Photonic Integration Platform Research Articles

Laser-written scalable sapphire integrated photonics platform

Laser-written scalable sapphire integrated photonics platform

Lithographically-defined cavities with high quality and purcell factors

Abstract We introduce and analyze a lithographically defined cavity (Li-cavity) incorporating a buried mesa defect in a planar vertical structure, which induces transverse photonic confinement while enabling compatibility with electrical injection. We systematically investigate the influence of key cavity parameters on optical behavior and fundamental properties using a comprehensive three-dimensional optical model. Our analysis reveals that the Li-cavity exhibits low optical scattering, resulting in high Q and Purcell factors, even at sub-wavelength dimensions. Furthermore, the Li-cavity supports single-mode operation within a broader aperture size range compared to conventional cavity designs, promising enhanced optical power of single-mode emission. Adequately designed structures demonstrate superior Q and Purcell factors at wavelength scale sizes,- outperforming conventional micropillar cavities. These improved properties and customizable device characteristics stem from a simple fabrication process that precisely controls the cavity size, shape, and optical mode. Superior characteristics, along with its adaptability to diverse materials, wavelengths, and photonic integration platforms, promise a broad range of applications and potential adaptation of this design to diverse photonic devices.

Chiral sensing via dielectric waveguide-nanoparticle array interactions

Identifying the handedness of chiral materials in small quantities remains a significant challenge in biochemistry. Nanophotonic structures offer a promising solution by enhancing weak chiroptical responses through increased optical chirality. Utilizing a silicon-based approach for chiral sensing on a photonic integrated platform is highly desirable. In this study, we explore the interaction between a dielectric waveguide and silicon nanoparticles for detecting the handedness of chiral analytes. A chiral core induces polarization rotation of wavefields traveling along a dielectric waveguide with a square cross-section. This polarization rotation affects waveguide coupling differently depending on the left- or right-handed arrangement of nanoparticles around the waveguide, enabling enantiomer detection through discernible transmission differences. From a basic design to more practical structures, we investigate configurations that maintain the same working principles. Theoretical results based on the transfer matrix method corroborate the numerical simulations.

InGaP χ(2) integrated photonics platform for broadband, ultra-efficient nonlinear conversion and entangled photon generation

Nonlinear optics plays an important role in many areas of science and technology. The advance of nonlinear optics is empowered by the discovery and utilization of materials with growing optical nonlinearity. Here we demonstrate an indium gallium phosphide (InGaP) integrated photonics platform for broadband, ultra-efficient second-order nonlinear optics. The InGaP nanophotonic waveguide enables second-harmonic generation with a normalized efficiency of 128, 000%/W/cm2 at 1.55 μm pump wavelength, nearly two orders of magnitude higher than the state of the art in the telecommunication C band. Further, we realize an ultra-bright, broadband time-energy entangled photon source with a pair generation rate of 97 GHz/mW and a bandwidth of 115 nm centered at the telecommunication C band. The InGaP entangled photon source shows high coincidence-to-accidental counts ratio CAR > 104 and two-photon interference visibility > 98%. The InGaP second-order nonlinear photonics platform will have wide-ranging implications for non-classical light generation, optical signal processing, and quantum networking.

Pioneering the future with silicon carbide integrated photonics

Silicon carbide (SiC) integrated photonics is advancing rapidly, promising to overcome the limitations of other integrated photonics platforms and enable new quantum devices. This progress is driven by SiC’s exceptional optical properties and significant advancements in epitaxial growth technologies, enabling wafer-scale production and manufacturability. The development of photonic components in SiC and SiC on Insulators at the wafer scale marks a paradigm shift in the role of SiC in photonics, a field dating back over 20 years. These advancements are seamlessly incorporating SiC into both integrated photonics and the emerging quantum photonics sector. SiC’s wide bandgap, high thermal conductivity, and robust nonlinear optical response make it ideal for a range of applications, from resilient photonic circuits in harsh environments to quantum devices that could revolutionize computing and communication. As research progresses, SiC-integrated photonics is poised to deliver cutting-edge, energy-efficient, and high-performance solutions that align with the goals of a sustainable and technologically advanced future.

Bound-state-in-continuum guided modes in a multilayer electro-optically active photonic integrated circuit platform: erratum

This erratum includes additional references omitted from the original paper [Optica 11, 706 (2024)OPTIC82334-253610.1364/OPTICA.516044].

(Invited) Epitaxial III-V Nanomaterials on the Si Platform for Quantum and Data Communications

As Si-based integrated photonic components begin to replace older technologies for optical data communications, the need for better integration of semiconductor lasers on the Si platform is greater than ever. In addition, emerging interest in integrated-photonic-based quantum computing and quantum sensing presents a further need for quantum light emitters—entangled and single-photon—on Si. III-V quantum dots represent a promising solution, both for the active region of telecommunications-wavelength lasers and for quantum emitters. However, epitaxial quantum dots grown on conventional (100) substrates typically lack the high symmetry required for entangled-photon emission.This presentation will discuss our recent work to develop a novel approach for III-V direct growth on Si via an ultrathin (<10 nm) single crystal strain relieving buffer layer, realized by the selective oxidation and condensation of an amorphous SiGe surface layer. The fabrication and properties of this novel Ge-rich buffer layer, as well as its use for subsequent III-V organometallic vapor-phase epitaxy will be presented.The second part of the talk will present our recent work on the epitaxial growth and characterization of (In,Ga)As quantum dots for the above-mentioned applications. Specifically, I will show that surface-energy-modifying surfactants (Sb, Bi) present the possibility to externally direct quantum dot formation “on-demand” in strained InAs layers on GaAs(111) substrates, where quantum dot formation by the Stranski–Krastanov process does not naturally occur. These nanostructures are prospective for high-symmetry entangled-photon emitters. The three-dimensional (3D) composition profile of InAs quantum dot layers is characterized by atom-probe microscopy (APT), elucidating the real-world quantum dot matrix. This 3D composition data is input into a finite element solver to determine the quantum dot energies and wavefunctions for electrons and holes. The modeling reveals that in high-density quantum dot layers, the electron and hole states are hybridized between multiple quantum dots in the matrix. This has important consequences for design of quantum dot light emitters. The predicted transition energies are in agreement with low-temperature photoluminescence. This work constitutes a promising approach for integrating telecommunications-wavelength quantum dot lasers and entangled photon emitters on the Si integrated photonics platform.

Silicon‐On‐Silicon Carbide Platform for Integrated Photonics

AbstractSilicon carbide (SiC)'s nonlinear optical properties and applications to quantum information have recently brought attention to its potential as an integrated photonics platform. However, despite its many excellent material properties, such as large thermal conductivity, wide transparency window, and strong optical nonlinearities, it is generally a difficult material for microfabrication. Here, it is shown that directly bonded silicon‐on‐silicon carbide can be a high‐performing hybrid photonics platform that does not require the need to form SiC membranes or directly pattern in SiC. The optimized bonding method yields defect‐free, uniform films with minimal oxide at the silicon–silicon–carbide interface. Ring resonators are patterned into the silicon layer with standard, complimentary metal–oxide–semiconductor (CMOS) compatible (Si) fabrication and measure room‐temperature, near‐infrared quality factors exceeding 105. The corresponding propagation loss is 5.7 dB cm−1. The process offers a wafer‐scalable pathway to the integration of SiC photonics into CMOS devices.

Concurrent phase-matchings for multi-wavelength conversion in coupled dual waveguides

Thin film lithium niobate, as a highly promising integrated photonics platform, has emerged as an ideal material platform for wavelength conversion owing to its exceptional second-order nonlinear characteristics. Here, we present the first demonstration of concurrent phase-matchings for multi-wavelength conversion in coupled thin film lithium niobate waveguides without poling technique. In the coupled dual waveguide system, employing modal phase-matching, we validate three effective phase-matching conditions for second harmonic generation, arising from additional momentum compensation due to the coupling of waveguides. Simultaneously, we confirm that phase-matching wavelengths can be tuned by adjusting the gap between waveguides. The concurrent phase-matchings in coupled dual waveguide systems can be readily extended to other nonlinear optical processes, such as difference frequency generation and spontaneous parametric down conversion. Our work contributes to advancing the exploration of efficient on-chip nonlinear optical processes within the realms of nanophotonics and quantum optics.

Fabrication of ultra-high-Q Ta2O5 microdisks by photolithography-assisted chemo-mechanical etching

Tantalum pentoxide (Ta2O5) is widely recognized as a promising material platform for photonic integration. This is primarily attributed to its exceptional properties including large bandgap of 3.8 eV, broad transparency window ranging from 300 nm to 8000 nm, high nonlinear refractive index of ∼7.2 × 10−19 m2/W, low optical loss, moderate refractive index of 2.05, low intrinsic material stress, compatibility with CMOS technology, and high solubility for rare-earth ions. However, dry etching of Ta2O5 is challenging and typically results in sidewall roughness with substantial scattering losses. Here, we report on fabrication of a high-Q whispering gallery mode (WGM) microdisk with a diameter of 120 µm and a loaded Q factor of 1.92 × 106 by femtosecond laser photolithography assisted chemo-mechanical etching (PLACE) on amorphous Ta2O5 film. Thanks to the suppression of sidewall scattering, the loaded Q factor is two orders of magnitude higher than the best reported value in dispersion engineered Ta2O5 microresonators.

Strong third-order nonlinearity in amorphous silicon carbide waveguides.

Silicon carbide (SiC) photonic integrated platform has attracted significant research interest for on-chip optical applications, owing to its exceptional optical properties such as a broad transparency window, high refractive index, and strong nonlinearity. Among the various types of SiC, amorphous SiC (a-SiC) has particularly emerged as an accessible choice for forming thin-film SiC-on-insulator (SiCOI) stacks, demonstrating promising capabilities for wafer-scale photonic applications. In this work, we prepare three a-SiCOI samples using the plasma-enhanced chemical vapor deposition, with different refractive indices. We fabricate optical waveguides, conduct four-wave mixing measurements, and characterize the nonlinear refractive index in these samples. Our findings reveal that an increase in the refractive index of a-SiC leads to a corresponding increase in the nonlinear refractive index, which is comparable to that of silicon. Hence, a-SiC offers an approach to develop a SiC platform with a wider bandgap than that of silicon, minimizing two-photon absorption while also providing a higher refractive index and stronger nonlinearity compared to crystalline SiC.

Polarization-insensitive multimode interference coupler on an x-cut thin-film lithium niobate platform.

Thin-film lithium niobate (TFLN) is a promising integrated photonics platform but currently lacks a polarization-insensitive multimode interference (MMI) coupler, a crucial component for polarization-related optical communication applications such as polarization management, polarization-division multiplexing, and polarization-insensitive modulation systems. This paper presents a novel, to the best of our knowledge, approach by rotating the MMI structure on an anisotropic x-cut TFLN at specific angles to compensate for the difference in the beat length between the two polarizations. A polarization-insensitive 1 × 2 MMI coupler is experimentally achieved with measured transmittances of -2.5 to -4 dB for both output ports and polarization modes in the wavelength range of 1520-1580 nm.

Photonics for Neuromorphic Computing: Fundamentals, Devices, and Opportunities.

In the dynamic landscape of Artificial Intelligence (AI), two notable phenomena are becoming predominant: the exponential growth of large AI model sizes and the explosion of massive amount of data. Meanwhile, scientific research such as quantum computing and protein synthesis increasingly demand higher computing capacities. As the Moore's Law approaches its terminus, there is an urgent need for alternative computing paradigms that satisfy this growing computing demand and break through the barrier of the von Neumann model. Neuromorphic computing, inspired by the mechanism and functionality of human brains, uses physical artificial neurons to do computations and is drawing widespread attention. This review studies the expansion of optoelectronic devices on photonic integration platforms that has led to significant growth in photonic computing, where photonic integrated circuits (PICs) have enabled ultrafast artificial neural networks (ANN) with sub-nanosecond latencies, low heat dissipation, and high parallelism. In particular, various technologies and devices employed in neuromorphic photonic AI accelerators, spanning from traditional optics to PCSEL lasers are examined. Lastly, it is recognized that existing neuromorphic technologies encounter obstacles in meeting the peta-level computing speed and energy efficiency threshold, and potential approaches in new devices, fabrication, materials, and integration to drive innovation are also explored. As the current challenges and barriers in cost, scalability, footprint, and computing capacity are resolved one-by-one, photonic neuromorphic systems are bound to co-exist with, if not replace, conventional electronic computers and transform the landscape of AI and scientific computing in the foreseeablefuture.

Frequency‐Space Selective Fano Resonance Based on a Micro‐Ring Resonator on Lithium Niobate on Insulator

AbstractCorresponding to the different phase‐shifts of the interference modes, the whispering gallery mode resonator‐based Fano resonance exhibits a variety of unique spectral lineshapes that can be applied to sensing, optical signal processing, and so on. However, most approaches to lineshape tuning aim to alter the propagation phase‐shift or coupling strength, and generally suffer from relatively low efficiency and limited tuning range. In this paper, with a carefully designed waveguide‐taper coupled micro‐ring resonator structure and the assistance with the grating‐coupler, for the first time a near full‐lineshape selectivity of the Fano resonance is demonstrated in two isolated tuning dimensions of the frequency and transverse space, which means arbitrary lineshapes including the Lorentzian‐dip, asymmetric Fano peak or electromagnetically‐induced‐transparency (EIT)‐like peak can be obtained at a specific resonance wavelength in the whole C‐band. In addition to the different types of line shapes, the extinction ratio can also be enhanced by dynamically tuning the coupling position. This research provides an efficient approach to manipulate the transmission spectra of the Fano resonance, which is of great importance in promoting its further applications on integrated photonics platforms.

Anisotropy-free arrayed waveguide gratings on X-cut thin film lithium niobate platform of in-plane anisotropy

Arrayed waveguide grating is a versatile and scalable integrated light dispersion device, which has been widely adopted in various applications, including, optical communications and optical sensing. Recently, thin-film lithium niobate emerges as a promising photonic integration platform, due to its ability of shrinking largely the size of typical lithium niobate based optical devices. This would also enable multifunctional photonic integrated chips on a single lithium niobate substrate. However, due to the intrinsic anisotropy of the material, to build an arrayed waveguide grating on X-cut thin-film lithium niobate has never been successful. Here, a universal strategy to design anisotropy-free dispersive components on a uniaxial in-plane anisotropic photonic integration platform is introduced for the first time. This leads to the first implementation of arrayed waveguide gratings on X-cut thin-film lithium niobate with various configurations and high-performances. The best insertion loss of 2.4 dB and crosstalk of −24.1 dB is obtained for the fabricated arrayed waveguide grating devices. Applications of such arrayed waveguide gratings as a wavelength router and in a wavelength-division multiplexed optical transmission system are also demonstrated.

Ultracompact and multifunctional integrated photonic platform.

Realizing a multifunctional integrated photonic platform is one of the goals for future optical information processing, which usually requires large size to realize due to multiple integration challenges. Here, we realize a multifunctional integrated photonic platform with ultracompact footprint based on inverse design. The photonic platform is compact with 86 inverse designed-fixed couplers and 91 phase shifters. The footprint of each coupler is 4 μm by 2 μm, while the whole photonic platform is 3 mm by 0.2 mm-one order of magnitude smaller than previous designs. One-dimensional Floquet Su-Schrieffer-Heeger model and Aubry-André-Harper model are performed with measured fidelities of 97.90 (±0.52) % and 99.34 (±0.44) %, respectively. We also demonstrate a handwritten digits classification task with the test accuracy of 87% using on-chip training. Moreover, the scalability of this platform has been proved by demonstrating more complex computing tasks. This work provides an effective method to realize an ultrasmall integrated photonic platform.

Integrated photonics cascaded attenuation circuit towards single-photon detector calibration

Integrated photonics platforms are a key driver for advancing scalable photonics technologies. To rigorously characterize and calibrate on-chip integrated photodetectors for ultra-sensitive applications such as quantum sensing and photonic computing, a low-power calibration source down to single-photon levels is required. To date, such sources still largely rely on off-chip bulk or fiber optic setups to accurately attenuate a laser beam referenced to a sub-mW-level primary standard. Here, we demonstrate an on-chip integrated attenuation solution where a mW-level beam is coupled to a silicon nitride photonics circuit, and is attenuated by a series of cascaded directional couplers (DCs). With an integrated silicon photodetector, we measured an attenuation at 685 nm wavelength of up to 16.61 dB with an expanded uncertainty of 0.24 dB for one DC stage. With appropriate scattering mitigation, we infer from our results that a total attenuation of 149.5 dB (expanded uncertainty of 0.5 dB) can be obtained with 9 stages of cascaded DCs, thus allowing single-photon power levels to be obtained directly on-chip from a moderate-power laser source.

Low-Loss Buried InGaAs/InP Integrated Waveguides in the Long-Wave Infrared.

In this work, we present a photonic integrated platform based on buried InGaAs waveguides with InP cladding that operates over a large mid-infrared (mid-IR) spectral range. Thanks to wet-etch fabrication patterning and Fe doping, low propagation losses below 1.2 dB/cm (0.3 cm-1 loss coefficient) have been obtained between 4.6 and 11.2 μm wavelengths (890-1960 cm-1 wavenumber), in both transverse electric (TE) and transverse magnetic (TM) polarization modes. The possibility of monolithically integrating such waveguides with mid-IR sources offers promising perspectives for developing broadband, homogeneously integrated systems.

Bound-state-in-continuum guided modes in a multilayer electro-optically active photonic integrated circuit platform.

In many physical systems, the interaction with an open environment leads to energy dissipation and reduced coherence, making it challenging to control these systems effectively. In the context of wave phenomena, such lossy interactions can be specifically controlled to isolate the system, a condition known as a bound-state-in-continuum (BIC). Despite the recent advances in engineered BICs for photonic waveguiding, practical implementations are still largely polarization- and geometry-specific, and the underlying principles remain to be systematically explored. Here, we theoretically and experimentally study low loss BIC photonic waveguiding within a two-layer heterogeneous electro-optically active integrated photonic platform. We show that coupling to the slab wave continuum can be selectively suppressed for guided modes with different polarizations and spatial structure. We demonstrate a low-loss same-polarization quasi-BIC guided mode enabling a high extinction Mach-Zehnder electro-optic amplitude modulator within a single Si3N4 ridge waveguide integrated with an extended LiNbO3 slab layer. By elucidating the broad BIC waveguiding principles and demonstrating them in an industry-relevant photonic configuration, this work may inspire innovative approaches to photonic applications such as switching and filtering. The broader impact of this work extends beyond photonics, influencing research in other wave dynamics disciplines, including microwave and acoustics.

High-Speed Electro-Optic Modulators Based on Thin-Film Lithium Niobate.

Electro-optic modulators (EOMs) are pivotal in bridging electrical and optical domains, essential for diverse applications including optical communication, microwave signal processing, sensing, and quantum technologies. However, achieving the trifecta of high-density integration, cost-effectiveness, and superior performance remains challenging within established integrated photonics platforms. Enter thin-film lithium niobate (LN), a recent standout with its inherent electro-optic (EO) efficiency, proven industrial performance, durability, and rapid fabrication advancements. This platform inherits material advantages from traditional bulk LN devices while offering a reduced footprint, wider bandwidths, and lower power requirements. Despite its recent introduction, commercial thin-film LN wafers already rival or surpass established alternatives like silicon and indium phosphide, benefitting from decades of research. In this review, we delve into the foundational principles and technical innovations driving state-of-the-art LN modulator demonstrations, exploring various methodologies, their strengths, and challenges. Furthermore, we outline pathways for further enhancing LN modulators and anticipate exciting prospects for larger-scale LN EO circuits beyond singular components. By elucidating the current landscape and future directions, we highlight the transformative potential of thin-film LN technology in advancing electro-optic modulation and integrated photonics.