ACS Photonics最新文献

The ability to optically trap and manipulate artificial microswimmers, such as active Janus particles (JPs), provides a breakthrough in active matter research and applications. However, it presents significant challenges because of the asymmetry in the optical properties of JPs and remains incomprehensible. Illustrating the interplay between optical and thermophoretic forces, we demonstrate dynamically stable optical trapping of Pt-silica JPs, where the force-balanced position evolves spontaneously within a localized volume around the focal point and in a vertically shifted annular confinement at low and high laser powers, respectively. Intriguingly, the orientational and orbital dynamics of JP remain strongly coupled in the delocalized confinement. Furthermore, we demonstrate simultaneous optical trapping of multiple JPs. This first report on thermophoresis of Pt-silica JPs and localized-to-delocalized crossover in the position distributions of an optically trapped active JP, verifying theoretical predictions, advances our understanding of confined active matter and their experimental realizations.

Scanning optoacoustic mesoscopy is aimed at high resolution imaging within a depth range of several millimeters in mammalian tissues, which is highly relevant for diagnosing a variety of microcirculatory disorders. Multispectral imaging further allows for quantifying functional biomarkers, such as blood oxygenation or lipid content, facilitating early detection of conditions like peripheral artery disease, diabetic microangiopathy, or tumor angiogenesis. While conventional system implementations rely on bulky and expensive solid-state laser sources, we report a fully integrated optoacoustic mesoscopy system based on low-cost laser diodes. The proposed multispectral imaging design encloses three laser diodes operating at 753, 805, and 878 nm along with pulse drivers and fiber-coupling micro-optics within a single 22 × 12 × 10 cm³ sized module. The system emits 100 ns duration light pulses at 16 μJ per-pulse energy and is further characterized by a high per-pulse energy stability (0.5% standard deviation). The clinical imaging capabilities of the system are subsequently demonstrated by mapping blood oxygen saturation in the human wrist. This compact, cost-effective platform paves the way for clinical translation of optoacoustic mesoscopy in point-of-care and resource-limited settings.

Image sensors capturing both red-green-blue (RGB) and near-infrared (NIR) images (i.e., RGB–NIR image sensors) have been actively developed due to their promising applications, such as security and biometric measurements. For such applications, there is a strong demand for developing high-sensitivity RGB–NIR image sensors capable of operating even under low-light conditions, such as at night. However, the conventional sensor architecture based on pixelated color filters limits the detectable light power because filters waste the light through absorption, which restricts the sensor’s sensitivity. Here, we developed a filter-free RGB–NIR image sensor based on CMOS-compatible pixelated color splitters. The splitters are designed by leveraging dispersion-engineered meta-optics, enabling four colors on pixels to be classified without using filters. A prototype image sensor integrating such splitters significantly enhances light detection while providing high-quality images, adaptability to various imaging optics, and compatibility with state-of-the-art image processing. These demonstrations pave the way for developing high-sensitivity RGB–NIR image sensors that surpass sensitivity limits while blending with CMOS image sensor technologies.

Lithium niobate on insulator (LNOI) is increasingly recognized as a versatile platform for photonic integrated circuits, owing to its superior electro-optic and nonlinear properties. However, developing polarization beam splitters (PBSs) on the X-cut LNOI presents challenges due to its inherent low birefringence, intrinsic anisotropy, and vertical asymmetry. In this study, we introduce an approach utilizing anisotropic subwavelength perturbations on an in-plane anisotropy platform, facilitating effective control over polarization-dependent mode fields. By engineering side-wall subwavelength structures to selectively manipulate the evanescent coupling of quasi-TE₀ and quasi-TM₀ modes, we identify an exceptional coupling point that enables highly asymmetric coupling behavior. For the proposed design, the fabricated device exhibits peak extinction ratios of ∼40 dB and ∼36 dB and ultralow excess losses of 0.1 dB and 0.3 dB for quasi-TE₀ and -TM₀ modes, respectively. Further bandwidth enhancement is achieved using an adiabatically tapered design, which extends the bandwidth to preserve high extinction ratios across the entire C-band. The devices are fabricated via a single-step lithography process, highlighting their scalability and simplicity. This approach is broadly applicable to other anisotropic low-birefringence platforms and offers a promising route toward dense polarization-sensitive photonic integration.

Two-photon endomicroscopy has become a robust, label-free, high-resolution technique for optical biopsy. Achieving this resolution level in compact probes critically relies on the design of micro-objectives. Conventional micro-objectives, including gradient-index lenses and microlens assemblies, are limited by their bulky packaging and low numerical aperture, ultimately constraining their performance. As flat dielectric optical elements, metalenses provide a promising pathway toward miniaturized endomicroscopic probes while maintaining high-resolution imaging capability. In this work, a high-aspect-ratio titanium dioxide dielectric metalens was designed and fabricated to operate at 780 nm. A metalens-based two-photon endomicroscopy platform was developed, featuring a compact probe that enabled label-free imaging of two-photon fluorescence and second-harmonic generation in unstained skin sections. This flat dielectric metalens approach offers a promising pathway for developing advanced multimodal endoscopic and endomicroscopic imaging platforms.

Fast broadband wavelength-swept lasers (WSLs) are core components in optical sensing fields such as fiber Bragg grating (FBG) sensing and optical coherence tomography. This work presents a novel WSL based on a distributed feedback (DFB) laser array combined with enhanced self-heating effects, achieving a 400 kHz sweep rate and a continuous (gap-free) wavelength tuning range of 60 nm, with a tuning speed exceeding 24 nm/μs. To the best of our knowledge, this work achieves the highest sweeping frequency reported for broadband (>30 nm) WSLs based on DFB laser arrays up to now. The reconstruction-equivalent-chirp technique simplifies grating fabrication and improves the accuracy of wavelength interval control, with the wavelength error measured to be within ±0.2 nm. Reducing the doping concentration in the p-waveguide region enhances the self-heating effect, enabling a continuous tuning range of over 5 nm per channel. The DFB laser array exhibits side-mode suppression ratios >45 dB, output power >55 mW, and relative intensity noise below −130 dB/Hz. The proposed WSL was successfully applied in an FBG sensor interrogation system, where the wavelength fluctuation over 5000 continuous interrogation cycles was less than 2 pm (within ±1 pm), demonstrating outstanding wavelength sweeping repeatability. In temperature measurement experiments (−30 to 90 °C) and strain measurement experiments (−800 με to 800 με), the interrogation linearity of all FBG sensors was greater than 0.9993. In vibration measurement experiments, the system successfully measured high-frequency vibration signals at 45 kHz, 85 kHz, and 128 kHz, with an acquisition time resolution of 2.496 μs. This work provides a new direction for the development of high-speed broadband WSLs.

Photonic neural networks (PNNs) hold great promise for artificial intelligence (AI) acceleration computing with their high-speed and energy-efficient processing capabilities. However, it is still difficult to obtain compact, nonvolatile, and programmable photonic integrated components. Thus, a configurable photonic crystal nanobeam cavity (PCNC) with nonvolatility is introduced based on Sb₂Se₃ for PNNs. Furthermore, the unique features of Sb₂Se₃, such as low loss in the telecommunication band and significant change in the refractive index between crystalline and amorphous phases, are utilized. By integrating Sb₂Se₃ into a PCNC structure, we achieve nonvolatile programmability of the PCNC. In addition, it is demonstrated that our device can be tuned to different resonant states, corresponding to various logic levels, making it suitable for configuring synaptic weights in PNNs. Using combinatorial selection and adjustment of seven segmented regions of Sb₂Se₃, we achieve 32 discrete states for synaptic-like programmability. While integrating with a 5-bit quantized photonic convolutional neural network (PCNN), the system attains 98.78% accuracy on the MNIST data set. Therefore, our work presents a novel approach to developing nonvolatile, high-bit quantized, small-footprint, and scalable PNNs, opening up new potential pathways for applications in fields such as edge computing and image processing.

MINFLUX microscopy allows for localization of fluorophores with nanometer precision by using targeted scanning with an illumination profile with a minimum. However, current scanning patterns and the overall procedure are based on heuristics and may therefore be suboptimal. Here, we present a rigorous Bayesian approach that offers maximal resolution from either a minimal number of detected photons or a minimal number of exposures. We estimate using simulated localization runs that this approach should reduce the number of photons required for 1 nm resolution by a factor of about four.