2 research outputs found
Graphene thermal infrared emitters integrated into silicon photonic waveguides
Cost-efficient and easily integrable broadband mid-infrared (mid-IR) sources
would significantly enhance the application space of photonic integrated
circuits (PICs). Thermal incandescent sources are superior to other common
mid-IR emitters based on semiconductor materials in terms of PIC compatibility,
manufacturing costs, and bandwidth. Ideal thermal emitters would radiate
directly into the desired modes of the PIC waveguides via near-field coupling
and would be stable at very high temperatures. Graphene is a semi-metallic
two-dimensional material with comparable emissivity to thin metallic thermal
emitters. It allows maximum coupling into waveguides by placing it directly
into their evanescent fields. Here, we demonstrate graphene mid-IR emitters
integrated with photonic waveguides that couple directly into the fundamental
mode of silicon waveguides designed for a wavelength of 4,2 {\mu}m relevant for
CO sensing. High broadband emission intensity is observed at the
waveguide-integrated graphene emitter. The emission at the output grating
couplers confirms successful coupling into the waveguide mode. Thermal
simulations predict emitter temperatures up to 1000{\deg}C, where the blackbody
radiation covers the mid-IR region. A coupling efficiency {\eta}, defined as
the light emitted into the waveguide divided by the total emission, of up to
68% is estimated, superior to data published for other waveguide-integrated
emitters.Comment: 24 page
Characterization of Silicon Waveguides For Non-Dispersive Infrared Gas Sensors
Carbon dioxide is an important gas for life on Earth. But as human activities have been expanding throughout modern history, the CO2 concentration in the atmosphere is increasing. High concentrations of carbon dioxide can lead to various consequences, such as climate change and poor air quality both indoors and outdoors. It is therefore of importance to detect this gas, in order to understand our environment, and to avoid health impacts that it may cause. Non-dispersive infrared sensors are widely used in CO2 sensing and are based on optical absorption technology. This thesis investigates the optical performance of suspended waveguides for non-dispersive infrared sensors, with regard to different material qualities, i.e. monocrystalline and polycrystalline silicon, and geometries of these waveguides. The waveguides that are studied in this thesis consist of splitters, and at the end of each splitter a grating coupler that projects the IR radiation perpendicularly from the plane of the chip. Measurements are conducted to evaluate the IR radiation propagation loss of the waveguides and their feasibility for sensing carbon dioxide. It has been found that longer waveguides suffer from high propagation losses. When comparing the polycrystalline silicon with monocrystalline silicon waveguides, it has been observed in the measurements that the IR radiation propagates better in monocrystalline silicon waveguides than in polycrystalline silicon because of their crystal structures. The measured propagation loss in polycrystalline silicon waveguides is less than the loss obtained for the monocrystalline silicon waveguides, although some intensities from the grating couplers are excluded in the calculations, due to low signal strength. It is also concluded that the studied waveguides are feasible for detecting carbon dioxide with a concentration of 1%. Further investigation regarding the feasibility of gas sensing using lower concentrations of CO2 would be interesting for future work