VO2 phase change control of au nanorod emission enhancement of magnetic dipolar emitters

In this work, we combine the enhancement of the emitter efficiency due to the proximity of a resonant nanostructure, and the possibility to modulate it by means of a thin layer of a phase change material (PCM). PCMs have been used as active subwavelength elements that can switch between the phases that differ in electric and optical properties. The phase change results in a modulation of amplitude or phase of transmission or reflection over nanoscale propagation lengths, and it is compatible with fast optical systems [1,2]. Vanadium Dioxide (VO 2 ) is a promising candidate for nanoscale modulation since it shows dramatic contrast in its complex refractive index as it undergoes a structural phase transition from monoclinic (semiconductor) to rutile (metallic) phase at 68°C [3], induced thermally, electrically or optically. The proposed structure can be fabricated as follows: a thin V0 2 layer is deposited on a glass substrate, and covered by a thin spacer layer of silica, which is doped by luminescent ions; above the spacer, Au nanorods are added to provide the plasmonic resonant enhancement. Sandwiched magnetic dipoles feel strong resonance when V0 2 is metallic due to the strong magnetic field arising from the current loops between Au nanorod and V0 2 ; this resonance blue-shifts and decreases when V0 2 is dielectric. We first maximize the absorption change between the two phases at the emission line of Er 3+ , i.e. 1540 nm. With these optimized geometric parameters, we investigate emission of single dipoles in the layer under the nanorod, considering different positions, types, and orientations. We show the power emitted to the far-field by the magnetic dipole, averaged over the positions under the nanorod. We show that the emitted far-field follows the high contrast at the resonant wavelength of the optimized absorption, proving the control of the enhanced emission and its switching off. Finally, we investigate the influence of the periodicity, as the upper part of the design can be fabricated as a patterned 2D array of nanorods. We believe that such an approach can be of great importance for active modulation of efficient light sources at the nanoscale.