Photonic Integrated Circuits Research Articles

High-performance silicon photonic single-sideband modulators for cold-atom interferometry.

The laser system is the most complex component of a light-pulse atom interferometer (LPAI), controlling frequencies and intensities of multiple laser beams to configure quantum gravity and inertial sensors. Its main functions include cold-atom generation, state preparation, state-selective detection, and generating a coherent two-photon process for the light-pulse sequence. To achieve substantial miniaturization and ruggedization, we integrate key laser system functions onto a photonic integrated circuit. Our study focuses on a high-performance silicon photonic suppressed-carrier single-sideband (SC-SSB) modulator at 1560 nanometers, capable of dynamic frequency shifting within the LPAI. By independently controlling radio frequency (RF) channels, we achieve 30-decibel carrier suppression and unprecedented 47.8-decibel sideband suppression at peak conversion efficiency of -6.846 decibels (20.7%). We investigate imbalances in both amplitudes and phases between the RF signals. Using this modulator, we demonstrate cold-atom generation, state-selective detection, and atom interferometer fringes to estimate gravitational acceleration, g ≈ 9.77 ± 0.01 meters per second squared, in a rubidium (87Rb) atom system.

Efficient wideband tunable radio frequency-optical conversion via triply resonant photonic molecules.

Electro-optic (EO) transduction of weak radio frequency (RF) and millimeter-wave signals, such as those received by an antenna, onto laser sidebands for processing in the optical domain requires efficient EO modulators. Microrings offer spatial density and efficiency advantages over Mach-Zehnder modulators (MZMs), but conventional single-ring modulators suffer a fundamental trade-off between resonantly enhanced conversion efficiency and the RF carrier frequency that it can accommodate. Dual-cavity "photonic molecule" modulators resolve this trade-off, allowing high efficiency independent of the RF carrier frequency by providing separate resonant supermodes to enhance the laser local oscillator (LO) and the narrowband RF-detuned sideband. However, the RF frequency is fixed at design time by geometry, with efficiency dropping quickly for RF carriers away from the design value. We propose a novel, to the best of our knowledge, triple-cavity configuration with an off-resonant middle ring acting as an effective tunable coupler between two active modulator cavities. This configuration provides wideband tunability of the target RF carrier while maintaining efficient sideband conversion. When the middle ring is passive (high Q), this configuration provides wide RF tunability with no efficiency penalty over the fixed dual-cavity case and could become an important building block for future RF/mm-wave photonic integrated circuits (PICs).

Tunable quantum emitters on large-scale foundry silicon photonics

Controlling large-scale many-body quantum systems at the level of single photons and single atomic systems is a central goal in quantum information science and technology. Intensive research and development has propelled foundry-based silicon-on-insulator photonic integrated circuits to a leading platform for large-scale optical control with individual mode programmability. However, integrating atomic quantum systems with single-emitter tunability remains an open challenge. Here, we overcome this barrier through the hybrid integration of multiple InAs/InP microchiplets containing high-brightness infrared semiconductor quantum dot single photon emitters into advanced silicon-on-insulator photonic integrated circuits fabricated in a 300 mm foundry process. With this platform, we achieve single-photon emission via resonance fluorescence and scalable emission wavelength tunability. The combined control of photonic and quantum systems opens the door to programmable quantum information processors manufactured in leading semiconductor foundries.

Efficient Poling‐Free Wavelength Conversion in Thin Film Lithium Niobate Harnessing Bound States in the Continuum

AbstractOver the past two decades, there has been a surge of interest in photonic integrated circuits (PICs) to enable low‐cost industrial mass manufacture of miniaturized optical systems while simultaneously improving performance and energy efficiency following the trajectory of electronics and large‐scale integration. An essential characteristic of any PIC lies in the ability of waveguides to efficiently confine light. The phenomenon of bound states in the continuum (BIC) shows promise in achieving confinement of light for modes that otherwise would suffer from high leakage losses, which can occur in many PIC platforms. In this contribution, the usefulness of operating near a BIC to achieve efficient second harmonic generation of ≈300% W−1 cm−2 in Silicon Nitride (SiN) loaded lithium niobate on insulator (LNOI) waveguides without needing to either pole or etch the lithium niobate is experimentally demonstrated. The guided fundamental mode is phase matched at the telecom wavelength to a higher order mode at the second harmonic wavelength that is engineered as a bound state in the continuum to mitigate leakage losses. This demonstrates the promise of using BIC in weakly confining waveguides for nonlinear optical applications all while avoiding the poling process by engineering waveguide geometry.

Polyethylene imine-modified photonic crystal microfluidic chip for highly sensitive detection of microbial spores

To address the lengthy cycles, complex operations, high costs, and insufficient sensitivity of biomarker detection in traditional biological control agents, photonic crystal treated with PEI was developed for highly sensitive detection of Sclerotinia sclerotiorum microbial spores. By incorporating gelatin molecules, photonic crystal is endowed with excellent photothermal stability and high stability in aqueous solutions. The photonic crystal surface is conferred a positive charge by PEI, which can be used to enhance the adsorption of spores. Efficient enrichment of Sclerotinia sclerotiorum and Purpureocillium lilacinum spores is achieved, with coefficients of determination 0.963 and 0.971, respectively. The detection range is from 102 to 106 spores/ml, and the photonic crystal exhibited good reusability. The prepared photonic crystal enables rapid, non-destructive, and accurate quantitative detection of microbial spores.

Suspended nanomembrane silicon photonic integrated circuits

Leveraging the low linear and nonlinear absorption loss of silicon at mid-infrared (mid-IR) wavelengths, silicon photonic integrated circuits (PICs) have attracted significant attention for mid-IR applications including optical sensing, spectroscopy, and nonlinear optics. However, mid-IR silicon PICs typically show moderate performance compared to state-of-the-art silicon photonic devices operating in the telecommunication band. Here, we proposed and demonstrated suspended nanomembrane silicon (SNS) PICs with light guiding within deep-subwavelength waveguide thickness for operation in the short wavelength mid-IR region. We demonstrated key building components, namely, grating couplers, waveguide arrays, micro-resonators, etc., exhibiting excellent performances in bandwidths, back reflections, quality factors, and fabrication tolerance. Moreover, we show that the proposed SNS PICs have high compatibility with the multi-project wafer foundry services. Our study provides an unprecedented platform for mid-IR integrated photonics and applications.

Nonexistence of integrable nonlinear magnetic fields with invariants quadratic in momenta

Nonlinear, completely integrable Hamiltonian systems that serve as blueprints for novel particle accelerators at the intensity frontier are promising avenues for research, as Fermilab’s Integrable Optics Test Accelerator (IOTA) example clearly illustrates. Here, we show that only very limited generalizations are possible when no approximations in the underlying Hamiltonian or Maxwell equations are allowed, as was the case for IOTA. Specifically, no such systems exist with invariants quadratic in the momenta, precluding straightforward generalization of the Courant–Snyder theory of linear integrable systems in beam physics. We also conjecture that no such systems exist with invariants of higher degree in the momenta. This leaves solenoidal magnetic fields, including their nonlinear fringe fields, as the only completely integrable static magnetic fields, albeit with invariants that are linear in the momenta. The difficulties come from enforcing Maxwell equations; without constraints, we show that there are many solutions. In particular, we discover a previously unknown large family of integrable Hamiltonians.

Fabrication of Quasi-Sinusoidal Surface Relief Optical Transmission Gratings in Pyrex and IOG Glasses by Implantation with Oxygen and Nitrogen Ion Microbeams of the 5-6 MeV Energy Range.

A method for the fabrication of high diffraction efficiency optical transmission gratings with quasi-sinusoidal profile in glasses by microbeams of medium-mass ions of 5-6 MeV energy was devised and demonstrated. Gratings with a 30 μm grating constant have been manufactured and characterized by interference microscopy and microprofilometry. The obtained surface profiles of the gratings were found to be quasi-sinusoidal with up to 265 nm amplitude. Measured highest first-order diffraction efficiencies were around 26% in both Pyrex and IOG glasses. Such gratings could serve as coupling elements in integrated optics and photonic integrated circuits.

Investigation of Dual-Layer Si-ITO-Dielectric Based Hybrid Plasmonic Electro-Absorption Modulator at 1.55 µm Wavelength

ABSTRACT In this paper, a dual-layer plasmonic material-based electro-absorption modulator (EAM) is designed and investigated. Indium-tin-oxide (ITO), along with dielectric materials such as boron nitride (hBN) and hafnium dioxide (HfO2), is integrated into the Si waveguide for tuning the light propagating inside the device. The device showed enhanced performance in terms of extinction ratio (ER) = 34.48 dB/µm, the figure of merit (FOM) = 493, and insertion loss (IL) = 0.06 dB/µm for On-state at 1.55 µm wavelength. Also, the dual-state behavior of the EAM was observed and investigated. An IL of 22.22 dB/µm and 25.39 dB/µm was observed for the Off-On and On-Off configurations, respectively. A modulation frequency ( f 3 dB ) of 1.72 THz and 340 GHz was achieved for the EAM with hBN and HfO2 as the dielectric material. The investigated EAM with different dielectric materials has the potential to be integrated into future-generation photonic integrated circuits (PICs).

Ultra-wideband mm-wave remote antenna unit for radio-over-fiber distributed antenna systems in silicon photonics

This article presents what we believe to be a novel chip-scale 25-45-GHz re-configurable mm-wave remote antenna unit (RAU) for radio over fiber (RoF) distributed antenna systems. The proposed RAU architecture optimizes energy efficiency by operating directly at mm-wave frequencies, and spectral efficiency by selecting re-configurable RF photonic filters topology. Additionally, it achieves frequency agility by rejecting interferes and a small form factor by utilizing the SOI photonics process. Two photonic integrated circuits (PICs) that act as downlink and uplink units are presented while occupying a total area of 12.33 mm2. The downlink selects a single channel within the desired frequency range, while the uplink rejects up to four interferes. The building blocks of the proposed architecture are discussed and their design consideration and parameters are shown. Then, a comprehensive system analysis of the proposed RAU architecture including key performance indicators is presented. A scalable 5-channel system is demonstrated each with a 3-dB Bandwidth of 5-GHz. Moreover, this architecture can be continuously tuned and re-configured within a wide frequency range to cover all 5-channels. To the best of the authors’ knowledge, this is the first wideband modular and re-configurable mm-wave RAU that covers the entire mm-wave sub-45-GHz band implemented in silicon photonics.

Packaging of micro-lens arrays to photonic integrated circuits using beam shape evaluation

We propose a method for aligning and attaching micro-lens arrays to photonic integrated circuits (PICs). Unlike the conventional approach of assessing power coupled to a fiber directly, our method utilizes a beam profiler. This profiler allows us to optimize the lens position by analyzing the transmitted beam shape from the PIC edge coupler through the lens. In conjunction, we employ grating couplers to introduce external light, acting as a ‘beacon’ for optimization. The use of grating couplers enables efficient coupling of external light into the PIC, providing a reference point for alignment. Importantly, our method accommodates both regular waveguide-side-up and upside-down (through-Silicon) orientations of the PIC. This versatility allows us to reproduce coupling results across a 6-channel array, demonstrating robust performance. This innovative approach not only ensures precise alignment and attachment but also opens up new possibilities for photonic packaging. The flexibility to work in different orientations is likely to lead to advancements in the design and assembly of photonic devices.

Polygon search algorithm for ultra-compact multifunctional integrated photonics design

Ultra-compact multifunctional integrated photonic modules have great practical significance to photonic integrated circuits (PICs). However, the design effect and efficiency of the existing mainstream inverse design algorithms are incompetent when designing these modules. We analyze their shortcomings in this task, and propose a new, to our knowledge, inverse design algorithm named polygon search (PS) algorithm to address these problems. We utilize the PS algorithm to design an integrated dual-channel mode-conversion-crossing waveguide module. This module integrates three functions: interconversion between TE0 and TE1, interconversion between TE0 and TE2, and channel crossing within only a 4 μm×4 μm footprint, and its performance is verified by experimental testing. It not only greatly reduces the total footprint of many PICs but also greatly improves their fabricating robustness. Furthermore, we propose a PS-designed mode mixer and a PS-designed bending waveguide, and connect them with the integrated modules to form a four-channel crossing-mode-division-multiplexing system. This system can provide multiple modes on the basis of channel crossing and transmit the output signal in the same direction in parallel within a single output waveguide, which significantly increases the communication bandwidth and decreases the footprint of PICs. At last, we demonstrate the effect and efficiency advantages of the PS algorithm over several mainstream inverse design algorithms by a comprehensive contrast experiment and explain these advantages in theory from several perspectives.

Quantum states generation and manipulation in a programmable silicon-photonic four-qubit system with high-fidelity and purity

We present a programmable silicon photonic four-qubit integrated circuit for the generation and manipulation of diverse quantum states. The silicon photonic chip integrates photon-pair sources, pump-reducing filters, wavelength-division-multiplexing filters, Mach–Zehnder interferometer switches, and single-qubit arbitrary gates, enabling versatile state preparation and tomography. We measure Hong–Ou–Mandel interference with an impressive 98% visibility using four-photon coincidence, laying the foundation for high-purity qubits. Our analysis involves estimating the fidelity and purity of distinct quantum states through maximum-likelihood estimation applied to tomographic measurements. In our experimental results, we showcase the following achievements: a heralded single qubit achieving 98.2% fidelity and 98.3% purity, a Bell state reaching 95.2% fidelity and 94.8% purity, and a four-qubit system with two simultaneous Bell states exhibiting 87.4% fidelity and 84.6% purity. Finally, a four-qubit Greenberger–Horne–Zeilinger (GHZ) state demonstrates 85.4% fidelity and 81.7% purity. In addition, we certify the entanglement of the four-photon GHZ state through Bell’s inequality violations and a negative entanglement witness.

Towards High-Performance Pockels Effect-Based Modulators: Review and Projections.

The ever-increasing demand for high-speed data transmission in telecommunications and data centers has driven the development of advanced on-chip integrated electro-optic modulators. Silicon modulators, constrained by the relatively weak carrier dispersion effect, face challenges in meeting the stringent requirements of next-generation photonic integrated circuits. Consequently, there has been a growing interest in Pockels effect-based electro-optic modulators, leveraging ferroelectric materials like LiNbO3, BaTiO3, PZT, and LaTiO3. Attributed to the large first-order electro-optic coefficient, researchers have delved into developing modulators with expansive bandwidth, low power consumption, compact size, and linear response. This paper reviews the working principles, fabrication techniques, integration schemes, and recent highlights in Pockels effect-based modulators.

TRENDS OF THE MICROWAVE PHOTONIC RADARS

Today, the world's leading countries are intensively working on the development of new generation radars - microwave photonic radars. Microwave photonic radars make it possible to significantly reduce the mass and size characteristics of radar stations, to increase the information capability and range of target detection due to the reduction of losses in long communication lines when using optical fiber, to ensure high immunity due to the significantly lower sensitivity of optical-electronic equipment and fiber-optic lines of communication connection to external electromagnetic influences. Microwave photonics provides wide bandwidth, flat response, low loss transmission, multi-dimensional multiplexing, ultra-fast analog signal processing and immunity to electromagnetic interference. Radar implementation in the optical domain can provide better resolution, coverage, and speed performance, which would be difficult to implement with traditional electronics. The review article examines the state of development and system architectures of such photonic radars as optoelectronic hybrid radars, all-optical radars, multifunctional microwave photonic radar systems, distributed microwave photonic radars, software-defined radars, and cognitive radars. New technologies in this field and possible future directions of research are discussed. As an example, a broadband microwave photon radar reproduced on the basis of a microcircuit is considered. The broadband signal generator and receiver are built into the silicon crystal on the insulator. A high-precision distance measurement with a resolution of 2.7 cm and an error of less than 2.75 mm was obtained. Visualization of multiple targets with complex profiles has been implemented. But the performance of most integrated microwave photonic chips is not yet satisfactory for practical radar applications. Monolithic integration of key microwave photonic subsystems is also not mature enough for practical applications, so hybrid integration of devices fabricated on their optimal integration platforms is of practical interest. At present, indium phosphide, silicon nitride and silicon on insulator are the three leading platforms for photonic integration

Implementation of photonic crystal based optical full adder using ring resonators

In this paper, the implementation of an all-optical full adder based on a two-dimensional photonic crystal is proposed. The proposed structure consists of hexagonal lattice of silicon rods embedded in air substrate. To design the proposed optical full adder, three nonlinear ring resonators, some linear waveguides, and some point defects are used. The switching mechanism of the ring resonators is based on nonlinear Kerr effect. The performance of the proposed structure has been analyzed and investigated by using plane wave expansion (PWE) and finite difference time domain (FDTD) methods. The minimum contrast ratio of the structure is 17.02 dB. The response time of the structure is 0.724 ps and can operate at a bit rate of 1.381 Tb/s. The proposed structure is simple, compact, and offers high contrast ratio, fast response time along with high bit rate and therefore can be a promising candidate for high speed data processing, computing, networking, and optical integrated circuits.

Low-loss and high-index contrast ultraviolet-C free-standing waveguides made of thermal silicon oxide.

Photonics in the ultraviolet provides an avenue for key advances in biosensing, pharmaceutical research, and environmental sensing. However, despite recent progress in photonic integration, a technological solution to fabricate photonic integrated circuits (PICs) operating in the UV-C wavelength range, namely, between 200 and 280 nm, remains elusive. Filling this gap will open opportunities for new applications, particularly in healthcare. A major challenge has been to identify materials with low optical absorption loss in this wavelength range that are at the same time compatible with waveguide design and large-scale fabrication. In this work, we unveil that thermal silicon oxide (TOX) on a silicon substrate is a potential candidate for integrated photonics in the UV-C, by removing the silicon substrate under selected regions to form single-side suspended ridge waveguides. We provide design guidelines for low-loss waveguide geometries, avoiding wrinkling due to residual intrinsic stress, and experimentally demonstrate waveguides that exhibit optical propagation losses below 3 and 4 dB/cm at a wavelength of 266 nm with claddings of air and water, respectively. This result paves the way for on-chip UV-C biological sensing and imaging.

Ultra-high NA graphene oxide flat lens on a fiber facet with near diffraction-limited focusing

The realization of a high numerical aperture (NA) fiber lens is critical for achieving high imaging resolution in endoscopes, enabling subwavelength operation in optical tweezers and high efficiency coupling between optical fibers and photonic chips. However, it remains challenging with conventional design and fabrication. Here we propose an ultrathin (400 nm) graphene oxide (GO) film lens fabricated in situ on a standard single-mode fiber facet using the femtosecond laser direct writing technique. An extremely high NA of 0.89 is achieved with a near diffraction-limited focal spot (FWHM=0.68λ), which is verified theoretically and experimentally. The diameter of the fabricated fiber GO lens is as small as 12 μm with no beam expansion structure. The proposed fiber GO lens is promising for applications such as super-resolution imaging, compact optical tweezers, medical endoscopes, and on-chip integration.

Graphene Thermal Infrared Emitters Integrated into Silicon Photonic Waveguides.

Cost-efficient and easily integrable broadband mid-infrared (mid-IR) sources would significantly enhance the application space of photonic integrated circuits (PICs). Thermal incandescent sources are superior to other common mid-IR emitters based on semiconductor materials in terms of PIC compatibility, manufacturing costs, and bandwidth. Ideal thermal emitters would radiate directly into the desired modes of the PIC waveguides via near-field coupling and would be stable at very high temperatures. Graphene is a semimetallic two-dimensional material with comparable emissivity to thin metallic thermal emitters. It allows maximum coupling into waveguides by placing it directly into their evanescent fields. Here, we demonstrate graphene mid-IR emitters integrated with photonic waveguides that couple directly into the fundamental mode of silicon waveguides designed to work in the so-called "fingerprint region" relevant for gas sensing. High broadband emission intensity is observed at the waveguide-integrated graphene emitter. The emission at the output grating couplers confirms successful coupling into the waveguide mode. Thermal simulations predict emitter temperatures up to 1000 °C, where the blackbody radiation covers the mid-IR region. A coupling efficiency η, defined as the light emitted into the waveguide divided by the total emission, of up to 68% is estimated, superior to data published for other waveguide-integrated emitters.

Monolithically Integrated Michelson Interferometer Using an InGaAs/InAlAs Quantum Cascade Laser at λ = 4 µm

In the present article, we propose a monolithically integrated Michelson interferometer using a λ = 4 µm InGaAs/InAlAs quantum cascade laser as the light source. By using simple fringe detection and a four-point interpolation on each fringe, we will be able to detect minimal object displacements of 500 nm—corresponding to 25% of half the laser emission wavelength. Such an interferometric photonic integrated circuit has interesting applications for precision computerized numerical controlled machines. Since the industrial standard of such machines currently consists of glass-based linear encoders with a resolution of 5 µm, our interferometer-based system will enable an improvement of at least one order of magnitude.