Fig. 1. Schematic diagram of common structures and energy flow of MEMS infrared thermal emitter

Fig. 2. Simple examples of 1D, 2D, and 3D photonic crystals^[32]

Fig. 3. Structure and corresponding spectrogram^[35]. (a) Cross section schematic diagram of narrowband transmitter based on photonic crystals; (b) schematic diagram of numerical modeling; (c) emission spectrum

Fig. 4. Thermal emitter based on photonic crystals^[36]. (a) Side view of the device; (b) top view of the device; (c) schematic diagram of scanning electron microscope (SEM)

Fig. 5. Thermal radiation spectrum and photonic crystal plate structure. (a) Localized radiation spectrum of the design cavity at 600 K (solid line) and blackbody radiation at the same temperature (dashed line) ^[37]; (b) schematic picture of the single-peak narrow-bandwidth thermal emitter based on MQW rods that form a 2D PC slab, the two conduction subbands of the QW are shown in the top inset, and the lower inset shows the in-plane electric field (Ex) distribution of the resonant mode^[38];(c) schematic of a GaN-based thermal emitter on a sapphire substrate with GaN/AlGaN MQWs and triangular-lattice photonic crystal structures^[39]

Fig. 6. Schematic diagram of grating coupling thermal surface waves into free space^[45]

Fig. 7. Experimental results. (a) Atomic force microscope image of the realized grating^[47]; (b) structure diagram of narrowband light source based on SPP^[48]

Fig. 8. Structure diagram and spectral emission diagram of cross slit grating^[42]. (a) SEM image of the cross slit grating sample; (b) measurement (dots) and calculation (dashed line) of the emissivity spectrum in the direction normal to the surface

Fig. 9. Novel thermal emitter based on BIC resonance supported by an interleaved grating waveguide structure ^[25]. (a) Schematic model; (b) cross sectional view of a single unit cell of the structure

Fig. 10. Narrowband thermal light source based on PSG^[18]. (a) Schematic diagram; (b) emissivity, reflectivity, and transmissivity spectrum of the PSGs under normal incidence at TM polarization

Fig. 11. Schematic diagram of metasurface. (a) Cross shaped metasurface MEMS infrared light source^[54]; (b) propagation of light on MIM structured metasurface^[54]; (c) square metasurface structure^[55]

Fig. 12. SEM images of the fabricated IR emitter^[11]. (a) Schematic of the top of the emitter; (b) schematic of the cross-section of the emitter; (c) schematic of the top layer etching of the emitter

Fig. 13. Dual-band metasurface thermal emitter ^[66]. (a) Structure; (b) emission spectrum in the vertical surface direction

Fig. 14. Narrowband on-chip light source based on metamaterials^[1]. (a) Structure diagram of narrowband thermal emitter on chip; (b) schematic diagram of the structure of a single MPE cell, in which the arrow is the direction of the field intensity during resonance (the red arrow is the electric field E, and the blue arrow is the magnetic field H)

Fig. 15. Schematic diagram of all-dielectric metasurfaces on conductive substrates^[17]

Fig. 16. Gas sensor light source. (a) Infrared spectrum for gases absorption peaks^[69]; (b) gas sensor using broadband light source^[11]; (c) gas sensors using narrowband light sources^[11]

Fig. 17. Schematic diagram of TPV power generation^[70]

Fig. 18. Preparation and mechanism of the artificially engineered macrophages^[77]