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Micro-electro mechanical systems (MEMS)-based phase-only spatial light modulators (PLMs) have the potential to overcome the limited speed of liquid crystal on silicon (LCoS) spatial light modulators (SLMs) and operate at speeds faster than 10 kHz. This expands the practicality of PLMs to several applications, including communications, sensing, and high-speed displays. The complex structure and fabrication requirements for large, 2D MEMS arrays with vertical actuation have kept MEMS-based PLMs out of the market in favor of LCoS SLMs. Recently, Texas Instruments has adapted its existing DMD technology for fabricating MEMS-based PLMs. Here, we characterize the diffraction efficiency for one of these PLMs and examine the effect of a nonlinear distribution of addressable phase states across a range of wavelengths and illumination angles.

Since the invention of lasers, spatial-light-modulated laser processing has become a powerful tool for various applications. It enables multidimensional and dynamic modulation of the laser beam, which significantly improves the processing efficiency, accuracy, and flexibility, and presents wider prospects over traditional mechanical technologies for machining three-dimensional, hard, brittle, or transparent materials. In this review, we introduce: (1) The role of spatial light modulation technology in the development of femtosecond laser manufacturing; (2) the structured light generated by spatial light modulation and its generation methods; and (3) representative applications of spatial-light-modulated femtosecond laser manufacturing, including aberration correction, parallel processing, focal field engineering, and polarization control. Finally, we summarize the present challenges in the field and possible future research.

Ising machines are novel computing devices for the energy minimization of Ising models. These combinatorial optimization problems are of paramount importance for science and technology, but remain difficult to tackle on large scale by conventional electronics. Recently, various photonics-based Ising machines demonstrated fast computing of a Ising ground state by data processing through multiple temporal or spatial optical channels. Experimental noise acts as a detrimental effect in many of these devices. On the contrary, here we demonstrate that an optimal noise level enhances the performance of spatial-photonic Ising machines on frustrated spin problems. By controlling the error rate at the detection, we introduce a noisy-feedback mechanism in an Ising machine based on spatial light modulation. We investigate the device performance on systems with hundreds of individually-addressable spins with all-to-all couplings and we found an increased success probability at a specific noise level. The optimal noise amplitude depends on graph properties and size, thus indicating an additional tunable parameter helpful in exploring complex energy landscapes and in avoiding getting stuck in local minima. Our experimental results identify noise as a potentially valuable resource for optical computing. This concept, which also holds in different nanophotonic neural networks, may be crucial in developing novel hardware with optics-enabled parallel architecture for large-scale optimizations.

Deep learning-based methods have achieved remarkable success in the problem of low-light image enhancement. However, previous works mainly focused on model training using paired or unpaired datasets. Are they still competitive in the absence of accurate classification of image light levels? Instead of classifying image data based on illumination, the approach presented in this paper directly uses images with mixed light levels to train the model. We propose a Unsupervised Low-light Enhancement network, dubbed ULE-Net, that inserts a Light Modulation Module (LMM) into the network to dynamically control the light level of the output image during the calculation process. In the training phase, the available light space of the image is traversed to realize the learning of multi-light levels. The binary conversion problem of low-light image to normal image is successfully converted to a discrete/continuous light conversion problem in the image light space. Through extensive experiments, our proposed method outperforms recent methods in various metrics of visual quality. Meanwhile, our enhancement results are likewise competitive with the most state-of-the-art methods when training with the COCO dataset in the field of non-low-light image. Additionally, our approach demonstrates that for the issue of low-light image enhancement, the light level requirement of the training image is completely arbitrary.

It has been found that the dielectric constants of transparent conductive oxides (TCOs) can be adjusted in an extremely large range by tuning the carrier density. Due to the remarkable light confinement property of the epsilon-near-zero (ENZ) effect of TCOs, it has attracted extensive interests of light modulation. However, the operation wavelength bandwidth is usually limited by optical resonance that is applied to enhance the light-TCOs interaction. In this work, a dual-resonance light coupling scheme is proposed to expand the modulation depth-bandwidth product with almost one order-of-magnitude improvement. In a metallic subwavelength grating structure with deep trenches backed by a ground plane, the ENZ mode can be coupled to both magnetic resonance and Fabry-Perot resonance respectively by tuning the bias. Decent light modulation can be obtained in a large operation wavelength band covering two resonances by optimizing the dual-resonance configuration. Such a reconfigurable efficient broadband modulation is important for robust communication link and possesses remarkable capacity for wavelength division multiplexing.

Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of the scattering matrix and often requires engineered optical properties. For instance, thin film CPA benefits from complex nanostructures with suitable resonance, albeit at a loss of operational bandwidth. In this work, we theoretically and experimentally demonstrate a broadband CPA based on light-with-light modulation in epsilon-near-zero (ENZ) subwavelength films. We show that unpatterned ENZ films with different thicknesses exhibit broadband CPA with a near-unity maximum value located at the ENZ wavelength. By using Kerr optical nonlinearities, we dynamically tune the visibility and peak wavelength of the total energy modulation. Our results based on homogeneous thick ENZ media open a route towards on-chip devices that require efficient light absorption and dynamical tunability.

The development of a stimulated Raman scattering (SRS) microscope with a wavefront modulation unit is presented. In the apparatus, two beams for introducing the SRS process were focused into the sample with an objective lens. In the pathway of the Stokes beam, which is one of the two incident beams, a spatial light modulator (SLM) was located. Using the SLM, the wavefront of the Stokes beam was modulated to make the shape of the focal point a concentric circular pattern. By this spot shaping technique, the area where the SRS signal generates is restricted. The instrument response function (IRF) of the SRS microscope was examined by measuring the SRS intensity while scanning the sample position. From the result, the width of the IRF was reduced by about 15% by the wavefront modulation. It is suggested that the introduction of SLM is a way to improve the IRF of vibrational spectroscopic microscopes.

The recent realization that 2D layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. Light modulation is an essential operation in photonics and optoelectronics. With existing and emerging technologies increasingly demanding compact, efficient, fast and broadband optical modulators, high-performance light modulation solutions are becoming indispensable. The recent realization that 2D layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. In this Review, we cover the state of the art of optical modulators based on 2D materials, including graphene, transition metal dichalcogenides and black phosphorus. We discuss recent advances employing hybrid structures, such as 2D heterostructures, plasmonic structures, and silicon and fibre integrated structures. We also take a look at the future perspectives and discuss the potential of yet relatively unexplored mechanisms, such as magneto-optic and acousto-optic modulation.

The phenomena of magneto-optical polarization rotation and circular magnetic dichroism are well known in the Faraday configuration. We present another effect, an odd magneto-optical linear dichroism, arising in nanostructures with polarization-dependent mode Q-factors and magneto-optical components. It reveals itself as the magneto-optical modulation of light intensity for the two opposite magnetization directions in the Faraday configuration. The effect was demonstrated on a magnetophotonic crystal with a cavity mode, the polarization-dependent Q-factor of which is due to oblique incidence. For a polarization angle of 60° (or 120°) and an angle of incidence around 60°, the magneto-optical intensity modulation maximizes and reaches 6%.

The classical Pancharatnam-Berry phase, a variant of the geometric phase, arises purely from the modulation of the polarization state of a light beam. Due to its dependence on polarization changes, it cannot be effectively utilized for wavefront shaping in systems that require maintaining a constant (co-polarized) polarization state. Here, we present a novel topologically protected phase modulation mechanism capable of achieving anti-symmetric full 2π phase shifts with near-unity efficiency for two orthogonal co-polarized channels. Compatible with -but distinct from- the dynamic phase, this approach exploits phase circulation around a hidden singularity on the surface of the Poincaré sphere. We validate this concept in the microwave regime through the implementation of multi-layer chiral metasurfaces. This new phase modulation mechanism expands the design toolbox of flat optics for light modulation beyond conventional techniques. Arising from singularity on the surface of Poincaré sphere, topology-protected phase for co-polarized light enables 2π phase modulation, which complements the classical cross-polarized Pancharatnam-Berry phase and expands the versatility of flat optics.