Optics letters最新文献

Due to the complicated physical mechanisms of topological systems and the pronounced sensitivity and intrinsic asymmetry of Fano resonance, achieving structural designs for specific high-quality topological Fano resonances is particularly challenging. In this Letter, we propose a framework that integrates deep learning with multi-objective particle swarm optimization (MOPSO) to achieve the on-demand structural design of high-Q Fano resonance in a topological system. In our framework, the residual and fully connected neural networks serve as surrogate models to predict the Fano spectrum and the quality factor, achieving accuracies of 97.04% and 98.96%, respectively. The effectiveness of the framework is demonstrated by designing topological Fano resonance at frequencies of 98, 100, and 102 THz. Our results may offer a versatile route for multi-performance optimization and inverse design of topological photonic crystals.

The quadrature phase unwrapping method (QPUM) is pivotal for achieving ultra-precise measurements in laser self-mixing (SM) interferometry systems. However, traditional quadrature construction methods demand a pair of strict quadrature signals; any mismatch creates error. In this paper, a vector composition quadrature construction algorithm, with only simple operations of addition and subtraction, is presented for strictly quadrature signal construction for two SM signals enclosing a certain phase shift. Taking a multi-longitudinal laser SM phase-shifting generation system as an example, we verified the feasibility of this method through experiments and simulations. The results demonstrate that, even under speckle interference, the vector composition algorithm achieves a displacement reconstruction error of 65 nm for the non-stationary motion target with a 3.193 µm peak-to-peak displacement. Moreover, for a pair of 100-second signals, our algorithm consumes only 1/34.2 of the time required by the conventional method-achieving a 97% reduction in computational cost. Combining computational simplicity, rapid signal processing, precise quadrature phase shifting, speckle immunity, and zero calibration, this technique is an ideal candidate for robust, high real-time self-mixing demodulation in online measurements and low-power scenarios.

Periodic polarization scrambling (PS) has been found to be an effective way of eliminating polarization noises in a pulse-coded Brillouin optical time-domain analysis fiber sensor. It is realized by periodically changing the phase difference between the two orthogonal components of a light. Here, we use phase modulation to generate periodic PS, which utilizes the different modulation efficiencies of the fast and slow axes of a phase modulator. This method not only reduces system complexity but also alleviates the non-local effect compared to our previous approach based on differ-frequency acousto-optic modulation (AOM). Experimental results show that it enhances the signal-to-noise ratio of Brillouin gain by ~4 dB compared to the commonly used random PS. Further, owing to the reduction of the non-local effect, ~4-MHz Brillouin frequency shift measurement error is avoided compared to the AOM-based approach.

As a promising solution to expanding the capacity of free-space optical (FSO) communications, orbital angular momentum (OAM) multiplexing faces the inherent diffraction issue. As the number of multiplexed OAM modes increases, higher-order modes are inevitably employed, whose stronger intrinsic diffraction leads to more pronounced beam divergence and thus reduced received optical power. To address the challenges, we propose a novel, to the best of our knowledge, divergence suppression approach for multiplexed OAM beams. By controlling the radial-phase distribution of multiplexed OAM beams, the beams can propagate along a pre-designed trajectory and maintain the received beam size independent of OAM modes. We experimentally implement the radial-phase controlled multiplexed (RPCM) OAM beams and demonstrate its effectiveness of enabling more multiplexed OAM modes and longer transmission distance. Compared to conventional multiplexed (CM) OAM beams, RPCM OAM beams can increase the average received power by approximately 25 dB and 30 dB for turbulence strengths D/r₀=1 and D/r₀=4, respectively.

Traditional electromagnetically induced transparency (EIT) typically exhibits low quality (Q) factors and limited tunability. Bound states in the continuum (BIC) offer a promising solution for achieving high-Q EIT. In this work, we engineer a high-Q EIT resonance on a silicon-membrane metasurface by coupling a quasi-BIC with a Brillouin zone folding guided mode resonance (BZF-GMR). In the unit cell of metasurfaces featuring dual rectangular nanoholes, asymmetric perturbation (rotating one nanohole) converts a symmetry-protected BIC, dominated by a toroidal dipole, into a high-Q quasi-BIC that functions as a dark mode. Simultaneously, it tunes a magnetic dipole-dominated BZF-GMR into the bright mode. Synergistic coupling between these modes produces a prominent EIT resonance, characterized by an 8.4 ps group delay and a high-Q of $5.9times 10^{3}$ (corresponding experimental Q-factor of 250). Furthermore, the EIT resonance wavelength and Q-factor are precisely tuned by varying the asymmetry parameter. The design holds robustness against parameter variations. The fabrication and characterization of silicon metasurface samples validate our design approach. Our results demonstrate a reliable strategy for achieving a high-Q EIT resonance, with promising applications in slow light, high-sensitivity sensing, nonlinear enhancement, and ultrafast optical modulation.

The rapid increase in the size of image sensors and growing computational power have generated demand for large-scale diffraction calculations across a wide range of optical applications. For instance, synthetic-aperture digital holography requires diffraction calculations exceeding 10,000 × 10,000 pixels, whereas computer-generated holography may require more than 100,000 × 100,000 pixels. Conventional diffraction calculations generally assume equal pixel counts in the source and destination planes. However, when high-resolution diffraction results are verified on lower-resolution display devices, the resolution mismatch incurs unnecessary computational costs. Downsampling can reduce the computation cost, but it introduces aliasing artifacts. In this paper, we propose a method that combines single-step Fresnel diffraction with a subsampled fast Fourier transform. This approach enables fast and memory-efficient computation of diffraction results at the desired resolution from high-resolution data, while avoiding aliasing noise.

Foundry fabricated silicon heralded photon pair sources underpin a wide range of quantum photonics applications. Traditional photonics foundry platforms, originating in classical datacom applications, have waveguide cross-sections <0.2 μm², which significantly enhance surface absorption and roughness-induced scattering effects on propagating optical fields. Given the critical importance of loss for quantum information applications, here we consider the generation of photon pairs in a low-loss, thick (3 μm) silicon foundry platform and explore the associated nonlinearity-loss-footprint tradeoffs, with a view toward understanding the optimal silicon thickness for resonator-based photon pair sources.

High-precision optical sensing is fundamental to applications in biomedicine, environmental monitoring, and integrated photonics. A key challenge at the nanoscale is to combine strong field confinement with high spectral sensitivity, which conventional resonators or plasmonic platforms struggle to achieve due to broad linewidths and fabrication sensitivity. We propose a hybrid polaritonic structure where localized surface plasmon polaritons coherently couple to a Tamm plasmon polariton, giving rise to topological phase singularities. These singularities occur at near-zero reflectance, producing abrupt phase transitions and divergent phase sensitivity that far exceed amplitude-based sensing schemes. The platform further exhibits robustness against structural perturbations, such as positional shifts of embedded plasmonic defects. Our results demonstrate a compact, tunable, and topologically protected mechanism for refractive-index sensing, surpassing conventional surface plasmon resonance sensors and opening a route toward singularity-enhanced photonic devices.

We demonstrate that integrating a high-index doped silica glass waveguide into a large-normal-dispersion fiber ring cavity allows cooperative management of dispersion and nonlinear effects. The tightly confined and birefringent photonic waveguide locally releases the polarization, enabling the generation of vector dissipative solitons. Femtosecond dissipative solitons are obtained with intracavity compression ratios of up to 10.1 and a minimum pulse width of 254 fs. Compared with the fiber-only cavity, integrating the photonic waveguide increases the mode-locking RF signal-to-noise ratio by >10 dB and yields a 67.5% reduction in the integrated relative intensity noise (from 0.0873% to 0.0284%) together with a 58.1% decrease in timing jitter (from 1.567 ps to 0.657 ps). The hybrid cavity further strengthens long-term stability, with the 1-hour RMS power fluctuation decreasing from 0.1000% to 0.0381%, with 61.9% improvement. This work extends the capabilities of integrated photonics in mode-locked lasers and advances the development of low-noise ultrafast fiber lasers.

We demonstrate an in-situ pressure-sensitivity calibration method for a fiber Bragg grating Fabry-Perot interferometric pressure sensor inscribed in a side-hole fiber. The calibration of pressure sensitivity is achieved by applying pressure internally to the sensor through the side holes in the fiber cladding. Both simulations and experiments confirm that the pressure sensitivity under internal pressurization closely matches that under external loading, enabling direct in-situ calibration. The sensor system maintains a resolution better than 1 psi up to 300°C and good repeatability. We also discuss exploiting the method for resolving measurement ambiguity arising from the rotation of the principal polarization axes of the sensor.