Optical Switching Applications Research Articles

Non-linear optical properties of Sb doped InSe4 chalcogenide films for optical switching applications

Non-linear optical properties of Sb doped InSe4 chalcogenide films for optical switching applications

Spatial modulation of refractive index in a dense atomic ensemble using Laguerre–Gaussian beams

We propose a scheme to investigate the spatial modulation of the refractive index in a dense atomic ensemble under the action of the Laguerre–Gaussian (LG) beams. Theoretical derivations based on a density-matrix approach associated with numerical simulations are utilized to study the behaviors of the index of refraction, showing that the azimuthal and radial mode indices (i.e., l 2 and p 2) of the LG beams significantly affect the real and imaginary parts of the refractive index. To be specific, the number of the dispersive peaks is determined by ( p 2 + 1 ) | l 2 |, and there are 2 | l 2 | lossless petals in conjunction with p 2 concentric absorption rings centered on the vortex center. Furthermore, by tuning the phase values of the electric and magnetic components of the electromagnetic field, the index of refraction can be drastically tuned from negative to zero to positive and accompanied by periodic absorption and amplification. This investigation provides a powerful tool for manipulating the index of refraction through a nonlinear interaction between atoms and the vortex beams and suggests potential applications in optical switching, logic gates, and optical storage with spatially varying refractive indices.

Structural and optical exploration of promising zinc (8-hydroxyquinoline) thin films for wide-scale optoelectronic applications

This research presents a detailed sequential study of the thickness effect on structural, morphological, and optical properties of vacuum thermally deposited zinc 8-hydroxyquinoline (ZnQ2) thin films. The FTIR results demonstrate that ZnQ2's molecular structure has a high degree of stabilization. On the other hand, the change in thickness affects the film's roughness. The film roughness decreases to 2.398 nm as the film thickness increase to 143 nm, and then roughness increases again at a thickness of 185 nm. The optical absorption features of the prepared films are explained. The optical energy gap has been calculated and found to be in the range of (2.79–2.87) eV. Furthermore, the refractive index dispersion has been analyzed. ZnQ2 thin film of thickness 87 nm achieved the highest linear optical susceptibility, nonlinear optical susceptibility, and nonlinear refractive index. The high peak located at photon energy 4.4 eV assures the validity of the material's proposal for optical switching applications. Besides, compared to many other organic complexes, ZnQ2 is a highly recommended candidate for efficient organic optoelectronic and optical switching applications.

Double broadband enhanced absorber based on graphene-coupled metal disk resonator structure

A double broadband terahertz absorber based on nonstructured graphene with a dielectric coupled gold disk structure was investigated in this paper. The results show that one absorption band can be switched from reflection state (“OFF”) to absorption state (“ON”), and the other absorption band can be switched from reflection state (“OFF”) to absorption state (“ON”), with bandwidths of over 90% absorption ranging from 0.46 to 1.4 THz and 2.38 to 3.35 THz, respectively. Furthermore, the double broadband terahertz absorber has polarization and background refractive index insensitivity. The Fabry Perot resonance between the graphene sheet and the bottom gold reflector is primarily responsible for the double broadband absorption in graphene, which can be enhanced by the addition of a gold disk resonator. Because of the aforementioned properties, the proposed absorber has potential applications in multiple optical switches, terahertz photoelectric detectors, modulators, and sensors.

Photochromic ceramics Ca2SnO4: Ho3+ with excellent reversible photoluminescence intensity modulation properties

Inorganic photochromic (PC) materials with high light intensity modulation capability have great potential for applications in optical memory devices, optical switches, and fluorescent anticounterfeiting because of their favorable physical and chemical stability and simple synthesis. In this study, PC ceramics Ca2.02−xSnO4:xHo3+ are synthesized by a high-temperature solid-state reaction method and the microstructure and optical properties of the ceramics are analyzed. By studying their PC behavior, it is found that the coloring effect is best under 290 nm light irradiation, the ceramics change from light yellow to dark gray, and the original color of discolored ceramics basically restores after 10 min of 440 nm light irradiation. The original color can be completely recovered after heating to 623 K for 10 min. To study the reversible photoluminescence (PL) light intensity modulation performance of the material based on the PC behavior of ceramics, the maximum attenuation modulation ratio of 93.48% is detected at 550 nm after 6 min of 290 nm light irradiation, which is higher than most comparable PC ceramics. The recovery modulation ratio is 1164% after 8 min of 440 nm light irradiation. Using 290 nm light for coloring, followed by bleaching with 440 nm light or holding at 623 K for 10 min for 10 cycles, the ceramic light intensity modulation performance is almost unchanged and shows good reversibility. Finally, the mechanism behind the ceramic photochromic and reversible photoluminescence modulation is explained.

Temperature Dependence of Optical Bistability in Superconductor–Semiconductor Photonic Crystals Embedded with Graphene

We theoretically investigate the optical bistability in superconductor–semiconductor photonic crystals composed of graphene. The photonic crystals are symmetric to the center and arranged alternately by the superconductor (HgBa2Ca2Cu3O8+δ) and semiconductor (GaAs) layers. The system supports a defect mode, and graphene is located at the layer interface where the local electric field is the strongest. Consequently, the optical nonlinearity of graphene has been greatly enhanced, and low-threshold optical bistability can be achieved with an incident wavelength red-detuning to the defect mode. The upper and lower thresholds of bistability increase with the increase in the value of low environmental temperature, while the interval between the upper and lower thresholds decreases. This research has a potential application in temperature-controlled optical switches and temperature-controlled optical memory.

Excitation of multiple Fano resonances on all-dielectric nanoparticle arrays.

In this paper, an all-dielectric metasurface consisting of a unit cell containing a nanocube array and organized periodically on a silicon dioxide substrate is designed and analyzed. By introducing asymmetric parameters that can excite the quasi-bound states in the continuum, three Fano resonances with high Q-factor and high modulation depth may be produced in the near-infrared range. Three Fano resonance peaks are excited by magnetic dipole and toroidal dipole, respectively, in conjunction with the distributive features of electromagnetism. The simulation results indicate that the discussed structure can be utilized as a refractive index sensor with a sensitivity of around 434 nm/RIU, a maximum Q factor of 3327, and a modulation depth equal to 100%. The proposed structure has been designed and experimentally investigated, and its maximum sensitivity is 227 nm/RIU. At the same time, the modulation depth of the resonance peak at λ = 1185.81 nm is nearly 100% when the polarization angle of the incident light is 0 °. Therefore, the suggested metasurface has applications in optical switches, nonlinear optics, and biological sensors.

Polarization-selective narrow band dual-toroidal-dipole resonances in a symmetry-broken dielectric tetramer metamaterial.

Here we propose a metasurface consisting of symmetry-broken dielectric tetramer arrays, which can generate polarization-selective dual-band toroidal dipole resonances (TDR) with ultra-narrow linewidth in the near-infrared region. We found, by breaking the C4v symmetry of the tetramer arrays, two narrow-band TDRs can be created with the linewidth reaching ∼ 1.5 nm. Multipolar decomposition of scattering power and electromagnetic field distribution calculations confirm the nature of TDRs. A 100% modulation depth in light absorption and selective field confinement has been demonstrated theoretically by simply changing the polarization orientation of the exciting light. Intriguingly, it is also found that absorption responses of TDRs on polarization angle follow the equation of Malus' law in this metasurface. Furthermore, the dual-band toroidal resonances are proposed to sense the birefringence of an anisotropic medium. Such polarization-tunable dual toroidal dipole resonances with ultra-narrow bandwidth offered by this structure may find potential applications in optical switching, storage, polarization detection, and light emitting devices.

Tunable ultrawideband perfect absorber based on vanadium dioxide

An ultrawideband metamaterial perfect absorber based on vanadium dioxide is proposed. It achieves >95 % absorption of vertically incident electromagnetic waves in the range of 3.50 to 10 THz. The absorption intensity can be dynamically adjusted in the range of 0.2% to 99.98% by varying the conductivity of VO2. The mechanism of ultrawideband perfect absorption is interpreted using electric field distribution analysis and impedance-matching theory. The absorption rate related to the structural parameters of the absorber is investigated by numerical simulation. Finally, its polarization angle-insensitive and incidence angle-insensitive properties are demonstrated. This proposed absorber has potential applications in optical switching, electromagnetic stealth, and sensing applications.

Dynamic control of Fano-like interference in the graphene periodic structure

We propose and investigate a graphene periodic subsurface structure consisting of a coplanar pair of graphene ring resonators and a graphene ribbon. The Fano-like interference can be actively regulated by the applied magnetic field, incident angle and Fermi energy. Since the excited charges of graphene monolayer have cyclotron properties in the external magnetic field, the transmittance and line-shape can be effectively controlled. At a certain frequency, different magnetic fields have different effects on the conductivity tensor of graphene, which affects the metallic properties of graphene, leading to changes in the transmittance. The Fano-like line-shape can be regulated by adjusting the incident angle to delay the phase between adjacent graphene sheets. In addition, the resonance frequency can be electrically regulated through Fermi energy. Finite element method is introduced to analyze the graphene periodic structure and the results are demonstrated by multimode interference coupled mode theory. The Faraday rotation angle exceeding 85° are observed in a small magnetic flux density B of about 0.5 T. Moreover, a plasma-optic switching with high ON/OFF ratio and large modulation depth (MD) is designed, whose ON/OFF ratio (η) and MD are 19.921 dB and 98.982%, respectively. Notably, combining the influence of magnetic flux density on transmittance and the modulation of resonance frequency by Fermi energy, optical switching can be implemented at any frequency within the frequency range studied. These results provide methods for active regulation of electromagnetic waves in the terahertz field and have potential applications in optical switching and integrated photonic circuit.

Transition from electromagnetically-induced transparency to absorption in a single microresonator.

Electromagnetically induced transparency (EIT) and absorption (EIA) are two phenomena that can be observed in whispering-gallery-mode (WGM) optical microresonators. Transition from EIT to EIA has potential applications in optical switching, filtering and sensing. In this paper an observation of the transition from EIT to EIA in a single WGM microresonator is presented. A fiber taper is used to couple light into and out of a sausage-like microresonator (SLM) that contains two coupled optical modes with significantly different quality factors. By stretching the SLM axially the resonance frequencies of the two coupled modes are tuned to the same, a transition from EIT to EIA is then observed in the transmission spectra when the fiber taper is moved closer to the SLM. It is the special spatial distribution of the optical modes of the SLM that provide a theoretical basis for the observation.

Dynamically switchable multifunctional terahertz absorber based on graphene and vanadium dioxide hybrid metamaterials

A multifunctional terahertz absorber based on a hybrid configuration of vanadium dioxide ( V O 2 ) and graphene is proposed, which is enabled to dynamically switch between ultrabroadband and double-narrowband absorption characteristics using the phase-shifting property of V O 2 . When V O 2 is in the metallic phase and the Fermi energy level of graphene is 0.01 eV, ultrabroadband absorption from 3.04 THz to 8.78 THz can be achieved. The absorption can be continuously adjusted from 0.7% to 99.9% by changing the conductivity of the V O 2 through temperature. When V O 2 is in the insulating phase and Fermi energy level of graphene is 0.4 eV, the proposed absorber exhibits a double-narrowband absorption characteristic, achieving 99.8% and 97.3% absorption at 1.79 THz and 4.62 THz, respectively. Since graphene is an electronically controlled material, it is able to dynamically modulate the resonant frequency and absorption intensity by changing the Fermi energy level of graphene. In addition, the physical mechanism of the multifunctional absorber is revealed using electric field distribution and the impedance-matching theory. The proposed absorber has potential applications in optical switching, image processing, and stealth technology.

Stress-Induced Inversion of Linear Dichroism by 4,4'-Bipyridine Rotation in a Superelastic Organic Single Crystal.

The molecular crystals that manifest unusual mechanical properties have attracted growing attention. Herein, we prepared an organic single crystal that shows bidirectional superelastic transformation in response to shear stress. Single-crystal X-ray diffractions revealed this crystal-twinning related shape change is owed to a stress-controlled 90° rotation of 4,4'-bipyridine around the hydrogen bonds of a chiral organic trimer. As a consequence of the 90° shift in the aromatic plane, an interconversion of crystallographic a-, b-axes (a→b' and b→a') was detected. The molecular rotations changed the anisotropic absorption of linearly polarized light. Therefore, a stress-induced inversion of linear dichroism spectra was demonstrated for the first time. This study reveals the superior mechanical flexibilities of single crystals can be realized by harnessing the molecular rotations and this superelastic crystal may find applications in optical switching and communications.

Stress‐Induced Inversion of Linear Dichroism by 4,4′‐Bipyridine Rotation in a Superelastic Organic Single Crystal

AbstractThe molecular crystals that manifest unusual mechanical properties have attracted growing attention. Herein, we prepared an organic single crystal that shows bidirectional superelastic transformation in response to shear stress. Single‐crystal X‐ray diffractions revealed this crystal‐twinning related shape change is owed to a stress‐controlled 90° rotation of 4,4′‐bipyridine around the hydrogen bonds of a chiral organic trimer. As a consequence of the 90° shift in the aromatic plane, an interconversion of crystallographic a‐, b‐axes (a→b′ and b→a′) was detected. The molecular rotations changed the anisotropic absorption of linearly polarized light. Therefore, a stress‐induced inversion of linear dichroism spectra was demonstrated for the first time. This study reveals the superior mechanical flexibilities of single crystals can be realized by harnessing the molecular rotations and this superelastic crystal may find applications in optical switching and communications.

Enhancement of the photoluminescence modulation ratio in highly transparent KNN-based ceramics for optical information storage

The combination of high transmittance and large switching contrast in transmittance and photoluminescence intensity make the K0.5Na0.5NbO3–xPr ceramics promising for optical information storage and optical switch applications.

Hybrid bound states in the continuum in terahertz metasurfaces

Bound states in the continuum (BICs) have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics, biosensors, and ultrafast optical switches. The most common strategy to apply BICs in a metasurface is by breaking symmetry of resonators in the uniform array that leaks the otherwise uncoupled mode to free space and exhibits an inverse quadratic relationship between quality factor (<italic>Q</italic>) and asymmetry. Here, we propose a scheme to further reduce scattering losses and improve the robustness of symmetry-protected BICs by decreasing the radiation density with a hybrid BIC lattice. We observe a significant increase of radiative <italic>Q</italic> in the hybrid lattice compared to the uniform lattice with a factor larger than 14.6. In the hybrid BIC lattice, modes are transferred to <italic>Г</italic> point inherited from high symmetric <italic>X</italic>, <italic>Y</italic>, and <italic>M</italic> points in the Brillouin zone that reveal as multiple Fano resonances in the far field and would find applications in hyperspectral sensing. This work initiates a novel and generalized path toward reducing scattering losses and improving the robustness of BICs in terms of lattice engineering that would release the rigid requirements of fabrication accuracy and benefit applications of photonics and optoelectronic devices.

Nonlinear optical response of graphene oxide quantum dots fabricated from electrospun polyacrylonitrile fibers

The nonlinear optical response of graphene oxide quantum dots (GOQDs) fabricated by the carbonization and exfoliation of electrospun polyacrylonitrile (PAN) fibers is reported. Electrospun and carbonized fibers were characterized by SEM and XPS. SEM micrograph confirmed the formation of PAN fibers of 153.44 ± 6.44 nm, while by XPS the binding energies associated with sp2 and sp3 carbon hybridizations were found, after the carbonization process. On the other hand, the GOQDs obtained were characterized by photoluminescence (PL), UV–Vis, Raman spectroscopy, and High-Resolution Transmission Electron Microscopy (HRTEM). The GOQDs size of 10 nm was estimated by HRTEM. Raman spectroscopy showed the D and G bands associated with the sp2 and sp3 hybridizations of the GOQDs, by PL two energy values of 2.67 and 2.97 eV were calculated. The UV–Vis spectrum showed two absorption bands confirming the presence of GOQDs. The nonlinear characterization was carried out using the P-scan technique, previously photodepositing GOQDs onto an optical fiber, using a coherent radiation source at a wavelength of 1550 nm. The results obtained showed a saturable absorption behavior with a value of β=−2.474×10−4m/W and a nonlinear susceptibility of χ(3)≈−7.749×10−4(esu). The results of this work showed that GOQDs obtained can be used for optical switching applications.

Ultrafast nonlinear absorption with multiple transformations and transient dynamics of gold nanobipyramids.

The process and condition of saturable absorption (SA) and reverse saturable absorption (RSA) of ultrafast nonlinear optics in metal nanoparticles are essential for applications including light generation, amplification, modulation, and switching. Here, we first discover and explore the multiple transformations (SA-RSA-SA) of ultrafast nonlinear absorption behavior of metal nanoparticles in femtosecond pulses. Correspondingly, the energy level model and fitting formula of multiple transformations are established to illustrate the process of optical response. The femtosecond transient absorption spectra provide information about their ultrafast dynamics process and vibrational mode, which further reveals the multiple transformation mechanisms of nonlinear absorption in gold nanobipyramids (Au-NBPs). Furthermore, Au-NBPs exhibit a significantly higher SA modulation depth up to 42% in the femtosecond, which is much higher than the reported values of other nanomaterials. Our results indicate that Au-NBPs can be used as broadband ultrafast Q-switching and mode-locking, and the conversion offers new opportunities for metal nanostructures in applications of optical switching.

Junction‐Enhanced Polarization Sensitivity in Self‐Powered Near‐Infrared Photodetectors Based on Sb2Se3 Microbelt/n‐GaN Heterojunction

AbstractPolarization‐sensitive photodetectors (PDs) based on anisotropic materials spark considerable interest for their potential applications in security surveillance, optical switches, and remote sensing. However, high‐thickness or bulk anisotropic materials generally exhibit low polarization sensitivity, hindering their practical applications in polarization photodetection. Herein, a near‐infrared (NIR) PD based on a p‐type Sb2Se3 microbelt (MB)/n‐GaN heterojunction is proposed. The Sb2Se3 MB/GaN PD effectively combines the anisotropy of the Sb2Se3 MB with the heterogeneous integration. The PD presents self‐powered detection properties with a responsivity over 12 mA W−1, a specific detectivity exceeding 5 × 1010 Jones, and a response speed (the rising/decaying times ≈74 ms/75 ms) under NIR illumination. More importantly, the heterojunction‐based PD has a higher anisotropy ratio of 1.37, which is 1.3 times amplified as compared to the vertical photoconductive‐type PDs (the anisotropy ratio of 1.06). The p‐n junction's effect on carrier generation and recombination causes the increased polarization sensitivity of Sb2Se3 MB/GaN PDs, as confirmed by finite element method analysis. This work not only offers a deeper insight into polarization sensitivity regulated by junction or interface but also provides a practical method for developing high‐sensitivity polarization detectors based on high‐thickness or bulk anisotropic materials.

Coherent control of spatial and angular Goos-Hänchen shifts with spontaneously generated coherence and incoherent pumping.

We propose an efficient scheme to manipulate the Goos-Hänchen (GH) shift of a reflected beam from a metal-clad waveguide, where a coherent atomic medium with a Λ-type configuration is employed as the substrate. Using experimentally achievable parameters, we identify the conditions under which spontaneously generated coherence (SGC) allows us to enhance the spatial and angular GH shifts of the reflected beam. With the help of SGC, the relative phases of the probe and control fields can alter the absorption gain and refractive index of the atomic medium, thereby manipulating the magnitudes, signs, and positions of the spatial and angular shifts. Furthermore, the spatial and angular GH shifts can be coherently controlled via adjusting the incoherent pumping rate and the intensity of the control field. Our proposal provides an avenue for the manipulation of spatial and angular GH shifts and potential applications in optical switching and optical steering.