We report a large-size (4-inch) optical exceptional point structure at visible frequencies by designing a multilayer structure of absorbing and non-absorbing dielectrics. The optical exceptional point was implemented as indicated by the realized unidirectional reflectionless light transport at a wafer scale. The associated abrupt phase transition is theoretically and experimentally confirmed when crossing over the exceptional point in wavelengths. The large scale demonstration of phase transition around exceptional points will open new possibilities in important applications in free space optical devices.

Full noncontact laser ultrasound (LUS) imaging has several distinct advantages over current medical ultrasound (US) technologies: elimination of the coupling mediums (gel/water), operator-independent image quality, improved repeatability, and volumetric imaging. Current light-based ultrasound utilizing tissue-penetrating photoacoustics (PA) generally uses traditional piezoelectric transducers in contact with the imaged tissue or carries an optical fiber detector close to the imaging site. Unlike PA, the LUS design presented here minimizes the optical penetration and specifically restricts optical-to-acoustic energy transduction at the tissue surface, maximizing the generated acoustic source amplitude. With an appropriate optical design and interferometry, any exposed tissue surfaces can become viable acoustic sources and detectors. LUS operates analogously to conventional ultrasound but uses light instead of piezoelectric elements. Here, we present full noncontact LUS results, imaging targets at ~5 cm depths and at a meter-scale standoff from the target surface. Experimental results demonstrating volumetric imaging and the first LUS images on humans are presented, all at eye- and skin-safe optical exposure levels. The progression of LUS imaging from tissue-mimicking phantoms, to excised animal tissue, to humans in vivo is shown, with validation from conventional ultrasound images. The LUS system design insights and results presented here inspire further LUS development and are a significant step toward the clinical implementation of LUS.

Pixelated quantum-dot color conversion film (QDCCF) is attractive for next-generation, high-pixel-density, full-color displays. However, how to achieve white balance of these QD converted displays puts forward a new challenge, because the final light-emitting area is redefined by the apertures of the QD formed subpixels. Based on this, this paper presents an effective white-balance realization approach by precisely defining an asymmetric aperture ratio among three primary-color subpixels of the QDCCF. Based on the measured photoluminescence characteristic of quantum-dot photoresist (QDPR), the theoretical aperture ratio can be derived by the spectral radiation energy and external quantum efficiency (EQE) of QDCCFs for the target D65 white-balance state. A bilayered device architecture, combining a blue mini-LED backlight and a pixelated QDCCF, was simulated and experimentally assembled to verify the theoretical design. The simulated chromatic coordinates obtained from the QDCCF precisely agree with the target white-balance point. Experimental patterning and pixelation of the designed QDCCF were achieved by a precise photolithography process. Measured results show that a white-light output was achieved with the chromatic coordinates of (0.2822, 0.2951) and the color gamut of 115.09% NTSC (National Television System Committee) standard. The deviation of the experimental chromatic coordinates is within ±0.05 to the D65 standard light source. The proposed white-balance realization approach featured by the aperture adjustable subpixels of a chromatic QDCCF may open up a new route for color reproduction in emerging display technologies.

Ultraviolet photodetectors (UVPDs) which play important roles in military and civil applications are normally fabricated by using wide band gap semiconductors (WBSs) as building blocks. Unfortunately, the commercialization of UVPDs based on WBSs is often limited by their relatively high fabrication cost owing to the use of very complicated growth instruments. In this work, a sensitive UVPD based on non-WBS lead sulfide (PbS) with a relatively small band gap was proposed. Device analysis revealed that the UVPD made of 48.5 nm PbS nanofilm was highly sensitive to UV illumination at 365 nm. Specifically, the responsivity and specific detectivity under 365 nm illumination were 22.25 A W–1 and 4.97 × 1012 Jones, respectively, which are comparable to or better than most of the conventional WBS-based UVPDs. The PbS nanofilm-based UVPD also exhibits excellent environmental stability. Experimental results and simulations based on technology computer-aided design software confirmed that the abnormal properties of PbS nanofilms are related to the relatively thin thickness and wavelength-dependent absorption coefficients. These results open up an opportunity for narrow band gap semiconductors to realize low-cost-sensitive UVPDs in future optoelectronic devices and systems.

In this study, simple-structured wavelength sensors were developed by depositing two back-to-back Au/MAPbI3/Au photodetectors on an MAPbI3 single crystal. This sensor could quantitatively distinguish wavelengths. Further device analysis showed that both photodetectors possess entirely disparate optoelectronic properties. Consequently, the as-developed wavelength sensor could accurately distinguish incident-light wavelengths ranging from 265 to 860 nm with a resolution of less than 1.5 nm based on the relation between the photocurrent ratios of both photodetectors and the incident light wavelengths. Notably, a high resolution and wide detection range are among the optimum reported values for such sensors and enable full-color imaging. Furthermore, technology computer-aided design (TCAD) simulations showed that a mechanism involved in distinguishing wavelengths is attributed to the wavelength-dependent photon generation rate in MAPbI3 single crystals. The high-performance MAPbI3 wavelength sensor can potentially drive the research progress of perovskites in wavelength recognition and full-color imaging.