image: Figure | Working principle of full-space adjoint-enabled meta-optics for intracavity field shaping. a, Schematic of conventional semi-space wavefront shaping for extracavity 2D field landscapes. b, Schematic of the proposed full-space vector field shaping for 3D intracavity landscapes, which simultaneously accounts for forward and backward propagating waves inside the enclosed cavity. b, Scanning electron microscopy (SEM) image of the initial metasurface mask and its corresponding distorted imaging result. b, SEM image of the optimized freeform metasurface mask and its high-fidelity super-resolution imaging result, with 5-fold enhancement in pattern fidelity.
Credit: Mingbo Pu et al.
Precise shaping and manipulation of intra- and extracavity optical fields is a core objective in optics and photonics. Breakthroughs in modern optoelectronic devices—from camera lenses and microscopes to super-resolution systems and laser chips—critically depend on multidimensional optical field control. Researchers have leveraged metasurfaces to achieve on-demand manipulation of amplitude, phase, and polarization in open free space, enabling functionalities such as achromatic metalenses and 3D holographic imaging. However, realizing precise 3D field shaping within enclosed optical cavities using metasurfaces remains fundamentally challenging.
Optical cavities—miniaturized structures with reflective boundaries—underpin lasers, quantum light sources, and super-resolution imaging. Unlike 2D shaping in open free space, light inside an enclosed cavity undergoes multiple round trips, causing intense multiple scattering and interference. The strong vectorial nature of the intracavity field further complicates its 3D shaping, forming a highly challenging problem (Fig. 1a). This is akin to controlling every ray in a mirrored room—exponentially difficult. In meta-optics, most state-of-the-art inverse design methods apply only to semi-open free space and cannot shape complex 3D vectorial fields on demand within cavities. This limitation critically bottlenecks the performance of meta-optoelectronic devices.
In a new paper published in Light: Science & Applications, a team led by Professor Xiangang Luo and Mingbo Pu from the Institute of Optics and Electronics, Chinese Academy of Sciences, in collaboration with the National University of Defense Technology, proposed a full-space adjoint topological optimization framework for meta-optics, achieving for the first time on-demand precise shaping of complex vector fields inside an optical cavity and offering a new paradigm for intracavity field control.
Based on a series of preliminary works [Laser & Photonics Reviews 2022, 16: 2200265; Advanced Materials 2022, 34: 2108709; Laser & Photonics Reviews 2025, 19: 2401819], this work overcomes the limitations of conventional topological optimization, which considers only the half-space transmission of adjoint fields and ignores their omnidirectional dipole radiation. By tailoring the optimization to the closed cavity boundaries, the new full-space adjoint strategy simultaneously covers all forward- and backward-propagating field components, enabling subwavelength-scale full-vector wave optimization that tackles the challenges of multiple scattering and interference inside enclosed cavities.
As a proof-of-concept, the team implemented it in a plasmonic cavity super-resolution imaging system—a typical optical cavity requiring faithful transfer of evanescent waves carrying fine structural information to the image plane. Cavity-induced field distortion severely degrades imaging fidelity, so achieving both ultrahigh resolution and high fidelity has been a persistent challenge. Using full-space adjoint optimization, the team designed a freeform metasurface mask that precisely tailors the full-vector evanescent fields locally. Experiments (Fig. 1b) show that the optimized system maintains λ/5 (~70 nm) optical super-resolution while improving imaging fidelity by a factor of five and drastically reducing edge pattern errors. Even complex large-area patterns like "Maxwell's Equations" are reconstructed with high fidelity, perfectly restoring previously missing details.
“The full-space adjoint framework provides a universal tool for complex vector field engineering in enclosed photonic systems,” the scientists explained.
Looking forward, this work establishes a general inverse-design framework for meta-optics in closed optical cavities, breaking the limitations of conventional free-space paradigms. Beyond direct applications in super-resolution and near-field imaging, the method can be extended to quantum optics and nanolasers. Notably, the core principle is universal, applicable not only to optical waves but also to acoustic and electron waves, offering a new route for wave control in various confined systems.
Journal
Light Science & Applications
Article Title
Full-space inverse-designed meta-optics for complex vector field shaping of intracavity landscapes