A chip-based silicon nitride platform for mid-infrared nonlinear photonics

We developed a chip-based silicon nitride platform with thick waveguides (> 2 mm) that overcomes the usual fabrication limitation. We demonstrate both microresonator frequency comb generation at 2:5 mm and supercontinuum generation extending beyond 4:0 mm in this platform

Emending the Teacher : From Marcus the "Magician" to Valentinus and Back

akzeptierte Manuskriptversio

Discutindo a educação ambiental no cotidiano escolar: desenvolvimento de projetos na escola formação inicial e continuada de professores

A presente pesquisa buscou discutir como a Educação Ambiental (EA) vem sendo trabalhada, no Ensino Fundamental e como os docentes desta escola compreendem e vem inserindo a EA no cotidiano escolar., em uma escola estadual do município de Tangará da Serra/MT, Brasil. Para tanto, realizou-se entrevistas com os professores que fazem parte de um projeto interdisciplinar de EA na escola pesquisada. Verificou-se que o projeto da escola não vem conseguindo alcançar os objetivos propostos por: desconhecimento do mesmo, pelos professores; formação deficiente dos professores, não entendimento da EA como processo de ensino-aprendizagem, falta de recursos didáticos, planejamento inadequado das atividades. A partir dessa constatação, procurou-se debater a impossibilidade de tratar do tema fora do trabalho interdisciplinar, bem como, e principalmente, a importância de um estudo mais aprofundado de EA, vinculando teoria e prática, tanto na formação docente, como em projetos escolares, a fim de fugir do tradicional vínculo “EA e ecologia, lixo e horta”.Facultad de Humanidades y Ciencias de la Educació

Photonic Damascene process for integrated high Q microresonator based nonlinear photonic devices

Chip-based optical waveguides formed by a silicon nitride (Si3N4) core and a silicon dioxide (SiO2) cladding are an important platform for low loss waveguides and nonlinear optics. High Q microresonators based on this material system have become a standard platformfor Kerr frequency comb generation. After their discovery in 2007, Kerr frequency combs have attracted significant interest due to their novel properties, featuring repetition rates from the microwave to the terahertz range, and the potential to realize mass-producible, compact frequency comb systems. The excitation of dissipative Kerr solitons (DKS) has quickly become the preferred operational state, allowing generation of fully coherent frequency combs with designable properties. However, the design and fabrication of microresonators that allow for DKS excitation has remained challenging. In this thesis, a novel fabrication process, the photonic Damascene process, is introduced that solves problems of previous fabrication processes. Inverting the process order and depositing the Si3N4 thin film onto a pre-patterned substrate allows for wafer-scale, crack-free fabrication of low loss photonic waveguides. Through process optimization, high dimensional accuracy similar to existing process schemes and good process stability is achieved. This enables a significant advance in the sample design and understanding of the important design elements required for microresonators with excellent linear and nonlinear performance. Especially, the design of the coupling between the microresonator and the bus waveguide is found to be critical. Together, the advances in design and fabrication allow for the demonstration of octave spanning DKS frequency combs in microresonators with 1-THz free spectral range. Finally, a systematic study of the loss processes in the photonic waveguides is presented and allows for the first time a quantification of the scattering and absorption loss rates. The ultra-smooth sidewalls of waveguides fabricated with a novel reflow process lead to dominant absorption losses. Material analysis techniques reveal for the first time the critical role of transition metal impurities, found to be present in significant amounts, for integrated photonic waveguides. The findings of this thesis provide the technological basis for design and fabrication of chipscale microresonator based Kerr frequency comb generators. In the future it will enable custom-designed and application-specific nonlinear waveguide devices that drive the further proliferation of Kerr comb technology

Waveguide Fabrication Method

A waveguide fabrication method including the steps of providing a substrate including at least one waveguide recess structure and a stress release recess structure for receiving a waveguide material, and depositing the waveguide material onto the substrate and into both the waveguide recess structure and the stress release recess structure

Photonic chip-based soliton frequency combs covering the biological imaging window

Dissipative Kerr solitons (DKS) in optical microresonators provide a highly miniaturised, chip-integrated frequency comb source with unprecedentedly high repetition rates and spectral bandwidth. To date, such frequency comb sources have been successfully applied in the optical telecommunication band for dual-comb spectroscopy, coherent telecommunications, counting of optical frequencies and distance measurements. Yet, the range of applications could be significantly extended by operating in the near-infrared spectral domain, which is a prerequisite for biomedical and Raman imaging applications, and hosts commonly used optical atomic transitions. Here we show the operation of photonic-chip-based soliton Kerr combs driven with 1 micron laser light. By engineering the dispersion properties of a Si3N4 microring resonator, octave-spanning soliton Kerr combs extending to 776 nm are attained, thereby covering the optical biological imaging window. Moreover, we show that soliton states can be generated in normal group–velocity dispersion regions when exploiting mode hybridisation with other mode families

Formation Rules and Dynamics of Photoinduced χ(2) Gratings in Silicon Nitride Waveguides

Silicon nitride has emerged as a prominent platform for building photonics integrated circuits. While its nonlinear properties based on third-order effects have been successfully exploited, an efficient second harmonic generation in standard stoichiometric silicon nitride (Si3N4) waveguides can also be achieved after all-optical poling, as was recently shown. The root of such a phenomenon has been attributed to the inscription of a self-organized periodic space-charge grating along the waveguide, allowing an effective χ(2) and automatic quasi-phase-matching of pump and second harmonic. However, the different parameters and their role in increasing the efficiency of the process are still not fully comprehended. In this work, we use optical means to identify the general conditions of mode matching occurring during all-optical poling. The overlap integral between pump and second harmonic optical modes is shown to be the governing parameter in determining the features of the χ(2) gratings. Two-photon microscopy measurements of the χ(2) gratings reveal the presence of a secondary periodicity in some of the waveguides used in the study. According to overlap integral simulations, such an effect can occur due to mode mixing in the waveguide bends. From a study of poling dynamics, we observe that poling efficiency and rate increase as a function of optical pump power and waveguide length. However, in order to initiate poling, a critical pump intensity, which is lower for longer waveguides, must be coupled into a waveguide. Temporal and thermal stability tests reveal the nature of charge traps responsible for grating inscription. After applying thermally activated hopping as a conductivity mechanism in our samples, we show that only shallow traps seem to be activated during the all-optical poling process

X-ray nanotomography using near-field ptychography

International audiencePropagation-based imaging or inline holography in combination with computed tomography (holotomography) is a versatile tool to access a sample's three-dimensional (3D) micro or nano structure. However, the phase retrieval step needed prior to tomographic reconstruction can be challenging especially for strongly absorbing and refracting samples. Near-field ptychography is a recently developed phase imaging method that has been proven to overcome this hurdle in projection data. In this work we extend near-field ptychography to three dimensions and we show that, in combination with tomography, it can access the nano structure of a solid oxide fuel cell (SOFC). The quality of the resulting tomographic data and the structural properties of the anode extracted from this volume were compared to previous results obtained with holotomography. This work highlights the potential of 3D near-field ptychography for reliable and detailed investigations of samples at the nanometer scale, with important applications in materials and life sciences among others. (C) 2015 Optical Society of Americ