Fig. 1. (a) Distributions of SPP near the metal-dielectric surface^[3], (b) dependence of SPP mode on the distance in the direction perpendicular to the metal surface^[3], (c) dispersion curve of SPP mode on the metal-dielectric surface^[3]

Fig. 2. (a) Schematic of matching wavevector using a prism^[19], (b) schematic of matching wavevector using a grating^[19]

Fig. 3. Structural illumination microscopic imaging based on SPP^[30] (a) The schematic illustration, (b) the imaging results

Fig. 4. (a) Subwavelength hole array arranged in a metallic layer^[35], (b) dispersion curves of SSP^[35]

Fig. 5. (a) and (b) show the structure and dispersion relation of an ultra-thin subwavelength grating^[38], respectively, (c) sketch of periodic wedges^[43], (d) the high-impedance surface based on “mushroom” structure^[50], (e) the light splitter made by a gradient grating^[52], (f) Photograph of the nearly zero-thickness gratings on a flexible substrate^[54], (g) the simulated field of three-dimensional flexible ultra-thin gratings^[54]

Fig. 6. (a) Schematic of graphene monolayer and other related carbon materials^[75], (b) the intraband and interband transitions of the graphene, (c) the optical conductivity of graphene as a function of frequency under different Fermi energy

Fig. 7. (a) Diagram of an infrared near-field experiment^[79], where G represents the graphene and the dashed line is the edge of graphene, (b)-(e) present the images of infrared amplitude of GSP under zero gate voltage, which is obtained by near-field optical microscopy

Fig. 8. (a) Schematic of interaction between an electron beam and SSP structure^[96], (b) the output spectrum of the system in (a)^[96], (c) the interaction between multiple electron beams and a crystal-like SSP structure^[101], (d) regenerated terahertz source induced by a FP cavity^[104], (e) periodic-cylinders-loaded beam-scanning terahertz radiation^[105], (f) multi-frequency coherent terahertz free-space radiation^[106]

Fig. 9. (a) SPP excitation on a sliver layer based on free electrons^[110], (b) terahertz radiation by exciting GSP which is launched by the interaction between electron beams with graphene ribbons^[112], (c) dielectric Cherenkov radiation generated by the interaction between an electron bunch with graphene^[113], (d) Coherent tunable terahertz radiation by exciting GSP with a cyclotron electron beam in a graphene-loaded cylindrical waveguide^[116]

Fig. 10. (a) Propagation of terahertz waves on a periodically corrugated metal wire^[39], (b) schematic of a V-shaped SSP structure ^[46], (c) the field distributions of SSP on V-shaped under different bending radiuses^[46] (d) the domino-shaped SSP structure^[45], (e) the power divider, directional couplers, and ring resonators based on domino-shaped SSP structure^[45], (f)-(h) serval designs for three-dimensional SSP transmission^[121]

Fig. 11. (a) SSP waveguide and conventional T-line based on 65nm CMOS technology^[123], (b) loss of SSP waveguide and T-line at terahertz wavelengths^[123], (c) time-domain signals propagate on two closely packed SSP waveguides with high integrity^[124]

Fig. 12. (a) Combination of periodic domino structure with conventional parallel plate waveguide^[125], (b) the electric field distribution when the waveguide is twisted^[125], (c) texturing the subwavelength grating on the output face of a parallel plate waveguide to controlling the reflection and transmission of the waveguide modes^[128], (d) embedding two gratings in the top and bottom plates of the waveguide^[129], (e) realizing the mode conversion by controlling the phase differences between surface waves^[129], (f) achieving efficient modes bending through the high-confined SSP modes, (g)-(i) the SSP-based filter^[130], stripe antenna^[132] and broadband power divider^[133]

Fig. 13. (a) Gradient metallic grating and its dispersive curves^[51], (b) the group velocity of SSP as a function of frequency^[51], (c) the splitter based on gratings with different groove height^[135], (d) the electric field maps of the splitter at 0.5 THz and 1 THz ^[135]

Fig. 14. (a) Schematic of SSP excitation based on a prism^[147], (b) the coupling of SSP through the scattering of a metallic tip^[148], (c) the fan-shaped grating using for exciting LSSP^[61], (d) the calculated scattering cross section of fan-shaped grating as a function of frequency^[61], where the pictures in the insert are hexpole, octopole, and decapole modes of electric resonances

Fig. 15. The sketch map of imaging process with limited resolution ^[164] (a) the target, (b) the totally spatial spectrum of the target, (c) the far-field spatial spectrum, (d) the reconstructed image using the far-field spatial spectrum

Fig. 16. (a) The probe based on gradient corrugated metal wires^[39], (b) the focusing of SSP waves by gradually varying the domino structure^[45], (c) the SP2 mode in a truncated grating^[38], (d) the electric field snapshot of two targets illuminated by the probe ^[38], (e) the radiationless focusing of SSP waves through 7th-order Fabry-Perot resonance^[167], (f) the two-dimensional superfocusing behavior by an ultra-thin grating^[167]

Fig. 17. (a) The superlens built by hyperbolic metamaterials^[171], (b) schematic of multilayer graphene superlens^[175], (c) the resonantly amplifying of evanescent waves by single layer of graphene^[175], (d) hyperlens based on graphene^[85], (e) the planar graphene superlens working in the canalization regime^[86], (f) the sketch of fan-shaped graphene hyperlens^[176], (g) the far-field image of two targets with subwavelength distance^[176], (h) the field distribution of a graphene superlens using the four-waves mixing^[177]

Fig. 18. (a) The imaging of multiplexer based on reconfigurable SSP waveguide^[179], (b) the open-end grating with combination of varactors^[182], (c) the short-end grating with combination of varactors^[183]

Fig. 19. (a) The SSP coupler based on reflective metasurfaces^[190], (b) the SSP coupler based on transmissive metasurfaces ^[191], (c) the conversion between SSP structure and the conventional coplanar waveguide ^[192], (d) the schematic of a coupler for the reflective metallic grating ^[194], (e) the sketch of directional SSP coupler [195], (f) the far-field angular scattering patterns and the near-field two-dimensional electric field distributions at 0.36 THz, 0.38 THz, and 0.40 THz ^[195]