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Optics Express

InP channel waveguides as quantum signal sources with a study of TPA and FCA effects

Muneeb Farooq, Francisco M. Soares, Jack Browne, Lakshmi Narayanan Venkatasubramani, Liam P. Barry, Francisco J. Díaz-Otero

Published Nov 17, 2025• 2 citations

Abstract

Integrated quantum signal sources play a key role in quantum communications in space, where compactness is of utmost importance. InP is an excellent candidate that can provide an on-chip single photon source as a device, where an excitation laser and waveguide for photon generation can be integrated on a single chip, because of its direct bandgap and high nonlinearity. However, one of the significant challenges that remains with InP is the elevated magnitude of the imaginary component of the third-order susceptibility ℑ[ χ (3) ] at 1550 nm wavelength. The higher value of ℑ[ χ (3) ] leads to two-photon absorption (TPA) and free carrier absorption (FCA) at very low powers, which drastically impacts the photon generation rate. In this paper, HHI and IMOS-based channel waveguides are modelled for the first time as an integrated platform for single photon generation, exploring spontaneous four-wave mixing (SFWM), considering TPA and FCA effects. The IMOS-based waveguide is more dynamic in generating entangled photons over a broader wavelength range, which would benefit photon demultiplexing at later stages. Nonlinear losses become dominant at power levels of 11 mW and 2 mW in HHI and IMOS waveguides, respectively, saturating the generation of single photons. TPA-free photon generation rates at these respective power levels are 4.1 MHz and 4.6 MHz , with generation bandwidths of 12.6 nm and 20.1 nm in the HHI channel and waveguide based on the IMOS platform, respectively. The saturated generation rates obtained are close to 0.15 GHz for both platforms. The on-chip monolithic integration of lasers with the proposed devices will potentially lead to more compact and stable single photon sources without relying on external lasers, in the telecommunications regime.

DOI: 10.1364/oe.580039

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We propose to leverage a silicon-organic hybrid integration structure to implement an integrated entangled photon pair source with high photon pair generation rate. This method combines the weak nonlinear absorption of organic materials with the high light confinement of silicon waveguides. Due to the supression of TPA and FCA, the pump power saturation threshold of the hybrid waveguide can be greatly increased. Therefore, with the high nonlinear coefficient and strong pump power, this hybrid integrated structure can achieve high photon pair generation rate. This work shows that silicon-organic hybrid integration could be a competitive platfrom for quantum photonic circuits.

Integrated Silicon photonics has played an important role in advancing the applications of quantum information and quantum science. However, due to different material properties, it is challenging to integrate all components with excellent performance based on homogeneous material. Here, by combining high nonlinearity and low losses in a heterogeneous silicon platform, we efficiently generate high-quality photon pairs through spontaneous four-wave mixing in hydrogenated amorphous silicon waveguide and route them off-chip through low loss silicon nitride waveguide. A record high coincidence- to- accidental rate value of 1632.6 (

\pm

260.4) is achieved in this heterogeneous design with a photon pair generation rate of 1.94 MHz. We also showcase a wide range of multi-channel photon sources with coincidence- to- accidental rate consistently at 200. Lastly, we measure heralded single-photons with a lowest

g^{(2)}_H(0)

of 0.1085

\pm

0.0014. Our results demonstrate the heterogeneous silicon platform as an ideal platform for efficient generation of photon pairs and routing them off-chip with low losses. It also paves a way for the future hybrid photonic integrated circuit by collecting distinct features from different materials.

Abstract Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust, and scalable chip formats with applications in long-distance quantum-secured communication, quantum-accelerated information processing, and non-classical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers making them impractical, not reproducible prototype devices, hindering scalability and the transfer out of the lab into real-world applications. Here we demonstrate a fully integrated quantum light source, which overcomes these challenges through the combined integration of a laser cavity, a highly efficient tunable noise suppression filter (> 55 dB) exploiting the Vernier effect, and a nonlinear microring for entangled photon pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically-pumped InP gain section and a Si₃N₄ low-loss microring filter system and demonstrates high-performance parameters, i.e., a pair emission over four resonant modes in the telecom band (bandwidth ∼ 1 THz), and a remarkable pair detection rate of ∼ 620 Hz at a high coincidence-to-accidental ratio of ∼80. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), verified by quantum interference measurements with visibilities up to 96% (violating Bell-inequality) and by density matrix reconstruction through state tomography showing fidelities of up to 99%. Our approach, leveraging a hybrid photonic platform, enables commercial-viable, low-cost, compact, light-weight, and field-deployable entangled quantum sources, quintessential for practical, out-of-lab applications, e.g., in quantum processors and quantum satellite communications systems.

Integrated silicon photonics has played an important role in advancing the applications of quantum information and quantum science. However, it is challenging to integrate all components with state-of-the-art performance using only a homogeneous platform. Here, by combining high nonlinearity and low losses in a heterogeneous silicon platform, we efficiently generate high-quality photon pairs through spontaneous four-wave mixing in a hydrogenated amorphous silicon waveguide and route them off-chip through a low-loss silicon nitride waveguide. A record high coincidence-to-accidental ratio value of 1632.6 (±260.4) is achieved in this heterogeneous design with a photon pair generation rate of 1.94 MHz. We also showcase a wide range of multichannel photon sources with a coincidence-to-accidental ratio consistently around 200. Lastly, we measure heralded single-photons with the lowest g H (2) (0) of 0.1085 ± 0.0014. Our results demonstrate the heterogeneous silicon platform as an ideal platform for the efficient generation of photon pairs and off-chip routing with low losses. It also paves the way for a future hybrid photonic integrated circuit by collecting distinct features from different materials.