Flow cytometers are a vital tool for cellular phenotyping but are primarily limited to centralized laboratories due to their bulkiness and cost. Significant efforts have been made to construct on-chip flow cytometers for point-of-care applications, and a promising approach is filter-on-chip flow cytometers utilizing the conventional Bayer RGB filter on imaging cameras to miniaturize key optoelectronic components. However, conventional RGB filters fail to provide spectral channels of sufficient diversity and specificity for accurate identification of fast-moving fluorescence signals. Here, we present an optofluidic system with integrated metasurfaces that serve to increase the number and diversity of the spectral channels. Inverse design of spatially coded metasurfaces is used to maximize the classification accuracy of spectral barcodes generated along the particle trajectory obtained from single-shot imaging. The accuracy of this system is shown to be superior to generic RGB filter approaches while also realizing classification of up to 13 unique combinations of fluorophores, significantly enhancing the capability of portable flow cytometers.

Sensing nano-objects, from nanoparticles to molecules, has become a crucial need in environmental monitoring, medical diagnostics, and drug development. Detection of single particles and molecules is highly desirable, as it provides specific information on size, dynamics, and interactions. Current nanophotonic implementations rely on complex optical readout schemes, limiting their application in the field. Here we demonstrate a nanophotonic fiber-tip sensor with a compact sensor footprint and a simple readout scheme. We leverage advanced design methods to simultaneously achieve a small mode volume V m =0.74(λ/n)3, narrow linewidth Δλ=0.4nm, and a large modulation ΔR≈20% in reflection from the fiber. This unique combination of properties opens the way to sensing weak nanoscale perturbations in the vicinity of the fiber tip. In particular, we experimentally demonstrate the real-time detection of single 50 nm nanoparticles. This opens a route towards real-time sensing of single nanoparticles, and potentially single molecules, in environmental monitoring and diagnostics.

Time-bin (TB) and energy-time (ET) entanglements are crucial resources for long-distance quantum information processing. However, their standard implementations suffer from the so-called post-selection loophole that allows for classical simulation and thus prevents quantum advantage. The post-selection loophole has been addressed in proof-of-principle experiments. An open problem though is to close it in real-life applications based on integrated technologies. This is especially important since, so far, all integrated sources of TB and ET entanglements suffer from the post-selection loophole. Here, we report post-selection loophole-free certification of TB or ET entanglement in integrated technologies, by implementing in a silicon nitride chip the “hug” scheme [Phys. Rev. Lett. 102, 040401 (2009)PRLTAO0031-900710.1103/PhysRevLett.102.040401] and certifying genuine TB entanglement through the violation of a Bell inequality.

The Imbert–Fedorov (IF) shift, which refers to a tiny transverse splitting induced by spin–orbit interaction at a reflection/refraction interface, is sensitive to the refractive index of a medium and momentum state of incident light. Most studies have focused on the shift for an incident light beam with a spin angular momentum (SAM), i.e., circular polarization. We demonstrate experimentally that the relative IF shifts of vortex beams with large opposite orbital angular momentums (OAMs) are highly enhanced in resonant structures when light refracts through a double-prism structure (DPS), in which the thickness and temperature of the air gap are precisely sensed via the observed relative IF shifts. The thickness and temperature sensitivities increase as the absolute value of opposite OAMs increases. Our results offer a technological and practical platform for applications in sensing of thickness and temperature, ingredients of environment gas, spatial displacement, chemical substances and deformation structure.

Compact and high-speed electro-optic phase modulators play a vital role in various large-scale applications including optical computing, quantum and neural networks, and optical communication links. Conventional electro-refractive phase modulators such as silicon (Si), III-V and graphene on Si suffer from a fundamental tradeoff between device length and optical loss that limits their scaling capabilities. High-finesse ring resonators have been traditionally used as compact intensity modulators, but their use for phase modulation has been limited due to the high insertion loss associated with the phase shift. Here, we show that high-finesse resonators can achieve a strong phase shift with low insertion loss by simultaneous modulation of the real and imaginary parts of the refractive index, to the same extent, i.e., ΔnΔk∼1. To implement this strategy, we demonstrate an active hybrid platform that combines a low-loss SiN ring resonator with 2D materials such as graphene and transition metal dichalcogenide [tungsten disulphide (WSe2)], which induces a strong change in the imaginary and real parts of the index. Our platform consisting of a 25 µm long Gr-Al2O3-WSe2capacitor embedded on a SiN ring of 50 µm radius (∼8% ring coverage) achieves a continuous phase shift of (0.46±0.05)πradians with an insertion loss (IL) of 3.18±0.20 dB and a transmission modulation (ΔTRing) of 1.72±0.15dB at a probe wavelength (λp) of 1646.18 nm. We find that our Gr-Al2O3-WSe2capacitor exhibits a phase modulation efficiency (Vπ2⋅L) of 0.530±0.016V⋅cm and can support an electro-optic bandwidth of 14.9±0.1GHz. We further show that our platform can achieve a phase shift ofπradians with an IL of 5 dB and a minimum ΔTof 0.046 dB. We demonstrate the broadband nature of the binary phase response, by measuring a phase shift of (1.00±0.10)πradians, with an IL of 5.20±0.31dB and a minimal ΔTRingof 0.015±0.006dB for resonances spanning from 1564 to 1650 nm. This SiN–2D hybrid platform provides the design for compact and high-speed reconfigurable circuits with graphene and transition metal dichalcogenide (TMD) monolayers that can enable large-scale photonic systems.

Ultrafast laser driven, single-cycle THz pulsed sources hold immense potential for scientific and industrial applications; however, their limited average power hinders their widespread application. In particular, applications where high repetition rates in the multi-MHz region and beyond are required are more severely affected, due to the lower pulse energies available for frequency conversion. In this respect, resonant enhancement both in passive and active resonators is a well-known technique for boosting the efficiency of nonlinear frequency conversion; however, this route has remained poorly explored for the generation of broadband THz pulses due to the inadequacy of typically employed nonlinear crystals. Here, we demonstrate that using thin lithium niobate crystals inside multimode diode-pumped mode-locked thin-disk lasers is a promising platform to circumvent these difficulties. Using a 50 µm thin lithium niobate plate intracavity of a compact high-power mode-locked thin-disk laser, we generate milliwatt-level broadband THz pulses with a spectrum extending up to 3 THz at 44.8 MHz repetition rate, driven by 264 W of intracavity average power. This approach opens the door to efficient high-power single-cycle THz generation using affordable nonlinear crystals at very high repetition rates, scalable to kilowatt-level driving power with low cost and complexity.

Manipulating flux transportation of optical fields holds great promise across various kinds of applications, encompassing laser micro-processing, optical trapping, microscopic imaging, and illumination engineering. In recent decades, freeform optics, lauded for its capacity to efficiently control the wavefronts of optical beams with high design freedom, has garnered significant attention as a potent tool for shaping light. Nevertheless, the predominant focus in current research has centered on the development of freeform optical elements (FOEs) tailored to project a designated two-dimensional flux density onto a specific target plane. This limitation confines the potential applications of freeform light shaping optics to a rather restricted domain. Moreover, the constraints imposed by geometric optics pose a further limitation on FOEs, particularly in their ability to sculpt coherent light, such as laser beams, as these are particularly susceptible to diffraction effects. Within the context of this study, we propose a design paradigm that harnesses freeform optics to craft light trajectories in three dimensions. This approach inherently gives rise to caustics, which are singularities within the realm of flux transfer in geometric optics. Crucially, our proposed method yields the capability to generate sharply defined light patterns, empirically giving better results for mitigating diffraction effects in contrast to previous design methodologies, which is observed by experiments. This design philosophy empowers FOEs to undertake new roles and functionalities by shaping caustics. To substantiate the potential of our proposal, we present a diverse array of design examples. These encompass scenarios ranging from the illumination of parallel planes to the sculpting of light propagation into three-dimensional curves, as well as the reshaping of beam intensities with an extended depth of field. We expect that the proposed work can broaden the scope of freeform optics, particularly within non-imaging applications, and propel freeform optical elements into hitherto unexplored territories.

Image stacks provide invaluable 3D information in various biological and pathological imaging applications. Fourier ptychographic microscopy (FPM) enables reconstructing high-resolution, wide field-of-view image stacks without z-stack scanning, thus significantly accelerating image acquisition. However, existing FPM methods take tens of minutes to reconstruct and gigabytes of memory to store a high-resolution volumetric scene, impeding fast gigapixel-scale remote digital pathology. While deep learning approaches have been explored to address this challenge, existing methods poorly generalize to novel datasets and can produce unreliable hallucinations. This work presents FPM-INR, a compact and efficient framework that integrates physics-based optical models with implicit neural representations (INRs) to represent and reconstruct FPM image stacks. FPM-INR is agnostic to system design or sample types and does not require external training data. In our experiments, FPM-INR substantially outperforms traditional FPM algorithms with up to a 25-fold increase in speed and an 80-fold reduction in memory usage for continuous image stack representations.

We report on the extension of the spectral sensitivity of superconducting nanowire single-photon detectors to a wavelength of 29 µm. To our knowledge, this represents the first demonstration of a single-photon counting detector at these long infrared wavelengths. We achieve saturated internal detection efficiency from 10 to 29 µm, while maintaining dark count rates below 0.1 counts per second. Extension of superconducting nanowire single-photon detectors to this spectral range provides low-noise and high-timing-resolution photon counting detection, effectively providing a new class of single-photon sensitive detectors for these wavelengths. These detectors are important for applications such as exoplanet spectroscopy, infrared astrophysics, physical chemistry, remote sensing, and direct dark-matter detection.

Mid-infrared spectroscopy, an important technique for sensing molecules, has encountered barriers from sources either limited in tuning range or excessively bulky for widespread use. We present a compact, efficient, and broadly tunable optical parametric oscillator surmounting these challenges. Leveraging dispersion-engineered thin-film lithium niobate-on-sapphire photonics and a singly resonant cavity allows broad, controlled tuning over an octave from 1.5–3.3 µm. The device generates >25mW of mid-infrared light at 3.2 µm with 15% conversion efficiency. The ability to precisely control the device’s mid-infrared emission enables spectroscopy of methane and ammonia, demonstrating our approach’s relevance for sensing. Our work signifies an important advance in nonlinear photonics miniaturization, bringing practical field applications of high-speed, broadband mid-infrared spectroscopy closer to reality.