Optics express最新文献

We propose a fully ground-based, forward-scattering bistatic Doppler-lidar network for minute-cadence, wide-area horizontal-wind mapping. A narrow-linewidth pulsed transmitter illuminates a range-gated volume, while distributed ground receivers arranged on a ring collect small-angle (5°-15°) forward-scattered returns from the same volume. We develop a unified performance model that couples geometric conditioning with photon statistics, spectral sensitivity, and sky-background radiance. Sensitivity analyses quantify the impacts of receiver number, ring radius, wavelength, background level, and the accumulated pulse number N_p = PRF × T_int. The results provide design rules that link uncertainty thresholds to cadence and layout, and they support scalable tiled deployments for large renewable-energy sites and wind corridors.

We report detection of 10.1 ± 0.2-dB squeezed light from a broadband periodically poled lithium niobate (PPLN) waveguide optical parametric amplifier (OPA). Based on our previous report, where a similar PPLN waveguide shows 8.3-dB squeezing [T. Kashiwazaki et al., Appl. Phys. Lett.122, 234003 (2023)10.1063/5.0144385], we reduce phase fluctuations and overall optical losses in the measurement system. In particular, we introduce a phase detection technique that does not require tapping a part of the squeezed light to get a phase locking signal. We use a phase-detection OPA seeded by a tapped probe and pump light before a squeezer OPA. This configuration breaks the conventional trade-off between generating a phase-locking signal with a high signal-to-noise ratio and suppressing the degradation of the squeezing level caused by optical tapping. With all these improvements, the phase fluctuation angle is reduced from 14 mrad to 9 mrad, and the total optical loss from 12% to 8%. Achieving more than 10 dB of squeezing by the broadband waveguide OPA is a significant step towards the realization of fault-tolerant ultra-fast universal optical quantum computation.

Diffuse optical tomography is a non-invasive technique for assessing tissue structure and function by detecting scattered near-infrared light. A key question is how to select source-detector configurations and measurement modalities to maximize sensitivity, particularly for brain defect (e.g., tumor, stroke, etc.) monitoring. This study proposes Fisher information as a rapid, quantitative metric to optimize source-detector placement. We compare the performance of continuous-wave and time-resolved measurements and also explore the impact of cerebrospinal fluid on system design. This method confirms some known results but also highlights some counterintuitive results, including the finding that optimal source-detector distance depends on the type of detector and its related noise statistics and that the low-scattering cerebral spinal fluid layer in the brain can enhance measurement sensitivity. This is found to depend on how exactly the data is collected and processed, with fully time-resolved data always showing a net gain. Our results provide an efficient framework for analyzing and designing diffuse optical imaging systems for non-invasive monitoring and imaging via diffuse light.

The development of efficient O-band light sources on silicon is crucial for next-generation short-reach optical interconnects. While significant progress has been made in the C-band, the integration of III-V/Si lasers for the O-band presents distinct challenges, including the optimization of material gain and the implementation of robust single-mode selection mechanisms. In this work, we address these challenges by implementing a multi-cavity Vernier-effect III-V/Si laser architecture that requires neither fine-pitch Bragg gratings nor complex ring structures. By precisely controlling the longitudinal cavity lengths, the device achieves single-mode lasing with a side-mode suppression ratio (SMSR) exceeding 45 dB.

A lossless key-accompanying transmission method based on noise-masked three-dimensional (3D) index mapping over four-core fiber is proposed. This scheme utilizes a four-dimensional (4D) chaotic model to mask the bits of the original data and orthogonal frequency division multiplexing (OFDM) symbols. Its initial value key is transformed into binary bits, and the error-free transmission of the key is ensured by periodic key repetition. And the masking of the key is achieved by introducing noise bits. In the process of constellation mapping, the 16 constellation points are divided into inner constellations and outer constellations. The traceless loading of the key is achieved by controlling the mapping rule using noisy key bits. A 115-kilometer four-core fiber transmission experiment of the noise-masked 3D index mapping method was successfully verified. The experimental results show that the difference between different cores of the four-core fiber is no more than 0.35 dB. There is almost no signal-noise ratio (SNR) penalty before and after signal encryption. The difference in sensitivity at the receiver is only 0.05 dB, which proves that this scheme can achieve lossless key transmission. As this scheme adopts the method of key repetition, it can ensure the correct demodulation of the key and the precise index of the constellation B. Compared with the traditional 16 quadrature amplitude modulation (QAM) signal, a sensitivity gain of 0.75 dB can be achieved. As for the illegal receiver, due to the lack of correct keys and encryption methods, the accuracy rate of key extraction is 0%, and the bit error rate (BER) remains at around 0.5. Even if the key index position is displaced by one bit, the BER will soar above 0.48. And through five repetitions, 100% correct recovery of the key at the legitimate receiver can be guaranteed. This scheme has excellent transmission effect and security, and can effectively guarantee the performance of the next-generation communication system.

We investigate a distinct spectral modulation observed in high-Q pulsed dye lasers. The results show that this modulation does not arise from an internal etalon effect, but from the interference between internal reflections within the cavity and the traveling wave in the resonator. Accurate perpendicular alignment of the dye cell relative to the resonator axis is required to enable feedback from these reflected waves. Within the narrow angular range where this feedback occurs (a few hundred microradians), both the modulation pattern and the wavelength spacing between maxima are strongly affected. The optical quality of the components, particularly the dye cell, and precise alignment are critical for reliable modulation control. These findings provide practical insights for improving wavelength tuning and performance stability in such laser resonators.

The terahertz (THz) technology has various potential applications in imaging, sensing, and communication. However, the scarcity of THz radiation sources remains a fundamental bottleneck constraining the progress of THz technology. In this article, a continuous-wave THz radiation source based on a vacuum photocathode diode is designed, which combines the advantages of semiconductor electronics, vacuum electronics, and optics. To address the limited physical mechanisms and simulation methods, the mechanism of this device is theoretically analyzed, and a simulation methodology based on COMSOL Multiphysics is developed. Simulation results show that the radiated power exceeds 0.12 mW over 0.1-1.3 THz, peaking at 1.27 mW (0.2 THz). Its critical components (miniaturized THz antenna, vacuum photocathode diode) are processed using the micro-electro-mechanical system (MEMS) technology. Measurement results show that the vacuum diode achieved a current density of 142.6 mA/cm² under 450 mW laser excitation. This research provides a systematic design methodology and MEMS fabrication exploration for this novel THz source, laying a solid foundation for its further development and application.

Localization-based photoacoustic tomography (PAT) has been widely used for resolving the spatial distribution of absorptive targets. However, most existing implementations rely on high-density transducer arrays and reconstruction algorithms that require substantial computational resources, which restrict their accessibility and scalability. We present a multilateration-based photoacoustic tomography (MPAT) that enables precise 3D localization of photoacoustic sources using only a small number of ultrasonic transducers without the need for image reconstruction. Simulations and experiments indicate that MPAT provides 3D multilateration with micrometer-level precision using a small number of transducers and accurately captures both static distributions and dynamic particle trajectories. This study introduces the MPAT method and establishes a theoretical and experimental framework for its systematic evaluation, providing a basis for reconstruction-free and geometry-flexible particle multilateration using sparse transducer measurements.

We designed and fabricated a single-fiber needle probe integrated with a fiber Bragg grating (FBG) capable of simultaneously performing optical coherence tomography (OCT) imaging and temperature sensing. The Bragg wavelength of the FBG is designed to fall within the spectral bandwidth of the OCT light source, enabling dual-mode functionality with a single OCT source. The probe exhibits a lateral resolution of approximately 30 μm, operates at a working distance of about 0.9 mm in air, and features a temperature sensitivity of 10.14 pm/℃. Grating reflectance has a significant influence on OCT imaging performance; hence, multiple fiber probes with varying grating parameters were investigated. Results indicate that limiting grating reflectance to ≤24% serves as a reference threshold for balancing high-quality imaging with precise temperature sensing. Finally, experiments conducted on ex vivo mouse brains and porcine backfat further demonstrate the potential applications of this dual modal OCT needle probe.

Separating absorption and scattering in turbid media remains a major challenge in optical characterization. This work takes a step toward addressing it by applying non-contact estimation of the absorption coefficient (µ_a) within a phase-analysis framework originally developed for extracting the reduced scattering coefficient (μs'). The iterative multi-plane optical properties extraction (IMOPE) technique reconstructs diffuse-reflectance (DR) phase from multi-plane intensity measurements, enabling phase-based analysis for μs' extraction. Here, the DR model is extended to incorporate sensitivity to variations in µ_a, establishing a route for phase-driven absorption assessment, demonstrating opposing trends for µ_a and μs' increments. Monte Carlo simulations and TiO₂-based phantoms with independently controlled μs' and µ_a validate the theoretical predictions. This study experimentally validates a phase-based µ_a extraction scheme at λ₁ = 473 nm, with cross-wavelength verification at λ₂ = 632.8 nm, demonstrating strong agreement, 91%, 95% for λ_1, λ₂, respectively, between extracted and designed absorption values. A detailed TiO₂ phantom preparation protocol is provided to support experimental reproducibility. Finally, we present an initial framework for estimating µ_a from the reconstructed phase, laying the groundwork for future quantitative separation of absorption and scattering in turbid media.