Coupling control in photonic crystal molecules

We experimentally show that the mode splitting in two-evanescently coupled Photonic Crystal L3 cavities (three holes missing in the ΓK direction of the underlying triangular lattice) can be controlled through barrier engineering. The “potential barrier”s is formed by the air-holes in between the two cavities. By changing the hole radius of the central row in the barrier up to ~30%, the frequency splitting can be strongly reduced. Moreover, the sign of the splitting can be reversed in such a way that the fundamental mode can be either the symmetric or the anti-symmetric one without altering neither the cavity geometry nor the inter-cavity distance.