The growing maturity of nanofabrication has ushered massive sophisticated optical structures available on a photonic chip. The integration of subwavelength-structured metasurfaces and metamaterials on the canonical building block of optical waveguides is gradually reshaping the landscape of photonic integrated circuits, giving rise to numerous meta-waveguides with unprecedented strength in controlling guided electromagnetic waves. Here, we review recent advances in meta-structured waveguides that synergize various functional subwavelength photonic architectures with diverse waveguide platforms, such as dielectric or plasmonic waveguides and optical fibers. Foundational results and representative applications are comprehensively summarized. Brief physical models with explicit design tutorials, either physical intuition-based design methods or computer algorithms-based inverse designs, are cataloged as well. We highlight how meta-optics can infuse new degrees of freedom to waveguide-based devices and systems, by enhancing light-matter interaction strength to drastically boost device performance, or offering a versatile designer media for manipulating light in nanoscale to enable novel functionalities. We further discuss current challenges and outline emerging opportunities of this vibrant field for various applications in photonic integrated circuits, biomedical sensing, artificial intelligence and beyond. Recent years have witnessed substantial potential in allying meta-optics with diverse waveguide platforms to enable exotic manipulation of guided light signals. This review cataloged recent advances on meta-waveguides for photonic integration.
Twenty-five years ago Allen, Beijersbergen, Spreeuw, and Woerdman published their seminal paper establishing that light beams with helical phase-fronts carried an orbital angular momentum. Previously orbital angular momentum had been associated only with high-order atomic/molecular transitions and hence considered to be a rare occurrence. The realization that every photon in a laser beam could carry an orbital angular momentum that was in excess of the angular momentum associated with photon spin has led both to new understandings of optical effects and various applications. These applications range from optical manipulation, imaging and quantum optics, to optical communications. This brief review will examine some of the research in the field to date and consider what future directions might hold.
Lightweight, miniaturized optical imaging systems are vastly anticipated in these fields of aerospace exploration, industrial vision, consumer electronics, and medical imaging. However, conventional optical techniques are intricate to downscale as refractive lenses mostly rely on phase accumulation. Metalens, composed of subwavelength nanostructures that locally control light waves, offers a disruptive path for small-scale imaging systems. Recent advances in the design and nanofabrication of dielectric metalenses have led to some high-performance practical optical systems. This review outlines the exciting developments in the aforementioned area whilst highlighting the challenges of using dielectric metalenses to replace conventional optics in miniature optical systems. After a brief introduction to the fundamental physics of dielectric metalenses, the progress and challenges in terms of the typical performances are introduced. The supplementary discussion on the common challenges hindering further development is also presented, including the limitations of the conventional design methods, difficulties in scaling up, and device integration. Furthermore, the potential approaches to address the existing challenges are also deliberated. This review outlines the exciting developments in high-performance dielectric metalenses whilst highlighting the challenges of using dielectric metalenses to replace conventional optics in miniature optical systems.
Observations of circumstellar environments that look for the direct signal of exoplanets and the scattered light from disks have significant instrumental implications. In the past 15 years, major developments in adaptive optics, coronagraphy, optical manufacturing, wavefront sensing, and data processing, together with a consistent global system analysis have brought about a new generation of high-contrast imagers and spectrographs on large ground-based telescopes with much better performance. One of the most productive imagers is the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE), which was designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE includes an extreme adaptive optics system, a highly stable common path interface, several types of coronagraphs, and three science instruments. Two of them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager and Spectrograph (IRDIS), were designed to efficiently cover the near-infrared range in a single observation for an efficient search of young planets. The third instrument, ZIMPOL, was designed for visible polarimetric observation to look for the reflected light of exoplanets and the light scattered by debris disks. These three scientific instruments enable the study of circumstellar environments at unprecedented angular resolution, both in the visible and the near-infrared. In this work, we thoroughly present SPHERE and its on-sky performance after four years of operations at the VLT.
The so‐called ‘flat optics’ that shape the amplitude and phase of light with high spatial resolution are presently receiving considerable attention. Numerous journal publications seemingly offer hope for great promises for ultra‐flat metalenses with high efficiency, high numerical aperture, broadband operation… We temperate the expectation by referring to the current status of metalenses against their historical background, assessing the technical and scientific challenges recently solved and critically identifying those that still stand in the way.
Metasurfaces are 2D artificial materials consisting of arrays of metamolecules, which are exquisitely designed to manipulate light in terms of amplitude, phase, and polarization state with spatial resolutions at the subwavelength scale. Traditional micro/nano-optical sensors (MNOSs) pursue high sensitivity through strongly localized optical fields based on diffractive and refractive optics, microcavities, and interferometers. Although detections of ultra-low concentrations of analytes have already been demonstrated, the label-free sensing and recognition of complex and unknown samples remain challenging, requiring multiple readouts from sensors, e.g., refractive index, absorption/emission spectrum, chirality, etc. Additionally, the reliability of detecting large, inhomogeneous biosamples may be compromised by the limited near-field sensing area from the localization of light. Here, we review recent advances in metasurface-based MNOSs and compare them with counterparts using micro-optics from aspects of physics, working principles, and applications. By virtue of underlying the physics and design flexibilities of metasurfaces, MNOSs have now been endowed with superb performances and advanced functionalities, leading toward highly integrated smart sensing platforms.
Hyperspectral imaging in the visible spectrum offers significant potential for diverse applications, but is often constrained by bulky hardware and limited robustness in low‐light conditions. To overcome these challenges, a simulation‐based proof‐of‐concept for a metasurface‐encoded single‐pixel hyperspectral imaging system (MESH) is presented, in which structured spatial modulation is combined with a compact set of 50 broadband metasurface filters designed using a binary pattern generation strategy to ensure low interfilter correlation. Hyperspectral datacubes comprising 301 channels from 400 to 700 nm are reconstructed via a sparsity‐constrained optimization algorithm, while a physics‐enhanced deep learning model is further introduced to enable fast and accurate recovery. Simulation results demonstrate that MESH achieves a spectral resolution of 1.17 nm. Even at a total compression ratio of 2.1%, the deep learning model maintains high reconstruction quality, with a peak signal‐to‐noise ratio of 30.96 dB, structural similarity of 0.8526, and spectral angle mapping of 0.0742 rad, indicating accurate intensity recovery, structural preservation, and spectral integrity. The present study provides a simulation‐based verification of feasibility and design guidelines, laying the groundwork for future experimental validation of the MESH system, which is expected to further demonstrate its practical applicability and performance for deployment in low‐light and resource‐constrained environments.
Integrated optics have been stuck in two-dimensional (2D) topologies for decades until the femtosecond laser direct writing (FLDW) technique enables direct lithography of three-dimensional (3D) geometries and nanoscale structures with rapid prototyping and large-scale manufacturing capabilities in a variety of transparent substrates. The 3D capability of FLDW makes diverse light-wave remapping geometries possible, thereby realizing efficient interconnection of optical systems at different spatial scales, offering a 3D integrated-optics footprint capable of scaling a benchtop optical system down to a 3D glass chip. This work summarizes the history and important milestones in developing FLDW waveguides. Basically, all revolutionary improvements in waveguide key performance, including low propagation loss and small bending radius, were accompanied by the discovery and development of new mechanisms for laser-induced refractive index modification. At the same time, advanced laser beam-shaping methods for tightly focused spatiotemporal fields have been technically grafted onto the fine control of laser–matter interaction in FLDW, notably achieving variable cross-section, arbitrary refractive index and mode-field distribution, thus providing new degrees of freedom beyond the limitations of traditional 2D planar waveguides for more complex photonics circuit design. In this work, we present a comprehensive review of the field, encompassing fundamental mechanisms (such as refractive index modification) as well as key technological advances that enable true 3D integration. On the basis of this, we summarize the basic integrated waveguide components fabricated by FLDW and point out the prospective challenges and future research directions. Tentative routes towards large-area, ultra-broadband, hybrid, multifunctional, all-optical system integration in 3D glass chips are also suggested.
Terese von Knorring, Tobias Buhl Ihlemann, Paul Blanche
et al.
Photoacoustic imaging (PAI) shows promise for skin cancer diagnosis by detecting chromophores like melanin, hemoglobin, lipids, and collagen. While most studies focus on malignant lesions, understanding normal skin variability across anatomical regions is crucial for validating PAI's clinical application and its use in melanoma diagnosis. We assessed normal skin in 20 healthy volunteers from three different body locations using a clinical PAI system and compared suspicious looking pigmented skin lesions, including melanomas, to adjacent normal skin (n = 74). Higher deoxyhemoglobin levels were observed in the ankle compared to the cheek and volar forearm, while melanin, lipids, and collagen showed minimal variation. Patients with malignant lesions had significantly higher deoxyhemoglobin levels (p = 0.001) than adjacent normal skin, a difference not seen in benign lesions. These findings suggest that PAI may help diagnose malignancies by identifying increased vascularity in skin cancers, while anatomical differences should be considered during diagnostic work-up.
Abstract Phase transitions induce significant changes in the electrical and photonic properties of materials. Ultra-sensitive photodetectors leveraging material phase transitions can be realized near the transition temperature. Photodetectors based on Ta2NiSe5, a room-temperature excitonic insulator phase transition material, exhibit exceptional performance from visible to terahertz frequencies. Specifically, in the terahertz range, the electronic bandwidth is 360 kHz, and the specific detectivity (D*) reaches 5.3 × 1011 cm·Hz1/2·W−1. The van der Waals heterostructure of Ta2NiSe5/WS2 further enhances performance.
The Friedrich–Wintgen bound state in the continuum (FW BIC) provides a unique approach for achieving high quality factor (Q‐factor) resonance, which has attracted wide attention and promoted the development of various applications. However, the FW BIC is usually considered as accident BIC resulting from the continuous parameters tuning, and a systematic approach to generate the FW BIC is still lacking. To address this issue, a method is proposed for actively generating FW BIC in a hybrid plasmonic–photonic structure near the commercially important communication wavelength. The hybrid system comprises an electrically tunable borophene plasmon mode and a Brillouin zone folding‐induced BIC (BZF‐BIC) supported by a dielectric dimer grating. More interestingly, the BZF‐BIC can be directly excited by the localized borophene plasmon (LBP) mode through near‐field coupling as LBP mode can be considered as a dipole source. The interaction between them can further form the FW BIC and support electromagnetically induced transparency‐like with maximum group index up to 2043, indicating its great potential for slow light applications. The results provide a promising strategy and theoretical support for the generation of FW BIC in active plasmonic optical devices.
In this paper, a novel strategy of employing microwave photonic (MWP) time-frequency limiter (TFL) for microwave photonic multiband radar is proposed to suppress the interference, achieving real-time response to the interference scenarios and high-resolution target detection. By mapping the echo signal into optical domain, the time-frequency characteristic is re-constructed through stimulated Brillouin scattering (SBS), realizing the selective suppression on high-power optical signal mapped by the interference. Based on this concept, a MWP TFL system based on the optical spectrum processing is constructed, and proof-of-concept experiments are demonstrated to verify the feasibility of the proposed strategy under different interference scenarios. Employing the proposed MWP TFL, the signal-to-noise ratio of the detection results, which is severely degraded by asynchronous interference, can be improved by 27.97 dB, and the suppression ratio on the false targets generated by the synchronous interference can reach 34.10 dB. The experimental results shows that the strategy can further enhance the survivability of multiband radar without compromising the range resolution for target detection. In addition, experiments are carried out to demonstrate the capability of the proposed strategy under different interference-to-signal ratios, showing a good adaptability to the complex interference scenarios.