Quantum entanglement is one of the fundamental resource for several quantum information applications. Entanglement can be made between two distinct photons or between two degrees of freedom of the photon. Here I will review few integrated quantum photonic circuits based on inter or intra photon entanglement that implement quantum random number generators, quantum ghost spectroscopy devices, undetected photon quantum intereference and, finally, hearlded single photon sources.

There is an increasing demand for superconducting nanowire single photon detectors (SNSPDs) which combine high efficiency, low dark counts and fast response time. They play a crucial role in developing strategic application areas such as photon-based quantum computing and quantum key distribution. We demonstrate the fabrication of high crystalline quality NbN-based waveguide-integrated SNSPDs using a completely CMOS-compatible process on 200 mm SOI wafers. We achieve a detection efficiency over 80 % at 100 Hz dark count rate, a short decay time below 4 ns and a maximum count rate of 200 MHz.

Recent advances in oxide thin film deposition techniques are very promising for extending the operating wavelength of silicon photonics into the UV range. The use of this wavelength range for applications is still limited due to the difficulty to handle UV optical signals. UV photonic integrated circuits will solve this problem and they will open new avenues for biological, healthcare and optical quantum computing applications. This talk will review recent results achieved with atomic layer deposition of alumina on thermal oxide wafers for UV optical microscopy applications. We will discuss the main advantages of UV photonic integrated circuits for the implemention of structured illumination microscopy and quantitative phase imaging.

Applications such as quantum and biological sensing require visible wavelengths of operation. While incumbent integrated photonic platforms such as silicon nitride enable low-loss light propagation at these wavelengths, the autofluorescence suffered in silicon nitride causes unwanted signals that will significantly reduce performance in sensing applications. Sputtered metal oxides have recently emerged as a promising alternative platform for integrated photonics from visible to NIR, with the added advantage of a drastic reduction in autofluorescence in the visible regime. Here, I present our recent results in propagation loss and autofluorescence characterization of our sputtered metal oxide platforms in the visible light regime.

To overcome the increased absorption of commercially available waveguide platforms for UV wavelengths, Al2O3 has been suggested due to its low losses below 450 nm. In this work, we demonstrate Al2O3 waveguides fabricated via reactive sputtering, electron beam lithography and dry etching with losses as low as 2.3 dB/cm at 369 nm. A variety of building blocks required for typical photonic devices are realized using the process which shows promise as a waveguide platform for applications that require UV wavelengths.

Reactive sputtering provides a scalable and robust approach to fabricate erbium doped waveguide amplifiers and can be used to integrate devices with other waveguide platforms. In this work, we present recent results on high gain (>25 dB) in Al2O3:Er3+ amplifiers fabricated via reactive sputtering, which are vertically integrated with underlying LioniX TriPleX Si3N4 circuitry.

Erbium-doped amplifiers are key elements not only for modern telecom systems but also for integrated narrow linewidth lasers that are used for sensing and THz generation. Ion exchange on glass is a technological platform that allows realizing very efficient erbium-doped waveguide amplifiers with low coupling losses and quite high net gains. However, integrated lasers require a shorter amplifying waveguide that is operated in a strongly saturated regime. For this reason, a co-doping with Er and Yb is used. In this paper, we present the characterizations of Er-Yb co-doped waveguide amplifiers in terms of spectroscopic and guiding properties. Then small signal and satured gains measurements are presented. Finally, all these experimental data are employed to derive and assess a theoretical model of the ion-exchanged waveguide amplifier.

The integration of active devices such as lasers, modulators or photodetectors on silicon photonics platforms has enabled the development of efficient, performant, low-cost and scalable high-speed integrated transceivers for optical communications. In this invited contribution, we will review the most relevant work in the field so far and we will present our recent progress on high-speed integrated transceivers for silicon photonics. The most relevant figures of merit for integrated lasers and electro-absorption modulators for high-speed optical communications will be discussed, as well as our vision for future developments.

The splitting of the fundamental modes in a microcavity requires a strong coupling between light and matter and plays a significant role in quantum technology. A linear dynamic magnetoactive fluid cavity supporting ultrasonic waves is designed to enhance wave-matter interaction and induce splitting of resonant cavity-acoustic modes due to magneto-thermal and photothermal effects. The magneto-caloric force due to a temperature gradient within the cavity was used to realize a self-driven fluid cavity without an external mechanical pump. This force can be modulated remotely by a DC magnetic field or laser-induced surface-temperature change of the fluid within the cavity. An ultrasonic wave propagating through this cavity with moving fluid can be influenced by Doppler shift and rheological modifications leading to acoustic Zeeman-like splitting induced by external optical irradiation in the presence of a magnetic field. The laser-induced control of the fluid flow within the cavity enables the frequency and amplitude modulation of broadband ultrasonic waves traveling through the cavity leading to the nonreciprocal transmission of acoustic waves.

Electro-optical computing systems are promising for future energy-efficient computing, while scalable, dual electrical-optical functionality and low energy-consumption electrical-optical devices are not yet implemented on-chip. In this work, with a tailored design for better heat confinement, we implement scalable phase-change devices with dual electrical-optical functionality. They show ultralow programming energy for both electrical and optical switching in a pico-joule scale, which is orders lower than other integrated electro-optical phase change devices, multilevel switching until 20% contrast, good cyclability, and readout in both electrical and optical domains.

Silicon photonics platform has undergone substantial development to tackle future challenges of various applications, including datacom, sensing, and optical communications. Numerous efficient devices and circuits have been proposed, and products are already available in the market. However, the intrinsic properties of silicon-based materials do not fully overcome the limitations in terms of speed, power consumption and scalability. As a result, new strategies have emerged, mainly focusing on the integration of new materials and the exploitation of nonlinear optical properties. In this context, the paper will present the current status and prospects of Si and SiGe photonics and its potential applications.

Silicon nitride (SiN) have become an essential material for integrated photonics. It is needed whenever very low optical losses, high optical power, low thermal sensitivity or broad wavelength range is required. SiN waveguides therefore present a great interest for applications as diverse as quantum photonics, data-communication, neuromorphic computing, LiDAR, sensing and microwave optic. We present our latest results on two distinct platforms: An 8” LPCVD SiN platform featuring ultra-low loss (5dB/m) and a 12” Physical Vapor Deposition (PVD) SiN platform allowing low loss in the C-band with a low-temperature deposition.

Nanostructuring of versatile high-index photonic materials, like lithium niobate or silicon, offers the dense integration of highly functional devices. We will present our recent advances towards meta devices, including waveguides and metasurfaces, consisting of nanoresonators as their versatile building blocks. Furthermore, we will present a nanofabrication scheme towards strongly guiding wafer-scale integrated circuits. Both approaches are the basis for enabling various applications, where we explore foremost the quantum information field.

We discovered intrinsic quantum emitters in silicon nitride (SiN), which provide bright, high-purity single-photon emission at room temperature and the capability of seamless integration with SiN photonic waveguides. We established methods of creation of these quantum emitters and performed foundational photophysical studies at room and cryogenic temperatures. We explore the possibility of generating indistinguishable photons at high repetition rates at cryo-temperatures and by using plasmonic metamaterials, which may enable broader applications of SiN quantum emitters. Plasmonic speed-up of spontaneous emission rate beyond the rate of detrimental decoherence processes may also enable the generation of indistinguishable photons even at non-cryogenic temperatures.

Correlated phenomena play a central role in condensed matter physics, but in many cases there are no tools available that allow for measurements of correlations at the relevant length scales (nanometers - microns). We have recently demonstrated that nitrogen vacancy (NV) centers in diamond can be used as point sensors for measuring two-point magnetic field correlators. This novel quantum sensing platform will allow us to measure new physical quantities that are otherwise inaccessible with current tools, particularly in condensed matter systems where two-point correlators can be used to characterize charge transport, magnetism, and non-equilibrium dynamics.

Spontaneous parametric down conversion in nonlinear material is widely exploited to generate entangled photon pairs in quantum optics experiments and applications, including quantum computing and communication. Periodically poled thin film lithium niobate (PPTFLN) has emerged as a promising platform for efficient entangled photon pair generation, offering enhanced nonlinear interaction through quasi-phase matching (QPM) and tight confinement of light. However, achieving optimal performance requires careful control of the QPM condition since the waveguide in TFLN is highly dispersive to changes in the geometric parameter. In this study, we fabricate PPTFLN rib waveguides to generate entangled photon pairs at telecommunication wavelengths, varying geometric parameters. QPM condition is confirmed with the second harmonic generation experiments and Pair generation rate and coincidence-to-accidental count ratio are also estimated by temporal coincidence measurement. Digital etching process is introduced to control the QPM condition, resulting in incremental peak wavelength shift by discrete etching step. This is expected to contribute to synchronizing wavelength of quantum nodes.

Mainstream Machine learning (ML) leverages on a simplified model of the neuron, the Perceptron, which is efficiently implemented in software running on digital computers. Still, biological neurons process information by exchanging time-depending signals, e.g. spikes. Understanding how to harness ”neurons” closer in behaviour to their biological model, is fascinating but challenging. One of the challenges is related to scaling up the number of interconnected neurons. Photonics is regarded as a promising approach [1]. Particularly, the large bandwidth available in optical communication channels suggests applications in specialized computing tasks, where latency is critical. Aiming at an all-optical implementation, computing-related functions such as reconfigurable matrix multiplication [2] and nonlinear activation functions [3] are available in Silicon photonics. Semiconductor lasers have shown a neuron-like response such as excitability [4], i.e. the emission of a well-defined pulse as the excitation goes above a threshold, while microring-based ”neurons”, exploiting the thermo-optical nonlinearity, have been demonstrated in a silicon photonic circuit [5]. Here we consider a photonic crystal based semiconductor laser, heterogeneously integrated on top of a Silicon on Insulator (SOI) waveguide.

The nanolaser is composed by two sections for the gain and saturable absorber: a metal screen ensure selective pumping of the gain section with a CW laser beam. By a suitable choice of the parameters (Q-factor, gain vs absorption ratio and pumping rate), the laser operates in different regimes: excitable, pulsing with variable rate (i.e. implements the Leak Integrate and Fire model of the neuron), bistable and CW. Excitability is shown in the figure: panels (c) to (e) relate to the response to a pulsed excitation as a function of its energy (here estimated before the input coupler to the silicon chip) when the pump is set just below the threshold of self-pulsing. Panel (f) shows the spiking probability, estimated as the fraction of traces where spikes are emitted (the event is detected when signal goes above -40 arb.u.). The spiking probability follows the expected trend with the excitation, already observed in VCSELs [6] and agrees very well with our stochastic implementation of the Yamada model of self-pulsing lasers. This result paves the way to electrically pumped, interconnected spiking nanolasers, operating with manageable (0.1 mA) current levels and sub-nanosecond time scales.

References
[1] B. J. Shastri et al., “Photonics for artificial intelligence and neuromorphic computing,” Nat. Photon. 15, 102 (2021).
[2] Y. Shen et al., “Deep learning with coherent nanophotonic circuits,” Nat. Photon. 11, 441 (2017).
[3] A. Jha et al., “Reconfigurable all-optical nonlinear activation functions for neuromorphic photonics,” Opt. Lett. 45, 4819 (2020).
[4] H.J. W¨unsche et al., ”Excitability of a semiconductor laser by a two-mode homoclinic bifurcation” , Phys. Rev. Lett. 88, 023901 (2001).
[5] T. Van Vaerenbergh et al., “Cascadable excitability in microrings,” Opt. Express 20, 20292 (2012).
[6] F. Selmi et al., “Relative Refractory Period in an Excitable Semiconductor Laser,” Phys. Rev. Lett. 112 183902 (2014).

We present a photonic tensor accelerator (PTA) employing nearly all dimensions (complex amplitude, polarization, wavelength and spatial mode) of light for scalable tensor multiplication. In this architecture, multiplications are performed through coherent mixing and accumulations are performed via simultaneous photodetection of multiple degrees of freedom within one dimension of light. We have implemented the PTA on micro-optics and integrated-photonics platforms. Experimental results of the PTA as well as its applications in artificial neural networks and computing will be presented.

We present the use of holographic UV writing to fabricate 2D grating couplers in doped planar silica-on-silicon, enabling the creation of large (~1 cm) and efficient circular beam delivery into free space. Our fabrication process inscribes a channel waveguide with in-plane 60° blazed grating to expand a fibre-coupled beam within a planar core layer, followed by an out-of-plane 45° blazed grating to couple light out of the substrate. Our out-of-plane gratings are fabricated using a modified interferometric arrangement with a prism and index matching water layer, the arrangement and latest results will be presented here.

We demonstrate a GaAs based Quantum Dot (QD) optoelectronic integration platform with results for surface grating couplers (SGC) and edge emitting lasers. SGCs usually perform poorly in systems without a large refractive index contrast and here we utilize thin oxidized Al0.98Ga0.02As layers to overcome this issue. The results show an increase from 10% to 30% in surface grating coupling efficiency, for the unoxidized compared to oxidized, and substrate-loss decrease from 70% to 20%. Electrically pumped edge-emitting lasers on the same platform exhibit comparable performance to more standard 1300nm QD designs. We describe the design, fabrication and characterization of these devices.

In this work we propose, fabricate and test a new integrated platform for 1xN power splitters. Given an array of N coupled and non-equally spaced waveguides, any arbitrary 1xN splitting ratio is achieved by properly setting the array length and the dimension of the (N-1) nano-gaps between the N adjacent waveguides. We provide the first experimental demonstration of 1xN splitting with an arbitrary power ratio ratio for both the fundamental mode as well as higher-order modes. These results find direct application in the framework of the emerging on-chip multimode technology.

Over the past 15 years since their first demonstration, subwavelength grating metamaterials in silicon photonic devices have become widely used and attracted rapidly growing research interest while also breaking into commercial applications. We will discuss recent advances in this research field, with a focus on novel components and circuits for beam steering applications, on-chip filtering and quantum optics. On-chip optical waveguides comprised of Mie resonant particle chains have only recently been demonstrated and promise to be the foundation of a new and exciting branch of integrated metamaterials research. We will review the early work in this area.

The patterning of silicon with a period at the subwavelength scale has opened new degrees of freedom to control not only the propagation of light but also of sound. In this invited contribution, we will present our latest results on subwavelength-engineered silicon optomechanical waveguides. We harness subwavelength nanostructuration in a silicon slot waveguide to shape the distribution of the optical mode and maximize the coupling with the mechanical mode. Based on this approach, we demonstrate an enhanced Brillouin gain and a high tunability of the mechanical frequency.

Zero-index metamaterials show the unique feature of uniform spatial phase distributions, enabling the interaction of single electromagnetic mode with matter over an infinite area in an arbitrary shape. This feature brings various novel optical physics and devices, such as supercoupler, large-area single-mode laser, and extended superradiance. However, the state-of-the-art zero-index waveguide shows a propagation loss as high as 1000 dB/mm, hampering most potential applications of zero-index metamaterials. Although zero-index metamaterials based on bound state in the continuum can show a lower propagation loss of 45 dB/mm, the photonic crystal slab configuration which are boundless in the in-plane direction limits the devices’ footprint and flexibility drastically. Here we demonstrated a one-dimensional metawaveguide with zero refractive index along the propagation direction, featuring a high flexibility, a compact footprint, and a low propagation loss of 5.45 dB/mm near the zero-index wavelength. This metawaveguide could enable many zero index-based linear, nonlinear, and quantum photonic devices such as entangled photon pair sources based on spontaneous four-wave mixing.

Photonic integrated circuits (PICs) have the potential to drastically expand the capabilities of optical information science and engineering. However, PICs are commonly fabricated using selective material etching, a subtractive process. Thus, the chip’s functionality cannot be substantially altered once fabricated. Here, we propose to exploit wide-bandgap non-volatile phase-change materials (PCMs) to create a rewritable PIC platform. A PCM-based PIC can be written using a nano-second pulsed laser, akin to rewritable compact disks. The whole circuit can then be erased by heating, and a completely new circuit can be rewritten. We numerically designed a dielectric-assisted PCM waveguide consisting of a thick dielectric layer on top of a thin layer of wide-bandgap PCMs. The low-loss PCMs and our engineered waveguiding structure lead to negligible optical loss. Furthermore, we analyzed the spatio-temporal laser pulse shape to write the PCMs. Finally, we experimentally demonstrated such a rewritable PIC. Our proposed platform will enable low-cost manufacturing and have a far-reaching impact on the rapid prototyping of PICs, validation of new designs, and photonic education.

Lithium niobate, and more recently thin film lithium niobate on insulator (LNOI, TFLN), is a widely used material in integrated photonics due to its excellent optical and electro-optic properties. With the increasing demand for high-speed, high integration density photonic devices, lithium niobate integrated photonics has become an active research area. The focus of the presented technology development is on low-loss waveguides (below 0.1 dB/cm) that enable the integration of a wide variety of devices, including modulators, resonators and frequency converters, on a single chip for applications in quantum technologies. Implications and challenges of wafer-scale fabrication will be discussed.

Cascaded linear and non-linear operations form the basis for all integrated photonic applications ranging from routing to computations. Because of the weak interaction between photons, achieving substantial optical nonlinearities at low power remains challenging. In this work, we demonstrate a new photonic framework where signals carried in different wavelengths can be added and encoded in a new wavelength with low optical loss. Using this approach, we can realize highly nonlinear all-optical neurons operated fully in the near-infrared domain at low power.

Currently, there is no short-reach transceiver standard for 800 Gb/s available. The market is only now starting to develop for 400G whereas 800G deployments are expected after 2023 (relevant standards will be ratified). In this rationale leveraging the performances of the new generation of III/V high-power DFB and DML will allow to reach a compact transceiver, providing low loss, high data rates and low cost. In this invited presentation, we will show our recent achieving of high-performance Si-BH technology for HP-DFB and DMLs. This technology is expected to exhibit low propagation loss and high coupling efficiency for photonic integrations specifications

The quantum dot (QD) laser proposed by the author in 1982 has now achieved the best performance as a semiconductor laser in most laser characteristics except direct modulation characteristics. We proved the temperature independence of the threshold current in 2004 and further achieved continuous operation at a high temperature of 220°C in 2011. This high-temperature operating characteristic has solidified the QD laser as a promising light source for short-range optical interconnect in silicon photonics, where the thermal effects of LSIs are inevitable. In this talk, recent advances of QD lasers in silicon photonics will be discussed toward high-temperature operation for co-package and near-package optics technologies. QD-based single-photon sources for future quantum integrated circuit systems will also be briefly mentioned.

Tunable and ultra-narrow linewidth lasers that are fully integrated remain a missing component and challenge for the thin-film lithium niobate platform, while being useful for applications ranging from data communication to signal processing. Here, we present, for the first time, the demonstration of fully integrated, extended cavity diode lasers combining C-band semiconductor gain chips with TFLN using photonic wire bonding. By leveraging the scalability of photonic wirebonding the laser, with two intra-cavity RSOAs, produces a high on-chip output power of 35 mW and shows single frequency operation with more than 61 dB side mode suppression. By adjusting on-chip heaters the laser can be tuned over >40 nm across the entire gain bandwidth. Using delayed self-heterodyne detection an ultra-narrow, intrinsic linewidth of 1.4 kHz is measured.

Integrated optical filters play a key role in modern optical systems, finding extensive applications in quantum optics, biosensing, programmable photonics, and telecommunications. Among the most commonly used structures utilized for implementing integrated optical filters are ring resonators and Bragg gratings. Bragg gratings are characterized by a periodically perturbed refractive index profile along the propagation direction. By precisely engineering the strength of the perturbation along the grating length, filters with arbitrary spectral responses can be achieved. In this work we summarize our recent contributions to integrated Bragg filters in Si-photonics, covering designs for applications ranging from telecommunications to quantum optics.

We present our latest results on subwavelength-engineered silicon optical antennas and two-dimensional optical phased arrays.

We present state of the art hybrid integrated GaSb/Si3N4 light sources towards building miniaturized and affordable sensors. Presented laser configurations include: 1) Widely tunable 2.7 µm wavelength laser with 170 nm continuous tuning range. 2) Discretely tunable laser for simultaneously multiwavelength spectroscopy of S2H, H2O and CO2-gasses with greatly simplified calibration procedure compared to conventional tunable lasers. 3) Lasers with ultra-pure spectrum at 2 µm wavelength reaching down to 6 kHz-linewidth towards use in atom spectroscopy or to seed advanced lasers. Used configurations and material systems are wavelength agnostic in 1.9 – 3 µm range and therefore capable to capture wide range of applications. We discuss about applications in environmental and industrial gas sensing and detection of biomarkers such as lactate, urea and glucose.

On-chip hollow-core waveguides represent a promising platform for microfluidic analysis, nonlinear optics and quantum information processing, due to light guidance directly inside the medium of interest. Recently, we have introduced two types of 3D nanoprinted on-chip hollow-core waveguides, namely the hollow-core light cage and the microgap waveguide which have unique properties for on-chip sensing. Here we will present our results for water-based spectroscopy, refractive index sensing, nanoparticle tracking, and optical fiber interfacing.

Publisher's Note: This conference presentation, originally published on 13 March 2024, was withdrawn on 25 March 2024 per author request.

Silicon nitride (SiN) has emerged as a promising platform for the development of photonic integrated circuits (PICs) covering a wide range of application areas from the visible to the infrared regime. Optical microcavity has evolved to be a highly versatile component in PICs, enabling the development of various disciplines, including lasers, filters, sensors, tele/data communication, and quantum technologies. SiN microring resonators are particularly compatible with already established micro or nanofabrication protocols and display useful properties, such as ultra-compactness, low loss, and planar nature. In this work, we have demonstrated the hybrid nanophotonic chip modeling, nanofabrication, two-dimensional semiconductor (TMDC) integration, and chip testing of high-Q ultra-compact SiN microring resonators supporting the Terahertz (THz) free spectral range (FSR) cavity modes at the visible wavelength. Counterpart, the monolithic integration of solid-state color centers with photonic elements of the same material is a promising approach to overcome the constraints of fabrication complexity and coupling losses in traditional hybrid integration approaches. We have engineered a novel