Highly confined mode above the light line in a two-dimensional photonic crystal slab

We found that certain modes above the light line can satisfy total internal reflection in a two-dimensional photonic crystal slab, resulting in negligible vertical leakage. A heterogeneous cavity utilizing such a mode was designed and constructed for the microwave spectrum. Numerical calculations show the mode has a quality factor (Q) of 6×105 neglecting the material loss and 7600 including it. The measured Q (9000), resonance frequency, and mode pattern agreed well with the calculation. The mode has more than 50% of electric field energy in void space and is promising to have stronger interaction with materials introduced there.