Theoretical and Experimental Examination of Simple Coaxial Photonic Crystals for Undergraduate Teaching

A study implementing a coaxial photonic crystal with a simple structure composed of only one type of coaxial cable is described. The coaxial photonic crystal consists of alternating sections of a single cable and N parallel cables, with impedances of ZH and ZH/N, respectively. The high mismatch in impedance at the interfaces enables access to a highly superluminal group velocity with few cables. An easily realizable method is also presented to measure both the amplitude of transmission and the phase of the crystal by using an oscilloscope and a function generator. The measurements were validated by an advanced vector network analyzer and matched the results of theoretical analysis based on the transfer matrix method. The experiment only requires electronic components and equipment that are typically used in undergraduate teaching laboratories.