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We propose an efficient inverse design approach for multifunctional optical elements based on adaptive deep diffractive neural networks (a-D2NNs). Specifically, we introduce a-D2NNs and design two-layer diffractive devices that can selectively focus incident radiation over two well-separated spectral bands at desired distances. We investigate focusing efficiencies at two wavelengths and achieve targeted spectral line shapes and spatial point-spread functions (PSFs) with optimal focusing efficiency. In particular, we demonstrate control of the spectral bandwidths at separate focal positions beyond the theoretical limit of single-lens devices with the same aperture size. Finally, we demonstrate devices that produce super-oscillatory focal spots at desired wavelengths. The proposed method is compatible with current diffractive optics and doublet metasurface technology for ultracompact multispectral imaging and lensless microscopy applications.
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Compact Dual‐Band Multi‐Focal Diffractive Lenses
Abstract This paper presents the design, fabrication, and characterization of dual‐band multi‐focal diffractive microlenses with sub‐wavelength thickness and the capability to simultaneously focus visible and near‐infrared spectral bands at two different focal positions. This technology utilizes high‐index and low‐loss sputtered hydrogenated amorphous Si, enabling a sub‐wavelength thickness of only 235 nm. Moreover, the proposed flat lens concept is polarization insensitive and can be readily designed to operate across any desired wavelength regime. Imaging under unpolarized broadband illumination with independent focal planes for two targeted spectral bands is experimentally demonstrated, enabling the encoding of the depth information of a sample into different spectral images. In addition, with a small footprint of only 100 µm and a minimum feature size of 400 nm, the proposed dual‐band multi‐focal diffractive microlenses can be readily integrated with vertical detector arrays to simultaneously concentrate and spectrally select electromagnetic radiation. This approach provides novel opportunities for spectroscopic and multispectral imaging systems with advanced detector architectures.
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- Award ID(s):
- 1709704
- PAR ID:
- 10453886
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Laser & Photonics Reviews
- Volume:
- 15
- Issue:
- 2
- ISSN:
- 1863-8880
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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