Optics letters最新文献

It is shown that a quasiperiodic spatiotemporal grating formed in a dispersive medium enables the propagation of linear localized pulses of the probe field without dispersive spreading. Increasing the amplitude or modulation depth of the grating allows for the accommodation of a larger number of probe pulses. In the case of a formally infinite grating, these pulses propagate without distortion at the velocity of the spatiotemporal lattice. When the grating has finite spatial and temporal extents, a wide Gaussian probe pulse evolves into a sequence of non-interacting localized pulses that propagate over long distances with significantly reduced dispersion.

Ultraviolet (UV, 200-400 nm) detection with high efficiency and excellent spectral resolution is essential in spectral analysis. This Letter proposes a UV narrowband all-dielectric metasurface absorber with an ultra-thin absorption layer. The design incorporates lossless Al₂O₃ resonators placed on a thin (20 nm) lossy Ga₂O₃ film, which enhances the absorption intensity at a specific wavelength. The near-perfect narrowband absorption enhancement results from the spectral overlap of the magnetic dipole (MD) and the electric dipole (ED) absorption modes by surface lattice resonance (SLR). The proposed absorber exhibits high-efficiency and high-quality (Q) absorption performance (A > 95%, Q ∼ 231) and allows for flexible control over the absorption wavelength through simple parameter adjustments. These features make it ideal for narrowband emission, spectrum detection, and multispectral sensing.

We present a method to selectively suppress unwanted higher-order resonances in all-dielectric tri-layer structural color filters, achieving reflective red (R), green (G), and blue (B) colors through controlled optical interference. By applying a gradient-based optimization technique, we fine-tune the designs to improve color purity by eliminating undesired resonances outside the passband of the tri-layer structure. The filters are composed of a low-refractive-index (LRI) layer sandwiched between two high-refractive-index (HRI) layers. Higher-order modes in the HRI layers and the fundamental mode in the LRI layer are exploited to generate B and G colors. For the R color, the reverse configuration is used: the HRI layers employ the fundamental mode, and the LRI layer operates in a higher-order mode, which introduces an unwanted peak at λ = 450 nm, significantly affecting color purity. To address this, we reduce the LRI thickness to half of the quarter-wave thickness (QWT) and increase the HRI thickness to a quarter of the QWT, shifting interference from constructive to destructive at λ = 450 nm while preserving constructive interference at λ = 642 nm. This effectively suppresses the higher-order mode, resulting in a pure R color. Our study provides valuable insights into the optical design of multilayer thin-film structures, with potential applications in reflective displays, image sensors, and colored solar cells.

Structured light featuring multiple customizable degrees of freedom has become a powerful tool for femtosecond laser processing, enabling much higher throughput and considerable finesse and flexibility. A non-iterative beam shaping technique avoids solving inversion problems of light propagation, but the types of available beam profiles are finite. Here, a phase-only method that can prescribe the beam intensity along an arbitrary two-dimensional curve, called free lens modulation, is applied in femtosecond laser patterned exposure. Single polygonal microstructures with diverse morphology and high surface quality can be fabricated in less than 1 s while outperforming common iterative algorithms in contour fidelity. Moreover, a microfluidic device with a filtering function is designed and demonstrated by integrating microtrap arrays composed of polygons into a microchannel based on the holographic approach. The method offers new inspiration for the rapid construction of large-area microfluidic devices and integrated microsystems with customizable functional applications.

We demonstrate significant second harmonic generation (SHG) and sum frequency generation (SFG) on a thin-film lithium niobate (TFLN) platform by loading a silicon nitride (SiN) microring resonator, which avoids the dry etching of lithium niobate. By optimizing SiN-loaded TFLN waveguide geometry, the phase-matching conditions between the fundamental pump laser and the SHG/SFG signals are designed. Combining with enhancement by the microring resonator, remarkable SHG and SFG signals with conversion efficiencies of 16.43%/W and 5.90%/W are realized, respectively. Compared to traditional TFLN photonic platform, this CMOS-compatible strategy offers an opportunity for achieving large-scale on-chip nonlinear photonic devices based on TFLN.

We present a general theory of multicolor soliton microcombs. These frequency combs require engineered dispersion and have an optical spectrum consisting of multiple spectral windows. Our theory is based on a multiple-scale approach applied to the Lugiato-Lefever equation (LLE) and provides a framework to investigate different pumping configurations. For multi-frequency pumping, we predict a decreasing pumping threshold as the number of spectral windows increases due to an enhanced effective nonlinear parameter. However, comb formation does not require multi-frequency pumping and can emerge even with a single driving field.

Multimode waveguide bend (MWB) with compactness and high performance is essential for modern mode-division multiplexing (MDM) systems. Here, we present a four-mode MWB optimization method, allowing for direct optimization of the bend's central width, enabling precise control of the MWB's overall curvature variation and preventing excessive narrowing of the waveguide width to suppress loss. The realized bending effective radius is 10 μm, equivalent to the most compact design to date, while being based on a simpler method using dual Bezier mathematical curves. The calculated excess losses demonstrate very low rates of 0.0114, 0.0111, 0.0047, and 0.0310 dB for the first four TE modes at 1550 nm, representing the best transmission efficiency. Notably, there is a significant improvement in the performance of high-order mode, which was previously considered challenging at such a small size.

A ring laser is defined by its perimeter, which directly enters the conversion factor between the measured Sagnac frequency and the actual rotation rate. Large ring lasers employed in geodesy and fundamental physics require stability of the perimeter at or below the parts-per-billion level. We present two complementary approaches to actively control the perimeter length of such ring lasers, reaching a relative length stability of 4 × 10^-10. One of these approaches is based on a phase detection between the beat of two resonances of different longitudinal mode indices and a stable local oscillator. The other approach employs a highly stable wavelength meter to measure the absolute frequency of the laser light. These methods can readily be implemented and bring the stability of heterolithic devices on par with monolithic designs.

The interaction between surface acoustic waves (SAWs) and magnons is an interesting phenomenon that can be used to control spins in spintronic devices, and thus the visualization of the related spatiotemporal dynamics can be useful. In this study, we used dual-frequency-comb-based asynchronous optical sampling to record the spatiotemporal evolution of the surface vibration associated with an optically excited SAW and that of the spin precession associated with the magnon under the same excitation condition at effectively 160 frames/ns. Isotropic and anisotropic propagation were observed for phonons and magnons, respectively, demonstrating the capability of measuring such dynamics with high resolution.

We perform modeling and dynamic simulations of all-semiconductor photonic crystal surface-emitting lasers (PCSELs). A two-dimensional photonic crystal consists of a GaAs layer with InGaP features, repeating periodically in both lateral directions. In our dynamic simulations, we demonstrate that photonic crystals with large isosceles triangular features, having a base angle close to 71.5°, enable suppression of higher-order modes and achieve single-mode lasing in large-area all-semiconductor PCSELs under moderate and high pump levels.