Fig. 4

Measured momentum space, field distributions in real space, and retrieved dispersion and group velocity of the designer polaritons on the type-I hyperbolic metasurface. a Measured momentum space of the designer polaritons in the FBZ, and measured Hz field distributions on the plane 5 mm over the metasurface (22 by 22 unit cells) at 0.198, 0.213, 0.228, and 0.243 GHz, respectively. The red star in the right inset represents the source location. b Photograph of the metasurface sample. Inset: two unit cells of the metasurface. c Retrieved squeezing factor and group velocity of the designer polaritons from the experimental results. Here, the blue dots are the experimental data; the blue curve represents exponential fits to the experimental data; the orange curve is the group velocity obtained from the blue curve