Philippe Velha

Ultra-High Q/V Fabry-Perot microcavity on SOI substrate

We experimentally demonstrate an ultra high Q/V nanocavity on SOI substrate. The design is based on modal adaptation within the cavity and allows to measure a quality factor of 58.000 for a modal volume of 0.6(lambda/n)(3) . This record Q/V value of 10(5) achieved for a structure standing on a physical substrate, rather than on membrane, is in very good agreement with theoretical predictions also shown. Based on these experimental results, we show that further refinements of the cavity design could lead to Q/V ratios close to 10(6).

Ultra-high-reflectivity photonic-bandgap mirrors in a ridge SOI waveguide

Microcavities consisting of two identical tapered mirrors etched into silicon-on-insulator ridge waveguides are investigated for operation at telecommunication wavelengths. They offer very small modal volumes of approximately 0.6 (λ/n)3 and calculated intrinsic Q factors of 400 000. We have measured a Q factor of 8900 for a loaded cavity, in agreement with the theoretical value. In contrast to recent works performed on suspended membranes, the buried SiO2 layer is not removed. The cavities possess strong mechanical robustness, thus making them attractive from the viewpoint of integration in large systems. The cavity Q factor is much larger than those previously obtained for similar geometries on a substrate.

Nanofabrication of high aspect ratio (∼50:1) sub-10 nm silicon nanowires using inductively coupled plasma etching

The development of nanofabrication techniques for creating high aspect ratio (∼50:1) sub-10 nm silicon nanowires (SiNWs) with smooth, uniform, and straight vertical sidewalls using an inductively coupled plasma (ICP) etching process at 20 °C is reported. In particular, to improve the quality and flexibility of the pattern transfer process for high aspect ratio SiNWs, hydrogen silsesquioxane, a high-resolution, inorganic, negative-tone resist for electron-beam lithography has been used as both the resist for defining sub-10 nm patterns and the hard mask for etching the underneath silicon material. The effects of SF6/C4F8 gas flow rates, chamber pressure, platen power and ICP power on the etch rate, selectivity, and sidewall profile are investigated. To minimize plasma-induced sidewall damage, moderate plasma excitation power (ICP power of 600 W) and low ion energy (platen power of 6–12 W) were used. Using the optimized etch process at room temperature (20 °C), the authors have successfully fabricated sub-1...

Defect-Enhanced Silicon-on-Insulator Waveguide Resonant Photodetector With High Sensitivity at 1.55

We describe the fabrication and characterization of a silicon waveguide resonant photodetector compatible with the optical-to-electrical conversion of wavelengths at, or around, 1550 nm. Sub-band responsivity is provided through the introduction of defects via inert self-implantation and subsequent annealing. The detector is located within a 20- m radius silicon microring resonator. An 18-dB resonant enhancement in absorption coefficient and 12-dB enhancement in photocurrent were measured, leading to a resonant responsivity of approximately 39 mA/W at 20-V reverse bias.

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A low temperature nickel process has been developed that produces Ohmic contacts to n-type germanium with specific contact resistivities down to (2.3 ± 1.8) × 10−7 Ω-cm2 for anneal temperatures of 340 °C. The low contact resistivity is attributed to the low resistivity NiGe phase which was identified using electron diffraction in a transmission electron microscope. Electrical results indicate that the linear Ohmic behaviour of the contact is attributed to quantum mechanical tunnelling through the Schottky barrier formed between the NiGe alloy and the heavily doped n-Ge.

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Microcavities offering small modal volumes V_0.6 __/n_3 and consisting of two identical tapered Bragg mirrors etched into a monomode silicon-on-insulator ridge waveguide are studied for operation at telecommunications wavelengths. The authors have measured a Q factor of 8900, for a loaded cavity with a peak transmission at resonance in excess of 60%. The measured Q value quantitatively agrees with the calculation results and is 20 times larger than those previously reported for similar geometries without tapers.

Ohmic contacts to n-type germanium with low specific contact resistivity

A chalcogenide-assisted silicon waveguide is realized by depositing a thin layer of A(2)S(3) glass onto a conventional silicon on insulator optical waveguide. The photosensitivity of the chalcogenide is exploited to locally change the optical properties of the waveguide through exposure to visible light radiation. Waveguide trimming is experimentally demonstrated by permanently shifting the resonant wavelength of a microring resonator by 6.7 nm, corresponding to an effective index increase of 1.6·10(-2). Saturation effects, trimming range, velocity and temporal stability of the process are discussed in details. Results demonstrate that photo-induced treatments can be exploited for a post-fabrication compensation of fabrication tolerances, as well as to set and reconfigure the circuit response.

Ultracompact silicon-on-insulator ridge-waveguide mirrors with high reflectance

We report on four-wave mixing in coupled photonic crystal nano-cavities on a silicon-on-insulator platform. Three photonic wire cavities are side-coupled to obtain three modes equally separated in energy. The structure is designed to be self-filtering, and we show that the pump is rejected by almost two orders of magnitude. We study both the stimulated and the spontaneous four-wave mixing processes: owing to the small modal volume, we find that signal and idler photons are generated with a hundred-fold increase in efficiency as compared to silicon micro-ring resonators.

Photo-induced trimming of chalcogenide-assisted silicon waveguides

We report on the application of defect-enhanced silicon waveguide photodiodes operating at 1550 nm as power monitors for use in photonic integrated circuits. In-line monitors of 250-μm length provide an efficiency of 97 mA/W by absorbing only 8% of the optical mode. The monitors were integrated onto micro-ring waveguide ports to provide measures of optical resonance characteristics and a feedback to a thermal resonance tuner. The suitability of these photodetectors for control of micro-ring resonators is demonstrated.

Stimulated and spontaneous four-wave mixing in silicon-on-insulator coupled photonic wire nano-cavities

We design compact (a few wavelength long) and efficient (>99%) injectors for coupling light into slow Bloch modes of periodic thin film stacks and of periodic slab waveguides. The study includes the derivation of closed-form expressions for the injection efficiency as a function of the group-velocity of injected light, and the proof that 100% coupling efficiencies for arbitrary small group velocities is possible with an injector length scaling as log(c/vg). The trade-off between the injector bandwidth and the group velocity of the injected light is also considered.