Band 14, Heft 5

Structural coloration, a color-generation mechanism often found in nature, arises from light–matter interactions such as diffraction, interference, and scattering, with micro- and nanostructured elements. Herein, we systematically study anisotropic, 3D-architected grating structures with polarization-tunable optical properties, inspired by the vivid blue of Morpho butterfly wings. Using two-photon lithography, we fabricate multilayered gratings, varying parameters such as height (through scanning speed and laser power), periodicity, and number of layers. In transmission, significant color transitions from blue to brown were identified when varying structural parameters and incident light polarization conditions (azimuthal angle and ellipticity). Based on thin film diffraction efficiency theory in the Raman–Nath regime, optical characterization results are analytically explained, evaluating the impact of each parameter variation. Overall, these findings contribute to technological implementations of polarization-sensitive, 3D-architected gratings for structural color applications.

As a two-dimensional material at the nanoscale, optical metasurfaces have excellent and flexible optical field control methods. In particular, the application of the concept of bound states in the continuum (BIC) enables optical metasurfaces to achieve resonance effects with high quality factors (Q factor). In comparison to plasmonic metasurfaces, all dielectric metasurfaces can effectively reduce the Ohmic losses in the structure. In this study, we propose a q-BIC metasurface with a high quality factor (maximum Q factor of 247), which is all dielectric and symmetry-breaking, and investigate the enhancement effect of this structure on optical chirality in the near-infrared band. In the simulation and experiment, the transmission spectra of the structure in the near-infrared band exhibited differences at different light source incidence angles when illuminated with circularly polarised light of varying rotation directions (external chirality). The maximum far-field circular dichroism (CD) achieved was 0.17 in the simulation and 0.038 in the experiment. Subsequently, the near-field chirality enhancement of the structure was investigated, which has the potential to increase the optical chirality of the incident light by up to 22 times. Furthermore, the introduction of a chiral medium to a non-chiral metasurface results in a chiral transfer effect, enabling the achievement of circular dichroism beyond the intrinsic capabilities of the individual substances involved (maximum CD = 0.0055). The high-Q factor of the all-dielectric metasurface paves the way for a plenty of potential applications in optical chiral fields, including chiral sensing, ultra-sensitive analysis of biomaterials and soft matter.

We propose and validate a new approach for wideband waveguide grating couplers (GC). The wideband operation is achieved using a slot waveguide grating structure above the conventional channel waveguide. With this slot waveguide grating structure, both the grating strength, mode effective index and dispersion in the grating region can be flexibly tuned to enable high coupling efficiency and wideband operation. 3D FDTD simulations predicted coupling efficiency of −4.08 dB with unprecedented 1 dB bandwidth of 229 nm. The experimental result in coupling with standard single mode fiber in the C band to a lithium niobate waveguide achieved −4.47 dB coupling efficiency with 1 dB bandwidth of 171 nm and 3 dB bandwidth of over 200 nm. The unprecedented wide optical bandwidth is achieved without using bottom metal reflectors or the etching of grating structures on the lithium niobate material.

Two-photon polymerization (TPP) lithography can process 3D micro–nano structures with high precision and has wide applications in the fields of micro-optics. Metasurfaces can flexibly control electromagnetic fields at subwavelength scale, achieving functions such as multidimensional multiplexing holography and achromatic imaging. Meta-devices are usually fabricated via EBL-based process, which is complex and difficult to fabricate meta-devices composed of meta-atoms with different heights. Here, we design a color dual-wavelength metasurface hologram without spatial multiplexing. By combining the propagation phase and the geometric phase, the phase response of two wavelengths is achieved in the same polarization state, and the metasurface is prepared using TPP 3D laser printing technology. The experimentally reconstructed images are consistent with theoretical predictions. This not only verifies the feasibility of this 3D printing technology in the preparation of metasurface samples operating in visible band but also provides potential applications in holographic display, optical encryption, anticounterfeiting, and other fields.

Metalens has shown its significantly ultra-light and ultra-thin features. However, large-aperture achromatic metalens is constrained by both maximum dispersion range and computational memory. Here, we propose a fully device optimizing framework that engineers phase dispersion and amplitude transmittance to create centimeter-size achromatic metalens operating in long-wave infrared regime (8–12 μm). Via wrapping group delay within a defined range and optimizing dispersion phase of desired wavelengths, chromatic aberrations can be effectively corrected. We verify our design by characterizing all-silicon 3.18-cm-diameter and 6.36-cm-diameter LWIR achromatic metalenses. Diffraction-limited tight-focusing can be achieved, and the normalized focal length shift is less than 3.3 × 10 −4 . Thermal imaging performance is verified on targets of holes or letters with a diameter or line width exceeding 2 mm. These findings facilitate the development of large-aperture achromatic metalenses and open up possibilities for lightweight imaging systems in long-wave infrared.

The hybridization of multiple excitons in a heterobilayer composed of two transition metal dichalcogenides (TMDCs) based on strong light–matter interaction is interesting from the viewpoint of both fundamental research and practical application. Here, we investigate numerically and experimentally the hybridization of three excitons in a heterobilayer mediated by the surface plasmon polaritons (SPPs) excited on a thin Au film and the transverse-electric (TE) polarized waves excited on a Si 3 N 4 /Ag heterostructure via photon–exciton coupling. Relying on numerical simulation, we observe anticrossing behaviors in the angle-resolved reflection spectra calculated for MoS 2 /WS 2 /Au and WS 2 /MoS 2 /Si 3 N 4 /Ag heterostructures, which reveal the coupling between the surface wave (SPPs or TE waves) and the multiple excitons in the heterobilayer. In experiments, we employ the oligomers of polystyrene (PS) nanospheres as scatters to transfer the surface waves into far-field radiations. Similarly, we observe anticrossing behaviors in the angle-resolved scattering spectra measured for the oligomers of PS nanospheres. Relying on the coupled oscillator model, we observe Rabi splitting energies of Ω SPP ∼206.79 meV for the SPPs and Ω TE ∼237.60 meV for the TE waves. Based on the calculated current density distributions and Hopfield coefficients, we demonstrate the hybridization of the three excitons in the WS 2 /MoS 2 heterobilayer mediated by the TE waves. Our findings open new horizons for manipulating light–matter interaction in TMDC heterobilayers and suggest the potential applications of exciton hybridization in energy transfer.

Adaptive optics is a technology that corrects wavefront distortions to enhance image quality. Interferometric focus sensing (IFS), a relatively recently proposed method within the field of adaptive optics, has demonstrated effectiveness in correcting complex aberrations in deep tissue imaging. This approach determines the correction pattern based on a single location within the sample. In this paper, we propose an image-based interferometric focus sensing (IBIFS) method in a conjugate adaptive optics configuration that progressively estimates and corrects the wavefront over the entire field of view by monitoring the feedback of image quality metrics. The sample conjugate configuration allows for the correction of multiple points across the full field of view by sequentially measuring the correction pattern for each point. We experimentally demonstrate our method on both the fluorescent beads and the mouse brain slices using a custom-built two-photon microscope. We show that our approach has a large effective field of view as well as more stable optimization results compared to the region of interest based method.

Infrared (IR) camouflage has garnered growing attention with progress in IR detection technology. The emergence of metamaterial with powerful electromagnetic field regulation ability provides an effective solution for thermal emission manipulation in IR camouflage. However, the intricated micro/nano machining technology of metamaterial greatly limits its moving toward practical application, and single-band IR camouflage makes it difficult to resist multiband cooperative detection systems. Here, a flexible, fine, and mask-free femtosecond laser direct writing (FsLDW) technology was introduced to pattern on ultra-thin metals. Based on this efficient technique, the optically transparent metamaterial emitter with multiband compatible camouflage is fabricated. The emitter is demonstrated to achieve high reflectance ( R 3–5 µm = 0.79 and R 8–14 µm = 0.70) in the dual-band atmospheric window and low reflectance ( R 1.06 µm = 0.3, R 1.55 µm = 0.1) for IR and laser stealth. In addition, the high emissivity ( ɛ 5–8 µm = 0.64) for the nonatmospheric window effectively dissipates the accumulated heat, showing promising prospects in radiative cooling by comparison with Ag at the same heating power. This work offers a clue for coordinated control of multiband electromagnetic waves and heat through simple structural design, which is expected to promote its camouflage applications and thermal management in the military.

The generation of optical vortex beams is pivotal for a myriad of applications, encompassing optical tweezing, optical communications, and quantum information, among others. The metasurface-based approach has realized significant advancements in vortex production, utilizing either dynamic or geometric phases. The dynamic design exhibits indifference to the polarization state of incident light, while the geometric design is inextricably tied to it. In the study, we put forth the proposition that combining dynamic and geometric phases could unlock the potential of metasurface design in generating optical vortices. A hybrid design that harnesses the combined dynamic and geometric phases can attain the same objective while offering tunable functional control over the polarization of light. We establish a correlation between the structural parameters of metasurface and the topological charge of the resulting vortices. The experimental results fully demonstrate the design’s flexibility and its effective control over the polarization constraints of incident light. Our research uncovers the capacity for vortex generation through the manipulation of hybrid phases introduced by metasurfaces, indicating significant potential for the design of optical devices and the future advancement of innovative optical applications.

Vortex beams, as beams carrying orbital angular momentum (OAM), exhibit unique donut-shaped intensity distributions and helical wavefronts. They are widely applied in fields such as optical communication, nanoparticle manipulation, and quantum information. Traditional vortex beam generation methods, such as those based on Pancharatnam–Berry phase design, can effectively generate vortex beams, but the conversion efficiency and design flexibility are limited by polarization states and incident angles. In addition, the generated and propagated vortex beams require separate metasurface for wavefront deflection and refocusing for practical applications. This work proposes a novel metasurface design approach based on resonant phase, where phase coverage of 2 π is achieved by varying the radius of the nanocylinders. In addition to the efficient vortex beam generation in the visible regime, we have tackled the challenge of simultaneous control of vortex beam’s anomalous deflection and refocusing, through different encoding sequences superimposed based on the principle of Fourier convolution and metalens design. This all-in-one multifunctional metasurface design offers new technological pathways for secure optical communication and quantum manipulation applications.