Special polarization characteristic features of a three-dimensional terahertz photonic crystal semi-quantitatively evaluated by using a FEM

A previous work [1] experimentally confirmed that the special polarization characteristic features of a three-dimensional terahertz (THz) photonic crystal with a silicon inverse diamond structure whose lattice point shape was vacant regular octahedrons, did not apply to general physical and optical basic rules in appearance. One of the basic rules is that, according to Maxwell's equations, the electric-field direction of the reflected wave rotates by 180 degrees from that of the incident wave in the case of complete reflection (Bragg reflection) and normal incidence. It is said that three-dimensional photonic crystals have no polarization anisotropy within photonic band gap (stop gap, stop band) of high symmetry points in normal incidence. Experimental results, however, confirmed that the polarization orientation of a reflected wave was rotated by 90 degrees for that of an incident wave at a frequency within photonic band gap. In this work, measured reflected spectra [1] were semi-quantitatively evaluated by being compared with reflection ones by using a FEM (finite element method). These results suggest that measured polarization anisotropy does not apply to Maxwell's equations in appearance but applies to these equations in essential as expected.