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3D photonic crystals: low-cost high-quality filters for THz applications

We report a low cost and material independent fabrication technique to reproduce sub-millimeter 3D photonic crystals. The crystal is made by stacking mechanically machine dielectric substrates. Interstitial defects can be introduced in the structures. This technique is illustrated by experimental studies with highly resistive silicon based crystals with and without defects. A terahertz time-domain spectroscopy set-up is used for broad band transmission characterization of the crystals. Systematic measurements of the transmission characteristics for different crystal thicknesses and incident angles were performed. A wide compete photonic band gap centered at 265 GHz with a 19 percent band-gap to mid-gap frequency ratio, and excellent filtering properties are observed with only six crystal periods. The influence of the defects was experimentally studied and an external control of their mode's transmission coefficients is demonstrated. The transmission coefficient of the defect modes is controlled by illuminating the interstitial silicon defects with a 330 mW laser beam. Numerical simulations reproduce this behavior by modeling the illumination as an increase of the defect absorption.