Alexandre Bazin

Hybrid III-V semiconductor/silicon nanolaser

Heterogeneous integration of III-V compound semiconductors on Silicon on Insulator is one the key technology for next-generation on-chip optical interconnects. In this context, the use of photonic crystals lasers represents a disruptive solution in terms of footprint, activation energy and ultrafast response. In this work, we propose and fabricate very compact laser sources integrated with a passive silicon waveguide circuitry. Using a subjacent Silicon-On-Insulator waveguide, the emitted light from a photonic crystal based cavity laser is efficiently captured. We study experimentally the evanescent wave coupling responsible for the funneling of the emitted light into the silicon waveguide mode as a function of the hybrid structure parameters, showing that 90% of coupling efficiency is possible.

Ultrafast all-optical switching and error-free 10 Gbit/s wavelength conversion in hybrid InP-silicon on insulator nanocavities using surface quantum wells

Ultrafast switching with low energies is demonstrated using InP photonic crystal nanocavities embedding InGaAs surface quantum wells heterogeneously integrated to a silicon on insulator waveguide circuitry. Thanks to the engineered enhancement of surface non radiative recombination of carriers, switching time is obtained to be as fast as 10 ps. These hybrid nanostructures are shown to be capable of achieving systems level performance by demonstrating error free wavelength conversion at 10 Gbit/s with 6 mW switching powers.

Design of Silica Encapsulated High-Q Photonic Crystal Nanobeam Cavity

We report on the design of photonic crystal nanobeam cavity fully encapsulated in silica. The proposed design, based on the principle of gentle confinement of the electromagnetic field, is mostly analytical and emphasizes on the most realistic options for fabricating nanocavities, in particular in III-V semiconductor materials. After determining the field decay inside the photonic bandgap of a nanobeam photonic crystal, we engineer the envelope of the cavity mode into a Gaussian shape by shifting only progressively the lattice constant. We discuss the various implementations of such shifts and give a simple algorithm to position each hole. The resonant wavelengths are found to depend linearly on the central lattice constant and on the radius of the holes. High Q factors above 10 6 and modal volume V close to ( λ/n) 3 are obtained. In particular, Q factors remain high for a wide range of values of the central lattice constant and of holes radii, hence showing exceptional tunability properties as well as robustness with respect to common fabrication defects.

Net on-chip Brillouin gain based on suspended silicon nanowires

The century-old study of photon–phonon coupling has seen a remarkable revival in the past decade. Driven by early observations of dynamical back-action, the field progressed to ground-state cooling and the counting of individual phonons. A recent branch investigates the potential of traveling-wave, optically broadband photon–phonon interaction in silicon circuits. Here, we report continuous-wave Brillouin gain exceeding the optical losses in a series of suspended silicon beams, a step towards selective on-chip amplifiers. We obtain efficiencies up to the highest to date in the phononic gigahertz range. We also find indications that geometric disorder poses a significant challenge towards nanoscale phonon-based technologies.

Experimental demonstration of a hybrid III-V-on-silicon microlaser based on resonant grating cavity mirrors.

We present the experimental demonstration of a novel class of hybrid III-V-on-silicon microlasers. We show that by coupling a silicon cavity to a III-V waveguide, the interaction between the propagating mode in the III-V waveguide and the cavity mode in the silicon resonator results in high, narrowband reflection back into the III-V waveguide, forming a so-called resonant mirror. By combining two such mirrors and providing optical gain in the III-V wire between these two mirrors, laser operation can be realized. This optically pumped device measures 55 by 2 μm, requires microwatt-level threshold pump power, and shows single-mode laser emission with a side-mode suppression ratio of up to 39 dB.

Thermal management in hybrid InP/silicon photonic crystal nanobeam laser

Thermal properties of InP-based quantum well photonic crystal nanobeam lasers heterogeneously integrated on silicon on insulator waveguides are studied. We show both numerically and experimentally the reduction of the thermal resistance of the III-V cavities by adjusting the composition of the layer which bonds the III-V materials to the silicon wafer and by adding an over-cladding on top of the cavities. Using a bonding layer made of benzocyclobutene and SiO(2) and an over-cladding of MgF(2), we found a decrease by a factor higher than 35 compared to air-suspended photonic crystal nanobeam cavities. Such optimized structures are demonstrated to operate under continuous wave pumping for several 10s of minutes despite the adverse effect of non-radiative surface recombination of carriers.

Subduing surface recombination for continuous-wave operation of photonic crystal nanolasers integrated on Silicon waveguides

Detrimental surface recombination of carriers in InP-based photonic crystal nanobeams containing quantum wells is reduced by employing chemical treatment followed by silica encapsulation. Carrier lifetime is shown to recover to 2.63ns close to the bulk value. This enables us to obtain optically pumped room-temperature continuous-wave nanolasers at 1.55µm integrated onto Silicon on insulator waveguide platform with a threshold of 8µW.

Uniformity of the lasing wavelength of heterogeneously integrated InP microdisk lasers on SOI.

We report a high lasing wavelength uniformity of optically pumped InP-based microdisk lasers processed with electron-beam lithography, heterogeneously integrated with adhesive bonding on silicon-on-insulator (SOI) waveguide circuits and evanescently coupled to an underlying waveguide. We study the continuous wave laser emission coupling out of the SOI via a grating coupler etched at one side of the waveguide, and demonstrate a standard deviation in lasing wavelength of nominally identical devices on the same chip lower than 500 pm. The deviation in the diameter of the microdisks as low as a few nanometers makes all-optical signal processing applications requiring cascadability possible.

Tetramerization and interdomain flexibility of the replication initiation controller YabA enables simultaneous binding to multiple partners

YabA negatively regulates initiation of DNA replication in low-GC Gram-positive bacteria. The protein exerts its control through interactions with the initiator protein DnaA and the sliding clamp DnaN. Here, we combined X-ray crystallography, X-ray scattering (SAXS), modeling and biophysical approaches, with in vivo experimental data to gain insight into YabA function. The crystal structure of the N-terminal domain (NTD) of YabA solved at 2.7 Å resolution reveals an extended α-helix that contributes to an intermolecular four-helix bundle. Homology modeling and biochemical analysis indicates that the C-terminal domain (CTD) of YabA is a small Zn-binding domain. Multi-angle light scattering and SAXS demonstrate that YabA is a tetramer in which the CTDs are independent and connected to the N-terminal four-helix bundle via flexible linkers. While YabA can simultaneously interact with both DnaA and DnaN, we found that an isolated CTD can bind to either DnaA or DnaN, individually. Site-directed mutagenesis and yeast-two hybrid assays identified DnaA and DnaN binding sites on the YabA CTD that partially overlap and point to a mutually exclusive mode of interaction. Our study defines YabA as a novel structural hub and explains how the protein tetramer uses independent CTDs to bind multiple partners to orchestrate replication initiation in the bacterial cell.

Towards a monolithically integrated III-V laser on silicon: optimization of multi-quantum well growth on InP on Si

High-quality InGaAsP/InP multi-quantum wells (MQWs) on the isolated areas of indium phosphide on silicon necessary for realizing a monolithically integrated silicon laser is achieved. Indium phosph ...