Measurement of photonic band structure using coherent microwave transient spectroscopy

Abstract

The photonic band structure of a 2-D dielectric array has been investigated using the coherent microwave transient spectroscopy (COMITS) technique. COMITS, which is based on electromagnetic transients radiated and received by optoelectronically pulsed antennas, is capable of measuring the complex transmission function of a sample in the 15 GHz-140 GHz frequency range in a single experiment. A 2-D photonic crystal was constructed using 1.2-mm diameter alumina ceramic rods arranged in a uniform square lattice of periodicity 3 mm. The lateral extent of the sample was much larger than the diameter of the broadband microwave beam, eliminating any end effects. The frequency dependent amplitude transmission of the sample clearly indicates the fundamental and higher photonic band gaps along the symmetry directions. The position of the measured fundamental gap is in agreement with theoretical predictions for a 2-D system.1 Furthermore, the phase sensitive nature of the COMITS technique has been used to investigate propagation at frequencies above the fundamental gap. These results are presented together with the effect of polarization on these 2-D samples.