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.
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.
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