Band 14, Heft 19

Micro–nano fabrication technology is critical to high-end fabrication, bridging the gap between microscopic and macroscopic scales. Femtosecond laser fabrication, owing to its ultrafast nonlinear effects and three-dimensional direct writing capabilities, has demonstrated unique advantages in the fabrication of functional micro–nano structures. Phase holographically modulated femtosecond laser technology, as a representative of spatial optical field modulation, modulates the phase of the incident laser field to flexibly transform a single focal point into various spatial optical fields, including multifocal arrays, patterned optical fields, and three-dimensional optical fields, according to specific fabrication requirements. This technology not only improves fabrication precision and efficiency but also provides greater flexibility in femtosecond laser fabrication. This review systematically summarizes recent technological advances, focusing on four aspects: algorithms for generating phase holograms, exceeding the diffraction limit to improve fabrication resolution, optimizing fabrication quality, and improving fabrication efficiency. It aims to provide theoretical foundations and technical references to support the practical application of modulated femtosecond laser technology in the fabrication of functional micro–nano structures.

The photonic spin Hall effect (PSHE) is the deep subwavelength spin component shift of light induced by the spin–orbit interaction of photons. Here, we demonstrate a polarimetric scheme to directly measure the surface plasmon resonance-enhanced angular PSHE in the Kretschmann configuration using a gold film. In contrast to the weak measurement scheme that indirectly measures the spatial term-dominated PSHE using a well-collimated source, we focused the incident beam to a small beam waist and significantly enhanced the angular PSHE. Imbert–Fedorov shift manifested as a displacement offset of the reflected beam, have been taken into account to extract only the PSHE shift. In practical measurements, accounting for this shift enables accurate separation of PSHE from polarization-induced artifacts. Measuring PSHE provides an additional spin degree of freedom, enabling an innovative approach toward spin-controlled nanophotonic applications, including optical sensing, precision metrology, and high-contrast microscopy.

The spatial inhomogeneity of electromagnetic energy density in an optical field typically gives rise to conservative gradient forces, which serve as the fundamental mechanism for trapping nanoparticles in optical tweezers. Surprisingly, however, we demonstrate that even in the absence of an energy density gradient, optical gradient forces can still act on isotropic, achiral particles when the incident field consists of counter-propagating plane waves engineered to exhibit polarization-controlled antisymmetry between the electric and magnetic energy density gradients. Through both numerical simulations and analytical derivations based on multipole expansion theory, we show that this anomalous gradient force arises from the electromagnetic symmetry breaking induced by the particle itself, irrespective of its size. Notably, this electromagnetic symmetry breaking-induced gradient force reaches its maximum under elliptical polarization at the specific position, rather than linear or circular polarization, underscoring the critical role of polarization configuration in modulating energy density gradients. These findings reveal a previously unrecognized mechanism for optical gradient force generation and deepen our understanding of the role of hidden antisymmetry in structured light fields.

We study the impact of structural disorder on a radiative lifetime of symmetry-protected bound state in the continuum (BIC) and a bright mode in a one-dimensional periodic chain of coupled Mie resonators. Through experimental, simulation, and theoretical approach, we reveal an unusual linear decay in the radiative quality factor of the BIC with the increase of the disorder amplitude, contrasting with the quadratic decay observed in recent studies. We also investigate modes with different symmetries and show that the behavior of the quality factor in a strongly disordered system depends on the mode’s multipolar origin. In addition, we found that in a disordered finite chain, the quality factor of Fabry–Pérot modes is governed by intraband interactions of modes. To study the behavior of localized states in disordered systems, we also analyze the emergence of Anderson localization. Our findings are pivotal for the practical application of BICs, particularly in natural and self-assembled photonic structures where structural disorder plays a crucial role.

Sensitive and miniaturized optical sensing device is highly desirable in various biosensing applications. This study reports a dual-band, high-quality-factor ( Q factor) quasi-bound states in the continuum (quasi-BIC) metasurface for refractive index sensing, operating across the visible (700–800 nm) and near-infrared (950–1,000 nm) spectral ranges. By incorporating asymmetric dual nanoholes into an all-dielectric silicon metasurface, symmetry-protected BIC modes are transformed into quasi-BIC, resulting in two distinct Fano-type resonance peaks. Numerical simulations and experimental validations demonstrate that precise control over resonance wavelengths and quality factors can be achieved by adjusting the nanohole radius and positional offsets (Δ), yielding a theoretical Q -factor of 2,250. The sensor exhibits a refractive index sensitivity of 151.6 nm/RIU for the visible band (Q-BIC I) and 61.1 nm/RIU for the near-infrared band (Q-BIC II), with a signal-to-noise ratio (SNR) of 285, significantly outperforming existing nanohole-based biosensors. Fabricated using CMOS-compatible processes, the device employs cost-effective visible-light detectors, eliminating the need for specialized infrared materials. This work advances the development of high-sensitivity, miniaturized refractive index sensing platforms, offering promising applications in biomedical diagnostics and environmental monitoring.

On-chip photonic networks require adequately spatially ordered matter-photon interconversion qubit sources with emission figures-of-merit exceeding the requirements that would enable the desired functional response of the network. The mesa-top single quantum dots (MTSQDs) have recently been demonstrated to meet these requirements. The substrate-encoded size-reducing epitaxy (SESRE) approach underpinning the realization of these unique quantum emitters allows control on the shape, size, and strain (lattice-matched or mismatched) of these epitaxial single quantum dots. We have exploited this unique feature of the MTSQDs to reproducibly create arrays of quantum dots that exhibit single photon superradiance, a characteristic of the SESRE-enabled delicate balance between the confinement potential volume, depth, the resulting exciton binding energy, and the degree of confinement of the center of mass (CM) motion of the exciton. Scanning transmission electron microscope (STEM) studies reveal the structural (atomic scale) and chemical (nanometer scale) nature of the material region defining the notion of the shape and volume (here large) of the electron confinement region ( i.e. the QD). In the exciton’s weak CM confinement regime, owing to its coherent sampling of the large volume, an enhancement of the MTSQD oscillator strength to ∼30 is demonstrated. Theoretical modelling with input from the STEM findings provides corroboration for single photon superradiance causing enhancement of the oscillator strength by ∼2.5–3. Our findings allow fabricating and studying interconnected networks enabled by these unique matter qubit-light qubit interconversion units that can be realized for lattice matched and mismatched material combinations covering UV to mid-infrared wavelength range.

We present a novel design approach for vibrational strong coupling (VSC) that enables spectrally accessible and controllable vibrational-polaritonic states using a graphene-integrated deep silver (Ag) grating. The deep Ag grating supports strong infrared resonances arising from hybrid magnetic polariton and surface plasmon modes, facilitating coherent coupling with the molecular vibrations of a test molecule, poly(methyl methacrylate) (PMMA). Integrating graphene into the deep Ag grating introduces discrete graphene plasmon (GP) modes that interact with the vibrational-polaritonic modes, providing spectral tunability and control over otherwise static polaritonic states. Consequently, the upper and lower polaritonic modes split into two distinct branches due to the sharp GP modes. The mixing ratio among the grating mode, molecular vibration, and GP mode is significantly modulated by adjusting the chemical potential applied to the graphene and varying the number of graphene layers incorporated into the grating. This ability to spectrally access and control polaritonic states makes the graphene-integrated Ag grating a promising platform for VSC applications, which potentially enables the use of polaritonic states as distinct quantum states for polaritonic chemistry.

The deep learning revolution has increased the demand for computational resources, driving interest in efficient alternatives like all-optical diffractive neural networks (AODNNs). These systems operate at the speed of light without consuming external energy, making them an attractive platform for energy-efficient computation. One task that could greatly benefit from an all-optical implementation is spatial super-resolution. This would allow overcoming the fundamental resolution limitation of conventional optical systems, dictated by their numerical aperture. Here, we examine whether the success of digital super-resolution networks can be replicated with AODNNs considering networks with phase-only nonlinearities. We find that while promising, super-resolution AODNNs face two key physical challenges: (i) a tradeoff between reconstruction fidelity and energy preservation along the optical path and (ii) a limited dynamic range of input intensities that can be effectively processed. These findings offer a first step toward understanding and addressing the design constraints of passive, all-optical super-resolution systems.

Quantum sensing is rapidly advancing, creating new opportunities in fields such as fundamental science and advanced manufacturing. The optically pumped atomic magnetometer (OPM), known for its high sensitivity and compact form factor, has become a promising candidate for a range of applications. However, traditional OPM systems relying on bulky optical components and phase accumulation often face limitations in modulation precision and miniaturization. In this study, we introduce a miniaturized OPM design that incorporates a polarized metasurface and uses a single laser source for both pumping and detection. The polarized metasurface enables the transformation of linearly polarized light with arbitrary polarization azimuths into circularly polarized light, allowing for subwavelength-scale optical field manipulation and integrated beam splitting. In the developed system, both the circularly polarized pump beam and the zeroth-order linearly polarized probe beam are generated from the same metasurface device, forming a dual-path magnetometer architecture. This design significantly reduces the optical system size while achieving a sensitivity of 4.91 pT/Hz 1/2 in the 2–10 Hz frequency range, exceeding the performance of conventional dual-beam OPMs with comparable configurations. Experimental results demonstrate that the proposed OPM effectively utilizes the metasurface’s optical properties to balance high sensitivity and system miniaturization. This work offers a practical approach for the integrated design of compact quantum sensing systems.

The multimodal detection system has gradually been perfected, essentially covering the entire optical spectrum, posing a significant threat to the survival of objects. To counter this escalating detection threat, the demand for multispectral-compatible camouflage (MCC) is increasingly urgent. However, there are inherent conflicts in the principles of camouflage for visible light, infrared (IR), and lasers, necessitating spectrally selective design to reconcile these conflicting requirements. Here, we propose a multilayer film structure with heterostructure coupling, utilizing resonant cavities, destructive interference, and double-metal defect layers to achieve MCC, integrating IR, laser, and visible light. These MCC films exhibit low emissivity in the dual IR bands (∼0.2 at 3–5 μm and ∼0.4 at 7.5–13 μm) for high-temperature thermal camouflage, low reflectance at 10.6 μm (∼0.3) for reducing laser signal, and demonstrate excellent insensitivity to angles and polarization. By varying the thickness of the resonant cavity, a wide color gamut in the visible light range is achieved, maintaining efficient IR and laser compatibility while integrating diverse structural colors. This work offers a promising and pattern-free method for MCC design, holding great potential in thermal management and camouflage.

Space–time modulated systems have recently emerged as a powerful platform for dynamic electromagnetic processing in both space and time. Most of the related research so far has assumed abrupt parameter profiles. This paper extends the field to generalized graded-index (GRIN) interfaces, which are both more practical than ideal profiles and offer new avenues for wave manipulations. It presents an exact solution for wave propagation across arbitrary space–time modulated GRIN interfaces and describes versatile chirping effects. The solution is based on a generalization of the impulse response method from linear time-invariant to linear space–time-varying systems. The proposed framework shows that space–time GRIN systems represent a novel approach for generating a new form of chirping that is not inherently based on dispersion, with promising applications in pulse shaping and signal processing.

The effective medium theory (EMT) provides a simplified framework to calculate the electromagnetic responses and is generally considered exact in the all-dielectric system with deep-subwavelength constituents. In this work, we perform the Goos–Hänchen (GH) shift that invalidates the EMT on the multilayered dielectric structures under the common conditions. This breakdown of the EMT arises from the high sensitivity of the GH shift on the phase and magnitude of Fresnel reflection coefficient. The degree of such breakdown shows strong dependence on the polarization angle of incidence and the layer and filling fraction of the structures. Notably, we find that the GH shift is potentially applicable to nano-meter scale thickness sensing, which cannot be displayed based on EMT in some cases. Our findings will provide useful guidance to reduce the calculation errors of the electromagnetic responses and promote the design of precise metrology devices.