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From biological ecosystems to spin glasses, connectivity plays a crucial role in determining the function, dynamics, and resiliency of a network. In the realm of non-Hermitian physics, the possibility of complex and asymmetric exchange interactions ($$\left| {\kappa _{ij}} \right| \ne \left| {\kappa _{ji}} \right|$$ κ i j ≠ κ j i ) between a network of oscillators has been theoretically shown to lead to novel behaviors like delocalization, skin effect, and bulk-boundary correspondence. An archetypical lattice exhibiting the aforementioned properties is that proposed by Hatano and Nelson in a series of papers in late 1990s. While the ramifications of these theoretical works in optics have been recently pursued in synthetic dimensions, the Hatano–Nelson model has yet to be realized in real space. What makes the implementation of these lattices challenging is the difficulty in establishing the required asymmetric exchange interactions in optical platforms. In this work, by using active optical oscillators featuring non-Hermiticity and nonlinearity, we introduce an anisotropic exchange between the resonant elements in a lattice, an aspect that enables us to observe the non-Hermitian skin effect, phase locking, and near-field beam steering in a Hatano–Nelson laser array. Our work opens up new regimes of phase-locking in lasers while shedding light on the fundamental physics of non-Hermitian systems.

Zoom metalens doublet exhibits unprecedented advantages over the traditional zoom lens in many aspects, like ultra-compactness, CMOS compatibility, and miniaturization. However, most of them can only work in a narrow band due to chromatic aberration. Here, we numerically demonstrate a broadband achromatic zoom metalens doublet inspired by the Moir\'e lens principle. This design is achieved by globally optimizing the multi-wavelength phase profiles of the metalens doublet in the visible. The doublet can achieve achromatic continuous 1-10 zoom range at wavelengths of 440 nm, 540 nm, and 640 nm, featuring high focusing efficiency up to 86.5% and polarization insensitivity., Comment: 4 pages, 5 figures

The measurement of the polarizations and phase profiles of a light beam in one shot is of crucial importance for fundamental researches and daily life. Recently, optical metasurfaces, the ultrathin inhomogeneous interface made of planner nanostructure arrays, have become multi-functional and compact platforms for various emerging applications. Here, we propose and demonstrate an integrated, ultra-compact and miniaturized optical multi-parameter detector, based on efficient metalens arrays featuring the basic pixel composed of 2×2 polarization-dependent metalenses. This multifunctional detector determines not only the spatially variant polarizations through relative focusing intensities, but also the phase gradient profiles via submicron displacements of focal points. To demonstrate its performance, we experimentally measure the beams of 18 scalar polarizations and 7 tilted wavefronts with our system, showing average relative errors of as low as 3.89% for polarization detections and 3.72% for phase gradient detections. Our work can be applied to polarization imaging, optical element topography diagnosis, complex structure light detection, target recognition and health care.

These days, unsupervised super-resolution (SR) is soaring due to its practical and promising potential in real scenarios. The philosophy of off-the-shelf approaches lies in the augmentation of unpaired data, i.e. first generating synthetic low-resolution (LR) images ${\mathcal{Y}^g}$ corresponding to real-world high-resolution (HR) images ${\mathcal{X}^r}$ in the real-world LR domain ${\mathcal{Y}^r}$, and then utilizing the pseudo pairs $\left\{ {{\mathcal{Y}^g},{\mathcal{X}^r}} \right\}$ for training in a supervised manner. Unfortunately, since image translation itself is an extremely challenging task, the SR performance of these approaches is severely limited by the domain gap between generated synthetic LR images and real LR images. In this paper, we propose a novel domain-distance aware super-resolution (DASR) approach for unsupervised real-world image SR. The domain gap between training data (e.g. ${\mathcal{Y}^g}$) and testing data (e.g. ${\mathcal{Y}^r}$) is addressed with our domain-gap aware training and domain-distance weighted supervision strategies. Domain-gap aware training takes additional benefit from real data in the target domain while domain-distance weighted supervision brings forward the more rational use of labeled source domain data. The proposed method is validated on synthetic and real datasets and the experimental results show that DASR consistently outperforms state-of-the-art unsupervised SR approaches in generating SR outputs with more realistic and natural textures. Codes are available at https://github.com/ShuhangGu/DASR.

By changing the relative rotation between two metasurfaces, an adjustable metasurface doublet with a zoom factor ranging from 1 to 18 can be realized and used as a zoom imaging system.

For the design of achromatic metalenses, one key challenge is to accurately realize the wavelength dependent phase profile. Because of the demand of tremendous simulations, traditional methods are laborious and time consuming. Here, a novel deep neural network (DNN) is proposed and applied to the achromatic metalens design, which turns complex design processes into regression tasks through fitting the target phase curves. During training, x − y projection pairs are put forward to solve the phase jump problem, and some additional phase curves are manually generated to optimize the DNN performance. To demonstrate the validity of our DNN, two achromatic metalenses in the near-infrared region are designed and simulated. Their average focal length shifts are 2.6% and 1.7%, while their average relative focusing efficiencies reach 59.18% and 77.88%.

Metasurface-based lenses (metalenses) offer specific conceptual advantages compared to ordinary refractive lenses. For example, it is possible to tune the focal length of a metalens doublet by varying the relative angle between the two metalenses while fixing their distance, leading to an extremely compact zoom lens. An improved polarization-insensitive design based on silicon-nanocylinders on silica substrates is presented. This design is realized and characterized experimentally at 1550 nm wavelength. By varying the relative angle between the metalenses in steps of 10 degrees, tuning of the doublet focal length is demonstrated from -54 mm to -+3 mm to +54 mm. This results in a zoom factor of an imaging system varying between 1 and 18. For positive focal lengths, the doublet focusing efficiency has a minimum of 34% and a maximum of 83%. Experiment and theory are in very good agreement.

Ultraviolet (UV) light is widely used in nanofabrication and biomedical fields. However, in order to shape the wavefront of the UV beam, UV light needs to travel a relatively long distance in optical media that usually have strong UV absorptions. Thus the traditional UV lens is inefficient, costly, and easily aging under the radiation. Hopefully, dielectric metalenses represent a promising alternative. We design and numerically study a polarization-insensitive and achromatic metalens at UV spectra from 234 to 274 nm. The metalens consists of 1519 AlN nanopillars and its focal length is about 4.7 μm, with a