We demonstrate a 23.3 GHz GaAs-on-SiN mode-locked laser heterogeneously integrated on a commercial SiN platform using micro-transfer printing. A compact Fabry-Pérot cavity with a central saturable absorber enables colliding-pulse, second-harmonic mode locking. The device delivers up to 1 mW on-chip optical power from a single output port and generates eight comb lines within a 10 dB optical bandwidth. The pulse-forming operation is confirmed by autocorrelation measurements, yielding a deconvolved pulse width of 4.8 ps. This approach provides a scalable route toward electrically pumped high-repetition-rate pulse sources for nonlinear SiN photonic circuits.

While the ^229Th nuclear isomer has recently been observed and laser-excited, converting optical nuclear manipulation into a chip-scale solid-state frequency standard remains an open challenge. Here, we present a nanophotonic platform to realize an all-solid-state nuclear clock based on the low-energy isomeric transition of ^229Th embedded in high-Q fluoride photonic resonators. By coupling ensembles of thorium nuclei to confined optical modes, we show that resonant field build-up in the cavity can substantially enhance the nuclear excitation rate, enabling optical interrogation at practical laser intensities. We model the nuclei-photon interaction dynamics and outline a technological roadmap toward addressing this challenge, including resonator fabrication in fluoride crystals, thorium implantation, nuclear excitation with integrated lasers, and on-chip detection of vacuum-ultraviolet photons. As an initial proof of concept, we implant a crystalline fluoride whispering-gallery-mode resonator with ^229Th and assess the impact of implantation-induced damage on resonator performance. Our platform leverages recent advances in materials integration and nanophotonics to chart a realistic route toward compact and scalable nuclear frequency standards.

The realization of integrated, high-speed ultraviolet (UV) modulation is pivotal for the advancement of quantum information processing, portable atomic clocks, and secure solar-blind communications. While mature photonic platforms have facilitated sophisticated system-level integration across visible and infrared spectra, high-speed active modulation in UV remains with traditional bulk crystals. Consequently, a scalable integrated solution that simultaneously combines low insertion loss and extreme compactness with high modulation efficiency has remained challenging. Here, we report the first integrated UV electro-optic modulator on a thin-film lithium tantalate (TFLT) platform. By employing a compact lumped-electrode design, we achieve a record-low VπL of 85 mV·cm at 375 nm, providing an up to four orders of magnitude improvement in terms of bandwidth/Vπ L over bulk technologies. The device demonstrates a robust extinction ratio of 22.7 dB, a low insertion loss of 1.3 dB, and a Vπ of 4.2V. Although the measured 3-dB bandwidth of 922 MHz is currently limited by photodetector performance, the small device footprint of 1.16 mm and electrode design of 200 μm indicate intrinsic potential for high-speed operation beyond 67 GHz which is confirmed by the electrical-to-electrical response. This work establishes TFLT as a disruptive platform for wafer-scale compatible active UV photonics, enabling the next generation of scalable quantum and communication systems.

We present a variability-aware simulation framework for heterogeneously integrated lithium niobate traveling-wave modulators. The framework incorporates fabrication-variation data obtained from our dedicated pilot line and enables efficient optimisation of geometric parameters to ensure stable device performance across wafer-scale manufacturing. The proposed multi-parameter optimisation method enables the efficient identification of modulator designs that simultaneously achieve target performance metrics (Vpi, optical insertion loss, and 3dB electro-optic bandwidth) while maintaining robustness against fabrication-induced variations. Using this methodology on two representative modulator architectures, we theoretically demonstrate that reliable wafer-scale integration of lithium niobate modulators on silicon photonics via micro-transfer printing is feasible and can be systematically engineered.

We demonstrate a widely tunable E-band InP-on-Si laser heterogeneously integrated using micro-transfer printing ( µ TP). The InP-based quantum-well gain material is designed with a photoluminescence peak centered around 1400 nm. Pre-fabricated InP semiconductor optical amplifiers (SOAs) are micro-transfer printed onto the IMEC 200 mm silicon-on-insulator (SOI) photonics platform. Using a silicon Vernier filter, continuous wavelength tuning from 1398 to 1439 nm is achieved, corresponding to a 41 nm tuning range spanning the upper E-band. The laser exhibits a side-mode suppression ratio exceeding 45 dB over the entire tuning range and delivers up to 3 mW output power in the silicon waveguide. A relative intensity noise (RIN) level down to −145 dBc/Hz is measured, indicating low-noise operation relevant for optical communication applications.

The rapid growth of artificial intelligence (AI) and other data center applications is driving the demand for photonic interconnects that combine high-speed with low energy consumption, making scalability a critical requirement. Micro-transfer printing (MTP) has emerged as a promising technique for the wafer-scale heterogeneous integration of thin film lithium niobate (TFLN) onto silicon photonics (SiPho) platforms. Here, we demonstrate heterogeneous SiPho TFLN integration across four full 200 mm wafers with a 3sigma placement accuracy down to 420 nm and a printing yield of larger than 95percentage. Low insertion loss less than 2 dB over 600 phase modulators (300 amplitude modulators) is achieved. A half wave voltage of 4 V in push pull configuration, and high-speed modulation with a bandwith larger than 70 GHz is demonstrated on a subset of tested devices.

The commercialization of next-generation technologies, including optical interconnects, quantum computing, AR/VR, and medical diagnostics, requires a low-loss photonic platform offering compact, multifunctional systems in the visible and near-infrared range. Although silicon nitride (SiN) is an excellent material due to its ultra-low loss and broad transparency window, integrating active components such as light sources, modulators and photodetectors from diverse material platforms in a scalable, reliable way remains challenging. Micro-transfer printing is an emerging wafer-scale heterogeneous integration technology that can be implemented as a back-end post-processing step without disrupting the primary in-line fabrication process. In this work, we present a dual LPCVD SiN layer platform fabricated in a 200 mm CMOS pilot line, that incorporates micro-transfer printing modules, allowing the integration of active components on well defined recesses. A hydrogenated amorphous silicon layer is also available to increase the versatility of the platform allowing for evanescently-coupled III-V lasers as well as other passive functionality in the near-infrared region. We report full wafer-scale measurements showing low optical SiN losses of 4 dB/cm and 0.23 dB/cm at a wavelength of 488 nm and 940 nm respectively. In addition, a transition loss of only 0.35 dB is obtained from the SiN to the a-Si:H layer, in good agreement with simulated values. Finally, to showcase more advanced functionality, GaAs-based gain sections are micro-transfer printed on several dies, achieving consistent die-to-die lasing at 970 nm with on-chip optical powers of approximately 1 mW. These results showcase the potential of the integrated photonics platform towards unlocking a wide range of new applications in the sub-1-μm spectral region.

ABSTRACT Silicon and silicon nitride waveguide platforms have established themselves as ideal candidates for high‐volume photonic integration, owing to their compatibility with mature semiconductor manufacturing processes. In parallel, lithium niobate has garnered significant attention for its superior electro‐optic and nonlinear properties, positioning it as a key enabler for high‐speed and advanced photonic functionalities. Nonetheless, the heterogeneous integration of lithium niobate with silicon photonics remains a technical challenge and an active area of investigation. We provide a comparative analysis of integration methods, detail the microtransfer printing process flow and highlight key demonstrators, including modulators, nonlinear devices and emerging applications such as optomechanics and quantum photonics. The scalability of microtransfer printing is discussed in the context of high‐volume manufacturing. This review underscores the potential of microtransfer printing to bridge the gap between high‐performance lithium niobate devices and industrial‐scale photonic integration.

This paper highlights micro-transfer printing (MTP) as a promising scalable approach to heterogeneous integration for silicon photonics. MTP uniquely achieves high integration density, high throughput, and high material efficiency through a low-temperature, back-end integration process. Current demonstrations, including integrated III-V lasers and thin-film electro-optic modulators, confirm MTP's potential. Industrial adoption requires resolving challenges related to final integration yield and throughput, device reliability, and supply chain maturity.

ABSTRACT Quantum photonic integrated circuits (QPICs) are a promising platform for scalable quantum technologies. A major outstanding challenge is the efficient interconnection of diverse quantum photonic components, where optical losses must remain below the ∼10% threshold required for advanced quantum applications. In this paper, the optical coupling between GaAs single‐photon sources and a low‐loss SiN interposer is investigated, where reliable high‐efficiency transitions have not yet been achieved. To address this, a fully numerical framework is introduced for the optimization of waveguide mode couplers that directly incorporates experimentally characterized fabrication variations critically impacting performance, including waveguide misalignment, width deviation, and sidewall roughness. Using this approach, low‐loss GaAs/SiN transitions are designed and experimentally demonstrated with reproducible coupling efficiencies of –0.43 dB ± 0.14 dB. These results establish a viable path toward low‐loss heterogeneous QPICs tailored to advanced quantum applications.

The rapid expansion of cloud computing and artificial intelligence has driven the demand for faster optical components in data centres to unprecedented levels. A key advancement in this field is the integration of multiple photonic components onto a single chip, enhancing the performance of optical transceivers. Here silicon photonics, benefiting from mature fabrication processes, has gained prominence in both academic research and industrial applications. The platform combines modulators, switches, photodetectors and low-loss waveguides on a single chip. However, emerging telecommunication standards require modulation speeds that exceed the capabilities of silicon-based modulators. To address these limitations, thin-film lithium niobate has been proposed as an alternative to silicon photonics, offering a low voltage–length product and exceptional high-speed modulation properties. More recently, the first demonstrations of thin-film lithium tantalate circuits have emerged, potentially addressing some of the disadvantages of lithium niobate, enabling a reduced bias drift and enhanced resistance to optical damage. As such, this material arises as a promising candidate for next-generation photonic platforms. However, a persistent drawback of such platforms is the lithium contamination, which complicates integration with CMOS fabrication processes. Here we present for the first time the integration of lithium tantalate onto a silicon photonics chip. This integration is achieved without modifying the standard silicon photonics process design kit. Our device achieves low half-wave voltage (3.5 V), low insertion loss (2.9 dB) and high-speed operation (>70 GHz), paving the way for next-generation applications. By minimizing lithium tantalate material use, our approach reduces costs while leveraging existing silicon photonics technology advancements, in particular supporting ultra-fast monolithic germanium photodetectors and established process design kits. Lithium tantalate is heterogeneously integrated with silicon photonic integrated circuits via a micro-transfer printing process in a manner fully compatible with existing workflows. A Mach–Zehnder modulator with an insertion loss of 2.9 dB and 70 GHz operation is demonstrated.

We demonstrate the first co-integration of a wafer-scale single-layer graphene electro-absorption modulator (EAM) with a high-speed SiGe bipolar CMOS (BiCMOS) electronic integrated circuit (EIC), achieving robust operation up to 25 GBd. The scalable graphene EAM, fabricated in a 300 mm CMOS pilot line, exhibits an intrinsic electro-optic (EO) bandwidth of 11.2 GHz. To overcome the RC-limitation and simultaneously enable low-voltage operation, the EIC was co-designed with a 30 Omega internal termination impedance and amplifies the voltage swing by a factor of 3. This optimization increased the effective EO bandwidth and allowed the co-integrated system to produce open eye diagrams at 25 GBd from a low 500mVpp input drive voltage. We report measured Q-factors and an estimated bit error rate of 1.37 & times;10-7 at 25 GBd using a 5-tap feed-forward equalizer. This work demonstrates the first functional EO link co-integrating a graphene modulator with a BiCMOS electronic driver. By validating this wire-bonded interface, we establish a feasible and practical route towards energy-efficient, scalable photonic interconnects.

We demonstrate for the first time transfer printing of thin-film single-crystalline sapphire onto a silicon nitride waveguide. This enables the future integration of thin-film titanium-sapphire-on-silicon-nitride photonics.

In this letter, we demonstrate an actively mode-locked laser at telecom wavelength made of graphene electro-absorption modulator on a photonic integrated circuit, inserted in a dispersion-engineered cavity with III-V semiconductor optical amplifiers as gain medium. Stable low-jitter pulse trains at 10 GHz with 2.9 ps deconvoluted pulse widths are achieved, with performances comparable to a commercial lithium niobate high-speed modulator. These results highlight the potential of integrated graphene-based devices for the realization of compact and stable optical clocks operating at high repetition rate.

Although graphene's THz absorption rate increases with number of graphene layers, the absorbance is limited and unsatisfactory as a practicable absorber. Patterned graphene or graphene-based surface plasmon resonance has been proved to enhance THz absorption, but the performance is prone to be affected by graphene defects and local multilayer stacks. In this paper, we proposed to use a double circular metal ring (DCMR) array to enhance both the graphene's THz absorption with an ultrawide bandwidth and the tolerance of graphene's physical impurities. A DCMR array is patterned on the top surface of graphene layer with dielectric substrates, which excites a broadband spoof surface plasmons polaritons (SPPs) in the THz frequency range. The broadband spoof SPPs locally confine and strengthen THz wave interaction with graphene, and further enhance graphene's THz absorption, which is confirmed by numerically simulated dispersion relations. A four-layer graphene composite structure is fabricated to validate the scenario, which consists of graphene, a SiO2-capped doped-silicon substrate covered by graphene, and the DCMR array on the top surface of graphene. Time domain spectroscopy test shows that the THz absorption enhancement of the graphene composite with DCMR array covers the frequency range from 0.3 to 1.1 THz with 110% bandwidth. The THz absorption of the proposed graphene composite increases to more than 70% over a wide bandwidth of 77% at 0.65 THz compared with the graphene composite without DCMR array.

A new wet etching process is developed for lithium tantalate waveguide fabrication and propagation losses are measured. With such process, low loss structures can be fabricated without requiring etching machinery. Furthermore, it opens possibilities in realizing heterogeneously integrated lithium tantalate modulators using waveguides.

A recent push has been made towards the heterogeneous integration of laser sources at wavelengths around 800 nm through wafer bonding [1], [2]. However, for nonlinear applications such as microcomb generation for spectroscopy and absolute frequency referencing in atomic clocks, higher-power integrated laser sources are required. The main power limitation inherent to wafer bonded lasers is the low thermal conductivity of the silicon oxide layer between the heat-generating III-V layers and the silicon substrate, leading to thermal roll-off. To avoid this problem, the superior flexibility of micro-transfer printing can be used to directly print III-V laser sources on the silicon substrate in recesses etched in silicon nitride (SiN) photonic-integrated circuits [3], vertically aligning the III-V mode with the silicon nitride waveguide and facilitating greatly improved thermal characteristics. In this work, we show the fabrication of micro-transfer printable edge-emitting Fabry-Perot laser coupons. These coupons are successfully printed on a silicon substrate, showing high laser power (> 70 mW at 150 mA) around 795 nm without thermal roll-off.

Quantum-dot (QD) semiconductor optical gain is highly regarded for its wide gain spectra, high saturation power, and superior thermal properties, making it an excellent choice for laser applications, especially in high power and mode-locking operation regimes1,2,3,4. In this work, we present the development progress of heterogeneous integrated O-band InAs/GaAs quantum dot lasers on an 800 nm thick silicon nitride ($Si_{3}N_{4}$) platform using micro-transfer-printing (μTP), a technology available under license from X-Celeprint, Ltd. Among different light coupling schemes for the III-V devices to $Si_{3}N_{4}$ circuits, we choose edge-coupling approach which offers a good thermal sink, broadband, low-loss and polarization agnostic coupling, and a small footprint5,6,7. We employed adiabatic taper coupling structures (see Fig. 1A) that have large mode areas at the edges to achieve high coupling efficiency (> 92%). These wide taper structures demonstrate promising fabrication and misalignment tolerance, as illustrated by the FDTD simulation in Fig. 1.B,C, and D. Integration of the InAs/GaAs amplifiers on $Si_{3}N_{4}$ platforms, utilizing the discussed coupling scheme, shows great potential for high-power and mode-locked laser applications in on-chip optical atomic clocks, LIDAR, and datacom systems.