Optics express最新文献

Two-photon (2P) microscopy is a powerful technique for deep-tissue fluorescence imaging; however, tissue scattering limits its effectiveness for depth imaging using conventional approaches. Despite typical strategies having been put forward to extend depth imaging capabilities based on wave-front shaping (WFS), computationally recovering images remains a significant challenge using the 2P signal. In this work, we demonstrate the successful reconstruction of fluorescent objects behind scattering layers using 2P microscopy, utilizing the optical memory effect (ME) along with the speckle autocorrelation technique and a phase retrieval algorithm. Our results highlight the effectiveness of this method, offering significant potential for improving depth imaging capabilities in 2P microscopy through scattering media.

Two-beam interference patterns generated with ultrashort laser pulses are essential for applications such as direct laser interference patterning. Here, coherent beams are made to interfere by overlapping on the processed surface. The area of the generated interference pattern can be adjusted by the transverse beam dimensions. The present study investigates the spatial limit of interference patterns. The results demonstrate that the boundaries of the interference pattern depend solely on the spectral energy distribution of the laser pulse, and the angle between the interfering beams. The variation in pulse duration, which arises in the non-bandwidth-limited case while maintaining the same spectral energy distribution, has no effect.

An erratum correcting the spelling of an author's name in [Opt. Express33, 34098 (2025)10.1364/OE.570519]. This correction has no influence on the results and conclusions of the original paper.

We present a non-destructive photoluminescence (PL) imaging strategy for probing damage growth behavior in fused silica under laser irradiation. Transient wide-field PL image measurements were conducted at varying excitation intensities to investigate the dynamics of radiative defect generation and annihilation in laser-induced damage sites. Our results reveal that, while low excitation intensities predominantly induce PL quenching due to defect annihilation, high-intensity excitation (>0.3 GW/cm² at 532 nm) triggers pronounced PL brightening (PLB), indicative of radiative defect generation. Image analysis demonstrates that PLB events are strongly correlated with subsequent damage growth (10 J/cm² at 351 nm), whereas overall PL intensity is not. No optically detectable morphological changes were observed during PLB, confirming the non-destructive nature of the technique. We propose that PLB arises from defect-assisted absorption of multiple photons at pre-existing absorptive centers, which enhances local absorptivity and initiates further defect formation. These findings establish PLB monitoring as a sensitive diagnostic tool for identifying damage sites with elevated absorptivity, enabling targeted maintenance and improved laser damage management in optical materials.

Recent advances in differentiable design methodologies for freeform illumination optics have attracted considerable research interest in non-imaging optics. These approaches represent the freeform optical surfaces with trainable parameters and refine surface profiles iteratively according to the differentiable ray-tracing simulation. Currently, the B-spline surface model has emerged as the prevalent parametric framework due to its inherent global smoothness and local support property. While the local support characteristic ensures local shape adjustment capabilities, enhancing system performance and optimization efficiency, it can also lead to large curvature regions during the optimization process. Effectively constraining the surface curvature remains a challenging problem. To address this issue, we combine physical priors and directed triangular meshes to implement a topological constraint for the intersection points of sampled rays with the target plane. Design examples demonstrate that the proposed constraint can effectively control the curvature while maintaining the optical performance of the system, with a maximum reduction of the mean curvature by approximately one order of magnitude, significantly improving the manufacturability of the surface.

This study investigates the optical constants of amorphous silicon (a-Si) thin films, deposited using direct current (DC) magnetron sputtering technique with varying thicknesses (5 nm to 50 nm), in the extreme ultraviolet (EUV) range using monochromatized synchrotron radiation. In addition to EUV reflectometry, complementary characterization techniques, including X-ray reflectometry (XRR) and transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDX), were employed to evaluate the film thickness, interface quality, and elemental composition. Variations in optical behavior were observed with changing thicknesses. Additionally, a notable deviation in the reconstructed optical constants at the Si L₂, ₃ absorption edges was identified. This new experimental dataset on the optical constants of a-Si significantly expands the existing literature data, particularly in the near-edge regions, and enhances our understanding of the optical properties of a-Si thin films.

We present a net-coupled staircase code (NCSC) architecture, which leverages the multiple multiplexing dimensions to construct parallel forward error correction (FEC) code chains. Spatial coupling between chains is introduced through cyclic sub-block rearrangement. The net-like structure enhances global information exchange and strengthens inter-codeword constraints. Analysis based on graph models and density evolution shows that the NCSC achieves an improvement in the error correction threshold of up to 0.0461 for t = 7. The proposed scheme is experimentally demonstrated by the 240-Gbps transmission system over 20-km standard single-mode fiber (SSMF). The results demonstrate improvements in receiver sensitivity compared to the sub-block rearranged staircase code (SRSC) using an identical component code. At a post-FEC BER of 4.94E-5, gains of 0.89 dB and 0.78 dB are achieved for code block lengths of m = 48 and m = 100, respectively.

The cryogenic environment offers a promising platform for integrated quantum photonic systems thanks to its low noise characteristics and compatibility with key quantum components, such as superconducting detectors and quantum dots. To harness the full potential of cryogenic integrated quantum photonic circuits, the development of cryogenic adapted on-chip optical filters with exceptional performance is crucial, particularly for efficient extraction of single photon signals from intense pump light in nonlinear processes like spontaneous four-wave mixing. In this work, we demonstrate a cryogenic-compatible Bragg filter, featuring a sinusoidal coherency-broken cascaded architecture for ultrahigh rejection and narrowband. Two subwavelength gratings are deployed to eliminate the residual transverse magnetic mode photons induced by imperfect polarization alignment. Furthermore, a niobium nitride film is deposited on the chip surface as a light absorption layer to suppress background noise caused by scattered photons. The fabricated filter exhibits a rejection ratio of 82 dB at room temperature, and maintains 76 dB at a cryogenic temperature of 2.2 K, with corresponding bandwidths of 0.9 nm and 0.8 nm, respectively. These results confirm the suitability of this filter for the cryogenic working environment, providing crucial support for the cryogenic-compatible integrated quantum photonic circuits.

Targeted detection of subsurface metal microstructure is crucial for evaluating the performance of engineering structures. This paper presents a nondestructive inspection method for characterizing subsurface metal microstructure by integrating quantum sensing, electromagnetic transmission theory, and optical field imaging. In a field of view of 1000×1000 µm², the induced microwave fields of six different metallic materials were characterized by NV centers, and the relationship between the induced microwave fields and the conductivity of the metallic materials was analyzed theoretically. Meanwhile, the induced microwave fields generated by different metallic defect structures were characterized, and the reasons for the differences in microwave fields were analyzed based on the microstrip transmission theory. This phenomenon verifies the feasibility of utilizing quantum, combined with optical field imaging, to characterize subsurface metallic materials and structures. The method is expected to be applied in materials evaluation and engineering maintenance, thus effectively enhancing quantum testing technology applications.

Millimeter-wave (30-300 GHz) communication is considered a key enabler for future indoor and access networks due to its ultra-wide bandwidth and capability of supporting high data rates. However, millimeter-wave signals suffer from severe free-space path loss and are sensitive to obstructions; their excessive penetration loss further limits reliable indoor and urban coverage. To overcome these challenges, we experimentally demonstrate a photonics-assisted dual-hop radio-over-fiber (ROF) system for routing and relaying W-band millimeter-wave signals. The proposed dual-hop communication system utilizes photonic technology to deliver millimeter-wave signals from the central station to end users. Without requiring electrical frequency conversion, the system reduces signal distortion and preserves transmission quality. Using this scheme, we successfully achieved 80 Gbit/s 16-QAM transmission over a 21-km fiber link and two 1-m wireless hops at 90 GHz when the routing optical wavelength was 1550 nm. Moreover, by sweeping the routing wavelength from 1545 to 1554 nm, the system sustained a maximum data rate of 80 Gbit/s. Unlike conventional millimeter-wave systems, the proposed dual-hop architecture supports signal relay without strict line-of-sight requirements, which significantly improves transmission flexibility and coverage.