Single-photon detection using superconducting nanowire detectors has become a benchmark technology for quantum photonic applications, offering exceptional performance across a wide spectral range. However, their operation at cryogenic temperatures (typically 1–4 K) substantially increases system cost and complexity, limiting their integration into compact and scalable on-chip quantum systems where photon generation, manipulation, and detection must coexist. As a promising alternative, thin horizontal silicon p–n junctions enable room-temperature operation and are fully compatible with photonic integrated circuits (PICs), offering a viable route toward large-scale quantum photonic integration. Nevertheless, current silicon-based SPAD platforms exhibit high dark count rates (DCR), typically around 100 kHz/μm, primarily due to non-optimized doping concentrations. In this work, we present a systematic optimization of the doping profile using coupled process and device simulations to establish a direct correlation between ion implantation parameters and SPAD performance. By identifying optimal doping conditions, the DCR is suppressed by 98.18% for planar SPADs and 95.01% for rib-SPADs. We further analyze the trade-off between photon detection efficiency and dark noise, and investigate the influence of excess bias and device length on overall performance. The avalanche buildup time is also evaluated to characterize the temporal response of the optimized SPAD structures. The resulting design framework provides CMOS-compatible guidelines for engineering scalable, cost-effective, and room-temperature single-photon detectors suitable for monolithic integration within quantum PICs.

Group IV color centers in diamond are promising single-photon emitters for quantum information processing and networking. Among them, the tin-vacancy (SnV) center stands out due to its long spin coherence times at cryogenic temperatures above 1 K. While SnV centers have been realized using various fabrication routes, their in situ formation via microwave plasma-enhanced chemical vapor deposition (MW PE CVD) remains relatively unexplored. In this study, SnV centers, identified by a zero-phonon line (ZPL) near 620 nm, were synthesized in nanocrystalline diamond and free-standing microcrystalline diamond using tin oxide (SnO2) as a dopant source at substrate temperatures of 750 degrees C and 850 degrees C. Photoluminescence measurements reveal that lowering the substrate temperature enhances both the ZPL intensity and spatial uniformity of SnV centers. These results highlight substrate temperature as a key parameter for controlling SnV incorporation during MW PE CVD growth and provide insights into optimizing fabrication strategies for diamond-based quantum technologies.

Single-photon avalanche diodes (SPADs) integrated into photonic integrated circuits (PICs) can offer a promising alternative to cryogenic superconducting detectors, combining CMOS compatibility with room-temperature operation. A comprehensive optoelectronic multiphysics simulation framework to model waveguide integrated SPADs is shown here. Based on imec's isipp50G technology, simulated devices show the potential of peak photon detection efficiencies (PDE) above 75% at 600 nm, when coupled with a SiN signal waveguide. This work establishes a scalable methodology for design technology co-optimization (DTCO) of SPADs for integrated photonics and identifies critical pathways towards performance improvements, mainly in dark count rate (DCR) reduction, paving the way for their full optimization and integration into quantum photonic circuits.

We present a scalable quadratic nonlinear platform by micro-transfer printing periodically poled lithium niobate on a 200 mm silicon photonics platform. We achieve chip-to-chip reproducibility, deterministic phase-matching and establish printable entan- gled photon-pair sources.

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.

Bragg Scattering Four-Wave mixing (BS-4WM) is used in fibers to frequency shift single photons. We investigate how its phase matching condition can be controlled by changing the fiber temperature. We then are able to optimize the efficiency of the BS-4WM process for selected wavelengths that will ultimately allow a scheme of active multiplexing of single photons.

Thin-film lithium niobate (TFLN) modulators have been pushing the limits of high-speed modulation to higher bandwidths and lower driving voltages. However, these typically occupy large footprints, limiting their integration density. For many applications, compact low-voltage modulators are desired where the bandwidth is limited by other factors, e.g., lifetimes of atomic transitions. Furthermore, integration on a CMOS-compatible platform is desirable for scaling to larger systems and to leverage existing technologies. In this work, we heterogeneously integrate a compact low-voltage lithium niobate racetrack modulator of 250 μm × 500 μm on a silicon nitride (SiN) platform. The device consists of a racetrack-shaped X-cut TFLN slab, which is micro-transfer printed onto a SiN all-pass racetrack resonator. The modulator achieves a tuning efficiency of 1.7 pmV-1 (or 3.5 pmV-1 for double-arm operation) and a Q-factor of 285,000 (with intrinsic Qi = 608,000), ensuring low operating voltages up to a measured 3-dB bandwidth of 1.18 GHz. These results pave the way toward densely integrated compact low-voltage amplitude modulators on a scalable CMOS platform.

Lithium niobate photonics provides a low-loss platform with great properties for high-speed modulation, wavelength conversion and quantum optics. Micro-transfer printing allows scalable integration with CMOS compatible silicon photonics technologies.

State-of-the-art periodically-poled lithium niobate waveguides struggle with extreme fabrication sensitivity, resulting in unpredictable phase-matching wavelengths. We developed a micro-transfer-printed periodically-poled lithium niobate waveguide that enables deterministic phase-matching at a predefined wavelength through optical feedback.

Efficient low-loss coupling to micro-transfer-printed lithium niobate remains a challenge. We developed a highly-selective lithium niobate etch that enables selective etching of tapered coupling structures into the lithium niobate thin film after micro-transfer printing.

We introduce a silicon squeezer designed for high levels of squeezing and compatibility with state-of-the-art integrated balanced detection systems. Our approach combines linear elements, such as dispersion control and cavity design, with the strategic selection of pump parameters to enhance nonlinear performance. To optimize signal confinement and reduce phase mismatches in four-wave mixing (FWM), we meticulously adjust the waveguide dimensions, cladding materials, bend radii, and directional coupler settings. This comprehensive strategy is aimed at minimizing FWM discrepancies and ensuring effective signal confinement, demonstrating our commitment to addressing the complexities of high-performance squeezing in silicon platforms.

We report the Geiger operation of a nanophotonic silicon APD, quantify its dark counts rate and detection probability at 300K. While characterized in free space, simulations of coupling to a nanophotonic waveguide quantify future improvements.

Wavelength conversion processes such as spontaneous parametric down conversion (SPDC) and optical parametric amplification (OPA) are key elements in integrated quantum optics. On-chip integration of these functionalities would allow for increased performance and huge scaling opportunities. However, CMOS-compatible platforms such as silicon and silicon nitride (SiN) lack a $\chi^{(2)}$ nonlinearity due to their inversion symmetry. This work provides a solution by heterogeneously integrating periodically poled lithium niobate (PPLN) onto SiN wave-guides through micro-transfer printing $(\mu \text{TP})$ [1]. The $\mu \text{TP}$ method is a scalable back-end process, allowing the fabrication of the photonic integrated circuit to remain CMOS-compatible.

A high-speed modulator on silicon nitride is demonstrated using 2 mm-long micro-transfer printed lithium niobate coupons. This device has a 3-dB bandwidth >50GHz, and an insertion loss of 3.3 dB that allowed us to transmit 70 Gb/s.

Integrated photonic systems require fast modulators to keep up with demanding operation speeds and increasing data rates. The silicon nitride integrated photonic platform is of particular interest for applications such as datacom, light detection and ranging (LIDAR), quantum photonics, and computing owing to its low losses and CMOS compatibility. Yet, this platform inherently lacks high-speed modulators. Heterogeneous integration of lithium niobate on silicon nitride waveguides can address this drawback with its strong Pockels effect. We demonstrate the first high-speed lithium niobate modulator heterogeneously integrated on silicon nitride using micro-transfer printing. The device is 2 mm long with a half-wave voltage Vπ of 14.8 V. The insertion loss and extinction ratio are 3.3 and 39 dB, respectively. Operation beyond 50 GHz has been demonstrated with the generation of open eye diagrams up to 70 Gb/s. This proof-of-principle demonstration opens up possibilities for more scalable fabrication of these trusted and performant devices.

Several established photonic platforms lack a nonzero Pockels and nonlinear coefficient. We developed a micro-transfer printing method to heterogeneously integrate thin-film lithium niobate and gallium phosphide with an experimentally shown transfer yield of near-unity.

High-speed Pockels modulation and second-order nonlinearities are key components in optical systems, but CMOS-compatible platforms like silicon and silicon nitride lack these capabilities. Micro-transfer printing of thin-film lithium niobate offers a solution, but suspending large areas of thin films for long interaction lengths and high-Q resonators is challenging, resulting in a low transfer yield. We present a new source preparation method that enables reliable transfer printing of thin-film lithium niobate. We demonstrate its versatility by successfully applying it to gallium phosphide and silicon, and provide an estimate of the transfer yield by subsequently printing 25 lithium niobate films without fail.

The saturable absorption of a double-layer graphene modulator is experimentally demonstrated on a silicon slot waveguide platform. Saturation was found to start at ~0.8W with a maximum saturation depth of 1.9 dB for a $50 \mu \mathrm{m}$ long graphene modulator.

Microtransfer printing of silicon and lithium niobate thin films on generic integrated photonic platforms is demonstrated. An unprecedented integration yield is achieved using crack barriers as a way to mitigate stress-induced shears in the material.