Optics express最新文献

The nonnegligible fiber nonlinearity and the relentless growth in transmission rates in modern optical systems has brought unprecedented challenges to the existing optical signal-to-noise ratio (OSNR) monitoring techniques. In this work, a novel phase-aware, nonlinear-tolerant, and interpretable physics-informed neural network (PINN) OSNR estimator based on the nonlinear Schrödinger equation (NLSE) and the fractional Fourier transform (FrFT) is proposed and experimentally validated for the first time. The proposed PINN OSNR estimator reveals the impact of phase-related information on OSNR estimation via an indirect phase-aware strategy based on NLSE. The FrFT is applied to achieve joint time-frequency and amplitude-phase features and further enhance OSNR estimation performance. Integration of the NLSE into the loss function allows the model to be closely aligned with the intrinsic physical characteristics of optical transmission systems, endowing it with improved interpretability and enhancing its robustness under unseen conditions. Experimental results yield consistently favorable results across high-nonlinearity, higher-order modulation coherent systems, and out-of-distribution data. The proposed model achieves average OSNR monitoring errors of 0.13, 0.26, and 0.19 dB for quadrature phase shift keying (QPSK), 16 quadrature amplitude modulation (16QAM), and 64QAM systems, respectively, and achieves an average estimation error of 1.12 dB with a maximum error of 2.6 dB on out-of-distribution data.

We report the monolithic integration of InAs/GaAs quantum dot laser diodes (QDLDs) on 4° off-cut Si (001) substrates using a fully MOCVD-grown process. A V-groove-assisted cleaving method and low-temperature ohmic contact formation were developed to address cracking and facet roughness inherent to off-cut substrates. The resulting devices exhibited low threading dislocation density (7 × 10⁶ cm^-2), high QD uniformity, and mirror-quality cleaved facets. Room-temperature continuous-wave lasing at 1298 nm with a threshold current of ∼310 mA and single-facet output power up to 50 mW was achieved. These results demonstrate a manufacturable route for Si-based QD light sources with high performance and thermal robustness up to 105 °C.

Oxygen (O₂) detection is of vital importance for life safety, medical monitoring, environmental monitoring, and industrial process control. It is a key technical support for preventing asphyxiation, assessing ecological health, and ensuring production safety. However, the existing O₂ sensors are unable to perform real-time online detection and highly sensitive detection. A trace laser photoacoustic gas sensor based on red light diode laser was developed for ppm-level O₂ sensing. This sensor utilizes resonant photoacoustic spectroscopy technology, combined with a high-sensitivity microphone and light power intensity modulation technology, to achieve highly selective and low-concentration detection of specific target gases (O₂). The core of the system adopts a red light band semiconductor laser with a high output power of 3W as the excitation source, fully leveraging the advantage that the detection excitation laser power of photoacoustic spectroscopy is proportional to the detection sensitivity, effectively reducing the system cost and volume while maintaining excellent detection performance. Experiments show that the detection limit of this sensor for O₂ can reach the ppm (parts per million) level. The detection limit of photoacoustic spectroscopy is enhanced by replacing the long optical path with high-power laser excitation. It demonstrates broad application potential in non-invasive medical diagnosis of human breathing, environmental air monitoring, and industrial process safety control. This research provides an effective technical solution for the development of high-performance, low-cost, and portable trace gas analysis instruments.

Freeform gradient-index (F-GRIN) media offer significant degrees of freedom for the design of advanced imaging systems. As manufacturing capabilities evolve toward complex refractive index distributions, a unified representation is increasingly required. In this paper, rotation-invariant orthogonal polynomials in the unit ball (ROPB) are proposed to provide a canonical 3D representation for F-GRIN. ROPB integrates spatial coordinates through rotation-invariant base functions, ensuring orthogonality and continuity in the unit ball. The index distribution and aberration properties of ROPB terms are analyzed to facilitate their application in optical design. Furthermore, the efficacy of ROPB is validated through the performance enhancement of an ultrashort throw ratio projection system. The results demonstrate that the ROPB can not only effectively guide the optical design of F-GRIN systems but also mitigates aberrations in non-rotationally symmetric systems, providing a feasible solution for the more compact and high-performance optical design.

Deformable mirrors are widely used in astronomy, laser communications, and vision science, but conventional contact-based designs are limited by small achievable strokes (< 10 µm). To address this limitation, we developed a contactless deformable mirror based on a magnetorheological elastomer membrane actuated by an array of permanent magnets. The 50 mm diameter, 275 µm thick membrane, composed of PDMS with magnetite nanoparticles, exhibited surface roughness between 3 - 7 nm. Under magnetic flux densities from 21 mT to 77 mT, the mirror achieved deformations up to 0.97 mm using a 37 magnet hexagonal array. Numerical simulations performed in COMSOL showed excellent agreement with experiments, confirming the potential of magnetic actuation to overcome the stroke limitations of conventional deformable mirrors.

Phosphor-converted LEDs (pc-LEDs) are the dominant source for general illumination. However, their limited modulation bandwidth poses a significant challenge for Visible Light Communication (VLC). Existing research has proposed blue-yellow light shunt systems and frequency response models that incorporate Correlated Color Temperature (CCT) and phosphor delay. Nonetheless, they lack targeted equalization schemes. To address this, in this paper, a dual-branch pre-equalization scheme is proposed to match the physical characteristics of pc-LEDs. The frequency domain is divided into high and low segments bounded by a frequency-division point, and their frequency responses are reshaped to design an equalizer accordingly. The two branches compensate for the yellow light response dominated by low frequencies and the blue light response dominated by high frequencies, respectively. Moreover, a prediction formula is derived to intelligently determine the optimal frequency-division point based on CCT and phosphor delay. Simulation results verify the accuracy of the formula that yields a prediction error of less than 0.05 MHz. This scheme can effectively improve the communication performance of the system. In a 2.5-meter Line-of-Sight (LOS) link, the data rate reaches 130 Mbps at 3000 K, 120 Mbps and 115 Mbps at 4000 K and 5000 K respectively. Even with the consideration of phosphor delay, the data rate remains above 115 Mbps.

The degradation of orbital angular momentum (OAM) modes propagating through atmospheric turbulence fundamentally limits free-space optical communication capacity. We report a universal analytical formula governing this degradation: η_l = [1|(D/r₀/a_l)^5/3]^-1, where a_l=1.64/(∣l∣+1)/2. Based on Kolmogorov turbulence statistics, we derive an analytical integral expression for purity and obtain a closed-form scaling law through Kolmogorov-constrained closure. The exponent 5/3 emerges directly from the Kolmogorov phase structure function, while the mode-dependent coefficient a_l is determined by numerical calibration. We validate our theory against 560,000 independent Monte Carlo simulations spanning topological charges l = 1-10 and turbulence strengths D/r₀ = 0.01-20. The measured exponent b = 1.665 ± 0.042 agrees with the theoretical prediction to within 0.13%, and all fits achieve R² > 0.99. We further extend this framework to non-Kolmogorov turbulence, showing that the exponent generalizes to b(α) = α - 2 for arbitrary spectral index α. A practical lookup table enables rapid link budget estimation without Monte Carlo simulation. These results provide both physical insight into OAM degradation mechanisms and a theoretical foundation for designing high-capacity OAM communication systems.

Ultraviolet C (UVC) light sources are central to micro/nano fabrication. Current research focuses on optimizing exposure by increasing irradiance, improving precision, and implementing real-time dose control, creating an urgent demand for high-performance UVC photodetectors. To enhance responsivity, many UV detectors leverage metal nanoparticles (NPs) formed by solid-state dewetting on photosensitive substrates. However, limited characterization and simulation capabilities hinder detailed analysis of how these metasurfaces enhance responsivity, constraining device design and optimization. Therefore, developing methods to simulate and analyze the optical properties of metal NPs is essential. In this study, we propose an approach: reconstructing models of metasurfaces formed by solid-state dewetting and simulating them to support UVC photodetector design. Specifically, we combine U-Net deep learning with molecular dynamics (MD) simulations to construct accurate metasurface models, and employ the finite-difference time-domain (FDTD) method to evaluate the optical properties within each functional layer. Guided by these simulations, we fabricated a p-i-n UVC photodetector based on an ITO/Si structure, achieving an ultrashort response time (7.04 µs) and high sensitivity (0.84 A/W). Crucially, this detector also serves as an experimental platform to elucidate the mechanism by which localized surface plasmon resonance (LSPR) enhances responsivity. We achieved this by correlating the measured UVC electrical response with simulated metasurface absorption and LSPR effects. Our "algorithm-guided simulation" strategy provides a framework for designing high-performance UVC photodetectors. Furthermore, it strengthens the theoretical basis for LSPR effects through closed-loop "simulation-device-mechanism" verification.

Chalcogenide phase-change material (Ge₂Sb₂Te₅) has attracted considerable research interest in recent years for tunable structural color applications, owing to its pronounced contrast in optical properties between amorphous and crystalline states. However, the strong absorption of conventional Ge₂Sb₂Te₅ has significantly limited its applicability in the near-infrared (NIR) wavelength range. Herein, we utilize the near-zero absorption characteristic of the emerging phase-change material Sb₂Se₃ in the NIR band to construct a Fabry-Pérot cavity structure. This structure not only enables resonance peaks with high transmittance and large modulation range, but also allows a multi-channel filter to be achieved by increasing the thickness of Sb₂Se₃. This tunable multi-channel spectrally selective filter presents significant application potential in advanced fields such as multi-gas sensing, laser beam combining, and adaptive multi-spectral imaging.

Reconfigurable integrated photonics leveraging phase-change materials (PCMs) is a rapidly evolving field with diverse applications, including optical computing and programmable optics. Its development is driven by the high optical contrast and nonvolatility enabled by reversible phase switching in PCMs. Consequently, the design and modeling of such devices are critical for enabling their practical applications. In this work, we compare multiple inverse design algorithms for integrated optical structures, using a mode converter based on the low-loss PCM Sb₂Se₃ as a representative example. To bridge the gap between idealized designs and the realistic performance of integrated devices, the resulting mode converters are numerically assessed for key metrics such as mode contrast, insertion loss, and robustness against fabrication variations. To further investigate their applicability, we develop a photonic tensor core incorporating these mode converters as weight elements. We then analyze the operational range of output optical power and the image convolution quality achieved by the photonic core, highlighting the impact of the choice of weight elements on its overall performance.