No abstract

A polarization-independent and omnidirectional nearly perfect absorber in the visible region has been proposed. The absorber is two-layer structure consisting of a subwavelength metal grating layer embedded in the high refractive index and lossless dielectric layer on the metal substrate. Extraordinary optical absorption with absorption peaks of over 99% can be achieved over the whole visible region for both TM and TE polarization. This absorption is attributed to cavity mode (CM) resonance caused by the coupled surface plasmon polaritons (SPP). Through adjusting the grating thickness, the absorption peak can be tuned linearly, which is highly advantageous to design various absorbers. Furthermore, the absorbance retains ultra-high over a wide angular range of incidence for both TM and TE polarization. This nearly perfect absorber offers great potential in the refractive index (RI) sensors, integrated photodetectors, solar cells and so on.

No abstract

Whispering-gallery-mode (WGM) optical resonators are ideal systems for achieving electromagnetically induced transparency-like phenomenon. Here, we experimentally demonstrate that one or more transparent windows can be achieved with coupled-mode induced transparency (CMIT) in a single bottle WGM resonator due to the bottle's dense mode spectra and tunable resonant frequencies. This device offers an approach for multi-channel all-optical switching devices and sensitivity-enhanced WGM-based sensors.

This study presents a simple, flexible and cost-effective process to fabricate microlens arrays. The polymeric microlens arrays are fabricated using a polydimethylsiloxane (PDMS) mold-based hot embossing process. The desired profile of the lens is achieved with the use of air pressure to deform the PDMS membrane. The deformation of the PDMS membrane is determined by numerical simulation. Simulation results show that the sag height of the PDMS membrane varies nearly linearly along with the change of the negative pressure. The shape of the PDMS membrane is transferred to the PDMS mold with UV curing and casting processes. Then, PDMS is used as a mold insert, and polycarbonate microlens arrays with different sag heights are fabricated with the hot embossing technique. The surface profile of the fabricated microlens keeps spherical with the variation of the sag height induced by the negative pressure. For the negative pressure −3600 and −5900 Pa, sag heights with 40 and 65 µm are obtained and the corresponding focal lengths are changed from 1.0 to 0.6 mm. Good uniformity and imaging quality of the microlenses is confirmed by the experimentally evaluated and measured optical properties of the replica.

No abstract

The amplified spontaneous emissions in blue quantum dots (QDs) are still constrained by their high thresholds due to the challenge in engineering alloyed core–shell interface in the QDs with a wide bandgap to suppress Auger recombination. Compared with their red and green counterparts, the larger reactivity difference between the alloyed shell precursors makes it hard to regulate the composition and structure of the shell, and the smaller potential barrier between the core and the alloyed shell in blue QDs renders charge carriers tunneling into surface defects easier. Here, we employ a Lewis soft base ligand, 1‐decanethiol, to balance the mismatched reactivity between Zn and Cd precursors for crafting a thick gradient alloyed shell with gradually increased potential barrier, which can not only restrict the charge carriers tunneling but also smooth the confinement potential. As a result, the resulting blue QDs show a long Auger lifetime of 1.3 ns, and a low threshold of 6.9 µJ cm−2 excited by a femtosecond laser, which is the record value among all reported blue‐emitting nanocrystals and comparable to those of state‐of‐the‐art red and green QDs.

No abstract