Materials and devices for optical switching and modulation of photonic integrated circuits

Abstract

The drive towards photonic integrated circuits (PIC) necessitates the development of new devices and materials capable of achieving miniaturization and integration on a CMOS compatible platform. Optical switching: fast modulation and add-drop switches, key components in a PIC, were investigated. A MEMS-based approach was utilized to control switching in planar ring resonator waveguide structures. A switch extinction ratio of 15 dB, switch speed of 60 is and 1 mW operating power were demonstrated. A metal-insulator transition material, V02, was identified as a material with potential for enhancing the switch speed with speeds in excess of gigahertz rates with minimal device footprint. Fundamental material transport properties and nonstoichiometry in VO2 were characterized. Nonstoichiometry as high as 5% was measured. A Frenkel defect model was used to describe the behavior in V02 in which vanadium interstitials were attributed to be the dominant ionic defect in the reducing regime. Frozen-in vanadium interstitials, acting as shallow donors lying 20 meV below the conduction band in the semiconducting phase, enhance the low temperature conductivity and free carrier concentration.

(cont.) VO2 was shown to exhibit an activated mobility in its semiconducting and "metallic" phases with room temperature mobility estimated to be 5x10-2 cm2/Vs. Electrical switch contrasts of as high as -5000 and optical extinction ratios of approximately 16 dB were demonstrated. Free carrier absorption due to shallow donor vanadium interstitials was identified as a dominant absorption mechanism at near-IR wavelengths. Control of the degree of nonstoichiometry was shown to influence the near-IR absorption effects. To address the need for an integrated fast switch for data encoding, a thin film electro-optic (E-O) modulator, based on barium titanate (BaTiO3) or barium titanate-strontium titanate (SrTiO3) superlattices, was developed. Mach-Zhender E-O modulators were designed, fabricated with CMOS compatible processing steps and tested. Effective electro-optic values as high as 73pmN/V, 2.5 times better performance compared to commercial bulk LiNbO3 technology was demonstrated, with device area less than 30,000 [mu]2.