Engineering the mode parity of the ground state in photonic crystal molecules.

We propose a way to engineer the design of photonic molecules, realized by coupling two photonic crystal cavities, that allows an accurate control of the parity of their ground states. The spatial distribution of the fundamental mode of photonic molecules can be tuned from a bonding to an antibonding character by a local and continuous modification of the dielectric environment in between the two coupled cavities. In the systems that we investigate the transition could be experimentally accomplished by post-fabrication methods in either a reversible or an irreversible way. We notably find that the mode parity exchange is tightly related to a dramatic variation of the far field emission pattern, leading to the possibility to exploit these systems and techniques for future applications in optoelectronics.