Optics letters最新文献

We present a light-driven inching random laser composed of a liquid crystal elastomer body and a random lasing tip region. Under optical illumination, the composite random laser undergoes bending deformation, enabling a remote-controlled motion on flat and blazed grating surfaces. The inching random laser is optically guided to a designated target position, where the integrated random-lasing tip generates emission characterized by a bandwidth collapse and a distinct lasing threshold. The light-driven inching random laser offers a promising platform for delivering intense optical signals at a desired location.

Graded index (GRIN) lenses are essential for in vivo imaging and endoscopy. Implantable probes made from short segments of standard GRIN fiber offer important benefits over commercial GRIN lenses; however, they struggle with aberrations. This study introduces a technique that combines structured speckle illumination with compressive sensing (CS) to enable aberration-free imaging with GRIN fiber-based probes. We develop a wave-optic mode-expansion model to simulate the propagation of coherent illumination and incoherent fluorescence response in an aberrated GRIN probe. Through numerical experiments involving sequential speckle illumination and CS for image reconstruction, we achieve high-resolution, aberration-free imaging throughout the entire field of view (FOV). In contrast to standard microscopy methods, the reconstructed image quality is independent of the fiber length. The proposed method opens avenues to minimally invasive single- and multisite deep brain microscopy.

The generation of tunable narrowband pulses is increasingly being pursued in terahertz science, for example, to study the nonlinear response of individual modes of solids and molecules. Here, we extend the chirp-and-delay method to achieve collinear phase-matched difference-frequency generation in the organic crystal N-benzyl-2-methyl-4-nitroaniline (BNA-S), which results in tunable narrowband terahertz pulses. In this configuration, the fundamental frequency of a Ti:sapphire amplifier is used-eliminating the need for optical parametric amplifiers typically required for THz generation in other organic crystals. Chirped-pulse excitation suppresses multiphoton absorption in BNA, improving stability and extending crystal lifetime. The source delivers THz transients tunable from ~0.25 THz to ~2 THz with adjustable spectral width.

Optical vortices have attracted significant interest due to their distinctive topological properties and wide-ranging applications, including free-space communication, quantum information, image analysis, and micromanipulation. Vortex formation can arise from the interaction of light with structured or anisotropic media, including chiral systems. Among the most effective platforms for generating optical vortex beams are optical valves and liquid crystal cells, which leverage molecular self-organization to produce complex light fields. We show, both experimentally and theoretically, that illuminating an optical valve with a donut-shaped beam generates a vortex rosette, consisting of a low-amplitude central vortex surrounded by a ring of interacting vortex-antivortex pairs. This structure imparts a nontrivial topological charge to the transmitted light, endowing it with novel characteristics akin to those of a q-plate. To elucidate the origin of these vortex rosettes, we derive an amplitude equation from first principles, offering insight into the underlying mechanisms driving their emergence.

Fourier ptychography microscopy (FPM) is a powerful computational imaging technique; however, its performance is limited by the stringent matched-illumination requirement, especially when using high-numerical-aperture (NA) objective lenses. To address this challenge, we propose a phase-contrast modulation-based FPM (PCM-FPM). By introducing a 0.5π phase shift to the non-scattered components of object waves generated under unmatched illuminations from six LEDs, PCM-FPM encodes otherwise undetectable low-frequency phase information into measurable intensity variations. Then, a novel iterative reconstruction algorithm, to our knowledge, processes these six phase-contrast intensity images to recover full-spectrum phase details. Both simulations and experimental results, acquired with an illumination NA of 0.7 and a 100×/1.44 objective lens (OL), demonstrate the superior phase imaging performance of PCM-FPM. This approach represents a significant advancement in FPM with strong potential for broader application.

Solar Ground-Layer Adaptive Optics (GLAO) is the preferred solution for achieving wide-field, high-resolution imaging in ground-based solar telescopes. However, current GLAO guide-star (GS) arrangement optimization relies on extensive iterative simulations, which are time-consuming and resource-intensive, and do not provide a prior reference for system design. To address this issue, an analysis of GLAO wavefront sensing in the spatial frequency is conducted. A filter is constructed to optimize the detection of conformal aberrations, leading to the development of an analytical framework for GS arrangement optimization. This framework provides accurate prior optimization results for any GS configuration. The correctness of the theory is validated through comparison with Monte Carlo simulations, and the practical utility of this method in optimizing solar GLAO system performance is demonstrated.

This Letter demonstrates that non-paraxial 2D TE-polarized light fields form 2D optical vortices near intensity zeros, with the amplitude having the form x+iz, where x and z are the transverse and longitudinal Cartesian coordinates. Near the intensity zeros, the longitudinal projections of the wave vector have gigantic values of both signs. Negative values of the longitudinal projections of the wave vectors indicate that a reverse energy flow occurs near the intensity zeros. Around the intensity zeros, the energy flow circulates both clockwise (if the topological charge of the optical vortex is -1) and counterclockwise (if the topological charge of the optical vortex is +1). The gigantic values of the wave vectors near the intensity zeros indicate that the wavelength of the light is small, and therefore the phase velocity of rotation of light around the intensity zero is small, compared to the speed of light in a vacuum. A giant wave vector, energy flow circulation, and energy return flow are formed in a substantial subwavelength region around intensity zeros of fractions of a wavelength in size, demonstrating the presence of superoscillations.

Fiber-wireless systems offer a promising way to enhance high-capacity wireless services and extend transmission distances by leveraging the low loss and broad bandwidth of optical fiber. They depend on efficient electro-optic receivers in millimeter-wave (mmWave) and terahertz (THz) fiber-wireless systems to convert high-frequency wireless signals into the optical domain. However, traditional down-conversion relies on real-valued IF processing using a balanced mixer, which can generate conjugate spectra that appear as image interference during optical modulation. To address this, we introduce a hybrid electro-optic receiver design that directly connects an electrical I/Q mixer with an optical I/Q modulator, enabling direct electro-optic conversion of complex IF signals. By preserving the inherent I/Q orthogonality, the proposed approach allows optical single-sideband modulation without optical filtering and avoids image components associated with conjugate spectra. Building on this innovative hybrid optoelectronic communication system, we have successfully demonstrated the transmission of 16 Gbaud QPSK signals over a 2-m wireless link and a 5-kilometer single-mode fiber at 142.8 GHz with error-free performance.

In this work, we report our experimental studies on the start time of a passively mode-locked soliton fiber laser based on nonlinear polarization rotation (NPR), with a focus on the impact of different operation states. We found that given the same cavity configuration, the statistical distributions of the start time are strongly correlated with the operation states determined by the pump power and the NPR-induced loss of the laser. While the start time for the single-pulse state exhibits a long-tail distribution, for the multi-pulse state a much faster start time is observed at the same pump level. We also find that the start-time distribution of the multi-pulse state is dramatically sensitive to both the laser pump power and the NPR-induced loss. Numerical simulations have been performed to reproduce these statistical features, revealing their delicate dependence upon the intra-cavity balance between gain and loss. Our work sheds some light on the statistical self-starting dynamics of the mode-locked fiber laser and may provide valuable guidance to practical laser design.

Elliptically or circularly polarized terahertz (THz) radiation plays a crucial role in advanced applications such as chiral spectroscopy, spintronics, and polarization-sensitive imaging and communication. Here, we demonstrate an efficient method for generating elliptically polarized THz radiation from a single-color laser-driven water column. By tilting the water column along the laser propagation direction and displacing the laser axis from the column center, both vertical and horizontal THz components are produced with a nonzero relative phase. As a result, elliptically polarized THz radiation with an ellipticity up to 0.75±0.02 is achieved in our experiment. Furthermore, the ellipticity and handedness of the emitted THz waves can be flexibly controlled by adjusting the tilt angle and the horizontal offset of the water column. This work provides a simple and robust scheme for controllable generation of elliptically polarized THz radiation, opening new opportunities for THz-based spectroscopy, imaging, and information technologies.