Search Results (77)

The reservoir computing approach based on a semiconductor laser with optoelectronic time-delay feedback is distinguished by its simplicity, speed, and reliability. However, the response of the reservoir to the input signal in this configuration is a superposition of the laser relaxation oscillations, which has limited complexity, which may therefore reduce computational performance when solving problems requiring high nonlinearity. We experimentally demonstrate a combination of postprocessing techniques that overcome this limitation through upsampling and state space expansion using a nonlinear transformation of nodal functions, and show how this results in an order-of-magnitude reduction in prediction error for the Santa Fe task. Full article

Zinc oxide (ZnO) thin films were deposited by radio-frequency reactive magnetron sputtering at a cryogenic substrate temperature of −78 °C to explore a novel low-thermal-budget route for semiconductor growth. Despite the extremely low temperature, X-ray diffraction revealed spontaneous partial crystallization of wurtzite ZnO upon warming to room temperature, driven by strain relaxation and stress coupling at the ZnO/SiO₂ interface. Atomic-force and scanning-electron microscopies confirmed nanoscale hillock and ridge morphologies that correlate with in-plane compressive stress and out-of-plane tensile strain. Spectroscopic ellipsometry, modeled using a general oscillator (GO) mathematical model approach, determined a film thickness of 60.81 nm, surface roughness of 3.75 nm, and a direct optical bandgap of 3.40 eV. Photoluminescence spectra exhibited strong near-band-edge emission modulated with LO-phonon replicas at 300 K, indicating robust exciton–phonon coupling. This study demonstrates that ZnO films grown at cryogenic conditions can undergo substrate-induced self-crystallize upon warming, which eliminates the need for thermal annealing. The introduced cryogenic self-crystallization regime offers a new pathway for depositing crystalline semiconductors on thermally sensitive or flexible substrates where heating is undesirable, enabling future optoelectronic and photonic device fabrication under ultra-low thermal-budget conditions. Full article

Nitrogen-fused conjugated heterocycles have attracted growing interest owing to their tunable electronic properties and potential in organic optoelectronics. In this study, two centrosymmetric donor–acceptor-type emitters PP-6F and PPA-3F were designed by incorporating trifluorophenyl and anthracene acceptor units into a pyrrolo[3,2-b]pyrrole (PP) framework. The experimental and theoretical results reveal that subtle modulations in molecular conformation and π-conjugation pathways strongly affect the excited-state characteristics. PP-6F, featuring a nearly coplanar donor–acceptor configuration, exhibits efficient π-electron delocalization and a dominant local excitation (LE) emission with a large oscillator strength. In contrast, the bulky anthracene in PPA-3F increases the donor–acceptor dihedral angle, reduces conjugation coupling, and promotes orbital separation, leading to a hybrid intramolecular charge transfer and local excitation (ICT/LE) excited state. The rigid anthracene framework suppresses structural reorganization and nonradiative decay, allowing PPA-3F to retain a relatively high oscillator strength despite its charge-transfer nature. This work demonstrates that fine-tuning donor–acceptor dihedral angles and conjugation continuity within PP-based systems is an effective strategy for balancing LE and ICT emissions and developing high-efficiency nitrogen-fused organic emitters and scintillators. Full article

Copper nitride (Cu₃N) is gaining attention as an eco-friendly thin-film semiconductor in a myriad of applications, including storage devices, microelectronic components, photodetectors, and photovoltaic cells. This work presents a detailed optoelectronic study of Cu₃N thin films grown by reactive RF-magnetron sputtering under pure N₂. An overview of the state-of-the-art literature on this material and its potential applications is also provided. The studied films consist of Cu₃N polycrystals with a cubic anti-ReO₃ type structure exhibiting a preferential (100) orientation. Their optical properties across the UV-Vis-NIR spectral range were investigated using a combination of multi-angle spectroscopic ellipsometry, broadband transmission, and reflection measurements. Our model employs a stratified geometrical approach, primarily to capture the depth-dependent compositional variations of the Cu₃N film while also accounting for surface roughness and the underlying glass substrate. The complex dielectric function of the film material is precisely determined through an advanced dispersion model that combines multiple oscillators. By integrating the Tauc–Lorentz, Gaussian, and Drude models, this approach captures the distinct electronic transitions of this polycrystal. This customized optical model allowed us to accurate extract both the indirect (1.83–1.85 eV) and direct (2.38–2.39 eV) bandgaps. Our multifaceted characterization provides one of the most extensive studies of Cu₃N thin films to date, paving the way for optimized device applications and broader utilization of this promising binary semiconductor, and showing its particular potential for photovoltaic given its adequate bandgap energies for solar applications. Full article

In this research, precision temperature sensing for electromagnetically harsh environments was achieved utilizing a low-threshold frequency-stable optoelectronic oscillator (OEO) leveraging stimulated Brillouin scattering (SBS). The sensing mechanism relied on the temperature-dependent frequency shift in the SBS-induced notch filter. By embedding this filter in the OEO feedback loop, the oscillator’s output frequency was locked to the difference between the optical carrier frequency and the SBS notch center frequency. The temperature variations were translated into microwave frequency shifts through OEO oscillation, which was quantified with heterodyne detection. To suppress environmental perturbations, a Faraday rotation mirror (FRM) was integrated at the fiber end, creating a dual-pass SBS interaction that simultaneously enhanced the vibration immunity and reduced the SBS power threshold by 2.7 dB. The experimental results demonstrated a sensitivity of 1.0609 MHz/°C (R² = 0.999) and a long-term stability of ±0.004 °C. This innovative scheme demonstrated significant advantages over conventional SBS-OEO temperature sensing approaches, particularly in terms of threshold reduction and environmental stability enhancement. Full article

Strong coupling between plasmons and excitons in two-dimensional materials offers a powerful route for manipulating light–matter interactions at the nanoscale, with potential applications in quantum optics, nanophotonics, and polaritonic devices. Here, we design and numerically investigate a low-loss coupling platform composed of a silver nanocuboid dimer and monolayer of WS₂ using finite-difference time-domain (FDTD) simulations. The dimer supports a subradiant bonding plasmonic mode with a linewidth as narrow as 60 meV. This ultralow-loss feature enables strong coupling with monolayer WS₂ at relatively low coupling strengths. FDTD simulations combined with the coupled oscillator model reveal a Rabi splitting of ~60 meV and characteristic anticrossing behavior in the dispersion relations. Importantly, we propose and demonstrate two independent tuning mechanisms—loss engineering through nanocuboid tilt and coupling-strength modulation through the number of WS₂ layers—that enable transitions between weak and strong coupling regimes. This work provides a low-loss and tunable plasmonic platform for studying and controlling strong light–matter interactions in plasmon-two-dimensional material systems, with potential for room-temperature quantum and optoelectronic devices. Full article

This study investigates the influence of vacancy engineering and nitrogen doping on the structural, electronic, and optical properties of T-graphene fragments (TFs) using density functional theory (DFT) and time-dependent DFT (TD-DFT). A central vacancy and five pyridinic nitrogen doping configurations are explored to modulate the optoelectronic behavior. All systems are thermodynamically stable, exhibiting tunable HOMO–LUMO gaps, orbital distributions, and charge transfer characteristics. Optical absorption spectra show redshifts and enhanced oscillator strengths in doped variants, notably v-NTF2 and v-NTF4. Nonlinear optical (NLO) analysis reveals significant enhancement in both static and frequency-dependent responses. v-NTF2 displays an exceptionally high first-order hyperpolarizability (⟨β⟩ = 1228.05 au), along with a strong electro-optic Pockels effect (β (−ω; ω, 0)) and second harmonic generation (β (−2ω; ω, ω)). Its third-order response, γ (−2ω; ω, ω, 0), also exceeds 1.2 × 10⁵ au under visible excitation. Conceptual DFT descriptors and energy decomposition analysis further supports the observed trends in reactivity, charge delocalization, and stability. These findings demonstrate that strategic nitrogen doping in vacancy-engineered TFs is a powerful route to tailor electronic excitation, optical absorption, and nonlinear susceptibility. The results offer valuable insight into the rational design of next-generation carbon-based materials for optoelectronic, photonic, and NLO device applications. Full article

In this paper, we propose an optoelectronic feed-forward millimeter-wave generator based on the Mach–Zehnder interferometer (MZI) structure. The phase noise of the local oscillation (LO) input is extracted by loop design and used for phase noise suppression of the output, thereby optimizing the phase noise performance of the generator output. The scheme achieves separation of the phase noise by using an MZI structure and a mixing-frequency oscillator to realize the differential and integration process of the phase noise from the LO input source, respectively. Then, it is combined with a feed-forward operation to skillfully realize phase noise rejection of the resulting high-frequency output. The proposed scheme has been demonstrated to facilitate millimeter-wave generation at 40 GHz and 50 GHz. The measured phase noise is as low as −120 dBc/Hz at a 10 kHz offset, and the experimental setup achieves phase noise suppression of up to 36 dB at this frequency offset. Through systematic theoretical analysis and experimental verification, the excellent capabilities of the proposed scheme in high-frequency signal generation and phase noise suppression are fully demonstrated, which provides a new technological path for high-performance millimeter-wave generation, avoiding the deterioration of the phase noise introduced using high-frequency optoelectronic devices other than photodetectors (PDs) to process the signals. Full article

This study investigates the influence of rotation on wave propagation in a semiconducting nanostructure thermoelastic solid subjected to a ramp-type heat source within a two-temperature model. The thermoelastic interactions are modeled using the two-temperature theory, which distinguishes between conductive and thermodynamic temperatures, providing a more accurate description of thermal and mechanical responses in semiconductor materials. The effects of rotation, ramp-type heating, and semiconductor properties on elastic wave propagation are analyzed theoretically. Governing equations are formulated and solved analytically, with numerical simulations illustrating the variations in thermal and elastic wave behavior. The key findings highlight the significant impact of rotation, nonlocal parameters $e_{0}a$, and time derivative fractional order (FO) $\alpha$ on physical quantities, offering insights into the thermoelastic performance of semiconductor nanostructures under dynamic thermal loads. A comparison is made with the previous results to show the impact of the external parameters on the propagation phenomenon. The numerical results show that increasing the rotation rate $\mathsf{\Omega }=5$ causes a phase lag of approximately 22% in thermal and elastic wave peaks. When the thermoelectric coupling parameter ${\mathsf{\epsilon }}_3$ is increased from $-0.8\times {10}^{-42}$ to $1.2\times {10}^{-42}$. The temperature amplitude rises by 17%, while the carrier density peak increases by over 25%. For nonlocal parameter values $\mathsf{\epsilon }=0.3\to 0.6$, high-frequency stress oscillations are damped by more than 35%. The results contribute to the understanding of wave propagation in advanced semiconductor materials, with potential applications in microelectronics, optoelectronics, and nanoscale thermal management. Full article

Nonlinear dynamical states generated by self-delayed feedback based on fiber structures have broad applications. However, fiber-based optoelectronic feedback or pure optical feedback systems exhibit long delays, and the coupling mechanisms between these two loops differ significantly from those in short-delay systems. A systematic investigation of feedback coupling mechanisms under long-delay conditions is of great significance for optimizing such systems. In this paper, the nonlinear dynamic state generated by directly modulated distributed feedback semiconductor laser (DM-DFBL) self-delayed feedback with an optoelectronic oscillation loop is studied. Both numerical and experimental results show that the DM-DFBL’s dynamical states vary with changes in optical and electrical feedback intensities. In the self-delayed feedback, the DM-DFBL exhibits an evolutionary path from a chaos (CO) state to a period-one (P1) state and finally becomes a steady state with the decrease of optical feedback intensity. In the optoelectronic oscillation loop, the DM-DFBL generates a microwave frequency comb (MFC), a full-frequency oscillation, and a P1 state. Additionally, the dynamic state of the DM-DFBL can be disturbed, and the stability of the P1 state and the QP state can be enhanced when the optoelectronic oscillation loop is introduced. These conclusions contribute to the precise control of dynamic evolution. Full article

Gallium Arsenide (GaAs) Schottky technology stands out for its superior performance in terms of conversion loss for terahertz mixers at room temperatures, which establishes it as a dominant solution in receivers for high-data-rate wireless communications. However, Indium Gallium Arsenide (InGaAs) Schottky mixers offer a notable advantage in terms of reduced power requirements due to their lower barrier height, enabling optical pumping with the incorporation of photodiodes acting as photonic local oscillators (LOs). In this study, we present the first comparative analysis of GaAs and InGaAs diode technologies under both electrical and optical pumping, which are also being compared for the first time, particularly in the context of a wireless communication system, transmitting up to 80 Gbps at 0.3 THz using 16-quadrature amplitude modulation (QAM). The terahertz transmitter and the optical receiver’s LO are based on modified uni-traveling-carrier photodiodes (MUTC-PDs) driven by free-running lasers. The investigation covers a total of two mixers, including narrow-band GaAs and InGaAs. The results reveal that, despite InGaAs mixers exhibiting higher conversion loss, the bit error rate (BER) can be as low as that with GaAs. This is attributed to the purity of optically generated LO signals in the receiver. This work positions InGaAs Schottky technology as a compelling candidate for terahertz reception in the context of optical wireless communication systems. Full article

We report a coherent tri-frequency microwave signal generation approach using an optoelectronic oscillator (OEO). In the previous literature, the OEO-based schemes can only generate coherent microwave signals with dual frequencies. In this work, we demonstrate that the generation of coherent tri-frequency microwave signals is also possible using an OEO loop. The key component in our scheme is a tri-passband electrical filter, which has a narrow passband in the middle and two wide passbands on both sides. The OEO loop initially oscillates at the central frequency of the narrow passband with a single-tone f₁. By injecting a microwave signal, f_inj, into the OEO loop, down- and up-converted microwave signals at frequencies of f₂ = f₁ − f_inj and f₃ = f₁ + f_inj, respectively, are generated by frequency mixing in a microwave mixer. The two wide passbands of the electrical filter allow the oscillation of the converted signals at a wide frequency bandwidth by simply tuning the frequency of the injected signal. Moreover, the tri-frequency microwave signals are phase-locked through frequency mixing and mutual injection locking. The proposed scheme is theoretically analyzed and experimentally validated. In the experiments, coherent tri-frequency microwave signals with low phase noise are successfully generated at a fixed frequency of 14 GHz and two tunable frequency ranges from 9 to 12 GHz and from 16 to 19 GHz, respectively. Full article

A frequency stabilization scheme for a wideband-tunable optoelectronic oscillator (OEO) based on fundamental and subharmonic RF injection locking is proposed, achieving a tuning range of 2–22 GHz with low phase noise. The injection-locked performance of the OEO using the fundamental RF signal and its 1/n subharmonic is investigated. The fundamental injection locking achieves a phase noise of <−130 dBc/Hz @ 10 kHz offset across the entire tuning range. An examination of phase noise behavior at different subharmonic orders reveals that fundamental and subharmonic injection locking achieve a five-order-of-magnitude improvement in Allan variance (0.1 s) and approximately 40 dB phase noise reduction at a 10 Hz offset from the carrier. This approach leverages the low-phase-noise advantage of the OEO while benefiting from the high stability of low-frequency external RF sources, enabling multi-frequency point frequency stabilization optimization. Full article

This letter presents a scheme for obtaining a microwave photonic frequency multiplier with low phase noise, in which an optoelectronic oscillator (OEO) is integrated with a directly modulated laser (DML)-based injection-locking technique. The system achieves frequency multiplication factors of 10 and 20, producing 10.01009 and 19.99095 GHz microwave signals with high side-mode suppression ratios of 62.0 and 50.2 dB. The measured single-sideband phase noise values are −121.87 and −111.95 dBc/Hz@10 kHz, which are 34.9 and 31.0 dB lower than those of traditional electronic frequency multiplication methods for 1 GHz signals. By utilizing the nonlinear characteristics of the DML, combined with injection locking and the OEO system, this cost-effective scheme reduces the system complexity while enhancing the stability and phase noise performance, offering a highly efficient solution for microwave frequency multiplication. Full article

A high-sensitivity magnetic field sensor based on an optoelectronic oscillator (OEO) with a Mach–Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The magnetic field sensor consists of a fiber Mach–Zehnder interferometer, with the lower arm of the interferometer wound around a magnetostrictive transducer. Due to the magnetostrictive effect, an optical phase shift induced by magnetic field variation is generated between two orthogonal light waves transmitted in the upper and lower arms of the MZI. The polarization-dependent property of a Mach–Zehnder modulator (MZM) is utilized to transform the magnetostrictive phase shift into the phase difference between the sidebands and optical carrier, which is mapped to the oscillating frequency upon the completion of an OEO loop. High-sensitivity magnetic field sensing is achieved by observing the frequency shift of the radio frequency (RF) signal. Temperature-induced cross-sensitivity is mitigated through precise length matching of the MZI arms. In the experiment, the high magnetic field sensitivity of 6.824 MHz/mT with a range of 25 mT to 25.3 mT is achieved and the sensing accuracy measured by an electrical spectrum analyzer (ESA) at “maxhold” mode is 0.002 mT. The proposed sensing structure has excellent magnetic field detection performance and provides a solution for temperature-insensitive magnetic field detection, which would have broad application prospects. Full article