Optical metasurfaces have emerged as a groundbreaking technology in photonics, offering unparalleled control over light–matter interactions at the subwavelength scale with ultrathin surface nanostructures and thereby giving birth to flat optics. While most reported optical metasurfaces are static, featuring well-defined optical responses determined by their compositions and configurations set during fabrication, dynamic optical metasurfaces with reconfigurable functionalities by applying thermal, electrical, or optical stimuli have become increasingly more in demand and moved to the forefront of research and development. Among various types of dynamically controlled metasurfaces, electrically tunable optical metasurfaces have shown great promise due to their fast response time, low power consumption, and compatibility with existing electronic control systems, offering unique possibilities for dynamic tunability of light–matter interactions via electrical modulation. Here we provide a comprehensive overview of the state-of-the-art design methodologies and technologies explored in this rapidly evolving field. Our work delves into the fundamental principles of electrical modulation, various materials and mechanisms enabling tunability, and representative applications for active light-field manipulation, including optical amplitude and phase modulators, tunable polarization optics and wavelength filters, and dynamic wave-shaping optics, including holograms and displays. The review terminates with our perspectives on the future development of electrically triggered optical metasurfaces.

Photoacoustic computed tomography (PACT) is a rapidly developing biomedical imaging modality and has attracted substantial attention in recent years. Image reconstruction from photoacoustic projections plays a critical role in image formation in PACT. Here we review six major classes of image reconstruction approaches developed in the past three decades, including delay and sum, filtered back projection, series expansion, time reversal, iterative reconstruction, and deep-learning-based reconstruction. The principal ideas and implementations of the algorithms are summarized, and their reconstruction performances under different imaging scenarios are compared. Major challenges, future directions, and perspectives for the development of image reconstruction algorithms in PACT are also discussed. This review provides a self-contained reference guide for beginners and specialists in the photoacoustic community, to facilitate the development and application of novel photoacoustic image reconstruction algorithms.

An ultrasonic phase extraction method is proposed for co-cable identification without modifying transceivers in coherent optical transmission systems. To extract the ultrasonic phase, we apply an improved residual frequency offset compensation algorithm, an optimized unwrapping algorithm for mitigating phase noise induced by phase ambiguity between digital signal processing (DSP) blocks, and an averaging operation for improving the phase sensitivity. In a 64-GBaud dual-polarization quadrature phase shift keying (DP-QPSK) simulation system, the phase sensitivity of the proposed method reaches 0.03 rad using lasers with 100-kHz linewidth and a 60-kHz ultrasonic source, with only 400 k-points (kpts) stored data. Also verified by an experiment under the same transmission conditions, the sensitivity reaches 0.39 rad, with 3 kpts of data stored and no averaging due to the equipment limitation. The results have shown this method provides a better choice for low-cost and real-time co-cable identification in integrated sensing and communication optical networks.

The orbital angular momentum (OAM) of photons provides a pivotal resource for carrying out high-dimensional classical and quantum information processing due to its unique discrete high-dimensional nature. The cyclic transformation of a set of orthogonal OAM modes is an essential building block for universal high-dimensional information processing. Its realization in the quantum domain is the universal quantum Pauli-X gate. In this work, we experimentally demonstrate a cyclic transformation of six OAM modes with an averaged efficiency higher than 96% by exploiting a nonreciprocal Mach–Zehnder interferometer. Our system is simple and can, in principle, be scaled to more modes. By improving phase stabilization and inputting quantum photonic states, this method can perform universal single-photon quantum Pauli-X gate, thus paving the way for scalable high-dimensional quantum computation.

In the field of quantum metrology, transition matrix elements are crucial for accurately evaluating the black-body radiation shift of the clock transition and the amplitude of the related parity-violating transition, and can be used as probes to test quantum electrodynamic effects, especially at the 10-3–10-4 level. We developed a universal experimental approach to precisely determine the dipole transition matrix elements by using the shelving technique, for the species where two transition channels are involved, in which the excitation pulses with increasing duration were utilized to induce shelving, and the resulting shelving probabilities were determined by counting the scattered photons from the excited P1/22 state to the S1/22 ground state. Using the scattered photons offers several advantages, including insensitivity to fluctuations in magnetic field, laser intensity, and frequency detuning. An intensity-alternating sequence to minimize detection noise and a real-time approach for background photon correction were implemented in parallel. We applied this technique to a single Yb+ ion, and determined the 6p P1/22-5d D23/2 transition matrix element 2.9979(20) ea0, which indicates an order of magnitude improvement over existing reports. By combining our result with the 6p P1/22 lifetime of 8.12(2) ns, we extracted the 6s S1/22-6p P1/22 transition matrix element to be 2.4703(31) ea0. The accurately determined dipole transition matrix elements can serve as a benchmark for the development of high-precision atomic many-body theoretical methods.

Responsivity is a critical parameter for sensors utilized in industrial miniaturized sensors and biomedical implants, which is typically constrained by the size and the coupling with external reader, hindering their widespread applications in our daily life. Here, we propose a highly-responsive sensing method based on Hamiltonian hopping, achieving the responsivity enhancement by 40 folds in microscale sensor detection compared to the standard method. We implement this sensing method in a nonlinear system with a pair of coupled resonators, one of which has a nonlinear gain. Surprisingly, our method surpasses the sensing performance at an exceptional point (EP)—simultaneous coalescence of both eigenvalues and eigenvectors. The responsivity of our method is notably enhanced thanks to the large frequency response at a Hamiltonian hopping point (HHP) in the strong coupling, far from the EP. Our study also reveals a linear HHP shift under different perturbations and demonstrates the detection capabilities down to sub-picofarad (<1 pF) of the microscale pressure sensors, highlighting their potential applications in biomedical implants.

In this paper, the concept of anisotropic impedance holographic metasurface is proposed and validated by realizing holographic imaging with multipoint focusing techniques in near-field areas at the radio frequency domain. Combining the microwave holographic leaky-wave theory and near-field focusing principle, the mapped geometrical patterns can be constructed based on the correspondence between meta-atom structural parameters and equivalent scalar impedances in this modulated metasurface. Different from conventional space-wave modulated holographic imaging metasurfaces, this surface-wave-based holographic metasurface fed by monopole antenna embedded back on metal ground enables elimination of the misalignment error between the air feeding and space-wave-based metasurface and increase of the integration performance, which characterizes ultra-low profile, low cost, and easy integration. The core innovation of this paper is to use the classical anisotropic equivalent surface impedance method to achieve the near-field imaging effect for the first time. Based on this emerging technique, a surface-wave meta-hologram is designed and verified through simulations and experimental measurements, which offers a promising choice for microwave imaging, information processing, and holographic data storage.

The utilization of multimode fibers (MMFs) displays significant potential for advancing the miniaturization of optical endoscopes. However, the imaging quality is constrained by the physical conditions of MMF, which is particularly serious in small-core MMFs because of the limited mode quantity. To break this limitation and enhance the imaging ability of MMF to the maximum, we propose a mode modulation method based on the singular value decomposition (SVD) of MMF’s transmission matrix (TM). Before injection into the MMF, a light beam is modulated by the singular vectors obtained by SVD. Because the singular vectors couple the light field into eigenchannels during transmission and selectively excite the modes of different orders, the optimal distribution of the excited modes in MMF can be achieved, thereby improving the imaging quality of the MMF imaging system to the greatest extent. We conducted experiments on the MMF system with 40 μm and 105 μm cores to verify this method. Deep learning is utilized for image reconstruction. The experimental results demonstrate that the properties of the output speckle pattern were customized through the selective excitation of optical modes in the MMF. By applying singular vectors for mode modulation, the imaging quality can be effectively improved across four different types of scenes. Especially in the ultrafine 40 μm core MMF, the peak signal-to-noise ratio can be increased by up to 7.32 dB, and the structural similarity can be increased by up to 0.103, indicating a qualitative performance improvement of MMF imaging in minimally invasive medicine.

Nondeterministic-polynomial-time (NP)-complete problems are widely involved in various real-life scenarios but are still intractable in being solved efficiently on conventional computers. It is of great practical significance to construct versatile computing architectures that solve NP-complete problems with computational advantage. Here, we present a reconfigurable integrated photonic processor to efficiently solve a benchmark NP-complete problem, the subset sum problem. We show that in the case of successive primes, the photonic processor has genuinely surpassed electronic processors launched recently by taking advantage of the high propagation speed and vast parallelism of photons and state-of-the-art integrated photonic technology. Moreover, we are able to program the photonic processor to tackle different problem instances, relying on the tunable integrated modules, variable split junctions, which can be used to build a fully reconfigurable architecture potentially allowing 2N configurations at most. Our experiments confirm the potential of the photonic processor as a versatile and efficient computing platform, suggesting a possible practical route to solving computationally hard problems at a large scale.

A novel electro-optic deflector based on a quadratic electro-optical potassium lithium tantalate niobate (KLTN) crystal operating slightly above the ferroelectric phase transition is presented. The new deflection scheme was based on the electric field gradient generation along the vertical axis caused by the trapezoidal geometry of the crystal. A deflection angle of 6.5 mrad was attained for a low voltage of 680 V. The deflector was used as an electro-optic modulator for implementing active Q-switching in a thulium-doped yttrium lithium fluoride (Tm:YLF) laser (1880 nm). The laser was operated at three different repetition rates of 0.4, 0.5 and 0.7 kHz, and reached high energies per pulse up to 6.9 mJ.