Ultraviolet (UV) photonics-based device and equipment have various applications in sterilization, military covert communication, medical treatment, nanofabrication, gem identification and so on. The traditional constituent UV components are bulky, inefficient, expensive and easily aging under UV radiation. An all-dielectric metasurface offers a promising way to control the amplitude, polarization and phase of light by engineering the size, shape and distribution of its constituent elements. However, UV components based on all-dielectric metasurfaces are difficult to be realized, due to significant absorption loss for most dielectric materials at the UV region. Here we demonstrate the design of a UV metalens, composed of high-aspect-ratio aluminum nitride nanorods. The in-plane on-axis, off-axis and out-of-plane focusing characteristics have been investigated at representative UVA (375 nm), UVB (308 nm) and UVC (244 nm) wavelengths, respectively. Furthermore, we design UV router for mono-wavelength and multiple wavelengths, that is, guiding UV light to designated different spatial positions. Our work is promising for the development of UV photonic devices and would facilitate the integration and miniaturization of the UV nanophotonics.
Visible light communication (VLC) has attracted widespread attention for wireless communications. The popularity of GaN-based light-emitting diodes (LEDs) has also laid a solid foundation for the application of VLC. As the light source of VLC, LED's modulation bandwidth directly determines the speed of communication. Herein, reviewing progress on modulation bandwidth improvement schemes of GaN LEDs transmitter is reviewed, covering aspects from epitaxial to devices. Epitaxial approaches include c-polar facet epitaxial optimization, non/semipolar facet epitaxial growth, and chip scheme such as micro-LEDs, nano-LEDs, resonant cavity-LEDs (RC-LEDs), plasmon, and metacavity LEDs. In terms of white LEDs, approaches to tackle the slow Stokes transfer and long carrier life for conventional phosphors including new color-conversion materials (CCMs) and new energy transfer routes are reviewed. This review promotes the development of GaN-based LEDs as the transmitter for high-speed VLC.
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