All-optical switching and nonlinear optical properties of HBT in ethanol solution

This paper demonstrates an all-optical switching model system comprising a single pulsed pump beam at 355 nm and a CW He-Ne signal beam at 632.8 nm with 2-（2＇-hydroxyphenyl）benzothiazole （HBT） in ethanol solution. The origins of the optical switching effect were discussed. By the study of nonlinear optical properties for HBT in ethanol solvent, this paper verified that the excited-state intramolecular proton transfer （ESIPT） effect of HBT and the thermal effect of solvent worked on quite different time scales and together induced the change of the refractive index of HBT solution, leading to the signal beam deflection. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitive optical switching devices.

All-optical switchings of 3-hydroxyflavone in different solvents

3-hydroxyflavone （3-HF） is an organic molecule with an excited-stated intramolecular proton transfer （ESIPT） effect. All-optical switchings and beam deflections of 3-HF in three kinds of solvents （cyclohexane, ethanol and dimethyl sulfoxide） have been investigated by using the third-harmonic generation （355 nm） of a mode-locked Nd：YAG laser as a pump beam and a continuous-wave （cw） He-Ne laser （632.8 nm） as a probe beam. The nonlinear refractive indices of 3-HF in the three different solvents are determined by using the Z-scan technique under an ultraviolet （UV） pump beam at a wavelength of 355 nm. It has been found that the optical switching and beam deflection effects result from the change in refractive index of 3-HF under the irradiation of the pump beam. On the basis of the analyses of absorption spectra and fluorescence spectra, we conclude that the change in refractive index of 3-HF is due to not the thermal effect but the ESIPT effect of 3-HF under the pump beam. As the ESIPT is exceedingly fast, 3-HF might be an excellent candidate for high-speed optical switching.

Fabrication of high-quality colloidal photonic crystals with sharp band edges for ultrafast all-optical switching

Application of the pressure controlled isothermal heating vertical deposition method to the fabrication of colloidal photonic crystals is systematically investigated in this paper. The fabricated samples are characterized by scanning electron microscope and transmission spectrum. High-quality samples with large transmissions in the pass bands and the sharp band edges are obtained and the optimum growth condition is determined. For the best sample, the transmission in the pass bands approaches 0.9 while that in the band gap reaches 0.1. More importantly, the maximum differential transmission as high as 0.1/nm is achieved. In addition, it is found that the number of stacking layers does not increase linearly with concentration of PS spheres in a solution, and a gradual saturation occurs when the concentration of PS spheres exceeds 1.5 wt.%. The uniformity of the fabricated samples is examined by transmission measurements on areas with different sizes. Finally, the tolerance of the fabricated samples to baking was studied.

All-optical switching in silicon photonic waveguides with an epsilon-near-zero resonant cavity [Invited]

Strong nonlinearity of plasmonic metamaterials can be designed near their effective plasma frequency in the epsilon-near-zero(ENZ) regime. We explore the realization of an all-optical modulator based on the Au nonlinearity using an ENZ cavity formed by a few Au nanorods inside a Si photonic waveguide. The resulting modulator has robust performance with a modulation depth of about 30 dB/μm and loss less than 0.8 dB for switching energies below 600 fJ. The modulator provides a double advantage of high mode transmission and strong nonlinearity enhancement in the few-nanorod-based design.

The Tolerance of All-Optical Switching Based on Cascaded Second-Order Nonlinearity in PPLN APE Waveguide

Based on solving the couple mode equation numerically, the characterization of the signal power on the gate power was analyzed. And the relationship of the tolerance of the grating period and the bulk temperature on the interaction length was analyzed.

Ultrafast all-optical switching of dual-band plasmon-induced transparency in terahertz metamaterials

An active ultrafast formation and modulation of dual-band plasmon-induced transparency(PIT) effect is theoretically and experimentally studied in a novel metaphotonic device operating in the terahertz regime,for the first time,to the best of our knowledge.Specifically,we designed and fabricated a triatomic metamaterial hybridized with silicon islands following a newly proposed modulating mechanism.In this mechanism,a localized surface plasmon resonance is induced by the broken symmetry of a C_(2)structure,acting as the quasi-dark mode.Excited by exterior laser pumps,the photo-induced carriers in silicon promote the quasi-dark mode,which shields the near-field coupling between the dark mode and bright mode supported by the triatomic metamaterial,leading to the dynamical modulation of terahertz waves from individual-band into dual-band PIT effects,with a decay constant of 493 ps.Moreover,a remarkable slow light effect occurs in the modulating process,accompanied by the dual-transparent windows.The dynamical switching technique of the dual-band PIT effect introduced in this work highlights the potential usefulness of this metaphotonic device in optical information processing and communication,including multi-frequency filtering,tunable sensors,and optical storage.

All-Optical Switching Using Fabry-Perot Laser Diodes (Invited paper)

In this paper, we investigate all-optical packet switching using a multi-wavelength mutual injection-locked Fabry-Perot laser diode. We observe error-free packet-switching of a 10 Gb/s signal with an extinction ratio of 16.9.

Laser Trimming for Adjustment of Grating Offset in Phase-Shifted Fiber Grating Coupler for All-Optical Switching Application

We theoretically investigated laser trimming to adjust grating offset in phase-shifted fiber grating coupler (FGC) for all-optical switching application. It was clarified that the trimming made the extinction ratio higher in all-optical FGC switch.

Timescales and contribution of heating and helicity effect in helicity-dependent all-optical switching

The heating and helicity effects induced by circularly polarized laser excitation are entangled in the helicity-dependent all-optical switching(HD-AOS),which hinders understanding the magnetization dynamics involved.Here,applying a dual-pump laser excitation,first with a linearly polarized(LP) laser pulse followed by a circularly polarized(CP) laser pulse,the timescales and contribution from heating and helicity effects in HD-AOS were identified with a Pt/Co/Pt triple-layer.When the LP laser pulses preheat the sample to a nearly fully demagnetized state,the CP laser pulses with a power reduced by 80% switch the sample’s magnetization.By varying the time delay between the two pump pulses,the results show that the helicity effect,which gives rise to the deterministic helicity-induced switching,arises almost instantly within 200 fs close to the pulse width upon laser excitation.The results reveal that the transient magnetization state upon which CP laser pulses impinge is the key factor for achieving HD-AOS,and importantly,the tunability between heating and helicity effects with the unique dualpump laser excitation approach will enable HD-AOS in a wide range of magnetic material systems having wideranging implications for potential ultrafast spintronics applications.

Au/MXene based ultrafast all-optical switching

All-optical switches have arisen great attention due to their ultrafast speed as compared with electric switches.However,the excellent optical properties and strong interaction of two-dimensional(2D)material MXene show great potentials in next-generation all-optical switching.As a solution,we propose all-optical switching used Au/MXene with switching full width at half maximum(FWHM)operating at 290 fs.Compared with pure MXene,the Au/MXene behaves outstanding performances due to local surface plasmon resonance(LSPR),including broadband differential transmission,strong near-infrared on/off ratio enhancement.Remarkably,this study enhances understanding of Au/MXene based ultrafast all-optical switching red-shifted about 34 nm in comparison to MXene,validating all optical properties of Au/MXene opening the way to the implementation of optical interconnection and optical switching.

Tunable interaction-free all-optical switching in a five-level atom-cavity system

A scheme is proposed for tunable all-optical switching based on the double-dark states in a five-level atom-cavity system. In the scheme, the output signal light of the reflection and the transmission channels can be switched on or off by manipulating the control field. When the control light is coupled to the atom-cavity system, the input signal light is reflected by the cavity. Thus, there is no direct coupling between the control light and the signal light. Furthermore, the position of the double-dark states can be changed by adjusting the coherent field, and,thus, the switching in our scheme is tunable. By presenting the numerical calculations of the switching efficiency,we show that this type of the interaction-free all-optical switching can be realized with high switching efficiency.

Polarization-tunable nonlinear absorption patterns from saturated absorption to reverse saturated absorption in anisotropic GeS flake and an application of all-optical switching

Due to the unique anisotropic chemical and physical properties,two-dimensional(2D)layered materials such as IV-VI monochalcogenides with puckered honeycomb structure,have received considerable interest recently.Among the IV-VI layered MX(M=Ge,Sn;X=Se,S)compounds,germanium sulfide(Ge S)stands out for its strongest anisotropic thermal conductivities and figure-of-merit values.Additionally,the layer-independent direct energy bands(Eg^1.6 e V,E1~2.1 e V)of Ge S flake provide excellent insights into further applications as visible photodetectors.Herein,the polarization-tunable nonlinear absorption(NA)patterns of Ge S flake have been systematically investigated.Specifically both the polarization-dependent Raman spectroscopy and the linear absorption(LA)spectroscopy were employed to characterize the lattice orientation and absorption edges of the251-nm Ge S flake.Considering the low damage threshold of Ge S flake,the Ge S/graphene heterostructure was fabricated to increase the threshold without changing the nonlinear properties of Ge S.Our NA results demonstrated that a 600-nm femtosecond laser with different polarizations would excite the saturated-absorption(SA)effect along armchair and reversesaturated-absorption(RSA)effect along zigzag in the Ge S/graphene heterostructure.Moreover,the function of the polarization-based Ge S/graphene heterostructure all-optical switch was experimentally verified.Notably,thanks to the polarization-dependent NA patterns(SA/RSA)of Ge S,the"ON"and"OFF"states of the all-optical switch can be accomplished by high and low transmittance states of continuous-wave laser(532 nm,80 n W),whose state can be controlled by the polarization of femtosecond switching laser(600 nm,35 fs,500 Hz,12 GW cm-2).The ON/OFF ratio can achieve up to 17%by changing polarization,compared with the ratios of 3.0%by increasing the incident power of switching light in our experiment.The polarization-tunable absorption patterns introduced in this work open up real perspectives for the next-generation optoelectronic devices based on Ge S/graphene heterostructure.

Broadband nonlinear optical resonance and all-optical switching of liquid phase exfoliated tungsten diselenide

As a kind of two-dimensional transition metal dichalcogenide material, tungsten diselenide(WSe_2) has attracted increasing attention, owing to its gapped electronic structure, relatively high carrier mobility, and valley pseudospin, all of which show its valuable nonlinear optical properties. There are few studies on the nonlinear optical properties of WSe_2 and correlation with its electronic structure. In this paper, the effects of spatial self-phase modulation(SSPM) and distortion influence of WSe_2 ethanol suspensions are systematically studied, namely,the nonlinear refractive index and third-order nonlinear optical effect. We obtained the WSe_2 dispersions SSPM distortion formation mechanism, and through it, we calculated the nonlinear refractive index n_2,nonlinear susceptibility χ^(3), and their wavelength dependence under the excitation of 457 nm, 532 nm, and671 nm lasers. Moreover, by use of its strong and broadband nonlinear optical response, all-optical switching of two different laser beams due to spatial cross-phase modulation has been realized experimentally. Our results are useful for future optical devices, such as all-optical switching and all-optical information conversion.

Ultrafast polarization-dependent all-optical switching of germanium-based metaphotonic devices

Metamaterials play an important role in the modulation of amplitude and group delay in the terahertz(THz)regime on account of their optical properties,which are rare in natural materials.Here an ultrafast anisotropic switch of the plasmon-induced transparency(PIT)effect is experimentally and numerically demonstrated by metamaterial devices composed of two pairs of planar split-ring resonators and a pair of closed-ring resonators.By integration with a germanium(Ge)film,a recovery time of 3 ps and a decay constant of 785 fs are realized in the metadevice.Stimulated by the exterior optical pump,the PIT windows at different frequencies are switched off with an excellent property of slow light for vertical and horizontal THz polarizations,realizing an astonishing modulation depth as high as 99.06%.This work provides a new platform for ultrafast anisotropic metadevices tunable for amplitude and group delay.

Investigation of the influence of key parameters on system performance in all-optical label switching based on FSK/ASK orthogonal modulation format

The transmission characteristics of the optical label switching system based on the FSK/ASK orthogonal modulation format is investigated. The factors that affect the transmission performance, such as the FSK tone space, dispersion compensation and coupler split ratio, are studied by numerical simulation. The proposed scheme is also experimentally demonstrated with a transmission of 155 Mbit/s FSK label combined with 10 Gbit/s ASK payload.

Wedge-shaped HfO_(2) buffer layer-induced field-free spin-orbit torque switching of HfO_(2)/Pt/Co structure

Field-free spin-orbit torque(SOT)switching of perpendicular magnetization is essential for future spintronic devices.This study demonstrates the field-free switching of perpendicular magnetization in an HfO_(2)/Pt/Co/TaO_(x) structure,which is facilitated by a wedge-shaped HfO_(2)buffer layer.The field-free switching ratio varies with HfO_(2)thickness,reaching optimal performance at 25 nm.This phenomenon is attributed to the lateral anisotropy gradient of the Co layer,which is induced by the wedge-shaped HfO_(2)buffer layer.The thickness gradient of HfO_(2)along the wedge creates a corresponding lateral anisotropy gradient in the Co layer,correlating with the switching ratio.These findings indicate that field-free SOT switching can be achieved through designing buffer layer,offering a novel approach to innovating spin-orbit device.

Enhancement of modulation depth of an all-optical switch using an azo dye-ethyl red film

The polymethyl methacrylate （PMMA） film doped with an azo dye ethyl-red （ER） film is employed to demonstrate the properties of an all-optical switch by its photoinduced dichroism and birefringence. We show how to enhance remarkably the modulation depth of all-optical switches almost to 100% by using two linear polarization beams： one beam is inclined at 45° with respect to the probing beam and serves as a pumping beam, and the other beam is perpendicular to the probing beam and used as an erasing beam. Furthermore, a maximum-to-minimum output intensity ratio of 2000：1 is achieved in experiment, which is very useful and important for optical storages and image displays.

Tunable Three-Wavelength Fiber Laser and Transient Switching between Three-Wavelength Soliton and Q-Switched Mode-Locked States

We report a passive mode-locked fiber laser that can realize single-wavelength tuning and multi-wavelength spacing tuning simultaneously.The tuning range is from 1528 nm–1560 nm,and up to three bands of soliton states can be output at the same time.These results are confirmed by a nonlinear Schrodinger equation model based on the split-step Fourier method.In addition,we reveal a way to transform the multi-wavelength soliton state into the Q-switched mode-locked state,which is period doubling.These results will promote the development of optical communication,optical sensing and multi-signal pulse emission.

High-efficiency ultra-fast all-optical photonic crystal diode based on the lateral-coupled nonlinear elliptical defect

An all-optical Fano-like diode featuring a nonlinear lateral elliptical micro-cavity and a reflecting column in the photonic crystal waveguide is proposed.The asymmetric micro-cavity is constructed by removing one rod and changing the shape of the lateral rod from a circle to an ellipse.A reflecting pillar is also introduced into the waveguide to construct an F-P cavity with the elliptical defect and enhance the asymmetric transmission for the incident light wave transmitting rightwards and leftwards,respectively.By designing the size of the ellipse and optimizing a reflecting rod at a suitable position,a maximum forward light transmittance of-1.14 dB and a minimum backward transmittance of-57.66 dB are achieved at the working wavelength of 1550.47 nm.The corresponding response time is about 10 ps when the intensity of the pump light beam resonant at 637 nm is 3.97 W/μm2.

Switching Frequency Improvement of a High Speed on/off Valve Based on Pre-excitation Control Algorithm

The high-speed on/off valve(HSV)serves as the fundamental component responsible for generating discrete fluids within digital hydraulic systems.As the switching frequency of the HSV increases,the properties of the generated discrete fluid approach those of continuous fluids.Therefore,a higher frequency response characteristic of HSV is the key to ensure the control accuracy of digital hydraulic systems.However,the current research mainly focuses on its dynamic performance,but neglect its FRC.This paper presents a theoretical analysis demonstrating that the FRC of the HSV can be enhanced by minimizing its switching time.The maximum switching frequency(MSF)is mainly determined by opening dynamic performance when HSV operates with low switching duty ratio(SDR),whereas the closing dynamic performance limits the MSF when HSV operates with high SDR.Building upon these findings,the pre-excitation control algorithm(PECA)is proposed to reduce the switching time of the HSV,and consequently enhance its FRC.Experimental results demonstrate that PECA shortens the opening delay time of HSV by 1.12 ms,the closing delay time by 2.54 ms,and the closing moving time by 0.47 ms in comparison to the existing advanced control algorithms.As a result,a larger MSF of 417 Hz and a wider controllable SDR range from 20%to 70%were achieved at a switching frequency of 250 Hz.Thus,the proposed PFCA in this paper has been verified as an effective and promising approach for enhancing the control performance of digital hydraulic systems.