Romain Guider

Ultrafast All-Optical Switching in a Silicon-Nanocrystal-Based Silicon Slot Waveguide at Telecom Wavelengths

We demonstrate experimentally all-optical switching on a silicon chip at telecom wavelengths. The switching device comprises a compact ring resonator formed by horizontal silicon slot waveguides filled with highly nonlinear silicon nanocrystals in silica. When pumping at power levels about 100 mW using 10 ps pulses, more than 50% modulation depth is observed at the switch output. The switch performs about 1 order of magnitude faster than previous approaches on silicon and is fully fabricated using complementary metal oxide semiconductor technologies.

Silicon Nanocrystals as an Enabling Material for Silicon Photonics

Silicon nanocrystals (Si-nc) is an enabling material for silicon photonics, which is no longer an emerging field of research but an available technology with the first commercial products available on the market. In this paper, properties and applications of Si-nc in silicon photonics are reviewed. After a brief history of silicon photonics, the limitations of silicon as a light emitter are discussed and the strategies to overcome them are briefly treated, with particular attention to the recent achievements. Emphasis is given to the visible optical gain properties of Si-nc and to its sensitization effect on Er ions to achieve infrared light amplification. The state of the art of Si-nc applied in a few photonic components is reviewed and discussed. The possibility to exploit Si-nc for solar cells is also presented. In addition, nonlinear optical effects, which enable fast all-optical switches, are described.

NanoSi low loss horizontal slot waveguides coupled to high Q ring resonators

Si-based horizontal slot waveguides coupled to ring resonators have been fabricated and characterised. The central layer of the slot has been filled by Silicon nanocrystals (Si-nc) obtained by deposition of silicon rich silicon oxide and then thermal annealing. A comparison of various deposition and annealing parameters to form the Si-nc is performed. Propagation losses as low as 3 dB/cm and ring resonator quality factor of 30,000 have been achieved at 1550 nm.

Monolithic Whispering-Gallery Mode Resonators With Vertically Coupled Integrated Bus Waveguides

We report on the realization of a silicon-based microresonator/waveguide coupled system, fully integrated on a silicon chip. The device uses a vertical coupling scheme of the resonator and a buried strip waveguide. We demonstrate that its high optical quality follows from the accurate planarization of the waveguide topography, which is achieved by multiple depositions-and-reflows of a borophosphosilicate glass over strip waveguides. More importantly, we demonstrate wafer-scale mass fabrication of freestanding planar resonators suspended in air and coupled to integrated bus waveguides, as well as controlled selective excitation of different mode families of the resonator. This opens the door for the realization of stable all-integrated complex resonator systems for optomechanical and metrological applications, with the potential to substitute todays intensive use of complicated fiber-taper coupling schemes.

Asymmetric Mach–Zehnder Interferometer Based Biosensors for Aflatoxin M1 Detection

In this work, we present a study of Aflatoxin M1 detection by photonic biosensors based on Si3N4 Asymmetric Mach–Zehnder Interferometer (aMZI) functionalized with antibodies fragments (Fab′). We measured a best volumetric sensitivity of 104 rad/RIU, leading to a Limit of Detection below 5 × 10−7 RIU. On sensors functionalized with Fab′, we performed specific and non-specific sensing measurements at various toxin concentrations. Reproducibility of the measurements and re-usability of the sensor were also investigated.

Design and Optimization of SiON Ring Resonator-Based Biosensors for Aflatoxin M1 Detection.

In this article, we designed and studied silicon oxynitride (SiON) microring-based photonic structures for biosensing applications. We designed waveguides, directional couplers, and racetrack resonators in order to measure refractive index changes smaller than 10−6 refractive index units (RIU). We tested various samples with different SiON refractive indexes as well as the waveguide dimensions for selecting the sensor with the best performance. Propagation losses and bending losses have been measured on test structures, along with a complete characterization of the resonator’s performances. Sensitivities and limit of detection (LOD) were also measured using glucose-water solutions and compared with expected results from simulations. Finally, we functionalized the resonator and performed sensing experiments with Aflatoxin M1 (AFM1). We were able to detect the binding of aflatoxin for concentrations as low as 12.5 nm. The results open up the path for designing cost-effective biosensors for a fast and reliable sensitive analysis of AFM1 in milk.

Oscillatory vertical coupling between a whispering-gallery resonator and a bus waveguide.

We report on a theoretical and experimental study of the optical coupling between a whispering-gallery type resonator and a waveguide lying on different planes. In contrast to the usual in-plane geometry, the present vertical one is characterized by an oscillatory behavior of the effective coupling as a function of the vertical gap. This behavior manifests itself as oscillations in both the resonance peak waveguide transmission and the mode quality factor. An analytical description based on coupled-mode theory and a two-port beam-splitter model of the waveguide-resonator vertical coupling is developed for arbitrary phase-matching conditions and is successfully used to interpret the experimental observations.

Optical characterization of a SCISSOR device

Here, we report on the design, fabrication and characterization of single-channel (SC-) and dual-channel (DC-) side-coupled integrated spaced sequences of optical resonators (SCISSOR) with a finite number (eight) of microring resonators using submicron silicon photonic wires on a silicon-on-insulator (SOI) wafer. We present results on the observation of multiple resonances in the through and the drop port signals of DC-SCISSOR. These result from the coupled resonator induced transparency (CRIT) which appears when the resonator band (RB) and the Bragg band (BB) are nearly coincident. We also observe the formation of high-Q (> 23000) quasi-localized modes in the RB of the drop transmission which appear when the RB and BB are well separated from each other. These multiple resonances and quasi-localized modes are induced by nanometer-scale structural disorders in the dimension of one or more rings. Finally, we demonstrate the tunability of RB (and BB) and localized modes in the DC-SCISSOR by thermo-optical or free-carrier refraction.

Photoluminescence of hydrophilic silicon nanocrystals in aqueous solutions

Stable aqueous solutions of undecylenic-acid-grafted silicon nanocrystals (Si-nc) were prepared. The time evolution of the photoluminescence properties of these hydrophilic silicon nanocrystals has been followed on different timescales (hours and days). On a short timescale (hours), Si-nc tend to agglomerate while the PL lineshape and intensity are stable. Agglomeration can be reduced by using suitable surfactants. On a long timescale (days), oxidation of Si-nc occurs even in the presence of surfactants. These two observations render Si-nc very useful as a labeling agent for biosensing.

Coupled-resonator-induced-transparency concept for wavelength routing applications

We investigated the presence of high quality factor resonances due to Coupled Resonator Induced Transparency in complex sequences of coupled resonators devices, and proposed a new concept of wavelength router based on this effect.