Driven by exponential global data growth and the demand for high-speed and low-power processing, photonic integrated circuits (PICs) have emerged as a cornerstone of next-generation chip technologies^[1]. As electronic circuits hit physical limits, constrained by speed, heat dissipation, and scaling bottlenecks, PICs, which transmit data using photons, provide a viable alternative with high bandwidth, ultrafast processing, and low energy consumption. Beyond planar PICs, which have achieved substantial advancements, three-dimensional (3D) PICs—based on 3D path routing and arbitrary cross-sectional shapes—have developed rapidly. 3D PICs introduce novel 3D architectures to photonic chips, enabling 3D stereoscopic integration and facilitating the full utilization of photons across the multiple degrees of freedom. Additionally, integrating two-dimensional (2D) materials, which have unique structures and distinct properties, into 3D PICs opens new avenues for developing high-performance and functionally innovative devices^[2]. As a maskless non-contact fabrication technology in ambient air, ultrafast laser processing is widely employed in micro/nano-precision engineering applications due to its broad material compatibility^[3]. Laser nanofabrication enables both the direct creation of 3D PICs composed of 3D waveguides in diverse materials and the high-precision patterning of 2D materials^[4]. This approach thus paves many new ways to realize multi-dimensional PICs.

In a review article recently published in Photonics Insights^[5], Jia et al. have provided thorough analyses of laser nanofabrication techniques for multi-dimensional PIC manufacturing, with a distinct focus on integrating 2D materials with 3D architectures, as shown in Fig. 1. This review stands out to fill a critical gap in existing literature. While the previous reviews explored 2D or 3D PICs fabrication, Jia et al. highlight the synergies between 2D materials and 3D structures, revealing new pathways in the enhanced functionality and integration. Additionally, they propose that laser nanofabrication, as a transformative tool, can enable the integration of 2D materials with 3D PICs, thereby opening new horizons to create next-generation photonic devices.

Laser nanofabrication involves the dynamic interactions between lasers and materials^[6,7]. A particular strength of this review article lies in its comprehensive coverage of the laser nanofabrication strategies for both 3D and 2D PICs. For 3D systems, the authors skillfully connect the theoretical mechanisms, such as two-photon polymerization in polymers and refractive index modulation in glass with practical breakthroughs, exemplified by hybrid beam splitters in LiTaO3 crystals (which combine type I/II modification to minimize the propagation and bending loss). These processes are applied to fabricate embedded waveguides, micro-resonators, beam splitters, and other optical elements via the direct laser writing and three-dimensional laser printing, which illustrates the adaptability of the laser fabrication across 3D photonic platforms^[8]. For 2D systems, this review article outlines the laser-based modification and high-resolution patterning of materials like graphene, transition metal dichalcogenides (TMDCs), and black phosphorus, demonstrating how these atomically thin materials enhance device performance^[9]. For instance, the laser-induced phase transitions in MoTe2 enable high-mobility components, while the precise thinning of TMDCs via laser irradiation achieves atomic-layer control—critical for tailoring optical bandgaps. This review also highlights laser nanofabrication’s flexibility in customizing 2D materials for specific PIC functions, from broadband polarizers to ultrafast modulators.

Furthermore, they discuss the advanced beam-shaping techniques being employed to enhance laser writing efficiency and quality. These techniques are categorized into three key types: focal spot shaping, aberration compensation, and multifocal generation. Focal spot shaping optimizes the geometry of the laser focal spot via novel methods like slit beam shaping, astigmatic beam shaping, and simultaneous spatiotemporal focusing. Spatial light modulators (SLMs), enabling dynamic tuning, facilitate the fabrication of low-loss waveguides. Aberration compensation employs adaptive optics (e.g., SLMs and deformable mirrors) to correct spherical aberrations in high-refractive-index materials, improving the uniformity of structures like 3D photonic crystals. Multifocal generation, achieved via the microlens arrays or SLMs, enables parallel processing by generating multiple foci, significantly boosting fabrication efficiency and bridging laboratory-scale research and industrial applications.

Beyond highlighting the advances in the fabrication techniques, this review article also focuses on heterogeneous integration strategies, such as photonic wire bonding (PWB) and direct 2D/3D chip connections. PWB uses the in-situ two-photon polymerization to create free-form polymer waveguides, enabling low-loss connections between III–V laser arrays and silicon photonic circuits without high-precision alignment. Direct integration examples include 3D polymeric bridge waveguides on Si3N4 chips for polarization rotation, and 3D-printed facet-attached microlenses for efficient fiber-to-SiP coupling. Due to their excellent device performance, 2D/3D integrated PICs have been applied in various fields. In optical communication, 2D/3D PICs enable the on-chip signal generation, modulation, and detection with improved integration density and reduced loss. In the quantum information systems, 2D materials serve as quantum light sources and nonlinear media, which can be embedded into 3D photonic cavities or waveguides to facilitate single-photon generation and routing. In the photonic neural networks, the hybrid platforms support functionalities, such as reconfigurable weights, nonlinear activation, and optical memory within multilayered circuit architectures. Therefore, the integration strategy significantly extends the application scope of PICs.

Despite highlighting the remarkable progress, this review also identifies the key challenges being faced. First, integrating active materials with 2D/3D chips remains difficult, as laser-compatible materials often lack desired performance (e.g., polymer thermal stability), while high-performance materials (e.g., 2D crystals) pose processing challenges. Second, equipment efficiency limitations, such as the slow point-by-point writing of laser nanofabrication compared to industrial lithography, require advancements in multibeam parallel writing and automation^[10]. Third, integrating 2D materials into nonplanar or multilayer 3D architectures remains difficult due to the critical issues of poor interfacial adhesion, lattice mismatch, and differential thermal expansion. Finally, scaling from lab demonstrations to commercial production requires much improvement in resolution, material compatibility, and cost-effectiveness.

To conclude, Jia et al.’s review article is a landmark work that summarizes multi-dimensional fabrication, material integration, and application-driven innovation. By focusing on the under-explored intersection of 2D materials and 3D PICs, it not only consolidates current knowledge but also identifies critical pathways for future research. The synergy between technical depth and practical insights ensures it as an invaluable resource in advancing laser-nanofabricated PICs as a cornerstone of next-generation information technology.

Acknowledgment. This work was supported by the Human Resource Training Project of Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (No. HRTP-[2022]–53).