Slow-wave resonance in periodic stacks of anisotropic layers

We consider a Fabry-Perot resonance a transmission band edge resonance in periodic layered structures involving birefringent layers. In a previous publication Phys. Rev. E 72, 036619 2005 we have shown that the presence of birefringent layers with misaligned in-plane anisotropy can dramatically enhance the performance of the photonic-crystal resonator. It allows us to reduce its size by an order of magnitude without compromising on its performance. The key characteristic of the enhanced slow-wave resonator is that the Bloch dispersion relation k of the periodic structure displays a degenerate photonic band edge, in the vicinity of which the dispersion curve can be approximated as k 4, rather than k 2. Such a situation can be realized in specially arranged stacks of misaligned anisotropic layers. On the down side, the presence of birefringent layers results in the slow-wave resonance being coupled only with one elliptic polarization component of the incident wave, while the other polarization component is reflected back to space. In this paper we show how a small modification of the periodic layered array can solve the above fundamental problem and provide a perfect impedance match regardless of the incident wave polarization, while preserving the giant slow-wave resonance characteristic of a degenerate photonic band edge. Both features are of critical importance for many practical applications, such as the enhancement of various light-matter interactions, light amplification and lasing, optical and microwave filters, antennas, etc.