Current-Controlled Optical Modulation in Thin VO2 Wires

Abstract

We measured the current-voltage and infrared optical transmission characteristics of thin film VO 2 wires over the metal-insulator phase transition. The phase transition had electrical or thermal characteristics depending on the wire geometry and applied current.OCIS codes: (160.4760) Optical properties, (160.2100) Electro-optic materials, (160.3130) Integrated optics materials IntroductionThe dimensions of state-of-art optoelectronic devices are often limited to tens of microns, mainly due to the weak changes in the real or imaginary parts of the refractive index in conventional optical materials, such as silicon, germanium, lithium niobate, and compound semiconductors, with applied electrical signals. The large dimensions of these devices increase the real estate requirement and energy consumption of optoelectronic devices. For the ultimate miniaturization of optoelectronic devices, highly tunable materials should be considered.The phase transition material, vanadium dioxide, VO 2 , has attracted significant interest in the field of micro-and nano-photonics in recent years. VO 2 can reversibly change between a metallic and insulator phase when it is heated beyond the transition temperature, T > 67 0 C, but the phase transition can also be induced electronically, optically, and mechanically. Not only does the electrical conductivity of the material change by several orders of magnitude across the phase transition, the real and imaginary parts of the refractive index also change by O(1) in the telecom wavelength bands [1] . VO 2 has recently been utilized on plasmonic and silicon devices to achieve compact (< 5 m long) and low power optical switches with large extinction ratios > 10 dB [1,2]. A drawback is that the device operation used the thermo-optic switching of VO 2 , which had switching times in the range of tens of microseconds.To improve upon the performance, phase transition of VO 2 needs to be better understood. In this work, we report the first directly imaged electrically-induced optical modulation of thin VO 2 wires at the infrared wavelengths near 1550 nm. We find that the geometry of the wire significantly affects the phase transition. Under some conditions, we can observe a two-step phase transition in VO 2 , which we can separately attribute to thermally and electronically induced effects. This result opens the path toward high-speed VO 2 optoelectronic devices that suppress the thermally-induced transition.