A scalable quadratic nonlinear silicon photonics platform with printable entangled photon-pair sources
Tom Vandekerckhove, De Witte, Jasper, Lisa De Jaeger, Ewoud Vissers, Janssen, Sofie, Peter Verheyen, Singh, Neha, Dieter Bode, Martin Davi, Filippo Ferraro, Philippe P. Absil, Sadhishkumar Balakrishnan, Joris Van Campenhout, Dries Van Thourhout, Günther Roelkens, Stéphane Clemmen, Bart Kuyken
The integration of second-order optical nonlinearities into scalable photonic platforms remains a key challenge due to their large sensitivity to fabrication variations. Here, we present a scalable quadratic nonlinear platform that harnesses the maturity and scalability of existing CMOS processes by heterogeneously integrating periodically poled lithium niobate (PPLN) onto a silicon photonics platform. A generic PPLN design enables frequency conversion on two distinct waveguide geometries with efficiencies comparable to LNOI rib waveguides. We achieve reproducible phase-matching across the full radius of a commercial 200 mm silicon photonics wafer, leveraging superior CMOS fabrication tolerances. Furthermore, we introduce a tuning mechanism for both blue- and red-shifting of the operating wavelength, fully compensating fabrication-induced offsets. This enables deterministic phase-matching over an entire wafer and yields a strategy for wafer-scale phase-matched quadratic nonlinearities. Finally, we realize printable photon-pair sources via spontaneous parametric down-conversion, highlighting the platform's potential for large-scale quantum optical circuits. These results pave the way for wafer-scale integration of second-order optical nonlinearities in large photonic systems.
The integration of second-order optical nonlinearities into scalable photonic platforms remains a key challenge due to their large sensitivity to fabrication variations. Here, we present a scalable quadratic nonlinear platform that harnesses the maturity and scalability of existing CMOS processes by heterogeneously integrating periodically poled lithium niobate (PPLN) onto a silicon photonics platform. A generic PPLN design enables frequency conversion on two distinct waveguide geometries with efficiencies comparable to LNOI rib waveguides. We achieve reproducible phase-matching across the full radius of a commercial 200 mm silicon photonics wafer, leveraging superior CMOS fabrication tolerances. Furthermore, we introduce a tuning mechanism for both blue- and red-shifting of the operating wavelength, fully compensating fabrication-induced offsets. This enables deterministic phase-matching over an entire wafer and yields a strategy for wafer-scale phase-matched quadratic nonlinearities. Finally, we realize printable photon-pair sources via spontaneous parametric down-conversion, highlighting the platform's potential for large-scale quantum optical circuits. These results pave the way for wafer-scale integration of second-order optical nonlinearities in large photonic systems.
Abstract The integration of second‐order optical nonlinearities into scalable photonic platforms remains a key challenge due to their large sensitivity to fabrication variations. Here, a scalable quadratic nonlinear platform is presented that harnesses the maturity and scalability of existing CMOS processes by heterogeneously integrating periodically poled lithium niobate (PPLN) onto a silicon photonics platform. A generic PPLN design enables frequency conversion on two distinct waveguide geometries with efficiencies comparable to reported lithium niobate on insulator (LNOI) rib waveguides. Reproducible phase‐matching is achieved across the full radius of a commercial 200 mm silicon photonics wafer, leveraging superior CMOS fabrication tolerances. Furthermore, a tuning mechanism is introduced for both blue‐ and red‐shifting of the operating wavelength, fully compensating fabrication‐induced offsets. This enables deterministic phase‐matching over an entire wafer and yields a strategy for wafer‐scale phase‐matched quadratic nonlinearities. Finally, printable photon‐pair sources are realized via spontaneous parametric down‐conversion (SPDC), highlighting the platform's potential for large‐scale quantum optical circuits. These results pave the way for wafer‐scale integration of second‐order optical nonlinearities in large photonic systems.
Abstract Integrated photon-pair sources are crucial for scalable photonic quantum systems. Thin-film lithium niobate is a promising platform for on-chip photon-pair generation through spontaneous parametric down-conversion (SPDC). However, the device implementation faces practical challenges. Periodically poled lithium niobate (PPLN), despite enabling flexible quasi-phase matching, suffers from poor fabrication reliability and device repeatability, while conventional modal phase matching (MPM) methods yield limited efficiencies due to inadequate mode overlaps. Here, we introduce a layer-poled lithium niobate (LPLN) nanophotonic waveguide for efficient photon-pair generation. It leverages layer-wise polarity inversion through electrical poling to break spatial symmetry and significantly enhance nonlinear interactions for MPM, achieving a notable normalized second-harmonic generation (SHG) conversion efficiency of 4615% W-1 cm-2. Through a cascaded SHG and SPDC process, we demonstrate photon-pair generation with a normalized brightness of 3.1×106 Hz nm-1 mW-2 in a 3.3 mm long LPLN waveguide, surpassing existing on-chip sources under similar operating configurations. Crucially, our LPLN waveguides offer enhanced fabrication reliability and reduced sensitivity to geometric variations and temperature fluctuations compared to PPLN devices. We expect LPLN to become a promising solution for on-chip nonlinear wavelength conversion and non-classical light generation, with immediate applications in quantum communication, networking, and on-chip photonic quantum information processing.
Broadband nonlinear optical devices play a critical role in both classical and quantum optics. Here, we design and fabricate a 6.82-mm-long step-chirped periodically poled lithium niobate~(CPPLN) waveguide on lithium niobate on insulator, which enables quasi-phase matching over a broad bandwidth for second-harmonic generation~(SHG) and spontaneous parametric down-conversion~(SPDC). The SHG achieves an average efficiency of 54.4\%/W/cm2 over the first-harmonic wavelength range of 1510~nm-1620~nm, paving the way for realizing SPDC across a wide range of pump wavelengths. For SPDC, by tuning the pump wavelength to 775~nm, 780~nm, and 785~nm, we achieve broadband photon-pair generation with a maximum full bandwidth and brightness up to 99~THz~(846~nm) and 20~GHz/mW/nm, respectively. Our findings provide an efficient and experiment-friendly approach for generating broadband photon pairs, which holds significant promise for advancing applications in quantum metrology.
Broadband nonlinear optical devices play a critical role in both classical and quantum optics. Here, we design and fabricate a 6.82-mm-long step-chirped periodically poled lithium niobate (CPPLN) waveguide on lithium niobate on insulator, which enables quasi-phase matching over a broad bandwidth for second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC). The SHG achieves an average efficiency of 91%/W/cm 2 over the first-harmonic wavelength range of 1510 nm–1620 nm, paving the way for realizing SPDC across a wide range of pump wavelengths. For SPDC, by tuning the pump wavelength to 775 nm, 780 nm, and 785 nm, we achieve broadband photon-pair generation with a maximum full bandwidth and brightness up to 99 THz (846 nm) and 21 MHz/mW/nm, respectively. Our findings provide an efficient and experiment-friendly approach for generating broadband photon pairs, which holds significant promise for advancing applications in quantum metrology.
Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications. However, the patterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost. Here, we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepper lithography and an automated poling process. To address the inhomogeneous broadening of the quasi-phase matching (QPM) spectrum induced by film thickness variations across the wafer, we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section. \hl{Using the segmented micro-heaters, we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57% enhancement of conversion efficiency. We achieve a high normalized conversion efficiency of 3802%W−1cm−2 in a 6 mm long PPLN waveguide, recovering 84% of the theoretically predicted efficiency in this device.} The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing, precision sensing and metrology, and low-noise-figure optical signal amplification.
Heterogeneous integration of gain and strongly nonlinear materials with ultra-low-loss silicon nitride (SiN) photonics offers a route to scalable quantum circuits, but concurrent wafer-scale manufacturability, low interlayer loss, and high performance have been challenging to realize. Here we demonstrate a wafer-scale III-V-on-SiN quantum photonic platform that directly integrates III-V layers to foundry-fabricated SiN circuits. The SiN layer provides 200-300 nm thick waveguides with <1 dB/m loss and a mature passive photonics ecosystem, while III-V materials provide large χ(2) and χ(3) nonlinearities for parametric gain, frequency conversion and quantum light generation. Adiabatic interlayer couplers yield <25 mdB loss to InGaP waveguides and resonators with intrinsic quality factors exceeding 106, enabling 15× brighter entanglement sources and efficient nonlinear conversion on SiN. Integrated components--including low-loss beam splitters, waveguide crossers, and tunable interferometers--are complemented by III-V lasers and InP photodetectors with amplifiers achieving up to 99−12+1% quantum efficiency and 3 GHz bandwidth. This architecture unites ultra-efficient sources, nonlinear elements and detectors on a wafer-scale, low-loss platform, establishing a path toward large-scale, low-noise quantum photonic systems.