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Optics Express

High-brightness photon-pair source based on high-Q multimode waveguide racetrack resonator

Jinzhao Wang, Zheng Cao, Jiewen Li, Yuanlin Li, Kunrun Lu, Xin Hua, Xi Xiao, Jianan Duan, Zibo Miao, Dongpeng Kang, Feng He, Xiaochuan Xu

Published Sep 26, 2025• 2 citations
Publisher

Abstract

Efficient generation of correlated photon pairs through spontaneous four-wave mixing (SFWM) in silicon devices serves as a crucial resource for integrated quantum photonic technologies. Enhancing the intracavity field in high-quality-factor (Q) resonators enables energy-efficient photon-pair generation, with the photon-pair generation rate (PGR) scaling cubically with the Q factor. In this work, we demonstrate a high-brightness on-chip photon-pair source based on a racetrack resonator with a high Q factor of 1.75 × 105, fabricated on a silicon-on-insulator (SOI) platform requiring only a single-etch process. By combining uniform multimode waveguides with optimized Euler bends, we suppress fundamental mode loss and minimize round-trip cavity dispersion, thereby improving both field enhancement and frequency matching for SFWM processes. With a continuous-wave pump of only 44.67 µW, we achieve an on-chip brightness of 1.54 GHz·mW−2·nm−1. These results establish a fabrication-friendly and efficient photon-pair source architecture for integrated quantum photonic systems.

DOI
10.1364/oe.575161

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Efficient generation of correlated photon pairs through spontaneous four-wave mixing (SFWM) in silicon devices serves as a crucial resource for integrated quantum photonic technologies. Enhancing the intracavity field in high-quality-factor (Q) resonators enables energy-efficient photon-pair generation, with the photon-pair generation rate (PGR) scaling cubically with the Q factor. In this work, we demonstrate a high-brightness on-chip photon-pair source based on a racetrack resonator with a high Q factor of 1.75 × 105, fabricated on a silicon-on-insulator (SOI) platform requiring only a single-etch process. By combining uniform multimode waveguides with optimized Euler bends, we suppress fundamental mode loss and minimize round-trip cavity dispersion, thereby improving both field enhancement and frequency matching for SFWM processes. With a continuous-wave pump of only 44.67 µW, we achieve an on-chip brightness of 1.54 GHz·mW−2·nm−1. These results establish a fabrication-friendly and efficient photon-pair source architecture for integrated quantum photonic systems.
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.
Entangled photon-pair sources are essential components for emerging quantum information-processing technologies. Among various platforms, on-chip microresonators offer strong potential due to their resonant enhancement and suitability for wafer-scale integration. In this study, we demonstrate ultrabright entangled photon-pair generation from high- Q silicon microring resonators. By optimizing the device geometry and coupling configuration to suppress sidewall scattering and selectively excite the fundamental mode, we achieve single-mode resonance with an intrinsic Q -factor of 1.26 × 10 6 using only standard fabrication processes available in CMOS foundries. The resulting high- Q resonator yields a record-high brightness coefficient of 3.9 × 10 9 Hz/GHz/mW 2 . At an on-chip pump power of 240 μW, we obtain a maximum brightness of 22.0 MHz/GHz and a maximum photon-pair generation rate of 9.19 MHz. At a low-pump power of 10 μW, Franson-type two-photon interference exhibits a visibility of 98.0 ± 0.2%, confirming high-quality time–energy entanglement. These results show that narrow bandwidth and high generation rate can be achieved simultaneously in CMOS-compatible silicon photonic sources, thereby advancing their use in quantum repeaters and scalable quantum networks.
The intrinsic third-order nonlinearity in silicon has proven it to be quite useful in the field of quantum optics. Silicon is suitable for producing time-correlated photon pairs that are sources of heralded single-photon states for quantum integrated circuits. A quantum signal source in the form of single photons is an inherent requirement for the principles of quantum key distribution technology for secure communications. Here, we present numerical simulations of a silicon ring with a 6 μ m radius side-coupled with a bus waveguide as the source for the generation of single photons. The photon pairs are generated by exploring the process of degenerate spontaneous four-wave mixing (SFWM). The free spectral range (FSR) of the ring is quite large, simplifying the extraction of the signal/idler pairs. The phase-matching condition is considered by studying relevant parameters like the dispersion and nonlinearity. We optimize the ring for a high quality factor by varying the gap between the bus and the ring waveguide. This is the smallest ring studied for photon pair generation with a quality factor in the order of 10 5 . The width of the waveguides is chosen such that the phase-matching condition is satisfied, allowing for the propagation of fundamental modes only. The bus waveguide is pumped at one of the ring resonances with the minimum dispersion (1543.5 nm in our case) to satisfy the principle of energy conservation. The photon pair generation rate achieved is comparable to the state of the art. The photon pair sources exploiting nonlinear frequency conversion/generation processes is a promising alternative to atom-like single-photon emitters in the field of integrated photonics. Such miniaturized structures will benefit future on-chip architectures where multiple single-photon source devices are required on the same chip.
To achieve photon-pair generation scaling, we optimize the quality factor of microring resonators for efficient continuous-wave-pumped spontaneous four-wave mixing. Numerical studies indicate that a high intrinsic quality factor makes high pair rate and pair brightness possible, in which the maximums take place under overcoupling and critical-coupling conditions, respectively. We fabricate six all-pass-type microring resonator samples on a silicon-on-insulator chip involving gap width as the only degree of freedom. The signal count rate, pair brightness, and coincidence rate of all the samples are characterized, which are then compared with the modified simulations by taking the detector saturation and nonlinear loss into account. Being experimentally validated for the first time to the best of our knowledge, this work explicitly demonstrates that reducing the round-trip loss in a ring cavity and designing the corresponding optimized gap width are more effective to generate high-rate or high-brightness photon pairs than the conventional strategy of simply increasing the quality factor. (C) 2018 Chinese Laser Press
We demonstrate a high-brightness on-chip photon pair source based on a high-Q racetrackshaped silicon microresonator, achieving a quality factor of approximately 1.75×1051.75 \times 10^{5}1.75×105 and an on-chip photon pair generation brightness of 9.8MHz⋅mW−1⋅nm−19.8 \text{MHz} \cdot \text{mW}^{-1} \cdot \text{nm}^{-1}9.8MHz⋅mW−1⋅nm−1 .
Photon-pair sources are critical building blocks for photonic quantum systems. Leveraging Kerr nonlinearity and cavity-enhanced spontaneous four-wave mixing, chip-scale photon-pair sources can be created using microresonators built on photonic integrated circuit. For practical applications, a high microresonator quality factor Q is mandatory to magnify photon-pair sources' brightness and reduce their linewidth. The former is proportional to Q^{4}, while the latter is inversely proportional to Q. Here, we demonstrate an integrated, microresonator-based, narrowband photon-pair source. The integrated microresonator, made of silicon nitride and fabricated using a standard CMOS foundry process, features ultralow loss down to 0.03 dB/cm and intrinsic Q factor exceeding 10^{7}. The photon-pair source has brightness of 1.17×10^{9} Hz/mW^{2}/GHz and linewidth of 25.9 MHz, both of which are record values for silicon-photonics-based quantum light source. It further enables a heralded single-photon source with heralded second-order correlation g_{h}^{(2)}(0)=0.0037(5), as well as an energy-time entanglement source with a raw visibility of 0.973(9). Our work evidences the global potential of ultralow-loss integrated photonics to create novel quantum light sources and circuits, catalyzing efficient, compact, and robust interfaces to quantum communication and networks.