Electrically Reconfigurable Phase-Change Transmissive Metasurface.

Programmable and reconfigurable optics hold significant potential for transforming a broad spectrum of applications, spanning space explorations to biomedical imaging, gas sensing, and optical cloaking. The ability to adjust the optical properties of components like filters, lenses, and beam steering devices could result in dramatic reductions in size, weight, and power consumption in future optoelectronic devices. Among the potential candidates for reconfigurable optics, chalcogenide-based phase change materials (PCMs) offer great promise due to their non-volatile and analogue switching characteristics. Although PCM have found widespread use in electronic data storage, these memory devices are deeply sub-micron-sized. To incorporate phase change materials into free-space optical components, it is essential to scale them up to beyond several hundreds of microns while maintaining reliable switching characteristics. This study demonstrated a non-mechanical, non-volatile transmissive filter based on low-loss PCMs with a 200 µm×200 µm switching area. The device/metafilter can be consistently switched between low- and high-transmission states using electrical pulses with a switching contrast ratio of 5.5 dB. The device was reversibly switched for 1250 cycles before accelerated degradation took place. The work represents an important step toward realizing free-space reconfigurable optics based on PCMs. This article is protected by copyright. All rights reserved.

Monolithic beam combined quantum cascade laser arrays with integrated arrayed waveguide gratings.

Quantum cascade lasers (QCLs) are ubiquitous mid-infrared sources owing to their flexible designs and compact footprints. Manufacturing multiwavelength QCL chips with high power levels and good beam quality is highly desirable for many applications. In this study, we demonstrate an λ ∼ 4.9 µm monolithic, wavelength beam-combined (WBC) infrared laser source by integrating on a single chip array of five QCL gain sections with an arrayed waveguide grating (AWG). Optical feedback from the cleaved facets enables lasing, whereas the integrated AWG locks the emission spectrum of each gain section to its corresponding input channel wavelength and spatially combines their signals into a single-output waveguide. Our chip features high peak power from the common aperture exceeding 0.6 W for each input channel, with a side-mode suppression ratio (SMSR) of over 27 dB when operated in pulsed mode. Our active/passive integration approach allows for a seamless transition from the QCL ridges to the AWG without requiring regrowth or evanescent coupling schemes, leading to a robust design. These results pave the way for the development of highly compact mid-IR sources suitable for applications such as hyperspectral imaging.

High-efficiency mid-infrared InGaAs/InP arrayed waveguide gratings.

Photonic integrated circuits and mid-infrared quantum cascade lasers have attracted significant attention over the years because of the numerous applications enabled by these compact semiconductor chips. In this paper, we demonstrate low loss passive waveguides and highly efficient arrayed waveguide gratings that can be used, for example, to beam combine infrared (IR) laser arrays. The waveguide structure used consists of an In0.53Ga0.47As core and InP cladding layers. This material system was chosen because of its compatibility with future monolithic integration with quantum cascade lasers. Different photonic circuits were fabricated using standard semiconductor processes, and experiments conducted with these chips demonstrated low-loss waveguides with an estimated propagation loss of ∼ 1.2 dB/cm as well as micro-ring resonators with an intrinsic Q-factor of 174,000. Arrayed waveguide gratings operating in the 5.15-5.34 µm range feature low insertion loss and non-uniformity of ∼ 0.9 dB and ∼ 0.6 dB, respectively. The demonstration of the present photonic circuits paves the path toward monolithic fabrication of compact infrared light sources with advanced functionalities beneficial to many chemical sensing and high-power applications.

Non-Equilibrium Sodiation Pathway of CuSbS2.

Binary metal sulfides have been explored as sodium storage materials owing to their high theoretical capacity and high stable cyclability. Nevertheless, their relative high charge voltage and relatively low practical capacity make them less attractive as an anode material. To resolve the problem, addition of alloying elements is considerable. Copper antimony sulfide is investigated as a representative case. In this study, we do not only perform electrochemical characterization on CuSbS2, but also investigate its nonequilibrium sodiation pathway employing in-/ex situ transmission electron microscopy, in situ X-ray diffraction, and density functional theory calculations. Our finding provides valuable insights on sodium storage into ternary metal sulfide including an alloying element.

Pulverization-Tolerance and Capacity Recovery of Copper Sulfide for High-Performance Sodium Storage.

Finding suitable electrode materials is one of the challenges for the commercialization of a sodium ion battery due to its pulverization accompanied by high volume expansion upon sodiation. Here, copper sulfide is suggested as a superior electrode material with high capacity, high rate, and long-term cyclability owing to its unique conversion reaction mechanism that is pulverization-tolerant and thus induces the capacity recovery. Such a desirable consequence comes from the combined effect among formation of stable grain boundaries, semi-coherent boundaries, and solid-electrolyte interphase layers. The characteristics enable high cyclic stability of a copper sulfide electrode without any need of size and morphological optimization. This work provides a key finding on high-performance conversion reaction based electrode materials for sodium ion batteries.