The operation of an optical neural network via feed-forward (FF) configuration is experimentally simulated in the laboratory. The FF setup is tested using optical injection (OI), and the behavior of follower laser diodes (FLDs) subjected to chaotic modulation is examined. The last two laser diodes (LDs) are exposed to different weights of chaotic modulated signals through optical filtration and current modulation. Observations of the emissions from these two FLDs during FF operation are verified by frequency spectra calculated from time series data. Signal broadening is assessed by measuring the full width at half maximum (FWHM), and chaotic signal spikes are analyzed by counting the number of peaks associated with signal amplitudes for the FLDs. Additionally, LD control parameters, including the bias voltage of the influencer laser diodes FLD and two additional FLDs, are examined. A maximum FWHM of 1.8 GHz for FLD is observed with a bias voltage of 3.9V (B) and a modulated signal attenuation of -12dB. To determine the synchronization state, the correlation between the ILDs and FLDs is calculated. Results indicate fluctuations between negative and positive values, with the best correlation value ILD1-FLD4 -0.8. These results confirm anti-synchronized ILD-FLDs, which represents a promising feature for potential secure communication architectures based on chaotic optical neural networks, subject to further experimental verification.
We investigate the control effect of time reflection on the propagation of Airy derivative pulses, with particular emphasis on the first-order derivative case, referred to as the Airyprime pulse. The spectrum of the Airyprime pulse undergoes either compression or expansion depending on whether the dispersion regime is normal or anomalous. By adjusting the refractive index and the position of the time reflection interface, both the main-lobe splitting distance and the shift of the high-frequency spectral peak can be effectively controlled. Additionally, the maximum peak intensity consistently appears near the temporal boundary-a property we define as temporal boundary following performance (TBFP). Further numerical simulations reveal that Airy derivative pulses exhibit a more pronounced TBFP compared with conventional Airy pulses, and this performance can be further enhanced by increasing either the refractive index or the derivative order. In the anomalous dispersion regime, the presence of time reflection increases the spectral modulation depth, resulting in transmitted pulses with higher energy and more significant velocity variations. These findings suggest potential applications in optical manipulation and pulse amplification.
The nonlinear optical (NLO) properties of twisted donor-acceptor (D-A) molecules composed of perylene diimide (PDI) and [6]helicene units were systematically investigated using density functional theory (DFT). The results indicate that the number of helicene units had a greater influence on the energy gap (E gap ) than their relative spatial arrangement, enabling efficient directional through-space charge transfer (TSCT) from [6]helicene to PDI. Molecule 1, bearing a single [6]helicene unit, exhibited the smallest E gap (2.531 eV), highlighting its potential as a narrow-bandgap organic semiconductor with pronounced CT characteristics. Notably, the first hyperpolarizability (β tot ) value was governed primarily by the consistency of the helicene rotation directions rather than by whether the helicene units were located on the same or opposite sides of the PDI core. Molecules 3 (1.8 × 10 −29 esu) and 5 (1.3 × 10 −29 esu) showed larger β tot values because their two helicene units rotated in the same direction, which induced synergistic chirality and dipole alignment, resulting in a stronger non-centrosymmetric charge distribution and enhanced β tot value. These findings emphasized that the rotation direction of the helicene units played a crucial role in regulating the TSCT and thereby controlling the NLO properties of twisted D-A molecules. These insights provide a new strategy for designing high-performance organic NLO materials.
This study investigates the critical role of metal doping position in modulating electronic properties of thiacalix[4]arene (TC4A) and fullerene (C[Formula: see text]) supramolecular complexes. Alkali metals were introduced into the TC4A cavities or the C[Formula: see text] cages, generating two distinct configurations (M@TC4A-C[Formula: see text] and M@C[Formula: see text]-TC4A). A striking finding was that embedding alkali metal into the C[Formula: see text] cage leads to a marked increase in the first hyperpolarizability ([Formula: see text]). A likely origin of large [Formula: see text] values for the M@C[Formula: see text]-TC4A configuration arises from the lower transition energy and pronounced charge transfer transition in the main excited state. This work provides theoretical guidance for developing high-performance nonlinear optical devices.
This study presents a highly responsive surface plasmon resonance (SPR) biosensing platform that employs a WS 2 /graphene hybrid interface for refractive index (RI) driven identification of vitiligo-affected skin tissues, including the epidermis, dermis, collagen, keratin, and melanin layers. Comprehensive structural optimization is performed by examining the angular reflectance characteristics using the transfer matrix formalism. The configuration is numerically investigated in COMSOL Multiphysics through the wave-optics module, enabling detailed evaluation of the transverse magnetic field distribution. Simulation outcomes confirm that incorporating WS 2 with graphene substantially strengthens the electromagnetic coupling via enhanced field localization and increased penetration depth, which collectively elevate the sensing capability. Sensitivity benchmarking is conducted by tuning the number of WS 2 and graphene layers, revealing that the optimized design attains a peak sensitivity of [Formula: see text]/RIU, quality factor of 136.79 RIU[Formula: see text]. Overall, the proposed WS 2 /graphene-enhanced SPR architecture emerges as a robust, label-free, and noninvasive diagnostic tool for vitiligo sensing applications.
Pure AlCOB and Nd:AlCOB glasses with compositions xNd 2 O 3 -(1-x)Al 2 O 3 -8CaO-3B 2 O 3 (x = 0 and 0.05) were prepared by the melt-quenching method and characterized by XRD, EDAX, FTIR, DTA, UV–Vis–NIR spectroscopy, photoluminescence and Z-scan measurements. XRD confirmed the amorphous nature of both glasses, while FTIR identified BO 3 - and BO 4 -based structural units. The optical cut-off shifted from 326 to 374 nm after Nd 2 O 3 addition, and the effective directallowed Tauc gap decreased from 3.72 ± 0.03 to 3.11 ± 0.03 eV. The reduction is associated with Nd-induced short-range network distortion, non-bridging oxygen formation, localized states and increased polarizability. Nd:AlCOB showed T_g at 421 °C and crystallization events near 512 and 582 °C. Under 582 nm excitation, emission bands occurred at 985/997, 1060 and 1330 nm, corresponding to transitions from the 4 F 3/2 level. The intense 1.06 μm emission and measurable third-order optical nonlinearity indicate the potential of Nd:AlCOB as a near-infrared laser-active and nonlinear optical glass.
A passively Q-switched single-frequency orange–yellow pulsed laser at 593[Formula: see text]nm is demonstrated using an LD-pumped Nd:YVO 4 crystal to generate simultaneous dual-fundamental waves at 1064[Formula: see text]nm and 1342[Formula: see text]nm. A Ti 3 C 2 T[Formula: see text] film (modulation depth 7.24%) serves as the saturable absorber. Intracavity photon densities are balanced at a 1:1 ratio via a Brewster window, while a Fabry–Pérot etalon enforces single longitudinal mode operation. Sum-frequency generation in an LBO crystal produces 593[Formula: see text]nm pulses. At a pump power of 5.8[Formula: see text]W, the laser delivers an average power of 50.8[Formula: see text]mW at 525.6[Formula: see text]kHz, with 36[Formula: see text]ns pulse width and 6.55[Formula: see text]MHz Lorentzian optical linewidth. Over 4[Formula: see text]h, power instability and RMS noise remain below [Formula: see text]% and 0.32%, respectively. The combination of Brewster window polarization control, F–P etalon mode selection, and Ti 3 C 2 T[Formula: see text] film Q-switching provides a feasible route to stable, low-noise single-frequency orange–yellow pulsed emission.
Monitoring the progression of bone fracture healing is essential for successful clinical outcomes. Conventional X-ray imaging involves repeated radiation exposure, necessitating frequent and radiation-free evaluation techniques. Interfragmentary strain (IFS) is a key biomechanical marker of healing progression. This study proposes a non-invasive optical instrumentation for monitoring fracture healing via IFS measurement. An ex vivo tibial fracture stabilization model was developed using Agilus elastomer callus replicas of varying stiffness. Fiber Bragg Grating (FBG) sensors mounted on Schanz pins measured strain under controlled axial displacement. Results demonstrated reduced strain with increasing callus stiffness, establishing a non-invasive and radiation-free assessment of fracture consolidation.
The heterojunction engineering can provide an effective platform for optimizing and synthesizing the properties of nanomaterials. Herein, the TiS 2 powder was synthesized via the solid-phase sintering method and the TiS 2 /graphene (TiS 2 /G) heterostructure film with enhanced saturable absorption was developed by using the liquid-phase exfoliation and the layer-by-layer spin-coating techniques. Measurement results at 2.8[Formula: see text][Formula: see text]m revealed that it exhibited a modulation depth of [Formula: see text]5.7%, an obvious enhancement compared to the [Formula: see text]4.2% of pure TiS 2 film, meanwhile, the saturation intensity was [Formula: see text]0.12[Formula: see text]MW/cm 2 , markedly lower than [Formula: see text]0.17[Formula: see text]MW/cm 2 of solo TiS 2 device. With this SAM, a robust passively Q-switched Er:YAP bulk laser operating at [Formula: see text]2.8[Formula: see text][Formula: see text]m was demonstrated. The maximal signal-to-noise ratio of the stable pulse sequence reached 35[Formula: see text]dB at an absorbed pump power of 6.1[Formula: see text]W, with a repetition rate of 177.3[Formula: see text]kHz, a pulse width of 232[Formula: see text]ns and an average output power of 0.42[Formula: see text]W. This functional TiS 2 /Graphene heterostructure film can provide an available optical modulator for a robust passively Q-switched laser operation in the mid-infrared band.
The spatial light modulator (SLM) based on a metasurface incorporating organic electro-optic (OEO) polymer shows great promise due to its highly efficient modulation. However, precise regulation of the modulated light polarization state is necessary to achieve satisfactory modulation, which might be demanding in some scenarios. On the other hand, micro–nano modulators based on organic polymers face the challenges of low-[Formula: see text] and limited light–matter interaction length. Here, we present a high-[Formula: see text] and polarization-insensitive single-pixel SLM consisting of periodic cylindrical silicon nanopillars and coated with polymer. Consequently, it achieves polarization insensitivity for incident light at any polarization state, in principle with a simulated [Formula: see text] factor of 1051.3 and an experimental [Formula: see text] factor of 465.2. At the telecommunications wavelength, the maximum tuning sensitivity is 0.083[Formula: see text]nm/V and the maximum extinction ratio is 15.9[Formula: see text]dB. Its comprehensive performance is competitive for polarization-insensitive SLM. The modulator also features high-speed modulation and simple processing, enabling practical applications of metasurface.
In this paper, we investigate the effect of Er[Formula: see text]ion concentration on the transfer of orbital angular momentum (OAM) in an Er[Formula: see text]-doped yttrium aluminum garnet (YAG) crystal with a three-level ladder-type configuration, mediated by the optical nonlinear process of three-wave mixing (TWM). The OAM information from the incident vortex probe field can be transferred to the generated mixing field through the optical nonlinear process. Due to the change of electric dipole moment and spontaneous emission decay induced by Er[Formula: see text]ion concentration, the OAM transfer depends sensitively on the ion concentration. Furthermore, under different Er[Formula: see text] ion concentrations, the intensity and detuning of the control field have different effects on the conversion efficiency of OAM. More importantly, the conversion efficiency of OAM can be significantly enhanced by choosing suitable values of the control intensity and detuning at [Formula: see text] Er[Formula: see text]ion concentration. Finally, we explore the effect of Er[Formula: see text]ion concentration on the spatial distribution of the probe absorption. Moreover, the spatial absorption of the probe field is shown to evolve with propagation distance within the medium. It is obvious that the spatial pattern of the probe absorption can be effectively controlled via adjusting the detuning of the probe field. Therefore, our scheme enables efficient OAM transfer via second-order nonlinear three-wave mixing in an Er[Formula: see text]-doped YAG crystal by selecting suitable Er[Formula: see text] ion concentration, and may find potential applications in nonlinear quantum optics.
HA-PMMA organic nanofiber was drawn using electrospinning technique in which organic guest orthorhombic structure Hippuric Acid (HA) embedded inside host polymer Poly (methyl methacrylate) (PMMA). SEM results show the drawn HA-PMMA fiber matrix was well-aligned, uniform, and beadless. The average diameter of HA-PMMA nanofiber is 135.4[Formula: see text]nm. The average crystalline size of HA-PMMA fiber matrix is 20.67[Formula: see text]nm. The transparency of the visible region of the HA-PMMA nanofiber was confirmed using UV–Vis spectroscopy study. SHG response of the sample was confirmed by the generation of green light under 1064[Formula: see text]nm laser excitation using Kurtz–Perry powder setup. Z-scan measurements for the third-order intensity dependent optical characteristics were analyzed using a continuous green wave laser. From the Z-scan test, a Gaussian beam obtained by open aperture (OA) confirms the saturable absorption property and closed aperture (CA) confirms the self-defocusing response of HA-PMMA nanofiber. These intriguing third-order nonlinear results confirm that HA-PMMA nanofiber may find use in photonics and optoelectronics.
This study addresses the critical need for enhanced nonlinear optical (NLO) materials by strategically doping [Formula: see text]-graphdiyne (GDY), a two-dimensional carbon allotrope with inherent NLO sensitivity, with superalkalis. Leveraging the ultra-low ionization potentials of superalkalis, we introduce novel dopants beyond conventional metal-oxide clusters: halogen-based Li 2 X (X[Formula: see text][Formula: see text][Formula: see text]F, Cl, Br) and nitrogen-based NY 4 (Y[Formula: see text][Formula: see text][Formula: see text]H, Li). Employing density functional theory (DFT) at the [Formula: see text]B97XD/6-31G(d,p) level, ground-state geometries, interaction energies, and charge transfer mechanisms were systematically evaluated. The sobEDAw analysis explicitly resolves the bonding essence between superalkalis and GDY as a closed-shell noncovalent donor–acceptor interaction, dominated by electrostatic contributions (51–56% of total attractive energy) with supplementary dispersion (33–37%) and induction (11–14%) components. Time-dependent DFT (TD-DFT) with the CAM-B3LYP functional quantified dynamic NLO properties, focusing on the first hyperpolarizability. The polarizable continuum model (PCM) calculations assessed solvent effects. A comparative study with graphene and graphyne was conducted to establish the structural advantage of GDY. Results reveal stable adducts governed by noncovalent interactions, with vertical distances and interaction energies dependent on dopant polarizability and size. Charge transfer from superalkalis to GDY significantly reduces the HOMO-LUMO gap (from 7.07[Formula: see text]eV in pristine GDY to 3.5[Formula: see text]eV in NH 4 GDY) and dramatically enhances first hyperpolarizability up to [Formula: see text] a.u. for NH 4 GDY, versus 0.07 a.u. in pure GDY. The second hyperpolarizability ([Formula: see text] is also significantly enhanced, reaching [Formula: see text] a.u. for NH 4 GDY. The two-level model attributes this enhancement to minimized excitation energies and optimized oscillator strengths. Model size convergence tests validate the reliability of the cluster model. This work establishes halogen/nitrogen superalkalis as potent dopants for GDY-based NLO materials, providing foundational insights for next-generation photonic devices.
True random numbers are essential for secure communication and quantum information technologies. We present a photonic Quantum Random Number Generator (QRNG) that utilises non-Gaussian operations to amplify intrinsic quantum randomness. The scheme uses a two-mode optical circuit initialized in a single-photon state, incorporating phase rotation, a cubic phase gate, squeezing and a balanced beam splitter to create strong nonclassical correlations. Photon-number measurements generate unbiased binary outcomes through raw bit extraction. The random number samples that pass standard statistical NIST SP800 22, 90B, Dieharder, ENT, AIS-31 test, and hamming distance confirm the robustness and reliability of the proposed approach.
While two-dimensional (2D) nanomaterials have become the primary choice for saturable absorbers (SAs) in ultrafast fibre lasers, their use remains limited by complex fabrication processes and high costs, hindering widespread adoption. In this work, we propose and demonstrate a novel SA using crystal violet (CV) dye, an effective yet easily fabricated material, which was drop-cast onto an arc-shaped fibre to form the SA. The inherent optical properties of the CV dye enable a robust nonlinear absorption response, with a modulation depth of 9.5% and a saturation intensity of 3.0 MW/cm2. When placed in a ytterbium-doped fibre laser (YDFL) cavity, it initiates and stabilizes mode locking, accompanied by nonlinear polarization rotation (NPR). The cavity successfully generates stable picosecond pulses at 1035.16 nm, with a pulse width of 14.14 ps, a 3 dB bandwidth of 3.06 nm, a fundamental repetition rate of 3.33 MHz, and a high signal-to-noise ratio (SNR) of 45.28 dB. This CV-based SA matches the mode-locking performance of advanced 2D materials while offering unparalleled advantages by leveraging a commercially available, highly cost-effective dye with a vastly simplified fabrication process. This work highlights the vital role of organic dyes in modern ultrafast photonics applications and demonstrates that CV dyes can provide compact, stable, and economically viable pathways for advanced optical modulators.
In this study, the nonlinear optical properties of ZrGeTe 4 at 1.5 [Formula: see text]m wavelength and its application in passively [Formula: see text]-switched fiber lasers are systematically investigated for the first time. The recovery time of ZrGeTe 4 is measured using the pump-probe technique, which is crucial for evaluating its performance in fast optical switching. For the characterization, SEM, EDS, AFM, and TEM were employed to confirm the particle size of the prepared ZrGeTe 4 nanoparticles, and the nonlinear optical properties of ZrGeTe 4 SA were further investigated by measuring their modulation depth and saturation intensity. The experimental results show that the [Formula: see text]-switched laser based on ZrGeTe 4 SA achieves a wide modulation frequency range from 14.95 kHz to 69.39 kHz, and the pulse width can be tuned from 7.22 [Formula: see text]s to 1.24 [Formula: see text]s. Meanwhile, the output power of the laser varies from 0.25[Formula: see text]mW to 3.88[Formula: see text]mW, and the single pulse energy ranges from 16.72[Formula: see text]nJ to 57.36[Formula: see text]nJ, demonstrating excellent [Formula: see text]-switched performance. This study not only reveals the excellent nonlinear optical properties of ZrGeTe 4 at 1.5 [Formula: see text]m but also provides a new high-performance SA for passively [Formula: see text]-switched fiber lasers, which plays an important role in promoting the development of laser technology, especially in the fields of compact, high-efficiency laser devices.
Precise wavelength stability and narrow spectral linewidths are essential for enhancing the performance of optical sensors in biomedical diagnostics and environmental gas detection. This work presents a detailed investigation of fiber Bragg gratings (FBGs) integrated within a dual-mode laser sensor system based on intra-cavity absorption spectroscopy. The Bragg wavelength stability was characterized over extended periods, demonstrating fluctuations of up to ±0.3[Formula: see text]nm without thermal insulation, which were significantly reduced to ±0.1[Formula: see text]nm with the implementation of styrofoam enclosures. Furthermore, the laser’s full width at half maximum (FWHM) was analyzed under varying injection currents, attaining a minimum linewidth of 0.06[Formula: see text]nm, thereby improving spectral selectivity. To the best of our knowledge, this is the first systematic investigation of long-term Bragg wavelength stability and FWHM behavior in a dual-mode intra-cavity absorption spectroscopy configuration, providing quantitative stability limits directly relevant to the design of highly selective gas sensors.
Elucidating the energy transfer (ET) process and further controlling the up/down luminescence in lanthanide ion-doped luminescent materials is significant in various related fields such as color display, biomedical imaging, and quantum computing. In this work, studies were performed on the ET process in erbium (Er 3+ ) and samarium (Sm 3+ ) ions co-doped BaFCl nanoparticles by measuring luminescence from spectral and time dimensions. Efficient ET was realized via the usual Er 3+ to Sm 3+ pathway by varying Sm 3+ doping concentration, achieving high efficiency of 47%. Further analysis reveals that the ET is caused by dipole-dipole interactions. Another ET process from Sm 3+ to Er 3+ was also simultaneously observed under excitation with high laser powers. Further, the dynamic luminescence decay lifetimes of Er 3+ were verified and their mechanism was analyzed in detail. The revealed ET channel provided valuable insights and different perspectives for future research on Er 3+ /Sm 3+ co-doped nanomaterials.
We investigate broadband supercontinuum in the infrared region using octagonal Ga 8 Sb[Formula: see text]S[Formula: see text] photonic crystal fibers by proposing two fiber designs with ultra-flattened all-normal and anomalous dispersion profiles with [Formula: see text][Formula: see text]ps/[Formula: see text] and [Formula: see text][Formula: see text]ps/[Formula: see text] in the wavelength regions of 3.908–8[Formula: see text][Formula: see text]m and 4.077–8.495[Formula: see text][Formula: see text]m, respectively. The first fiber with all-normal dispersion produces supercontinuum bandwidths of 7.532[Formula: see text][Formula: see text]m and 10.314[Formula: see text][Formula: see text]m (30[Formula: see text]dB level) at pump wavelengths of 4.5[Formula: see text][Formula: see text]m and 5.0[Formula: see text][Formula: see text]m, respectively, with a low peak power of 10[Formula: see text]kW due to the combination of the self-phase modulation and stimulated Raman scattering. With three zero dispersion wavelengths, the second fiber enables a supercontinuum bandwidth of 11.536[Formula: see text][Formula: see text]m (30 dB level) at the pump wavelength of 5.0[Formula: see text][Formula: see text]m with a peak power of 8[Formula: see text]kW under the influence of soliton dynamic suppression. These results, as a platform for developing broadband supercontinuum sources, are required for applications in the infrared region.
