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Waveguide integrated optical modulators in the mid-infrared wavelength range are of significant interest for molecular spectroscopy. This is because on-chip synchronous detection can improve the performance of detection systems and can also be used for free-space communications where optical modulators working in atmospheric transparency windows are needed. Here we report optical modulation in a mid-infrared photonic circuit, reaching wavelengths larger than 8 µm. Optical modulation in the wavelength range from 5.5 to 11 µm is shown, relying on a broadband Ge-rich graded-SiGe platform. This demonstration experimentally confirms the free-carrier absorption effect modeling. These results pave the way towards efficient high-performance electrically-driven integrated optical modulators in the mid-infrared wavelength range. Mid-infrared optical modulators are important for detecting compounds in a wide range of applications, but are typically limited to short wavelengths. Now, a SiGe waveguide is used to fabricate an optical modulator that can reach wavelengths spanning 5.5 µm to 11 µm.

Integration of nanomaterials within optical nanocavities provides a unique potential for flexible control of light emitters properties by photonic band gap engineering and cavity Purcell effects. Here, we propose a one-dimensional heterostructure nanocavity exhibiting both non-coupled and coupled cavity modes, i.e. simultaneously acting as a single cavity and as a photonic molecule. The main cavity resonances are engineered to yield a wide spectral separation and for the first time to match the emission wavelengths of two different kinds of semiconducting single wall carbon nanotubes (s-SWNTs). By probing the photoluminescence (PL) from s-SWNTs coupled with the nano cavity modes, coupling of the s-SWNTs PL simultaneously into the several cavity modes is demonstrated. For modes governed by the photonic molecule behavior, the wavelength splitting of the two coupled modes is dominated by the cavity barrier width. The excitation of the bonding (B) and anti-bonding (AB) cavity modes then yields PL resonant enhancement that can be tuned by the pumping position and polarization filter. These results demonstrate the potential of the proposed multimode photonic molecule to tailor light-nanomaterial interactions on chip, paving the way for the development of tunable hybrid photonic circuits relying on nanoemitters in cavities for light generation purposes.

We present here the implementation of an optoelectronic oscillator (OEO) that leverages the optical comb produced by a silicon add-drop ring resonator to directly convert signals from optical to microwave domain. The OEO comprises a CW laser, an intensity modulator, a silicon add-drop ring, a photodetector, and radiofrequency amplifier. By using millimeter-long silicon-on insulator micro-ring resonator, we generated an oscillation signal with a frequency determined by the free spectral range (FSR) of the ring. In this scheme, the sharp transmission peaks in the drop port of an add-drop silicon resonator are used as the optical comb. The optimised ring has a length of 5.8 mm with a measured FSR of 112 pm, an extinction ratio of 20 dB and an optical quality factor of 2.2 × 10 5 . The complete OEO loop yields a 14.12 GHz signal with a phase noise level of -100 dBc/Hz at an offset of 100 kHz from the carrier. This result shows that OEOs directly based on millimeters long silicon rings are a promising path for generating low-noise microwave signals.

Subwavelength grating (SWG) metamaterials have garnered a great interest for their singular capability to shape the material properties and the propagation of light, allowing the realization of devices with unprecedented performance. However, practical SWG implementations are limited by fabrication constraints, such as minimum feature size, that restrict the available design space or compromise compatibility with high-volume fabrication technologies. Indeed, most successful SWG realizations so far relied on electron-beam lithographic techniques, compromising the scalability of the approach. Here, we report the experimental demonstration of an SWG metamaterial engineered beam splitter fabricated with deep-ultraviolet immersion lithography in a 300-mm silicon-on-insulator technology. The metamaterial beam splitter exhibits high performance over a measured bandwidth exceeding 186 nm centered at 1550 nm. These results open a new route for the development of scalable silicon photonic circuits exploiting flexible metamaterial engineering.

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.

The large mode size mismatch between standard single-mode optical fibers and silicon-on-insulator (SOI) waveguides poses a significant challenge to efficiently couple light from the optical fiber to the chip, and vice versa. Surface grating couplers are often used for this purpose, however, their operational bandwidth is limited to a few tens of nanometers, as a consequence of the wavelength-dependent radiation angle. This constraint seriously hampers the use of surface grating couplers for next-generation passive optical networks (PONs), in which the wavelengths used for the upstream and downstream channels are separated more than 150 nm. In this work, we present a dual-band grating coupler for 10 Gbit symmetric PONs. Our device operates as a wavelength multiplexer/demultiplexer, simultaneously coupling and combining/splitting two optical signals at the wavelengths of λ_1=1270 nm and λ_2=1577 nm. The coupler is based on engineering a surface grating coupler to obtain opposite radiation angles for the two respective wavelengths. To achieve a higher coupling efficiency, the material platform thicknesses were optimized as a tradeoff between the waveguide propagation loss and the substrate reflectivity. By judiciously choosing the period (Λ=500 nm) and the duty cycle (DC=55%) of the grating section, an efficient dual-band grating coupler is designed with a minimum feature size of 225 nm. The coupler was fabricated in ST Crolles using their 300 mm SOI platform and 193-nm deep-ultraviolet lithography, demonstrating that large-scale fabrication is feasible. Measured fiber-chip coupling efficiencies were -4.9 dB and -5.2 dB with a 3-dB bandwidth of >27 nm and 56 nm at λ_1=1270 nm and λ_2=1577 nm, respectively.

Integrated silicon nanophotonics has progressed a lot over past decades with great promises for many surging applications in optoelectronics, information and communication technologies, sensing or health monitoring. Enabling low-cost, dense integration, and compatibility with modern semiconductor nanofabrication processes, silicon nanophotonics deliver compact and high-performance devices on single chips. A variety of nanophotonic functionalities, both passive and active, are nowadays available on semiconductor substrates, leveraging the maturity of open-access silicon foundries and epitaxial germanium integration. It encompasses essential functions such as light generation and amplification, fast electro-optical modulation, and reliable conversion of optical into electrical signals. Germaniumbased optical photodetectors are main building blocks within the library of integrated silicon nanophotonics, with performances that are nowadays on par with their III-V-based counterparts. Germanium photodetectors integrated at the end of waveguides are attractive for next-generation on-chip interconnections, because of their compactness, bandwidth and speed, energy consumption and cost. In this work, we present our latest advances on silicon-germanium p-i-n waveguide-integrated photodetectors based on lateral silicon-germanium-silicon heterojunctions. Our hetero-structured photodetectors were fabricated on top of 200-mm silicon-on-insulator substrates using industrial-scale fabrication processes compatible with complementary metal-oxide-semiconductor technology. Silicon-germanium p-i-n photodetectors operated under low bias voltages exhibited low dark-currents (~100 nA), cut-off frequencies beyond 50 GHz, and photo-responsivities of about 1.2 A/W. Photodetector sensitivities of -14 dBm and -11 dBm were achieved for communication data rates of 10 Gbps and 25 Gbps, respectively. P-i-n photodetectors with lateral heterojunction operated in an avalanche regime offered an additional degree of freedom to improve device performances. High-speed and low-noise characteristics were obtained in our p-i-n photodetectors upon avalanche operation, with a gain-bandwidth product of 210 GHz and a low carrier impact ionization ratio of about 0.25. The measured sensitivity of avalancheoperated devices was -11 dBm for 40 Gbps signal detection. As demonstrated in the reported achievements, heterostructured p-i-n photodetectors are thus suitable communication devices in future intra-data center links or high-speed optical interconnects.

We theoretically explore the potential of Si3N4 on SiO2 waveguide platform toward a wideband spectroscopic detection around the optical wavelength of 2 μm. The design of Si3N4 on SiO2 waveguide architectures consisting of a Si3N4 slot waveguide for a wideband on-chip spectroscopic sensing around 2 μm, and a Si3N4 multi-mode interferometer (MMI)-based coupler for light coupling from classical strip waveguide into the identified Si3N4 slot waveguides over a wide spectral range are investigated. We found that a Si3N4 on SiO2 slot waveguide structure can be designed for using as optical interaction part over a spectral range of interest, and the MMI structure can be used to enable broadband optical coupling from a strip to the slot waveguide for wideband multi-gas on-chip spectroscopic sensing. Reasons for the operating spectral range of the system are discussed.

4 pags., 5 figs., 1 tab., Surface grating couplers are fundamental building blocks for coupling the light between optical fibers and integrated photonic devices. However, the operational bandwidth of conventional grating couplers is intrinsically limited by their wavelength-dependent radiation angle. The few dual-band grating couplers that have been experimentally demonstrated exhibit low coupling efficiencies and rely on complex fabrication processes. Here we demonstrate for the first time, to the best of our knowledge, the realization of an efficient dual-band grating coupler fabricated using 193 nm deep-ultraviolet lithography for 10 Gbit symmetric passive optical networks. The footprint of the device is 17 × 10 µm. We measured coupling efficiencies of −4.9 and −5.2 dB with a 3-dB bandwidth of 27 and 56 nm at the wavelengths of 1270 and 1577 nm, corresponding to the upstream and downstream channels, respectively., Spanish Ministry of Science, Innovation and Universities (MICINN) (RTI2018-097957-B-C33, TEC2015-71127-C2-1-R with FPI Scholarship BES-2016-077798); Community of Madrid - FEDER funds (S2018/NMT-4326); Horizon 2020 Research and Innovation Program (Marie Sklodowska-Curie 734331); H2020 European Research Council (ERC POPSTAR 647342); European Commission (H2020- ICT-26127-2017 COSMICC 688516); French Industry Ministry (Nano2022 project under IPCEI program); Agence Nationale de la Recherche (ANR-MIRSPEC-17-CE09-0041).

Optical photodetectors are at the forefront of photonic research since the rise of integrated optics. Photodetectors are fundamental building blocks for chip-scale optoelectronics, enabling conversion of light into an electrical signal. Such devices play a key role in many surging applications from communication and computation to sensing, biomedicine and health monitoring, to name a few. However, chip integration of optical photodetectors with improved performances is an on-going challenge for mainstream optical communications at near-infrared wavelengths. Here, we present recent advances in heterostructured silicon-germanium-silicon p-i-n photodetectors, enabling high-speed detection on a foundry-compatible monolithic platform.

International audience; Midinfrared spectroscopy is a universal way to identify chemical and biological substances. Indeed, when interacting with a light beam, most molecules are responsible for absorption at specific wavelengths in the mid-IR spectrum, allowing to detect and quantify small traces of substances. On-chip broadband light sources in the midinfrared are thus of significant interest for compact sensing devices. In that regard, supercontinuum generation offers a mean to efficiently perform coherent light conversion over an ultrawide spectral range, in a single and compact device. This work reports the experimental demonstration of onchip two-octave supercontinuum generation in the mid-infrared wavelength, ranging from 3 to 13 μm (that is larger than 2500 cm −1) and covering almost the full transparency window of germanium. Such an ultrawide spectrum is achieved thanks to the unique features of Ge-rich graded SiGe waveguides, which allow second-order dispersion tailoring and low propagation losses over a wide wavelength range. The influence of the pump wavelength and power on the supercontinuum spectra has been studied. A good agreement between the numerical simulations and the experimental results is reported. Furthermore, a very high coherence is predicted in the entire spectrum. These results pave the way for wideband, coherent, and compact mid-infrared light sources by using a single device and compatible with large-scale fabrication processes.

Ge-rich SiGe photonic circuits have been used to demonstrate a whole set of devices operating in a wide spectral range in the mid-IR. Optical modulation has been demonstrated recently up to 11 micron wavelength.

International audience; Near-field imaging of the propagation of a diffraction-free Bessel-type beam in a guided wave configuration generated by means of a metasurface-based axicon lens integrated on a silicon waveguide is reported. The operation of the axicon lens with a footprint as small as 11 μm2 is based on local engineering of the effective index of the silicon waveguide with plasmonic nanoresonators. This generic approach, which can be adapted to different types of planar lightwave circuit platforms, offers the possibility to design nano-engineered optical devicesbased on the use of plasmonic resonators to control light at the nanoscale.

Application of photonics for smart farming could have a tremendous impact on the economy and the well-being of world population. Silicon Photonics should be a promising platform to apply the photonic technologies at reasonable cost in agricultural-based countries for their economic agriculture products. Among several group-IV materials, Silicon Nitride (SiN) is one of the most interesting Si-compatible materials suitable for on-chip spectroscopic sensing in the near- and mid-IR region as it has a relatively large transparent windows and a sufficiently-high refractive index of ~ 2. In this presentation, we will discuss the use of Si3N4 on SiO2 waveguides for a wideband spectroscopic sensing. The target design would include optical wavelength from 2.5 µm to 3.5 µm, in which several agriculturally-important gas molecules can be detected such as H2O (water vapor), CO2 (carbon dioxide), N2O (Nitrous oxide), NH3 (Ammonia), C2H4 (Ethylene), CH4 (Methane), and the spectral range is also within the transparent windows of Si3N4 on SiO2 waveguide. Significantly, we focus our effort on achieving a waveguide structure that can support single-mode optical propagation for a broad spectral range within 2.5-3.5 µm, and at the same time, can maintain a good sensing performance for multi-gas spectroscopic sensing despite the compromised evanescent field confinement values owing to the wideband design. We investigated the detection performance in term of compactness, polarization dependence, detection limit, and fabrication tolerance.

The Si transparency (1.1 μm – 8 μm wavelength) contains the strongest absorption features of a wide range of chemical and biological substances. However, the use of SOI in the mid-IR is hampered by the large absorption of the buried oxide (BOX) for wavelengths above 4 μm. Silicon membranes have garnered great interest for their unique capability to overcome the BOX limitation while leveraging the advantages of Si photonics. On the other hand, silicon is uniquely poised for the implementation of wideband mid-IR sources based on nonlinear frequency generation. Promising supercontinuum and frequency comb generation have already been demonstrated in Si. Still, current implementations have a limited flexibility in the engineering of phase-matching conditions and dispersion, which complicates the shaping of the nonlinear spectrum. Patterning Si with features smaller than half of the wavelength (well within the capabilities of standard large-volume fabrication processes) has proven to be a simple and powerful tool to implement metamaterials with optimally engineered properties. Here, we present the design of nanostructured silicon membrane waveguides with ultra-wideband flat anomalous dispersion in a wavelength span exceeding 5 µm. Our three-dimensional finite difference time domain (FDTD) calculations predict flat anomalous dispersion near 50 ps/km⋅nm between 2.5 µm and 8 µm wavelength. These results illustrate the potential of subwavelength metamaterial engineering to control chromatic dispersion in Si membrane waveguides. This is a promising step towards the implementation of wideband nonlinear sources in the mid-IR for silicon photonics.

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

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.

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.

We propose the realization of an on-chip dual identical narrowband Bragg filter at ∼ 1310 and ∼ 1950 n m wavelengths simultaneously based on the silicon-on-insulator (SOI) platform. By taking advantage of subwavelength corrugation behavior at large wavelengths and the difference in the mode areas of the involved modes at the two widely separated wavelengths, undesired diffraction losses are circumvented while achieving Bragg resonances at the two wavelengths simultaneously. A double-corrugation Bragg grating rib waveguide filter is proposed, with two sets of gratings, the inner one close to the rib operating near 1310 nm wavelength, with the outer grating being designed to achieve a transmission dip around 1950 nm. Introducing a proper lateral misalignment to the set of inner grating indents, a dual identical narrowband Bragg filter with ∼ 0.47 n m 3 dB bandwidth at ∼ 1310 n m and ∼ 1950 n m is achieved. The proposed design strategy based on the SOI platform relies on a single-etching fabrication process and presents potential applications in situations where equal-bandwidth filtering is needed in on-chip communications and sensing.

Slotted photonic crystal (SPC) cavities provide strong evanescent fields, high quality factors, and small mode volumes. Hence, SPC cavities have been identified as promising candidates for the implementation of high-performance sensors and the development of hybrid devices combining silicon with other active materials. Nevertheless, most state-of-the-art demonstrations rely on electron beam lithography and operate in the telecommunications band near the 1550 nm wavelength. Here, we report the experimental demonstration of SPC cavities operating in the datacom O-band, near 1340 nm wavelength, fabricated using deep-ultraviolet (DUV) lithography. The O-band provides very interesting properties for sensing, communications, and hybrid integration: namely, lower optical absorption of water, lower dispersion in standard optical fibers, and the emission of active materials like carbon nanotubes. On the other hand, DUV fabrication opens interesting opportunities for large volume production. The proposed cavities exhibit a high quality factor exceeding 20,000 and a small mode volume of 0.023 ( λ / n ) 3 . These results open interesting perspectives to exploit enhanced light–matter interaction in SPC cavities harnessing industrial-like fabrication processes.

In this article we address the nanoscale engineering of the effective index of silicon on insulator waveguides by using plasmonic metasurface resonances to realize a graded index lens. We report the design, implementation, and experimental demonstration of this plasmonic metasurface-based graded index lens integrated on a silicon waveguide for operation in the near-infrared domain. The 2D-graded index lens consists of an array of gold cut wires fabricated on the top of a silicon waveguide. These gold cut wires modify locally the effective index of the silicon waveguide and allow the realization of this gradient lens. The reported solution represents a promising alternative to the bulky or multilayered metamaterials approach in the near IR domain. This enabling technology may have found its place in silicon photonic applications by exploiting the plasmonic resonances to control the light at nanoscale.

We demonstrated a class of highly nonlinear hybrid waveguide structures based on infiltration of As2S3 chalcogenide glass into silicon slot waveguides. The nonlinear properties of the hybrid waveguides were precisely quantified via a bidirectional top-hat D-scan method, enabling a direct comparison between properties measured using different device geometries. We experimentally demonstrate hybrid As2S3-Si slot waveguides with a two-photon absorption (TPA) figure of merit exceeding 2 at near infrared wavelengths. These waveguides largely satisfy the critical criterion for efficient nonlinear integrated photonics (FOMTPAwg>1), allowing phase shifts greater than π with minimal overall losses. These results pave the way for efficient and robust ultrafast all-optical devices and circuits in large-scale silicon photonics technology.

International audience; The availability of low-loss optical interfaces to couple light between standard optical fibers and high-index-contrast silicon waveguides is essential for the development of chip-integrated nanophotonics. Input and output couplers based on diffraction gratings are attractive coupling solutions. Advanced grating coupler designs, with Bragg or metal mirror underneath, low-and high-index overlays, and multi-level or multi-layer layouts, have proven less useful due to customized or complex fabrication, however. In this work, we propose a rather simpler in design of efficient off-chip fiber couplers that provide a simulated efficiency up to 95% (−0.25 dB) at a wavelength of 1.55 µm. These grating couplers are formed with an L-shaped waveguide profile and synthesized subwavelength grating metamaterials. This concept jointly provides sufficient degrees of freedom to simultaneously control the grating directionality and out-radiated field profile of the grating mode. The proposed chip-to-fiber couplers promote robust sub-decibel coupling of light, yet contain device dimensions (> 120 nm) compatible with standard lithographic technologies presently available in silicon nanophotonic foundries. Fabrication imperfections are also investigated. Dimensional offsets of ± 15 nm in shallow-etch depth and ± 10 nm in linewidth's and mask misalignments are tolerated for a 1-dB loss penalty. The proposed concept is meant to be universal, which is an essential prerequisite for developing reliable and low-cost optical couplers. We foresee that the work on L-shaped grating couplers with sub-decibel coupling efficiencies could also be a valuable direction for silicon chip interfacing in integrated nanophotonics.

International audience; We present a new FTS approach that harnesses both spatial heterodyning and thermo-optical path tuning to overcome the resolution-bandwidth tradeoff in conventional counterparts. We experimentally demonstrate a mid-infrared SiGe FTS, with a resolution exceeding 15 cm-1 in a wide bandwidth of 603 cm-1 .

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

Semiconducting single walled carbon nanotubes (s-SWNT) have an immense potential for the development of active optoelectronic functionalities in ultra-compact hybrid photonic circuits. Specifically, s-SWNT have been identified as a very promising solution to implement light sources and detectors in the silicon photonics platform. Here we present our most recent results on the hybrid integration of s-SWNT with silicon resonators, including micro-rings, micro-disks and photonic crystal cavities. We show chirality-wise resonant enhancement of s-SWNT emission, allowing on-chip selection of (8,6) or (8,7) SWNT chiralities present in a high-purity polymer-sorted solution. We also demonstrate that, opposite to the common knowledge, the longitudinal component in transverse-magnetic optical modes can efficiently interact with drop-casted s-SWNTs arranged along the chip surface. The proposed hybrid integration approach unlocks new tools to optimize light-SWNT interaction in silicon photonic circuits and open a new route towards single-chirality selection in hybrid Si-SWNT devices, even if the SWNT solution contains various chiralities. Hence, these results stand as an important step towards the implementation of s-SWNT-based devices for the silicon photonics platform.

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.

International audience; In this article, we report an experimental demonstration of enabling technology exploiting resonant properties of plasmonic nanoparticles, for the realization of wavelength sensitive ultra-minituarized (4×4 µm) optical metadevices. To this end the example of a 1.3/1.6 µm wavelength demultiplexer is considered. Its technological implementation is based on the integration of gold cut wire based metalines on the top of a silicon on insulator waveguide. The plasmonic metalines modify locally the effective index of the Si waveguide and thus allow for the implementation of wavelength dependent optical pathways. The 1.3/1.6µm wavelength separation with extinction ratio between two demultiplexer's channels reaching up to 20dB is experimentally demonstrated. The considered approach, which can be readily adapted to other planar lightwave circuits platforms and nanoresonators of different types of materials, is suited for the implementation of a generic family of wavelength sensitive guided wave optical metadevices. http://dx.

The recent advances in the development of quantum cascade laser with room temperature operation in the mid infrared paved the way for the realization of wideband communication systems. Particularly, two mid-infrared atmosphere transparency windows lying between 3-5 μm and between 8-14 μm exhibit great potential for further implementation of wideband free space communications. Additionally this wide unregulated spectral region shows reduced background noise and low Mie and Rayleigh scattering. Despite the development of a plethora of photonic components in mid infrared such as sources, detectors, passive structures, less efforts have been dedicated to investigate polarization management for information transport. In this work, the potential of Ge-rich SiGe waveguides is exploited to build a polarization insensitive platform in the mid-infrared. The gradual index evolution in SiGe alloys and geometric parameter optimization are used to obtain waveguides with birefringence below 2×10-4 and an unprecedented bandwidth in both atmosphere transparency windows i.e. near 3.5 μm and 9 μm. Following waveguide birefringence optimization an ultra-wideband and polarization insensitive multimode interference coupler was designed. The optimized structure shows a 4.5 μm wide bandwidth in transverse electric and transverse magnetic polarization at 9 μm wavelength. The developed ultra-wideband polarization insensitive photonic building blocks presented in this work pave the way for further implementation of free space communication systems in the mid infrared spectral region., Silicon Photonics XIV, February 2-7, 2019, San Francisco, USA, Series: Proceedings of SPIE; no. 10923

International audience; Wideband and polarization-independent wavelength filters with low sensitivity to temperature variations have great potential for wavelength division multiplexing applications. However, simultaneously achieving these metrics is challenging for silicon-on-insulator photonics technology. Here, we harness the reduced index contrast and the low thermo-optic coefficient of silicon nitride to demonstrate waveguide Bragg grating filters with wideband apolar rejection and low thermal sensitivity. Filter birefringence is reduced by judicious design of a triangularly shaped lateral corrugation. Based on this approach, we demonstrate silicon nitride Bragg filters with a measured polarization-independent 40 dB optical rejection with negligible off-band excess loss, and a sensitivity to thermal variations below 20 pm/°C.

International audience; Near-infrared germanium (Ge) photodetectors monolithically integrated on top of silicon-on-insulator substrates are universally regarded as key enablers towards chip-scale nanophotonics, with applications ranging from sensing and health monitoring to object recognition and optical communications. In this work, we report on the highdata-rate performance pin waveguide photodetectors made of a lateral hetero-structured silicon-Ge-silicon (Si-Ge-Si) junction operating under low reverse bias at 1.55 mu m. The pin photodetector integration scheme considerably eases device manufacturing and is fully compatible with complementary metal-oxide-semiconductor technology. In particular, the hetero-structured Si-Ge-Si photodetectors show efficiency-bandwidth products of similar to 9 GHz at -1 V and similar to 30 GHz at -3 V, with a leakage dark current as low as similar to 150 nA, allowing superior signal detection of high-speed data traffic. A bit-error rate of 10(-9) is achieved for conventional 10 Gbps, 20 Gbps, and 25 Gbps data rates, yielding optical power sensitivities of -13.85 dBm, -12.70 dBm, and -11.25 dBm, respectively. This demonstration opens up new horizons towards cost-effective Ge pin waveguide photodetectors that combine fast device operation at low voltages with standard semiconductor fabrication processes, as desired for reliable on-chip architectures in next-generation nanophotonics integrated circuits.

In this paper, we present an experimental study, validated by two different approaches, of the influence of the top cladding refractive index on the transmission and slow light properties of dispersion engineered silicon slot photonic crystal waveguides. We demonstrate that even though the operation wavelength is very sensitive to refractive index changes, the structures remain, nevertheless, robust in terms of group index, group velocity dispersion properties, and bandwidth figures of merit.

Silicon photonics has emerged as a very promising technology platform for the implementation of high-performance, low-cost, ultra-compact circuits that can monolithically cointegrate electronic, opto-electronic and optic functionalities. However, Si neither has efficient light emission or detection in the telecom wavelength range, nor exhibits efficient electro-optic Pockels effect, hindering the implementation of integrated active devices like sources, detectors, or modulators. Current approaches relay on different materials to provide active functionalities in Si photonics, resulting in highly complex integration schemes that compromise cost-effectiveness. Semiconducting single-wall carbon nanotubes (SWNTs) are capable of emitting and detecting near-infrared light at room temperature and exhibit intrinsically fast electro-optic effects. They have also proven promising uses in micro-electronic devices, making them an ideal material to provide active functionalities in the Si photonic platform. In this work, we propose and experimentally validate the possible use of slot photonic waveguides to improve interaction between SWNTs and Si waveguide modes. Fabricated Si slot micro-ring shown an experimental similar to 60% photo-luminescence improvement compared to previous demonstration based on Si strip waveguide resonators. These results prove the potential of Si slot waveguides for the implementation of efficient SWNT-based Si photonic devices.

A polarization tolerant optical receiver is a key building block for the development of wavelength division multiplexing based high-speed optical data links. However, the design of a polarization independent demultiplexer is not trivial. In this Letter, we report on the realization of a polarization tolerant arrayed waveguide grating (AWG) on a 300-mm silicon nitride (SiN) photonic platform. By introducing a series of individual polarization rotators in the middle of the waveguide array, the polarization dependence of the AWG has been substantially reduced. Insertion losses below 2.2 dB and a crosstalk level better than − 29 d B has been obtained for transverse electric and transverse magnetic polarizations on a four-channel coarse AWG. The AWG temperature sensitivity has also been evaluated. Thanks to the low thermo-optical coefficient of SiN, a thermal shift below 12 pm/°C has been demonstrated.

[EN] Waveguide Bragg grating filters with narrow bandwidths and high optical rejections are key functions for several advanced silicon photonics circuits. Here, we propose and demonstrate a new, to the best of our knowledge, Bragg grating geometry that provides a narrowband and high rejection response. It combines the advantages of subwavelength and modal engineering. As a proof-of-concept demonstration, we implement the proposed Bragg filters in 220-nm-thick Si technology with a single etch step. We experimentally show flexible control of the filter selectivity, with measured null-to-null bandwidths below 2 nm, and strength of 60 dB rejection with a null-to-null bandwidth of 1.8 nm., Agence Nationale de la Recherche (ANR-MIRSPEC-17-CE09-0041, ANR-SITQOM-15-CE24-0005); European Research Council (ERC POPSTAR 647342).

We theoretically investigated the use of a Si3N4 on SiO2 waveguide as an optical interaction part with sensed molecules for multi-gas wideband on-chip spectroscopic sensing. From the analysis, we show that a simple strip Si3N4 waveguide can be employed to achieve acceptable values of performance in term of detection limit, compactness, polarization, and fabrication tolerance for the detection of water vapor (H2O), carbon dioxide (CO2), Nitrous oxide (N2O), Ammonia (NH3), Ethylene (C2H4), and Methane (CH4) gas molecules, with a wideband operation between 2.7 and 3.4 µm optical wavelength. The results show that a simple Si3N4 waveguide structure could attain competitive performance required for generic on-chip spectroscopic sensing for environmental and agricultural usage.

International audience; Due to the rotational and vibrational frequency, molecules show unique absorption spectrum in the mid-infrared fingerprint region from 500 to 1500 cm-1. Hence, the demonstration of integrated on-chip spectrometers with compact sizes, cost-effective and high performance is important. Here, we demonstrate the first polarization insensitive broadband operational mid infrared spatial heterodyne Fourier-Transform spectrometer (SHFTS) working beyond 5 µm wavelength. A resolution better than 15cm-1 for both TE/TM polarizations has been experimentally demonstrated in an unprecedented bandwidth of 800 cm-1 (from 5 µm to 8.5 µm wavelength) for our integrated on-chip SHFTS, using a graded-index Ge-rich SiGe photonics platform.

International audience; Thin films of lead salt nanocrystals (NCs) offer attractive opportunities as active media for near-infrared optoelectronics but suffer from limiting trade-offs between optical and electrical properties. While NCs separated by nanometer-long ligands are good light emitters, NCs capped with shorter molecules provide a high carrier mobility but degrade the photo- and electroluminescence and broaden the narrow emission spectrum. Here we show that this severe quenching and spectral broadening can be averted with an unconventional use of metallic antennas. The resulting NC-antenna hybridization not only provides a strong boost in luminescence, but also makes it possible to remodel the emission spectrum in radical ways, even at wavelengths where the NC assembly does not emit light. These results cannot be explained with the standard theory of single-emitter luminescence assisted by optical antennas. We propose an alternative model based on a statistical description of light emission by an ensemble of emitters and discuss important consequences of our findings for nano-optics and solution-processed optoelectronics.

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.

We report nanophotonic silicon-based devices for hybrid integration: 1D photonic crystal (PhC) on optical fiber, i. e. fiber Bragg grating (FBG) sensing probe integrated in fiber laser structure for chemical sensors and slotted planar 2D PhC cavity combined with carbon nanotube (CNT) towards light nanosources. The experiments have been carried out by integrating 1D PhC on optical fiber in fiber laser structure. This structure possesses many advantages including high resolution for wavelength shift, high optical signal-to-noise ratio (OSNR) of about 50~dB, the small full width at half-maximum (FWHM) of about 0.014~nm therefore its accuracy is enhanced, as well as the precision and capability are achieved for remote sensing. Low nitrate concentration in water from 0 to 80 ppm has been used to demonstrate its sensing ability in the experiment. The proposed sensor can work with good repeatability, rapid response, and its sensitivity can be obtained of \(3.2\times 10^{ - 3}\) nm/ppm with the limit of detection (LOD) of 3~ppm. For 2D PhC cavity, enhancement of photoluminescence of CNT emission is observed. The semiconducting single-walled carbon nanotubes (s-SWNTs) solution was prepared by polymer-sorted method and coupled with the confined modes in silicon slotted PhC cavities. The enhancement ratio of 1.15 is obtained by comparing between the PL peaks at two confined modes of the cavity. The PL enhancement result of the integrated system shows the potential for the realization of on-chip nanoscale sources.

[EN] Bragg filters stand as key building blocks of the silicon-on-insulator (SOI) photonics platform, allowing the implementation of advanced on-chip signal manipulation. However, achieving narrowband Bragg filters with large rejection levels is often hindered by fabrication constraints and imperfections. Here, we show that the combination of single-side corrugation asymmetry and subwavelength engineering provides a narrowband response with large corrugations, overcoming minimum feature size constraints of conventional Si Bragg filters. We comprehensively study the impact of the corrugation asymmetry in conventional and subwavelength single-etched SOI Bragg filters, showing their potential for bandwidth reduction. Finally, we experimentally demonstrate novel subwavelength geometry based on shifted corrugation teeth, achieving null-to-null bandwidths and rejections of 0.8 nm and 40 dB for the symmetric configuration and 0.6 nm and 15 dB for the asymmetric case. (c) 2018 Optical Society of America, Agence Nationale de la Recherche (ANR) (Project SITQOM DS0710).

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 considered an enabling technology for next generation datacom applications, providing ultra-compact and high-bandwidth transceivers that are cost-effectively fabricated at the existing CMOS facilities. Among photonic devices developed in silicon, Bragg gratings are routinely used for the realization of key functionalities including wavelength filtering, dispersion engineering and sensing. However, the realization of Bragg filters that simultaneously provides narrowband operation and high rejection remains a challenge in the Si platform. Indeed, the small core size of Si wires, together with the high index contrast between the silicon and the oxide cladding results in a strong interaction of the optical mode with the Bragg structure. Several approaches have been proposed to implement narrowband Bragg filters in Si wires including ultra-small corrugations (a few nanometres), periodic claddings, sub-wavelength engineering or inter-mode coupling. Nevertheless, these filters typically have comparatively weak light rejection performance due to fabrication errors limiting the accurate control of the grating geometry over few millimeter-long waveguide structures. In this work, we present a novel waveguide Bragg grating geometry that leverages the large index contrast between Si and air in membrane waveguides to overcome these limitations, yielding both narrow bandwidth and high rejection ratio. We use a novel waveguide corrugation geometry that radiates out the higher order modes, allowing effective single-mode operation for micrometric fully etched membrane waveguides. The high mode confinement of these waveguides results in weak interaction with the sidewall corrugation, thus narrowband operation is achieved. On the other hand, the high rejection ratio is achieved by combining reflection and radiation effects within the Bragg resonance. Based on this concept, we designed and experimentally demonstrated notch filters in single-etch suspended Si waveguides with cross-sections as large as 0.5 µm (height) by 1.1 µm (width). We show a narrow bandwidth of 4 nm for a 500 nm wide corrugation, with a high rejection ratio exceeding 50 dB for a filter length of only 700 µm

We report on the co-integration of an additional passive layer within a Silicon Photonic chip for advanced passive devices. Being a CMOS compatible material, Silicon Nitride (SiN) appears as an attractive candidate. With a moderate refractive index contrast compared to SOI, SiN based devices would be intrinsically much more tolerant to fabrication errors while keeping a reasonable footprint. In addition, it's seven times lower thermo-optical coefficient, relatively to Silicon, could lead to thermal-tuning free components. The co-integration of SiN on SOI has been explored in ST 300mm R&D photonic platform DAPHNE and is presented in this paper. Surface roughness of the SiN films have been characterized through Atomic Force Microscopy (AFM) showing an RMS roughness below 2nm. The film thickness uniformity have been evaluated by ellipsometry revealing a three-sigma of 21nm. Statistical measurements have been performed on basic key building blocks such as SiN strip waveguide showing propagation loss below 0.7dB/cm and 40µm radius bends with losses below 0.02dB/90°. A compact Si-SiN transition taper was developed and statistically measured showing insertion losses below 0.17dB/transition on the whole O-band wavelength range. Moreover, advanced WDM devices such as wavelength-stabilized directional couplers (WSDC) have been developed.

International audience; We report the design of a Bragg-mirror based Fabry-Perot cavity integrated on SiGe waveguides working at 7.25 µm. The demonstration of such resonant structures will be a major step forward for sensing applications in mid-infrared.

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.