An inverse-designed metalens is proposed, designed, and fabricated on an optical fiber tip via a 3D direct laser-writing technique through two-photon polymerization. A computational inverse-design method based on an objective-first algorithm was used to design a thin circular grating-like structure to transform the parallel wavefront into a spherical wavefront at the near-infrared range. With a focal length about 8 μm at an operating wavelength of 980 nm and an optimized focal spot at the scale of 100 nm, our proposed metalens platform is suitable for two-photon direct laser lithography. We demonstrate the use of the fabricated metalens in a direct laser lithography system. The proposed platform, which combines the 3D printing technique and the computational inverse-design method, shows great promise for the fabrication and integration of multiscale and multiple photonic devices with complex functionalities.

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Machine learning methods have found novel application areas in various disciplines as they offer low computational cost solutions to complex problems. Recently, metasurface design has joined these applications, and neural networks enabled significant improvements within a short period of time. However, there are still outstanding challenges that need to be overcome. Here, we propose a data preprocessing approach based on the governing laws of the physical problem to eliminate dimensional mismatch between a high dimensional optical response and a low dimensional feature space of metasurfaces. We train forward and inverse models to predict optical responses of cylindrical meta-atoms and to retrieve their geometric parameters for a desired optical response, respectively. Our approach provides accurate prediction capability even outside the training spectral range. Finally, using our inverse model, we design and demonstrate a focusing metalens as a proof-of-concept application, thus, validating the capability of our proposed approach. We believe our method will pave the way toward practical learning-based models to solve more complicated photonic design problems.

Integrated optical sensors have garnered much interest for lab-on-chip applications such as chemical and biological sensing and detection. Among various ways for detection schemes, spectral analysis performed by a spectrometer has shown great promise. Typically, such spectrometry is carried out in a relatively large device, owing to the fact that spectral resolution is often dictated by large optical path length. Here, a high-resolution compact spectrometer utilizing random scattering events in a disordered medium is demonstrated. The spectrometer is inverse designed by objective-first method and fabricated using two-photon polymerization technique. The compact spectrometer consists of a disordered photonic structure and an inversed-designed mode decomposer. A spectral resolution of 0.25 nm with a bandwidth of 30 nm in the near-infrared regime is realized from a spectrometer occupying a relatively small footprint of 30 × 12.8 µm 2 . The proposed platform has a great potential to be used as a versatile lightweight and compact spectrometer for various applications including on-chip spectrometer and sensing.