Physicists Jonas Henrique Osório and Cristiano Monteiro de Barros Cordeiro are the authors of a chapter in the book Application of Optical Fiber for Sensing, published at the end of 2018 by the publisher IntechOpen. In the text, the researchers address the concept of using optical fibers with simplified structures for the development of different types of sensors. The chapter presents the main data from Osório's doctoral thesis, which was defended at the Gleb Wataghin Institute of Physics (IFGW) at Unicamp, under the supervision of Cordeiro. In the following interview, Osório, who is currently doing his post-doctorate at the XLIM Instiute, linked to the Université de Limoges (France), explains what an optical fiber with a simplified structure is and what its potential applications are.
Is the published chapter related to the research developed during your doctoral thesis, which at the time resulted in an article published by Scientific Reports, the Nature Group's scientific magazine?
Yes, the article published in 2017 falls within the context of the chapter published in 2018. The chapter, however, addresses the concept of using optical fibers with simplified structures - which we call minimalist design - in a broader way, applying them to other types of sensors in addition to those reported in the 2017 article. It is worth saying that the chapter presents in a more compact way the main results present in my doctoral thesis, defended in July 2017.
What new did the article published in 2017 propose?
In the article published in 2017, we propose and demonstrate that the use of a new fiber - which we call hair fiber with an embedded core, or embedded-core fiber - was capable of providing high sensitivity for carrying out pressure sensing. This fiber consists of a capillary fiber [a type of tube] with a region doped with germanium in the wall of this capillary. It is in this region doped with germanium, called the nucleus, that light propagates. In the 2017 article, we showed that one of the properties of light that propagates through embedded-core fiber - a property called birefringence - is highly dependent on the pressure conditions to which the fiber is subjected. The variation in birefringence as a function of pressure variations can be measured optically. This allowed us to demonstrate a highly sensitive pressure sensor made from a fiber with a simplified structure.
Why is this fiber considered “simplified”?
We classify the embedded-core fiber as a fiber with a simplified structure because, generally, the fibers that allow the construction of pressure sensors with high sensitivity have sophisticated designs. Typically, these fibers have an arrangement of holes that run longitudinally along the entire length of the fiber. Such a complex structure means that these fibers have manufacturing processes that require great technical effort. The fiber embedded-core, as it is essentially a hair fiber, has a simplified manufacturing process that can be completed more easily. The chapter, in turn, addresses this topic of using optical fibers with simplified structures from a broader perspective. In the chapter, we discuss three such fibers, namely the superficial core hair fiber [surface-core fiber], embedded-core fiber and hair fibers made from polymeric material [PMMA, polymethyl methacrylate]. All of them have a simplified manufacturing method compared to other microstructured fibers. In the chapter, we show that such fibers provide great opportunities for building sensors for a wide variety of parameters such as hydrostatic pressure, temperature, refractive index and curvature. Therefore, we identify our approach as a new avenue for obtaining sensors based on optical fibers.
Can you provide more details on how the design of these fibers is simplified?
One of the possible alternatives to become an optical fiber sensitive to some parameter of interest consists of using so-called microstructured fibers. Such fibers normally have arrangements of holes that run longitudinally along the fiber and provide the same properties that allow it to monitor variations in external parameters. An example of application of such fibers is the area of pressure sensing. In this context, fibers are typically planned with microstructures capable of providing an asymmetric distribution of forces within the fiber when pressure is applied to it. This implies variations in an optical property called birefringence. Optical measurements make it possible to measure this variation and relate it to pressure variations in order to build the sensor. However, although such fibers allow sensing measurements to be carried out with excellent performance, the designs used are very sophisticated. This demands a lot of technical effort from the researcher when manufacturing such fibers. This process involves delicate sample preparation and a series of pulls in an optical fiber manufacturing tower. It is in this context that our approach is inserted. The fibers described in the chapter have much less complex structures than the microstructured fibers previously reported. Therefore, our fibers have a simpler manufacturing process, which saves time from a manufacturing point of view. Furthermore, even with a simplified design, our fibers offer high sensitivity for carrying out sensing measurements, a sensitivity that can be of the same order or greater than the values reported for more sophisticated fibers.
You are currently doing your post-doctorate in France. What institution are you linked to? Are you continuing your doctorate research?
I currently have a postdoctoral research position at XLIM Institute, linked to the Université de Limoges, France. My current research topic remains in the area of optical fibers, but I am not researching sensing applications. My current research deals with the study of hollow optical fibers - called hollow-core photonic-crystal fibers - for the transmission of light in the visible and ultraviolet spectrum.
Can the fact that you are working in France contribute to the establishment of future scientific partnerships between French researchers and Unicamp?
Certainly yes. The fact of working in a new group allows, in addition to developing new skills and knowledge, to meet new researchers and potential collaborators. This, in the future, could contribute to the establishment of research partnerships between Unicamp and researchers here.
