Sub‐Picosecond Response Time of a Hybrid VO₂:Silicon Waveguide at 1550 nm

Abstract

Hybrid material systems are a promising approach for extending the capabilities of silicon photonics. Given the weak electro‐optic and thermo‐optic effects in silicon, there is intense interest in integrating an ultrafast‐switching phase‐change material with a large refractive index contrast into the waveguide, such as vanadium dioxide (VO2). It is well established that the phase transition in VO2 thin films can be triggered by ultrafast, 800 nm laser pulses, and that pump‐laser fluence is a critical determinant of the recovery time of thin films irradiated by femtosecond pulses. However, thin‐film experiments are not reliable guides to a VO2:Si system for all‐optical, on‐chip switching because of the differences in VO2 optical constants in the telecommunication band, and the complex sample geometry and alignment issues in a waveguide geometry. This paper reports the first demonstration that the reversible, ultrafast photoinduced phase transition in VO2 can achieve sub‐picosecond response when small VO2 volumes are integrated into a silicon waveguide as the active element. The result suggests that VO2 can be pursued as a strong candidate for waveguide switching with sub‐picosecond on‐off times.

Tunable Mie-Resonant Dielectric Metasurfaces Based on VO2 Phase-Transition Materials

“…Importantly, the different effects shown could easily be shifted to other wavelengths by design, throughout the range of VO2 tunability (near-IR to far-IR). This interplay between Mie resonances and the phase-change metamaterials uncovers a great potential of tunable dielectric metasurfaces for manipulating light in a rapid manner as the phase transition can be driven by fast light pulses, 45,46 paving the way to nanoscale optical switches, modulators, and sensors based on all-dielectric Mie-resonant metasurfaces.…”

Toward Nonvolatile Switching in Silicon Photonic Devices

“…Very recently, sub‐picosecond switching times with switching energies down to 6 nJ have been demonstrated for VO 2 /Si photonic waveguides by using out‐of‐plane optical excitation. [ 105 ] However, the material change is volatile, and the strategies for enabling a nonvolatility switching performance have not yet been demonstrated in waveguide devices. In addition, VO 2 is also not favorable for developing phase actuators owing to the large optical loss in the metallic state.…”

“…[93,[101][102][103][104] Only very recently, sub-ps switching times with switching energies between 6 and 360 nJ have been reported for a hybrid VO 2 /Si photonic waveguide with out-of-plane optical pumping. [105] Therefore, a photothermal mechanism is still mostly dominant, and the difference in the timescales may be explained by the different characteristics of the control light source and the size of the VO 2 patch. Furthermore, the all-optical switching response remains volatile.…”

Toward nonthermal control of excited quantum materials: framework and investigations by ultrafast electron scattering and imaging

“…Crystal cracking upon rapid heating has also been a well-known problem [266] in studying bulk or epitaxially grown materials in the pump-probe studies [25]. To remediate these effects, employing free-standing nanobeams or microbeams [267,268] or small-volume [269] VO 2 crystals can not only preserve the intrinsic first-order transition characteristics but also maintain the integrity over repeated experimental cycles without causing the sample to crack.…”