Photonic Structures for Optical Communication
SILICON MODULATORS USING METAL-INSULATOR SWITCHING OF VANADIUM DIOXIDE
We present silicon (Si) vanadium-dioxide (VO2) hybrid optical modulators motivated by the need for compact Si-compatible optical switches operating at THz speeds. VO2 is a functional oxide undergoing metal-insulator transition (MIT) near 67C, with huge changes in electrical resistivity and near-infrared transmission. The MIT can be induced thermally, optically (by ultra-fast laser excitation in less than 100 fs), and possibly with electric field. VO2 is easily deposited on Si and its ultrafast switching properties in the near-infrared can be used to tune the effective index of ring resonators in the telecommunication frequencies instead of depending on the weak electro-optic properties of silicon. In an all optical geometry, we have demonstrated photothermal modulation in a ring resonator geometry and modulation in both linear and ring resonator geometries in response to nanosecond optical pulses. Also in a linear geometry, we have demonstrated the potential for electrically triggering the MIT in an electro-optic absorption based modulator. Currently, we are pursuing methods to continue increasing device performance speed while simultaneously achieving high modulation depths and maintaining small device footprints.
(a) Optical transmission of the 1.5um radius hybrid Si-VO2 ring resonator as a function of wavelength, before and after photothermal triggering the MIT with a 532nm pump laser. The lines are Lorentzian fits. Inset: IR camera images revealing vertical radiation at a fixed probe wavelength. (b) Time dependent optical transmission (measured at resonant frequency when VO2 is in its insulating state) of ring resonator in response to varying pulse fluences.
(a) Schematic and (b) SEM of the linear absorption electro-optic modulator. (c) Measured optical transmission for varying electrical pulse durations.