A Joint Time-Frequency Domain Transformer for multivariate time series forecasting.

In order to enhance the performance of Transformer models for long-term multivariate forecasting while minimizing computational demands, this paper introduces the Joint Time-Frequency Domain Transformer (JTFT). JTFT combines time and frequency domain representations to make predictions. The frequency domain representation efficiently extracts multi-scale dependencies while maintaining sparsity by utilizing a small number of learnable frequencies. Simultaneously, the time domain (TD) representation is derived from a fixed number of the most recent data points, strengthening the modeling of local relationships and mitigating the effects of non-stationarity. Importantly, the length of the representation remains independent of the input sequence length, enabling JTFT to achieve linear computational complexity. Furthermore, a low-rank attention layer is proposed to efficiently capture cross-dimensional dependencies, thus preventing performance degradation resulting from the entanglement of temporal and channel-wise modeling. Experimental results on eight real-world datasets demonstrate that JTFT outperforms state-of-the-art baselines in predictive performance.

Perfect absorption for monolayer transition-metal dichalcogenides by critical coupling.

Due to the inherent atomical size, transition-metal dichalcogenides (TMDCs) have a weak coupling with free-space light and exhibit poor optical absorption, which restricts some practical applications. Exploring an effective way to boost their absorption is important and highly desired. In this work, based on the temporal coupled-mode theory, a generic guide to approach 100% absorption of an absorber is presented. From such a theory, the perfect absorption of TMDCs integrated with dielectric photonic structure is both theoretically and numerically demonstrated. This proposed structure has advantageous tunability at the wavelengths of interest by adjusting structure parameters. Moreover, the angular dependence of the light absorption of such a structure for different polarizations is also investigated. The present work of boosting light absorption would be particularly favorable for applications in advanced photodetectors and modulators.

Controllable lasing behavior enabled by compound dielectric waveguide grating structures.

The photonic density of states (PDOS) is one of the key physical quantities governing the lasing behavior for photonic band-edge lasers. The PDOS is conventionally altered by exploiting the high-Q band-edge mode within a device, which is typically achieved by increasing the contrast of periodic refractive index variation (Δn) or increasing the periodic number of the photonic crystals. In this paper, we propose a different approach to achieve a high-Q band edge mode within an active compound dielectric waveguide grating (CWDG). We demonstrate that the lasing threshold and intensity can be flexibly tuned by changing the filling factors of the CWDG. This design can effectively improve the performance of electrically pumped photonic band-edge lasers.

Scalable Fabrication of Quasi-Three-Dimensional Chiral Plasmonic Oligomers Based on Stepwise Colloid Sphere Lithography Technology.

We report a simple and scalable method for the fabrication of spiral-type chiral plasmonic oligomers based on the stepwise colloid sphere lithography technology. Through carefully adjusting the azimuthal angle Φ of polystyrene (PS) sphere array monolayer and the deposition thickness k n , the chiral plasmonic oligomers composed of four achiral particles can be successfully fabricated on a desired substrate. And their chiral sign, i.e., left-hand or right-hand, is dependent on the anticlockwise or clockwise deposition sequence of the achiral particles. The measured results show a large chiroptical resonance in the visible region, and this resonance can be easily adjusted by using different sizes of PS spheres. Our in-depth theoretical and experimental researches further reveal that the obtained chiral plasmonic oligomers are indeed a kind of quasi-three-dimensional chiral nanostructures, which own a three-dimensional geometrical morphology, but with nonreciprocity chiroptical effect. The ease and scalability (>1 cm(2)) of the fabrication method make chiral plasmonic oligomers promising candidates for many applications, such as chiral biosensor and catalysis.