One approach to overcome the poor efficiency of the Raman scattering as a sensing platform is to use microstructured optical fibers. In this type of fibers with a longitudinal holey structure, light interacts with the target sample, which is confined in the core, giving rise to a light intensity increase of the obtained Raman spectra due to the large interaction distances and the guidance of the scattered light. In this work, we present an ad-hoc fabricated liquid-core microstructured polymer optical fiber (LC-mPOF) as a bio-sensing platform for Raman Spectroscopy. Arising from an initial simulation stage, we create the desired preform using the drilling technique and afterwards the LC-mPOF is drawn in our fiber drawing tower. The guiding mechanism of the light through the solution has a major importance, being a key factor to obtain appreciable enhancements in Raman scattering. In this case, in order to optimize the Raman scattering signal of dissolved glucose (target molecule), we have filled the core with an aqueous solution of the target molecule, enabling in this way the modified total internal reflection mechanism. Experimental Raman measurements are performed and results are discussed.
One of the issues that affects the performance of plastic optical fibers (POFs) is the light scattering caused by the presence of inhomogeneities in the polymer, which is responsible for the optical energy loss and for the mode coupling in POFs. The aim of this work is to compare two different methods for measuring light scattered in step index polymer optical fibers (SI-POF) by using the side-illumination technique. On the one hand, scattered intensity and far-field patterns at single wavelength have been measured by varying the launching conditions: position of the excitation spot in the fiber and incidence angle. On the other hand, we have measured the spectral distribution of the scattered light in SIPOFs by exciting the fiber with a supercontinuum source. A theoretical model based on Mie theory has been used to analyze the obtained experimental results. From this analysis, the size and position of the most influential scattering centers in step-index POFs can be estimated. The results obtained employing both methods have been compared, resuming the advantages and drawbacks of each one for characterizing the optical quality on SI-POFs.