Guillaume Beaudin

Characterization and reduction of spectral distortions in Silicon-on-Insulator integrated Bragg gratings

A major issue in the fabrication of integrated Bragg grating filters in highly confined waveguides is the average effective index fluctuations caused by waveguide dimension variations. Lateral variations are caused by the sidewall roughness created during the etching process while vertical variations are coming from the wafer silicon layer thickness non-uniformity. Grating spectral distortions are known to result solely from the low spatial frequency components of these variations. As a result, in this work, we present an experimental method to quantify such relevant spatial components by stitching a hundred high-resolution scanning electron microscope images. Additionally, we propose two techniques to reduce, in the design, the phase noise impact on integrated Bragg gratings without relying on fabrication process improvements. More specifically, we show that the use of hybrid multimode/singlemode waveguides reduce by more than one order of magnitude the effect of sidewall roughness on integrated Bragg gratings while we show that the fabrication of ultra-compact gratings in spiral waveguides mitigate the impact of the silicon layer thickness variations.

Mesoporous germanium morphology transformation for lift-off process and substrate re-use

The morphology of electrochemically formed mesoporous Ge double-layer and its transformations during ultra-high-vacuum annealing at 600–700 °C are investigated by scanning electron microscopy. It was found that the transformation occurs via mass transport at constant volume. The process transforms the pores into faceted spherical voids. These findings determine the optimal conditions for the transformation of the mesoporous Ge into a useful structure, which consists of a 1.8 μm thick monocrystalline Ge film with buried lateral cavities allowing for subsequent lift-off. The monocrystalline nature of the film and its suitability as a seed layer for GaAs epitaxy are demonstrated by X-ray diffraction.

Waveguide-coupled drop filters on SOI using quarter-wave shifted sidewalled grating resonators.

We report on the design, fabrication, and demonstration of waveguide coupled channel drop filters at 1550 nm, on a silicon-on-insulator (SOI) substrate. These devices rely on resonant power transfer from a bus waveguide to side-walled Bragg resonators with quarter-wave shifts in the middle. By employing a second mirror resonator, and a tap-off waveguide, reflections along the bus waveguide can be reduced, leading to realization of circulator-free resonance filters. These devices were fabricated on SOI using e-beam lithography and inductively coupled plasma (ICP) etching. Fabricated devices with two coupled cavities are demonstrated to have rejection ratios greater than 20 dB and 3-dB bandwidths of 110 GHz, close to the values predicted by numerical modeling. We also demonstrate power tap-off at resonance of around 16 dB.

Design and Demonstration of Apodized Comb Filters on SOI

We report on the design, modeling, and characterization of apodized comb filters in the silicon-on-insulator platform. These devices are based on sampled gratings, wherein the comb response is generated by a convolution of a regular grating by a predetermined periodic sampling function. We show that dual and complementary apodization of the etch depth in the marks and spaces ensures a near-zero dc index change over the length of the device and avoids the unwanted sidelobes obtained in a single apodized device. Comb filters with a 40-dB side-mode suppression ratio, a 92-GHz clear bandwidth, 200-GHz channel spacing, and a 120-dB/dec rolloff have been theoretically proposed. An experimental demonstration of the fabricated devices is also presented, and the performance is compared with the numerical simulations.

3D harnessing of light with photon cage

We report on design, simulation and fabrication of ultimate and compact 3D close-geometries optical microcavities. These are based on the extension of the so-called 2.5D nanophotonic approach where a quasi 3D control of the photons has been soon demonstrated by our group. A tight control of photons, spectrally and spatially, in a small air region inside a circular regular pattern of high index material-based nanopillars is demonstrated when adjusting the number of pillars, their diameters and the diameter of the pillar-circle. Bottom-up approach based on InP nanowires grown by molecular beam epitaxy and top-down approach based on high aspect ratio anisotropic etching have been developed for fabricating these optical microcavities.

Waveguide coupled drop filters on SOI using vertical sidewalled grating resonators

A vertical grating resonator coupled drop filter with 20 dB channel extinction and 37% dropped channel tapping efficiency is proposed. We also show that by employing coupled cavities a flat-top filter response can be obtained.

Precise localized thinning and vertical taper fabrication for silicon photonics using a modified local oxidation of silicon (LOCOS) fabrication process.

This paper presents a method to locally fine tune silicon-on-insulator (SOI) device layer thickness for the fabrication of optimal silicon photonics devices. Very precise control of thickness can be achieved with a modified local oxidation of silicon (LOCOS) process. The fabrication process is robust, complementary metal-oxide-semiconductor (CMOS) compatible and has the advantage of creating vertical tapers (~5.3 µm long for ~210 nm of height) required for impedance matching between sections of different height. The technology is demonstrated by fabricating a TE-pass filter.

Silicon carbide microdisk on silicon pillar probed by evanescent coupling

We present fabrication, simulation and characterization of silicon carbide microdisk on silicon pillar aiming at non-linear operation from near-infrared to mid-infrared. We report experimental Q factor of 1800 at telecom wavelength.

Evanescent Field Coupler Optimized for High Refractive Index Differences (ECHRID)—A Platform for a SOI Photonics Optical Interface

This paper presents the Evanescent field Coupler optimized for High Refractive Index Differences (ECHRID), a proposed new platform for a silicon-on-insulator photonics interface. ECHRID devices are capable of optical performance levels on par with grating couplers and inverted tapers but can be fabricated at much lower cost without the need for high-resolution lithography. Numerical simulations and experimental results are presented that demonstrate average coupling efficiencies between large core injection waveguides and on-chip Si-based waveguides of over 99%, with a flat spectral response over a 120 nm range.

Thermo-optic characterization of silicon carbide microdisks for infrared applications

Silicon carbide (SiC) is a well-known material in the field of high temperature and high voltage electronics thanks to a high thermal conductivity, high electric field breakdown strength and high maximum current density [1]. Simultaneously with a strong inertness and a low thermal expansion, this makes silicon carbide a good material for extreme condition sensing [2]. The fact that the cubic structure (3C) of SiC can be grown on silicon makes it compatible with most of the silicon technology. At the same time, silicon carbide exhibits some good optical properties particularly promising for non-linear photonics from the near to the mid infrared range [3-4]. Its high refractive index (n∼2.6 at λ = 1.5μm) allows a good light confinement. Studies on other crystallographic structures [5] suggest that 3C-SiC may exhibit good non-linear properties with a nonlinear index comparable to silicon and nonlinear loss — often detrimental to non-linear processes — virtually inexistent thanks to wide its bandgap [6]. In this work, we report the linear optical and thermal characterization of silicon carbide microdisks on a silicon substrate designed for non-linear operations from near to mid-infrared wavelength.