Optics letters最新文献

Compared with traditional grating-based spectrometers, a coherent optical spectrum analyzer (COSA) can provide much higher resolution by converting optical spectral signals into electrical beat signals via heterodyne detection. However, the heterodyning process produces two symmetric sideband peaks for each spectral component, i.e., the mirror effect, which fundamentally limits the resolution. To overcome this constraint, we introduce an instantaneous frequency masking algorithm to eliminate the mirror effect in this study. Experimental results demonstrate a spectral resolution of 2 MHz using the same hardware previously limited to 6 MHz. Furthermore, a compact silicon-photonic wavelength reference for sweep linearization is utilized in the system, achieving long-term wavelength accuracy of ±0.1 pm. The proposed method establishes a cost-effective new paradigm for surpassing the inherent resolution limits of COSA.

A method for direct phase difference reconstruction using single-shot dual-wavelength off-axis digital holography is presented. This approach enables direct imaging of samples with high steps without the need to reconstruct phase images at each individual wavelength. As the dual wavelengths in the reference and object arms pass through a common path in this configuration, single-wavelength arrangements can be applied. Due to the unique capability of the presented method, a sodium-vapor lamp source has been utilized to obtain two closely spaced wavelengths (λ₁=589 nm and λ₂=589.6 nm), with a synthetic wavelength of Λ=578.8 µm in the Michelson configuration. The proposed method is validated by measuring the height of an air wedge using two approaches based on the synthetic and average wavelengths. The capability of the proposed technique to image samples with high-step structures is further demonstrated by measuring four consecutive steps, each separated by a height interval of 30 µm, as well as a glass plate with a thickness of approximately 140 µm.

We present a theoretical framework for spatial phase coherence in femtosecond rotational coherent Raman scattering (fs-RCRS), demonstrating how phase-matching geometry couples temporal dynamics to the transverse structure of the detected signal. On this basis, we identify two configurations with significant practical implications. In one case, the geometry allows single-shot measurements of collisional dephasing and rotational energy transfer, as well as multi-species detection. In the other, the geometry provides a straightforward scheme for one-dimensional thermometry. Together, these results establish geometry-driven space-time coherence as a versatile tool for femtosecond rotational spectroscopy and diagnostics.

In this Letter, we present a centroid detection method based on a Multi-pixel Photon Counter (MPPC) array and an intensity spatial distribution modulator array. This method is adept at efficiently determining the two-dimensional centroid position, even when only a small number of photons are detected. We have integrated every single-point MPPC with an intensity spatial distribution modulator, which enhances its ability to discern positions. Only two units are required to detect the two-dimensional centroid position of the spot. Additionally, a third unit can be used to monitor the overall intensity flicker of the spot, which significantly enhances the stability and robustness of the detection. Under 500 root mean square (RMS) photons detected, the sensor consistently extracts the two-dimensional centroid with an impressive frame rate of 30 kHz and a root mean square error (RMSE) of 7.11 μm. These results demonstrate a promising approach that could significantly improve the detection of faint targets with high sensitivity while still maintaining a fast frame rate. Therefore, this method has the potential to enhance the detection capability of tilt aberrations, thereby providing the foundation of the adaptive optics system for the coming extremely large telescopes.

Direct modulation lasers (DMLs) are a low-cost technology for short-reach intensity modulation and direct detection (IM/DD) systems due to their small footprint and low power consumption. However, their performance is limited by nonlinear distortion arising from chirp-dispersion interaction. Neural network (NN) autoencoders (AE)-based geometric shaping (GS) offers a promising solution through end-to-end (E2E) constellation optimization. This approach relies on differentiable and accurate channel models, leading to the adoption of NN-based models that require large training datasets and retraining for different configurations. In this Letter, we propose a low-complexity model-driven framework that establishes a surrogate channel based on composite second-order (CSO) distortion theory, enabling AE-based geometric constellation optimization to suppress chirp-dispersion interaction. This approach combines physics-based interpretability with deep learning's adaptive capabilities. Experimental results demonstrate a 1-dB receiver sensitivity improvement for 64-QAM signals after 10-km standard single-mode fiber (SSMF) transmission, confirming the effectiveness of the proposed scheme in mitigating nonlinear distortions.

Here, we report the group theory-based inverse design of meta-atoms for a dielectric metasurface in GaAs with predictable optical linear response and third harmonic generation (THG). Six sharp Fano resonances have been observed with a corresponding polarization dependence as predicted by group theory and the meta-atom's symmetry in the D_2h point group. THG has been observed for two modes under x-polarization excitation and one mode for y-polarization, in agreement with theoretical symmetry predictions. The polarization-dependent THG aspect ratio was observed to reach as high as 10⁸. Through strategic structural or symmetry-preserving perturbations, it was shown that the THG can be enhanced or reduced by a factor of 7. The highest THG conversion efficiency was estimated to be 3.1 × 10^-7 at the pump intensity of 1.51 MW/cm². This high THG conversion efficiency indicates that our group theory approach to modal engineering opens a new path, to the best of our knowledge, toward optical nonlinearity tuning in dielectric metasurfaces.

Copper (I) thiocyanate (CuSCN) is a highly promising hole-injection layer (HIL) for optoelectronic devices due to its excellent hole mobility, optical transparency, and solution-processability. However, challenges related to defect states and film quality persist. This study presents a simple strategy for air-induced surface chemical restructuring of CuSCN films, effectively reducing surface defects and increasing covalent character. Results show that quantum-dot light-emitting diodes (QLEDs) fabricated with air-processed CuSCN HIL demonstrate approximately two-fold improvements in both brightness and efficiency compared to devices made in nitrogen atmospheres. These findings offer valuable insights for the development of cost-effective, high-brightness QLEDs, applicable across various transport layer systems.

The ability to shape materials into precise three-dimensional geometries is crucial for advanced light-emitting functional devices. While laser nanoprinting enables the fabrication of custom 3D nanostructures, its reliance on two-photon polymerization (TPP) typically demands photoinitiators. This requirement complicates the integration of luminescent units, as their compatibility with the photoinitiators must be carefully managed. Herein, we introduce an aggregation-induced emission (AIE)-dye resin, in which the AIE dye serves a dual role as photoinitiator and emissive unit, enabling direct printing of arbitrary 3D nanostructures. This approach bypasses the traditional compromise between high-resolution patterning and luminescence performance.

We propose a scheme based on synthetic-flux-induced topological edge modes for realizing Hong-Ou-Mandel (HOM) interference between spatial polarization modes in a long-period grating waveguide. By engineering the relative modulation phase of the gratings, a tunable synthetic magnetic flux is generated, enabling controlled conversion between the TE and TM modes and forming an effective mode lattice. At a flux of π, the coupled-waveguide system supports compact, highly localized topological edge modes. Harnessing these boundary states, we achieve HOM interference with near-unity visibility that is insensitive to propagation distance and robust against variations of the coupling coefficients. These results may provide a route for fault-tolerant on-chip photonic quantum circuits.

We report on the development of a packaged optical whispering-gallery-mode (WGM) resonator exhibiting low vibration sensitivity. The fractional frequency shift is measured to be on the order of 10^-10/g along the vertical axis and 10^-11/g along the horizontal axis. The resonator, operating in the optical domain with an intrinsic quality factor of Q∼10⁹, is employed for laser frequency stabilization. The resulting laser exhibited a relative frequency stability 3×10^-12 level at 10 ms integration time. These results highlight the potential of optical WGM resonators as compact, mechanically robust frequency references for precision photonic systems.