Tunable flat band slow light in reconfigurable photonic crystal waveguides based on magnetic fluids

A kind of two-dimensional photonic crystal line-defect waveguide with 45°-rotated square lattice is proposed to present slow light phenomena. Infiltrating the photonic crystal waveguide with appropriate magnetic fluids can generate very wide flat bands of guided modes, which give rise to the excellent slow light properties. The bandwidth centered at λ0=1550 nm of the designed W1 waveguide is considerably large (around 54 nm). The obtained group velocity dispersion β2 within the bandwidth is ultralow (varying from −2118a/2πc2 to 1845a/2πc2, where a and c are the period of the lattice and the light speed in vacuum, respectively). Simultaneously, the normalized delay-bandwidth product is relatively large compared with other works. Reconfiguring the photonic crystal waveguide with magnetic fluids of different concentrations can remarkably tune the slow light parameters and the trade-off between them, while the type of magnetic nanoparticles constituting the magnetic fluids negligibly affect the slow light properties. The explicit linear variation of the slow light parameters with the magnetic fluid concentration is convenient for the practical tuning.