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arXiv:2510.11965 · Science Advances

Ultrafast optical gating in a nonlinear lithium niobate microcavity

Ouri Karni, Chirag Vaswani, Thibault Chervy

Published Apr 17, 2026• 0 citations
arXivHTMLPDF

Abstract

Advances in optical simulation and computation have renewed interest in high-finesse optical cavities for enhancing light-matter interactions, engineering complex photonic band structures, and storing quantum information. However, the extended interaction times in these cavities dictate slow optical readout and limited control over system transients. Addressing this challenge, we demonstrate an ultrafast intracavity optical gating scheme in high-finesse, second-order nonlinear microcavities incorporating thin films of lithium niobate. A femtosecond optical gate pulse, tuned to the transparency region of the cavity's dielectric mirrors, instantaneously upconverts the intracavity field via sum-frequency generation. The upconverted pulse promptly exits the cavity, providing space- and time-resolved information on the intracavity field. We validate this approach by tracking the dynamics of multiple resonant modes excited in a plano-concave microcavity, comparing well with analytical models. In addition, we demonstrate that intracavity difference-frequency generation can efficiently instantiate the cavity fields. Fully compatible with low-temperature microcavity experiments, this gating scheme enables future real-time control of light-matter interactions or quantum-optical state manipulations.

DOI
10.1126/sciadv.aed3664

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We have generated squeezed states of light by the process of second harmonic conversion within an optical cavity resonant at both fundamental and harmonic frequencies. The experiment consists of a standing-wave cavity containing a crystal of lithium niobate doped with magnesium oxide and driven by the field from a frequency-stabilized Nd:YAG laser (incident power, ~10 mW). The total field reflected from the cavity illuminates a pair of high quantum efficiency photodiodes, whose individual photocurrents are summed. Observations of squeezing are made by analyzing the spectral density of fluctuations for this sum photo-current while the cavity detuning is scanned through resonance. An intensity regulator holds the reflected light intensity constant during the scan by control of the incident light level. Reductions in photocurrent fluctuations of 12% relative to the vacuum-state or shot-noise level are achieved for frequency offsets near 4 MHz. Since significantly higher degrees of squeezing are predicted by our theoretical analysis, we discuss those processes that currently limit the observed noise reduction, including phase noise produced by the intracavity crystal in the absence of nonlinear conversion.
Electro-optical control of on-chip photonic devices is an essential tool for efficient integrated photonics. Lithium niobate on insulator (LNOI) is an emerging platform for on-chip photonics due to its large electro-optic coefficient and high nonlinearity [1]. Integrating quantum emitters into LNOI would extend their versatile use in classic photonics to quantum computing and communication [2, 3]. Here, we incorporate single rare-earth ions (REI) quantum emitters in electro-optical tunable lithium niobite (LN) thin films and demonstrate control of LN microcavities coupled to REI over a frequency range of 160 GHz with 5 \mus switching speed. Dynamical control of the cavities enables the modulation of the Purcell enhancement of the REIs with short time constants. Using the Purcell enhancement, we show evidence of detecting single Yb3+ ions in LN cavities. Coupling quantum emitters in fast tunable photonic devices is an efficient method to shape the waveform of the emitter [4]. It also offers a platform to encode quantum information in the integration of a spectral-temporal-spatial domain to achieve high levels of channel multiplexing, as well as an approach to generate deterministic single-photon sources [5, 6].
Electro-optical control of on-chip photonic devices is an essential tool for efficient integrated photonics. Lithium niobate on insulator (LNOI) is an emerging platform for on-chip photonics due to its large electro-optic coefficient and high nonlinearity. Integrating quantum emitters into LNOI would extend their versatility in classic photonics to quantum computing and communication. Here, we incorporate rare-earth ion (REI) quantum emitters into electro-optical tunable lithium niobite (LN) thin films and demonstrate control of LN microcavities coupled to REIs over a frequency range of 160 GHz with 5 µs switching speed. Dynamic control of the cavities enables modulation of the Purcell enhancement of REIs with short time constants. Using Purcell enhancement, we show evidence of detecting single Y b 3 + ions in LN cavities. Coupling quantum emitters in fast tunable photonic devices is an efficient method to shape the waveform of the emitter. It also offers a platform to encode quantum information in the integration of a spectral–temporal–spatial domain to achieve high levels of channel multiplexing, as well as an approach to generate deterministic single-photon sources.
Thin-film lithium niobate is a promising integrated nonlinear photonics platform due to its strong second- and third-order nonlinear response. However, these off-resonant nonlinear mechanisms typically require high input optical powers beyond the microwatt level. In this work, we achieve optical nonlinearity at picowatt input power by incorporating the strong resonant nonlinear absorption of rare-earth ions into high-quality-factor thin-film lithium niobate ring resonators. By precisely controlling the output coupling strength of the resonator, we demonstrate multiple nonlinear response behaviors including optical limiting and negative differential transmission, in which the output power decreases with increasing input power. These nonlinear responses are well described by a model of an ensemble of inhomogeneously broadened three-level atoms coupled to a cavity. We also demonstrate optical bistability and hysteresis of the device with a bistable lifetime of approximately 3 ms. This versatile low-power nonlinear device can serve as a fundamental building block for nonlinear thin-film lithium niobate photonic circuits.