Xiyuan Lu

Silicon carbide microdisk resonator

We demonstrate a silicon carbide (SiC) microdisk resonator with an intrinsic optical quality factor of 6.19×10(3), fabricated on the 3C-SiC-on-Si platform. We characterize the temperature dependence of the cavity resonance and obtain a thermo-optic coefficient of 2.92×10(-5)/K for 3C-SiC. Our simulations show that the device exhibits great potential for cavity optomechanical applications.

High-frequency silicon optomechanical oscillator with an ultralow threshold

We demonstrate a highly efficient optomechanical oscillator based upon a small silicon microdisk resonator with a 2-μm radius. The device exhibits a strong optomechanical coupling of 115 GHz/nm and a large intrinsic mechanical frequency-Q product of 4.32 × 10(12) Hz. It is able to operate at a high frequency of 1.294 GHz with an ultralow threshold of 3.56 μW while working in the air environment. The high efficiency, high frequency together with the structural compactness and CMOS compatibility of our device enables great potential for broad applications in photonic-phononic signal processing, sensing, and metrology.

Silicon-chip source of bright photon pairs.

Integrated quantum photonics relies critically on the purity, scalability, integrability, and flexibility of a photon source to support diverse quantum functionalities on a single chip. Here we report a chip-scale photon-pair source on the silicon-on-insulator platform that utilizes dramatic cavity-enhanced four-wave mixing in a high-Q silicon microdisk resonator. The device is able to produce high-quality photon pairs at different wavelengths with a high spectral brightness of 6.24×10(7) pairs/s/mW(2)/GHz and photon-pair correlation with a coincidence-to-accidental ratio of 1386 ± 278 while pumped with a continuous-wave laser. The superior performance, together with the structural compactness and CMOS compatibility, opens up a great avenue towards quantum silicon photonics with capability of multi-channel parallel information processing for both integrated quantum computing and long-haul quantum communication.

High Q silicon carbide microdisk resonator

We demonstrate a silicon carbide (SiC) microdisk resonator with optical Q up to 5.12 × 104. The high optical quality, together with the diversity of whispering-gallery modes and the tunability of external coupling, renders SiC microdisk a promising platform for integrated quantum photonics applications.

Optical Kerr nonlinearity in a high-Q silicon carbide microresonator

We demonstrate a high-Q amorphous silicon carbide (a-SiC) microresonator with optical Q as high as 1.3 × 10(5). The high optical quality allows us to characterize the third-order nonlinear susceptibility of a-SiC. The Kerr nonlinearity is measured to be n2 = (5.9 ± 0.7) × 10(−15) cm(2)/W in the telecom band around 1550 nm. The strong Kerr nonlinearity and high optical quality render a-SiC microresonators a promising platform for integrated nonlinear photonics.

High-frequency and high-quality silicon carbide optomechanical microresonators.

Silicon carbide (SiC) exhibits excellent material properties attractive for broad applications. We demonstrate the first SiC optomechanical microresonators that integrate high mechanical frequency, high mechanical quality, and high optical quality into a single device. The radial-breathing mechanical mode has a mechanical frequency up to 1.69 GHz with a mechanical Q around 5500 in atmosphere, which corresponds to a fm · Qm product as high as 9.47 × 1012 Hz. The strong optomechanical coupling allows us to efficiently excite and probe the coherent mechanical oscillation by optical waves. The demonstrated devices, in combination with the superior thermal property, chemical inertness, and defect characteristics of SiC, show great potential for applications in metrology, sensing, and quantum photonics, particularly in harsh environments that are challenging for other device platforms.

High-Q silicon carbide photonic-crystal cavities

We demonstrate one-dimensional photonic-crystal nanobeam cavities in amorphous silicon carbide. The fundamental mode exhibits intrinsic optical quality factor as high as 7.69 × 104 with mode volume ∼0.60(λ/n)3 at wavelength 1.5 μm. A corresponding Purcell factor value of ∼104 is the highest reported to date in silicon carbide optical cavities. The device exhibits great potential for integrated nonlinear photonics and cavity nano-optomechanics.

Twin photon pairs in a high-Q silicon microresonator

We report the generation of high-purity twin photon pairs in a high-Q silicon microdisk resonator, with a pair flux of 5.31 × 10s pairs/s within a bandwidth of 0.73 GHz, and a high CAR as large as 155, the highest value reported to date for twin photon pairs.

Selective engineering of cavity resonance for frequency matching in optical parametric processes

We propose to selectively engineer a single cavity resonance to achieve frequency matching for optical parametric processes in high-Q microresonators. For this purpose, we demonstrate an approach, selective mode splitting (SMS), to precisely shift a targeted cavity resonance, while leaving other cavity modes intact. We apply SMS to achieve efficient parametric generation via four-wave mixing in high-Q silicon microresonators. The proposed approach is of great potential for broad applications in integrated nonlinear photonics.

Heralding single photons from a high-Q silicon microdisk

Integrated quantum photonics has recently attracted considerable attention due to the promise of realizing chip-scale quantum information processing with unprecedented capability and complexity. Their implementation relies essentially on a high-quality chip-scale photon source to support diverse quantum functionalities. Microresonator-based photon sources are a promising solution for generating bright, pure, and single-mode photons with excellent power efficiencies. However, their low Klyshko efficiency, typically around a few percentages, is a major bottleneck restricting this type of device from practical quantum applications. In this paper, we improve the Klyshko efficiency of a telecom-band heralded single-photon source from a high-Q silicon microdisk to as high as 48%. We characterize the photon antibunching properties at the same time, with a conditional self-correlation below 0.01 at a detected photon pair flux up to 0.002 counts per 5 ns gate at a repetition rate of 3 MHz. At an optical peak power of 73 μW, the photon source has a large photon flux of 0.01 counts per gate, a high Klyshko efficiency of 46%, and a strong photon antibunching with a conditional self-correlation smaller than 0.05. In particular, we find a relation between the Klyshko efficiency and high-order correlations for the first time to our knowledge. This relation contributes to the understanding of photon statistics in the heralding process and also provides a method to verify the Klyshko efficiency. The improved heralding efficiency, together with the great photon antibunching property and power efficiency, renders the microresonator-based photon source promising for diverse quantum applications, including linear-optical quantum computing and quantum key distribution.