Research On The Optical Characteristics Of Hybrid Photonic-plasmonic Molecule

Compared with its electronic counterpart, the photonic molecule is regarded as one of the key components for a variety of optical applications due to their advantages of high speed, high bandwidth and low power, such as low-threshold semiconductor microlasers, optical switches, information processing and biochemical sensing, etc. However, the size of photonic devices is in the scale of several hundred of nanometer in practical applications due to the diffraction-limit. It greatly hinders the development of optoelectronic device integration. There is an urgent need for new mechanisms and technologies which can break the diffraction limit to realize optoelectronic integration with higher density and better performance. Surface plasmon is a very good solution to this problem. Surface plasmon polaritons are the collective oscillations of free electrons on the interface of metal and dielectric, which can effectively confine electromagnetic near field to subwavelength scale and thus break the diffraction limit. In recent years, researchers have found that the single optical disk based on the hybridization of surface plasmon and dielectric micro-cavity not only has high quality factor and small mode volume, but also can effectively reduce the size of the device to sub-wavelength dimension, which has exhibited considerable interests in the field of optical devices. However, there are no such reports, to the best of our knowledge, on the optical coupling between hybrid micro-cavities.In this paper, we focus on the coupling characteristics of the hybrid photonic-plasmonic molecule. The work we did includes two parts:Firstly, we propose the hybrid photonic-plasmonic molecule structure based on Si/metal, which is a sandwich-like geometry. The disk can support the whispering gallery (WG) mode. We have analyzed the relation between the coupling strength, the Q factor, the mode volume Veff with the coupling interval d. On the other hand, we have found and verified the phenomenon of whispering gallery mode splitting.Secondly, we study the far field emission characteristics of different WG modes in the hybrid photonic-plasmonic molecule. We first introduce the basic principle of near-to far-field transformation. Moreover, the far-field emission patterns of the coupling WG modes are investigated. The emission patterns of the hybrid photonic-plasmonic molecule show an enhanced directivity in the H-plane with fewer main beams of emission by varying the azimuthal mode number. Compared with photonic molecules, the hybrid photonic-plasmonic ones we propose have the advantages of high directivity similar to photonic molecules and subwavelength dimension while maintaining a high Q factor and a small mode volume.A new type of coupled resonator named "hybrid photonic-plasmonic molecule" comprising of two identical disks is studied in this paper. Its optical coupling properties are investigated by the three dimensional finite difference time domains (FDTD), such as mode splitting, Q factor enhancement and far-field emission. This paper provides a theoretical guideline for further optimizing the device performance and practically implementing this sort of hybrid micro-cavity in integrated photonic devices.