[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Effective Coupling of a Plasmonic Nanorod to a Microsphere Resonator

摘要： Coupled photonic-plasmonic systems have already proven successful as ultra-sensitive sensors with the potential of single virus detection. Such systems are e.g. composed of a plasmonic nanoparticle in vicinity of an optical resonator usually in the form of a microsphere, a mirroring or a microdisk. These systems are proven highly sensitive due to their large quality factor and are thus utilized as bio, pressure, gas or temperature sensors. When a plasmonic nanoparticle is positioned near such resonator, coupling of the plasmonic and photonic modes can result in an ultra-sensitive biosensor, since nanoparticle presence enhance ambient refractive index (RI) variation sensitivity. In this paper, photonic-plasmonic coupling of a gold nanorod in close vicinity of a silica microsphere is simulated in order to investigate various types of coupling settings in such systems. The presence of the nanorod results in a frequency shift as well as in a reduction of the quality factor, which are both highly dependent on nanorod properties such as size, distance between the particle and the sphere as well as the nanorod orientation relative to the sphere surface. A single gold nanorod is positioned in 50nm distance to a 15.5μm silica microsphere which supports a whispering gallery mode at 1550nm and both resonance frequency and quality factor are computed using the simulation platform COMSOL Multiphysics. The nanorod orientation is altered starting from the tangential direction with respect to the sphere surface (0o) to the perpendicular direction (90o). In the Fig 1a) the quality factor together with the damping constant is shown as a function of the nanorod orientation for at an operating wavelength of 1550nm. The 90o direction results in higher quality factor as well as a better mode stability although the frequency shift associated to a 90o turn is only about 10GHz. In Fig 1b) the frequency shift and quality factor for the perpendicular nanorod versus ambient medium RI is plotted, which confirms the ultra-sensitivity of the designed optical resonator up to a 10-3 RI shift. The electric field distribution outside and inside of the nanorod is illustrated in Fig. 1c) for the three directions 90o, 45o and 0o where the perpendicular nanorod shows the weakest interaction with the excited whispering gallery mode and thus yields the largest quality factor.