Laurent Bellieres

Sorting linearly polarized photons with a single scatterer

Intuitively, light impinging on a spatially mirror-symmetric object will be scattered equally into mirror-symmetric directions. This intuition can fail at the nanoscale if the polarization of the incoming light is properly tailored, as long as mirror symmetry is broken in the axes perpendicular to both the incident wave vector and the remaining mirror-symmetric direction. The unidirectional excitation of plasmonic modes using circularly polarized light has been recently demonstrated. Here, we generalize this concept and show that linearly polarized photons impinging on a single spatially symmetric scatterer created in a silicon waveguide are guided into a certain direction of the waveguide depending exclusively on their polarization angle and the structure asymmetry. Our work broadens the scope of polarization-induced directionality beyond plasmonics, with applications in polarization (de)multiplexing, unidirectional coupling, directional switching, radiation polarization control, and polarization-encoded quantum information processing in photonic integrated circuits.

Universal method for the synthesis of arbitrary polarization states radiated by a nanoantenna

Optical nanoantennas efficiently convert confined optical energy into free-space radiation. The polarization of the emitted radiation depends mainly on nanoantenna shape, so it becomes extremely difficult to manipulate it unless the nanostructure is physically altered. Here, a simple way is demonstrated to synthetize the polarization of the radiation emitted by a single nanoantenna so that every point on the Poincare sphere becomes attainable. The nanoantenna consists of a single scatterer created on a dielectric waveguide and fed from its both sides so that the polarization of the emitted optical radiation is controlled by the amplitude and phase of the feeding signals. The nanoantenna is created on a silicon chip using standard top-down nanofabrication tools, but the method is universal and can be applied to other materials, wavelengths and technologies. This work will open the way towards the synthesis and control of arbitrary polarization states in nano-optics.

Variable carrier reduction in radio-over-fiber systems for increased modulation efficiency using a Si 3 N 4 tunable extinction ratio ring resonator

Variable optical carrier reduction via the use of a Si(3)N(4) ring resonator notch filter with tunable extinction ratio is demonstrated in a 10 GHz radio-over-fiber system for improving the modulation efficiency. The extinction of the filter notch is tuned with micro-heaters, by setting the Mach-Zehnder coupler of the ring. Experimental results showing a modulation depth improvement of up to 20 dB are provided.

Midinfrared filters based on extraordinary optical transmission through subwavelength structured gold films

An experimental study is made of the enhanced optical transmission of nanostructured gold films in the midinfrared region. Results indicate that the excitation of surface plasmon polaritons due to periodicity plays a fundamental role in producing extraordinary optical transmission. The influence of the surrounding claddings, hole shape, and periodicity on the resonance wavelength and the quality factor is investigated. The aim is to use the subwavelength structures as ultracompact optical filters whose spectral features can be easily tuned and scaled. For filter design purposes, the results show that the main parameters affecting the resonance wavelength are the lattice constant and dielectric cladding. The hole shape and size are found to cause transmission enhancement and there is only a small resonance redshift when the hole area is increased. However, a lower quality factor is achieved when the hole area is increased.

On-chip wireless silicon photonics: from reconfigurable interconnects to lab-on-chip devices

Photonic integrated circuits are developing as key enabling components for high-performance computing and advanced network-on-chip, as well as other emerging technologies such as lab-on-chip sensors, with relevant applications in areas from medicine and biotechnology to aerospace. These demanding applications will require novel features, such as dynamically reconfigurable light pathways, obtained by properly harnessing on-chip optical radiation. In this paper, we introduce a broadband, high directivity (>150), low loss and reconfigurable silicon photonics nanoantenna that fully enables on-chip radiation control. We propose the use of these nanoantennas as versatile building blocks to develop wireless (unguided) silicon photonic devices, which considerably enhance the range of achievable integrated photonic functionalities. As examples of applications, we demonstrate 160 Gbit s−1 data transmission over mm-scale wireless interconnects, a compact low-crosstalk 12-port crossing and electrically reconfigurable pathways via optical beam steering. Moreover, the realization of a flow micro-cytometer for particle characterization demonstrates the smart system integration potential of our approach as lab-on-chip devices.

Experimental study of the sensitivity of a porous silicon ring resonator sensor using continuous in-flow measurements

A highly sensitive photonic sensor based on a porous silicon ring resonator was developed and experimentally characterized. The photonic sensing structure was fabricated by exploiting a porous silicon double layer, where the top layer of a low porosity was used to form photonic elements by e-beam lithography and the bottom layer of a high porosity was used to confine light in the vertical direction. The sensing performance of the ring resonator sensor based on porous silicon was compared for the different resonances within the analyzed wavelength range both for transverse-electric and transverse-magnetic polarizations. We determined that a sensitivity up to 439 nm/RIU for low refractive index changes can be achieved depending on the optical field distribution given by each resonance/polarization.

Experimental demonstration of integrated photonic free-label biosensor for CBRN threats using micro-ring resonators

In this work, we present integrated photonic sensor design to detect Chemical, Biological, Radiological and Nuclear (CBRN) threats, where high sensitivity and no false positive are strictly required. The sensor is formed by several parallel micro-ring resonators exposed to the environment and functionalized to recognized target analytes in a free-label way. Experimental demonstration of the working principle was performed using simulant compounds that permit tests of the features of the Photonic Integrated Circuit (PIC) in a safe environment. The results show the possibility of using PICs to detect as low as 20 ppb of Ovalbumin (simulant for Ricin A toxin) and 200 CFU/ml of Bacillus cereus spores (simulant for Bacillus anthracis). These results push forward the possibility of using PICs as biochemical sensors, also for critical objectives.

Fabrication of modulators and 2×2 switches in SOI based on the carrier depletion mechanism for optical interconnects

Silicon-photonic 2×2 electro-optical switching elements and modulators based on the carrier depletion mechanism using both dual-resonator and MZI layout configurations have been developed. The passive photonic structures were developed and optimized using a fast design-fabrication-characterization cycle. The main objective is to deliver smallfootprint, low-loss and low-energy silicon photonic electro-optical switching elements and modulators equipped with standard input-output grating couplers and radio-frequency electrical contact tips to allow their characterization in highspeed probe-station setups. The insertion losses, crosstalk, power consumption and BER performance will be addressed for each electro-optical structure. The fabrication steps, including low loss waveguide patterning, pn junction and low resistive ohmic contact formation have been optimized to produce high performance devices with relaxed fabrication tolerances, employing both optical and electron-beam lithography.