Optical fibers are ubiquitous and inexpensive substrates commonly used in telecom, and more recently as a platform for innovative concepts such ‘lab-on-a-fiber’ ones, where multiple functionalities are integrated in the fiber substrate.
One of the challenges for machining fibers is to overcome the substrate curvature, and to achieve high accuracy throughout the volume. Common techniques include the use of index-matching fluids and special fiber holding devices.
Here, we discuss the machining of optical fibers combined with chemical etching using a specific tooling configuration, mimicking the principal of a lathe, numerically controlled down to micron precision. An analysis of the beam propagating through the fiber is used to compensate for optical aberrations, inherent to such geometry. Further, we also show the combination of this process with a CO2-laser morphing technique to achieve high accuracy shapes with optical quality surfaces.
We successfully demonstrated and reported the highest solar-to-hydrogen efficiency with crystalline silicon cells and Earth-abundant electrocatalysts under unconcentrated solar radiation. The combination of hetero-junction silicon cells and a 3D printed Platinum/Iridium-Oxide electrolyzer has been proven to work continuously for more than 24 hours in neutral environment, with a stable 13.5% solar-to-fuel efficiency. Since the hydrogen economy is expected to expand to a global scale, we demonstrated the same efficiency with an Earth-abundant electrolyzer based on Nickel in a basic medium. In both cases, electrolyzer and photovoltaic cells have been specifically sized for their characteristic curves to intersect at a stable operating point. This is foreseen to guarantee constant operation over the device lifetime without performance degradation. The next step is to lower the production cost of hydrogen by making use of medium range solar concentration. It permits to limit the photoabsorbing area, shown to be the cost-driver component. We have recently modeled a self-tracking solar concentrator, able to capture sunlight within the acceptance angle range +/-45°, implementing 3 custom lenses. The design allows a fully static device, avoiding the external tracker that was necessary in a previously demonstrated +/-16° angular range concentrator. We will show two self-tracking methods. The first one relies on thermal expansion whereas the second method relies on microfluidics.