Hui Gao

The fabrication of visible-spectrum three-dimensional (3D) photonic crystals (PhCs) remains highly challenging, because existing manufacturing techniques cannot simultaneously achieve high processing precision and sufficient geometric freedom. Here, we propose a suspended pyrolysis-assisted two-photon polymerization (SP-TPP) printing strategy, achieving the controllable fabrication of visible-spectrum 3D PhCs. The resulting 3D diamond PhCs exhibit a remarkable lattice-period standard deviation of only 5.75 nm, approximately 1/45 of that achieved without suspended pyrolysis. Microscopic reflection spectra confirm these PhCs possess uniform optical responses across all spatial positions. By tuning the lattice period and structural duty cycle, the PhCs operating at diverse wavelengths are systematically realized. Moreover, through the demonstration of PhC prototype structures and in situ arrayed fabrication, the SP-TPP printing strategy paves the way for applications in photonic microcavities, 3D optical waveguides, optical splitters, and integrated micro-optical systems.

Vortex beams (VBs) carrying orbital angular momentum have attracted widespread interest for applications in optical communication, imaging, and manipulation, yet their generation still mainly relies on bulky optical components that hinder miniaturization and integration. Here, we propose a fiber-integrated hybrid refractive-diffractive device for high-efficiency and high-fidelity VB generation. Using a one-step two-photon polymerization process, a hyperbolic aspherical lens (HAL) for beam collimation and diffraction modulators for vortex phase shaping are monolithically integrated on the fiber tip. This approach supports both spiral phase plates and vortex gratings, enabling versatile VB generation. Optical characterization shows that the fiber-tip HAL achieves a magnification of 13.4× with a collimation angle of 0.38°. Far-field interference measurements confirm the generation of a coaxial VB and off-axis VB arrays. This fully fiber-integrated platform offers a scalable and efficient solution for VB applications in space-constrained photonic systems.

Multifunctional integration on optical fiber tips has attracted tremendous attention due to the high sensitivity, compact size, and immunity to electromagnetic interference of fiber-optic devices. However, achieving stable three-dimensional (3D) micro-structuring while maintaining both miniaturization and sensing performance remains a persistent challenge. Here, we present a monolithic 3D micro-encapsulation strategy based on femtosecond laser direct writing (FsLDW) and chemical vapor polymerization (CVP), enabling the multifunctional integration of Fabry–Pérot interferometers (FPIs) on fiber tips with submicron precision and enhanced structural robustness. This approach combines an FsLDW-nanoprinted air cavity with CVP of Parylene C coating, reducing the overall sensor footprint from the centimeter scale to approximately 100 μm without compromising sensing performance. As a proof of concept, we demonstrate the stable operation of encapsulated optical fiber sensors under continuous fluidic and mechanical disturbances, supporting both intensity and wavelength demodulation. The encapsulated FPI cavities achieve over an order of magnitude improvement in spectral stability and a 26.4 dB increase in long-term signal contrast, with performance sustained over 10,000 repeated test cycles. This work offers a scalable route toward high-density, multifunctional fiber-optic sensors with enhanced durability and long-term reliability for next-generation photonic integrated applications.

Emerging demands for dynamic wavefront modulation in holographic displays, augmented/virtual reality, and light detection and ranging require spatial light modulators (SLMs) with high pixel density and fast refresh rates. However, key parameters of existing liquid-crystal and metasurface-based SLMs, such as spatiotemporal product density, field of view and refresh rate, remain far below application requirements. Here we report an optically addressed metasurface SLM composed of independently tunable meta-atom supercells with a 756 nm pitch. This device reduces SLM pixel size to the submicrometre scale while achieving a spatiotemporal product density of 2.3 × 10¹² pixels s⁻¹ cm⁻², thereby meeting the critical threshold for true holography. It enables real-time complex-amplitude holography, three-dimensional focusing and beam steering over a ±20.6° field of view in the visible spectrum.

The advancement of modern optical imaging systems has generated a substantial demand for precision-engineered imaging components with complex functionalities. Despite various micro-nanofabrication techniques demonstrating significant advantages over traditional methods, critical challenges persist in achieving nanoscale resolution and freely designed intricate micro-optical structures. Femtosecond direct laser writing (FsDLW) emerges as a pivotal solution to these challenges, facilitating the fabrication of sophisticated architectures that transcend the diffraction limit through nonlinear multiphoton absorption. This technique processes exceptional capabilities, including extensive material compatibility, versatile micro-nanoscale fabrication, and true three-dimensional structuring. To date, FsDLW has been successfully employed in the manufacturing of diverse micro-optical imaging components. This review systematically elucidates the fundamental methodologies of FsDLW applicable to micro-optical device fabrication, alongside a comprehensive overview of the relevant material systems. Furthermore, recent advancements in micro-optical imaging devices and their emerging applications are critically assessed. Finally, we provide a prospective analysis of unresolved challenges and future research directions for imaging optical components.

Holography has emerged as an ideal method for future immersive naked-eye displays, as it possesses the capability to record and reconstruct light wavefronts. However, traditional dynamic holographic devices always have some shortcomings, such as a small field of view, twin imaging, and multiple orders of diffraction, which bring many challenges to their practical application. Metasurfaces, composed of subwavelength unit cells, offer great potential in manipulating light fields and addressing these limitations. The latest research progress in the field of dynamic metasurface holography is summarized from the implementation methods to design strategies, mainly including the typical research works on dynamic meta-holography based on tunable metasurfaces and multiplexed metasurfaces. The emerging applications of dynamic meta-holography have the potential to accelerate the development of light field manipulation and micro−/nanofabrication in higher dimensions. This chapter also explores potential applications and development paths in the field.

The popularity of deep learning has boosted computer-generated holography (CGH) as a vibrant research field, particularly physics-driven unsupervised learning. Nevertheless, present unsupervised CGH models have not yet explored the potential of generating full-color 3D holograms through a unified framework. In this study, we propose a lightweight multiwavelength network model capable of high-fidelity and efficient full-color hologram generation in both 2D and 3D display, called IncepHoloRGB. The high-speed simultaneous generation of RGB holograms at 191 frames per second (FPS) are based on Inception sampling blocks and multi-wavelength propagation module integrated with depth-traced superimposition, achieving an average structural similarity (SSIM) of 0.88 and peak signal-to-noise ratio (PSNR) of 29.00 on the DIV2K test set in reconstruction. Full-color reconstruction of numerical simulations and optical experiments show that In-cepHoloRGB is versatile to diverse scenarios and can obtain authentic full-color holographic 3D display within a unified network model, paving the way for applications towards real-time dynamic naked-eye 3D display, virtual and augmented reality (VR/AR) systems.