All-optical Switching Applications Research Articles

Nonlinear absorption conversion of epsilon-near-zero multilayer metamaterial at optical frequencies

Modern all-optical logic switches demand selective, precise, and rapid transmission of optical information. In this study, we investigate an epsilon-near-zero (ENZ) metamaterial composed of silver (Ag) and magnesium fluoride (MgF2), which demonstrates a low conversion threshold, strong nonlinear response, and nonlinear absorption conversion. Particularly noteworthy is its highest nonlinear absorption (β≈-2 × 106 cm/GW) occurring at the ENZ point (695 nm) under deposited condition. This research marks the first discussion of nonlinear absorption conversion in the ENZ multilayer metamaterial. The deposited metamaterial sample exhibits saturation absorption (SA), attributed to ground state free electron bleaching, while annealed sample shows a transition from SA to reverse saturation absorption (RSA) due to a three-photon absorption effect. Annealing significantly reduces the laser power threshold required for this conversion process, indicating reduced risk of laser-induced damage. Furthermore, the wavelength shift of the largest RSA (γ≈1.93 × 104 cm3/GW2) in the annealed sample aligns with the expected redshift direction of the ENZ region (735 nm). Our metamaterial design achieves enhanced nonlinear absorption and low-power absorption conversion, which holds significant potential for applications in all-optical logic switches.

Optomagnetism with a plasmonic skyrmion.

Research at the frontier between optics and magnetism is revealing a wealth of innovative phenomena and avenues of exploration. Optical waves are demonstrating the capacity to induce ultrafast magnetism, while optical analogs of magnetic states, such as magnetic skyrmions, offer the prospect of novel, to the best of our knowledge, spin-optical states. In this Letter, we strengthen the synergy between light and magnetism by exploring the ability of plasmonic Neel skyrmions to create an optomagnetic field, i.e., an opto-induced stationary magnetic field, within a thin gold film. We show that, when generated using a focused radially polarized vortex beam (RPVB), a plasmonic Neel skyrmion emerges as an optimum for inducing optomagnetism in a thin gold film. Optical skyrmions offer new degrees of freedom for enhancing and controlling optomagnetism in plasmonic nanostructures, with direct application in all-optical magnetization switching, magnetic recording, and the excitation of spin waves.

Strong light-matter interaction and non-linear effects in organic semiconducting CuPc nanotubes: realization of all-optical diode and switching applications.

Spatial self-phase modulation based on the optical Kerr effect has gained momentum in recent years to analyse the nonlinear optical properties of 2D inorganic nanomaterials. In the present work, we investigate the strong light-matter interaction of organic semiconducting materials based on SSPM, by developing Cu-phthalocyanine (CuPc) nanotubes via a solvothermal technique. The low bandgap of CuPc facilitates the study of its nonlinear optical properties for a broad spectrum range from 671 nm to 405 nm. Intense laser light passing through the CuPc dispersion produces concentric diffraction ring patterns at the far field from which high n2 and χ(3) values, 3.667 × 10-5 cm2 W-1 and 2 × 10-3 esu, respectively, are obtained for the 405 nm laser. This strong nonlinear optical response of CuPc has been utilized to realize non-reciprocal light propagation by constructing a CuPc/SnS2 hybrid structure, which makes an effective all-optical photonic diode. In addition, the all-optical switching is presented using CuPc nanotubes based on the spatial cross-phase modulation technique. In this technique a phase change is induced in the weak signal beam modulated by the strong controlling light beam, which helps to produce all-optical logic gates and all-optical switching devices. The experimental findings of this work unravel the potentially powerful applications of CuPc nanotubes in all-optical information transmission and all-optical photonic devices.

GaN film optical nonlinearity: wavelength dependent refractive index for All-Optical switching application

Gallium Nitride (GaN) is fast becoming a potential replacement for silicon in complex electronic and photonics circuitries and systems. At higher optical intensity, optical effects such as non-linear effects would become non-trivial. To this end, we investigated nonlinear optical properties of metal–organic chemical vapor deposited GaN. Specifically, continuous-wave laser Z-scan techniques were employed to obtain nonlinear refractive index, n2, of a 1-µm thin layer on a c-plane sapphire substrate. FESEM, PL, XRD and EDS analysis confirmed the good quality growth of GaN thin film. We detected a reversal of polarity of the n2 value at 637 nm and 405 nm of CW laser excitation and femtosecond laser pulse at 808 nm. This is substantiated by theoretical calculation of GaN’s n2 showing sign switchover at wavelength shorter than 420 nm. This presents a new all-optical switching scheme based on the switchover of wavelength dependent n2. These findings point to opportunities for GaN-based integrated photonics for nonlinear and quantum photonics applications.

Influence of Au on the nucleation of Ag nanoparticles in GeO2-PbO glasses and characterization of their ultrafast third-order nonlinear responses within the plasmon resonance region

Germanate (GeO2-PbO) glasses doped with AgNO3 and co-doped with AgNO3 and Au2O3 were synthesized via melting-quenching technique. Silver nanoparticles were nucleated within the sample doped only with AgNO3 and its plasmon resonance was characterized. The influence of the addition of Au2O3 on the silver nanoparticles nucleation and on the spectroscopic properties of the produced composite materials were investigated using TEM, STEM and UV–Vis spectroscopy. Using the nonlinear ellipse rotation technique, the pure electronic contribution to the samples nonlinear refraction and absorption were characterized within the visible range, including the localized surface plasmon (LSP) resonance wavelength of the metallic nanoparticles. The real and imaginary parts of the third-order nonlinear susceptibility of the glass, composite samples and of the individual nanoparticles were also obtained. In addition, all-optical switching figures of merit of the samples were also calculated. From these results, the dispersion curves of the electronic contribution to the third-order susceptibility of the metallic nanoparticles were obtained and two figures of merit for all-optical switching of the composite materials were calculated. The studied samples are potential candidates for all-optical switching applications with exception to the one with the highest volume filling factor, whose linear and nonlinear absorption coefficients associated to the local field factor deplete the material performance around the LSP resonance wavelength. As far as we know nonlinear ellipse rotation technique was not used before to evaluate the influence of metallic nanoparticles on the nonlinear optical properties of glasses.

Multifunctional and dynamically tunable coherent perfect absorber based on InSb and graphene metasurface

We propose a temperature-tunable and dual-broadband switchable coherent perfect absorber (CPA) composed of an annulus-disk-shaped InSb pattern and a complementary graphene layer. By controlling the Fermi level of graphene, the temperature of InSb, or the relative phase of incident beams, the working frequency and absorption of the CPA can be continuously adjusted. For a Fermi energy of 0 eV, the dual-band coherent perfect absorptivities exceed 99%. The designed structure achieves broadband absorptance of over 90% in the frequency range of 0.145 THz to 1.24 THz, with a relative bandwidth of about 158.12% for a Fermi energy of 0.5 eV. Moreover, the temperature-dependent permittivity of InSb enables thermal tuning of the dual-band CPA in the THz region. Furthermore, by altering the relative phase of input beams, the absorptivity can be continuously varied between less than 1.2% and more than 90% in the dual-band and broadband modes. Additionally, the designed CPA exhibits insensitivity to the polarization angle within the range of 0° to 90°. Therefore, this multifunctional CPA holds significant potential for applications in modulation, sensing, all-optical switches, and coherent photodetectors.

Tunable Low-Threshold Optical Bistability in Optical Tamm Plasmon Superlattices

We propose a scheme to obtain tunable low-threshold optical bistability of reflected beams in optical Tamm plasmon superlattices (TPS). The low-threshold optical bistability is triggered due to the strong third-order non-linearity of graphene and the local field enhancement in the TPS. Our results show that the optical Tamm plasmon superlattices have the ability to lower the bistable threshold even further than the single optical Tamm state. The results show that the hysteresis behavior and optical bistability threshold can be continuously adjusted by changing the applied voltage and the number of graphene layers (N ≤ 4). In particular, the optical bistability in the TPS is affected by the incident angle. Our results introduce a new possible route for low threshold optical bistability in the THz range and provide a new method in the field of all-optical switching applications.

Metal-centric organic compounds: boon to third-order nonlinear optical applications

Abstract In the recent past the molecular engineering of coordination metal complexes has attracted new interest in the field of nonlinear optics (NLO), which find their applications in optoelectronics and optical data storage technology it is the transition metal along with the organic moieties that induce the control over the optical nonlinearity these properties of the materials not only enhance the intensity but also have a drastic effect on the polarization of incident laser light. This is an important criterion for all-optical switching applications. Coordination metal complexes are a very good target to aim at because of their robustness, physical and chemical stability, and other variable degrees that lead to an increment in NLO responses, most importantly all these properties can be either manipulated or tailored or tunable according to the requirement. Apart from the metal center, these molecules acting as legend must be chromophoric with donor-acceptor nature. In these molecules, the NLO response is intrinsically based on the ‘push-pull’ mechanism of the electrons. Obviously to these molecules, when a metal is in contact, the electronic push-pull mechanism alters rendering the molecule non-symmetric. This review article mainly concentrates on small mononuclear metal complexes for NLO application.

Effect of antimony doping on the structural, optical, and optoelectrical properties of aluminum sulfide thin films synthesized by the electrodeposition method

In this research, undoped aluminum sulfide (Al2S3) and with various antimony (Sb) doping concentrations of 2.0, 4.0, 6.0, and 8.0 wt% were synthesized by an electrodeposition method. The α-Al2S3 phase of the hexagonal crystal structure was revealed using x-ray diffraction analysis. The crystallographic parameters of the electrodeposited thin films, for example crystallite size (D), dislocation density (δ), and microstrain (ε) were determined. The transmittance and reflectance spectra were further analyzed for linear, dispersion, optoelectrical, and nonlinear optical properties. The overall optical results were changed with various Sb doping concentrations, owing to the natural formation, and the dependence upon the amount of sulfur or sulfur deficiency in the undoped and Sb-doped Al2S3 thin films. Furthermore, the investigation of major charge carriers in the electrodeposited thin film revealed that the pure Al2S3 exhibited a p-type semiconductor, and the films were altered to be an n-type semiconductor after Sb doping. This demonstration can confirm that this kind of thin film is suitable for promising linear, and nonlinear optoelectronic devices. However, further improvement is required for certain applications in all optical switching or wavelength/photon energy conversions.

Frequency-resolved microscopic second-order hyperpolarizability of azochromophores: a study on nonlinear all-optical switching applications.

Azochromophores present interesting optical properties for application in all-optical switches (AOSs), such as ultrafast photoisomerization and considerable nonlinear optical response. However, determining the frequency-resolved microscopic second-order hyperpolarizability (real and imaginary parts) related to the pure electronic effects of molecules in solution is a challenging task. In this context, we have used femtosecond-laser induced nonlinear ellipse rotation (NER) measurements to obtain the electronic nonlinear refraction (n2(ω)) and two-photon absorption spectra (α2PA(ω)) of four azochromophores dissolved in methanol and acetone. The measurements ranging from ∼600 up to ∼1300 nm were performed in Disperse Red 1 (DR1), Disperse Red 13 (DR13), Disperse Red 19 (DR19), and Disperse Orange 3 (DO3). Because we carried the solution in a silica cuvette and used a short focal length, we were able to measure the solution's nonlinearities with high precision, as the silica from the cuvette walls worked as a suitable reference medium. Consequently, we precisely determined n2(ω), α2PA(ω), and the second-order hyperpolarizability (γ(ω)) for all molecules and explained the different magnitudes based on the push-pull character. Furthermore, the solvation effect due to the change from methanol to acetone solvent on the n2(ω), α2PA(ω), and γ(ω) is also reported. The results were elucidated using the sum-over-states (SOS) approach within the few-energy-level model and the results were obtained via quantum-chemical calculations using the cubic response function formalism within the density functional theory framework. Finally, we used these results to determine the frequency-resolved figure-of-merit for all-optical switching applications. Our results suggest that chromophores have the potential for applications in AOS based on Fabry-Perot filters.

Strong non-linear optical response of Sb2Se3 nanorods in a liquid suspension based on spatial self-phase modulation and their all-optical photonic device applications.

The field of nonlinear optics is constantly expanding and gaining new impetus through the discovery of fresh nonlinear materials. Herein, for the first time, we have performed spatial self-phase modulation (SSPM) experiments with an emerging anisotropic Sb2Se3 layered material in a liquid suspension for an all-optical diode and all-optical switching application. The third-order broadband nonlinear optical susceptibility (χ(3)single layer ∼ 10-9 esu) and nonlinear refractive index (n2 ∼ 10-6 cm2 W-1) of Sb2Se3 have been determined using a 671 nm laser beam. This result could be unambiguously explained by the anisotropic hole mobility of Sb2Se3. The linear relationship of χ(3) and carrier mobility emphasizes the establishment of nonlocal hole coherence, the origin of the diffraction pattern. Consequently, the time evolution of diffraction rings follows the 'Wind-Chime' model. A novel photonic diode based on Sb2Se3/SnS2 has been demonstrated using the nonreciprocal propagation of light. The self-phase modulation (SPM) technique uses laser lights of different wavelengths and intensities to demonstrate the all-optical logic gates, particularly OR logic gates. The exploration of nonlinear optical phenomena in Sb2Se3 opens up a new realm for optical information processing and communication. We strongly believe that this result will help to underpin the area of optical nonlinearities among its various applications.

Energy Efficient Single Pulse Switching of [Co/Gd/Pt]N Nanodisks Using Surface Lattice Resonances.

The impact of plasmonic surface lattice resonances on the magneto-optical properties and energy absorption efficiency has been studied in arrays of [Co/Gd/Pt]N multilayer nanodisks. Varying the light wavelength, the disk diameter, and the period of the array, it is demonstrated that surface lattice resonances allow all-optical single pulse switching of [Co/Gd/Pt]N nanodisk arrays with an energy 400% smaller than the energy needed to switch a continuous [Co/Gd/Pt]N film. Moreover, the magneto-optical Faraday effect is enhanced at the resonance condition by up to 5,000%. The influence of the disk diameter and array period on the amplitude, width and position of the surface lattice resonances is in qualitative agreement with theoretical calculations and opens the way to designing magnetic metasurfaces for all-optical magnetization switching applications.

Ultra-broadband coherent perfect absorption via elements with linear phase response

Increasing interest in perfect absorption of metasurface has initiated a discussion on the implementation of ultra-broadband coherent perfect absorption (CPA). Here, we present a mirror symmetric coherent absorption metasurface (CAMS) with polarization independence based on resistive thin films and annular metal patterns to force the fulfillment of ultra-broadband CPA in terahertz (THz) regime, controlling the interplay between electromagnetic waves and matter. By incorporating internal and external ring-shaped films with attached phase-delay lines, the desired phase response can be obtained, laying the foundation for implementing ultra-broadband coherent absorption. Simultaneously, by building a metal-medium composite structure superseding the dielectric substrate, additional promotion of the coherent absorptivity over the operation frequencies is realized. Manipulating the phase difference of two back-propagation coherent beams, the coherent absorptivity at 8.34-25.07 THz can be tailored successively from over 95.7% to as low as 38.1%. Moreover, with the incident angle up to 70° for the transverse electric wave, the coherent absorptivity is still over 74.8% from 8.34 THz to 25.07 THz. And for the transverse magnetic wave, at 6.67-24.2 THz, above 81.3% coherent absorptivity is visible with the incident angle increased from 0° to 60°. Our finding provides an interesting approach to designing ultra-broadband coherent absorption devices and may serve applications in THz modulators, all-optical switches, and signal processors.

Impact of aluminum doping on nonlinear absorption and ultrafast carriers dynamics of Al:CdO thin films

Al:CdO thin films with different aluminum doping concentrations were prepared via magnetron sputtering technique with various sputtering power. It is found that the band gap Eg of Al:CdO films gradually increases with the increase of Al doping concentration, while the crystallinity became poor at high doping concentration. The nonlinear absorption properties of the film were characterized by nanosecond Z-scan measurements. The Z-scan results show that the nonlinear absorption coefficient β of Al:CdO thin films could be effectively modulated by Al concentration, and the maximum of β (2 × 10−6 m/W) is achieved around 20 W sputtering power. The carrier dynamics of Al:CdO thin films were studied by femtosecond pump–probe measurements. The results show that the carrier relaxation lifetime, carriers absorption cross section and carriers refraction volume are larger in the high Al concentration film. The optical limiting properties of Al: CdO films were also studied. These results demonstrate that the Al:CdO film is a promising candidate for applications in all optical switches and laser devices.

Inverse design of broadband, strongly-coupled plexcitonic nonlinear metasurfaces

Hybrid photonic structures of plasmonic metasurfaces coupled to atomically thin semiconductors have emerged as a versatile platform for strong light–matter interaction, supporting both strong coupling and parametric nonlinearities. However, designing optimized nonlinear hybrid metasurfaces is a complex task, as the multiple parameters’ contribution to the nonlinear response is elusive. Here we present a simple yet powerful strategy for maximizing the nonlinear response of the hybrid structures based on evolutionary inverse design of the metasurface’s near-field enhancement around the excitonic frequency. We show that the strong coupling greatly enhances the nonlinear signal, and that its magnitude is mainly determined by the Rabi splitting, making it robust to geometrical variations of the metasurface. Furthermore, the large Rabi splitting attained by these hybrid structures enables broadband operation over the frequencies of the hybridized modes. Our results constitute a significant step toward achieving flexible nonlinear control, which can benefit applications in nonlinear frequency conversion, all-optical switching, and phase-controlled nonlinear metasurfaces.

The Second Harmonic Effect of Fractional-order Azimuthally Varying Vector Optical Field

We report for the first time the second-harmonic generation (SHG) of a fractional-order azimuthal varying vector optical field (FO-AVVOF). SHG process is achieved by a Type-II phase-matching BBO crystal. This nonlinear frequency conversion process reveals the topology multiplication rule and obtains the second harmonic optical field of the ultraviolet wavelength, which may have potential applications in ultraviolet micromachining and all-optical switching.

Three-photon absorption and Kerr nonlinearity in pristine and doped β-Ga2O3 single crystals

We report the spectral dependence of the three-photon absorption coefficient γ and third-order nonlinear refractive index n2 in pristine, Sn-doped and Fe-doped β-Ga2O3 crystals using 190 fs pulses in the range of 540–750 nm, i.e., photon energy between half and one-third of the bandgap Eg. The nonlinear coefficient n2 is found to be independent of Sn or Fe doping, and the maximum value of n2 is about 4 × 10−19 m2/W when the photon energy is near Eg/2. However, we observe that Fe doping can significantly enhance the γ value in the range of 540–600 nm (near Eg/2) while doping has negligible impact on γ for wavelength larger than 620 nm. Femtosecond pump-probe measurements show that Fe doping induced a fast (∼50 ps) carrier decay process after photo excitation, which could be attributed to the Fe induced deep trap states. We obtain three-photon figures of merit that allow operational intensities up to 100 GW/cm2. Our results indicate that β-Ga2O3 has great potential for all-optical switching applications in red and near IR regimes.

Photoswitching of 5-phenylazopyrimidines in crystalline powders and thin films

Solid-state photoswitching enables the development of smart materials. However, the close packing of molecules and the lack of free volume in this state prevent sterically demanding structural changes induced by irradiation, thereby precluding the use of azobenzene photoswitches. Nevertheless, we report here the solid-state photoswitching of their derivatives, 5-phenylazopyrimidines, in crystalline powders and in amorphous thin layers. After identifying trans-cis photoisomerization by NMR spectroscopy, we demonstrated the applicability of 5-phenylazopyrimidines for future all-optical switching applications. For this purpose, we prepared thin films by spin-coating and confirmed their solid-state optical switching by optical transmission spectroscopy and their favorable surface topography by atomic force microscopy. Therefore, thin films of 5-phenylazopyrimidines are suitable for on-chip integration for emerging all-optical technologies.

Electrical control of all-optical graphene switches.

Graphene has emerged as an ultrafast photonic material for on-chip all-optical switching applications. However, its atomic thickness limits its interaction with guided optical modes, resulting in a high switching energy per bit. Herein, we propose a novel technique to electrically control the switching energy of an all-optical graphene switch on a silicon nitride waveguide. Using this technique, we theoretically demonstrate a 120 µm long all-optical graphene switch with an 8.9 dB extinction ratio, 2.4 dB insertion loss, a switching time of <100 fs, a fall time of <5 ps, and a 235 fJ switching energy at 2.5 V bias, where the applied voltage reduces the switching energy by ∼16×. This technique paves the way for the emergence of ultra-efficient all-optical graphene switches that will meet the energy demands of next-generation photonic computing systems, and it is a promising alternative to lossy plasmon-enhanced devices.

Two-dimensional electromagnetically induced grating via spontaneously generated coherence and incoherent pump

A new scheme for two-dimensional (2D) electromagnetically induced grating is proposed based on spontaneously generated coherence in a Λ-type atomic system, in which the atom interacts with two orthogonal standing-wave fields and an incoherent pumping field. Due to spatial periodical modulation, the zero absorption or even gain accompanied with large dispersion is obtained in atomic medium, and electromagnetically induced grating is formed. Thus the weak probe field could be diffracted into first-order or high-order directions with high efficiency. The diffraction feature and efficiency of the gratings could be adjusted by the probe field detuning, the interaction length, the incoherent pumping field intensity, and the relative phase as well. The scheme of 2D grating we presented may have some potential application in beam splitting and all-optical switching.