Optics letters最新文献

We investigate the emergence of specific modes in finite periodic (FP) parity-time (PT) symmetric photonic structures using the transfer matrix (T-matrix) formalism. Three distinct resonant states are identified-the coherent perfect absorber-laser (M_CL), the unidirectional invisibility (M_UI), and the anti-reflection (M_AR) modes. We show that, unlike in a single-period PT bilayer-where the M_CL mode arises only once-FP structures support recurring M_CL modes as the number of periods increases. M_AR modes appear between successive M_CL modes. The required imaginary part of the refractive index (n^'') for the emergence of each mode is determined by the ratio l/N, where l is the mode order and N the number of periods. For small l/N, n^'' increases linearly, whereas for large l/N, n^'' approaches the PT critical point. Furthermore, the phase diagram shows that M_CL modes exist solely in the PT-broken phase, while M_AR modes remain confined to the PT-symmetric phase. These findings are validated using photonic nanobeam simulations, demonstrating the systematic realization of the three modes in FP PT-symmetric photonic systems.

Thin-film lithium niobate on sapphire provides an excellent platform for simultaneously confining acoustic and optical modes without suspended structures, enabling efficient acousto-optic modulation through strong piezoelectric coupling. Here, we identify the challenges in realizing the forward Brillouin interaction at visible wavelengths and overcome the limitation by introducing a quasi-phase-matching scheme through periodic waveguide width modulation. We predict a 69.9% inter-modal optical conversion efficiency over 0.36 mm using only 5 mW acoustic power. Our study paves the way for high-performance visible-wavelength acousto-optic devices on integrated platforms.

Photothermal microscopy enables high-sensitivity imaging of light-absorbing molecules; however, conventional implementations suffer from axial side-lobe artifacts that degrade accurate observation of three-dimensional structures. This study introduces a dual-probe photothermal microscopy approach that combines two probes at distinct axial positions with polarization-space-division balanced detection to suppress these artifacts without compromising probe power. Experiments using gold nanoparticles revealed that the side-lobe-to-main-lobe ratio decreased from 0.18 in conventional detection to 0.032 with the proposed method. Cross-sectional imaging of cedar pollen further demonstrated substantial suppression of spurious signals. This approach is compatible with dynamic specimens and extends the capability of photothermal microscopy for precise structural analysis.

Broadband frequency combs with mode spacings of ≥1 GHz provide a valuable resource for optical frequency metrology and astrophotonics. Significant average powers are often needed to reach the pulse energies required for supercontinuum generation at 1 GHz repetition rates, putting this beyond the reach of most simple ultrafast lasers. Here, by using dispersion-engineered Si₃N₄ waveguides, we report octave-spanning comb generation from 539 to 1078 nm (-20 dB bandwidth) pumped with a three-element 1 GHz Ti:sapphire laser powered by a single laser diode. Laser repetition-rate stability of 790 mHz is achieved over a 1-hour duration, and carrier-envelope-offset control and stabilization to a single-frequency cw laser is presented. The system offers a simple route to a coherent, broadband supercontinuum spanning the visible to the near-infrared, with potential as an enabling technology for optical frequency metrology, quantum-timekeeping and astrophysical spectrograph calibration.

Whether a photon exhibits wavelike or particlelike behavior depends on the observation method, as clearly demonstrated by the quantum erasure (QE) experiments. Here, we propose a novel, to the best of our knowledge, version of the QE experiment that leverages a single photon prepared in an arbitrary polarization superposition state. Unlike traditional approaches that have a definite erasure method, the erasure in our experiment is determined intrinsically by the photon's quantum state at the moment of measurement. Furthermore, we observe continuous morphing between wave and particle behavior, enabled by continuous path information erasure in the photon's transverse mode. This dynamic transition challenges the classical dichotomy of waves and particles. These findings provide deeper insight into Bohr's complementarity principle and expand the conceptual framework of quantum mechanics.

In this Letter, we demonstrate an operational analysis of fully guided single-mode squeezing in the telecom C-band, highlighting its entanglement potential and sensing performance under realistic purity constraints. We observe -1.81±0.05 dB of squeezing at 1550 nm, equating to -4.11±0.05 dB of generated squeezing (after accounting for losses) using a Zn-indiffused MgO-doped periodically-poled lithium niobate (MgO:ppLN) ridge waveguide. To demonstrate the practicality of this fully-guided squeezer, we employ experimentally measured quadrature variances to compute performance metrics such as purity, entropy, and quantum Fisher information for phase sensitivity estimation to demonstrate ∼11% quantum advantage over coherent states through quantum Cramer-Rao bound. We further quantify the entanglement potential of the single-mode squeezed vacuum and establish the nonclassicality of the corresponding two-mode squeezed states using Duan's inseparability criterion. The source also shows potential for continuous-variable quantum teleportation, with a computed fidelity of ∼73.4%. These results establish practical benchmarks for fiber-compatible squeezed-light sources in telecom-band continuous-variable quantum applications.

We present a hybrid lithography approach integrating digital micromirror device (DMD) projection with multi-beam interference enabled by a Dammann grating. This approach allows for the rapid fabrication of two-dimensional complex periodic structures with low exposure dose and simplified image design. Simulations and experimental results confirm the tunability of patterned structures through three key parameters: DMD image modulation, grating angle adjustment, and exposure dose control. Periodic dot arrays, gradient-duty-ratio superlattices, and photonic crystal waveguides, such as beam splitters, right-angle bends, and resonant rings, were successfully fabricated. Notably, compared to conventional direct DMD lithography, our approach achieves a 25-fold improvement in energy efficiency. The versatility and scalability of DMD-Dammann interference lithography demonstrate its potential for high-throughput fabrication of photonic crystal devices and optical microarrays.

Structured-light techniques have demonstrated superior performance in 3D shape measurement. However, measuring multiple objects with diverse reflective properties remains challenging due to mutual reflection interference. This Letter proposes a spectral division multiplexing-based region projection (SRP) technique, where different surfaces are encoded with structured light of distinct spectra, effectively isolating mutual reflection in the spectral domain and fundamentally eliminating indirect reflection artifacts. First, surface location and regional fringe projection can be realized based on the mapping relationship between the camera and the projector. Subsequently, a hetero-spectral division multiplexing strategy is designed, ensuring that different sub-regions within a single frame contain distinct spectral information. As a result, independent phase retrieval for each measured object can be achieved using spectral channel separation, thereby achieving complete high-precision 3D measurement free from interreflection artifacts. Experiments validated the feasibility of the proposed method.

Laser nanomanufacturing requires energy-efficient, high-throughput methods using inexpensive feedstocks and continuous operation. We demonstrate high-power ultraviolet nanosecond microparticle laser fragmentation in liquids as a controlled, high-yield, high-throughput route to ligand-free silver nanoparticles. Two synchronized 343 nm, 200 W beams enable sufficient laser fluence and single-pulse-per-volume conditions. Matching the thermal diffusion length to the microparticle diameter converts surface-confined absorption into deep photothermal heating, driving single-pulse phase explosion instead of photomechanical rupture. The productivity reaches 10 g h^-1 of Ag nanoparticles <10 nm, at almost quantitative microparticle-to-nanoparticle conversion of up to 98% mass yield, achieving record throughput and mass conversion. Ionic-strength-mediated surface chemistry provides in-situ control over nanoparticle size. This establishes a scalable, green synthesis platform linking mechanistic understanding with industrial level throughput.

Achieving giant Goos-Hänchen (GH) shifts in plasmonic structures is crucial for photonic applications, including information storage and ultrasensitive sensing. However, high-loss plasmonic structures inhibit the realization of high quality (Q) factor resonances. In this Letter, leveraging the transition from local to nonlocal plasmonic (NP) resonances, we demonstrate giant GH shifts reaching values of ~10³ wavelengths, which are assisted by NP resonances with high Q factors. Furthermore, we propose an ultrasensitive biosensor based on the enhanced GH shifts by NP resonances with high Q factors. Our work reveals the tremendous potential of NP resonances for various applications in plasmonic structures.