Ultra-low threshold continuous-wave quantum dot mini-BIC lasers.

Highly compact lasers with ultra-low threshold and single-mode continuous wave (CW) operation have been a long sought-after component for photonic integrated circuits (PICs). Photonic bound states in the continuum (BICs), due to their excellent ability of trapping light and enhancing light-matter interaction, have been investigated in lasing configurations combining various BIC cavities and optical gain materials. However, the realization of BIC laser with a highly compact size and an ultra-low CW threshold has remained elusive. We demonstrate room temperature CW BIC lasers in the 1310 nm O-band wavelength range, by fabricating a miniaturized BIC cavity in an InAs/GaAs epitaxial quantum dot (QD) gain membrane. By enabling effective trapping of both light and carriers in all three dimensions, ultra-low threshold of 12 µW (0.052 kW cm-2) is achieved at room temperature. Single-mode lasing is also realized in cavities as small as only 5 × 5 unit cells (~2.5 × 2.5 µm2 cavity size) with a mode volume of 1.16(λ/n)3. The maximum operation temperature reaches 70 °C with a characteristic temperature of T0 ~93.9 K. With its advantages in terms of a small footprint, ultra-low power consumption, and adaptability for integration, the mini-BIC lasers offer a perspective light source for future PICs aimed at high-capacity optical communications, sensing and quantum information.

Skin-Inspired Surface-Microstructured Tough Hydrogel Electrolytes for Stretchable Supercapacitors.

Double-network tough hydrogels have raised increasing interest in stretchable electronic applications as well as electronic skin (e-skin) owing to their excellent mechanical properties and functionalities. While hydrogels have been extensively explored as solid-state electrolytes, stretchable energy storage devices based on tough hydrogel electrolytes are still limited despite their high stretchability and strength. A key challenge remains in the robust electrode/electrolyte interface under large mechanical strains. Inspired by the skin structure that involves the microstructured interface for the tight connection between the dermis and epidermis, we demonstrated that a surface-microstructured tough hydrogel electrolyte composed of agar/polyacrylamide/LiCl (AG/PAAm/LiCl) could be exploited to allow stretchable supercapacitors with enhanced mechanical and electrochemical performance. The prestretched tough hydrogel electrolyte was treated to generate surface microstructures with a roughness of tens of micrometers simply via mechanical rubbing followed by the attachment of activated carbon electrodes on both sides to realize the fabrication of the stretchable supercapacitor. Through investigating the properties of the tough hydrogel electrolyte and the electrochemical performance of the as-fabricated supercapacitors under varied strains, the surface-microstructured hydrogel electrolyte was shown to enable robust adhesion to electrodes, improving electrochemical behavior and capacitance, as well as having better performance retention under repeated stretching cycles, which surpassed the pristine hydrogel with smooth surfaces. Our approach could provide an alternative and general strategy to improve the interfacial properties between the electrode and the hydrogel electrolyte, driving new directions for functional stretchable devices based on tough hydrogels.