Slow light effect with low group velocity and low dispersion by adjusting parameters of elliptical scatterers for terahertz frequency

Elliptical scatterers possess the properties of anisotropy and multiple degrees of freedom. With the plane wave expansion method, the slow light effect with high ng and low dispersion can be achieved by optimizing the structure parameters of photonic crystal waveguide with line defect, including changing the length of major axis or minor axis, and rotating scatterers relative to the direction of line defect. With operating frequency f = 1 THz (wavelength λ = 300 μm), the simulation shows: 1) selecting the group index ng from 38.5 to 107.4, slow light with low-dispersion bandwidth (ng varies within a 10% range) from 0.385 to 1.272 μm, ultralow-dispersion bandwidth (ng varies within a 1% range) from 0.188 to 0.548 μm, and scalar product ngΔλ /λ from 0.138 to 0.180 were obtained by changing the length of major axis or minor axis; 2) selecting the group index ng from 38.6 to 107.7, slow light with low-dispersion bandwidth from 0.436 to 1.443 μm, ultralow-dispersion bandwidth from 0.201 to 0.907 μm, and scalar product ngΔλ /λ from 0.157 to 0.186 were achieved by rotating scatterers θ = 30° relative to the direction of line defect. Moreover, slow light with near-zero dispersion (dispersion parameter D less than 0.01 ps/mm·nm) can also be obtained by these methods, which implies that choosing suitable scatterers and adjusting their parameters we can efficiently achieve slow light with high ng with wideband and low dispersion.