Ultrafast All-optical Switching Research Articles

Femtosecond-scale all-optical switching in oxyfluorogallate glass induced by nonlinear multiphoton absorption.

Herein, all-optical switching based on a new type of oxyfluorogallate glass with high switching efficiency and ultrafast response time was reported in the near-infrared wavelength range, which is of great importance for applications in optical telecommunication. The structural and optical properties, as well as the nonlinear optical effects, of the oxyfluorogallate glass were investigated, demonstrating a good figure of merit applicable to nonlinear optical devices. Using pump–probe experiments, we found that the switching time in the oxyfluorogallate glass due to nonlinear multiphoton absorption was approximately 350 fs, which was limited by the pulse duration of the near-infrared probe pulse. Additionally, the largest on–off amplitude of this optical switching device could reach ∼12%, which is in sharp contrast to that of quartz glass. Thus, this study provides a suitable material for the manufacture of integrated photonic devices, which are crucial for promoting the application of glass on-chip photonics.

Probing microcavity switching events on the picosecond time scale using quantum dots as a broadband internal fluorescent source

We report on ultrafast all-optical switching experiments performed on pillar microcavities containing a collection of quantum dots (QDs). Using QDs as a broadband internal light source and a detection setup based on a streak camera, we track in parallel the frequencies of a large set (>10) of resonant modes of an isolated micropillar during the entire duration of switching events and with a 2 ps temporal resolution. Being much faster and more convenient than standard approaches based on pump–probe spectroscopy, this method is very well suited for in-depth studies of cavity switching, noticeably in view of applications in the field of quantum photonics. We report as a first demonstrative example an investigation of the switch-on time constant τon dependence as a function of the pump power and the observation of a remarkably low value of τon(≈1.5 ps) for optimized pumping conditions. As a second illustration, we report the observation of a transient lifting of the degeneracy of a polarization-degenerate cavity mode, induced by a non-centrosymmetric injection of free carriers.

Single femtosecond laser pulse excitation of individual cobalt nanoparticles

Laser-induced manipulation of magnetism at the nanoscale is a rapidly growing research topic with potential for applications in spintronics. In this work, we address the role of the scattering cross section, thermal effects, and laser fluence on the magnetic, structural, and chemical stability of individual magnetic nanoparticles excited by single femtosecond laser pulses. We find that the energy transfer from the fs laser pulse to the nanoparticles is limited by the Rayleigh scattering cross section, which in combination with the light absorption of the supporting substrate and protective layers determines the increase in the nanoparticle temperature. We investigate individual Co nanoparticles (8 to 20 nm in size) as a prototypical model system, using x-ray photoemission electron microscopy and scanning electron microscopy upon excitation with single femtosecond laser pulses of varying intensity and polarization. In agreement with calculations, we find no deterministic or stochastic reversal of the magnetization in the nanoparticles up to intensities where ultrafast demagnetization or all-optical switching is typically reported in thin films. Instead, at higher fluences, the laser pulse excitation leads to photo-chemical reactions of the nanoparticles with the protective layer, which results in an irreversible change in the magnetic properties. Based on our findings, we discuss the conditions required for achieving laser-induced switching in isolated nanomagnets.

All-Optical Emission Control and Lasing in Plasmonic Lattices

We report on reversible all-optical emission control and lasing in plasmonic nanoparticle lattices. By incorporating photochromic molecules into the liquid gain medium composed of organic fluorescent molecules, we realize all-optical control over gain and absorption, the two key parameters associated with both conventional and nanoscale lasing. We demonstrate reversible photoswitching between two distinct modes of operation: (1) spontaneous emission to the lattice mode, characterized by broad emission line width, low emission intensity, and large angular distribution; and (2) lasing action, characterized by very narrow (sub-nm) line widths due to the emergence of increased gain and temporal coherence in the system, approximately 3 orders of magnitude increase in emission intensity, and narrow 0.7° angular divergence of the beam. A rate-equation model is employed to describe the operation of the switchable plasmonic laser. Our results provide the first demonstration of optically tunable losses in plasmonic lattice lasers, which is an important milestone for the development of active plasmonics and paves the way for ultrafast all-optical switching of plasmonic nanolasers.

Preparation of Ag@ZnO core–shell nanostructures by liquid-phase laser ablation and investigation of their femtosecond nonlinear optical properties

Ag@ZnO core–shell nanostructures, ZnO nanoparticles (NPs), and Ag NPs were synthesized by laser ablation in water using 8 ns, 1064 nm, and 50 mJ/pulse. The structural, morphological, componential, and optical properties of as-synthesized NPs were examined by X-ray diffraction, transmission electron microscopy, electron diffraction spectrum, and ultraviolet–visible absorption, respectively. The third-order nonlinear optical properties of aqueous dispersions of three NPs were characterized by performing Z-scan experiments with femtosecond laser pulses at 800 nm. It is shown that three NPs exhibit the positive refractive nonlinearity in the absence of nonlinear absorption and the third-order nonlinear refraction index increases in the order of NPs ZnO < Ag < Ag@ZnO. The results indicate that the Ag@ZnO core–shell nanostructure is a promising candidate for applications in ultrafast all-optical switching.

Ultrafast all-optical switching enabled by epsilon-near-zero-tailored absorption in metal-insulator nanocavities

Ultrafast control of light−matter interactions is fundamental in view of new technological frontiers of information processing. However, conventional optical elements are either static or feature switching speeds that are extremely low with respect to the time scales at which it is possible to control light. Here, we exploit the artificial epsilon-near-zero (ENZ) modes of a metal-insulator-metal nanocavity to tailor the linear photon absorption of our system and realize a nondegenerate all-optical ultrafast modulation of the reflectance at a specific wavelength. Optical pumping of the system at its high energy ENZ mode leads to a strong redshift of the low energy mode because of the transient increase of the local dielectric function, which leads to a sub-3-ps control of the reflectance at a specific wavelength with a relative modulation depth approaching 120%.

Enhanced ultrafast optomagnetic effects in room-temperature ferromagnetic Pt nanoclusters embedded in silica by ion implantation

Ferromagnetic-like behavior at room temperature (300 K) was observed in Pt particles embedded in ion-implanted silica matrices. Results in samples integrated by ultra-small photoluminescent Pt clusters (<2 nm) were compared with samples containing exclusively larger plasmonic Pt nanoparticles (>3 nm). The ferromagnetic behavior coexists simultaneously with a diamagnetic response. Enhanced diamagnetic response of one order of magnitude was observed compared to typical diamagnetism in pure silica, and it is increased with the mean diameter of the Pt particles. Besides, a larger sensitivity to an external field was observed in the ferromagnetic response of the nanostructures with a characteristic saturation at 20 kOe. This ferromagnetic behavior was only observed in the samples with nucleated Pt particles. The magnitude of the saturation magnetization shows up to a fivefold increase in the samples with smaller particle size and larger particle density. Saturation magnetization was observed between 3–15 × 10−4 emu g−1, with remanent magnetization of 0.2–0.6 × 10−4emu g−1, measured at 300 K. Coercitive fields also decrease in samples with smaller size and particles density, with values of 114 and 300 Oe. At lower temperatures (5 K) the saturation magnetization increases, as it would be expected from a ferromagnetic state. Optomagnetic response was studied by inverse Faraday effects and induced photomagnetization with circular polarized picosecond pulsed light at 1064 nm wavelength. Results showed that samples with a stronger ferromagnetic response exhibit larger Faraday rotation up to 5.3 × 103deg cm−1 by light excitations with irradiances between 50 and 180 GW cm−2. These findings have immediate applications in multifunctional solid-state magneto-optical devices such as optical isolators, high-data storage devices and ultrafast all-optical switching of magnetization.

Ultrafast all-optical GaAs nanoswitch for photonic integrated circuitry

All-dielectric nanophotonics offers favourable opportunities for engineering of devices for various practical tasks. In this regard, a very promising field is integrated photonic circuitry, where the implementation of all-dielectric components can significantly increase the performance of nanodevices. In this paper, we numerically investigate a system formed by an ultrafast all-optical switch – a GaAs dimer nanoantenna – and a GaAs strip waveguide. The simulation of the light scattering in that system shows the relative change of the waveguide transmission coefficient ∆T/T up to 12.3 % for the fluence of the pumping pulse 0.19 mJ·cm−2. This proof-of-principle result paves the way for potential applications of the system as a logic element for nanophotonic chips.

Ultrafast all-optical switching in the presence of Bloch surface waves

It is commonly known that Bloch surface waves (BSW) can be excited at the photonic crystal/dielectric boundary that leads to many features attractive for application these states as the basis of sensors and nanophotonic devices. The narrow spectral-angular resonance of BSW is very sensitive to properties of top layer and surrounding medium. There are few ways to enhance nonlinear optical response of a top layer without violation of BSW excitation conditions. In this work we choose graphene monolayer as a source of strong nonlinearity with tiny thickness. We study temporal nonlinear optical response of graphene in the case of Bloch surface waves excitation revealing subpicosecond switching time of probe dynamics.

Applicable ultrafast all-optical switching by soliton self-trapping in high index contrast dual-core fibre

The improvement potential of ultrafast all-optical switching by soliton self-trapping, using all-solid dual-core fibres with high index contrast, was analyzed numerically. The study of the femtosecond nonlinear propagation was performed based on coupled generalised nonlinear Schrödinger equations considering three fibre architectures: homogeneous cladding all-solid, photonic crystal air-glass, and photonic crystal all-solid. The structural geometries of all three architectures were optimised in order to support high-contrast switching performance in the C-band, considering pulse widths at the 100 fs level. Comparing the three structural alternatives, the lowest switching energies at common excitation parameters (1700 nm and 70 fs pulses) were predicted for the homogeneous cladding dual-core structure. Further optimization of the excitation wavelength and pulse width resulted in lower switching energies and simultaneous improvement of the switching contrasts at the combination of 1500 nm, 75 fs pulses and a fibre length of 43 mm. The spectral aspect in this optimised case expresses a broadband and uniform switching character with a span of over 200 nm and a contrast exceeding 30 dB at more frequency channels.

Ultrafast and energy-efficient all-optical switching with graphene-loaded deep-subwavelength plasmonic waveguides

All-optical switches have attracted attention because they can potentially overcome the speed limitation of electric switches. However, ultrafast, energy-efficient all-optical switches have been challenging to realize due to the intrinsically small optical nonlinearity in existing materials. As a solution, we propose graphene-loaded deep-subwavelength plasmonic waveguides (30 nm x 20 nm). Thanks to extreme light confinement, we have significantly enhanced optical nonlinear absorption in graphene, and achieved ultrafast all-optical switching with a switching energy of 35 fJ and a switching time of 260 fs. The switching energy is four orders of magnitudes smaller than that in previous graphene-based devices and is the smallest value ever reported for any all-optical switch operating at a few picoseconds or less. This device can be efficiently connected to conventional Si waveguides and employed in Si photonic integrated circuits. We believe that this graphene-based device will pave the way towards on-chip ultrafast and energy-efficient photonic processing.

Bacterially synthesized tellurium nanostructures for broadband ultrafast nonlinear optical applications

Elementary tellurium is currently of great interest as an element with potential promise in nano-technology applications because of the recent discovery regarding its three two-dimensional phases and the existence of Weyl nodes around its Femi level. Here, we report on the unique nano-photonic properties of elemental tellurium particles [Te(0)], as harvest from a culture of a tellurium-oxyanion respiring bacteria. The bacterially-formed nano-crystals prove effective in the photonic applications tested compared to the chemically-formed nano-materials, suggesting a unique and environmentally friendly route of synthesis. Nonlinear optical measurements of this material reveal the strong saturable absorption and nonlinear optical extinctions induced by Mie scattering over broad temporal and wavelength ranges. In both cases, Te-nanoparticles exhibit superior optical nonlinearity compared to graphene. We demonstrate that biological tellurium can be used for a variety of photonic applications which include their proof-of-concept for employment as ultrafast mode-lockers and all-optical switches.

Solution-Processed Lead Iodide for Ultrafast All-Optical Switching of Terahertz Photonic Devices.

Solution-processed lead iodide (PbI2 ) governs the charge transport characteristics in the hybrid metal halide perovskites. Besides being a precursor in enhancing the performance of perovskite solar cells, PbI2 alone offers remarkable optical and ultrasensitive photoresponsive properties that remain largely unexplored. Here, the photophysics and the ultrafast carrier dynamics of the solution processed PbI2 thin film is probed experimentally. A PbI2 integrated metamaterial photonic device with switchable picosecond time response at extremely low photoexcitation fluences is demonstrated. Further, findings show strongly confined terahertz field induced tailoring of sensitivity and switching time of the metamaterial resonances for different thicknesses of PbI2 thin film. The approach has two far reaching consequences: the first lead-iodide-based ultrafast photonic device and resonantly confined electromagnetic field tailored transient nonequilibrium dynamics of PbI2 which could also be applied to a broad range of semiconductors for designing on-chip, ultrafast, all-optical switchable photonic devices.

Tunable CdS/TiO2 all-optical switches with defect layers

The switching characteristics of one-dimensional photonic crystal (PC) all-optical switches of cadmium sulfide (CdS)/titanium dioxide (TiO2) with defect layers are investigated. The excited defect modes with high intensity, perfect symmetric and a very narrow band were found in the photonic bandgap range of the PC transmission spectrum when inserted cadmium sulfide defect layers in the PC structure. It results from the high optical non-linearity of the cadmium sulfide defect layer and the strong localized effects of the incident light. These effects are attributed to the light localization in the defect layers of the multilayer structures. Additionally, the number and position of the defect modes are tuned according to the number and separation of the defect layers. The steep response of on and off and the tuning properties of the perfect defect modes can be exploited for ultrafast all-optical switches in all-optical circuits. The results demonstrate that cadmium sulfide defective PCs are good candidates for the fabrication of ultrafast all-optical switching devices.

Ultrafast Carrier Redistribution in Single InAs Quantum Dots Mediated by Wetting-Layer Dynamics

Individual epitaxial semiconductor quantum dots (QDs) have been extensively considered as an ``artificial atom'' platform for quantum optics and photonics applications. The QD carrier dynamics responsible for ultimate device performance is indeed complex, due in part to rich interaction with the wetting layer's two-dimensional carrier reservoir. The authors investigate this interaction with time-resolved experiments and rate-equation modeling, showing that these analyses are important for understanding the limitations of single-photon photoluminescence emission, improving lasers and fast optical modulators, and developing next-generation ultrafast all-optical switches.

Writing magnetic memory with ultrashort light pulses

Laser pulses are the shortest stimulus known to control the magnetization of materials and to switch magnetic devices on the picosecond to femtosecond timescales. Femtosecond laser pulses have been able to trigger the fastest changes in the magnetic state of matter, and thus these pulses may lead to technologies with increased speed and energy efficiency of magnetic data storage and memory. In the past decade, materials enabling optical control of magnetism and concepts of devices employing such opto-magnetic phenomena have been shown. In this Review, we explore ultrafast all-optical switching (AOS) of magnetization as the least-dissipative and fastest method for magnetic writing. We outline the physical processes responsible for mechanisms of AOS, define the materials suitable for optical control of magnetism and test these mechanisms and materials against three important criteria of recording: speed, accompanying dissipations and scalability. In particular, we emphasize that switching magnetization with the help of light outperforms other methods in terms of the speed of the write–read magnetic recording event (less than 20 ps) and the unprecedentedly low heat load (<6 J cm−3). Finally, we outline the integration of AOS in spintronic devices and the perspective of large-scale integration towards magnetic random access memory and other memory applications with low-energy dissipations. Laser pulses can trigger fast changes in magnetic state, facilitating new magnetic data storage and memory devices. This Review outlines the mechanisms of all-optical switching and the materials suitable for the optical control of magnetism and tests these mechanisms and materials in terms of speed, accompanying dissipations and scalability. Finally, the large-scale integration of devices in memory applications with low-energy dissipations is discussed.

Broadly Tunable Plasmons in Doped Oxide Nanoparticles for Ultrafast and Broadband Mid-Infrared All-Optical Switching.

Plasmons in conducting nanostructures offer the means to efficiently manipulate light at the nanoscale with subpicosecond speed in an all-optical operation fashion, thus allowing for construction of high performance all-optical signal-processing devices. Here, by exploiting the ultrafast nonlinear optical properties of broadly tunable mid-infrared (MIR) plasmons in solution-processed, degenerately doped oxide nanoparticles, we demonstrate ultrafast all-optical switching in the MIR region, which features subpicosecond response speed (with recovery time constant of <400 fs) as well as an ultrabroadband response spectral range (covering 3.0-5.0 μm). Furthermore, with the degenerately doped nanoparticles as Q-switch, pulsed fiber lasers covering 2.0-3.5 μm were constructed, of which a watt-level fiber laser at 3.0 μm band shows superior overall performance among previously reported passively Q-switched fiber lasers at the same band. Notably, the degenerately doped nanoparticles show great potential to work in the spectral range over 3.0 μm, which is beyond the accessibility of commercially available but expensive semiconducting saturable absorber mirror (SESAM). Our work demonstrates a versatile while cost-effective material solution to ultrafast photonics in the technologically important MIR region.

Single‐Shot Multi‐Level All‐Optical Magnetization Switching Mediated by Spin Transport

All-optical ultrafast magnetization switching in magnetic material thin film without the assistance of an applied external magnetic field is explored for future ultrafast and energy-efficient magnetic storage and memories. It is shown that femtosecond (fs) light pulses induce magnetization reversal in a large variety of magnetic materials. However, so far, only GdFeCo-based ferrimagnetic thin films exhibit magnetization switching via a single optical pulse. Here, the single-pulse switching of Co/Pt multilayers within a magnetic spin-valve structure ([Co/Pt]/Cu/GdFeCo) is demonstrated and four possible magnetic configurations of the spin valve can be accessed using a sequence of single fs light pulses. The experimental study reveals that the magnetization final state of the ferromagnetic [Co/Pt] layer is determined by spin-polarized currents generated by the light pulse interactions with the GdFeCo layer. This work provides an approach to deterministically switch ferromagnetic layers and a pathway to engineering materials for opto-magnetic multi-bit recording.

Roles of heating and helicity in ultrafast all-optical magnetization switching in TbFeCo

Using the time-resolved magneto-optical Kerr effect method, helicity-dependent all-optical magnetization switching (HD-AOS) is observed in ferrimagnetic TbFeCo films. Our results reveal the individual roles of the thermal and nonthermal effects after a single circularly polarized laser pulse. The evolution of this ultrafast switching occurs over different time scales, and a defined magnetization reversal time of 460 fs is shown—the fastest ever observed. Micromagnetic simulations based on a single macro-spin model, taking into account both heating and the inverse Faraday effect, are performed which reproduce HD-AOS demonstrating a linear path for magnetization reversal.

Moderate fabrication and characterization of the microcrystalline Sr2CuO3 glass films with effective nonlinearities

Since nonlinear optical materials used in the ultrafast all-optical switching is an important part for the modern optical technology, cuprates have been widely investigated for their specific Cu-O chain structure and intriguing optical properties. We present a new preparation method of microcrystalline Sr2CuO3 glass films on glass substrates combining spin-coating and co-sintering techniques. Then, the as-prepared samples were polished for different times to obtain microcrystalline Sr2CuO3 glass films with varying thickness. The influence of polishing time on the structure, the valence state and the nonlinear optical response were discussed, respectively. The purity of the Sr2CuO3 phase, surface morphology and the chemical composites of these synthesized glass films were given with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Importantly, optical absorption spectroscopy and Z-scan technique were used to measure linear absorption and third-order optical nonlinearity of the films. The experiments showed that third-order nonlinear susceptibility of the 140 min polished film sample with a thickness of 18 μm was up to 1.23 × 10−12 esu, indicating its potential application in the nonlinear field.