Lithium Niobate Microring Resonators Research Articles

Ultra-efficient frequency conversion in quasi-phase-matched lithium niobate microrings

We demonstrate quasi-phase-matched frequency conversion in a chip-integrated lithium niobate microring resonator, whose normalized efficiency reaches 230,000%/W or 10−6 per single photon.

High performance fully etched isotropic microring resonators in thin-film lithium niobate on insulator platform.

We present our design, fabrication, and experimental results for very high-performance isotropic microring resonators with small radii (∼ 30 µm) based on single-mode strip waveguides and transverse magnetic (TM) polarization in a fully etched lithium niobate (Z-cut) thin-film on insulator. The loss of the devices is predicted to be < 10 dB/cm, and is measured to be ∼ 7 dB/cm. The measured optical responses of microring resonators exhibit an extinction of ∼ 25 dB (close to critical coupling), a 3 dB optical bandwidth of 49 pm (∼ 6 GHz) for all-pass structures, an extinction of ∼ 10 dB for add-drop structures, and a free spectral range of ∼ 5.26 nm, all of which are in excellent agreement with the design. This work is the first step towards ultra-compact and fully isotropic optical modulators in thin-film lithium niobate on insulator.

Soliton microcomb generation at 2 μm in z-cut lithium niobate microring resonators.

Chip-based soliton frequency combs have been demonstrated on various material platforms, offering broadband, mutually coherent, and equally spaced frequency lines desired for many applications. Lithium niobate (LN), possessing both second- and third-order optical nonlinearities, as well as integrability on insulating substrates, has emerged as a novel source for microcomb generation and controlling. Here we demonstrate mode-locked soliton microcombs generated around 2μm in a high-Q z-cut LN microring resonator. The intracavity photorefractive effect is found to be still dominant over the thermal effect in the 2μm region, which facilitates direct accessing soliton states in the red-detuned regime, as reported in the telecom band. We also find that intracavity stimulated Raman scattering is greatly suppressed when moving the pump wavelength from the telecom band to 2μm, thus alleviating Raman-Kerr comb competition. This Letter expands mode-locked LN microcombs to 2μm, and could enable a variety of potential applications based on LN nanophotonic platform.

Optical Parametric Generation in a Lithium Niobate Microring with Modal Phase Matching

The lithium niobate integrated photonic platform has recently shown great promise in nonlinear optics on a chip scale. Here, we report second-harmonic generation in a high-Q lithium niobate microring resonator through modal phase matching, with a conversion efficiency of 1,500% W$^{-1}$. Our device also allows us to observe difference-frequency generation in the telecom band. Our work demonstrates the great potential of the lithium niobate integrated platform for nonlinear wavelength conversion with high efficiencies.

Dispersion engineered high quality lithium niobate microring resonators.

Lithium niobate (LN) exhibits outstanding material properties with great potential for many applications. Recent advance in LN integrated photonics on chip-scale platforms has shown significant advantages in device engineering and functionality innovation. Precise engineering of group-velocity dispersion (GVD) is crucial for many important nonlinear photonic applications. In this paper, we demonstrate high-Q LN microring resonators, with optical Q above 1 million, whose GVD can be flexibly controlled in both normal and anomalous dispersion regimes, with a value between -0.128 ps2/m and 0.043 ps2/m in the telecom band, by controlling the device cross section and by utilizing the birefringence. We are able to achieve a small anomalous GVD of -0.015 ps2/m that is even smaller than that of a silica optical fiber. The flexible engineering of GVD paves a critical step towards broad nonlinear photonic applications in high-Q LN microring resonators.

Nanophotonic lithium niobate electro-optic modulators.

Since the emergence of optical fiber communications, lithium niobate (LN) has been the material of choice for electro-optic modulators, featuring high data bandwidth and excellent signal fidelity. Conventional LN modulators however are bulky, expensive and power hungry, and cannot meet the growing demand in modern optical data links. Chip-scale, highly integrated, LN modulators could offer solutions to this problem, yet the fabrication of low-loss devices in LN thin films has been challenging. Here we overcome this hurdle and demonstrate monolithically integrated LN electro-optic modulators that are significantly smaller and more efficient than traditional bulk LN devices, while preserving LN's excellent material properties. Our compact LN electro-optic platform consists of low-loss nanoscale LN waveguides, micro-ring resonators and miniaturized Mach-Zehnder interferometers, fabricated by directly shaping LN thin films into sub-wavelength structures. The efficient confinement of both optical and microwave fields at the nanoscale dramatically improves the device performances featuring a half-wave electro-optic modulation efficiency of 1.8 V∙cm while operating at data rates up to 40 Gbps. Our monolithic LN nanophotonic platform enables dense integration of high-performance active components, opening new avenues for future high-speed, low power and cost-effective communication networks.

Rib Microring Resonators in Lithium Niobate on Insulator

Rib microring resonators were fabricated via electron beam lithography and ion milling in lithium niobate on insulator (LNOI). LNOI is a single crystalline thin film of lithium niobate (LiNbO3) bonded to 1.8 $\mu \text{m}$ of SiO2 and an LiNbO3 substrate. Measurement results show a $Q$ -factor of 2800 as well as a modulation depth of 18.7 dB.

Free-Standing Lithium Niobate Microring Resonators for Hybrid Integrated Optics

We report on the fabrication of free-standing microrings using ion-sliced lithium niobate thin films bonded by benzocyclobutene on a lithium niobate substrate. The microrings can be detached from the benzocyclobutene layer using standard clean-1 solution and transferred onto any host substrate. This approach is suitable for building hybrid integrated optics devices with laterally and vertically coupled lithium niobate microring resonators. Gallium nitride was identified as a suitable material for the port waveguides in such a device due to the refractive index similar to lithium niobate. In our study, we transferred lithium niobate microrings on top of gallium nitride waveguides and aligned them for vertical coupling using a micropositioning tool. Transverse-electric-wave transmission spectra of the microring resonators with a radius of 20 ¿m exhibited a free spectral range of 8.1 nm and a finesse of ~ 23 at 1.55- ¿m wavelength. The resonance dips in these spectra showed an extinction ratio of up to 12 dB.

Optical Microring Resonators in Fluorine-Implanted Lithium Niobate for Electrooptical Switching and Filtering

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We present a new approach for the fabrication of electrooptically tunable microring resonators in lithium niobate. Planar optical waveguides for vertical light confinement <formula formulatype="inline"><tex Notation="TeX">$(\Delta n_{ o} = 0.17)$</tex></formula> are produced by fluorine ion implantation. Optical microrings and bus waveguides are then formed by laser lithography masking and Ar<formula formulatype="inline"><tex Notation="TeX">$^{+}$</tex> </formula> plasma etching. Electrodes are optically isolated from the optical microrings by a polyvinyl alcohol buffer layer with a high dielectric constant (<formula formulatype="inline"><tex Notation="TeX">$\varepsilon \sim 70$</tex> </formula> at 10 Hz) to improve electrooptic tuning. The microrings with a radius of 80 <formula formulatype="inline"><tex Notation="TeX">$\mu$</tex> </formula>m exhibit optical resonances with a modulation depth of 11 dB, a free spectral range of 2 nm, and an electrooptical tunability of 10 pm/V. </para>