Nonlinear optical oscillation dynamics in high-Q lithium niobate microresonators

Abstract

Recent advance of lithium niobate microphotonic devices enables the exploration of intriguing nonlinear optical effects. We show complex nonlinear oscillation dynamics in high-Q lithium niobate microresonators that results from unique competition between the thermo-optic nonlinearity and the photorefractive effect, distinctive to other device systems and mechanisms ever reported. The observed phenomena are well described by our theory. This exploration helps understand the nonlinear optical behavior of high-Q lithium niobate microphotonic devices which would be crucial for future application of on-chip nonlinear lithium niobate photonics.

Lithium niobate piezo-optomechanical crystals

“…The thermal relaxation rate Γ quantitatively agrees with the thermal-optical response time scale of ∼ 10 µs reported in Ref. [62] and is slightly faster due to smaller device volume. We note that for n c 5 × 10 4 , the thermal-optical shift starts to be dominated by the quadratic contribution, which agrees with the steady-state wavelength shift measurement in the last section.…”

High‐Q 2D Lithium Niobate Photonic Crystal Slab Nanoresonators

“…It shows a clear cubic dependence on the pump power, an intrinsic signature of third‐harmonic generation. To the best of our knowledge, this is the first time to observe third‐harmonic generation in on‐chip LN nanophotonic devices . The observed THG could contribute from cascaded SHG, direct THG from the third‐order optical nonlinearity, or a combination of these two processes.…”

“…We have demonstrated 2D LN PhC slab nanoresonators with optical Q up to 3.51 × 10 5 that is about three orders of magnitude higher than other 2D LN PhC nanoresonators reported to date . The high optical Q together with tight optical mode confinement results in intriguing nonlinear optical interactions, allowing us to observe both second‐ and third‐harmonic generation . Moreover, the devices exhibit specific polarization of the cavity modes, which enabled us to probe the intriguing anisotropy of nonlinear optical phenomena.…”

“…Lithium niobate (LN), known as “silicon of photonics,” exhibits outstanding electro‐optic, nonlinear optical, acousto‐optic, piezoelectric, photorefractive, pyroelectric, and photoconductive properties, promising for broad applications . The great application potential has attracted significant attention recently to develop LN photonic devices on chip‐scale platforms . However, realizing high‐quality 2D LN PhC structures remains significant challenge, which becomes the major obstacle hindering the exploration of optical phenomena in the nanoscopic scale that would potentially result in intriguing device characteristics and novel functionalities inaccessible by conventional means.…”

High-quality lithium niobate photonic crystal nanocavities

“…The overall blue shift is a typical feature of the photorefractive effect that originates from the electro-optic effect introduced by the space-charge electric field produced via photovoltaic drift current 49 . The slow relaxation of space charge distribution leads to a net decrease of refractive index which results in an overall blue shift of the cavity resonance 46,47,50 .…”