Integrated Optics: Devices, Materials, and Technologies XXIX

Attoseconds: When intense light interacts with a gas of atoms (or a transparent solid), electron wave packets are released. Attosecond pulse formation exploits the correlated electrons and holes, forcing the electron to return. Without the plasma connection, two of the most important strong-field process that accompany attosecond pulse formation—hot electron formation (inverse Bremsstrahlung) and non-sequential double ionization (collisional ionization)—seemed mysterious. These plasma-like processes lead to laser induced electron diffraction and orbital tomography. THz generation: Terahertz pulse formation by ionization has a similar linage. Using PIC codes to describe azimuthally polarized l=4 mm and 2 mm light interacting with a 150 µm thick jet of helium, we calculate THz pulses reaching 8.5 Tesla. But 10 Tesla is not a limit. 30 THz azimuthally polarized beams can be amplified in high-pressure CO2 reaching isolated magnetic fields of 1-gigagauss.

In recent years, topological phenomena in photonic systems have attracted much attention, with their striking features arising from robust states in the energy gaps of spatially periodic media. However, light waves are entities that extend in space as well as time, such that one may ask whether topological effects can also occur in the temporal domain, or even space-time. Intuitively, systems that are periodic in time may be gapped in momentum, leading to topological states localized at time interfaces. However, time - in contrast to space - exhibits a unique unidirectionality often referred to as the “arrow of time”. Inspired by these features, I will present our most recent experiments on topological states residing at temporal interfaces. Moreover, I will discuss the formation of spacetime-topological events and demonstrate unique features such as their limited collapse under disorder and causality-suppressed coupling.

Quantum technologies promise a change of paradigm for many fields of application, for example in communication systems, in high-performance computing and simulation of quantum systems, as well as in sensor technology. However, the experimental realization of suitable system still poses considerable challenges. Current efforts in photonic quantum science target the implementation of practical devices and scalable systems, where the realization of quantum devices and controlled quantum network structures is key for envisioned future technologies. Here we present our progress on the engineering of integrated photonic systems, which can overcome current limitations for the realization of scalable photonic systems. Specifically, our research currently focuses on three different but complementary topics: integrated devices based on lithium niobate circuits, engineering and harnessing the temporal-spectral structure of quantum states of light, and photonic quantum computation.

Microwave photonic (MWP) transversal signal processors offer an attractive solution for versatile high-speed information processing by combining the advantages of reconfigurable electrical digital signal processing and high-bandwidth photonic processing. With the capability of generating a number of discrete wavelengths from micro-scale resonators, optical microcombs are powerful multi-wavelength sources for implementing MWP transversal signal processors with significantly reduced size, power consumption, and complexity. By using microcomb-based MWP transversal signal processors, a diverse range of signal processing functions have been demonstrated recently. Here, we present a detailed analysis for the processing inaccuracy that are induced by the imperfect response of experimental components. We investigate the errors arising from different sources including imperfections in the microcombs, electro-optic modulator chirp, chromatic dispersion of the dispersive module, shaping errors of the optical spectral shapers, and noise of the photodetector. Next, we provide a global picture quantifying the impact of different error sources on the overall system performance.

Energy efficiency is a major metric for both photonic devices and integrated photonic circuit (PIC) system. Compact device size and high integration density, two intrinsic merits of silicon photonics, don’t necessarily translate into high energy efficiency. In this talk, we will attempt to discuss how heterogeneous integration innovations from material, device physics and architecture perspectives are able to enable low power device and large-scale PIC operation for both optical commutations and computing applications.

In this invited talk, we will present our recent work on the design and optimization of photonic devices and metasurfaces for both integrated optical systems and free-space applications. We will discuss how the use of advanced techniques based on optimization and machine learning can help efficiently exploring large design spaces, giving access to complex geometries that offers improved performance but cannot be easily handled with classical design approaches.

Rare-earth-doped glass has proved to be a highly effective material for the manufacture of optical amplifiers and lasers. In this presentation, we will review the work carried out at the CROMA laboratory on rare-earth-doped integrated lasers using the ion-exchange technology. We will first focus on narrow linewidth laser sources and their applications such as THz carrier generation for high-speed optical telecommunications. We will then present our efforts to monolithically integrate a saturable absorber into our laser cavities. These developments have led to Q-switched lasers that have been successfully used in various LIDAR systems.

Er-doped rare-earth oxide single crystal thin films, which can be directly grown on silicon substrate, are promising material candidates for high-gain on-chip optical amplifiers. We have previously grown high-quality Er-doped Gd2O3 (Er3+:Gd2O3) thin films on silicon-on-insulator substrates and demonstrated low-loss SiN strip-loaded waveguides based on these thin films. In this work, at cryogenic temperatures from liquid helium to nitrogen temperatures, we observed in the waveguide transmission spectra that the absorption dips of Er3+ ions in the telecommunication band evolved into peaks upon optical pumping, thus demonstrating an unambiguous optical gain. We estimate the that peak material gain of our thin films around 1536 nm is larger than 55 dB/cm for Er doping concentration of ~3×10^20 cm-3. These results indicate that single crystal Er3+:Gd2O3 thin films are very promising candidates for silicon-based on-chip active photonic devices.

The Al2O3 waveguide platform is an excellent candidate for monolithic and scalable fabrication of waveguide amplifiers. After successful demonstrations of sputter-deposited waveguides doped with Er3+, Yb3+ and Tm3+ ions, gain in the O-band is sought by means of Nd3+ ions, which form a four-level gain medium at a wavelength of 1330 nm. Preliminary results have shown on-chip gain of approximately 17 dB in a 7.52 cm long channel waveguide at 1064 nm. In this work, the optimization of Nd3+ doped Al2O3 optical waveguides to achieve net gain in the O-band is discussed.

The 2023 Nobel Prize in Chemistry awarded to three US-based scientists by recognizing their 40-year achievement in nanoparticles and colloidal quantum dot (QDs). In parallel, however, in 1981/82, we proposed the concept of 3D quantum-confined heterostructures (i.e., QDs) and their application to lasers as a new development in semiconductor nanophysics that began with semiconductor superlattices. Subsequent advances made QDs one of the fundamental nanostructures in photonics and electronics. In particular, QD lasers are the first practical quantum mechanical devices that take advantage of the fully discrete nature of electron energy, with approximately one million chips shipped to the market each year. Nowadays, QDs are also applied to quantum computing and quantum communications. In this talk, we review the early explorations of QD technology in physics and chemistry and describe recent advances in QD lasers as an essential light source for silicon photonics, enabling COP/IOI. We also discuss the current state of the art for realizing high-quality QD-based single-photon sources for quantum-integrated photonics.

Titanium:sapphire lasers are the workhorses of optics laboratories, and are crucial for fundamental research and numerous technological applications, including optical frequency combs, two-photon microscopy and quantum technologies. Following recent advances in photonics design, fabrication, and heterogenous integration, we demonstrate that a tunable continuous wave Titanium:sapphire (Ti:sapphire) laser can be miniaturized into sub-cubic centimeter volume together with its pump. We demonstrate a tunable chip scale laser in Ti:sapphire on insulator (Ti:SaOI) platform, and show how it can replace commercial tabletop Ti:sapphire lasers in solid state quantum optics experiments without loss in performance. Moreover, we demonstrate an integrated Ti:SaOI optical amplifier operating below 1 μm wavelength with a distortion-free amplification of picosecond pulses to peak powers reaching 1.0 kW. Our work represents a three-orders-of-magnitude reduction in cost and footprint of Ti:sapphire lasers, and introduces solid-state broadband amplification of sub-micron wavelength light.

Mode-locked miniaturized lasers in the infrared have been demonstrated through integration of laser diodes with low-loss photonic integrated circuits. However, additional challenges at shorter wavelengths, such as higher loss, smaller tolerances and availability of integrated saturable absorbers have prevented the realization of such lasers in the visible range. Here, we demonstrate the first hybrid integrated mode-locked diode laser in the visible (λ=640 nm), based on a gallium-arsenide gain chip and a low-loss silicon nitride feedback chip. The laser is passively mode-locked using a saturable absorber, realized through electrical isolation of part of the gain section by focused ion beam milling. The laser shows a broad range of driving parameters that support stable mode-locking, achieving a maximum average output power of 3.2 mW, with a spectral bandwidth of 1.5 nm. Measurements reveal a repetition rate of 7.84 GHz, with a corresponding Lorentzian RF linewidth component of 11.4 kHz.

Hybrid integration of semiconductor optical amplifiers (SOAs) with silicon nitride (Si3N4) waveguides enables compact on-chip light sources with outstanding properties for integrated photonics applications. For example, LiDAR systems used in robotics, drones, and autonomous vehicles, require high coherence, compactness, and power-scalability over multiple channels. To meet these requirements, we present a widely tunable and narrow-linewidth InP/Si3N4 hybrid-integrated laser, which is co-integrated with a 4-channel SOA-array for power amplification across multiple output channels. The co-integrated device is compact, with a total footprint of 6 × 4.7 mm2, making it suitable for standard 14-pin butterfly packaging. The laser features a wavelength tuning range of 90 nm, ranging from 1490-1585 nm and exhibits an intrinsic linewidth of 552 Hz. The SOA-array provides amplification for a total output power of 187 mW added up over four fiber-coupled output channels.

A low threshold optofluidic microlaser have been achieved using only polymeric materials and lamination process. The resonator is fabricated by two commercially available (3M) plane parallel Bragg mirrors composed of hundred layers with alternating high- and low-index layers of polyester and acrylic polymer with a high reflectivity (R>96%). The cavity, the mirrors and the substrates are assembled by a cold lamination process. This approach simplifies the fabrication procedure while retaining high optical surface quality, resulting in a compact, low-cost disposable device. As gain medium a water solution of Rhodamine B with a concentration of 0.9mM has been employed. A pulsed laser (557 nm wavelength, 5 ns pulse width, 10 Hz repetition rate) normally incident into the FP microcavity through a lens with a focal spot size of 140 μm has been used for the measurements. The device shows a threshold of 1 μJ/mm2 with emission peaks centered at around λ =632 nm.

Laser manipulation of ions is crucial for high-fidelity quantum information processors. Increasing the number of qubits improves quantum computer performance. However, scaling optical signal delivery to multiple ions is challenging. Here, we propose integrating photonic circuits into trapped-ion chips for efficient optical addressing of 88Sr+ ions and full qubit control. Combining machine learning with electromagnetic optimization reduces design costs and accelerates component discovery. We demonstrate a deep-adjoint-based multicolor focusing grating coupler (FGC) for precise ion control, achieving high radiation efficiency and minimal crosstalk. Compact FGCs outperform the state-of-the-art couplers and have potential applications in quantum computers, sensors, and optical clocks.

Within our work we combine periodically poled thin-film lithium niobate waveguides with large bandwidth polymer fiber-to-chip couplers in order to realize integrated squeezed light sources . Different design approaches based on periodically poled lithium niobate for spontaneous parametric down conversion and micro-ring resonators are discussed. Their characteristics are compared regarding reproducibility, fabrication complexity alongside with their performance in terms of squeezing level, threshold power and scalability. The as presented platform for squeezed light sources has the capability for versatile, low-loss integrated squeezers with squeezing levels >10dB. Additionally, the ability to simultaneously achieve high coupling efficiency to optical fibers via the use of polymer couplers holds great promise for large-scale CV quantum computing via time-multiplexing.

In the rapidly evolving field of quantum computing, precise and scalable control of qubits is paramount. We present a hybrid photonic processor designed for individual, parallel qubit control within neutral atom quantum computing systems. Our device synergizes silicon nitride (Si3N4) power divider and thin-film lithium niobate (TFLN) for high-speed electro-optic modulation, offering a compact and efficient alternative to traditional free-space optical setups. The processor features a Mach-Zehnder Interferometer (MZI) configuration, which facilitates precise modulation and compensation for fabrication variances and environmental changes. Experimental validation demonstrates the AWG's capability to generate customizable pulse shapes essential for single-atom control. The compact configuration achieves a switching speed surpassing 15 GHz and an extinction ratio of 50 dB, critical for high-fidelity single-atom manipulation. This hybrid integrated photonic processor is a significant advancement in optical single-atom addressing, offering a scalable and cost-effective solution for the deployment and growth of neutral atom quantum computers.

We present recent developments of a monolithically integrated Quantum Simulator (QS) platform where the silicon nitride quantum micro-photonic and the mature silicon microelectronic (CMOS, digital) functionalities are merged into a unique photonic-electronic platform. We will describe a 3D-integrated quantum simulator hardware, where (1) photonic quantum interference circuits are integrated on the same Si chip with (2) scalable arrays of single photon avalanche diodes (Silicon SPADs) operating at ~ 800nm and at room temperatures. Around this, we build an integrated system, in which on the “software level” quantum algorithms sustain the quantum simulation results from the hardware. In this last, a custom analog chip controls the QS module by managing the photon source, phase shifters which reconfigure the photonic circuits and the SPADs in order to control actively the quantum optical circuit. Finally, the output data are handled by the digital chip to feed the software algorithm.

We present the implementation of a PIC-based nonlinear frequency division multiplexed transmission system in which spectrally overlapping channels are stitched together without frequency guard bands to obtain a seamless spectrum. To coherently combine the channels with partial overlaps, the channels are generated using a comb source whose pulse repetition rate is synchronized with the clock used to generate the electronic signals. After that, all channels are linearly multiplexed using a PIC in which the delay and phase of all the optical paths are balanced and dynamically corrected. The proposed solution can fill large optical bandwidths while keeping the computational complexity to that of independently processing multiple low bandwidth channels.

The development of large-scale computational models and the need for low latency responses have correspondingly prompted a search for architectures which can reduce the cost and power demanded to realize these systems. In the context of Integrated Photonic Circuits, we present a further degree of improvement that can be achieved in crossbar systems by employing temporal buffering of a modulated signal on-chip. Herein, we demonstrate a system for local temporal interweaving on single photonic chip using a Lithium Niobate on Insulator platform. The as-fabricated device utilizes an on-chip modulator with a low Vpi of ~2.2V cm in conjunction with a circulating memory buffer clocked at 4 GHz. We effectively benchmark this system with a small device footprint on traditional image convolution applications.

Integrated photonics innovation is core to advancing optical technologies that extend Moore's Law and support the explosion of data processing for AI, ML and quantum computing. A key proving ground for hitting performance milestones is in real applications in the data center such as pluggable module-based solutions. NewPhotonics is pioneering and applying research on optical signal processing across the transceiver and receiver data flow to deliver high performance latency, power reduction and interoperability outcomes in transmitter chips. In both performance and scale the critical leap to optical-domain connectivity solutions is the key to addressing the speed, energy efficiency and footprint demands of an ever-increasing data-driven global marketplace. This presentation by NewPhotonics CTO Yosef Ben Ezra, PhD will convey key advances in equalization in all-optics innovation driving next-generation integrated photonic interconnect solutions.

A Photonic Vertical NAND FLASH memory consists of a vertical NAND FLASH transistor (which is a traditional vertical NMOSFET with multiple gates as Word Lines), VCSELs (Vertical Cavity Surface Emitting Lasers) in the top drain region, an optical waveguide, and photon sensors in the well region (Bit Line). When gate voltages are forced to the Word Lines, and a drain voltage is applied (Bit Line), the entire vertical NAND FLASH NMOSFET is turned on (READ operation). When the gate voltage is set to 0V, the vertical NAND FLASH NMOSFET is turned off, so as the lasers and photon sensors. Much faster WRITE and ERASE operations may also be accomplished with the photonic processes, as demonstrated in the following sections.

We introduce a cutting-edge photonic random-access memory (P-RAM) that utilizes the broadband transparent phase-change material Ge2Sb2Se5 (GSSe) to achieve multilevel, nonvolatile storage capabilities on a silicon-on-insulator platform. This technology leverages the ultra-low absorption characteristics of GSSe in its amorphous state to facilitate high-efficiency optical data storage with minimal insertion losses, marking a substantial improvement over traditional phase-change materials like GST.

Adaptive Optics (AO) is facilitating new forms of laser beam shaping from which novel forms of three-dimensional (3D) nano-structures may be tailored inside of transparent material by ultrashort-pulsed laser interaction. The assembly of such tailored nano-diffractive elements into micro-optic diffractive optics presents new opportunities for photonics integration and packaging that encompasses 3D processing over a broad range of applications based inside of bulk glasses, thin transparent films, and optical fibre. The presentation explores opportunities for integrating multi-functional photonic and opto-fluidic devices into a compact platform of lab-in-fiber (LIF) or fiber cladding photonics that bypass requirements for integration of planar waveguide circuits with fiber optic networks. Alternatively, the 3D laser nano-structuring promises new means for fiber-to-chip packaging with 3D waveguide circuits, for example, the formation of low profile interposers that permit low-loss grating coupling of optical fibers to silicon photonic chips.

The scope of photonic integrated circuits (PICs) has expanded to applications where the material properties of silicon present limitations. Silicon nitride (SiN) has emerged as a pivotal technology for the development of PICs, offering a complementary solution to silicon-based platforms due to its versatile optical properties. These properties have established SiN as an optimal material for a broad spectrum of applications, ranging from NIR to visible wavelengths. In this talk, we highlight our journey to demonstrate low-loss and low-temperature (<350°C) silicon nitride layers with refractive indices ranging between 1.5 and 2.7, showcasing their potential to enable enhanced linear and nonlinear functionalities in both near-infrared and visible wavelength regimes paving the way for innovative applications in various technological fields.

Thin-film lithium niobate (TFLN) platforms are increasingly recognized for their high second-order nonlinearity and excellent light confinement, facilitating efficient frequency mixing over millimeter-scale lengths. To overcome integration, coupling losses, and fabrication challenges, we have developed TFLN-based photonic platforms with adjustable thickness and user-friendly tapers. These platforms incorporate microguides transitioning from titanium-diffused waveguides to micrometer-thin suspended films, achieving coupling losses as low as 0.8 dB per facet with standard SMF28 fibers. A significant feature of these platforms is their high tunability: devices such as intensity modulators, polarization modulators, and frequency converters can be finely tuned via external controls like voltage, stress, or temperature. Key examples include a 200 µm Fabry-Perot micro-modulator with 60 pm/V tunability, a polarization modulator with 180° phase control, and a nonlinear frequency converter covering the C-band. Additionally, we introduce photonic-crystal-based sensors with 700 nm active lengths, supporting diverse applications from high-speed communications to artificial intelligence.

Photonics integrated circuits support an immense signal bandwidth with very linear behavior and low losses, making them ideal for analog signal processing in (fiber-based) distributed systems. Both optical and microwave signals (encoded on an optical carrier) can be filtered, equalized, shifted in frequency, and converted between domains. By chaining these different functions together in larger circuits with configurable connectivity, and making every element tunable, it becomes possible to create multi-functional analog signal processors. We will present our recent results in realizing such programmable photonic systems, which combine lasers, modulators, filters and detectors on a single chip, and interface them with the necessary driver and control electronics. We will also discuss the key challenges to scale such systems, including algorithms and software, and how they can redefine how developers and researchers use photonic chips.

This work presents a compact trident edge coupler fabricated on silicon nitride platform. We report an insertion loss as low as 0.7dB/facet, with a polarization dependent loss of 0.2-0.3dB over C-band, when coupled with a taper lensed fiber. The trident edge couplers are fabricated in a single etch step, without the need for substrate removal, and with a device footprint of less than 100μm. The combination of high efficiency, compact footprint, and non-stringent critical dimensions makes the trident coupler an excellent candidate for applications requiring extremely low loss fiber-to-chip coupling.

Integrated optical phased arrays (OPAs), fabricated in advanced silicon-photonics platforms, enable manipulation and dynamic control of free-space light in a compact form factor, at low costs, and in a non-mechanical way. This talk will highlight our work on developing OPA-based platforms, devices, and systems that enable chip-based solutions to high-impact problems in areas including LiDAR sensing for autonomous vehicles, augmented-reality displays, 3D printing, optical trapping for biophotonics, and trapped-ion quantum engineering.

This study introduces a novel waveguide system for capturing eye images in augmented reality (AR) glasses. While waveguides are commonly used to transmit light from display engines to users' eyes, they are generally unsuitable for imaging objects at close distances (15-25 mm), critical for eye-tracking applications. To overcome this limitation, we propose waveguide architectures with diffractive optical elements, enabling a direct view of the user's eye while meeting the compact form factor of AR glasses. These designs allow eye image capture for tracking purposes within the limited bandwidth of waveguide systems. We validated our approach by fabricating a prototype and capturing images of an eye robot and a test pattern at the eye relief distance. The captured images were evaluated using standard optical metrics: field of view, modulation transfer function, and uniformity, confirming their suitability for eye-tracking. This waveguide design achieves sufficient image quality for accurate eye-tracking, minimizing the keystone effect and enabling seamless calibration with a hidden, temple-integrated camera.

OSCP has developed a promising technology using both interferometric spiral and resonant ring-based PIC microchips exploiting the Sagnac effect to sense rotation with a high accuracy. The patented optical gyro design can achieve performance comparable to that of Fiber Optic Gyroscopes (FOG) while having a much smaller form factor and lower power consumption. In this paper, we report on progress towards developing our passive spiral-type Sagnac microchips, as well as on our active PIC microchips used to perform optical signal processing. We also present the integration of these passive and active PIC microchips with electronic hardware to achieve a low-power, small form factor optical gyroscope module.

Integrated Photonic Ultrasound Transducers (IPUTs) provide a route towards improved performance in medical ultrasound imaging. IPUTs consist of a waveguide-based ring resonator or Mach Zehnder Interferometer (MZI) on a thin membrane. The sensitivity of a single IPUT (100 um diameter, acoustic frequency near 1 MHz) is better than traditional ultrasound transducers. The sensitivity per unit area, however, can even be orders of magnitude larger due to the small IPUT dimensions. The key challenge is therefore to combine the responses of many IPUT elements into a single ultrasound transducer. We experimentally demonstrate that our proposed architecture of multi-element transducers leads to a sensitivity that scales linearly with the number of elements, and report a 100-fold reduction in Noise Equivalent Pressure compared to state of the art.

This research contributes to advancing the field of nanophononics by demonstrating practical applications of a plasmonic waveguide XOR logic gate at different telecommunication laser wavelengths. We demonstrate the feasibility and efficiency of employing plasmonic materials in developing compact and functional nanophotonic devices. Furthermore, the integration of numerical simulations, experimental validation, and digital image processing provides a comprehensive framework for the development and characterization of future nanophotonic systems.

Integrating plasmonic chains onto a dielectric waveguide enables efficient individual excitation of plasmonic nanostructures. Nevertheless, the broad operation bandwidth related to plasmonic resonance remains a drawback for some applications. We propose a novel design based on planarized encapsulated waveguides enabling flexible 3D positioning of the plasmonic chain with respect to the waveguide. Through numerical and experimental demonstrations, we show that a critical coupling regime between the waveguide and the resonant chain can be achieved by properly engineering the geometric parameters. This configuration allows for trapping all the waveguide mode energy inside the chain, resulting in a sharper spectral response with a strongly reduced group velocity. We apply temporal coupled mode theory to analyze this system and discuss the characteristics of this specific excited state of the plasmonic chain.

Methane concentrations often exceed the atmospheric background level of approximately 2 ppm across diverse industrial sites and landfills. Accurately registering subtle deviations from this atmospheric baseline, however, proves to be notoriously challenging, especially with chip-sized devices. Laser absorption spectroscopy with photonic integrated circuits (PICs) is emerging as a breakthrough in addressing this challenge. We have been developing optical waveguides [1], [2] for MIR and, recently, we designed and fabricated a silicon slot waveguide for operation at 3270.4 nm, which coincides with a strong absorption peak of methane [3]. The design was optimized for (i) a high air confinement, (ii) low lateral and substrate leakage, and (iii) single-mode operation at the target wavelength. Our slot waveguide employed for methane detection demonstrates a 1-σ detection limit (LOD) as low as 300 ppb. This is 1–2 orders of magnitude lower than the current state-of-the-art, and the first instance where an on-chip device shows the capability to register methane changes below atmospheric background levels. Furthermore, in our effort to make the sensor more applicable in practical settings, we acknowledge and address operational constraints, particularly focusing on the impact of atmospheric humidity on the sensor performance. We studied the impact by exposing the waveguide to 70–75% relative humidity, which yielded a total propagation loss of 13.8 ± 0.4 dB cm–1. Baking the waveguide at 115 ± 5 °C for 10 min and then keeping it in dry N2 atmosphere reduced the loss to the 8.3 ± 0.3 dB cm–1. Removing the water is thus a major concern and may require e.g., a hydrophobic coating to stabilize the loss in the future. References [1] M. Vlk et al., “Extraordinary evanescent field confinement waveguide sensor for mid-infrared trace gas spectroscopy,” Light Sci. Appl., vol. 10, no. 1, p. 26, Dec. 2021, doi: 10.1038/s41377-021-00470-4. [2] J. Salaj et al., “Suspended nanophotonic waveguide for isotope-specific CO2 detection,” Optica, vol. 11, no. 12, p. 1654, Dec. 2024, doi: 10.1364/OPTICA.533710. [3] H. D. Yallew et al., “Sub-ppm Methane Detection with Mid-Infrared Slot Waveguides,” ACS Photonics, vol. 10, no. 12, pp. 4282–4289, Dec. 2023, doi: 10.1021/acsphotonics.3c01085.

Photonic Integrated Circuits (PICs) operating in the mid-IR represent a rapidly developing field. The goal is to fill the technological gap with respect to the very well developed visible and near-IR PICs, thus enlarging the types of chip-integrated mid-IR photonic devices in view of applications. Recent developments on on low-loss passive waveguides on III-V semiconductor platforms are presented, optimized to operate in both the mid-IR atmospheric transparent windows (3-5 and 8-12 µm). We report on two material systems: GaAs/Al0.5Ga0.5As waveguides grown on GaAs substrate and In0.53Ga0.47As/InP waveguides grown on InP substrate. Different approaches have been investigated for the fabrication: ICP-RIE (in view of developing integrated racetrack resonators) and wet etching (to gauge the minimum loss value). The measurements, in TE and TM polarizations are based on the Fabry-Perot approach using a DFB laser at λ=8.5 µm and λ=4.6 µm. We will discuss how to further reduce the losses (0.1cm^-1 or less) and how to leverage on such low losses to develop two separate applications: ultra-high Q-factor resonators for Kerr comb generation, and integrated ultra-fast mid-IR modulators.

Photonic integrated circuits have revolutionized the telecom and datacom markets, similar to the earlier integrated electronics revolution. After two decades of rapid development, PICs are now poised to enter new application areas, such as IoT, smart environments, agriculture, automotive, digital health monitoring, security and safety. Moving beyond telecom wavelengths of 1.55 μm, these applications require expanding into the visible and mid-IR spectral ranges, with the mid-IR being particularly important for its unique chemical vapor fingerprints. In this presentation, we will discuss recent advancements by VIGO Photonics, WUT, and Lukasiewicz-IMiF in developing the MIRPIC integration platform, optimized for mid-IR. Key components like mid-IR light sources, detectors, and Ge-on-Si waveguides will be covered. The potential and market perspectives of the MIRPIC platform, developed under the IPCEI HyperPIC program, and the first mid-IR PICs foundry by VIGO Photonics will also be explored. This work received support from the National Center for Research and Development through projects MIRPIC (TECHMATSTRATEG-III/0026/2019-00) and HyperPIC (FENG.02.10-IP.01-0005/23, IPCEI ME/CT).

Recent works on the development of graded-SiGe photonic integrated circuits operating in the mid-infrared will be presented. More specifically, we will focus the presentation on : (i) integrated resonators operating around 8 µm wavelength with quality factors beyond 10^5, (ii) integrated high speed modulators operating in a wide spectral range, based on free carrier plasma dispersion effect. Then we will show that mid-IR graded SiGe photonics circuits can be fabricated on industrial-scale 200 mm wafers, and that low propagation losses can be obtained in a wide spectral range of the mid-IR. These results thus pave the way for a scalable silicon compatible mid-infrared platform.

Mid-infrared (MIR 3-15 µm) photonics is a burgeoning scientific and technological field with wide potential application domains including pollution detection, environmental monitoring, security, safety, astrophysics and many more...One of the key aspect is that many important molecules have fundamental ro-vibrational absorption lines in the MIR. An appealing approach, to create power efficient, sensitive, precise, compact molecular sensing devices is to develop an on-chip MIR platform integrating a bright and broadband light source, such as an integrated supercontinuum or a Kerr micro-comb. Ge-based platform (e.g. silicon germanium) has emerged as an attractive platform for nonlinear MIR photonics. We report on our latest progress on reconfigurable Ge-based photonics for bright and broadband MIR sources. We demonstrate that Phase change materials, like Sb2S3, are suitable for reconfigurable supercontinuum generation. We also report Ge-based ring resonators with quality factors reaching up to one million which is highly promising for power efficient MIR micro-comb generation.

Quantum walk combs have recently been found to be a robust method to obtain coherent and broadband mid-infrared (mid-IR) combs based on semiconductor and compact quantum cascade lasers (QCL). Together with the unique absorption characteristics of the mid-IR, this approach has great potential for spectroscopic sensing applications, among others. In addition, this approach can benefit from the remarkably low, broadband propagation losses of buried InGaAs/InP waveguides, and its homogeneous integration capability with QCLs.

Silicon (Si) photonics stands as a solid candidate to address the scaling challenges of emerging communication systems with an ever-growing number of interconnected devices. However, Si has major physical limitations that prevent on-chip integration of key functions including strong two-photon absorption limiting nonlinear optical phenomenon, an indirect bandgap nature hindering light emission and amplification and more specifically Si is a centrosymmetry semiconductor preventing ultra-fast and low power consumption optical modulation based on Pockels effect. The latter limitation strongly limits the evolution of the photonic integrated circuits (PIC). In this paper, an overview of the different approaches for light modulation in silicon will be presented including the plasma-dispersion effect, currently used in PIC and the Pockels based modulators integrated in Si circuits.

Lithium niobate on insulator is a promising platform for integrated quantum photonics. Its strong nonlinear coefficient and electro-optic effect allow the integration of photon pair sources and fast reconfigurable interferometers for many applications like boson sampling, QKD and quantum state generation. The photons are generated via spontaneous parametric down-conversion (SPDC). Two key aspects of the photon pairs are their bandwidth and the possibility to split them deterministically. Here we present a new source type where the generated photons travel in opposite directions and feature a narrow bandwidth of 5 nm in the forward and 20 nm in the backward propagation. The reduction of bandwidth and the separability are big advantages over the type-0-SPDC sources. Compared to the well-known type-2-SPDC sources we achieve a 3.6 times higher efficiency with similar bandwidths.

Optical parametric oscillators (OPOs) are key components for applications such as squeezing and random number generation. Their dense integration on-chip would allow the realization of computational networks such as Ising machines. However, the main challenges are related to the OPO footprint, the operation power and the coupling of the single OPOs. Here we present a thin film lithium niobate on insulator double resonant OPO where the nonlinear region is placed in a linear Fabry-Perot cavity formed by two Bragg reflectors, greatly reducing the footprint. Due to the presence of four different ports, the device geometry is suitable for device coupling and integration. The presented OPO generates a signal in the C-band and features a low on-chip threshold of 4 mW, which is lower than the state of the art for double resonant OPOs, and a 30 nm bandwidth, only limited here by reflection band of the mirrors adopted.

Waveguide-Integrated Superconducting Nanowire Single-Photon Detectors (WI-SNSPDs) combine the high sensitivity of SNSPDs with the scalability of photonic integrated circuits, revolutionizing photon detection. This talk will discuss recent advancements in WI-SNSPD technology, focusing on improved detection efficiency, timing resolution, and reduced dark count rates. These enhancements make WI-SNSPDs ideal for applications in quantum computing, quantum key distribution (QKD), and laser communications. By offering superior alignment accuracy and reduced optical losses, WI-SNSPDs promise more scalable and cost-effective solutions, paving the way for innovations in secure communications and high-speed data links.

This study presents a novel method for integrating optical isolators into photonic integrated circuits with a low thermal budget. The proposed approach uses Bismuth Terbium Iron garnet, which crystallizes at a lower temperature, and integrated micro-doped silicon heaters for local thermal treatment. This advancement enables the inclusion of optical isolators in standard manufacturing processes, overcoming previous limitations due to high thermal requirements.

Subwavelength silicon nanostructures provide unprecedented flexibility in the control of optomechanical effects. Here, we review our recent results on the use of nanostructures for the optimization of Brillouin interactions in suspended and non-suspended optomechanical cavities.

Subwavelength grating (SWG) metamaterials are periodic structures that enable precise control over the properties of electromagnetic waves propagating through them. Over the past two decades, photonic designers have leveraged this capability to demonstrate high-performance devices on silicon photonics chips. More recently novel SWG structures have been developed to engineer metamaterial anisotropy, enhancing performance and expanding the design space, but also increasing design complexity. This invited talk discusses our latest progress using inverse design algorithms together with advanced homogenization models of SWG metamaterials to demonstrate complex photonic devices with exceptional performance.

Optical microcavities have diverse applications in fields like quantum electrodynamics, semiconductor lasers, sensing, and nonlinear optics, but most microcavities are constrained to a few spatial mode profiles. Here, we present how dielectric metasurfaces can realize stable optical microcavities with holographic spatial mode profiles. We select a microscopic skier shape (20 x 20 um) as our desired mode profile. We then realize a Fabry-Perot-interferometer using two planar distributed Bragg reflectors (DBRs), with a metasurface placed on the surface of the second mirror. The metasurface is designed to negate the spatially dependent phase which the desired skier mode accumulates during one cavity round trip. By imaging the intracavity mode of the experimentally realized microcavity, we show that it selectively enhances light that couples to the desired skier mode at the design wavelength (633 nm). The holographic mode changes quickly with the cavity length, implying the possibility of implementing spatial profiles that change with cavity length. Dielectric metasurfaces provide phase and polarization control, suggesting polarization control in microcavities is also possible.

We will review the investigations that have been carried out over the past decade on waveguide Fabry-Pérot microcavities with an embedded input/output grating coupler, devices also known as Cavity-Resonant Integrated Grating Filters (CRIGFs). We will explain how the device geometry and use of various technological platforms (SiON, LiNbO3 on insulator, GaAs) has permitted the fabrication of spatially-localized wavelength filters that can operate from the near infrared to mid-infrared, subsequently enabling applications as edge-emitter laser spectral stabilization or as pixelated filter for (hyperspectral) imaging. Furthermore, we will show that the design can be adjusted to obtain critically-coupled high-quality factor microresonators with a view to induce efficient second harmonic generation or, more generally, nonlinear parametric conversion. Finally, we will present our most recent investigations that have been devoted to the selective excitation of the supported higher order spatial modes and how the latter can be used to implement reconfigurable logical gates.

In the last decade, aluminum nitride (AlN) has proven to be an attractive material for both linear and nonlinear integrated photonics, due to its large transparency window, its low propagation losses and the presence of both second and third-order nonlinear optical susceptibilities. However, the investigation and optimization of AlN layers for photonic applications have been scarcely explored in literature so far, although it represents an important stepping stone upon which will impact the final performance of AlN-based devices. Here we present a systematic comparison of various types of AlN epilayers grown on sapphire by metalorganic vapor-phase epitaxy. Optical losses are measured from waveguides and microring resonators fabricated from different AlN epilayers. The results are analyzed through a comprehensive material characterization study, showing the need to optimize growth techniques to push further the performance of AlN-on-sapphire photonic devices.

Aluminium Oxide (Al₂O₃) UV waveguides were fabricated in a 200 mm CMOS pilot-line. Single mode waveguides losses were measured to be 0.6±0.17 dB/cm and 0.2±0.04 dB/cm for UV and blue wavelengths. These waveguides have been fabricated along with other passive elements such as power splitters and couplers. Additionally, the thermal heaters as active elements have been realized with a ΔPπ of 57.6±0.2 mW.

We developed an MMI-type RGB coupler with 100-mW blue light input using a ZrO2-doped silica-based planar lightwave circuit (ZrO2-doped PLC) for a compact RGB laser light source. The fabricated coupler was about 7.5 µm wide and 900 µm long without fan-in/fan-out and had the transmittance of approximately –1.0 dB at R, G, and B wavelengths. Moreover, its transmittance did not change after a 445-nm, 100-mW, 300-h light input test.

The gallium nitride material family offers an attractive platform to extend the application range of integrated photonics down to wavelengths in the blue and ultraviolet spectral range. Simultaneously, it provides the possibility to integrate light sources such as LEDs and lasers with waveguides and meta-optics to gain full control over all dimensions of light. To this end, not only is control over the dimensional properties of nanophotonic structures necessary, but flexibility in the refractive index of involved materials is also highly beneficial. Porous gallium nitride fabricated by ion implantation and electrochemical etching can provide this versatility. In this contribution, we report on porous gallium nitride as an emerging material for 3D buried integrated photonics and discuss devices as well as technological boundary conditions.

Quantum communications are increasingly being developed since they ensure a private and secure transmission of data. However, their intrinsic strength, the impossibility of cloning a quantum data, entails also a major challenge that is the implementation of quantum repeaters. Based on the propagation of photon entanglement, these devices are not relying on optical amplifiers like their classic counterpart but are comparing pairs of photons thanks to quantum optical memories. Two main options are currently studied for implementing this function: the first one is using cold atoms while solid state solutions are based on erbium ions highly diluted into crystals operated at cryogenic temperatures. In this communication, we propose the integration of Er-doped Yttrium Orthosilicate, Y2SiO5 (YSO) on an ion-exchanged waveguide in order to combine the excellent quantum properties of Er-YSO with the reliability, efficiency and compactness of integrated devices on glass. We will present the design, fabrication and characterization of this hybrid waveguide as well as its qualification at low temperature.

The large bandgap of aluminum oxide (Al2O3) makes it a suitable candidate for exploring photonic integrated circuits that operate in the ultraviolet wavelength range. This work focusses on thermal modulators to showcase the capability of adding functionalities to passive aluminium oxide waveguides designed for ultraviolet wavelengths. Preliminary results, obtained with a Mach-Zehnder modulator at a wavelength of 369 nm, show thermal phase tuning with a Pπ of 53.8 mW and an extinction ratio of 24 dB.

Scandium (Sc)-doped aluminum nitride (AlN) has been widely used as a piezoelectric material in micro-electromechanical systems (MEMS) devices. Recently, it also draws interests in photonics research contributed by its enhanced nonlinear optical property. Here, we report the (n, k) values of Sc-doped AlN thin films under various doping concentrations. These thin films with thickness of around 500 nm are deposited on silica through co-sputtering process. Reduced optical bandgap energies are observed at higher Sc doping concentrations. Furthermore, the top surface roughness of < 1 nm has been obtained through atomic force microscopy (AFM) measurement for the 30% Sc-doped AlN film in a 1 × 1 μm^2 region. Also, with etching process optimization, the 10% Sc-doped photonic waveguide sidewall angle and roughness have been obtained as >80° and < 5 nm, respectively. Additionally, the patterned microring cavity has been characterized, with estimated intrinsic Q of 5.54×10^4. The reported results here pave the way towards Sc-doped AlN for integrated photonics, with potential applications in communication, sensing, and quantum computing.

We measure electro-optic coefficient with highly accurate transmission Teng and Man method to eliminate measurement error due to multi-reflection inside an active material.

Photonic integrated circuits (PIC) have been used in Optical Coherence Interferometry (OCT) for main OCT interferometers and clock resonators but it is still a nascent field. Two of the most important metrics for such use are the scattering and dispersion. These can be measured using Optical Frequency Domain Reflectometry (OFDR) and Optical Frequency Domain Transmission (OFDT). We use a MEMS tunable VCSEL in the 1050 nm range to perform these measurements.

Photonic biosensors, crucial for medical diagnostics, match or surpass traditional methods like ELISA and PCR in sensitivity, reliability, and efficiency. To be marketable, they must also be cost-effective and user-friendly. The cost per test is mainly influenced by the (disposable) cartridge containing the sensor chip and bioactive layer. Eliminating active components from the cartridge can reduce costs but complicates light coupling, especially at point-of-care locations, requiring sub-micrometer accuracy. We present a proof-of-concept system for point-of-care use that combines passive and active alignment. High accuracy is achieved during initial cartridge placement, establishing a “first light” state for active alignment. The system then fine-tunes positioning with actuators using a spiral alignment algorithm, optimizing coupling within 30 seconds and achieving a 36.5 dB SNR. Tests showed passive alignment accuracy of 1.3x0.8 µm. This automated system meets alignment requirements and adapts to variations in cartridge production accuracy.

We demonstrate a novel 4-channel microwave photonic demultiplexer fabricated in the Si3N4 TriPleX® waveguide platform. The demultiplexer allows for a fully reconfigurable passband bandwidth (BW), ranging from 42 MHz to 1.5 GHz, and central frequency tunability spanning in the whole Ka, Q and V band. Each channel is based on a high selectivity Coupled Ring Optical Waveguide (CROW) filter with 8 ring resonators, where the round trip length per ring is equal to 7.94 cm (free spectral range of 2.48 GHz). Reconfigurability is achieved by using power efficient (<1 μW) stress-optic lead zirconate titanate (PZT) - based actuators. The experimental evaluation of the filter shows fiber-chip-fiber insertion loss < 7.4 dB and a flattop passband with power ripple <1 dB. The 20 dB /1 dB BW steepness is given by a shape factor of 1.8, while the stopband suppression is equal to 55 dB. The group delay variation at the passband is < 2.5 ns.

Topology optimization is a powerful technique for inverse design, whose potential in nano and integrated optics is not fully explored yet due to fabrication limitations. In fact, most designs to date are obtained in 2.5D. 3D printing techniques, e.g. two-photon polymerization (2PP), are cost-efficient, provide faster prototyping capabilities than silicon foundries, and allow the manufacturing of free-form devices obtained via inverse design. Here, we explore for the first time the viability of 3D designs and their performance in comparison to 2.5D designs, laying the groundwork for potential integration of multiple functionalities, such as phase and polarization, within a single device instead of multiple discrete components. By overcoming the convergence issues characteristic of the polymer platform via multi-objective and multi-layer strategies, we realize 3D designs that are viable for manufacturing via 2PP for wavelength demultiplexing with better performance than their 2.5D counterpart.

This article presents a new optical measuring principle for torsion in which a laser beam is guided through a totally internally reflective (TIR) prism rod. The sensor system consists of a laser diode, the TIR prism rod and a detector. Torsion changes the angle at which the laser beam is reflected at the rod surfaces and thus the position at which the beam is decoupled from the rod and therefore its position on the detector. This effective change is amplified by multiple total internal reflections so that the deformation of the rod can be measured with high sensitivity. The verified optical principle enables the development of integrated optical sensors for mechanically stressed components like shafts to monitor their deformation during operation. These can be installed into highly stressed parts in order to measure the loads and monitor operating conditions and wear processes. Because of the encapsulation of the sensor, it is insensitive to environmental influences and disturbance, which means it can also be used where operating conditions or a lack of installation space make the use of conventional sensor technology, such as strain gauges or camera-based monitoring, impossible.

In this work, we measured human Serum Albumin proteins, which are vital proteins in the human body, using a photonic microring resonator (MRR) system. This system was combined with a novel readout unit utilizing an inexpensive dithering laser and a photodetector. Additionally, we developed a custom microfluidic delivery system. The MRRs were realized using silicon nitride-loaded amorphous silicon carbide waveguides. We assessed the thermal response of the MRR, which was calculated to be 16 pm/°C. During the Albumin measurements, the lowest concentration of 0.105 mg/mL exhibited a shift of 1.45·10⁻² nm after 15 minutes. In the next phase, these sensors will be used for detecting lung cancer autologous antibodies.

Integrated photon-pair sources utilizing spontaneous parametric down-conversion (SPDC) are gaining interest for their role in advancing quantum computing, metrology, and encryption technologies. Realizing efficient thin-film fabrication methods is crucial for mass production. Traditional techniques like etching, and lithography are time-consuming, expensive, and difficult to rectify. The two-photon polymerization (2PP) technique provides several advantages, including versatile substrate options, easy erasure and reprinting of structures, and rapid prototyping. We used 2PP to fabricate a strip-loaded lithium niobate waveguide chip as a photon pair source. Our platform showed an on-chip pair generation rate (PGR) of 34.35 MHz, a generation efficiency of 60.71 MHz/mW, and a coincidence-to-accidental ratio (CAR) of 5939. Erasing and reprinting the waveguides demonstrated the high reproducibility of our method. These results underscore the reliability and industrial potential.

We propose an optical information encryption approach using azimuth multiplexing, encoding images in cascaded diffractive optical elements (DOEs) with different rotation angles. While the approach works well in simulations, its experimental realization is challenging due to the sensitivity to positional shifts in DOEs. We aim to overcome these issues by enhancing shift tolerance. In this work, four different patterns were encrypted into cascaded DOEs designed using the proposed algorithm. The encrypted pattern can be correctly decrypted when the rotation angle of the first DOE is shifted by 0.5° from the designed rotation angle, indicating that it has a large shift tolerance. This approach is expected to facilitate the experimental realization of the complex optical image encryption system which will be tackled in the next step.

Diffractive optical elements (DOE) are conventionally designed without regard to the exact extension or aperture of the element. We designed superresolving DOEs that are band-limited and spatially confined by a circular amplitude aperture and based on a complex impulse response function as the design constraint. Our approach, based on the theory of super-oscillations, uses the Prior Discrete Fourier Transform in cylindrical coordinates to produce far-field patterns with rotational symmetry. We successfully fabricated two different spot designs (below the Airy limit), and two phase-fragmentation-variants. The DOE were tested at four wavelengths in the visible and the results agree well with design expectations.

The most popular solution when designing PIC-based sensors is ring resonators. Unfortunately, these structures are very sensitive to production variations, often causing problems with the predictability and repeatability of the entire sensor system. One of the most promising alternatives for these elements is using Mach-Zehnder interferometers (MZI). They provide lower manufacturing spreads and greater layout design freedom at the expense of increasing the final size of the PIC chip. This work presents the results of modeling and designing sensors based on MZI structures on the HYPHa (SiO2/TiO2) technological platform. The results consider the impact of the change in the refractive index of the tested substance on signal propagation in sensor systems operating at 633, 1310, and 1550 nm.

The wavelength range around 1700 nm is pivotal for a wide range of applications, such as gas sensing (e.g., CH4, C2H2, C2H4, C3H8), spectroscopy, LIDAR, and medical diagnostics. Here, we present a laser that operates in this wavelength range, achieved through the hybrid integration of an off-the-shelf InP-based gain chip with a low-loss Si3N4 feedback chip. The feedback chip contains a ring-resonator based filter, which enables wide wavelength tuning and ultra-coherent performance. The resulting laser demonstrates a tuning range from 1634 nm to 1777 nm with an output power reaching up to 7.7 mW. Moreover, the laser exhibits an intrinsic linewidth in the sub-kHz range (543 Hz).

Among the Light Detection and Ranging (LIDAR) active imaging methods, Frequency Modulation Continuous Wave (FMCW) grants high immunity to ambient light by using the laser source coherence to do heterodyne detection. Combined with flash method to illuminate the whole scene simultaneously we can achieve distance imaging without moving parts in the system and potentially higher frame rate. We present the simulated design of the emission optics integrated on a chip to compacify the system. Both optical functions, namely beam separation and scene illumination, are joined into a specific apodized grating coupler combining large horizontal and vertical illumination field, homogeneous farfield profile and emission perpendicular to the chip.

The dot product operator is a fundamental tool in various computational fields, particularly in photonic and edge computing applications. This paper explores the implementation and optimization of the dot product operator within photonic computing systems, leveraging the speed and energy efficiency of light-based processes. Two designs for a 4x4 dot product device were conceived, each with different input and output signal formats. The first design features an 8x3 pin configuration using Mach-Zehnder Interferometers (MZIs) for computation. The second design utilizes Phase Change Material (PCM), which undergoes reversible phase transitions for non-volatile memory applications, enabling binary multiplication. Simulations conducted at a data rate of 25 Gbits/s, with a continuous wave laser input, confirmed the designs' performance, supported by graphical representations and truth tables comparing theoretical and simulated results. Our study highlights the potential of these designs to enhance machine learning, real-time signal processing, and advanced communication systems.

A compactly integrated bidirectional optical true-time delay network (OTTDN) for radio frequency beam steering is proposed by introducing an asymmetrical power splitting scheme. The dual-port network can achieve both time delay tunability and bidirectional tunability through a single heater. A 20-GHz, ∼ ±13-ps bidirectional time delay is experimentally demonstrated.

Exceptional points are bifurcations in parameter space of non-Hermitian systems where both their eigenvalues and corresponding eigenvectors coalesce, leading to unique phenomena. Past works have demonstrated exceptional points in coupled systems as well as a single system with finely-controlled nano-scale perturbation. To demonstrate exceptional points on a single-component platform without nano-scale control, we are proposing integrated mode-converting multimode Fabry Pérot resonators. We aim to locate exceptional points in this novel photonics device. And we expect our work to find applications in advanced sensing systems and to be applied to active systems --- such as quantum-well lasers --- to explore coherent exceptional points phenomena using an internally-generated laser field.

Flow cytometry (FCM) contributes significantly to healthcare by enabling the rapid and accurate analysis of cell populations, which enhances our ability to diagnose, monitor, and assess treatment for conditions such as cancer and stroke. A multi-sensing biophotonic platform has been designed, integrating innovative FCM and Optical Coherence Tomography (OCT) photonic integrated circuits (PICs) and focusing on the detection of extracellular vesicles (EVs) down to 140 nm. The OCT module is utilized to ensure the validity of FCM measurements. The platform's micro-optic elements, designed for light manipulation within the sensing PICs, serve as interfaces between the photonic and fluidic components. Focusing lenses illuminate and collect light at specific flow channel points for FCM measurements at wavelengths of 520 and 638 nm, while the OCT module uses focusing micro-lenses for illumination and collection at 790 nm. This work presents the design, fabrication, and testing of the micro-lenses, achieving optical losses as low as 0.3 dB, equivalent to a coupling efficiency of up to 93%.

We propose a semi-analytical modeling based on a complex angle approach to evaluate the interaction between a surface guided mode and dielectric spheres placed on top of the waveguide. In this approach, time-saving compared to a 3D simulation, an evanescent incident wave is described as a plane wave geometrically rotated by a complex angle. We show how it can be used to evaluate the waveguide losses induced by dielectric microparticles placed close to its surface. We then apply this model to a sensor where microbeads or bacteria are selectively trapped on top of a glass surface waveguide thanks to dielectrophoresis.

The paper presents a novel design of a micro-ring resonator on silicon-on-insulator (SOI) wafers based on Bragg grating for refractive index sensing, operating in the near-infrared wavelength range. The device, termed grating slot micro-ring resonator (GSMRR), consists of two concentric silicon rings, each with Bragg gratings superimposed on them externally and internally, respectively. The analysis is conducted using Lumerical 3D FDTD, a commercial simulator in the photonics field. The device demonstrates high sensitivity in different sensing media, especially in gas sensing applications.

High-speed, small footprint photonic switches are crucial for data centers, telecommunications, and 5G due to handle increasing data traffic through a large number of input and output nodes. Photonic Integrated Circuit (PIC) technology, thanks to its miniaturization and performance efficiency, promises a scalable solution for the next generation of optical switches and interconnects. Among various PIC materials, thin film lithium niobate (TFLN) retains superior performance in terms of light modulation speed and power consumption. This places TFLN PICs as a versatile platform to deliver efficient solutions for the interconnects. Despite this, TFLN fabrication is less mature than silicon photonics, and foundry processes are necessary to get mature to guarantee a reliable performance and access to the manufacturing facility. Showcasing capabilities of our foundry process, we present a 2×2 Mach-Zehnder interferometer TFLN switch, operating at 1550 nm, with an average 10-90% rise time of 0.29 μs and an average 90-10% fall time of 0.28 μs.

This work presents an automated active alignment procedure for miniaturized photonic components in the case of single-photon level signals (low photon count), which can be used e.g., for producing quantum key distribution systems. We demonstrate the integration of miniaturized, substrate-free thin-film filter elements into laser-induced deep etched pockets on a photonic platform. The filter elements with an edge length of 500 µm function as beam splitters, allowing to combine/distinguish the four linear polarization states used in the BB84 quantum communication protocol. Placed under an angle of 45 degree to the propagation direction the filters are used to couple the single-photon level signal into a single-mode fiber. For the alignment of the assembly, a single photon avalanche detector is used in a feedback loop with a precision-optics assembly system. This technique enables the active alignment of optical components for single photon-level signals which are otherwise not detectable with conventional power meters.

Chemical and biological detection have diverse applications, and optical sensors are highly promising due to their sensitivity, dynamic range, and immunity to electromagnetic fields. Refractive index (RI) optical sensing is ideal for on-chip detection, offering high sensitivity and compatibility with CMOS technology like silicon-on-insulator (SOI), leading to compact, cost-effective devices. However, RI sensors typically lack selectivity. We present an SOI micro-ring resonator-based RI sensor capable of determining substances in a medium by measuring both real and imaginary parts of the refractive index across multiple wavelengths. Fabricated in an SOI multi-project wafer run, our sensor's measurements confirm its effectiveness in identifying substances.

Thin-film lithium niobate on insulator (TFLN) is a promising platform for photonic integrated circuits (PICs), with potential for electro-optical modulation and low-loss light propagation. To mature, TFLN PICs need to follow established platforms like silicon photonics. Standardizing TFLN PICs will enable large-scale production and reliable process design kits (PDKs). Measuring propagation losses in waveguides is essential for improving fabrication processes. Using ring resonator circuits, we observed significant loss reductions over different runs: from 2.7 dB/cm in the initial run to 0.67 dB/cm in the latest for 0.8 µm waveguides, and below 0.28 dB/cm for wider waveguides in the latest run. These improvements result from advances in lithography and etching, with the platform evolving to include more waveguides and metal layers.

Refractive index sensing plays a crucial role in a wide range of industries including industrial production, biochemical analysis, food safety inspection, clinical diagnosis, and environmental detection. The ability to accurately measure refractive index is essential for monitoring processes, ensuring product quality, and detecting potential hazards. Over the years, numerous methods for biological refractive index detection have been devised, leveraging the correlation between resonant position and changes in the biological refractive index. Optical gratings based on metasurface structures constructed from metal- dielectric materials represent a cutting-edge approach in the realm of glucose detection. These innovative structures harness the unique properties of metasurfaces to manipulate light energy at specific wavelengths, enabling precise modulation of resonances and transmission spectra. By integrating metal and dielectric materials in the design of these optical gratings, researchers have unlocked a powerful tool for detecting glucose concentrations with high sensitivity and selectivity. The interaction between the metasurface structure and g

Integrated photonics has the potential to transform telecommunications and computing as electronic circuits reach their physical limits. This study explores multi-photon lithography (MPL), an innovative method for fabricating photonic integrated circuits (PICs) with rapid manufacturability and design flexibility. However, MPL introduces surface roughness into 3D-printed structures, influenced by process parameters. Surface roughness, a key metric for assessing print quality, provides an accessible means to evaluate fabrication outcomes. This work investigates ridge waveguides on the photopolymer-on-glass (PoG) platform, combining statistical analysis of surface roughness metrics from laser scanning confocal microscopy (LSCM) with wave optics simulations in ANSYS Lumerical. Statistical analysis identifies process parameters affecting surface quality, while simulations quantify the impact of roughness on waveguide performance, including propagation losses caused by scattering. This framework links MPL process parameters to optical performance, optimizing fabrication and enabling accurate scattering loss calculations for 3D-printed photonic components.

Photonic integrated circuits represent a promising technology for creating compact and cost-effective optical devices with multiple functions on a single chip. The advancement of integrated optics is driven by research into new material platforms and production techniques. Lithium niobate (LN) is particularly attractive due to its advantageous optical properties. Integrated LN waveguides have been fabricated using multi-step methods, including lithographic patterning and dry etching. Additive manufacturing, however, allows for rapid single-step production, with multi-photon lithography (MPL) offering the highest spatial resolution. This contribution presents a novel etchless fabrication process using MPL to create strip-loaded waveguides on thin-film LN. It demonstrates the reusability of thin-film LN substrates by erasing and reprinting strips, promoting rapid and sustainable photonic chip production. The study includes various strip geometries and thin-film layer thicknesses, with experimental data supported by numerical simulations. Additionally, advantages and disadvantages of different strip-loaded LN waveguide designs for photonic packaging are discussed.

We present progress on an integrated photonics platform that simultaneously covers a broad spectral range from the ultraviolet (UV) to short-wave infrared (SWIR). Our platform has been designed with a thin film of SiN to support a multi-wavelength approach on the same wafer. We report the optimised design of input grating couplers incorporating variations on period, duty cycle, tapers and angles for multiple spectral ranges. We develop a photonics design kit for our platform including splitters and routing circuits tailored to the wavelengths of interest from UV-SWIR. We report on optimisation of the fabrication using e-beam lithography, dry etching and overcladding. The devices are assessed through optical measurements including coupling, propagation loss and device loss.

Integrated diamond photonic quantum registers have found success in the construction of long-distance quantum networks. Photonic crystal cavities (PhCCs) maximize the photon collection efficiency from quantum emitters as color centers in diamond, taking advantage of the Purcell effect and allowing for coherent coupling between the color center and an integrated diamond PhCC. The well-studied silicon vacancy center (SiV) presents a perfect candidate for integration in a PhCC because of its inversion symmetry and all-optically addressable spin states. This work presents design, fabrication and characterization of diamond PhCC from bulk diamond substrate for emission enhancement of the SiV. A fabrication procedure utilizing silicon nitride as a hard mask and Faraday cage angled etching (FCAE) is used to realize free-standing triangular diamond nanobeam PhCCs. Confocal laser microscopy is utilized to characterize the resonances of the fabricated PhCCs. Resonances close to the SiV Zero-Phonon-line (ZPL) were observed with quality factors above 5000. Geometry variations of the PhCC show resonance shifts in agreement with simulations.

Photonic Integrated Circuits (PICs) are crucial for quantum applications. Universal Photonic Processors (UPPs) are PICs that perform arbitrary transformations between quantum states of light. Scaling UPPs is challenging due to increased power consumption and calibration complexity. Femtosecond Laser Written (FLW) UPPs, which use thermal phase shifting, face issues stemming from thermal cross-talk between waveguides. This study shows that a vacuum environment reduces thermal cross-talk and power consumption: in vacuum, power for a 2pi phase shift drops from over 60 mW to under 15 mW, and cross-talk decreases from 13.2% to 1.8%, enhancing scalability.

Ultra-low loss silicon nitride waveguides have become ubiquitous in integrated photonics, spanning applications in frequency comb generation, spontaneous four-wave mixing photon sources, and high quality factor (Q-factor) cavities for laser self-injection locking. Here, we demonstrate the first low-loss silicon nitride waveguides in a 300 mm silicon photonics process with a thickness > 700 nm. We entirely mitigate stress-induced cracking by opting for a Damascene fabrication process rather than standard subtractive etching. We experimentally characterize the fabricated chips by measuring various microresonators across the wafer, observing highly uniform propagation loss and Q-factors in the telecommunication bands. In the O-band, we observe Q-factors as high as 976,000 and propagation loss as low as 0.485 dB/cm; in the C-band, we observe Q-factors as high as 1,041,000 and propagation loss as low as 0.348 dB/cm.

Advances in quantum computing pose significant threats to the security of conventional encryption standards. Although quantum key distribution systems offer inherent security, they face challenges in achieving practical secret-key rates over long transmission distances. Photonic Integrated Circuit technologies provide scalability and system efficiency for high key rates using multiplexed time-bin protocols. We present the architecture of a 16-channel multiplexed QKD system at a GHz clock rate realized on integrated photonic chips, promising further scalability. The sender module revolves around an indium-phosphide chip featuring tunable lasers, modulators, and combiners. On the receiver side, low fiber-to-chip coupling loss and waveguide-integrated superconducting nanowire single-photon detectors on silicon nitride provide the necessary detection efficiency.

Phase Change Materials (PCMs) have found success in Photonic Integrated Circuits (PICs) because of their significant optical property changes between amorphous and crystalline states. These properties enable applications such as optical switches, multi-level memories, and neuromorphic hardware accelerators. Typically, programming PCM cells in-plane, optically or electronically, is done through additional optical inputs or electronic contacts. To avoid this, an out-of-plane approach using a vertical-cavity surface-emitting laser (VCSEL) array with flip-chip bonding is employed. Combined with height control and focusing of the laser through micro-3d printed structures and lenses the intensity on the PCM cells can be maximized. This approach enhances the design flexibility for multi-PCM cell circuits.

This study introduces two silicon foundry-based polarization controllers. The first controller uses a thermal gradient to alter waveguide properties. The second polarization controller consists of two parts which help simplify the controlling process: one part adjusts the amplitude ratio, and the other controls the phase difference. Fabricated at AIM Photonics, these controllers were tested using on-chip and off-chip polarization measurement techniques. Results indicate partial state of polarization tunability with the first controller and full tunability with the second.

Long-Wave Infrared Free-space optical communications are a foreseen competitors to atmospheric FSO communications established in the telecom C-band, but mature building blocks are still missing to widely trigger their diffusion alongside classical solutions. Here we report the development of LWIR-based passive components realized on the InGaAs/InP material system, which is a promising platform for future integration with active components like quantum cascade lasers and detectors. We discuss the design, fabrication and characterization of ridge waveguides and beam splitters/combiners based on multi-mode interferometer with different input/output architectures (1x2, 2x2 and 2x4) operating at 9 µm wavelength. These preliminary performances indicate high potential for their future integration in a monolithic InP integrated photonic platform for high-speed LWIR FSO datacom.

We present a detailed analysis of the fabrication process development to make low-loss monolithic and hybrid waveguides on a thin-film BTO platform. A simulation study of the material’s behavior as low-loss waveguides in Lumerical Mode solver is presented and the waveguides have been fabricated with an optimized fabrication process flow. Lastly, a study of the effects of a-cut and c-cut BTO thin-films on lowering the V_π and enhancing the broadband response is presented.

Optical coherence tomography (OCT) is a biomedical imaging modality that plays an important role in ophthalmology. However, current clinical ophthalmic OCT systems are large and bulky, and performance improvements such as parallel imaging techniques are difficult to implement using the traditional fiber optic-based approach. Photonic integrated circuits (PICs) show great promise as a paradigm to implement high performance, miniaturized OCT systems, offering additional benefits in scalability. Advances in PIC technology have been primarily driven by telecommunications applications, which typically use wavelengths that are unsuitable for ophthalmic imaging due to the absorption of the vitreous fluid within the eye. In this work, we have developed passive integrated photonic components that are both broadband (~100nm, leading to increased OCT resolution) and operate at appropriate wavelengths for ophthalmic imaging (800nm and 1060nm).

In this work, we describe the design and modeling of integrated photonic devices based on photonic waveguides on silicon substrates. We have first designed and modeled integrated photonic chemical sensors, in which the sensing region is integrated with the on-chip optical waveguides that carry the light to and from the sensing regions having nanophotonics structures, such that the transduction in the light signal due to the presence of the analyte molecules could be detected. The fabrication of these sensor devices is also being carried out. We have also designed and modeled integrated switches based on phase-change materials (PCMs).

The focus of this work is a novel 3D photonic integrated interposer for the connection of multicore fibers with two core layers consisting of 4 cores each with conventional photonic integrated circuits for optical transceiver applications. The interposer, developed on Fraunhofer HHI's PolyBoard hybrid integration, contains 1x1 3D multimode interference (MMI) couplers. The development of the design, fabrication and characterization of the interposer will be presented.

The thin-film lithium niobate (TFLN) integrated photonic technology has matured tremendously in the past few years for high-performance electro-optic, nonlinear, and quantum-optic applications. We propose a compact passive photonic spectral filter on TFLN with an exceptionally high bandwidth of over 850 nm, rendering it suitable for a diverse host of applications. This design utilizes adiabatic and slot structure waveguides which simplify fabrication steps and enhance performance, ensuring efficient and versatile integrated photonic filtering.

To investigate nanoscale dynamics in materials, atomic force microscopy infrared spectroscopy (AFM-IR) systems require fast and small cantilevers. The current interferometric readout method introduces excessive noise when the dimensions of the cantilever is smaller than the laser beam spot size. To address this challenge, we propose a novel cantilever design with an embedded phase-shifted Bragg grating (PSBG). Optimized using Lumerical, the PSBG is designed to operate near 1550 nm. Experimental characterization of the PSBGs on both the cantilevers under self-deflection and the bulk substrate revealed a wavelength red shift of approximately 3 nm.