Monolithic Platform Research Articles

Ge2Sb2Se4Te on n = 1 ITO: a monolithic platform for integrated photonics with mode symmetrization and post-fabrication tuning

We demonstrate, to our knowledge, a novel monolithic platform for photonic integrated circuits (PICs) based on amorphous-Ge2Sb2Se4Te (am-GSST). Additionally, we explore the concept of mode symmetrization using the epsilon-near-zero behavior displayed by indium-tin-oxide (ITO) to achieve a substrate with n=1 at 1550 nm, the same as the air cladding. We designed, fabricated, and characterized various on-chip components using this platform, including waveguides with preliminary 5.57±0.365dB/mm propagation loss. Furthermore, we propose a post-fabrication tuning of the refractive index by using the phase change nature of GSST to crystallize local sections of the waveguides using electron beams. Our substrate-blind approach is a versatile platform for post-fabrication tunable PICs that could benefit intricate on-chip nanophotonic structures requiring enhanced and symmetric mode confinement.

Laterally Modulating Carrier Concentration by Ion Irradiation in CdO Thin Films for Mid‐IR Plasmonics

AbstractThis report demonstrates tunable carrier densities in CdO thin films through local ion irradiation, providing lateral control of mid‐IR optical properties. Ion‐solid interactions produce donor‐like defects that boost electron concentrations from the practical minimum of 2.5 × 1019 cm−3 to a maximum of 2.5 × 1020 cm−3 by metered ion exposure. This range is achieved using He, N, Ar, or Au ions at 1–2.8 MeV; when normalized by displacements per atom, all ion species produce comparable results. Since CdO is well‐described by the Drude model, irradiation‐tuned carrier densities directly alter the infrared dielectric function, and in turn, mid‐infrared optical properties. Further, it is demonstrated that by combining irradiation with traditional lithography, CdO films expose to ions in the presence of 3‐µm thick, patterned photoresist exhibit lateral carrier density profiles with ≈400‐nm resolution. Scanning near‐field optical microscopy reveals sharp optical interfaces with almost no companion contrast in surface morphology, microstructure, or crystallinity. Finally, CdO lateral homostructures supporting surface plasmon polaritons (SPPs) are demonstrated whose dispersion relation can be tuned through periodic patterning in a monolithic platform by simple nanofabrication. Numerical simulations show these polaritons result from strong coupling between excitations at CdO plasma frequencies and SPPs supported by the platinum substrate.

(Invited) Advanced III-V-on-Si Heterogeneously Integrated Platforms for Next Generation Silicon Photonics Integrated Circuits

The field of Silicon Photonics has experienced a solid and continuous progress over the last few years, gaining in technological maturity, design tools, and new methods [1]. The deployment of low-cost, compact, and power-efficient photonic circuits with a high wafer yield and robustness stands as one of the fundamental pillars that sustain such progress [2]. Presently, photonic circuit technology has diversified its number of available platforms. Despite the fact that indium phosphide (InP) [3] and silicon-on-insulator (SOI) platforms are still considered as the workhorses of integrated photonics in terms of maturity and deployment of active (InP) and passive (SOI) components, other alternatives such as germanium-on-silicon [4], silicon nitride-on-insulator [2] or hybrid solutions combining different functional materials with Si are gaining momentum [5]. A representative example is the heterogeneous III-V/Si platform [6], which has been used to develop compact photonic circuits with on-chip gain. Contrarily to the hybrid integration, the III-V-on-Si heterogeneous integration avoids the constraints of chip-to-chip alignment while enabling the simultaneous integration of hundreds of III-V gain chips in a scalable fashion. Still, the integration methods of such III-V materials on silicon need to be improved to attain the maturity level of the monolithic III-V platform, which benefits from a complete palette of technological solutions not yet available in the III-V-on-Si heterogeneous integration. More recently, an advanced heterogeneous scheme based on wafer-seed-bonding and epitaxial regrowth has emerged [7]–[9]. The ambition is to create a generic integration scheme combining the best offered by the III-V and the Si-photonics platforms. The regrowth capability gives access to the large epitaxial toolkit available in the conventional InP monolithic platform, where several epitaxial steps are often implemented [10][11]. To cite some of them, the epitaxial regrowth of III-V materials to bury III-V lasers bonded onto silicon are object of intense research nowadays to overcome the thermally inefficient buried oxide [12].In this paper, we will review the advances on III-V-on-Si heterogeneous integration through the implementation of several key demonstrators and building blocks for silicon photonics, including on-chip semiconductor optical amplifiers, lasers and electro-absorption modulators. We will discuss the progress and benefits of the direct seed bonding and regrowth as well as new device designs to improve the performance.

A Flexible Forecasting Stack

Forecasting extrapolates the values of a time series into the future, and is crucial to optimize core operations for many businesses and organizations. Building machine learning (ML)-based forecasting applications presents a challenge though, due to non-stationary data and large numbers of time series. As there is no single dominating approach to forecasting, forecasting systems have to support a wide variety of approaches, ranging from deep learning-based methods to classical methods built on probabilistic modelling. We revisit our earlier work on a monolithic platform for forecasting from VLDB 2017, and describe how we evolved it into a modern forecasting stack consisting of several layers that support a wide range of forecasting needs and automate common tasks like model selection. This stack leverages our open source forecasting libraries GluonTS and AutoGluon-TimeSeries , the scalable ML platform SageMaker , and forms the basis of the no-code forecasting solutions ( SageMaker Canvas and Amazon Forecast ), available in the Amazon Web Services cloud. We give insights into the predictive performance of our stack and discuss learnings from using it to provision resources for the cloud database services DynamoDB, Redshift and Athena.

Compact on-chip power splitter based on topological photonic crystal

We propose and demonstrate an on-chip 1×N power splitter based on topological photonic crystal (TPC) on a monolithic silicon photonic platform. Benefiting from the valley-locked propagation mode at the interface of TPCs with different topological phases, the proposed power splitter has negligible backscattering around the sharp bendings and good robustness to fabrication defects, which therefore enable lower insertion loss, better uniformity, and more compact footprint than the conventional designs. For the fabricated 1 × 2 (8) power splitter, the uniformity among the output ports is below 0.35 (0.65) dB and the maximum insertion loss is 0.38 (0.58) dB with compact footprint of 5 × 5 µm2 (10 × 12 µm2) within a bandwidth of 70 nm. In addition, the topological power splitter only requires simple configurations of TPCs with different topological phases, which is more reliable in design and fabrication compared with the conventional designs.

Ultra-broadband on-chip power splitters for arbitrary ratios on silicon-on-insulator.

We propose and demonstrate on-chip power splitters based on adiabatic rib waveguide enabling arbitrary splitting ratios on a monolithic silicon photonic platform. The devices are elaborately engineered based on adiabatic directional couplers with a trapezoid-structure in the longitudinal direction in the mode evolution region. The measurement results indicate that the proposed devices can achieve over 150 nm bandwidth for arbitrary splitting ratios of 50%:50%, 70%:30% and 90%:10%. The mode evolution footprint is greatly narrowed to below 79 µm with an insertion loss of less than 0.22 dB. The demonstrated arbitrary ratio power splitters offer a promising application prospect in high-density photonic integrated circuits.

Porous polymer monolithic columns to investigate the interaction of humic substances with herbicides and emerging pollutants by affinity chromatography

BackgroundUnderstanding the interaction mechanisms and the relevant binding constants between humic acids and emerging or regulated pollutants is of utmost importance in predicting their geochemical mobility, bioavailability, and degradation. Fluorescence spectroscopy, UV–vis spectroscopy, equilibrium dialysis, and solid-phase extraction combined with liquid chromatography-mass spectrometry have been employed to elucidate interactions of humic acids with organic micropollutants, especially pharmaceutical drugs. These methods demand large sample volumes, long equilibration times, and laborious extraction steps which may imply analytical errors. Monolithic high-performance affinity chromatography is an alternative and simpler method to investigate these interactions and determine the binding constants. ResultsPolymer monoliths based on aminated glycidyl methacrylate and ethylene glycol dimethacrylate served to immobilize Cu(II) and then humic acid to produce monolithic affinity chromatography columns with humic acid as the active interaction phase. About 86.5 mg of humic acid was immobilized per gram of polymer. The columns enabled a comparison of the binding strength of humic acid with herbicides and emerging pollutants at 25 °C and pH 6.0 ± 0.1. Paracetamol, acetylsalicylic acid, and salicylic acid did not retain. Among the compounds that interacted with humic acid, the order of increasing affinity, estimated by the global affinity constant (nKa) or partition coefficient (KD) was: caffeine < simazine < atrazine ∼ propazine < benzophenone. The nKa (L mol−1) values ranged from (4.9 ± 0.3) × 102 for caffeine to (1.9 ± 0.3) × 103 for benzophenone, whereas KD (L kg−1) varied from 14 ± 1 to 56 ± 8 for the same compounds. Significance and noveltyTo our knowledge, this is the first paper demonstrating the use of a monolithic platform to immobilize supramolecular structures of humic acids exploiting immobilized metal affinity to comparatively evaluate their affinity towards emerging pollutants exploiting the concepts of high-performance affinity chromatography. The proposed approach needs only small amounts of humic acid, which is a relevant feature in preparing columns with humic substances isolated and purified from remote areas.

Compact slow-light waveguide and modulator on thin-film lithium niobate platform

Abstract Lithium niobate Mach–Zehnder modulators (MZMs) with compact footprint and fast electro-optics (EO) responses are highly demanded for the next-generation optical interconnect systems. Here, we demonstrate slow-light (SL) effect using a coupled Bragg resonator structure on the thin-film lithium niobate (TFLN) platform, and an ultra-compact SL-MZM with length L of ∼370 μm is also constructed. The fabricated SL waveguides show a large optical passband width of ∼8 nm, an insertion loss of 2.9 dB, and a maximal optical group index of 7.50, corresponding to 3.4 times as large as that of regular TFLN rib waveguide. The fabricated SL-MZM exhibits a large EO bandwidth of &gt;50 GHz in an operating wavelength band of ∼8 nm as well. High-speed OOK transmissions at data rates of 64 Gbit/s and 80 Gbit/s are successfully achieved. To our best knowledge, it is first time to build SL waveguides and compact SL-MZMs with large EO bandwidths of &gt;50 GHz on the monolithic TFLN platform.

Monolithic 3D structural-substrate SERS sensing platform for ultrasensitive and highly-specific analysis of trace bisphenol A

Constructing advanced substrates with excellent features is promising for sensitive surface-enhanced Raman spectroscopy (SERS) detection. Here a novel capillary monolithic 3D structural-substrate SERS platform with Au@cDNA@Ag@Cyanine 3-aptamer nanoparticles (Au@cDNA@Ag@Cy3-Apt NPs) was fabricated for rapid, highly specific profiling of ultra-trace Bisphenol A (BPA). The proposed SERS platform combined both in-capillary SERS and aptamer-affinity recognition strategies, in which the superior SERS properties of Au–Ag NPs, aptamer selectivity, and the advantages of capillary monolith were integrated. A 3D hierarchically porous network was constructed in the monolithic column, which was endowed with rich hotspots for SERS, rapid sample permeation, and better analysis efficiency than most plane-shaped SERS modes. By varying the amount of Ag+ precursor, the Ag-shell thickness on SERS was finely tuned to guarantee Cy3 label in proximity to the plasmonic surface. Based on the biorecognition of aptamer, the selective identification of BPA occurred and exhibited a significant change in SERS intensity without obvious interference. As a result, the monolithic SERS platform featured facile operation, excellent specificity, and rapid analysis (10 min, much less than the solution-based or planar substrate SERS modes). Ultra-high sensitivity and robust reproducibility for BPA analysis was achieved with a low limit of detection (LOD) at 9.12 × 10-4 ng/L. The feasibility of this SERS platform for monitoring BPA in water and milk samples was also validated. This work lights a new access to capillary monolithic SERS-sensing platform for ultrasensitive and specific analysis of BPA.

A holistic tool to assess the cost and environmental performance of floating offshore wind farms

This study provides an integrated and novel holistic tool based on systematic and comprehensive methodologies with the flexible capacity to assess the economic aspects and environmental impacts of the life cycle of floating offshore wind farms. The tool considers production, installation, operation, maintenance, decommissioning and End-of-Life stages to give overall and broken-down results by stages, components, and materials. This allows for identifying the environmental and economic hotspots along the FOW life cycle, driving the decision-makers and engineers towards a sustainable floating wind technology, and enhancing cost reduction strategies. A monolithic concrete spar platform technology for 15 MW offshore turbines located in two sites (10 km off the coast of Gran Canaria - Spain and 60 km off the coast of Morro Bay - California) is used as study cases, to generate six scenarios with different wind farm capacities ranging 60 MW–1200 MW. The life cycle stages are considered in the structure of the tool to give overall and broken-down results by stages, components, and materials. The outcomes of scenarios calculated by the tool give LCOE values rranging from 67 to 115 €/MWh and GHG emissions between 7 and 10 kg CO2 eq./MWh, with uncertainties of ±9% and ±22% respectively.

Design of GaSb-based monolithic passive photonic devices at wavelengths above 2 µm

In this paper, we report, for the first time, a theoretical study on passive photonic devices including optical power splitters/combiners and grating couplers (GCs) operating at non-telecom wavelengths above 2 µm in a monolithic GaSb platform. Passive components were designed to operate, in particular, at around 2.6 µm for monolithic integration with active photonic devices on the III–V gallium antimonide material platform. The three popular types of splitters/combiners such as directional couplers, multimode interferometer-, and Y-branch-couplers were theoretically investigated. Based on our optimized design and rigorous analysis, fabrication-compatible 1 × 2 optical power splitters with less than 0.12 dB excess losses, large spectral bandwidth, and a 50:50 splitting ratio are achieved. For fiber-to-chip coupling, we also report the design of GCs with an outcoupling efficiency of ∼29% at 2.56 μm and a 3 dB bandwidth of 80 nm. The results represent a significant step towards developing a complete functional photonic integrated circuits at mid-wave infrared wavelengths.

Engineering Quantum Nanophotonic Components from Hexagonal Boron Nitride

AbstractIntegrated quantum photonics (IQP) provides a path to practical, scalable quantum computation, communications and information processing. Realization of an IQP platform requires controlled engineering of many nanophotonic components. However, the range of materials for monolithic platforms is limited by the simultaneous need for high‐quality quantum light sources, high optical performance, and availability of scalable nanofabrication techniques. Here, the fabrication of IQP components from the recently emerged material hexagonal boron nitride (hBN), including tapered waveguides, microdisks, and 1D and 2D photonic crystal cavities, is demonstrated. Resonators with quality factors greater than 4000 are achieved, and proof‐of‐principle complex, free‐standing IQP circuitry fabricated from single‐crystal hBN is engineered. The results show the potential of hBN for scalable integrated quantum technologies.

Plasmonic Ferroelectric Modulator Monolithically Integrated on SiN for 216 GBd Data Transmission

A high-speed plasmonic barium titanate (BTO, BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) Mach-Zehnder modulator is presented. We combine nanoscale plasmonics with BTO as solid-state active material and silicon nitride (SiN) for versatile and low loss waveguiding, and integrate them in a monolithic platform. We demonstrate a plasmonic BTO modulator processed onto foundry-produced SiN. The 15 µm long high-speed modulator features a flat electro-optic frequency response up to 70 GHz and is expected to be flat way beyond. A low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> L product of 144 Vµm is shown. Data experiments reaching 216 Gbit/s with a 216 GBd 2PAM signal and 256 Gbit/s with a 128 GBd 4PAM signal are demonstrated. The merger of the versatile silicon nitride platform with high-speed plasmonics using the highly nonlinear ferroelectric BTO is an attractive solution as a future Tb/s optical interconnect platform.

Modular wearable optoelectronic system using photoactive nanomembranes

Ultrathin, flexible, cost-effective, and high-performance optoelectronic materials, such as halide perovskites and two-dimensional (2D) nanomembranes, have recently attracted significant attention in the field of wearable bio-integrated systems owing to their exceptional theoretical performance (e.g., high mechanical stability without significant degradation of electrical and optical properties) that may potentially surpass those of conventional rigid/brittle/bulky semiconductors under the condition of external mechanical stress applied. Despite the progress made at the individual unit level, the currently used fabrication/integration process does not satisfy the requirements established for personalized wearable optoelectronic systems because no reconfigurable heterogenous integration of various photoactive materials into a monolithic soft skin-like platform has been performed yet. Herein, we report a modular wearable optoelectronic system that exhibits a unique combination of energy harvesting, sensing, and display capabilities based on two different types of photoactive nanomembranes (halide perovskites and 2D semiconducting MoS2 nanosheets) even under on-skin deformation. To ensure that this system is reconfigurable both physically and electrically, we added a water-resistant self-healing stretchable polymer and conducting composite films to its encapsulation/substrate layers and interconnects, respectively. The spontaneous modularity that is inherent in self-healing materials enabled the formation of an integrated optoelectronic system with the following functional units. i) Photovoltaic and photoemissive devices containing perovskite-based nanomembranes were used as efficient power supplies and for immediate visualization, respectively. ii) A MoS2 nanosheet-based photosensitive component quantitatively distinguished various brightness conditions. iii) An integrated modular system was capable of detecting either tactile stimuli or various motions. The proposed integration strategy can be potentially utilized for realizing high-performance on-demand/user-defined wearable optoelectronic systems.

Straight and curved distributed Bragg reflector design for compact WDM filters.

Grating-assisted contra-directional couplers (CDCs) wavelength selective filters for wavelength division multiplexing (WDM) are designed and experimentally demonstrated. Two configuration setups are designed; a straight-distributed Bragg reflector (SDBR) and curved distributed Bragg reflector (CDBR). The devices are fabricated on a monolithic silicon photonics platform in a GlobalFoundries CMOS foundry. The sidelobe strength of the transmission spectrum is suppressed by controlling the energy exchange between the asymmetric waveguides of the CDC using grating and spacing apodization. The experimental characterization demonstrates a flat-top and low insertion loss (0.43 dB) spectrally stable performance (<0.7 nm spectral shift) across several different wafers. The devices have a compact footprint of only 130µm2/Ch (SDBR) and 3700µm2/Ch (CDBR).

Compact, broadband, and low-loss power splitters using MZI based on Bézier bends.

We experimentally demonstrate wavelength-independent couplers (WICs) based on an asymmetric Mach-Zehnder interferometer (MZI) on a monolithic silicon-photonics platform in a commercial, 300-mm, CMOS foundry. We compare the performance of splitters based on MZIs consisting of circular and 3rd order (cubic) Bézier bends. A semi-analytical model is constructed in order to accurately calculate each device's response based on their specific geometry. The model is successfully tested via 3D-FDTD simulations and experimental characterization. The obtained experimental results demonstrate uniform performance across different wafer sites for various target splitting ratios. We also confirm the superior performance of the Bézier bend-based structure, compared to the circular bend-based structure both in terms of insertion loss (0.14 dB), and performance consistency throughout different wafer dies. The maximum deviation of the optimal device's splitting ratio is 0.6%, over a wavelength span of 100 nm. Moreover, the devices have a compact footprint of 36.3 × 3.8 μ m 2.

Cubic-wavelength mode volume photonic crystal nanobeam cavities in a monolithic CMOS platform.

We report on the design, fabrication, and experimental characterization of photonic crystal (PhC) nanobeam cavities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. Two types of cavities were designed, with opposite spatial mode symmetries. The opposite mode symmetry, combined with evanescent coupling, allows the nanobeam cavities to be used in reflectionless topologies, desirable in complex photonic integrated circuits (PICs). The devices were implemented and fabricated in a 45 nm monolithic electronics-photonics CMOS platform optimized for silicon photonics (GlobalFoundries 45CLO) and do not require any post-processing. Quality factors exceeding 100 000 were measured for both devices, the highest, to the best of our knowledge, among fully cladded PhC nanobeam cavities in any silicon-on-insulator (SOI) platform. Additionally, the ability of the cavities to confine light into small mode volumes, of the order of (λ/n)3, was confirmed experimentally using near-field scanning optical microscopy (NSOM). These types of cavities are an important step toward realizing ultra-low energy active devices required for the next generation of integrated optical links beyond the current microring resonator-based links and other CMOS PICs.

Versatile generation and manipulation of phase-structured light beams using on-chip subwavelength holographic surface gratings

Abstract Phase-structured light beams carrying orbital angular momentum (OAM) have a wide range of applications ranging from particle trapping to optical communication. Many techniques exist to generate and manipulate such beams but most suffer from bulky configurations. In contrast, silicon photonics enables the integration of various functional components on a monolithic platform, providing a way to miniaturize optical systems to chip level. Here, we propose a series of on-chip subwavelength holographic waveguide structures that can convert the in-plane guided modes into desired wavefronts and realize complex free-space functions, including the generation of complex phase-structured light beams, arbitrarily directed vortex beam emission and vortex beam focusing. We use a holographic approach to design subwavelength holographic surface gratings, and demonstrate broadband generation of Laguerre–Gaussian (LG) and linearly polarized (LP) modes. Moreover, by assigning appropriate geometric phase profiles to the spiral phase distribution, the off-chip vortex beam manipulation including arbitrarily directed emission and beam focusing scenarios can be realized. In the experiment, directed vortex beam emission is realized by using a fabricated tilt subwavelength holographic fork grating. The proposed waveguide structures enrich the functionalities of dielectric meta-waveguide structures, which can find potential applications in optical communication, optical trapping, nonlinear interaction and imaging.

3D Integrated Laser Attach Technology on a 300-mm Monolithic CMOS Silicon Photonics Platform

Enabling cost-effective and power-efficient laser source on a silicon photonics (SiPh) platform is a major goal that has been highly sought after. In the past two decades, tremendous effort has been made to develop various on-chip integration techniques to enhance SiPh circuits with efficient light-emitting materials. Here we review our recent advancements in hybrid flip-chip integration of III-V lasers on a 300-mm monolithic SiPh platform. By leveraging advanced complementary metal oxide semiconductor (CMOS) manufacturing processes, we have demonstrated wafer-scale laser attach based on a precisely controlled cavity formed on a silicon-on-insulator (SOI) substrate. The laser integration process is aided by precise mechanical alignment features on the SiPh wafer and high-precision fiducials on the laser. Efficient laser-to-SiPh-circuit butt-coupling with optical power up to 20mW was demonstrated through wafer- and module-level characterizations. Key performance metrics including side-mode suppression ratio, mode-hopping, and relative intensity noise were characterized after laser integration. In addition, early reliability assessments were performed on laser-attached SOI wafers and Si submount assemblies to understand the long-term performance stability of the lasers on the monolithic platform. To further enhance the performance of the laser-integrated chip, we explored alternative spot-size converters that could simultaneously enable improved coupling efficiency and relaxed fabrication tolerance, thus showing great promise over traditional designs.

Soliton formation and spectral translation into visible on CMOS-compatible 4H-silicon-carbide-on-insulator platform

Recent advancements in integrated soliton microcombs open the route to a wide range of chip-based communication, sensing, and metrology applications. The technology translation from laboratory demonstrations to real-world applications requires the fabrication process of photonics chips to be fully CMOS-compatible, such that the manufacturing can take advantage of the ongoing evolution of semiconductor technology at reduced cost and with high volume. Silicon nitride has become the leading CMOS platform for integrated soliton devices, however, it is an insulator and lacks intrinsic second-order nonlinearity for electro-optic modulation. Other materials have emerged such as AlN, LiNbO3, AlGaAs and GaP that exhibit simultaneous second- and third-order nonlinearities. Here, we show that silicon carbide (SiC) -- already commercially deployed in nearly ubiquitous electrical power devices such as RF electronics, MOSFET, and MEMS due to its wide bandgap properties, excellent mechanical properties, piezoelectricity and chemical inertia -- is a new competitive CMOS-compatible platform for nonlinear photonics. High-quality-factor microresonators (Q = 4 × 106) are fabricated on 4H-SiC-on-insulator thin films, where a single soliton microcomb is generated. In addition, we observe wide spectral translation of chaotic microcombs from near-infrared to visible due to the second-order nonlinearity of SiC. Our work highlights the prospects of SiC for future low-loss integrated nonlinear and quantum photonics that could harness electro-opto-mechanical interactions on a monolithic platform.