Broadband directional control of thermal radiation by metalens arrays

Controlling the directivity of thermal radiation, which is typically broadband, omnidirectional, unpolarized, and incoherent, is important for applications like thermal management, radiative cooling and thermal energy conversion. While recent advancements in photonic devices have demonstrated angular selectivity in thermal radiation, their operational bandwidth still remains narrow, posing a significant challenge for achieving broadband directional emission. Here, we design a microscale metalens array capable of directly extracting thermal photons from a heat source and collimating them into vertically emitted parallel light. The micro-nano structure array consists of periodically arranged metalens, each composed of truncated cones of varying sizes. This structure enables parallel emission of radiation from heat sources located at depths ranging from 25 μm to 500 μm, across a broad wavelength range of 6-15 μm. By integrating this into a 2.5D/3D packaged chip, we introduce a directional radiative heat dissipation strategy for chiplets under operation, which enhances the transmitted thermal energy by 71.8%. Our approach provides an additional cooling channel for microelectronic devices.