Fig. 7

Broken reciprocity in thermal photonics by using spatiotemporal modulated photonic systems. a The transmission line-based nonreciprocal structure at radio frequency band. The radiation pattern shows enhanced absorption (blue) and suppressed emission (red). b Spatiotemporally modulated grating structures for thermal emission control at near-infrared frequencies. The nonreciprocal relation between α and e results from the indirect photonic transitions between different guided resonance modes. c Floquet-driven photonic circuits induce nonreciprocal transmittance between two thermal reservoirs, leading to highly efficient thermal rectification. d Time-modulated resonators-based photon refrigeration. With modulation, thermal photons undergo up- and down-conversion which leads to a net cooling or heating effect. Figures adapted from: a, ref [150]; b, ref [151]; c, ref [152]; d, ref [155]