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Silicon photonics has been largely developed as a platform to address the future challenges in several applications including datacom, sensing or optical communications, among others. However, the properties of silicon itself is not enough to overcome all limitations in terms of speed, power consumption and scalability. New strategies have then been encouraged based on the hybrid integration of new materials in the silicon photonics platform. In this paper, we will introduce the recent advances in the hybrid integration of doped crystalline-oxides on silicon and silicon nitride waveguides. Especially, Yttria-stabilized zirconia (YSZ) with a lattice parameter compatible with the silicon lattice has been considered because it exhibits promising linear and nonlinear optical properties: low propagation loss, no two photon absorption (TPA) due to its large bandgap energy, a large transparency window from the ultraviolet to the mid-infrared and a good Kerr effect. Furthermore, YSZ can be doped with many dopants to develop active photonic devices with strong second- and third-order nonlinearities and light emission. We have recently demonstrated propagation loss in YSZ waveguides as low as 2dB/cm at a wavelength of 1380 nm, a nonlinear refractive index (Kerr effect) comparable with the SiN coefficient and light amplification in Er3+ doped YSZ on SiN waveguides. The recent results are very promising to pave the way for the development of low cost and low power consumption devices.

A two-octave spanning supercontinuum generation in the O-band communication window on an integrated silicon nitride platform is reported. The nitrogen-rich silicon nitride waveguides were fabricated through low temperature processes on an industrial platform (

International audience; The strong evolution of silicon photonics towards very low power consumption circuits leads to the development of new strategies for photonic devices, especially for power-hungry components such as optical modulators. One strategy is to use Pockels effect in Si waveguides. However, bulk Si is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities. Nonetheless, under a strain gradient, generated by depositing a stressed layer on Si waveguides, this restriction vanishes. In our work, we experimentally demonstrated a Pockels effect based electro-optic modulation at high frequency (> 5GHz) using a strained silicon Mach-Zehnder modulator.

Silicon nanophotonics represents a scalable route to deploy complex optical integrated circuits for multifold applications, markets, and end-users. Most recently, applications such as optical communications and interconnects, sensing, as well as quantum-based technologies, among others, present additional opportunities for integrated silicon nanophotonics to expand its frontiers from laboratories to industrial product development. Within a wide set of functionalities that silicon nanophotonic chips can afford, the availability of low-loss optical input/output interfaces has been regarded as a major practical obstacle that hampers long-term success of integrated photonic platforms. Indeed, fiber-chip interfaces based on diffraction gratings are an attractive solution to resonantly couple the light between planar waveguide circuits and standard single-mode optical fibers. Surface grating couplers provide much more alignment tolerance in fiber attach compared with most conventional edge-coupled alternatives, while retaining the much-needed control of the fiber placement on the chip surface and wafer-level-test capability that the in-plane convertors lack. Here, we report on our recent advances in the development of high-performance fiber-chip grating couplers that exploit the blazing effect. This is achieved with well-established dual-etch processing in interleaved teeth-trench arrangements or using L-shaped grating-teeth-profile geometries. The first demonstration of the L-shaped-based grating coupler yielded a coupling loss of -2.7 dB, seamlessly fabricated into a 300-mm foundry manufacturing process using 193-nm deep-ultraviolet stepper lithography. Moreover, silicon metamaterial L-shaped fiber couplers may promote robust sub-decibel coupling of light, reaching a simulated coupling loss of -0.25 dB, while featuring device layouts (>120 nm) compatible with lithographic technologies in silicon semiconductor foundries., SPIE OPTO 2020 - Smart Photonic and Optoelectronic Integrated Circuits XXII, February 3-6, 2020, San Francisco, California, Series: Proceedings of SPIE

Nonlinear all-optical technology is an ultimate route for the next-generation ultrafast signal processing of optical communication systems. New nonlinear functionalities need to be implemented in photonics, and complex oxides are considered as promising candidates due to their wide panel of attributes. In this context, yttria-stabilized zirconia (YSZ) stands out, thanks to its ability to be epitaxially grown on silicon, adapting the lattice for the crystalline oxide family of materials. We report, for the first time to the best of our knowledge, a detailed theoretical and experimental study about the third-order nonlinear susceptibility in crystalline YSZ. Via self-phase modulation-induced broadening and considering the in-plane orientation of YSZ, we experimentally obtained an effective Kerr coefficient of n ^ 2 YSZ = 4.0 ± 2 × 10 − 19 m 2 · W − 1 in an 8% (mole fraction) YSZ waveguide. In agreement with the theoretically predicted n ^ 2 YSZ = 1.3 × 10 − 19 m 2 · W − 1 , the third-order nonlinear coefficient of YSZ is comparable with the one of silicon nitride, which is already being used in nonlinear optics. These promising results are a new step toward the implementation of functional oxides for nonlinear optical applications.

We report on the first demonstration of high-speed optical modulation exploiting Pockels effect in strained silicon waveguides. Bandwidths larger than 20 GHz and low insertion loss have been achieved at a wavelength of 1550 nm.

On-chip optical amplifiers operating at telecom wavelengths are crucial elements for signal recovering and routing in photonic integrated circuits. In this work, we present the optical and structural properties of Er-doped yttria-stabilized zirconia (YSZ) thin films for the implementation of on-chip optical amplifiers in hybrid multifunctional photonic platforms. Photoluminescence excitation measurements have revealed strong luminescence at 1530 nm under 960 nm wavelength pumping, with lifetime values around 2 ms and a strong Er3++–Er3+ interaction for Er3+ doping concentrations beyond 1.5 atomic percentage (at%). This work contributes to establish the solid foundations for a class of Er-doped on-chip amplifiers using the robust and stable YSZ host matrix.

International audience; We report supercontinuum generation in nitrogen-rich (N-rich) silicon nitride waveguides fabricated through back-end complementary-metal-oxide-semiconductor (CMOS)-compatible processes on a 300 mm platform. By pumping in the anomalous dispersion regime at a wavelength of 1200 nm, two-octave spanning spectra covering the visible and near-infrared ranges, including the O band, were obtained. Numerical calculations showed that the nonlinear index of N-rich silicon nitride is within the same order of magnitude as that of stoichiometric silicon nitride, despite the lower silicon content. N-rich silicon nitride then appears to be a promising candidate for nonlinear devices compatible with back-end CMOS processes.

Silicon photonics, considered as a major photonic platform for optical communications in data centers, is today also developed for others applications including quantum photonics and sensing. Advanced silicon functionalities based on optical nonlinearities are then required. As the presence of inversion symmetry in the Si crystal structure prevents the exploitation of second-order optical nonlinearities, the generation of strain gradients in Si by a stressed material can be considered. However, due to the semiconductor nature of silicon with the presence of carriers, no clear evidence of second-order nonlinearities have been reported yet. Here we report an experimental demonstration of high-speed Pockels effect in silicon waveguides at 1550 nm. Additionally, a theoretical model is developed to describe its frequency behavior. A second-order nonlinear susceptibility $$\chi _{xxy}^{(2)}$$ χ x x y ( 2 ) of −1.8 ± 0.2 pm V−1 is then experimentally determined. These results pave the way for the development of fast linear electro-optic effect for advanced silicon photonics devices.

Uniform grating couplers based on versatile L-shaped waveguides are experimentally demonstrated, with coupling loss of -2.7 dB and back-reflections of -20 dB. Apodized couplers with subwavelength-grating metamaterials predict improved fiber-chip coupling down to -0.46 dB within device layouts compatible with lithographic technologies available in nanophotonic foundries., 2019 IEEE 16th International Conference on Group IV Photonics (GFP), August 28-30, 2019, Singapore, Singapore

Sub-wavelength gratings, segmented resonant-less structures with geometries featuring scales considerably smaller than the wavelength of light, have enabled an attractive technological concept to locally control light guiding properties in planar silicon chip architectures. This concept has allowed for additional degrees of freedom to tailor effective mode index, modal confinement, waveguide dispersion, as well as anisotropy, thereby providing a vital route towards high performing devices with engineered optical properties. Sub-wavelength integrated nanophotonics has opened up new horizons for realization of key building components that afford outstanding device performances, typically beyond those achieved by conventional design strategies, yet favorably benefiting from the sub-100-nm pattern resolution of established semiconductor manufacturing tools in nanophotonic foundries. The distinctive features of sub-wavelength grating structures are considered essential for future generation of chip-scale applications in optical communications and interconnects, biomedicine, as well as quantum-based technologies. In this work, we report recent advances in the development of high-performance on-chip nanophotonic waveguides and devices engineered with the sub-wavelength grating metamaterial structures. In particular, we discuss recent achievements of low-loss waveguides with controlled chromatic dispersion, high-efficiency fiber-to-chip surface grating couplers, micro-ring resonators, and grating-assisted waveguide filters, implemented on the mature silicon-on-insulator technology., Integrated Optics: Design, Devices, Systems and Applications, April 1-4, 2019, Prague, Czech Republic, Series: Proceedings of SPIE; no. 11031

New optical materials for hybrid photonic integration on silicon platform have become a hot research topic aiming at providing additional functionalities. In this regard, functional oxides are a very interesting class of materials due to their singular properties. Material engineering is commonly employed to tune and manipulate such properties at will, thus being functional oxides often used to build active reconfigurable elements in complex systems. Transparent oxides with moderate refractive indexes are targeted for hybrid integration due to the rewarding benefits envisioned. Yttria-Stabilized Zirconia (YSZ) is a chemically stable oxide1 with a transparency range that spans from the visible to the mid-IR2, with a refractive index around 2.1, which makes this functional oxide interesting for the development of low-loss waveguides when grown over a low contrast substrate. While these optical properties are very interesting for various applications, including on-chip optical communications and sensing, YSZ has remained almost unexplored in photonics up to now. Nevertheless, this complex functional oxide shows interesting optical properties such as low-moderate propagation losses of 2 dB/cm at telecom wavelengths3. In our work, we explore the deposition of erbium doped YSZ by pulsed layer deposition (PLD) on a multilayer approach providing outstanding luminescence in correspondence with C-band of telecommunication window (λ=1530 nm) and in the visible range by means of up-conversion processes. The optical properties of active layers of Er-doped YSZ grown on waveguides in different platforms and under resonant pumping will be discussed in this paper, as well as their propagation losses. Based on the preliminary study of these active hybrid systems, we envision light amplification functionalities based on rare-earth doped functional oxides.

Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, Silicon is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities, like second harmonic generation nor the linear electro-optic effect (i.e. Pockels effect). Nonetheless, by means of strain gradients, generated by depositing a stressed layer (typically SiN) on silicon waveguides, this restriction vanishe. Hence, for years, many attempts on characterizing the second order nonlinear susceptibility tensor through Pockels effect have been performed. However, due to the semiconductor nature of silicon, its analysis has been wrongly carried out. Indeed, carriers in Si, at the Si/SiN interface and in SiN have a screening effect when performing electro-optic modulation, which have led to overestimations of the second order nonlinear susceptibility and eventually rose a controversy on the real existence of Pockels effect in strained silicon waveguides. Here, we report on unambiguous experimental characterization of Pockels effect in the microwave domain, by taking advantage of the inherent limitation of carrier effect in high frequency range. Recent results on high-speed measurements will be presented and discussed. Both charge effects and Pockels effect induced under an electric field will be also analysed.

Integrated photonics has for several years included in its panoply the development of functions based on third-order non-linear optical phenomena, from the generation of supercontinuum or frequency comb sources to metrology or spectroscopy on chip applications. This natural evolution, after the development of high-speed transceivers in the last few years, particularly in silicon photonics, is based on a number of compromises and still has to solve problems, particularly concerning the integration of nonlinear materials on silicon and their exploitation. The work we present addresses two directions. The first is oriented towards the development of a supercontinuum source using Nitrogen-rich photonic circuits from an industrial CMOS platform, while the second aims at the development of hybrid highly nonlinear waveguides significantly reducing the impact of twophoton absorption in the telecom window around 1,55μm by exploiting silicon slot waveguides infiltrated by chalcogenide glasses (As2S3).

We report on experimental results of silicon micro-ring resonators based on non-resonant photonic metamaterial waveguides. High extinction ratio up to 30 dB and loaded Q-factors in a range of 1500 to 6000 were achieved at a wavelength of 1550nm.

With the fast growing demand of data, current chip-scale communication systems based on electrical links suffer rate limitations and high power consumptions to address these new requirements. In this context, Silicon Photonics has proven to be a viable alternative by replacing electronic links with optical ones while taking advantage of the well-established CMOS foundries techniques to reduce fabrication costs. However, silicon, in spite of being an excellent material to guide light, its centrosymmetry prevents second order nonlinear effects to exist, such as Pockels effect an electro-optic effect extensively used in high speed and low power consumption data transmission. Nevertheless, straining silicon by means of stressed thin films allows breaking the crystal symmetry and eventually enhancing Pockels effect. However the semiconductor nature of silicon makes the analysis of Pockels effect a challenging task because free carriers have a direct impact, through plasma dispersion effect, on its efficiency, which in turn complicates the estimation of the second order susceptibility necessary for further optimizations. However, this analysis is more relaxed working in high-speed regime because of the frequency limitation of free carriers-based modulation. In this work, we report experimental results on the modulation characteristics based on Mach-Zehnder interferometers strained by silicon nitride. We demonstrated high speed Pockels-based optical modulation up to 25 GHz in the C-band.

Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, silicon is a centrosymmetric crystal, i.e. silicon doesn’t have Pockels effect. Nevertheless, breaking the crystal symmetry of silicon can be used to overcome this limitation. In this work, the crystal modification is achieved by depositing a SiN high-stress overlayer. Recent results on high-speed measurements will be presented and discussed. Both charge effects and Pockels effect induced under an electric field will be also analyzed.

Fiber-chip grating couplers providing high-efficiency, robustness and cost-effectivity are recognized as a key building block for large-volume photonic applications. However, the efficiency of silicon-on-insulator (SOI) grating couplers is limited by the mismatch between the beam diffracted by the grating and the fiber mode, back-reflections at the grating-to-waveguide interface, and the power radiated towards the substrate. While the first two limitations can be overcome by grating apodization, the limited diffraction efficiency (directionality) towards the fiber remains a challenge. Typically, grating directionality is optimized by backside metallization, distributed Bragg mirrors, multi-level grating architectures or non-standard etching depths. However, these approaches yield comparatively complex structures, which in turn, come with the expense of extra fabrication costs, hindering the mass-scale development. Alternatively, the blazing effect has been exploited to provide remarkably high directionalities, relying on standard deep and shallow etch depths. Here, we report on the first experimental demonstration of an ultra-directional L-shaped fiber-chip grating coupler fabricated on 300 mm SOI wafer using 193-nm deep-ultraviolet lithography. The grating coupler is realized on a 300-nm-thick Si layer, combining standard full (300 nm) and shallow (150 nm) etch steps in an L-shaped arrangement. This approach yields a remarkably high grating directionality up to 98%. A single-step subwavelength-engineered transition provides an eight-fold reduction of the reflectivity, from ~8% to ~1%. We experimentally demonstrate a coupling efficiency of -2.7 dB, with a 3-dB bandwidth of 62 nm. These results open a new route towards exploiting the blazing effect for the large-volume realization of high-efficiency fiber-chip grating couplers in the low-cost 300 mm SOI photonic platform.

Grating couplers enable position-friendly interfacing of silicon chips by optical fibers. The conventional coupler designs call upon comparatively complex architectures to afford efficient light coupling to sub-micron silicon-on-insulator (SOI) waveguides. Conversely, the blazing effect in double-etched gratings provides high coupling efficiency with reduced fabrication intricacy. In this Letter, we demonstrate for the first time, to the best of our knowledge, the realization of an ultra-directional L-shaped grating coupler, seamlessly fabricated by using 193 nm deep-ultraviolet (deep-UV) lithography. We also include a subwavelength index engineered waveguide-to-grating transition that provides an eight-fold reduction of the grating reflectivity, down to 1% (-20 dB). A measured coupling efficiency of -2.7 dB (54%) is achieved, with a bandwidth of 62 nm. These results open promising prospects for the implementation of efficient, robust, and cost-effective coupling interfaces for sub-micrometric SOI waveguides, as desired for large-volume applications in silicon photonics.

International audience; We present on experimental results of straininduced Pockels effect in silicon based on Mach-Zehnder interferometer modulators. We theoretically studied both Pockels effect and carrier parasitic effect in silicon under an electric field. We demonstrated high speed Pockels-based optical modulation up to 25 GHz.

Silicon photonics has generated a strong interest in recent years, mainly for optical communications and optical interconnects in CMOS circuits. The main motivations for silicon photonics are the reduction of photonic system costs and the increase of the number of functionalities on the same integrated chip by combining photonics and electronics, along with a strong reduction of power consumption. However, one of the constraints of silicon as an active photonic material is its vanishing second order optical susceptibility, the so called χ(2) , due to the centrosymmety of the silicon crystal. To overcome this limitation, strain has been used as a way to deform the crystal and destroy the centrosymmetry which inhibits χ(2). The paper presents the recent advances in the development of second-order nonlinearities including discussions from fundamental origin of Pockels effect in silicon until its implementation in a real device. Carrier effects induced by an electric field leading to an electro-optics behavior will also be discussed.

With the increasing demand of data, current chip-scale communication systems based on metallic interconnects suffer rate limitations and power consumptions. In this context, Silicon photonics has emerged as an alternative by replacing the classical copper interconnects with silicon waveguides while taking advantage of the well-established CMOS foundries techniques to reduce fabrication costs. Silicon is now considered as an excellent candidate for the development of integrated optical functionalities including waveguiding structures, modulators, switches… One of the main challenges of silicon photonics is to reduce the power consumption and the swing voltage of optical silicon modulators while increasing the data rate speed. However, silicon is a centrosymmetric crystal, vanishing the second order nonlinear effect i.e. Pockels effect which is intrinsically a high speed effect. To overcome this limitation, mechanical stresses on silicon to break the crystal symmetry can be used depositing a strained overlayer. In this work, we have studied the effect of the stress layer in the modulation characteristics based on Mach-Zehnder interferometers. The deposition of silicon nitride as the stress layer and its optimization to induce the maximum effect will be presented.

The purpose of this work is to explore an alternative approach for high speed and low power consumption optical modulation based on the use of the Pockels effect in silicon. Unfortunately, silicon is a centro-symmetric crystal leading to a vanishing of the second order nonlinear coefficient, i.e. no Pockels effect. To overcome this limitation, on possibility would be to break the crystal symmetry by straining the silicon lattice with the epitaxial growth of crystalline functional oxides. Indeed, the induced strain due to lattice parameter mismatch and the difference in the thermal expansion coefficients between oxides and silicon are strong and may induce strong strain into silicon. Furthermore, functional oxides can exhibit very interesting multiferroicity and piezoelectricity properties that pave the way to a new route to implement silicon photonic circuits with unprecedented functionalities.

Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, silicon is a centrosymmetric crystal, i.e. silicon doesn’t have Pockels effect. Nevertheless, breaking the crystal symmetry of silicon can be used to overcome this limitation. This crystal modification is achieved by depositing a SiN high-stress overlayer. In this work, we present recent developments on the subject taking into account parasitic effects including plasma dispersion effect and fixed charge effect under an electric field. We theoretically and experimentally investigated Pockels effect in silicon waveguides and last results will be presented.

Hybrid integration of unconventional optical materials is arguably a promising way to substantially extend a range of chip functionalities on traditional silicon-based platforms. Especially, functional oxides are very promising because they exhibit many attractive properties, including superconductivity, piezoelectricity, ferroelectricity, and optical effects. In this article, we demonstrate hybrid photonic platform with an Erbium-doped (Er-doped) Yttria-Stabilized Zirconia (YSZ) thin film used as an active luminescent cladding on top of low-loss Silicon Nitride (SiN) waveguides. This active layer has been grown by a pulsed laser deposition (PLD) technique. Optical characterizations via photoluminescence (PL) measurements were performed in both normal and in-plane light incidence to demonstrate strong near-infrared (near-IR) emission of Er ions in the Er:YSZ thin film. Moreover, we also observed an intense in-plane guided PL emission in visible and near-IR wavelengths from hybrid Er:YSZ-on-SiNx waveguides. These results pave the way towards rare-earth-doped YSZ structures on silicon-based platforms, thereby affording required function versatility for future photonic integrated circuits.

Functional oxides are considered as promising materials for photonic applications due to their extraordinary and various optical properties. Especially, yttria-stabilized zirconia (YSZ) has a high refractive index (\ensuremath{\sim}2.15), leading to a good confinement of the optical mode in waveguides. Furthermore, YSZ can also be used as a buffer layer to expand toward a large family of oxides-based thin-films heterostructures. In this paper, we report a complete study of the structural properties of YSZ for the development of integrated optical devices on sapphire in telecom wavelength range. The substrate preparation and the epitaxial growth using pulsed-laser deposition technique have been studied and optimized. High-quality YSZ thin films with remarkably sharp x-ray diffraction rocking curve peaks in ${{10}^{\ensuremath{-}3}}^{\ensuremath{\circ}}$ range have then been grown on sapphire (0001). It was demonstrated that a thermal annealing of sapphire substrate before the YSZ growth allowed controlling the out-of-plane orientation of the YSZ thin film. Single-mode waveguides were finally designed, fabricated, and characterized for two different main orientations of high-quality YSZ (001) and (111). Propagation loss as low as 2 dB/cm at a wavelength of 1380 nm has been demonstrated for both orientations. These results pave the way for the development of a functional oxides-based photonics platform for numerous applications including on-chip optical communications and sensing.

Optical input/output interfaces between silicon-on-insulator (SOI) waveguides and optical fibers, allowing robust, costeffective and low-loss coupling of light, are fundamental functional elements in the library of silicon photonic devices. Surface grating couplers are particularly desirable as they allow wafer-scale device testing, yield improved alignment tolerances, and are compatible with state-of-the-art integration and packaging technologies. While several factors jointly contribute to the coupler performance, the grating directionality is a critical parameter for high-efficiency fiber-chip coupling. To address this issue, conventional coupler designs typically call upon comparatively complex architectures to improve light coupling efficiency. Increasing the intrinsic directionality of the grating by exploiting the blazing effects is another promising solution. In this paper, we report on our recent advances in development of low-loss grating couplers that afford excellent directionality, close to the theoretical limit of 100%. In particular, we demonstrate, by theory and experiments, several implementations of blazed grating couplers with layout features that are compatible with deepultraviolet (deep-UV) optical lithography. Devices can be advantageously implemented on various photonic platforms, including industry-specific and the offerings of publicly accessible foundries. The first experimental realizations of uniform deep-UV-compatible couplers yield losses of -2.7 dB at 1.55-µm and a 3-dB bandwidth of 62 nm. A subwavelength-index-engineered impedance matching transition is used to reduce back-reflections down to -20 dB., Silicon Photonics: from Fundamental Research to Manufacturing, April 22-26, 2018, Strasbourg, France, Series: Proceedings of SPIE; no. 10686

International audience; We present a novel and comprehensive analysis method that considers both plasma-dispersion effect and the strain-induced Pockels effect to faithfully describe the electro-optic effects taking place in a strained silicon waveguide under an applied voltage. The change of carrier distribution arising from the application of a voltage, leads to a redistribution of the electrostatic field which deeply affects the strain-induced Pockels effect. By simulating the strain gradients distribution inside the waveguide together with the free carrier concentration in silicon, we were able to describe that the effective index change due to Pockels effect in strained silicon waveguides and the applied voltage have a nonlinear relationship.