Self-assembled nanostructured optical fiber sensors (Invited Paper)

This paper summarizes nanostructured optical fiber sensors fabricated by molecular self-assemblychemistry. Strain, pressure, vibration and chemical sensors are described which are based on self-assembled fiber cores, cladding s, distal endface coatings and free-standing membranes.Keywords: Self-assembled materials, optical fiber sensor, coatings, chemical sensor 1.0 INTRODUC TION Molecular- level self-assembly offers an interesting new processing route for the fabrication of materials with combined constitutive properties typically not achieved using conventional manufacturing techniques.Recent research has demonstrated that such materials may be incorporated into optical fiber sensor systems in a variety of ways, namely as coatings on the distal ends of fibers to enable the specific detection of selected chemicals, as both coatings and claddings of low modulus light-transmi tting fibers that may be used to qualitatively measure strain and vibrational effects, and as free-standing reflective, transmissive or absorptive membrane materials that may be interrogated in extrinsic fiber sensor geometries to determine two-dimensional displacement and deformation. This paper briefly summarizes some of this work, and suggests possible directions in this area in the future. 1.1 Self- Assembly of MaterialsThe concept of materials that assemble themselves is conceptually attractive as a potential means of reducing the complexity and time associated with material manufacturing. Such is especially the case in the production of materials from the ‘bottom-up,’ molecular by molecule, due to the large number of molecules involved and the difficulty associated with placing each one into a three-dimensional material array. Self-assembly methods are not new, but have been studied for nearly the past century [1]. So-calledelectrostatic self- assembly (ESA) is particularly attractive because it has recently been demonstrated as an effective means of making thick macroscopic bulk materials rather than just ultrathin films or coatings. Itrelies on the formation of alternating simple polyelectrolyte monolayers as shown in Figure 1.As shown, the substrate surface has been thoroughly cleaned and functionalized, so the outermost surface layer effectively has a negative charge. In general, this charged substrate is then dipped into or sprayed with a solution containing polycationic complexes (polymers, nanoclusters, nanotubes, biomolecules) that are attracted to the anionic surface and self-assemble into a positive monolayer. The now positive substrate