High‐Q 2D Lithium Niobate Photonic Crystal Slab Nanoresonators

Abstract

Lithium niobate (LN), known as the “silicon of photonics,” exhibits outstanding material characteristics with great potential for broad applications. Enhancing light–matter interaction on the nanoscale would result in intriguing device characteristics that enable new physical phenomena to be revealed and novel functionalities inaccessible by conventional means to be realized. High‐Q 2D photonic crystal (PhC) slab nanoresonators are particularly suitable for this purpose, which, however, remains an open challenge to be realized on the lithium niobate platform. Here, an important step is taken toward this direction, demonstrating 2D LN PhC slab nanoresonators with optical Q as high as 3.51 × 105, about three orders of magnitude higher than other 2D LN PhC structures reported to date. The high optical quality, tight mode confinement, together with specific polarization characteristics of the devices enable the peculiar anisotropy of photorefraction quenching and unique anisotropic thermo‐optic nonlinear response to be revealed. They also allow the observation of third‐harmonic generation in on‐chip LN nanophotonic devices, and a strong orientation‐dependent generation of the second harmonic.

Photon-level tuning of photonic nanocavities

“…To obtain the optical quality of the device, the laser wavelength is scanned across the cavity resonance and the device transmission is recorded by an oscilloscope. knowledge, this value of optical Q represents the highest optical Q reported to date for photonic crystal nanocavities made on monolithic lithium niobate platform [19][20][21][22][23][24] . It is the second single-crystalline photonic crystal nanocavity other than silicon ones 28 that is able to achieve optical Q above one million.…”

“…is incorporated into the cavity to enhance resonant dipole interactions 6 which unfortunately require sophisticated operation conditions such as high vacuum and/or cryogenic environment, challenging for implementation in a practical environment. To date, it remains a significant challenge to realize device control at room temperature and ambient environment with only photon-level optical energy, which represents the ultimate efficiency of nonlinear optics.In this paper, we report extremely efficient seamless wavelength tuning of photonic nanocavities, with an optical energy of only a couple photons, via a lithium niobate (LN) photonic crystal nanocavity that exhibits an optical Q as high as 1.41 million, the highest value reported to date for photonic crystal nanocavities made on monolithic LN platform [19][20][21][22][23][24] , to the best of our knowledge. The device simultaneously exhibits an effective mode volume as small as 0.78(λ /n) 3 (where λ is the optical wavelength in vacuum and n is the refractive index of LN).…”

“…1(c), the fundamental TE-like cavity mode is a dielectric mode with the optical field dominantly located inside the LN medium, which is crucial for the nonlinear optical process described below.The devices were fabricated on a 300-nm-thick x-cut single-crystalline LN thin film bonded on a 3-µm silicon dioxide layer sitting on a silicon substrate. The photonic crystal device structure was patterned with ZEP-520A positive resist via electron-beam lithography, which was then transferred to the LN layer with an Ar + plasma milling process 24,27 . The resist residue was removed by a further O + plasma etching.…”

“…In this paper, we report extremely efficient seamless wavelength tuning of photonic nanocavities, with an optical energy of only a couple photons, via a lithium niobate (LN) photonic crystal nanocavity that exhibits an optical Q as high as 1.41 million, the highest value reported to date for photonic crystal nanocavities made on monolithic LN platform [19][20][21][22][23][24] , to the best of our knowledge. The device simultaneously exhibits an effective mode volume as small as 0.78(λ /n) 3 (where λ is the optical wavelength in vacuum and n is the refractive index of LN).…”

“…The devices were fabricated on a 300-nm-thick x-cut single-crystalline LN thin film bonded on a 3-µm silicon dioxide layer sitting on a silicon substrate. The photonic crystal device structure was patterned with ZEP-520A positive resist via electron-beam lithography, which was then transferred to the LN layer with an Ar + plasma milling process 24,27 . The Finally, we used diluted hydrofluoric acid to undercut the buried oxide layer to form a suspended photonic crystal structure.…”