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.

Spherical Aberration-Corrected Metalens for Polarization Multiplexed Imaging

“…Faraon and coworkers demonstrated a doublet metalens corrected over a wide range of incident angles [43]. In addition, the multiplexing of polarization carrying multiple functions has gradually become a cutting-edge research direction that contributes to techniques such as holography [14], anomalous beam steering [44][45][46][47][48], chiroptical-properties detection [49,50], and dual-band antennas [51]. Polarization multiplexing makes metasurface devices more powerful, functional, and compact.…”

Inverse design of ultracompact multi-focal optical devices by diffractive neural networks

“…The D 2 NNs are trained to maximize the focusing efficiencies for λ 1 at f 1 and λ 2 at f 2 . The engineered devices show efficiencies over 50% at both targeted wavelengths, which exceeds the limit of phasemodulated single layer DOEs [7,8,12]. We systematically investigate how the focusing efficiencies vary with the distance between the two diffractive layers and the pixel size, taking into account practical fabrication constraints.…”

“…1 (b), where the two diffractive layers of the D 2 NN correspond to the two phase plates of the device. We implement the Rayleigh-Sommerfeld (RS) first integral formulation within the D 2 NN in order to simulate the forward light propagation from one plane to the next one, according to the model [3,12,16]:…”

Hyperuniform scalar random fields for lensless, multispectral imaging systems

“…We now utilize a Gerchberg-Saxton (GS) phase retrieval algorithm [18] coupled to the Rayleigh-Sommerfeld first integral in order to propagate forward to the detector plane, where the lensless PSF is obtained, and backward to the mask plane, where the HPP is located. The Rayleigh-Sommerfeld (RS) first integral is defined by [19][20][21][22][23]:…”

“…2 (c). The spatial resolution is ∆x = 4 µm, which is suitable for fabrication using scalable photolithography of 4-level diffractive elements [20,21]. However, the retrieved HPP phase profile can also be readily implemented using planar metasurface technology [1], enabling advanced applications of HPPbased lensless imaging systems.…”