Can two degenerate modes have different resonant frequencies? I am asking question in context of resonance in photonic crystal cavities. I am reviewing a paper (I have attached it). Figure 2 (a) and (b) of this paper show modal profile for 2x2PCRR (photonic crystal ring resonator). In this figure two degenerate modes - quadruple0 and quadruple90 exist at different resonant frequencies!! This is possible? I thought degenerate modes have same energy and resonant frequency values.