Optics express最新文献

Dynamic spectral shaping at the nanoscale has been limited by large free-space setups and slow response times. Here, we propose a fully pixelated nano-opto-electro-mechanical nano-kirigami metasurface that enables arbitrary on-chip spectral synthesis within a 9 × 9 μm² area. By exploiting 2D-to-3D morphological transformations of nano-kirigami metasurfaces that tailor the resonance wavelength and the ratio of radiation loss to intrinsic loss of a Fabry-Pérot (FP)-like cavity, the device achieves broadband tunability (>200 nm), as well as versatile single- and multi-mode spectral shaping capabilities at the pixel level. Combined with a Bayesian optimization inverse-design framework, we demonstrate accurate reconstruction of arbitrary reflectance spectra, with a root-mean-square error below 0.1. This work establishes a promising pathway toward compact, programmable spectral processors for applications in spectroscopy, imaging, and communication.

This work presents what we believe to be a novel 3D multispectral fluorescence lifetime microscope that combines structured illumination microscopy (SIM) and single-pixel camera (SPC) techniques within a computational framework. The approach allows simultaneous acquisition of steady-state high-resolution spatial data and and low-resolution spatial-temporal spectral data, which are fused using data fusion algorithms to generate a five-dimensional dataset. Compressive sensing has been exploited to accelerate SPC acquisition. Experimental validation with fluorescent beads and cellular samples demonstrates high fidelity in spatial, spectral, and lifetime data compared to ground truth. Ultimately, our system advances the fast and non-invasive measurements of volumetric fluorescent samples. It provides spectral and temporal information without increasing acquisition time and still offers reliable, high spatial resolution measurements.

Near-field radiative heat transfer systems typically exhibit performance drift under temperature excursions and seldom provide multifunctionality. We present a fully passive architecture that integrates positive and negative thermal expansion materials to achieve both thermal rectification and flux stabilization simultaneously. The device exploits the strong inverse dependence of near-field heat flux on gap distance as the primary control mechanism, with temperature-dependent surface phonon polaritons providing auxiliary enhancement. This configuration delivers three key advances: dual-terminal flux stabilization that keeps the net heat flux within 5% under ±50 K symmetric fluctuations at both terminals, an operational window exceeding 100 K in emitter-temperature variation, and rectification efficiency exceeding 99% without compromising stabilization. The design is entirely passive, requiring no external power or feedback, and is broadly compatible with diverse materials. By tailoring polariton dispersion and evanescent-mode coupling through gap modulation, the platform advances photonic control of near-field thermal emission, combining diode-like directionality with autonomous flux stabilization, and establishes a path toward mid-infrared thermal photonic circuits, metasurface-based emitters, and radiative heat engines where both spectral selectivity and flux stability are essential.

Coherent Doppler wind lidar can simultaneously detect wind and rain parameters via the double-peak feature in the Doppler wind spectrum, formed by the difference in vertical velocity between aerosols and raindrops. This study aims to establish a theoretical and analytical framework for the synergistic influence of the single-particle effect and the raindrop spectral distribution on the Doppler wind spectrum. A Mie and vector complex ray model (VCRM) combined with the data from raindrop spectra measured by a micro rain radar, and an elastic lidar is proposed to estimate the atmospheric backscattering and extinction coefficients of raindrops. The observable atmospheric conditions characterizing the double-peak Doppler wind spectrum were quantitatively resolved using a validated theoretical model and measured raindrop spectral data. In a comparative experiment between single- and double-peak cases, when the aerosol backscattering intensity approaches the magnitude of the raindrop scattering intensity, the double-peak feature in the frequency spectrum emerges. Furthermore, using the Joss empirical raindrop spectral model, critical raindrop spectral parameters that can arise in the double-peak wind Doppler spectrum are suggested based on different background aerosol backscattering coefficients. When the aerosol extinction coefficient is of order 10^{- 5}m^-1, double-peak spectra can be observed for fine rainfall with a rate of 1.4 to 100 mm/h, widespread rainfall with a rate of 14.8 to 100 mm/h, and thunderstorms with a rate of 82 to 100 mm/h, respectively. The rates are decreased to 0.1-1.4 mm/h, 0.1-14.8 mm/h, and 0.1-82.1 mm/h, for fine rainfall, widespread rainfall, and thunderstorms, respectively, when the aerosol extinction coefficient is of order 10^{- 6}m^-1. It is worth noting that there are order-of-magnitude differences in the spectral parameters of raindrops required to trigger the double-peak feature across different precipitation systems, even for the same combination of aerosol concentration and rainfall intensity.

We have presented PIN Ge-on-insulator (GOI) photodetectors (PDs) incorporating tensile-strained GeSi/Ge multiple quantum wells (MQWs) within the intrinsic layer. To control strain relaxation and reduce dark current, the thickness of the Ge spacer cap above the GeSi/Ge MQWs was systematically optimized. The optimized design yields a dark current density of 2.20 mA/cm² and a responsivity of 1.01 A/W at 1550 nm, corresponding to a specific detectivity of 4.02 × 10¹⁰cm·Hz^1/2·W^-1 under -1 V. The PDs exhibit enhanced responsivity at 1550 nm due to constructive optical interference within the SiO₂ insulator layer. Moreover, the PD with a thicker spacer exhibits an extended cutoff wavelength of 1700nm, as confirmed by photoluminescence and spectral response measurements, which is attributed to the larger tensile strain in Ge-like Ge_0.86Si_0.14. These results demonstrate that GOI PDs with GeSi/Ge MQWs offer significant potential for high-performance, Ge-based extended short-wavelength infrared detection and imaging applications.

Herein, a series of pyramid-structured Si/PEDOT:PSS heterojunctions was successfully fabricated with etching times ranging from 0 to 40 minutes, and their lateral photovoltaic effects (LPEs) were systematically investigated. The results reveal that the LPE response is strongly dependent on the etching duration of the pyramid texture, with the device etched for 30 minutes achieving a maximum position sensitivity of 632.1 mV/mm and a minimum nonlinearity of only 1.87%. This performance enhancement stems from the enlarged built-in field, optimized carrier diffusion paths, and improved light absorption. More importantly, a pyroelectric effect arising from the polar interface was observed. The induced pyroelectric field effectively couples with the intrinsic built-in field, facilitating efficient separation of photoexcited carriers and resulting in a significantly increased position sensitivity of 1221.8 mV/mm, demonstrating an improvement of 193.2%, and a rapid response time of 0.15/0.15 ms. Furthermore, the LPE remains effective over a wide electrode spacing range from 0.4 to 3.8 mm. Although the LPE response decreases with expanding spacing, a notable position sensitivity of 186.4 mV/mm is still achieved at a spacing of 3.8 mm. Based on the distinct wavelength dependence of the LPE response and its pyroelectric improvement, a wavelength-resolved optical imaging system was further demonstrated. In addition, the imaging intensity can be tuned by adjusting the electrode spacing, highlighting the unique versatility of LPE-based devices.

Remote respiratory rate (RR) measurement methods can continuously and unobtrusively monitor human pulmonary rhythms, holding great potential for applications in both clinical and home-based health monitoring. However, in challenging scenarios such as subject motion or drastic illumination changes, the weak respiratory signals are easily overwhelmed by noise, making existing methods prone to failure. To address these challenges, this paper proposes a robust RR estimation framework based on a reflection model of torso video. First, we establish a reflection model of the torso region and construct a plane orthogonal to the white-light direction to suppress the interference induced by light intensity variations. Then, the torso is divided into multiple regions of interest (ROIs), and principal component analysis (PCA) is applied to reconstruct the common respiratory components across regions while suppressing local random motion noise. Finally, to address the uncertainty in the ordering of PCA components, we construct a respiratory signal selection index that integrates both time- and frequency-domain features; the RR estimation results are then refined based on the continuity of physiological parameter variations, further improving the practicality and stability of the algorithm. Results on our private dataset across multiple challenging scenarios validate the robustness of the proposed algorithm, while results on public datasets demonstrate its generalization ability.

A high-power, narrow-linewidth, continuous-wave 355 nm laser based on single-pass third-harmonic generation of a fiber laser in two LBO crystals is presented. Both type I and type II critical phase-matching in LBO crystals was investigated for the sum-frequency generation stage. A maximum output power of 5 W with a root-mean-square power stability of 0.73% was achieved by using a type-I critical PM LBO crystal, with a single-pass conversion efficiency of 1.7% from 1064 nm to 355 nm. The relative intensity noise of the 355 nm laser was below -110 dB/Hz in the frequency range above 200 Hz. Such a single-pass THG laser system, with its compact architecture and robustness, has great potential for applications in semiconductor manufacturing and inspection.

Conventional chaotic communication relies on high-quality chaos synchronization, but this is difficult to achieve in practice due to the extreme parameter sensitivity of communication systems based on chaos synchronization. Unlike previous works, the proposed scheme utilizes a source separation approach to decrypt the message at the receiver end by separating it directly from chaos at the receiver side. In this paper, we take Conv-TasNet as an example to illustrate the feasibility of the separation scheme and achieve decryption at a low bit error rate(BER). The robustness of the separation performance to noise (demonstrated as signal-to-noise ratio (SNR)), masking coefficient, bit rate of the message, and parameters of the chaotic transmitter are studied. Simulation results show that the proposed system has low sensitivity to time delay signature (TDS). Simultaneously, the bit rate of the message, the overall gain of the electro-optical feedback loop, the high-pass cutoff frequency, and the masking coefficient could significantly affect the separation performance.

We demonstrate channel-selective frequency up-conversion from telecom wavelengths around 1540 nm for optical fiber communication to visible wavelengths around 780 nm, based on second-order optical nonlinearity in a cavity of the converted modes. In our experiment, we selectively convert a light from any frequency mode within frequency-multiplexed telecom signals to a desired output mode, determined by the cavity resonances. Based on the experimental results of the frequency up-conversion, we derive the signal-to-noise ratio of the process at the single-photon level, and discuss its applicability to channel-selective quantum frequency conversion (CS-QFC) in the context of frequency-multiplexed quantum networks. Finally, we describe specific use cases of the CS-QFC, that demonstrates its utility as a reconfigurable switching element in frequency-multiplexed networks, particularly for selectively performing Bell-state measurements between two photons at different frequencies.