APL Photonics最新文献

Label-free single-cell 3D imaging is essential for accurate phenotyping by minimizing perturbations to native cellular states and facilitating downstream molecular analyses. Among the available modalities, 3D forward-scattering (dark-field) imaging offers the richest subcellular details but faces challenges from strong transmitted-beam interference. We present a high-throughput 3D forward-scattering imaging flow cytometry system employing optical needle-beam illumination, linear micro-mirror arrays for axial scatter detection, and spatiotemporal deconvolution algorithms. Experimental validations with microstructures, hydrogel beads, and HEK-293 cells confirm the method's capability for robust subcellular resolution at ∼400 cells/s, enabling advanced label-free cellular diagnostics and analysis. This platform enables label-free, high-content cellular analysis and is readily adaptable to integrated cell sorting and AI-driven classification, offering broad potential for biomedical research and diagnostics.

Label-free nonlinear microscopy offers a powerful tool for the biomedical sciences. It enables investigations of cells and tissues using signals that emerge from endogenous biomolecules and microstructures to derive contrast, thereby preserving the physiological viability and functionality of specimens. Today, the most advanced label-free nonlinear microscopes are multimodal imaging platforms that capitalize on the heterogeneity of biological specimens, capturing not one but many nonlinear signals. Thus, label-free multimodal nonlinear imaging attains a contrast palette with complementary signals, delivering data-rich images that not only allow spatial unmixing and quantification of biochemical species but also unleash the power of correlation analyses and artificial intelligence to extract further information from specimens. In this Perspective, we recap the nonlinear contrast palette and compare the two technological strategies often used to acquire multimodal nonlinear images: a sequential approach vs a simultaneous approach. We then present their strengths and weaknesses and discuss emerging computational strategies that enhance the interpretability of multimodal data.

Increasing the energy efficiency and reducing the footprint of on-chip photodetectors enable dense optical interconnects for emerging computational and sensing applications. While heterojunction phototransistors (HPTs) exhibit high energy efficiency and negligible excess noise factor, their gain-bandwidth product (GBP) has been inferior to that of avalanche photodiodes at low optical powers. Here, we demonstrate that utilizing type-II energy band alignment in an Sb-based HPT results in six times smaller junction capacitance per unit area and a significantly higher GBP at low optical powers. These type-II HPTs were scaled down to 2 μm in diameter and fully integrated with photonic waveguides on silicon. Thanks to their extremely low dark current and high internal gain, these devices exhibit a GBP similar to the best avalanche devices (∼270 GHz) but with one order of magnitude better energy efficiency. Their energy consumption is about 5 fJ/bit at 3.2 Gbps, with an error rate below 10^-9 at -25 dBm optical power at 1550 nm. These features suggest new opportunities for creating highly efficient and compact optical receivers based on phototransistors with type-II band alignment.

Brillouin spectroscopy has become an important tool for mapping the mechanical properties of biological samples. Recently, stimulated Brillouin scattering (SBS) measurements have emerged in this field as a promising technology for lower noise and higher speed measurements. However, further improvements are fundamentally limited by constraints on the optical power level that can be used in biological samples, which effectively caps the gain and signal-to-noise ratio (SNR) of SBS biological measurements. This limitation is compounded by practical limits on the optical probe power due to detector saturation thresholds. As a result, SBS-based measurements in biological samples have provided minimal improvements (in noise and imaging speed) compared with spontaneous Brillouin microscopy, despite the potential advantages of the nonlinear scattering process. Here, we consider how a SBS spectrometer can circumvent this fundamental trade-off in the low-gain regime by leveraging the polarization dependence of the SBS interaction to effectively filter the signal from the background light via the polarization pulling effect. We present an analytic model of the polarization pulling detection scheme and describe the trade-space unique to Brillouin microscopy applications. We show that an optimized receiver design could provide >25× improvement in SNR compared to a standard SBS receiver in most typical experimental conditions. We then experimentally validate this model using optical fiber as a simplified test bed. With our experimental parameters, we find that the polarization pulling scheme provides 100× higher SNR than a standard SBS receiver, enabling 100× faster measurements in the low-gain regime. Finally, we discuss the potential for this proposed spectrometer design to benefit low-gain spectroscopy applications such as Brillouin microscopy by enabling pixel dwell times as short as 10 μs.

Mid-infrared microscopy is an important tool for biological analyses, allowing a direct probe of molecular bonds in their low energy landscape. In addition to the label-free extraction of spectroscopic information, the application of broadband sources can provide a third dimension of chemical specificity. However, to enable widespread deployment, mid-infrared microscopy platforms need to be compact and robust while offering high speed, broad bandwidth, and high signal-to-noise ratio. In this study, we experimentally showcase the integration of a broadband, high-repetition-rate dual-comb spectrometer (DCS) in the mid-infrared range with a scanning microscope. We employ a set of 1-GHz mid-infrared frequency combs, demonstrating their capability for high-speed and broadband hyperspectral imaging of polymers and ovarian tissue. The system covers $1000{\text{cm}}^{-1}$ at $v_{\text{c}}=2941{\text{cm}}^{-1}$ with 12.86 kHz spectra acquisition rate and $5\mu \text{m}$ spatial resolution. Taken together, our experiments and analysis elucidate the trade-off between bandwidth and speed in DCS as it relates to microscopy. This provides a roadmap for the future advancement and application of high-repetition-rate DCS hyperspectral imaging.