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On-chip Brillouin optomechanics has great potential for applications in communications, sensing, and quantum technologies. Tight confinement of near-infrared photons and gigahertz phonons in integrated waveguides remains a key challenge to achieving strong on-chip Brillouin gain. Here, we propose a new strategy to harness Brillouin gain in silicon waveguides, based on the combination of genetic algorithm optimization and periodic subwavelength structuration to engineer photonic and phononic modes simultaneously. The proposed geometry is composed of a waveguide core and a lattice of anchoring arms with a subwavelength period requiring a single etch step. The waveguide geometry is optimized to maximize the Brillouin gain using a multi-physics genetic algorithm. Our simulation results predict a remarkable Brillouin gain exceeding 3300 1/(W m), for a mechanical frequency near 15 GHz.

openaire: EC/H2020/820423/EU//S2QUIP | openaire: EC/H2020/965124/EU//FEMTOCHIP | openaire: EC/H2020/834742/EU//ATOP The heterogeneous integration of low-dimensional materials with photonic waveguides has spurred wide research interest. Here, we report on the experimental investigation and the numerical modeling of enhanced nonlinear pulse broadening in silicon nitride waveguides with the heterogeneous integration of few-layer WS2. After transferring a few-layer WS2 flake of similar to 14.8 mu m length, the pulse spectral broadening in a dispersion-engineered silicon nitride waveguide has been enhanced by similar to 48.8% in bandwidth. Through numerical modeling, an effective nonlinear coefficient higher than 600 m(-1) W-1 has been retrieved for the heterogeneous waveguide indicating an enhancement factor of larger than 300 with respect to the pristine waveguide at a wavelength of 800 nm. With further advances in two-dimensional material fabrication and integration techniques, on-chip heterostructures will offer another degree of freedom for waveguide engineering, enabling high-performance nonlinear optical devices, such asfrequency combs and quantum light sources.

International audience; Metalenses are attracting a large interest for the implementation of complex optical functionalities in planar and compact devices. However, chromatic and off-axis aberrations remain standing challenges. Here, we experimentally investigate the broadband behavior of metalenses based on quadratic phase profiles. We show that these metalenses do not only guarantee an arbitrarily large field of view but are also inherently tolerant to longitudinal and transverse chromatic aberrations. As such, we demonstrate a single-layer, silicon metalens with a field of view of 86° and a bandwidth up to 140 nm operating at both 1300 nm and 1550 nm telecommunication wavelength bands.

The texture of the Ni monostanogermanide phase on a Ge(100) substrate was evaluated during a solid-state reaction, with a focus on the impact of Sn addition. Complementary X-ray diffraction analyses involving in situ X-ray diffraction, in-plane reciprocal space maps (RSMs) and pole figures were used to that end. A sequential growth of the phases for the Ni/Ge(Sn) system was found. An Ni-rich phase formed first, followed by the NiGe(Sn) phase. The NiGe and NiGe(Sn) layers were polycrystalline with different out-of-plane orientations. The number of out-of-plane diffraction peaks decreased with the Sn content, while the preferred orientation changed. In-plane RSM analyses confirmed these results. Sn addition modified the out-of-plane and in-plane orientations. Pole figure analysis revealed that numerous epitaxial texture components were present for the Ni/Ge system, while Sn addition reduced the number of epitaxial texture components. On the other hand, segregated Sn crystallized with an epitaxial alignment with the Ge substrate underneath.

A comprehensive study of the impact of Sn content on the Ni/GeSn phase sequence, the morphological and electrical properties evolution during the solid-state reaction (SSR) has been performed. The phase sequence was monitored by in-situ X-ray diffraction. These results were complemented by atomic force microscopy and sheet resistance measurements together with transmission electron microscopy imaging and energy-dispersive X-ray spectroscopy applied to specimens annealed both ex-situ and in-situ. The phase formation and Sn behavior during the solid-state reaction was followed. Sn segregation around grain boundaries hampered atom diffusion, delaying the growth of the Ni(GeSn) phase. In addition, a correlation between the Sn content and the morphological and electrical properties degradation has been observed.

Ni-based intermetallics are promising materials for forming efficient contacts in GeSn-based Si photonic devices. However, the role that Sn might have during the Ni/GeSn solid-state reaction (SSR) is not fully understood. A comprehensive analysis focused on Sn segregation during the Ni/GeSn SSR was carried out. In situ X-ray diffraction and cross-section transmission electron microscopy measurements coupled with energy-dispersive X-ray spectrometry and electron energy-loss spectroscopy atomic mappings were performed to follow the phase sequence, Sn distribution and segregation. The results showed that, during the SSR, Sn was incorporated into the intermetallic phases. Sn segregation happened first around the grain boundaries (GBs) and then towards the surface. Sn accumulation around GBs hampered atom diffusion, delaying the growth of the Ni(GeSn) phase. Higher thermal budgets will thus be mandatory for formation of contacts in high-Sn-content photonic devices, which could be detrimental for thermal stability.

The fruitful association of quantum and integrated photonics holds the promise to produce, manipulate, and detect quantum states of light using compact and scalable systems. Integrating all the building blocks necessary to produce high-quality photonic entanglement in the telecom-wavelength range out of a single chip remains a major challenge, mainly due to the limited performance of on-chip light rejection filters. We report a stand-alone, telecom-compliant device that integrates, on a single substrate, a nonlinear photon-pair generator and a passive pump-rejection filter. Using standard channel-grid fiber demultiplexers, we demonstrate the first entanglement qualification of such an integrated circuit, showing the highest raw quantum interference visibility for time-energy entangled photons over two telecom-wavelength bands. Genuinely pure, maximally entangled states can therefore be generated thanks to the high-level of noise suppression obtained with the pump filter. These results will certainly further promote the development of more advanced and scalable photonic-integrated quantum systems compliant with telecommunication standards.

We propose a universal approach to provide wideband multimode four-wave mixing independently of the intrinsic dispersion of the involved waveguide modes. Concepts from quantum mechanics and subwavelength engineering are adopted to design an effective lateral confinement photonic well, i.e., with a graded potential along the waveguide cross section providing flexible control over the modes’ confinement. The self-adaptive nature of the waveguide boundary allows different spatial modes with equi-spaced frequencies and shared propagation wavevector, thus automatically fulfilling both energy conservation and wavevector phase matching conditions. Capitalizing on this concept, we show phase-matching among modes separated by 400 nm (bridging from telecom wavelengths to almost ${2}\;{\rm{\mu m}}$ ), with less than 5% deviation in a remarkably large bandwidth exceeding 300 nm. Furthermore, we also show the flexibility of the proposed approach that can be seamlessly adapted to different technology platforms. This strategy opens a new design space for versatile on-chip nonlinear applications in which the manipulation of energy spacing and phase matching is pivotal, e.g., all-optical signal processing with four-wave mixing, mid-infrared supercontinuum or frequency comb light generation, or Brillouin scattering with selectable phonon energy.

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.

4 pags., 4 figs., Integrated mid-infrared micro-spectrometers have a great potential for applications in environmental monitoring and space exploration. Silicon-on-insulator (SOI) is a promising platform to tackle this integration challenge, owing to its unique capability for large volume and low-cost production of ultra-compact photonic circuits. However, the use of SOI in the mid-infrared is restricted by the strong absorption of the buried oxide layer for wavelengths beyond 4 µm. Here, we overcome this limitation by utilizing metamaterial-cladded suspended silicon waveguides to implement a spatial heterodyne Fourier-transform (SHFT) spectrometer operating at wavelengths near 5.5 µm. The metamaterial-cladded geometry allows removal of the buried oxide layer, yielding measured propagation loss below 2 dB/cm at wavelengths between 5.3 and 5.7 µm. The SHFT spectrometer comprises 19 Mach-Zehnder interferometers with a maximum arm length imbalance of 200 µm, achieving a measured spectral resolution of 13 cm and a free spectral range of 100 cm1 at wavelengths near 5.5 µm., French Industry Ministry (Nano2022 project under IPCEI program); Agence Nationale de la Recherche (ANR-MIRSPEC- 17-CE09- 0041); Spanish Ministry of Science and Innovation (RTI2018-097957- B-C33, PID2020-115353RA-I00); Comunidad de Madrid (S2018/NMT4326).

The miniaturization provided by silicon photonics offers tantalizing prospects for the realization of high- performance optical spectrometers in extremely compact and robust form factors. Here we demonstrate a broadband silicon nitride spatial heterodyne Fourier-transform spectrometer chip implementing a large-surface multiaperture input to achieve a high étendue., 2021 IEEE 17th International Conference on Group IV Photonics (GFP), December 7-10, 2021, Malaga, Spain

Silicon photonics spectrometers have great potential for applications in medicine and hazard detection. However, silicon spectrometers are very sensitive to fabrication imperfections and environmental conditions. Here, we study the use of deep-learning algorithms to improve tolerance of Fourier-transform spectrometers against fabrication imperfections and temperature variations., 2021 IEEE 17th International Conference on Group IV Photonics (GFP), December 7-10, 2021, Malaga, Spain