Abstract
Photonic analogs of electronic systems with topologically non-trivial behavior such as unidirectional scatter-free propagation has tremendous potential for transforming photonic systems. Like in electronics topological behavior can be observed in photonics for systems either preserving time-reversal (TR) symmetry or explicitly breaking it. TR symmetry breaking requires magneto-optic photonics crystals (PC) or generation of synthetic gauge fields. For on-chip photonics that operate at optical frequencies both are quite challenging because of poor magneto-optic response of materials or substantial nanofabrication challenges in generating synthetic gauge fields. A recent work by Ma, et al. [Phys. Rev. Lett.114, 223901 (2015)] based on preserving pseudo TR symmetry offers a promising design scheme for observing unidirectional edge states in a modified honeycomb photonic crystal (PC) lattice of circular rods that offers encouraging alternatives. Here we propose through bandstructure calculations the inverse system of modified honeycomb PC of circular holes in a dielectric membrane which is more attractive from fabrication standpoint for on-chip applications. We observe trivial and non-trivial bandgaps as well as unidirectional edge states of opposite helicity propagating in opposite directions at the interface of a trivial and non-trivial PC structures. Around 1550nm operating wavelength ~55nm of bandwidth is possible for practicable values of design parameters (lattice constant, hole radii, membrane thickness, scaling factor etc.) and robust to reasonable variations in those parameters.
Highlights
Non-trivial behavior in electronic systems have been studied intensively following the discovery of quantum hall effect [1, 2] (QHE) in two dimensional electron gas (2DEG) at low temperatures in an external magnetic field that breaks time-reversal symmetry
Like in electronics topological behavior can be observed in photonics for systems either preserving time-reversal (TR) symmetry or explicitly breaking it
For on-chip photonics that operate at optical frequencies both are quite challenging because of poor magneto-optic response of materials or substantial nanofabrication challenges in generating synthetic gauge fields
Summary
Non-trivial behavior in electronic systems have been studied intensively following the discovery of quantum hall effect [1, 2] (QHE) in two dimensional electron gas (2DEG) at low temperatures in an external magnetic field that breaks time-reversal symmetry. A characteristic feature of the topological protection is the one-way conducting electronic edge-states that propagate scatter-free even in the presence of large impurities This has opened up possibilities in quantum computation for achieving long lived qubits in decohering environments. The strategy basically involves opening up of a band gap about a Dirac point by compressing or expanding the honeycomb lattice This was shown theoretically for a photonic crystal system composed of an array of infinitely long dielectric cylinders. The circular hole array based membrane photonic crystal provides a simpler and more practical way to fabricate and experimentally demonstrate this behavior at optical frequencies on-chip
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