Abstract
The H1 photonic crystal cavity supports two degenerate dipole modes of orthogonal linear polarization which could give rise to circularly polarized fields when driven with a $\pi$/$2$ phase difference. However, fabrication errors tend to break the symmetry of the cavity which lifts the degeneracy of the modes, rendering the cavity unsuitable for supporting circular polarization. We demonstrate numerically, a scheme that induces chirality in the cavity modes, thereby achieving a cavity that supports intrinsic circular polarization. By selectively modifying two air holes around the cavity, the dipole modes could interact via asymmetric coherent backscattering which is a non-Hermitian process. With suitable air hole parameters, the cavity modes approach the exceptional point, coalescing in frequencies and linewidths as well as giving rise to significant circular polarization close to unity. The handedness of the chirality can be selected depending on the choice of the modified air holes. Our results highlight the prospect of using the H1 photonic crystal cavity for chiral-light matter coupling in applications such as valleytronics, spin-photon interfaces and the generation of single photons with well-defined spins.
Highlights
The dynamics of physical systems with open boundaries that could exchange energy with their surrounding environment can be described by non-Hermitian Hamiltonians
To the interaction between the two modified air holes via scattering [18]. Such interactions between air holes are more likely to occur for the h21h22 case since the modified air holes are closer to each other. These findings suggest that the air hole modifications of the h21h23 and h21h22 cases need to be optimized separately to obtain the intended chiral modes with high degree of circular polarization (DCP)
Comparing simulations results for the r1-modified and unmodified H1 photonic crystal (PhC) cavity, we find that the r1-modified PhC cavity requires larger modifications to the second nearest air holes in order to achieve chiral modes
Summary
When the two modes are driven with a π /2 phase difference, they give rise to circularly polarized cavity fields Such a nanocavity—given its small mode volume and prospects for high Q factor—would be an important component for chiral quantum optics [20], photonic circuits [21,22], spin nanolasers, optical sensors [23], and other applications. These functionalities are usually hindered by fabrication errors of the nanocavity which tend to lift the mode degeneracies, making it incapable of supporting circular polarization. We present simulation results of three-dimensional (3D) structures to show that practical devices are achievable
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