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Optics Letters

Exploring nonlinearity-loss tradeoffs in foundry fabricated silicon integrated photon pair sources

Tom Dixon, Yisbel Eloisa Marin, Imad I. Faruque, Krishna C. Balram

Published Jan 2, 2026• 1 citation
Publisher

Abstract

Foundry fabricated silicon heralded photon pair sources underpin a wide range of quantum photonics applications. Traditional photonics foundry platforms, originating in classical datacom applications, have waveguide cross-sections <0.2 μm 2 , which significantly enhance surface absorption and roughness-induced scattering effects on propagating optical fields. Given the critical importance of loss for quantum information applications, here we consider the generation of photon pairs in a low-loss, thick (3 μm) silicon foundry platform and explore the associated nonlinearity-loss-footprint tradeoffs, with a view toward understanding the optimal silicon thickness for resonator-based photon pair sources.

DOI
10.1364/ol.585144

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Foundry fabricated silicon heralded photon pair sources underpin a wide range of quantum photonics applications. Traditional photonics foundry platforms, originating in classical datacom applications, have waveguide cross-sections <0.2 μm 2 , which significantly enhance surface absorption and roughness-induced scattering effects on propagating optical fields. Given the critical importance of loss for quantum information applications, here we consider the generation of photon pairs in a low-loss, thick (3 μm) silicon foundry platform and explore the associated nonlinearity-loss-footprint tradeoffs, with a view toward understanding the optimal silicon thickness for resonator-based photon pair sources.
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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.
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Photon-pair sources are essential for complex and scalable quantum photonics circuits. Silicon photonics offers a scalable and low cost platform with a mature fabrication technology for realising this [1] . Recent demonstrations of photon-pair generation and quantum interference in the 2.1 µm band have paved the way towards mid-infrared integrated photon sources [2] , where many gases can be sensed with unique ‘fingerprint’ absorption lines. Producing long wavelength photons with large spectral detunings from the pump, utilising anomalous group-velocity dispersion and type-0 phase matching, is hard due to the highly dispersive nature of nanoscale silicon waveguides.