Slowing and trapping THz waves system based on plasmonic graded period grating

Graded and partial graded period grating structures are proposed to trap and slow terahertz (THz) waves. Different frequencies of THz waves can be trapped at different positions along the graded grating. The exact trapping positions of every different frequency can be estimated from a fitting curve. The separation distance between trapping point of every 0.1 THz is about 1 ~ 2 mm, which can be applied in a THz waves spectrometer. An ultraslow THz waveguide can be realized by using a partial graded grating. The propagated speed of THz waves can be designed and tuned by adjusting the period of the grating. This structure offers the advantage of reducing the speed of the THz waves and propagation them over an ultra-wide spectral band. The physical trapping mechanism of the THz waves is attributed to the transformation from surface modes to cavity modes. The localized cavity modes at the trapping position have a saturated stable state. The extra energy will be reflected back along the graded grating.