Tunable Nano-photonic Devices

Abstract

For high speed photonic systems and networks, encoding electronic signal onto optical carrier requires electro-optic modulators in which electromagnetic fields of the optical carrier can be manipulated electronically. The central focus of this research is twofold. First, tunable properties and tuning mechanisms of different optical materials like Graphene, Vanadium di-oxide, and Indium Tin Oxide are characterized systematically in telecommunication wavelength region. Then, these materials are implemented to design novel nano-photonic devices such as electrooptic modulators and tunable couplers with high efficiency and miniature footprint suitable for photonic integration. Specifically, we experimentally investigated the complex index of graphene in near infrared wavelength through the reflectivity measurement on a SiO2/Si substrate. The measured change of reflectivity as the function of applied gate voltage is highly correlated with theoretical modeling based on the Kubo formula. Based on a fiber-optic pump-probe setup we demonstrated that short optical pulses can be translated from pump wavelength to probe wavelength through dielectric-to-metal phase transition of vanadium di-oxide. In this process, pump leading edge induced optical phase modulation on the probe is converted into an intensity modulation through an optical frequency discriminator. We also theoretically modeled the permittivity of Indium Tin-Oxide with different level of doping concentration in near infrared region. We proposed an ultra-compact electro-optic modulator based on switching plasmonic resonance “ON” and “OFF” of ITO-on-graphene via tuning of graphene chemical potential through electrical gating. The plasmonic resonance of ITO-on-graphene significantly enhances the electromagnetic field interaction with graphene which allows the reduction of modulator size compare to graphene based modulators without ITO. We presented a scheme of modeiv multiplexed near infrared modulator by tuning of ITO permittivity as the function of carrier density through externally applied voltage. The wisely patterned ITO on top of an SOI ridge waveguide portrayed the independent modulation of two orthogonal modes simultaneously, which enhances functionality per area for on-chip photonic applications. We proposed a theoretical model of tunable anisotropic metamaterial composed of periodic layers of graphene and Hafnium Oxide where transversal permittivity can be tuned via changing the chemical potential of graphene. A novel metamaterial assisted tunable photonic coupler is designed by inserting the proposed artificial tunable metamaterial in the coupling region of a parallel waveguide coupler. The coupling efficiency can be tuned by changing the permittivity of metamaterial through external electrical gating.