Volume 13, Issue 20

Recent advancements in inverse design approaches, exemplified by their large-scale optimization of all geometrical degrees of freedom, have provided a significant paradigm shift in photonic design. However, these innovative strategies still require full-wave Maxwell solutions to compute the gradients concerning the desired figure of merit, imposing, prohibitive computational demands on conventional computing platforms. This review analyzes the computational challenges associated with the design of large-scale photonic structures. It delves into the adequacy of various electromagnetic solvers for large-scale designs, from conventional to neural network-based solvers, and discusses their suitability and limitations. Furthermore, this review evaluates the research on optimization techniques, analyzes their advantages and disadvantages in large-scale applications, and sheds light on cutting-edge studies that combine neural networks with inverse design for large-scale applications. Through this comprehensive examination, this review aims to provide insights into navigating the landscape of large-scale design and advocate for strategic advancements in optimization methods, solver selection, and the integration of neural networks to overcome computational barriers, thereby guiding future advancements in large-scale photonic design.

Graphene-based metamaterial sensors are of significant research value for detecting food preservatives at low concentrations due to their extremely high sensitivity levels. In this work, we proposed and experimentally demonstrated an anapole resonance-based graphene metasurface (An-graphene-Ms) sensor with its conductivity altered by electrostatic doping effects for detecting and differentiating between two preservatives, sodium benzoate and potassium sorbate, in the terahertz region. Sodium benzoate, owing to its benzene ring structure, established π – π stacking interactions between the π -electrons in the benzene ring and those in graphene, amplifying the sensing effect. The amplitude changes and phase differences of the An-graphene-Ms sensor for the sodium benzoate detection were greater than those for potassium sorbate at the same concentration. Additionally, to reveal the dependence of the resonance frequency on the time delay, the measured signals were investigated using the continuous wavelet transform (CWT), and the time-frequency combination of the metasurface sensor was performed. The 2D wavelet coefficient intensity cards are effectively constructed through CWT, which also presents a more accurate approach for distinguishing and determining the concentrations of the two preservatives.

Volumetric subcellular imaging has long been essential for studying structures and dynamics in cells and tissues. However, due to limited imaging speed and depth of field, it has been challenging to perform live-cell imaging and single-particle tracking. Here we report a 2.5D fluorescence microscopy combined with highly inclined illumination beams, which significantly reduce not only the image acquisition time but also the out-of-focus background by ∼2-fold compared to epi-illumination. Instead of sequential z -scanning, our method projects a certain depth of volumetric information onto a 2D plane in a single shot using multi-layered glass for incoherent wavefront splitting, enabling high photon detection efficiency. We apply our method to multi-color immunofluorescence imaging and volumetric super-resolution imaging, covering ∼3–4 µm thickness of samples without z -scanning. Additionally, we demonstrate that our approach can substantially extend the observation time of single-particle tracking in living cells.

Interference between the electric and magnetic dipole-induced in Mie nanostructures has been widely demonstrated to tailor the scattering field, which was commonly used in optical nano-antennas, filters, and routers. The dynamic control of scattering fields based on dielectric nanostructures is interesting for fundamental research and important for practical applications. Here, it is shown theoretically that the amplitude of the electric and magnetic dipoles induced in a vanadium dioxide nanosphere can be manipulated by using laser-induced metal-insulator transitions, and it is experimentally demonstrated that the directional scattering can be controlled by simply varying the irradiances of the excitation laser. As a straightforward application, we demonstrate a high-performance optical modulator in the visible band with high modulation depth, fast modulation speed, and high reproducibility arising from a backscattering setup with the quasi-first Kerker condition. Our method indicates the potential applications in developing nanoscale optical antennas and optical modulation devices.

The free electron spin dynamics in Kapitza–Dirac (KD) effect had been studied theoretically in one-dimensional standing wave of EUV to X-ray laser with extremely high intensity, which is far beyond experimental realization. Here, we propose to achieve the free electron spin-dependent KD effect in two-dimensional triangular optical lattice with spatial inversion symmetry breaking, and the theoretical results reveal that laser with wavelength in visible or near-IR and five orders of magnitude decreased intensity could lead to obvious spin-dependent KD effect. This work provides the way to realize the free electron spin-dependent KD effect experimentally.

Sophisticated infrared detection technology, operating through atmospheric transmission windows (usually between 3 and 5 μm and 8–13 μm), can detect an object by capturing its emitted thermal radiation, posing a threat to the survival of targeted objects. As per Wien’s displacement law, the shift of peak wavelength towards shorter wavelengths as blackbody temperature rises, underscores the significance of the 3–5 μm range for ultra-high temperature objects (e.g., at 400 °C), emphasizing the crucial need to control this radiation for the objects’ viability. Additionally, effective heat management is essential for ensuring the consistent operation of these ultrahot entities. In this study, based on a database with high-temperature resist materials, we introduced a material-informatics-based framework aimed at achieving the inverse design of simultaneous thermal camouflage (low emittance in the 3–5 μm range) and radiative cooling (high emittance in the non-atmospheric window 5–8 μm range) tailored for ultrahigh-temperature objects. Utilizing the transfer matrix method to calculate spectral properties and employing the particle swarm optimization algorithm, two optimized multilayer structures with desired spectral characteristics are obtained. The resulted structures demonstrate effective infrared camouflage at temperatures up to 250 °C and 500 °C, achieving reductions of 86.7 % and 63.7 % in the infrared signal, respectively. At equivalent heating power densities applied to the structure and aluminum, structure 1 demonstrates a temperature reduction of 29.4 °C at 0.75 W/cm 2 , while structure 2 attains a temperature reduction of 57.5 °C at 1.50 W/cm 2 compared to aluminum, showcasing enhanced radiative cooling effects. This approach paves the way for attenuating infrared signals from ultrahigh-temperature objects and effectively managing their thermal conditions.

The metamaterial with artificial synthetic gauge field has been proved as an excellent platform to manipulate the transport of the electromagnetic wave. Here we propose an inhomogeneous spoof surface plasmonic metasurface to construct an in-plane pseudo-magnetic field, which is generated by engineering the gradient variation of the opened Dirac cone corresponding to spatially varying mass term. The chiral zeroth-order Landau level is induced by the strong pseudo-magnetic field. Based on the bulk state propagation of the chiral Landau level, the photonic Dirac waveguide is designed and demonstrated in the experimental measurement, in which the unidirectionally guided electromagnetic mode supports the high-capacity of energy transport. Without breaking the time-reversal symmetry, our proposal structure paves a new way for realizing the artificial in-plane magnetic field and photonic Dirac waveguide in metamaterial, and have potential for designing integrated photonic devices in practical applications.

Silicon-based optical switches are integral to on-chip optical interconnects, and mode-division multiplexing (MDM) technology has enabled modes to function as carriers in routing, further boosting optical switches’ link capacity. However, traditional multimode optical switches, which typically use Mach–Zehnder interferometer (MZI) structures and mode (de)multiplexers, are complex and occupy significant physical space. In this paper, we propose and experimentally demonstrate a novel demultiplexing-free dual-mode 3 × 3 thermal-optical switch based on micro-rings (MRs) and mode exchangers (MEs). All MRs are designed to handle TE 1 mode, while the ME converts TE 0 mode to TE 1 mode, enabling separate routing of both modes. Bezier curves are employed to optimize not only the ME, but also the dual-mode 45° and 90° waveguide bends, which facilitate the flexible and compact layout design. Moreover, our structure can support multiple wavelength channels and spacings by adding pairs of MRs, exhibiting strong WDM compatibility. The switch has an ultra-compact footprint of 0.87 × 0.52 mm 2 . Under both “all-bar” and “all-cross” configurations, its insertion losses (ILs) remain below 8.7 dB at 1,551 nm, with optical signal-to-noise ratios (OSNRs) exceeding 13.0 dB. Also, 32 Gbps data transmission experiments validate the switch’s high-speed transmission capability.

We demonstrate a technique for flexibly controlling subwavelength focusing and scanning, by using the Fourier translation property of a topology-preserved flat lens. The Fourier transform property of the flat lens enables converting an initial phase shift of light into a spatial displacement of its focus. The flat lens used in the technique exhibits a numerical aperture of 0.7, leading to focusing the incident light to a subwavelength scale. Based on the technique, we realize flexible control of the focal positions with arbitrary incident light, including higher-order structured light. Particularly, the presented platform can generate multifocal spots carrying optical angular momentum, with each focal spot independently controlled by the incident phase shift. This technique results in a scanning area of 10 μm × 10 μm, allowing to realize optical scanning imaging with spatial resolution up to 700 nm. This idea is able to achieve even smaller spatial resolution when using higher-numerical-aperture flat lens and can be extended to integrated scenarios with smaller dimension. The presented technique benefits potential applications such as in scanning imaging, optical manipulation, and laser lithography.

The spin Hall effect of light, a phenomenon characterized by the transverse and spin dependent splitting of light at an optical interface, is highly promising for collecting precise quantitative data from interfaces and stands as an appealing option for improving precision metrology. This high level of precision is attributed to the principles of weak measurement. Since its conceptual introduction, the spin Hall effect of light has been empirically observed through weak measurement techniques, adhering closely to the initially proposed experimental configuration. Recently, it has been suggested that the setup can be downsized without compromising precision. Here, the first experimental demonstration of “compact weak measurement” is achieved by observing the spin Hall effect of both reflected and refracted light. Compared to the conventional weak measurement, this compact setup performs the same measurements but requires less free space by replacing the two convex lenses with a set of concave and convex lenses. The compact weak measurement demonstrates excellent agreement with theoretical predictions and experimental findings from traditional setups across both isotropic–isotropic and isotropic–anisotropic interfaces. The experimental validation of the compact configuration paves the way for the practical application of the spin Hall effect of light in devices with a smaller form factor.

Spectral reconstruction, critical for understanding sample composition, is extensively applied in fields like remote sensing, geology, and medical imaging. However, existing spectral reconstruction methods require bulky equipment or complex electronic reconstruction algorithms, which limit the system’s performance and applications. This paper presents a novel flexible all-optical opto-intelligence spectrometer, termed OIS, using a diffractive neural network for high-precision spectral reconstruction, featuring low energy consumption and light-speed processing. Simulation experiments indicate that the OIS is able to achieve high-precision spectral reconstruction under spatially coherent and incoherent light sources without relying on any complex electronic algorithms, and integration with a simplified electrical calibration module can further improve the performance of OIS. To demonstrate the robustness of OIS, spectral reconstruction was also successfully conducted on real-world datasets. Our work provides a valuable reference for using diffractive neural networks in spectral interaction and perception, contributing to ongoing developments in photonic computing and machine learning.

Over the past decade, significant advancements in high-resolution imaging technology have been driven by the miniaturization of pixels within image sensors. However, this reduction in pixel size to submicrometer dimensions has led to decreased efficiency in color filters and microlens arrays. The development of color routers that operate at visible wavelengths presents a promising avenue for further miniaturization. Despite this, existing color routers often encounter severe interpixel crosstalk, around 70 %, due to the reliance on periodic boundary conditions. Here, we present interpixel crosstalk-minimized color routers that achieve an unprecedented in-pixel optical efficiency of 87.2 % and significantly reduce interpixel crosstalk to 2.6 %. The color routers are designed through adjoint optimization, incorporating customized incident waves to minimize interpixel crosstalks. Our findings suggest that our color router design surpasses existing color routing techniques in terms of in-pixel optical efficiency, representing a crucial step forward in the push toward commercializing the next generation of solid-state image sensors.

The significance of a cryptograph method lies in its ability to provide high fidelity, high security, and large capacity. The emergence of metasurface-empowered cryptography offers a promising alternative due to its unparalleled wavefront modulation capabilities and easy integration with traditional schemes. However, the majority of reported strategies suffer from limited capacity as a result of restricted independent information channels. In this study, we present a novel method of cryptography that utilizes a dual-band complex-amplitude meta-hologram. The method allows for the encoding of 2 25 different patterns by combining a modified visual secret-sharing scheme (VSS) and a one-time-pad private key. The use of complex-amplitude modulation and the modified VSS enhances the quality and fidelity of the decrypted results. Moreover, the transmission of the private key through a separate mechanism can greatly heighten the security, and different patterns can be generated simply by altering the private key. To demonstrate the feasibility of our approach, we design, fabricate, and characterize a meta-hologram prototype. The measured results are in good agreement with the numerical ones and the design objectives. Our proposed strategy offers high security, ultra-capacity, and high fidelity, making it highly promising for applications in information encryption and anti-counterfeiting.