear optical loop mirror.The total cavity length was ～3.03 km, the longest ever built for a TDF laser to our best knowledge, which resulted in an ultralarge anomalous dispersion over -200 ps^2 around the emission wavelength. The produced h-shaped pulse can operate either in a fundamental or in a high-order harmonic mode-locking(HML) state depending on pump power and intra-cavity polarization state(PS). The pulse duration, no matter of the operation state, was tunable with pump power. However, pulse breaking and self-organizing occurred, resulting in high-order HML,when the pump power increased above a threshold. At a fixed pump power, the order of HML was switchable from one to another by manipulating the PS. Switching from the 8 th up to the 48 th order of HML was achieved with a fixed pump power of ～4.15 W. Our results revealed the detailed evolution and switching characteristics of the HML and individual pulse envelope with respect to both the pump power and PS. We have also discussed in detail the mechanisms of both the h-shaped pulse generation and the switching of its HML. This contribution would be helpful for further in-depth study on the underlying dynamics of long-duration particular-envelope pulses with ultralarge anomalous dispersion and ultralong roundtrip time.

Fabrication and comprehensive structural and spectroscopic properties of Er:Y_(2)O_(3)transparent ceramics

Transparent Er:Y_(2)O_(3)ceramics with sub-micron grain size(<1μm)were fabricated by using one-step vacuum sintering followed by hot isostatic pressing(HIPing)technique.The transmission of the undoped Y_(2)O_(3)reaches 83%.The structural characteristics including the phonon energy were investigated through X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)analysis and scanning electron microscopy(SEM)measurement.The overall spectroscopic properties of transmission,fluorescence emission up to 3000 nm,lifetime,up-conversion luminescence,and refractive index were systematically studied for both 0.25 at%and 7.0 at%Er:Y_(2)O_(3)ceramics with different thicknesses.The comparison of the spectra of the fluorescence emission and up-conversion luminescence under both 976 and 808 nm laser excitation was performed.The multiple high-energy-state transitional processes after the excited state absorption(ESA)processes involved in the up-conversion are discriminated between the multi-phonon non-radiative transitions and the radiative transitions according to the measured maximum phonon vibrational energy.The calculation was performed based on the Judd-Ofelt theory.

Watt-level broadly wavelength tunable mode-locked solid-state laser in the 2 μm water absorption region

We report on broadly wavelength-tunable passive mode-locking with high power operating at the 2 μm water absorption band in a Tm:CYA crystal laser. With a simple quartz plate, stable mode-locking wavelengths can be tuned from 1874 to 1973 nm, with a tunable wavelength range up to ~100 nm and maximum output power up to 1.35 W. The bandwidth is narrow as ~6 GHz, corresponding to a high coherence. To our knowledge, this is the first demonstration of wavelength-tunable mode-locking with watt-level in the 2 μm water absorption band.The high temporal coherent laser can be further applied in spectroscopy, the efficient excitation of molecules, sensing, and quantum optics.

Novel optical soliton molecules formed in a fiber laser with near-zero net cavity dispersion

Soliton molecules(SMs)are stable bound states between solitons.SMs in fiber lasers are intensively investigated and embody analogies with matter molecules.Recent experimental studies on SMs formed by bright solitons,including soliton-pair,soliton-triplet or even soliton-quartet molecules,are intensive.However,study on soliton-binding states between bright and dark solitons is limited.In this work,the formation of such novel SMs in a fber laser with near-zero group velocity dispersion(ZGVD)is reported.Physically,these SMs are formed because of the incoherent cross-phase modulation of light and constitute a new form of SMs that are conceptually analog to the multi-atom molecules in chemistry.Our research results could assist the understanding of the dynamics of large SM complexes.These findings may also motivate potential applications in large-capacity transmission and all-optical information storage.

Novel transparent ceramics for solid-state lasers

Recent progress on rare-earth doped polycrystalline YAG transparent ceramics has made them an alternative novel solid-state laser gain material. In this paper, we present results of our research on polycrystalline RE:YAG transparent ceramics. High optical quality YAG ceramics doped with various rare-earth(RE) ions such as Nd3+, Yb3+, Er3+,Tm3+, and Ho3+have been successfully fabricated using the solid-state reactive sintering method. Highly efficient laser oscillations of the fabricated ceramics are demonstrated.