2D noncarbon materials-based nonlinear optical devices for ultrafast photonics [Invited]

Ultrafast lasers play an important role in a variety of applications ranging from optical communications to medical diagnostics and industrial materials processing. Graphene and other two-dimensional（2D） noncarbon materials, including topological insulators（TIs）, transition metal dichalcogenides（TMDCs）, phosphorene, bismuthene, and antimonene, have witnessed a very fast development of both fundamental and practical aspects in ultrafast photonics since 2009. Their unique nonlinear optical properties enable them to be used as excellent saturable absorbers（SAs） that have fast responses and broadband operation, and can be easily integrated into lasers. Here, we catalog and review recent progress in the exploitation of these 2D noncarbon materials in this emerging field. The fabrication techniques, nonlinear optical properties, and device integration strategies of 2D noncarbon materials are first introduced with a comprehensive view. Then, various mode-locked/Q-switched lasers（e.g., fiber, solid-state, disk, and waveguide lasers） based on 2D noncarbon materials are reviewed. In addition, versatile soliton pulses generated from the mode-locked fiber lasers based on 2D noncarbon materials are also summarized. Finally, future challenges and perspectives of 2D materials-based lasers are addressed.

Neuro-Space Mapping for Modeling Heterojunction Bipolar Transistor

A neuro-space mapping(Neuro-SM) for modeling heterojunction bipolar transistor(HBT) is presented, which can automatically modify the input signals of the given model by neural network. The novel Neuro-SM formulations for DC and small-signal simulation are proposed to obtain the mapping network. Simulation results show that the errors between Neuro-SM models and the accurate data are less than 1%, demonstrating that the accurcy of the proposed method is higher than those of the existing models.

Nonlinear optics of two-dimensional transition metal dichalcogenides

Nonlinear optics(NLO)of transition metal dichalcogenides(TMDs)is promising for the on-chip photonic and optoelectronic applications.In this review,we will survey the current progress of NLO in TMDs.First,we will brief the basic theory of the NLO in TMDs.Second,several important nonlinear processes in TMDs such as harmonic generation,four-wave mixing,saturable absorption,and two-photon absorption will be presented and their potential applications are also discussed.Third,the main strategies to tune,modulate,and enhance the NLO in TMDs are reviewed,including the excitonic effect,symmetry modulation,optical cavity enhancement,valley selection,edge state,and material phase.Finally,we give an outlook regarding some important issues and directions of NLO in TMDs.

Few-layer MoS2-deposited microfiber as highly nonlinear photonic device for pulse shaping in a fiber laser [Invited]

Two-dimensional（2D） materials have emerged as attractive mediums for fabricating versatile optoelectronic devices. Recently, few-layer molybdenum disulfide（MoS2）, as a shining 2D material, has been discovered to possess both the saturable absorption effect and large nonlinear refractive index. Herein, taking advantage of the unique nonlinear optical properties of MoS2, we fabricated a highly nonlinear saturable absorption photonic device by depositing the few-layer MoS2 onto the microfiber. With the proposed MoS2 photonic device, apart from the conventional soliton patterns, the mode-locked pulses could be shaped into some new soliton patterns, namely,multiple soliton molecules, localized chaotic multipulses, and double-scale soliton clusters. Our findings indicate that the few-layer MoS2-deposited microfiber could operate as a promising highlynonlinear photonic device for the related nonlinear optics applications.

Classical and quantum photonic sources based upon a nonlinear GaP/Si-superlattice micro-ring resonator

We present a theoretical investigation,based on the tight-binding Hamiltonian,of efficient second-and third-order nonlinear optical processes in the lattice-matched undoped(GaP)N/(Si 2)M short-period superlattice that is waveguide-integrated in a microring resonator on an opto-electronic chip.The nonlinear superlattice structures are sit-uated on the optically pumped input area of a heterogeneous“XOI”chip based on silicon.The spectra ofχ(2)zzz(2ω,ω,ω),χ(2)xzx(2ω,ω,ω),χ(3)xxxx(3ω,ω,ω,ω)and the Kerr refractive index(n 2),have been simu-lated as a function of the number of the atomic monolayers for“non-relaxed”heterointerfaces;These nonlinearities are induced by transi-tions between valence and conduction bands.The large obtained val-ues make the(GaP)N/(Si 2)M short-period superlattice a good can-didate for future high-performance XOI photonic integrated chips that may include Si 3 N 4 or SiC or AlGaAs or Si.Near or at the 810-nm and 1550-nm wavelengths,we have made detailed calculations of the efficiency of second-and third-harmonic generation as well as the performances of entangled photon-pair quantum sources that are based upon spontaneous parametric down conversion and sponta-neous four-wave mixing.The results indicate that the(GaP)N/(Si 2)M short-period superlattice is competitive with present technologies and is practical for classical and quantum applications.

The Fabrication and SHG Test of QPM Periodically Poled KTiOPO_4

The Quasi-phase-matching periodically poled flux-grown KTP by high electrical field method is researched. A 8×5×1mm3,∧=9.0μm PPKTP wafer is successfully fabricated for the first order QPM SHG. The interactive length of the sample is about 3mm. The SHG scheme of Nd: YAG at 1064nm tested that the output power of cw 532nm green light is 0.2mw at room temperature with fundamental power of 1.2w. The normalized conversion efficiency is about 0.09% (W·cm)-1.

Transverse mode interaction-induced Raman laser switching dynamics in a silica rod microresonator

We investigate the mechanisms to realize the Raman laser switching in a silica rod microresonator with mode-interactionassisted excitation.The laser switching can be triggered between two whispering gallery modes[WGMs]with either the same or distinct mode families,depending on the pumping conditions.The experimental observations are in excellent agreement with a theoretical analysis based on coupled-mode equations with intermodal interaction terms involved.Additionally,we also demonstrate switching of a single-mode Raman laser and a wideband spectral tuning range up to~32.67 nm by selective excitation of distinct mode sequences.The results contribute to the understanding of Raman lasing formation dynamics via interaction with transverse mode sequences and may extend the microcavity-based Raman microlasers to potential areas in switchable light sources,optical memories,and high sensitivity sensors.

Electric-field-induced quasi-phase-matched three-wave mixing in silicon-based superlattice-on-insulator integrated circuits

We present a theoretical investigation,based on the tight-binding Hamiltonian,of efficient electric-field-induced three-waves mixing(EFIM)in an undoped lattice-matched short-period superlattice(SL)that integrates quasi-phase-matched(QPM)SL straight waveguides and SL racetrack resonators on an opto-electronic chip.Periodically reversed DC voltage is applied to electrode segments on each side of the strip waveguide.The spectra ofχ_(xxxx)^((3))and of the linear suscepti-bility have been simulated as a function of the number of the atomic monolayers for“non-relaxed”heterointerfaces,and by considering all the transitions between valence and conduction bands.The large ob-tained values ofχ_(xxxx)^((3))make the(ZnS)3/(Si2)3 short-period SL a good candidate for realizing large effective second-order nonlinearity,en-abling future high-performance of the SLOI PICs and OEICs in the 1000-nm and 2000-nm wavelengths ranges.We have made detailed calculations of the efficiency of second-harmonic generation and of the performances of the optical parametric oscillator(OPO).The re-sults indicate that the(ZnS)N/(Si2)M QPM is competitive with present PPLN technologies and is practical for classical and quantum appli-cations.