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.

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 kn, 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 cm2) of the fabrication method make chiral plasmonic oligomers promising candidates for many applications, such as chiral biosensor and catalysis.

The efficiency and bandwidth of an optical absorbing material, especially for the promising two-dimensional transition metal dichalcogenides (TMDCs) are critical to underpin advances in photonic and optoelectronic devices. In this work, we present a general method to manipulate the bandwidth of an absorber with high efficiency through coupling with the quasi-bound states in the continuum (quasi-BIC). We demonstrate this strategy by taking absorbing material monolayer TMDC coupled with the lossless symmetry-broken photonic crystal (PhC) slab. An optimal-efficiency TMDC-based absorber with over three orders of magnitude of bandwidth adjustment is realized, by simultaneously adjusting the structure asymmetry parameter of PhC slab and the locations of monolayer TMDC in the structure. Interestingly, the absorption bandwidth is tailored quadratically with the asymmetry parameter, which derived from the powerful physics of bound state in the continuum (BIC) in radiation engineering. Moreover, a superior-performance optical refractive index sensor is further designed. We demonstrate that our proposed method based on quasi-BIC structure can also effectively govern the sensing performance. Present work not only provides further insight into BIC physics, but also offers a promising strategy of smart engineering in active optical devices with the properties on demand.

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.