Optics letters最新文献

We propose and experimentally demonstrate a technique for shaping the light field in the sub-diffraction regime. Our technique relies on carefully engineering a phase singularity that is distributed continuously along a transverse curve. We develop a polynomial function to effectively describe this singularity curve, which results in an arbitrary light pattern with a feature size considerably down to the deep sub-diffraction limit. We experimentally verify the theoretical framework by demonstrating different cases of edge-singularity engineering for shaping the Gaussian envelope into desired morphologies. Our demonstrations open a novel, to the best of our knowledge, pathway to shaping the light field at the sub-diffraction-limit regime, which can find potential applications in various fields including the super-resolution imaging and precision detection.

Optical image recognition represents a promising alternative to traditional digital methods. In this paper, we present a fully optical system that performs subtraction convolution, meaning that common features between two light maps, a reference and an unknown to be recognized, are eliminated. This is due to the use of a material with induced absorption at the heart of the beam interaction: a thin film of TII photochromic molecules in epoxy resin. The increased absorption in the illuminated regions of the photochromic material causes the optical convolution between two light beams to eliminate the regions with common features, leaving only the dissimilar features in transmission. Both theoretical and experimental results demonstrate high selectivity and resolution, highlighting the great potential of photochromic materials for reconfigurable optical processors.

We present a method for reconstructing an arbitrary high-dimensional unitary transformation without detecting the qudit that it transforms. We demonstrate the method using orbital angular momentum states of light. Our method relies on quantum interference enabled by the path identity of undetected photons. The method is practically useful when suitable detectors are not available for the qudit on which the unitary transformation works.

The use of ultrashort X-ray pulses in studying the structure of matter has recently gained increasing relevance due to the emergence of new sources of such pulses. Pulse duration is typically rarely considered in structural studies, and the influence of its shape remains virtually unexplored. This article demonstrates that, when scattering ultrashort X-ray pulses on polyatomic systems, pulse shape is an important characteristic when using attosecond pulses. It is also shown that the influence of pulse shape on scattering spectra can be represented in a simple analytical form. As an example, the scattering of three ultrashort pulses of different shapes by a diamond crystal with NV centers and a fragment of a DNA molecule is considered.

Dynamic structural color based on phase change materials in visible wavelength is of great significance for the development of dynamic color filters and advanced display technology, in which angular effect is still a major challenge. This study proposes a five-layer asymmetric Fabry-Pérot cavity structure based on phase change material (Sb₂S₃) to generate high-purity, low-angular-dependence tunable structural colors. Experimentally achieved red, orange, and yellow colors exhibit high purity (>90%), with minimal spectral shift (<10 nm) at a 60° incident angle. By changing the structural phase of Sb₂S₃ from amorphous to crystalline, the red, orange, and yellow samples can be transformed into black, brown, and orange, respectively. This work features a simple structure and outstanding color performance, making it promising for application in various scenarios, including display technology and anti-counterfeiting labels.

Jones matrices are imperative in polarization holography, elucidating the polarization-dependent anisotropic characterization of birefringent materials. Jones matrices are experimentally measured from complex electric-field components of polarized light and require intricate imaging systems, thereby limiting their adaptability to multidisciplinary imaging applications. We propose a compact, self-referenced, and highly adaptive polarization-sensitive imaging system capable of acquiring the spatially resolved Jones matrix in real-time. This technique leverages a simple angular-multiplexing scheme, wherein the object and reference beams originate from the same wavefront, facilitated by a highly stable cyclic shearing interferometer (CSI). CSI enables the collinear yet partially shifted light beams carrying the sample's complex information, followed by a polarization image sensor to simultaneously record the complex orthogonal polarization components at the image plane over the Fourier-frequency domain. The feasibility of the proposed technique is experimentally validated by measuring the spatially resolved Jones matrix elements and associated anisotropic characteristics of birefringent samples (a birefringent USAF target and a biological sample) using Jones matrix decomposition.

Cross-spectral purity, a concept introduced by Mandel in 1961, refers to an optical field having identical spectra at two points whose superposition yields the same spectrum. Here, we generalize this concept after discretizing the modal structure of the field, so that cross-purity can then apply to any optical degree-of-freedom (DoF). Making use of two binary DoFs (polarization and two spatial modes), the separability of the associated 4×4 coherence matrix is the condition for cross-purity. We find that the rank of the coherence matrix (the number of non-zero eigenvalues) plays a surprising yet crucial role in determining optical cross-purity: whereas rank-1 and rank-2 fields are always cross-pure, rank-3 fields in contrast are never cross-pure, and only a subset of rank-4 fields are cross-pure.

We present a compressive sensing framework for long-wave infrared dual-comb spectroscopy over 7.5-11.5 μm, enabling accurate spectral reconstruction from undersampled interferograms. For single-species N₂O detection, spectral fidelity is preserved up to a compression factor of 20, with L₂ norm residuals below 1.3 × 10^-4. The retrieved N₂O concentrations maintain over 90% accuracy for compression factors up to 30. In the mixtures of CH₄, N₂O, and C₂H₄, all species are retrieved within 10% relative deviation up to a compression factor of 50. These results demonstrate that the proposed framework enables scalable, computationally efficient deployment of practical DCS systems for real-time trace gas sensing in resource-limited measurement scenarios.

We propose and demonstrate a method for high-precision chirp-rate measurement of linear frequency-modulated (LFM) microwave signals. By leveraging tunable fractional Fourier transform within an optical frequency-shift loop, the system processes LFM microwave signals in the optical domain and extracts their chirp rates via low-frequency detection, avoiding the need for high-speed electronics. In the experiment, chirp-rate measurement across a range of -1400 MHz/µs to 800 MHz/µs is achieved, with errors below ±0.2 MHz/µs. This high measurement precision is maintained over a signal frequency range of 5 GHz to 40 GHz, even at a signal-to-noise ratio of -7.55 dB. Moreover, the method is capable of measuring the chirp rates of multiple spectrally overlapping LFM microwave signals. These results validate the proposed method as a robust and simplified chirp-rate measurement solution in advanced electronic reconnaissance applications.

When particles interact with light, they can absorb momentum, leading to optical forces and torques that are widely used for manipulating microscopic objects. In this study, we demonstrate that a parity-time (PT) symmetric laser operating near and below the lasing threshold can generate giant optical pulling and pushing forces, surpassing conventional radiation pressure by several orders of magnitude. This remarkable enhancement arises from the spectral singularities of the PT-symmetric system, where both reflection and transmission coefficients diverge at real frequencies. The giant forces open up new possibilities for controlling micro- and nanoparticles through routing, trapping, and assembly.