ETD

• bound states in the continuum (BICs)
• metasurfaces
• microelectromechanical systems (MEMS)
• optomechanics
• polarization modulation
• trampoline resonators

My thesis work aimed at developing a polarization modulator in the infrared range, which exploits optomechanical interaction of Bound states In the Continuum (BICs) electromagnetic resonances and MicroElectroMechanical Systems (MEMS) vibrational modes. The topological nature of BICs, which form polarization vortices in the reciprocal space, can be exploited to rapidly switch the polarization of its eigenmodes by tilting the device via its torsional mechanical modes.
I focused on numerical simulations, experimental characterization, and device nanofabrication. Numerical results demonstrated the potential of the device as a linear polarization modulator: mechanical simulations showed significative angles of deflection of a trampoline resonator when exciting its first excited mode; photonic simulations showed the possibility to observe BICs hosted by a metasurface in the material of our final device. The experimental characterization, for which I built a dedicated setup in the lab, was carried out on two reference samples: mechanical motion of a Si3N4 suspended trampoline showed large deflection angles, as obtained via the optical lever method, and reflection spectra of a Si slab with a square array of circular holes showed narrow quasi-BIC resonances. The device nanofabrication, mostly performed at the University of Pisa while relying on an external company for a critical plasma etching, lead to about 30% yield which is a promising starting point to obtain the desired device.