Compact optical curvature sensor with a flexible microdisk laser on a polymer substrate

Competitive Growth of Ge Quantum Dots on a Si Micropillar with Pits for a Precisely Site-Controlled QDs/Microdisk System

Semiconductor quantum dots (QDs)/microdisks promise a unique system for comprehensive studies on cavity quantum electrodynamics and great potential for on-chip integrated light sources. Here, we report on a strategy for precisely site-controlled Ge QDs in SiGe microdisks via self-assembly growth of QDs on a micropillar with deterministic pits and subsequent etching. The competitive growth of QDs in pits and at the periphery of the micropillar is disclosed. By adjusting the growth temperature and Ge deposition, as well as the pit profiles, QDs can exclusively grow in pits that are exactly located at the field antinodes of the corresponding cavity mode of the microdisk. The inherent mechanism of the mandatory addressability of QDs is revealed in terms of growth kinetics based on the non-uniform surface chemical potential around the top of the micropillar with pits. Our results demonstrate a promising approach to scalable and deterministic QDs/microdisks with strong light-matter interaction desired for fundamental research and technological applications.

Ultraflexible and Lightweight Bamboo-Derived Transparent Electrodes for Perovskite Solar Cells

Wearable devices are mainly based on plastic substrates, such as polyethylene terephthalate and polyethylene naphthalate, which causes environmental pollution after use due to the long decomposition periods. This work reports on the fabrication of a biodegradable and biocompatible transparent conductive electrode derived from bamboo for flexible perovskite solar cells. The conductive bioelectrode exhibits extremely flexible and light-weight properties. After bending 3000 times at a 4 mm curvature radius or even undergoing a crumpling test, it still shows excellent electrical performance and negligible decay. The performance of the bamboo-based bioelectrode perovskite solar cell exhibits a record power conversion efficiency (PCE) of 11.68%, showing the highest efficiency among all reported biomass-based perovskite solar cells. It is remarkable that this flexible device has a highly bendable mechanical stability, maintaining over 70% of its original PCE during 1000 bending cycles at a 4 mm curvature radius. This work paves the way for perovskite solar cells toward comfortable and environmentally friendly wearable devices.

Microscale local strain gauges based on visible micro-disk lasers embedded in a flexible substrate

Microscale local strain gauges with low-power consumption and large strain range were demonstrated by integrating microdisk lasers in a deformable and flexible polymer substrate. The lasing spectra of microdisk lasers were sensitive to substrate deformation and can be modulated by strains. The measured relative wavelength tuning under strains of the novel strain sensors illustrated a linear behavior with the gauge factor being ~4.0 nm and ~6.7 nm per stretching unit for microdisk lasers with the diameter of 1.2 μm and 1.5 μm, which corresponding to a smooth wavelength tuning of 1.5 nm and 2.6 nm under 36% strain, respectively. In addition, to being used as microscale strain gauges, the visible lasers on the deformable substrate can also function as a tunable light source for the photonic integrated circuits and flexible laser projection displays.

Proposal and numerical study of a flexible visible photonic crystal defect cavity for nanoscale strain sensors

A flexible photonic crystal cavity, consisting of a III-V active layer embedded in a flexible medium, with a line-defect by removing three air holes for nanoscale structural deformation detection is proposed and optimized. The cavity can hold the photonic band-gap modes with the fundamental mode located at approximately 686 nm, overlapping with the photoluminescence spectrum of the InGaP/InGaAlP quantum wells. Results of finite-difference time-domain simulations indicate that the L3 cavity features an ultra-compact mode volume of 10^-3 µm³ and high quality factor of 10⁴ at a sub-micron footprint within the studied visible wavelength. Theoretical optical strain sensitivities of approximately 4.5 and 3 nm per ε (1% strain for both) for the x and y directions are predicted, respectively. When the cavity is under large bending curvatures, the Q factor rapidly decreases from 8000 to 2000.

A high sensitivity three-dimensional-shape sensing patch prepared by lithography and inkjet printing

A process combining conventional photolithography and a novel inkjet printing method for the manufacture of high sensitivity three-dimensional-shape (3DS) sensing patches was proposed and demonstrated. The supporting curvature ranges from 1.41 to 6.24 × 10(-2) mm(-1) and the sensing patch has a thickness of less than 130 μm and 20 × 20 mm(2) dimensions. A complete finite element method (FEM) model with simulation results was calculated and performed based on the buckling of columns and the deflection equation. The results show high compatibility of the drop-on-demand (DOD) inkjet printing with photolithography and the interferometer design also supports bi-directional detection of deformation. The 3DS sensing patch can be operated remotely without any power consumption. It provides a novel and alternative option compared with other optical curvature sensors.