Sensitivity of long period fiber gratings to nanoscale ionic self-assembled multilayers

We have shown that ionic self-assembled multilayers (ISAMs) deposited on optical fiber long period gratings (LPGs) yield dramatic resonant-wavelength shifts, even with nanometer-thick films. Precise control of the refractive index and the thickness of these films was achieved by altering the relative fraction of the anionic and cationic materials combined with layer-by-layer deposition. We demonstrate the feasibility of this highly controllable deposition-technique for fine-tuning grating properties for grating applications. In addition, we confirm theoretically that the resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. Finally, we demonstrate that ISAMs adsorbed on LPGs function effectively as biosensors. These simulations and experimental results confirm that ISAM-coaled-LPGs provide a thermally-stable, reusable, robust, and attractive platform for building efficient fiber optic sensors and devices.