All-optical Switching Applications Research Articles

Crystal structure, spectroscopic analyses, linear and third-order nonlinear optical properties of anthracene-based chalcone derivative for visible laser protection

Chalcone derivatives have fascinated the growing attention due to their nonlinear optical (NLO) and optical limiting (OL) properties. In the present study, a simple anthracene-based chalcone, (E)-1-(9-anthryl)-3-(4-nitrophenyl)prop-2-en-1-one (abbreviated as N-ANC), was synthesized as a new NLO material. Single-crystal X-ray diffraction, TGA/DTA, NMR (1H & 13C), FT-IR and UV–Vis–NIR spectroscopies, and DFT studies were performed. The intermolecular interactions were described by Hirshfeld surface analysis (HSA). In addition, static dipole moment (µ), and polarizability (α) were also computed by DFT calculations. Experimentally, the third-order NLO properties of N-ANC were investigated in solutions for two concentrations (1 and 5 mM) by Z-scan technique. Closed aperture Z-scan reveals that N-ANC possesses negative type of nonlinearity (self defocusing) with nonlinear refractive index n2 ~ 10−8 cm2W−1. In open aperture Z-scan, N-ANC exhibits strong two-photon absorption (TPA) with TPA coefficient β ~ 10−5 cmW−1. The evaluated one-photon and two-photon figures of merit of N-ANC satisfy the conditions for all-optical switching applications. Moreover, optical limiting nature based on TPA was performed and limiting threshold was evaluated. The results show that N-ANC exhibits good limiting characteristics because of its strong reverse saturable absorption (RSA) response, and thus, it is a promising material for NLO devices.

Optical bistability of graphene embedded in parity-time-symmetric photonic lattices

We investigate the optical bistability of graphene in parity-time-symmetric (PT-symmetric) photonic lattices incorporated with a defect at terahertz frequencies. The field localization of the defect mode can strengthen the nonlinearity of graphene to achieve low-threshold bistability. The nonlinearity is further enhanced, and the bistability threshold decreases, by increasing the gain-loss factor in the PT-symmetric structure. The interval of upper and lower bistability thresholds is broadened as the exceptional points split. Moreover, we show the phase transition between bistability and nonbistability by modulating the incident wavelength and chemical potential of graphene. The study may find great applications in all-optical switches and optical storage.

Graphene-based Plasmonic Switch using Resonant Coupling to the Local Plasmon Resonance

The authors propose a graphene-based subwavelength plasmonic switch, in which gating of a surface plasmon polariton is operated by inducing a local plasmon resonance within a $p$-type Si(100) layer. The resulting sharpness of its switching is the main advantage of this device, for example allowing a response to even a modest carrier-density modulation, such as has been demonstrated recently by others. Putting the pieces together here could strongly advance all-optical plasmonic switching applications, particularly in information processing.

Linear and nonlinear optical properties of chlorophyll-a extracted from Andrographis paniculata leaves

This paper reports the linear and third-order nonlinear optical (NLO) properties of chlorophyll-a, a natural pigment extracted from the medicinal plant Andrographis paniculata. Silica column chromatography technique was used to extract the chlorophyll-a from the plant leaves. The functional groups present in the extracted sample were recognized by Fourier transform infrared (FT-IR) spectra. The sample was also characterized by UV–Vis, fluorescent spectra and Z–scan techniques. Z–scan study reveals that the extracted natural pigment chlorophyll-a evinces a large negative nonlinear refractive index n2 and nonlinear absorption coefficient β respectively owing to self-defocusing and saturable absorption behaviors. Third-order NLO susceptibility χ(3) of chlorophyll-a was measured to be of the order of 10–6 esu. The sample fulfilled the conditions for figure of merit and we believe that the natural pigments extracted from the Andrographis paniculata leaves may be suitable for all-optical switching applications.

Design of silicon-wire waveguide ultracompact racetrack resonators: geometrical parameters for optimal coupling.

In this paper, it is shown that a suitable choice of the geometrical parameters of a silicon-wire waveguide microracetrack resonator structure can lead to a substantial improvement in the control of coupling coefficients and, hence, the design of ultracompact devices for high-performance channel add-drop filters and all-optical switching applications. On the one hand, some simple theoretical arguments and simulation results indicate that the reduction of the silicon-wire rectangular waveguide cross-section area (width×height) is possible, from standard (450 nm×220 nm) to (380 nm×200 nm) on both the bus and the resonator waveguides; this action, apart from still guaranteeing a quasi-TE single-mode operation, would provide an effective improvement into scale-of-integration by a 1.30 factor per device volume. On the other hand, it will be shown by a semianalytical method (analytical calculation + numerical simulation) that achieving the waveguide-racetrack optimal coupling condition for a particular application can be reduced to a prime calculation of the main resonator geometrical parameters (bend radius, straight length, air gap and overall coupling length). In particular, the design of high-performance ultracompact waveguide-racetrack resonator structures, with pre-established Q factor (Q≥2000), free spectral range (FSR≥15 nm), full width at half-maximum (FWHM≤5 nm), finesse (F≥40) or extinction ratio signals (ER≥20 dB) can be systematically obtained with this procedure.

Dromion-like soliton interactions for nonlinear Schrödinger equation with variable coefficients in inhomogeneous optical fibers

In this paper, a generalized nonlinear Schrodinger equation with variable coefficients is investigated. According to the analytic soliton solutions, the dromion-like structures between soliton interactions are revealed, and interaction properties are discussed. By changing the values of gain/loss, group velocity dispersion and self-phase modulation parameters, influences of them on interaction intensity and phase of solitons are presented. Besides, methods of controlling the path and spacing of solitons are suggested. Results of this paper may be potential valuable to the study of soliton interactions in inhomogeneous optical fibers and have applications in all-optical switches.

Broadband nonlinear optical response in Bi2Se3-Bi2Te3 heterostructure and its application in all-optical switching

Compared with homogeneous two-dimensional materials, two-dimensional nanomaterial heterostructures which consist of different kinds of two-dimensional materials exhibit stronger light-matter interaction. The topological insulator of Bi2Se3-Bi2Te3 heterostructures were synthesised by two-step reaction proceeding. The reaction arised in two steps: at first, Bi2Se3 nanosheets were prepared in the solvent of ethylene glycol (EG); secondly, Bi2Te3 was epitaxial grown on the Bi2Se3 nanosheets to form heterostructure materials. The spatial self-phase modulation (SSPM) effect of 457nm, 532nm and 671nm was achieved by dispersing the as-prepared Bi2Se3-Bi2Te3 heterostructure materials into ethanol as an optical medium. Furthermore, based on the effect of SSPM, a device called all-optical switching was also realized. As an interesting nonlinear optical materials, topological insulator Bi2Se3-Bi2Te3 heterostructures might be an effective proposal for photonics devices such as optical switchings, optical modulators, photodetectors, etc.

Four-wave mixing response in a hybrid atom-optomechanical system

We study the four-wave mixing (FWM) effect in a hybrid atom-optomechanical system, which is composed of an ensemble of two-level atoms trapped inside an optical cavity and a moveable cavity mirror serving as a mechanical resonator. It is shown that the FWM signal in this hybrid system can be significantly enhanced due to the coupling between the optical cavity and the atom ensemble. The larger the atom-cavity coupling strength is, the stronger the FWM will be. More interestingly, the FWM signal can be effectively modulated by the atom-pump detuning. It is demonstrated that, just by tuning this detuning to be positive or negative, the FWM signal can be easily switched on or off for the zero probe-pump detuning case. The obtained results may have potential applications in all-optical wavelength convertors, all-optical switches, or other optical devices.

Plasmonic resonant nonlinearity and synthetic optical properties in gold nanorod suspensions

We experimentally demonstrate self-trapping of light, as a result of plasmonic resonant optical nonlinearity, in both aqueous and organic (toluene) suspensions of gold nanorods. The threshold power for soliton formation is greatly reduced in toluene as opposed to aqueous suspensions. It is well known that the optical gradient forces are optimized at off-resonance wavelengths at which suspended particles typically exhibit a strong positive (or negative) polarizability. However, surprisingly, as we tune the wavelength of the optical beam from a continuous-wave (CW) laser, we find that the threshold power is reduced by more than threefold at the plasmonic resonance frequency. By analyzing the optical forces and torque acting on the nanorods, we show theoretically that it is possible to align the nanorods inside a soliton waveguide channel into orthogonal orientations by using merely two different laser wavelengths. We perform a series of experiments to examine the transmission of the soliton-forming beam itself, as well as the polarization transmission spectrum of a low-power probe beam guided along the soliton channel. It is found that the expected synthetic anisotropic properties are too subtle to be clearly observed, in large part due to Brownian motion of the solvent molecules and a limited ordering region where the optical field from the self-trapped beam is strong enough to overcome thermodynamic fluctuations. The ability to achieve tunable nonlinearity and nanorod orientations in colloidal nanosuspensions with low-power CW laser beams may lead to interesting applications in all-optical switching and transparent display technologies.

Terahertz polarization-insensitive and all-optical tunable filter using Kerr effect in graphene disks arrays

In this paper, we propose and investigate a novel terahertz all-optical tunable filter comprised of arrays of graphene microdisks deposited on a dielectric substrate. The proposed filter exhibits a wide-angle response and also due to the symmetric structure is polarization-insensitive. The transmission line theory (TLT) using the circuit model of graphene disks arrays consists of parallel series R-L-C is exploited to investigate the structure for various lattice fill-factor and chemical potential. The results obtained via this approach show excellent agreement with the results of a second different method using the Full-wave numerical modeling. The novel proposed TLT method using an easy to implement MATLAB code takes advantage of extremely short computational time (less than a few seconds) along with a significant reduction in the required memory in comparison to the Full-wave simulations. In addition, the Kerr nonlinearity is studied through the harmonic balance method in steady-state regime. Our investigation reveals that a linear Red-shift occurs in the transmission spectra as the intensity of incident light increases. The proposed filter has potential applications in spectral imaging, communication systems and all-optical switching in the terahertz band.

Micromagnetic Studies of Laser-Induced Magnetization Dynamics in FePt–C Films

Laser-induced magnetization switching has been studied extensively for its applications in heat-assisted magnetic recording (HAMR) and all-optical switching (AOS), since Beaurepaire etal. found that magnetizations can respond to the femtosecond time scale laser pulse [1]. With the help of heat and assistance of external field or helicity-dependent magneto-optical effect, magnetizations switch in an ultrafast regime of picoseconds [2]. Recently, micromagnetic simulations based on LLB equation have been used to study the magnetization dynamics and switching in FePt films [3], [4]. In this work, the hybrid Monte Carlo (HMC) micromagnetics developed by the authors [5], [6] will be utilized to analyze the laser-induced magnetization switching. In this work, we built a model of FePt-C granular film with Voronoi polycrystalline structure. Some magnetic and structural parameters are derived by experimental measurements [7]. The total simulated area is 32nm $\times 32$ nm $\times 8$ nm, divided into a regular mesh of 2.5nm $\times 2.5$ nm $\times 2$ nm micromagnetic cells and the number of crystalline grains is 48. At $\mathrm {T}=0\mathrm {K}$, in crystalline grains, the saturation $M_{s}(0)$ is 1300 emu/cc, the exchange constant $A_{1}^{\ast }$ is $6.8 \times 10 ^{-7}$ erg/cm and the anisotropy energy $K(0)$ is $4.5 \times 10 ^{7}$ erg/cm 3; at disorder grain boundary, $M'_{s}(0)$ is $0.1 M_{s}(0)$, $A_{2}^{\ast }$ is $0.2 A_{1}^{\ast }$ and $K'(0)$ is 0.1 K(0) [7]. In simulation of laser-induced magnetization dynamics, the temperature profile of the laser shooting process is vitally important. In LLB micromagnetics, two-temperature model (2TM) is commonly used to get the profile of the electron temperature, which is then introduced in LLB equation via the spin coupling parameter $\lambda $. But some parameters in 2TM model are quite arbitrary. In HMC micromagnetics, we use the time-resolved magneto-optical kerr effect (TR-MOKE) to get the spin temperature profile directly. The time resolved kerr rotation, which is proportional to magnetization, is measured with an external magnetic field 2 T applied in the direction of initial magnetization to ensure that all magnetizations are saturated in one direction. The measurement and simulation results are shown in Fig. 1 and Fig. 2. The measured kerr rotation signal is shown in Fig.1(a). In Fig. 1(a), in the process of $\sim 290$ fs laser shooting, the kerr rotation decreases rapidly and then recovers slowly, which results from the rapid demagnetization and slower recovery of magnetization. Additionally, with higher laser power, the kerr rotation decreases to a critical minimum point where the magnitude of magnetization gets closely to zero, so that we can get the scaling relationship between the kerr rotation signal and the magnetization. We assume a spin temperature profile in Fig.1(b), and the HMC micromagnetics is performed with $M_{s}(T)$ determined by the mean field Brillouin function based on the temperature profile $T(t)$ in Fig.1(b) [8]. The simulated averaged M(t) curves fit well with the measurements in Fig.1(a), which in turn convince the correct choice of the spin temperature profile in Fig.1(b). So that HMC micromagnetics can be further utilized to study the laser-induced magnetization dynamics with various external magnetic fields or circularly polarized light.

Photonic crystal directional coupler for all-optical switching, tunable multi/demultiplexing and beam splitting applications

ABSTRACTIn this paper, we introduce a new configuration based on the combination of photonic crystal directional coupler and nonlinear electromagnetically induced transparency (EIT) phenomenon in solid-state materials. The proposed structure has the abilities of switching, tunable multi/demultiplexing and tunable power beam splitting. These applications are attainable in the same structure by modulating the refractive index of special regions via EIT effect. This effect causes a high reduction in the required optical control power for the desired refractive index change, compared to the other nonlinear methods. Band structure calculations and simulations of optical field propagation through the device are done by plane wave expansion and finite difference time domain methods, respectively. In the switching mechanism, extinction ratios of 11.38 dB in the linear regime (with the control signal being off) and 26.63 dB in the nonlinear regime (with the presence of control signal) are achievable. Also, the proposed structure operates as a two-channel multi/demultiplexer for wavelengths of 1550 nm and 1480 nm in the linear regime, for wavelengths of 1550 nm and 1600 nm in both linear and nonlinear regimes, and for wavelengths of 1480 nm and 1600 nm in the nonlinear regime (the nonlinear regime is the same as the nonlinear regime for the switching). Since different refractive indices are obtained by changing the power of the control signal, the wavelengths for multi/demultiplexer operation can be tunable. Finally, simulation results show that the suggested structure can operate as a tunable power beam splitter at the wavelength of 1550 nm.

Non-Condon Effects in the Resonance Hyper-Raman Scattering of Chalcogen-Substituted Rhodamine Derivatives

Molecules with a strong two-photon response have gained significant interest because of their applications in two-photon imaging, all-optical switching, and energy up-conversion. The surface-enhanced hyper-Raman scattering (SEHRS) of tetramethyl chalcogenorosamines are taken on- and off-resonance and compared to time-dependent density functional theory calculations. Specifically, changes in the SEHRS spectra are tracked as a function of structural geometry because of perturbations induced by larger chalcogen atom substitutions to the xanthene ring. Here we show that the spectral changes and non-Condon effects can be understood by tracking the vibrational normal modes and the vibrationally induced changes to the highest occupied molecular orbitals. With a system in place to explore the relationship between structural geometry and nonlinear properties, various rhodamine derivatives can be characterized as a means to optimally design a series of two-photon bright compounds.

Design and modeling of mode-conversion in ring resonator and its application in all-optical switching

The present paper describes the mode conversion of the optical signal using single waveguide coupled silicon micro-ring resonator (MRR). The mode conversion occurs between quasi-TM and the quasi-TE mode at the through port output with the application of the suitable optical pump power. The modeling of mode-conversion using ring resonator is performed through MATLAB as well as by finite-difference-time-domain (FDTD) simulation and further used to perform the all-optical switch. The refractive index contrast, height to width ratio of the waveguide and the choice of suitable wavelength and power for optical pumping and source are responsible for mode-conversion in the ring resonator. The application of mode-conversion to design all-optical switch in MRR is also included in the paper. Mode-conversion in terms of electric field intensity at a resonant wavelength of around 1.53 μm occurs and is utilized to design all-optical switch. The results obtained from both MATLAB and FDTD justify each other and validate the proposed concept. Some ‘Figure of merits’ and ‘Spectral parameters’ are calculated in the report to analyze the performance of the design.

Optical Kerr effect and two-photon absorption in monolayer black phosphorus

A theoretical treatment of nonlinear refraction and two-photon absorption is presented for a novel two-dimensional material, monolayer black phosphorus (or phosphorene), irradiated by a normally incident and linearly polarized coherent laser beam of frequency ω. It is found that both the nonlinear refractive index n2(ω) and the two-photon absorption coefficient α2(ω) of phosphorene depend upon the polarization of the radiation field relative to phosphorene’s crystallographic axes. For the two principal polarization directions considered—viz, the armchair () and zigzag (), the calculated values of n2 and α2 are distinguished by the order of their magnitude, with the n2 and α2 values being greater for the direction. Furthermore, for almost all the incident photon energies below the fundamental absorption edge, except its neighborhood, the signs of n2 as well as α2 for the and polarization directions are opposed to each other. Also, for both the directions, the change of sign of n2 is predicted to occur in the way between the two-photon absorption edge and the fundamental absorption edge, as well as in the near vicinity of the latter, where the Kerr nonlinearity has a pronounced resonant character and the magnitude of n2 for the and polarization directions reaches its largest positive values of the order of 10−9 and 10−10 cm2 W−1, respectively. The implications of the findings for practical all-optical switching applications are discussed.

Temporal rocking in a nonlinear hybrid optomechanical system

We explore theoretically the optomechanical interaction between a light field and a mechanical mode mediated by a Kerr nonlinear medium inside a Fabry-Perot cavity. When the system is driven by a strong and fast amplitude-modulated light field, i.e., in the so-called temporal rocking region, the cavity field and the mechanical oscillator show the characteristics of multistability. The rocking breaks down the continuous phase symmetry of the cavity field to a bistable case of two equivalent states with exact π phase difference. In addition, the rocking can significantly enhance the optomechanical coupling between the light field and the mechanical oscillator, which can be used as a new handle to control the normal mode splitting of the mechanical spectrum. Moreover, the optomechanical cooling rate can be greatly modified by the rocking. With the optimized rocking parameters, the mechanical oscillator can be cooled down to its ground state more efficiently. Such a temporal rocking optomechanical system has potential applications in all-optical switching and enhancement of quantum effects.

Optically induced atomic lattice with tunable near-field and far-field diffraction patterns

Conventional periodic structures usually have nontunable refractive indices and thus lead to immutable photonic bandgaps. A periodic structure created in an ultracold atoms ensemble by externally controlled light can overcome this disadvantage and enable lots of promising applications. Here, two novel types of optically induced square lattices, i.e., the amplitude and phase lattices, are proposed in an ultracold atoms ensemble by interfering four ordinary plane waves under different parameter conditions. We demonstrate that in the far-field regime, the atomic amplitude lattice with high transmissivity behaves similarly to an ideal pure sinusoidal amplitude lattice, whereas the atomic phase lattices capable of producing phase excursion across a weak probe beam along with high transmissivity remains equally ideal. Moreover, we identify that the quality of Talbot imaging about a phase lattice is greatly improved when compared with an amplitude lattice. Such an atomic lattice could find applications in all-optical switching at the few photons level and paves the way for imaging ultracold atoms or molecules both in the near-field and in the far-field with a nondestructive and lensless approach.

On the tunability of quality-factor for optical Tamm plasmon modes

We present a comprehensive investigation to ascertain the impact of gold and silver films on modifying the quality-factor (Q-factor) of optical Tamm-plasmon (OTP) resonance in a metal-distributed Bragg reflector (M-DBR) geometry. Here, OTP mode is excited using direct incidence of white-light-source at normal incidence as well as oblique incidence on M-DBR geometry. The lifetime of OTP in gold and silver deposited films on DBR mirror was determined from OTP resonance linewidth. The lifetime and the Q-factor of OTP modes are found to depend on DBR bilayers, metal film thickness as well as on different plasmon active metals. This finding would facilitate tuning the Q-factor and consequently, the lifetime of OTP modes for various applications in all-optical switches and modulators. In addition, we discuss the spectral characteristics of OTP modes excited using normal and oblique incident of source.

Assessment of Front-Substituted Zwitterionic Cyanine Polymethines for All-Optical Switching Applications

Cyanine dyes in dilute solution have demonstrated the required third-order nonlinear optical properties necessary for all-optical switching (AOS) applications. However, in the solid state, interactions between the cyanine and its counterion typically induce significant geometric and electronic changes. When the counterion localizes toward one end of the cyanine, symmetry is broken and the figure-of-merit for AOS is dramatically reduced. Here, we use quantum-chemical methods to assess zwitterionic cyanines based on the heptamethine thiopyrylium dye as a means to eliminate untethered counterion interactions. In these zwitterionic systems, rigid π-conjugated substituents oppositely charged to the cyanine backbone are added to the thiopyrylium central carbon atom. For substituents that are unable to retain their anionic charge, and thus have a lower degree of zwitterionic character, electronic coupling between the substituent and cyanine backbone leads to profound geometry modifications and the thiopyrylium e...

Two narrow dark polaritons in triple-well microcavity based on double tunneling induced transparency

In this paper, we propose and demonstrate that two dark polaritons can be generated in a microcavity that several periods of asymmetric triple-quantum wells are embedded in. They are created by the intracavity coherent effects based on tunneling induced transparency and can be switched by using an external laser. The group time delay of this system is calculated to show the slow dark polaritons. The results have potential applications in all-optical switching and buffering in nano-scale.