Search Results (167)

Precise control of optical intensity distributions is important for beam shaping, optical trapping, and optical potential engineering. We implement a digital micromirror device (DMD)-based programmable beam-shaping platform for generating high-fidelity optical intensity distributions with user-defined geometries. The approach combines precise system calibration, Fourier-plane spatial filtering via an optimized pinhole, and an iterative intensity feedback algorithm to transform imperfect Gaussian input beams into flat-top, lattice, and composite intensity distributions. The feedback loop typically converges within seven iterations, producing highly uniform flat-top profiles with 98.7% uniformity (corresponding to a root-mean-square error (RMSE) of 1.3%). Systematic studies identify the optimal Fourier-plane aperture that balances diffraction suppression with optical throughput. These results demonstrate a practical route to programmable beam shaping and optical intensity control. Full article

Geometrical and structural disorders are inevitable in fabricated photonic structures and can significantly impact their optical performance. Here, we investigate the robustness of perfectly nonreciprocal diffraction (PND) against these two types of disorder in one-dimensional (1D) atomic lattices. The significantly distinct diffraction phenomenon can be uncovered when the optical lattices introduce controlled random perturbations into the geometrical and structural parameters of each lattice site. Our results demonstrate that the forward diffraction spectrum exhibits remarkable resilience to both disorder types. Conversely, the backward diffraction spectrum is highly sensitive, displaying distinct responses to uncorrelated and correlated disorders. Specifically, PND persists only below a critical strength for uncorrelated geometrical disorder but is well preserved under correlated geometrical disorder. In stark contrast, PND shows strong robustness against uncorrelated structural disorder yet is significantly degraded by its correlated counterpart. These contrasting phenomena are attributed to whether the disorder introduces random spatial phase shifts that disrupt the destructive interference underlying PND. Our findings provide fundamental insights into wave transport in disordered potentials and offer a pathway for designing robust nonreciprocal devices resilient to fabrication imperfections. Full article

Speckle patterns generated by coherent illumination of random media are ubiquitous in optical imaging and information processing. However, most existing studies have primarily focused on isotropic or homogeneous speckle fields, while controlled manipulation of speckle patterns with customized geometric morphologies has received comparatively little attention. Here, we propose a random phase-coded array (RPA) as a general framework for generating geometrically reshaped speckle, enabling the formation of nonconventional random light fields whose ensemble-averaged intensity distributions follow prescribed geometric shapes. In this framework, the speckle geometry is determined by the unit-cell structure of the RPA, the unit-cell size governs the overall spatial extent of the speckle pattern, and the illuminating beam size sets the characteristic speckle grain size. These relationships are rigorously validated through theoretical derivations and numerical simulations. As a result, the global statistical envelope of the random light field can be intuitively and flexibly controlled without compromising the fully developed speckle characteristics. Our experimental framework offers a straightforward, scalable, and versatile approach for generating customized random light fields, with potential applications in optical information processing, secure optical communication, computational imaging, and speckle-based metrology. Full article

Weak measurement enables the amplification of weak physical effects via post-selection and has become an important tool in precision optical metrology; however, conventional schemes based on mean-pointer shifts suffer from response saturation, limited linear range, and stringent stability requirements. Here, we propose and experimentally demonstrate a weak-measurement scheme based on spectral-interference trough shifts, where the zero-intensity points of the post-selected spectrum act as the measurement pointer, establishing an analytical mapping between the trough displacement and the target phase or time delay. Theoretical analysis shows that, under detector resolution limits, the measurement resolution depends solely on the frequency of extinction point and is independent of weak-value singular amplification or bias-phase modulation, thereby maintaining high sensitivity while avoiding pointer saturation. Experiments demonstrate that the trough-shift scheme achieves significantly better agreement between measured and theoretical sensitivities than biased weak measurement and provides a stable linear response without additional bias-compensation structures, reaching a minimum resolvable phase variation at the ${10}^{-7}$ level. Moreover, the approach intrinsically supports multi-period traceable measurements and exhibits strong robustness against intensity fluctuations and spectral distortions, offering a promising route toward high-sensitivity, large-dynamic-range, and stable weak measurement-based optical sensing. Full article

Geiger-mode avalanche photodiode (GM-APD) array light detection and ranging (LiDAR) has significant advantages in low-light scenes due to its single-photon-level detection sensitivity. However, it is susceptible to noise, which leads to a decrease in target localization accuracy. Traditional methods rely on long-term accumulation to distinguish signal photons from noise photons, making it difficult to achieve efficient processing, especially in scenarios with sparse echo photons and low signal-to-noise ratio (SNR), where performance is limited. To quickly and accurately obtain three-dimensional (3D) information of the target under such extreme conditions, this paper proposes a method for target detection and temporal window depth estimation based on intensity information guidance. First, noise suppression is performed on the intensity image according to its statistical characteristics, and an outlier detection mechanism based on neighborhood sparsity is introduced to remove outliers, thereby completing the target detection. Next, by exploiting the spatial continuity and reflectivity similarity of the target, local fusion of photon data within the target neighborhood is performed to construct highly consistent “superpixels”. Finally, according to the distribution difference between signal photons and noise photons on the time axis, temporal window screening is applied to the superpixels to extract depth information, and empty pixels are filled using a convex segmentation method to achieve depth estimation of the target. The experimental results demonstrate that under conditions of low photon counts and strong noise, the proposed method significantly outperforms traditional and existing methods in target recovery and depth estimation by effectively integrating target intensity information. Furthermore, this method achieves faster reconstruction speed, enabling high-precision and high-efficiency 3D target reconstruction. Full article

We propose a novel scheme that is used for the enhancement of phase sensitivity. The SU(1,1) interferometer with a two-mode squeezed coherent state input, using balanced homodyne detection (BHD) and intensity detection (ID), is shown. Our results demonstrate that the phase sensitivity achieved via BHD outperforms that of ID. The optimal phase sensitivity via BHD surpasses the Heisenberg limit (HL) and approaches the quantum Cramér–Rao bound. A larger photon number and parameter strength can make the phase sensitivity better. Furthermore, we show the effects of internal and external losses on phase sensitivity in detail. When external loss reaches 10%, the phase sensitivity can reach the HL. Next, we have a detailed discussion on the impact of the squeezing parameter and photon number on phase sensitivity, which shows that our scheme has better phase sensitivity and enhanced robustness. This interferometer system thus holds significant potential for applications in quantum precision measurement. Full article

Atomic interferometric gravity gradient measurement enables atomic interference by manipulating atoms with lasers of specific frequencies. Thus, the frequency and phase−locking performance of the laser system exerts a significant impact on key experimental parameters, including the loading rate and ultimate cooling temperature of atomic clouds, the state selection efficiency of Raman transitions, the contrast of atomic interference fringes, and the level of detection noise. As atomic interferometric gravity gradient measurement transitions from static laboratory measurements to mobile field operations, conventional laser frequency and phase−locking methods struggle to meet the demand for rapid re−locking after device movement and cannot achieve timely system recovery in the event of laser unlocks. This work proposes an automatic laser frequency and phase−locking system that can detect real−time deviations in laser frequency and phase and implement rapid and precise corrections. Meanwhile, by utilizing the reference signal source in the optical phase−locked loop, the system realizes laser frequency hopping to satisfy the diverse laser frequency requirements across all stages of atomic interferometric gravity gradient measurement. Full article

Aided by quantum sources, quantum metrology helps enhance measurement precision. Here, we construct a theoretical model for quantum imaging based on squeezed states and present the corresponding numerical results. Through discretization and quantum Fisher information theory, we investigate the two-point resolution and spatial multi-parameter estimation of optical fields with unknown spatial distributions. We calculate and compare imaging results based on squeezed vacuum states, coherent states, and squeezed coherent states; our results show that squeezed coherent states yield greater quantum Fisher information, which can effectively improve imaging quality. In addition, we analyze the influence of imaging basis functions, degree of squeezing, quantum correlations, and other factors on imaging performance. The proposed quantum imaging model and computational method can be extended to more complex scenarios, such as multi-mode squeezed-state imaging schemes and incoherent imaging systems. In the future, this approach is expected to find applications in practical imaging systems, including Raman microscopy and stimulated Brillouin scattering imaging. Full article

Efficient and robust energy transfer is fundamental to quantum information processing and light-harvesting technologies. However, conventional systems are often limited by short interaction ranges and high susceptibility to environmental disorder. In this study, we propose and theoretically investigate a topologically protected tripartite energy transfer system based on photonic crystal nanocavities. By utilizing topological corner states as localized interaction nodes and edge states as robust transmission channels, we construct a platform that mediates energy exchange among three distinct quantum emitters. Using the Lindblad master equation formalism, we analyze the spectral dependence of coupling strengths and transfer dynamics. Our results demonstrate that coherent coupling between nearest neighbors is the dominant mechanism driving high-efficiency transport, whereas next-nearest-neighbor interactions can induce destructive interference. Furthermore, compared to bipartite systems, the tripartite configuration exhibits an enhanced cumulative probability for charge separation. Crucially, numerical simulations confirm that the energy transfer efficiency and time remain virtually unaffected by random structural disorder or sharp interface bends, unequivocally validating the topological protection of the system. These findings establish a robust blueprint for scalable quantum interconnects and integrated photonic circuitry. Full article

We investigate a double-probe-field-driven cavity optomechanical system with a degenerate optical parametric amplifier (OPA). When the system is in a mechanical PT-symmetric case, we study the generation mechanism of the sum sideband and how to enhance the generation efficiency of the sum sideband by controlling parametric interactions. Our model consists of two directly coupled PT-symmetric mechanical resonators, which are coupled to a Fabry–Pérot cavity equipped with an optical parametric amplifier. Research indicates that in a PT-symmetric mechanical resonator, there exist special exceptional points (EPs). Near EPs, the generation efficiency of the sum sideband is significantly enhanced. Notably, the introduction of an OPA can remarkably boost the efficiency of sum sideband generation (SSG) and establish a new sideband matching condition for the upper sum sideband. We conduct a detailed analysis of the dependence of SSG on system parameters, such as mechanical coupling strength, OPA nonlinear gain, OPA pump light field phase, and probe field frequency detuning. The research reveals that even with a weak driving field, a significantly enhanced efficiency of SSG can be achieved by adjusting the OPA gain coefficient and phase. This research offers new insights into enhancing or regulating light propagation in nonlinear optomechanical devices and holds potential for applications in high-precision measurement and optical communication. Full article

Entangled-photon sources are indispensable components in free-space quantum key distribution (QKD) systems. Here, we present a compact, lightweight, and robust airborne entangled-photon source (AEPS) based on a Sagnac loop structure with single-mode fiber coupling. To meet the drone requirements for miniaturization, lightweight design, and high robustness, we developed a highly integrated entangled-photon source using customized miniature optical components and an adhesive bonding technique. The total volume and weight are only 38 × 40 × 24 mm³ and 58 g, respectively. Entangled-photon pairs at 810 nm are generated via Type-II spontaneous parametric down-conversion (SPDC) in a periodically poled KTiOPO₄ (PPKTP) crystal. We achieve a quantum state fidelity of F = 0.986 ± 0.0017, a photon-pair generation rate of 3.03 × 10⁶ pairs/s/mW, and a CHSH Bell parameter of S = 2.764 ± 0.082. Owing to its excellent size, weight, performance, and stability, the proposed entangled-photon source is particularly well suited for drone-based free-space mobile quantum communication. Full article

The ²²⁹Th nuclear clock, based on a low-energy nuclear transition, has attracted significant interest as a next-generation time and frequency standard. It is expected to surpass current leading optical atomic clocks in performance. Because nuclear transitions are naturally isolated from external electromagnetic fields, their sensitivity to blackbody radiation and environmental noise is much lower than that of electronic transitions. This gives the nuclear clock a unique advantage in both stability and accuracy. This paper reviews the current progress in nuclear clock research, focusing on the physical properties of the ²²⁹Th isomer, the operating principles, and the primary implementation methods of the nuclear clock. Comparing key technical approaches, specifically trapped ions and thorium-doped crystals, and introducing the VUV frequency comb technology used to drive the nuclear transition. Finally, we provide an outlook on the future development of the field. Full article

This study demonstrates a Mach–Zehnder-type internal-state atom interferometer in a sodium F = 1 spinor Bose–Einstein condensate (BEC), which is realized by applying a three-pulse radio-frequency sequence ($\pi /2$–$\pi$–$\pi /2$) to manipulate the two magnetic sublevels $|1,-1⟩$ and $|1,0⟩$. Phase-scanning experiments show that the visibility remains at a high level across all three pulse stages ($V>0.77$). In the hold-time scanning measurements, the visibility decays exponentially with hold time, yet the system maintains good coherence. This work establishes a foundation for precision measurements based on internal-state atom interferometers, as the approach simplifies the experimental apparatus while maintaining good quantum coherence and high-contrast interference fringes. Full article

This paper proposes a novel photonic crystal fiber-based 1 × 3 optical drop multiplexer design. According to numerical simulations, optical signals can be injected on the left core and divided into another core at various distances to separate the optical signals in a photonic crystal fiber structure. Throughout the length of the fiber, the innovative design controls the direction of light transmission between layers by alternating between multiple air-hole positions using pure silica layers. The optical systemic communications industry cannot function without wavelength multiplexers/demultiplexers. They function as a data combiner/separator. By employing an optical add-drop multiplexer, it becomes possible to add or remove signals from a stream of multiplexed signals without the need to be concerned about any potential interference with the existing signals, even when they are traveling at varying on-axis distances. This study provides findings about small optical drop multiplexers for fiber-to-the-home applications employing photonic crystal fiber at wavelengths of 0.85, 1.45, and 1.2 µm. Full article

A femtosecond laser serves as an excellent tool for efficiently fabricating large-area anti-reflective microhole arrays on infrared windows. The impact of the arrangement of the microholes during processing on final performance, however, remains unclear. Here, microhole arrays were fabricated on MgF₂ windows using a femtosecond laser. The optical performance was analyzed by the finite-difference time-domain method, focusing on the effects of in-plane arrangement deviation and double-sided alignment error. Simulation results indicate that the arrangement variations alter the average transmittance by less than 0.02%. Analysis via effective medium theory revealed that, within the target band, the microstructure array collectively functions as a thin film with a gradient refractive index. Its macroscopic properties show little sensitivity to minor misalignments at the microscopic scale. As a proof of concept, a large-area (20 mm × 20 mm) double-sided antireflection window was rapidly fabricated by employing a zigzag scanning strategy, which achieved an average transmittance exceeding 97.5% and exhibited a high degree of consistency between the simulated and experimental results. Upon final integration into the infrared thermal imaging system, this window not only enhanced the richness of detail in captured images but also improved target contrast. Full article