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International audience; The adsorption of phthalocyanine (H$_2$ Pc) on the 6H-SiC(0001)-(3 x 3) surface is investigated using X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS), and density functional theory (DFT) calculations. Spectral features are tracked from the submonolayer to the multilayer growth regime, observing a significant modification of spectroscopic signals at low coverage with respect to the multilayer films, where molecules are weakly interacting. Molecules stay nearly flat on the surface at the mono and submonolayers. Previously proposed adsorption models, where the molecule binds by two N atoms to corresponding Si adatoms, do not reproduce the experimental spectra at the submonolayer coverage. We find instead that another adsorption model where the molecule replaces the two central H atoms by a Si adatom, effectively forming Si-phthalocyanine (SiPc), is both energetically more stable and yields in combination a better agreement between the experimental and simulated spectra. This suggests that the 6H-SiC(0001)-(3 Â 3) surface may be a candidate substrate for the on-surface synthesis of SiPc molecules.

Rare-earth ions (REIs) doped into solid-state crystal hosts offer an attractive platform for realizing quantum interconnects that can function as quantum memories and quantum repeaters. The 4f valence electrons of REIs are shielded by 5s and 5p electrons and undergo highly coherent transitions even when embedded in host crystals. In particular, Er3+ has an optical transition in the telecom band that is suitable for low-loss communication. Recently, REIs in thin film systems have gained interest due to potential advantages in providing a flexible host crystal environment, enabling scalable on-chip integration with other quantum devices. Here, we investigate the structural and optical properties of Er-doped anatase TiO2 thin films on LaAlO3 (001) substrates. By choosing a system with minimal lattice mismatch and adjusting Er-dopant concentration, we achieve optical inhomogeneous linewidths of 5 GHz at 4.5 K. We show that 9 nm-thick buffer and capping layers can reduce the linewidth by more than 40%, suggesting a pathway to further narrowing linewidths in this system. We also identify that Er3+ ions mainly incorporate into substitutional Ti4+ sites with non-polar D2d symmetry, which makes Er dopants insensitive to the first order to local electric fields from impurities and is desirable for coherence properties of Er3+ spins.

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 (

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.

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.

Silicon photonics has generated an amazing interest for many years to address the challenges of numerous applications including optical communications, sensing, and quantum information to name few. A review of the main building blocks to emit, guide, modulate, and detect light on silicon chip is described and a special focus is given on the large possibilities offered by the hybrid integration on silicon photonics platform for the development of reliable and efficient on-chip functionalities.

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).

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.

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.