Fabrication and characterization of terahertz photonic crystals

Two dimensional (2D) terahertz (THz) photonic crystals were fabricated by stacking micro-machined high-resistance silicon substrates. The transmission spectra through 1 to 8 stacked silicon substrates with polarization parallel and perpendicular to the grooves were measured. At normal incidence with either polarization the normalized transmission spectrum quickly converges as the number of stacked substrates increases. For as few as three stacked Si substrates, the observed transmission spectra for the first two bands converge reasonably well to the calculated results for an infinite lattice. The agreement is better at frequencies lower than 0.4 THz, while it becomes worse at higher frequencies. At oblique incidence, the wave vector direction inside the photonic crystal depends on both incident angle and frequency. The calculated direction from the 2D energy dispersion determines the experimentally observed transmission spectrum. The agreement between the measured results and calculation is reasonable, though some discrepancies remain unaccountable.