Vanadium dioxide (VO(2)) is a promising reconfigurable optical material and has long been a focus of condensed matter research owing to its distinctive semiconductor-to-metal phase transition (SMT), a feature that has stimulated recent development of thermally reconfigurable photonic, plasmonic, and metamaterial structures. Here, we integrate VO(2) onto silicon photonic devices and demonstrate all-optical switching and reconfiguration of ultra-compact broadband Si-VO(2) absorption modulators (L < 1 μm) and ring-resonators (R ~ λ(0)). Optically inducing the SMT in a small, ~0.275 μm(2), active area of polycrystalline VO(2) enables Si-VO(2) structures to achieve record values of absorption modulation, ~4 dB μm(-1), and intracavity phase modulation, ~π/5 rad μm(-1). This in turn yields large, tunable changes to resonant wavelength, |Δλ(SMT)| ~ 3 nm, approximately 60 times larger than Si-only control devices, and enables reconfigurable filtering and optical modulation in excess of 7 dB from modest Q-factor (~10(3)), high-bandwidth ring resonators (>100 GHz). All-optical integrated Si-VO(2) devices thus constitute platforms for reconfigurable photonics, bringing new opportunities to realize dynamic on-chip networks and ultrafast optical shutters and modulators.

The debate about whether the insulating phases of vanadium dioxide (VO 2 ) can be described by correlations. We also found a potential candidate for the newly-found metallic monoclinic phase.

Phase-change materials (PCMs) have emerged as promising active elements in silicon (Si) photonic systems. In this work, we design, fabricate, and characterize a hybrid Si-PCM optical switch. By integrating vanadium dioxide (a PCM) within a Si photonic waveguide, in a non-resonant geometry, we achieve ~10 dB broadband optical contrast with a PCM length of 500 nm using thermal actuation.

Ultrafast phase transitions induced by femtosecond light pulses present a new opportunity for manipulating the properties of materials. Understanding how these transient states are different from, or similar to, their thermal counterparts is key to determining how materials can exhibit properties that are not found in equilibrium. In this paper, we reexamine the case of the light-induced insulator-metal phase transition in the prototypical, strongly correlated material VO 2 , for which a nonthermal Mott-Hubbard transition has been claimed. Here, we show that heat, even on the ultrafast timescale, plays a key role in the phase transition. When heating is properly accounted for, we find a single phase-transition threshold corresponding to the thermodynamic structural insulator-metal phase transition, and we find no evidence of a hidden transient Mott-Hubbard nonthermal phase. The interplay between the initial thermal state and the ultrafast transition may have implications for other transient states of matter.

We use resonant soft X-ray holography to image the insulator-metal phase transition in vanadium dioxide with element and polarization specificity and nanometer spatial resolution. We observe that nanoscale inhomogeneity in the film results in spatial-dependent transition pathways between the insulating and metallic states. Additional nanoscale phases form in the vicinity of defects which are not apparent in the initial or final states of the system, which would be missed in area-integrated X-ray absorption measurements. These intermediate phases are vital to understand the phase transition in VO, and our results demonstrate how resonant imaging can be used to understand the electronic properties of phase-separated correlated materials obtained by X-ray absorption.